JP2017062206A - Derivation method of fracture limit line in weld zone, manufacturing method of component including weld zone, program, and computer readable-recording medium having program recorded thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a derivation method of a fracture limit line in a weld zone by which the fracture limit line can be accurately derived for a joint by use of a weld technique in which the fracture limit line is not derived without performing a fracture limit derivation process.SOLUTION: A derivation method of a fracture limit line in a weld zone comprises the steps of: representing respective fracture limit lines by approximate expressions with respect to a steel type in which the fracture limit line in a spot weld zone and a lazer weld zone where a weld cooling rate is varied are derived in advance; representing a fracture limit line of the lazer weld zone by approximate expressions using a factor and a conversion factor of the approximate expression of the fracture limit line for the spot weld zone; generating a relation expression which a cooling rate Cof the lazer weld zone and the conversion factor satisfy; deriving the cooling rate Cfrom a feed rate of the lazer weld with respect to a steel type in which the fracture limit line of the lazer weld zone is not derived; calculating the conversion factor by substituting the derived Cin the relation expression; and converting the fracture limit line for the spot weld zone derived by the fracture limit line derivation process to the fracture limit line for the lazer weld zone by use of the calculated conversion factor.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for deriving a fracture limit line of a weld using a finite element method analysis (hereinafter referred to as “FEM analysis”), and a weld using the derivation method. The present invention relates to a method for manufacturing a member, a program for causing a computer to execute the derivation method, and a computer-readable recording medium on which the program is recorded.

  Welding, particularly spot welding, is widely used as a method for joining steel plates in an automobile assembly process. In a member assembled by spot welding, if the welding nugget diameter and the spot position are not appropriate, the welded portion may break during collision deformation, leading to a decrease in energy absorption performance. In recent years, laser welding capable of one-sided access and continuous welding has attracted attention, and is being put to practical use as a method for joining automobile members. When evaluating the impact energy absorption performance of members by FEM analysis, it is important to consider the fracture of these welds in order to improve the analysis accuracy, and it is possible to examine welding conditions to prevent the occurrence of fracture There is a need for a way to make it.

  As a technique related to such an analysis, for example, Patent Document 1 discloses a technique related to a method for predicting a fracture of a laser welded portion intended for an automobile steel plate. According to the technique disclosed in Patent Document 1, the shear stress and tensile stress at the fracture limit are calculated from the shearing force and peeling force applied to the welded part, and the fracture of the laser welded part can be predicted using this. It seems possible. However, this technique models the welded part with a beam element, and does not accurately reproduce the structure distribution in the vicinity of the welded part.

  Further, in Non-Patent Document 1 and Non-Patent Document 2, a welded metal portion of a spot welded portion, a heat-affected zone (hereinafter referred to as “ HAZ ")) A method of individually and quantitatively measuring the stress-strain, tensile strength, elongation at break, and fracture drawing of each part and base metal part, and the ultra-small test piece from the stress-strain relationship and the fracture drawing. A method for deriving the local breaking strain of each part by FEM analysis simulating the tensile test is disclosed. The breaking strain derived from this test piece may be referred to as “notch breaking strain”. In addition, these documents also disclose a method for constructing a fracture limit line (a fracture strain with the stress triaxiality as a parameter) by approximating a smooth fracture strain or a notch fracture strain by a power function. According to such a technique, FEM analysis is performed using the fracture limit line as a fracture criterion for each part of the spot welded part, and the joint strength and fractured part of a plurality of spot welded joints with different load modes applied to the welded part are accurately determined. It can be predicted.

  Non-Patent Document 3 discloses a method of applying the methods of Non-Patent Document 1 and Non-Patent Document 2 to FEM analysis of laser weld joint strength evaluation. According to this technique, FEM analysis is performed using the fracture limit line as a fracture criterion for each part of the laser welded part, and the joint strength and fractured part of a plurality of laser welded joints with different load modes applied to the welded part are accurately obtained. It can be predicted.

  With the techniques described in Non-Patent Document 1 and Non-Patent Document 2, it is possible to predict the fracture with respect to the tensile test conditions of the spot welded joint and to examine the detailed fracture factor. In this technology, the rupture strain may differ depending on the welding method. The smooth rupture strain and the notch rupture strain are obtained from the tensile test results and FEM analysis results of the smooth and notched micro test pieces for each welding method. Yes. Further, the smooth breaking strain and the notch breaking strain are approximated by a power function to obtain a breaking limit line (hereinafter, this process may be referred to as a “breaking limit line derivation process”). However, in these technologies, when performing FEM analysis for predicting fracture for joints consisting of steel types and welding conditions for which the fracture limit line has not yet been derived, a process for deriving the fracture limit line is required in advance for the steel type. The increase in the process of deriving the fracture limit line is a problem requiring work time and human labor. In response to this problem, Patent Document 2 discloses a technique related to a method for calculating a fracture limit line of a welded portion. Patent Document 3 discloses a technique related to a method for predicting a ductile fracture limit strain for a thick UOE steel pipe.

JP 2009-265028 A Japanese Patent Laying-Open No. 2015-87349 JP 2013-104658 A

Eisuke Nakayama, 5 others, Automobile Engineering Society Proceedings, 2005, Vol. 36, no. 1, p. 205-210 Hideki Ueda, 3 others, Proceedings of the Society of Automotive Engineers of Japan, 2013, Vol. 44, no. 2, p. 727-738 Hideki Ueda, 2 others, Outline of the National Welding Society Autumn Meeting 2014, No. 95, p. 326-327

  According to the technique disclosed in Patent Document 2, it is considered that the fracture limit line can be accurately derived without performing the fracture limit line derivation process for a joint made of a welding method in which the fracture limit line has not been derived. It is done. However, this technique cannot derive the fracture limit line of the laser weld unless the chemical composition of the steel type to be evaluated is specified. In laser welding, the cooling rate varies depending on the feed rate, and the weld metal hardness may vary. In that case, even if laser welds of the same steel type, the fracture limit line is different, but this technique does not consider it. In Patent Document 3, the ductile fracture limit strain is predicted by a method different from the numerical analysis such as FEM analysis.

  Therefore, the present invention provides a method for deriving the fracture limit line of a welded portion, which can accurately derive the fracture limit line without performing the fracture limit line deriving process, for a joint made of a welding method in which the fracture limit line has not been derived. A method for manufacturing a member having a welded portion using the method for deriving the fracture limit line, a program for causing a computer to execute the method for deriving, and a computer-readable recording medium storing the program are provided. The task is to do.

A break limit line is derived in advance and used as break limit line reference data for a spot welded part and a plurality of laser welded parts with different welding cooling rates of the same steel type. FIG. 1 shows, as an example, a fracture limit line of a spot welded portion of a tensile strength 590 MPa class steel plate and two types of laser welded portions with different welding cooling rates. Generally, the breaking strain decreases as the stress triaxiality increases, and the breaking strain and the stress triaxiality have a negative correlation as shown in FIG. Therefore, the break limit line can be approximated by a power function shown in Equation (1). The fracture limit line of the spot welded part can be expressed by the following formula (1), and the fracture limit line of the laser welded part can be expressed by the following formula (2).
ε _p = F _s · σ _triax ^ N _s (1)
_{ε p = F l · σ triax} ^ N l ... (2)
Here, ε _p is the fracture strain, σ _triax is the stress triaxiality (0.7 <σ _triax <2.0), and F _s , N _s , F _l , and N _l are for each steel type and part Each parameter is different.
Using the parameters F _s and N _s in the above equation (1), the above equation (2) can be rewritten into the following equation (3).
ε _p = F _s · F _r · σ _triax ^ (N _s · N _r ) (3)
Here, F _r and N _r are conversion coefficients used to rewrite equation (2) into equation (3).

As a result of intensive studies by the present inventors, the conversion coefficients F _r and N _{r in} the above equation (3) have the relationship shown in FIG. 2 with respect to the cooling rate C _r of the weld, and these are expressed by the following equation (4): And (5). To _{C r} of formula (4) and (5), by substituting the cooling rate of the weld, can be calculated transformation coefficients _{F r} and _{N r.} If the fracture limit line of the spot weld has been derived, since F _s and N _{s in} the above formula (1) are known, by substituting the calculated conversion coefficients F _r and N _r into the above formula (3), The fracture limit line of the laser weld can be derived. In addition, the cooling rate of a spot weld part and a laser weld part can be calculated | required by the measurement by a radiation thermometer etc.
F _r = −a1 · ln (C _r ) + a2 (4)
N _r = b1 · ln (C _r ) −b2 (5)
Here, a1, a2, b1, and b2 are parameters (> 0).

  Thus, even for a steel type for which the fracture limit line of the laser welded part has not been derived, the fracture limit line of the spot welded part has already been derived, and the welding part cooling rate (hereinafter referred to as “weld cooling rate”). If it is known, the fracture limit line of the laser weld can be easily obtained by using the method described above. In addition, spot welding is performed in the same manner as described above, except that the conversion coefficient used in representing the fracture limit line of the spot weld is used, using the coefficient used in the fracture limit line of the laser weld. If the fracture limit line of the laser weld is already derived and the cooling rate of the weld is known, the fracture limit line of the spot weld Can be easily obtained. The present invention has been completed based on such findings. The present invention will be described below.

  A first aspect of the present invention is a method for deriving a fracture limit line used when performing fracture prediction of a welded portion by a finite element method analysis, and the fracture of a spot welded portion is previously determined by a fracture limit line deriving process. For steel types from which the limit line and the fracture limit line of multiple laser welds with different welding cooling rates were derived, formulating the formula for the fracture limit line of the spot weld and the fracture limit line of the laser weld The conversion coefficient in the above steel type from which the fracture limit line was derived, used when expressing the formula of the fracture limit line of the laser weld using the process and the coefficient used in the formula of the fracture limit line of the spot weld A first conversion coefficient calculating step for calculating the cooling rate, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, a cooling rate obtained in the cooling rate specifying step, and a fracture limit line From the laser welding feed speed, the relational expression creating step for creating the relational expression that satisfies the conversion coefficient in the steel grade that has been taken out, and the steel grade for which the fracture limit line of the laser welded part has not been derived, Substituting the laser welding part cooling rate derivation process for deriving the cooling rate and the laser welding part cooling rate derived in the laser welding part cooling rate derivation process into the above relational expression created in the relational expression creation process. By using the second conversion coefficient calculation step for calculating the conversion coefficient in the steel type from which the fracture limit line of the laser weld is not derived, and using the conversion coefficient calculated in the second conversion coefficient calculation step, The fracture limit line for converting the previously derived fracture limit line of the spot welded part into the fracture limit line of the laser welded part in the above steel types for which the fracture limit line is not derived. Has a conversion step, the is a method of deriving the weld fracture limit line.

In the present invention, the “welded part” is particularly preferably a welded part of a steel material, a weld metal part (a nugget part in the case of spot welding, a weld bead part in the case of laser welding), a HAZ part, and a base material. It can be roughly divided into parts. Further, the “breaking limit line” is derived by approximating a smooth breaking strain and a notch breaking strain by a power function, for example, a breaking limit line of a base material part in a welded part, a breaking limit line of a HAZ part, and And the fracture limit line of the weld metal portion. The “break limit line” in the present invention is a reference value for fracture determination that can also be applied to welds in other welding means such as seam welding. In the present invention, the “cooling rate” is a cooling rate of the welded part in the welding process, and is generally expressed in units of a temperature difference per second (° C./s) during cooling from 800 ° C. to 500 ° C. There are many cases.
In the first aspect of the present invention, the conversion coefficient calculated using the previously derived break limit line of the spot weld and the break limit line of the laser weld satisfies the cooling rate of the spot weld and the laser weld. Create a relational expression. Furthermore, by deriving the cooling rate of the laser welded part of the steel type for which the fracture limit line of the laser weld has not been derived, and substituting this into the above-mentioned relational expression, the fracture limit line of the laser weld is obtained. Calculate the conversion factor of the steel type for which no is derived. This conversion coefficient is a coefficient for converting the fracture limit line of the spot welded part into the fracture limit line of the laser welded part. Therefore, by using this conversion coefficient and the fracture limit line of the spot welded part that has already been derived, Without performing the limit line derivation process, the fracture limit line of the laser weld can be obtained. The fracture limit line of the laser weld derived as described above is in good agreement with the fracture limit line of the laser weld derived by the fracture limit line derivation process. Therefore, according to the first aspect of the present invention, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process for the laser welded joint from which the fracture limit line has not been derived. It is possible to provide a method for deriving the fracture limit line.

In the first aspect of the present invention, in the formulating step, the fracture limit line of the spot welded part is expressed by the above formula (1), and the fracture limit line of the laser welded part is expressed by the above formula (2). The conversion coefficient represented by the above expression (3) and calculated in the first conversion coefficient calculation step may be F _r and N _r in the above expression (3).
In the first aspect of the present invention, the fracture limit line of the spot welded part is derived for the steel type from which the fracture limit line of the laser welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph). Therefore, F _s and N _s in the above formula (1) are specified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the laser weld into the above equation (3), the evaluation object can be obtained without performing the fracture limit line derivation process. It is possible to derive the fracture limit line of the laser weld of the steel type. The fracture limit line of the laser weld derived as described above is in good agreement with the fracture limit line of the laser weld derived by the fracture limit line derivation process. Therefore, even in such a form, for a laser welded joint whose fracture limit line has not yet been derived, the fracture limit line can be accurately derived without performing the fracture limit line deriving process. A method for deriving a limit line can be provided.

  A second aspect of the present invention is a method for deriving a fracture limit line, which is used when performing fracture prediction of a welded portion by finite element method analysis, and the laser welded portion is fractured in advance by a fracture limit line deriving process. For steel types from which the limit line and the welding limit rate were changed and for which multiple fracture limit lines for spot welds were derived, the fracture limit line for laser welds and the break limit line for spot welds are expressed by equations. Conversion in the above steel types from which the fracture limit line was derived, used to express the formula of the fracture limit line of the spot weld using the formulating step and the coefficient used in the formula of the fracture limit line of the laser weld A first conversion coefficient calculating step for calculating a coefficient, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, a cooling rate obtained in the cooling rate specifying step, and a fracture limit For the steel grade from which the fracture limit line of the spot weld is not derived, and a spot for grasping the cooling rate of the spot weld. By substituting the cooling rate of the spot welded portion grasped in the welded portion cooling rate grasping step and the spot welded portion cooling rate grasping step into the above relational expression created in the relational expression creating step, Using the second conversion coefficient calculation step for calculating the conversion coefficient in the above steel types for which the fracture limit line has not been derived, and using the conversion coefficient calculated in the second conversion coefficient calculation step, the fracture limit line of the spot weld is derived. Break line conversion process for converting the previously derived laser weld zone fracture limit line into the spot weld zone fracture limit line in the above steel types , Having a method for deriving weld fracture limit line.

In the present invention, the cooling rate of the spot welded portion can be determined by measurement with a radiation thermometer or the like. Further, for example, by changing the holding time and the like, it is possible to derive a plurality of break limit lines of the spot welded portions with different welding cooling rates.
In the second aspect of the present invention, the conversion coefficient calculated using the previously derived fracture limit line of the spot weld and the fracture limit line of the laser weld satisfies the cooling rate of the spot weld and the laser weld. Create a relational expression. Further, by grasping the cooling rate of the spot welded part of the steel type for which the fracture limit line of the spot weld has not been derived, and substituting this into the above-mentioned relational expression, the fracture limit line of the spot weld is obtained. Calculate the conversion factor of the steel type for which no is derived. Since this conversion coefficient is a coefficient for converting the laser welding fracture line to the spot welding fracture line, by using this conversion coefficient and the laser welding fracture line that has already been derived, The fracture limit line of the spot weld can be derived without performing the limit line derivation process. The fracture limit line of the spot weld that is derived in this way is in good agreement with the fracture limit line of the spot weld that is derived by the fracture limit line derivation process. Therefore, according to the second aspect of the present invention, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process for the spot weld joint from which the fracture limit line has not been derived. It is possible to provide a method for deriving the fracture limit line.

Further, in the second aspect of the present invention, in the formulating step, the fracture limit line of the spot welded part is represented by the following formula (X) and the following formula (Y), and the fracture limit line of the laser welded part: Is represented by the following formula (Z), and the conversion coefficients calculated in the first conversion coefficient calculation step may be F _r ′ and N _r ′ in the following formula (Y).
ε _p = F _s · σ _triax ^ N _s (X)
_{ε p = F l · F r} '· σ triax ^ (N l · N r') ... (Y)
ε _p = F _l · σ _triax ^ N _l (Z)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0).
In the second aspect of the present invention, the fracture limit line of the laser welded part of the steel type from which the fracture limit line of the spot welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is derived. Therefore, the coefficients F _l and N _l in the above formula (Z) are specified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the spot welded part into the above formula (Y), the evaluation target can be obtained without performing the fracture limit line derivation process. It is possible to derive a fracture limit line of a spot weld of a steel type. The fracture limit line of the spot weld that is derived in this way is in good agreement with the fracture limit line of the spot weld that is derived by the fracture limit line derivation process. Therefore, even in such a form, for spot welded joints where the fracture limit line has not yet been derived, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process. A method for deriving a limit line can be provided.

  A third aspect of the present invention is a method for deriving a fracture limit line used when performing fracture prediction of a welded portion by finite element method analysis, in which a spot welded portion fracture is performed in advance by a fracture limit line deriving process. For the steel types from which the limit line and the fracture limit line of a plurality of laser welds with different welding cooling rates were derived, the formula representing the break limit line of the spot weld and the fracture limit line of the laser weld by a formula Conversion factor in the above steel types from which the fracture limit line was derived, used to represent the formula of the fracture limit line of the laser weld using the process used to determine the fracture limit line of the laser weld The first conversion coefficient calculating step for calculating the cooling rate, the cooling rate specifying step for obtaining the cooling rate of the spot welded portion and the laser welded portion, the cooling rate obtained in the cooling rate specifying step, and the fracture limit line A relational expression creating step for creating a relational expression satisfying the conversion coefficient in the derived steel type is executed, and a relational expression created in the relational expression creating step is prepared in advance, and the laser welding part is broken. A laser welding part cooling rate deriving step for deriving a cooling rate of a laser welded part from a laser welding feed rate for a steel type for which a limit line has not been derived, and a laser welded part derived in the laser welding part cooling rate deriving step The second conversion for calculating the conversion coefficient in the above steel type in which the fracture limit line of the laser weld is not derived by substituting the cooling rate of the above into the relational expression created in the relational expression creating step prepared in advance Using the coefficient calculation process and the conversion coefficient calculated in the second conversion coefficient calculation process, the The beforehand derived spot weld fracture limit line, has a rupture limit line conversion step of converting into fracture limit line of the laser weld, and a method of deriving the weld fracture limit line.

  The third aspect of the present invention is a conversion in a steel type in which a cooling rate and a fracture limit line are derived, which are created by performing in advance the formulating process to the relational expression creating process in the first aspect of the present invention. This corresponds to a mode in which the laser welded part cooling rate derivation step to the fracture limit line conversion step are performed using the relational expression that the coefficient satisfies. Even in such a form, the fracture limit line of the laser weld can be obtained without performing the fracture limit line derivation process, and the fracture limit line of the laser weld derived in this way is the fracture limit. It agrees well with the fracture limit line of the laser weld derived by the line derivation process. Therefore, according to the third aspect of the present invention, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process for the laser welded joint from which the fracture limit line has not been derived. It is possible to provide a method for deriving the fracture limit line.

In the third aspect of the present invention, in the formulating step, the fracture limit line of the spot welded part is expressed by the above formula (1), and the fracture limit line of the laser welded part is expressed by the above formula (2). And the conversion coefficient may be F _r and N _r in the above formula (3).
In the third aspect of the present invention, the fracture limit line of the spot welded part of a steel type from which the fracture limit line of the laser welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is derived. Therefore, F _s and N _s in the above formula (1) are specified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the laser weld into the above equation (3), the evaluation object can be obtained without performing the fracture limit line derivation process. It is possible to derive the fracture limit line of the laser weld of the steel type. The fracture limit line of the laser weld derived as described above is in good agreement with the fracture limit line of the laser weld derived by the fracture limit line derivation process. Therefore, even in such a form, for a laser welded joint whose fracture limit line has not yet been derived, the fracture limit line can be accurately derived without performing the fracture limit line deriving process. A method for deriving a limit line can be provided.

  A fourth aspect of the present invention is a method for deriving a fracture limit line used when predicting fracture of a welded part by finite element method analysis, and the laser welding part is fractured in advance by a fracture limit line deriving process. For steel grades with multiple limit welds and spot welding welds with different welding cooling speeds, the laser weld weld breakage limit and the spot weld weld breakage limit are expressed as follows: In the above steel type from which the fracture limit line is derived, which is used when expressing the formula of the fracture limit line of the spot weld using the formulating process and the coefficient used in the formula of the fracture limit line of the laser weld A first conversion coefficient calculating step for calculating a conversion coefficient, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, a cooling rate obtained in the cooling rate specifying step, and a fracture limit The conversion coefficient in the steel type from which the line was derived and a relational expression creating step for creating a relational expression that satisfies the above are prepared, and the relational expression created in the relational expression creating step is prepared in advance, and the spot welded portion For steel grades for which no fracture limit line has been derived, the spot welded portion cooling rate grasping step for grasping the cooling rate of the spot welded portion, and the spot welded portion cooling rate grasped in the spot welded portion cooling rate grasping step, A second conversion coefficient calculation step of calculating a conversion coefficient in the steel type in which the fracture limit line of the spot weld is not derived by substituting into the relational expression created in the relational expression creation step prepared in advance; Using the conversion coefficient calculated in the second conversion coefficient calculation step, in advance in the steel type in which the fracture limit line of the spot weld is not derived, The issued a fracture limit line of the laser welding unit has a rupture limit line conversion step of converting into fracture limit line of spot welds, and a method of deriving the weld fracture limit line.

  The fourth aspect of the present invention is a steel type that is created by performing the formulating step to the relational expression creating step in the second aspect of the present invention in advance, and in the steel type from which the breaking limit line is derived. This corresponds to an aspect in which the conversion coefficient and the relational expression satisfied by the spot welding part cooling rate grasping process to the fracture limit line converting process are performed. Even in such a form, the fracture limit line of the spot welded portion can be obtained without performing the fracture limit line derivation process. It agrees well with the fracture limit line of spot welds derived by the line derivation process. Therefore, according to the fourth aspect of the present invention, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process for the spot welded joint from which the fracture limit line has not been derived. It is possible to provide a method for deriving the fracture limit line.

In the fourth aspect of the present invention, in the formulating step, the fracture limit line of the spot welded part is represented by the above formula (X) and the formula (Y), and the fracture limit line of the laser welded part. May be represented by the above formula (Z), and the conversion coefficient may be F _r ′ and N _r ′ in the above formula (Y).
In the fourth aspect of the present invention, the fracture limit line of the laser welded part of a steel type from which the fracture limit line of the spot welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is derived. Therefore, the coefficients F _l and N _l in the above formula (Z) are specified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the spot welded part into the above formula (Y), the evaluation target can be obtained without performing the fracture limit line derivation process. It is possible to derive a fracture limit line of a spot weld of a steel type. The fracture limit line of the spot weld that is derived in this way is in good agreement with the fracture limit line of the spot weld that is derived by the fracture limit line derivation process. Therefore, even in such a form, for spot welded joints where the fracture limit line has not yet been derived, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process. A method for deriving a limit line can be provided.

  According to a fifth aspect of the present invention, there is provided a finite element method using a fracture limit line derived by the method for deriving a fracture limit line of a weld according to the first aspect of the present invention to the fourth aspect of the present invention. Analysis is performed, and based on the analysis result, the plate assembly of the member, the size of the welded portion, and / or the welding position are determined, and the determined plate assembly, the size of the welded portion, and / or the welding are determined. It is a manufacturing method of the member provided with the welding part provided with the process of welding a member according to a position.

  The “welded part” in the fifth aspect of the present invention is a concept including a spot welded part and a laser welded part. In the fifth aspect of the present invention, when determining the size of the laser welded portion and the position of the laser welding, the laser welded portion derived by the first aspect of the present invention or the third aspect of the present invention is used. The fracture limit line may be used. When determining the size of the spot weld and the position of the spot weld, the fracture of the spot weld is derived by the second aspect of the present invention or the fourth aspect of the present invention. A limit line may be used. According to the first aspect of the present invention to the fourth aspect of the present invention, the fracture limit line can be derived with high accuracy, and therefore derived according to the first aspect of the present invention to the fourth aspect of the present invention. The finite element method analysis using the determined fracture limit line has high analysis accuracy. By welding the members using the results of the high-precision finite element method analysis, it is possible to manufacture a welded member in which the plate assembly, the size of the welded portion, and the welding position are appropriate.

  A sixth aspect of the present invention is a program for deriving a fracture limit line used when performing fracture prediction of a welded part by finite element method analysis. For steel types from which the fracture limit line and the fracture limit lines of multiple laser welds with different welding cooling rates were derived, the spot weld fracture limit line and the laser weld fracture limit line are expressed by equations. Conversion in the steel type from which the fracture limit line was derived, used in expressing the formula of the fracture limit line of the laser weld using the formulating step and the coefficient used in the formula of the fracture limit line of the spot weld A first conversion coefficient calculating step for calculating a coefficient, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, and a cooling rate specifying step. A relational expression creating step for creating a relational expression satisfying the above-mentioned cooling rate and the above conversion coefficient in the above steel grade from which the fracture limit line was derived, and a laser type for the steel grade from which the fracture limit line of the laser weld is not derived. Create the laser weld cooling rate deriving step to derive the laser weld cooling rate from the welding feed rate, and the laser weld cooling rate derived in the laser weld cooling rate deriving step in the relational expression creation process By substituting into the above relational expression, the second conversion coefficient calculation step for calculating the conversion coefficient in the steel type from which the fracture limit line of the laser weld is not derived, and the second conversion coefficient calculation step are calculated. In the above steel grade, where the fracture limit line of the laser weld is not derived, using the conversion factor obtained, the spot weld fracture derived in advance Boundary lines of a program for executing a fracture limit line conversion step of converting into fracture limit line of the laser welding unit, to the computer.

  A sixth aspect of the present invention is a program for causing a computer to execute the method for deriving a fracture limit line of a weld according to the first aspect of the present invention. As described above, according to the first aspect of the present invention, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process for the laser welded joint from which the fracture limit line has not been derived. is there. Therefore, according to the sixth aspect of the present invention, there is provided a program capable of accurately deriving a break limit line without performing a break limit line deriving process for a laser welded joint from which a break limit line has not been derived. Can be provided.

In the sixth aspect of the present invention, the fracture limit line of the spot welded portion represented by the formulating step is the formula (1), and the fracture limit line of the laser welded portion is the formula (1). 2) and the following expression (3), and the conversion coefficients calculated in the first conversion coefficient calculation step may be F _r and N _r in the above expression (3).
In the sixth aspect of the present invention, the fracture limit line of the spot welded part of the steel type from which the fracture limit line of the laser welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is known. , _{F s} and _{N s} in the formula (1) have been identified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the laser weld into the above equation (3), the evaluation object can be obtained without performing the fracture limit line derivation process. It is possible to derive the fracture limit line of the laser weld of the steel type. The fracture limit line of the laser weld derived as described above is in good agreement with the fracture limit line of the laser weld derived by the fracture limit line derivation process. Accordingly, a program is provided that can accurately derive the fracture limit line without performing the fracture limit line derivation process for the laser welded joint from which the fracture limit line has not been derived even in such a form. be able to.

  A seventh aspect of the present invention is a program for deriving a fracture limit line used when predicting fracture of a welded part by finite element method analysis. For steel grades with multiple fracture limit lines and spot welds with different welding cooling speeds, the laser weld fracture line and spot weld fracture line are expressed as follows: The above steel type from which the fracture limit line is derived, which is used to express the formula of the fracture limit line of the spot weld using the formulating step represented by and the coefficient used in the formula of the fracture limit line of the laser weld A first conversion coefficient calculating step for calculating a conversion coefficient in the above, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, and the cooling rate specifying step Regarding the steel type for which the fracture limit line of the spot weld is not derived, and the relation formula creating step for creating the relational expression that satisfies the obtained cooling rate and the conversion coefficient in the steel type from which the fracture limit line is derived. The above-mentioned relational expression created in the relational expression creating step, the spot welded part cooling rate grasping step for grasping the cooling rate of the spot welded part, and the cooling rate of the spot welded part grasped in the spot welded part cooling rate grasping step By using the second conversion coefficient calculation step for calculating the conversion coefficient in the above steel type from which the fracture limit line of the spot weld is not derived, and the conversion coefficient calculated in the second conversion coefficient calculation step. In the above steel types, where the fracture limit line of the spot weld is not derived, the fracture limit line of the laser weld derived in advance is derived. Is a program for executing a fracture limit line conversion step of converting into fracture limit line of spot welds, to the computer.

  A seventh aspect of the present invention is a program for causing a computer to execute the method for deriving a fracture limit line of a weld according to the second aspect of the present invention. As described above, according to the second aspect of the present invention, it is possible to accurately derive the fracture limit line without performing the fracture limit line derivation process for the spot welded joint from which the fracture limit line has not been derived. is there. Therefore, according to the seventh aspect of the present invention, there is provided a program capable of accurately deriving a break limit line without performing a break limit line deriving process for a spot welded joint from which a break limit line has not been derived. Can be provided.

Further, in the seventh aspect of the present invention, the fracture limit line of the spot welded portion represented by the formulating step is the formula (X) and the formula (Y), and the fracture of the laser welded portion. The limit line may be the above formula (Z), and the conversion coefficients calculated in the first conversion coefficient calculation step may be F _r ′ and N _r ′ in the above formula (Y).
In the seventh aspect of the present invention, the fracture limit line of the laser welded part of the steel type from which the fracture limit line of the spot welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is known. The coefficients F _l and N _l in the above formula (Z) are specified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the spot welded part into the above formula (Y), the evaluation target can be obtained without performing the fracture limit line derivation process. It is possible to derive a fracture limit line of a spot weld of a steel type. The fracture limit line of the spot weld that is derived in this way is in good agreement with the fracture limit line of the spot weld that is derived by the fracture limit line derivation process. Therefore, a program is provided that can accurately derive the fracture limit line without performing the fracture limit line derivation process for spot welded joints for which the fracture limit line has not been derived even in such a form. be able to.

  An eighth aspect of the present invention is a program for deriving a fracture limit line used when predicting fracture of a welded portion by finite element method analysis, and the spot welded portion is obtained in advance by a fracture limit line deriving process. For steel types from which the fracture limit line and the fracture limit lines of multiple laser welds with different welding cooling rates were derived, the spot weld fracture limit line and the laser weld fracture limit line are expressed by equations. Conversion in the above steel types from which the fracture limit line was derived, used to express the formula of the fracture limit line of the laser weld using the formula step and the coefficients used in the formula of the fracture limit line of the spot weld A first conversion coefficient calculating step for calculating a coefficient, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, and a cooling rate specifying step. A relational expression creating step for creating a relational expression that satisfies the cooling rate obtained and the conversion coefficient in the steel type from which the fracture limit line was derived was created in the relational expression creating step. A laser welding portion cooling rate deriving step for deriving a cooling rate of the laser welded portion from a feed rate of laser welding for a steel type for which a relational expression is prepared in advance and the fracture limit line of the laser welded portion has not been derived; By substituting the cooling rate of the laser welding part derived in the laser welding part cooling rate deriving step into the above relational expression prepared in the relational expression preparing step prepared in advance, the fracture limit line of the laser welded part is derived. A second conversion coefficient calculating step for calculating a conversion coefficient in the above steel type, and a variable calculated in the second conversion coefficient calculating step. Fracture limit line conversion step for converting the previously derived fracture limit line of the spot welded portion into the fracture limit line of the laser welded portion in the above steel type in which the fracture limit line of the laser welded portion has not been derived using the coefficient Is a program for causing a computer to execute.

  According to an eighth aspect of the present invention, a cooling rate and a fracture limit line created by causing a computer to execute the formulating step to the relational expression creating step in the sixth aspect of the present invention in advance are derived. This corresponds to a mode in which the computer executes the laser welding part cooling rate deriving step to the fracture limit line converting step using the relational expression satisfied by the conversion coefficient in the steel type. Even in such an embodiment, the fracture limit line of the laser weld can be derived without performing the fracture limit line derivation process, and the fracture limit line of the laser weld thus derived is It agrees well with the fracture limit line of the laser weld derived by the limit line derivation process. Therefore, according to the eighth aspect of the present invention, there is provided a program capable of accurately deriving a break limit line without performing a break limit line deriving process for a laser welded joint from which a break limit line has not been derived. Can be provided.

In the eighth aspect of the present invention, the fracture limit line of the spot welded portion represented by the formulating step is the formula (1), and the fracture limit line of the laser welded portion is the formula (1). 2) and the above equation (3), and the conversion coefficient calculated in the first conversion coefficient calculation step may be F _r and N _r in the above equation (3).
In the eighth aspect of the present invention, the fracture limit line of the spot welded part of the steel type from which the fracture limit line of the laser welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is known. , _{F s} and _{N s} in the formula (1) have been identified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the laser weld into the above equation (3), the evaluation object can be obtained without performing the fracture limit line derivation process. It is possible to derive the fracture limit line of the laser weld of the steel type. The fracture limit line of the laser weld derived as described above is in good agreement with the fracture limit line of the laser weld derived by the fracture limit line derivation process. Accordingly, a program is provided that can accurately derive the fracture limit line without performing the fracture limit line derivation process for the laser welded joint from which the fracture limit line has not been derived even in such a form. be able to.

  According to a ninth aspect of the present invention, there is provided a program for deriving a fracture limit line, which is used when performing fracture prediction of a welded portion by a finite element method analysis. For steel grades with multiple fracture limit lines and spot welds with different welding cooling speeds, the laser weld fracture line and spot weld fracture line are expressed as follows: The above steel type from which the fracture limit line is derived, which is used to express the formula of the fracture limit line of the spot weld using the formulating step represented by and the coefficient used in the formula of the fracture limit line of the laser weld A first conversion coefficient calculating step for calculating a conversion coefficient in the above, a cooling rate specifying step for obtaining a cooling rate of the spot welded portion and the laser welded portion, and the cooling rate specifying step Created in the relational expression creating step by causing the computer to execute a relational expression creating step for creating a relational expression satisfying the obtained cooling rate and the conversion coefficient in the steel type from which the fracture limit line is derived. For the steel grade for which the fracture limit line of the spot weld is not derived, and the spot weld cooling rate grasping step for grasping the cooling rate of the spot weld and the spot weld cooling rate grasp By substituting the cooling rate of the spot welded part grasped in the step into the relational expression prepared in the relational expression creating step prepared in advance, the conversion in the above steel type where the fracture limit line of the spot welded part is not derived A second conversion coefficient calculation step for calculating a coefficient, and the conversion coefficient calculated in the second conversion coefficient calculation step Using the above-mentioned steel grade in which the fracture limit line of the spot weld is not derived, the fracture limit line conversion step for converting the fracture limit line of the laser weld derived in advance into the fracture limit line of the spot weld, and Is a program for causing a computer to execute.

  According to a ninth aspect of the present invention, a cooling rate and a break limit line created by causing a computer to execute the formulating step to the relational expression creating step in the seventh aspect of the present invention in advance are derived. This corresponds to an aspect in which the computer executes the spot welded part cooling rate deriving step to the fracture limit line converting step using the relational expression satisfied by the conversion coefficient in the steel type. Even in such a form, the fracture limit line of the spot weld can be derived without performing the fracture limit line derivation process. It agrees well with the fracture limit line of spot welds derived by the limit line derivation process. Therefore, according to the ninth aspect of the present invention, there is provided a program capable of accurately deriving a break limit line without performing a break limit line deriving process for a spot welded joint from which a break limit line has not been derived. Can be provided.

Moreover, in the ninth aspect of the present invention, the fracture limit line of the spot welded portion represented by the formulating step is the above formula (X) and the above formula (Y), and the fracture of the laser welded portion. The limit line may be the above formula (Z), and the conversion coefficients calculated in the first conversion coefficient calculation step may be F _r ′ and N _r ′ in the above formula (Y).
In the ninth aspect of the present invention, the fracture limit line of the laser welded part of a steel type from which the fracture limit line of the spot welded part has not been derived (hereinafter referred to as “evaluation target steel type” in this paragraph) is known. The coefficients F _l and N _l in the above formula (Z) are specified. Therefore, by substituting these specified coefficients and the conversion coefficient calculated using the cooling rate of the spot welded part into the above formula (Y), the evaluation target can be obtained without performing the fracture limit line derivation process. It is possible to derive a fracture limit line of a spot weld of a steel type. The fracture limit line of the spot weld that is derived in this way is in good agreement with the fracture limit line of the spot weld that is derived by the fracture limit line derivation process. Therefore, a program is provided that can accurately derive the fracture limit line without performing the fracture limit line derivation process for spot welded joints for which the fracture limit line has not been derived even in such a form. be able to.

A tenth aspect of the present invention is a computer-readable recording medium on which a program according to the sixth aspect of the present invention to the ninth aspect of the present invention is recorded.
According to the sixth aspect of the present invention and the eighth aspect of the present invention, the fracture limit line is accurately derived without performing the fracture limit line derivation process for the laser weld joint from which the fracture limit line has not been derived. Is possible. Further, according to the seventh aspect of the present invention and the ninth aspect of the present invention described above, with respect to a spot welded joint from which the fracture limit line has not been derived, the fracture limit line is accurately obtained without performing the fracture limit line derivation process. It is possible to derive well. Therefore, according to the tenth aspect of the present invention, a program capable of accurately deriving the break limit line without performing the break limit line deriving process for a joint made of a welding technique in which the break limit line has not been derived. , And a computer-readable recording medium can be provided.

  In the present invention, the conversion coefficient of the fracture limit line is calculated using the specified cooling rate of the weld and the relational expression. Thereby, even when it is a case where the fracture limit line of the welding part which consists of the welding technique from which the fracture limit line has not been derived | led-out is derived | led-out and estimated, the conversion coefficient can be calculated using the cooling rate of the identified welding part. Then, by using this conversion coefficient and the fracture limit line of the welded portion formed by the derived welding technique, the weld limit consisting of the welding technique in which the fracture limit line is not derived without performing the fracture limit line derivation process. The fracture limit line can be easily derived and predicted. Therefore, according to the present invention, it is possible to accurately derive the fracture limit line of a welded portion without performing the fracture limit line derivation process for a joint made of a welding technique in which the fracture limit line has not been derived. Method for deriving the fracture limit line, method for manufacturing a member having a welded portion using the derivation method, a program for causing a computer to execute the derivation method, and a computer-readable recording medium storing the program Can be provided.

It is a figure which shows the fracture limit line of a spot weld part and a laser weld part. It is a figure which shows the relationship between conversion factor _Fr and _Nr, and the cooling rate _Cr . It is a figure explaining derivation | leading-out method S10 of the fracture limit line of the welding part which concerns on this invention. It is a figure which shows the relationship between the feed rate of laser welding, and a cooling rate. It is a figure explaining derivation | leading-out method S20 of the fracture limit line of the welding part which concerns on this invention. It is a figure explaining the derivation system 10 of the fracture limit line of a welding part. It is a figure explaining the derivation system 20 of the fracture limit line of a welding part. It is a figure which shows the deformation resistance curve of the steel kind of evaluation object. It is a figure which shows the fracture limit line of the steel kind of evaluation object. It is a figure which shows the joint shape of the laser-welded joint tension test model of an Example.

1. Background to completion of the present invention According to Non-Patent Documents 1 and 2 above, the cross-sectional area of the test part of the FEM analysis result simulating the tensile test of a smooth test piece and a notched micro test piece is the actual value of the fracture test piece. Can be defined as the local smooth fracture strain and notch fracture strain of the specimen. Similarly, the stress triaxiality at the breaking limit can be defined. Further, by performing this process for each weld metal portion, HAZ portion, and base material portion, it is possible to derive the smooth rupture strain and the notch rupture strain and the stress triaxiality at the rupture limit at each portion. Then, the fracture limit line can be constructed by approximating the relation between the fracture strain and the stress triaxiality by a power function.

  As shown in FIG. 1, the effect of stress triaxiality is smaller in the laser welded part than in the spot welded part, and the fracture strain at the fracture limit line is that of the laser welded part than that of the spot welded part. Shows a tendency to increase. Therefore, it is considered that the coefficient N in the equation that approximates the fracture limit line is smaller and the coefficient F is larger in the laser welded part than in the spot welded part. In addition, the cooling rate of the laser welded portion tends to be slower than that of the spot welded portion, and the hardness of the weld metal portion decreases as the cooling rate decreases. Thus, it is considered that there is a correlation between the cooling rate and the mechanical characteristics in the weld zone. Moreover, in the tensile test, the cross-sectional area of the fracture test piece is converted into a fracture drawing. Since the fracture drawing is one of the mechanical properties, the inventors considered that there is also a relationship between the fracture drawing and the breaking strain derived therefrom and the cooling rate. As a result of earnest research based on such an idea, the present inventors have found that the above formulas (4) and (5) and the coefficients in the constitutive formula of the fracture limit line of the spot welded part (formula (1)) It was found that the constitutive formula (formula (3)) rewritten from the constitutive formula of the fracture limit line (formula (2)) of the laser welded part can be specified. Moreover, the present inventors use the equations (4) ′ and (5) ′, which will be described later, and the coefficient in the constitutive equation (equation (Z)) of the fracture limit line of the laser welded portion to break the spot welded portion. It has also been found that a constitutive formula (formula (Y)) obtained by rewriting the constitutive formula of the limit line (formula (X)) can be specified.

The present invention has been made based on the above findings. That is, in the present invention, the fracture limit line of the derived spot weld and the conversion coefficients F _r and N _r obtained by substituting the cooling rate C _r into the above formulas (4) and (5), By using this, it is possible to accurately derive the fracture limit line of the laser weld that has not been derived without performing the fracture limit line derivation process. Further, in the present invention, the conversion limit F _r ′ and N _r ′ obtained by substituting the cooling rate into the rupture limit line of the derived laser weld and the following expressions (4) ′ and (5) ′. , The fracture limit line of the spot weld that has not been derived can be accurately derived without performing the fracture limit line derivation process.

  Hereinafter, the present invention according to the embodiment will be described in detail. The following embodiments are examples of the present invention, and the present invention is not limited to the embodiments described below.

2. Method for deriving the fracture limit line of the weld 2.1. Method for Deriving Fracture Limit Line of Laser Welded Part FIG. 3 shows a method for deriving a fracture limit line for a welded part according to one embodiment of the present invention (hereinafter simply referred to as “derivative method S10”). The derivation method S10 shown in FIG. 3 includes a formulating step S11, a first conversion coefficient calculating step S12, a cooling rate specifying step S13, a relational expression creating step S14, a laser weld cooling rate derivation step S15, 2 conversion coefficient calculation process S16 and fracture limit line conversion process S17.

2.1.1. Formulation process S11 (process S11)
In step S11, the rupture limit line of the spot welded portion is derived from a steel type in which the rupture limit line of the spot welded portion and the fracture limit lines of a plurality of laser welded portions having different welding cooling rates are derived by the rupture limit line derivation process. In this step, the line is expressed in the form of the above formula (1), and the fracture limit line of the laser weld is expressed in the form of the above formula (2) and the above formula (3). Here, the fracture limit line of the steel type from which the fracture limit line was derived can be expressed by an expression in which the coefficients of the above formulas (1) to (3) are replaced with specific numerical values. That is, “the above formula F (F is expressed in the form of (1), (2), or (3))” means that F _s , N _s , F _l , and N _l are specific numerical values. It means to express with the formula replaced with. In step S11, for example, a base material strength class 590 MPa grade steel plate can be used as a steel type in which the fracture limit lines of the spot welded portion and the two types of laser welded portions are known by the fracture limit line derivation process.

2.1.2. First conversion coefficient calculation step S12 (step S12)
Step S12 is a step of calculating the conversion coefficients F _r and N _r of the above formula (3) regarding the steel type of step S11 using the formula represented in step S11. From the above equations (2) and (3), F _r = F ₁ / F _s and N _r = N ₁ / N _s, so by substituting numerical values for F ₁ , F _s , N ₁ , and N _s , F _r and N _r can be calculated.

2.1.3. Cooling rate specifying step S13 (step S13)
Step S13., A process for obtaining the cooling rate C _r of the spot welds and laser welds. Step S13., The steels used in the step S11, so obtaining a cooling rate _{C r} of the spot welds and laser welds, the use of base material strength class 590MPa grade steel in step S11, step S13., For example, It can be set as the process of specifying the cooling rate of the spot welding part of the said steel plate, and two types of cooling rates of a laser welding part. The cooling rate of the spot welded portion and the laser welded portion can be obtained by measurement with a radiation thermometer or the like when the weld sample is manufactured. In laser welding, the relationship shown in FIG. 4 is established between the feed rate W _r and the cooling rate C _r . Therefore, the cooling rate C _r of the laser weld (the d1 and d2 parameters) function shown in the following formula (6) can be approximated by. It should be noted that by increasing the measurement conditions, it is possible to use an approximation (for example, logarithmic approximation, power approximation, etc.) other than the linear approximation shown in the following formula (6).
C _r = d1 · W _r + d2 (6)

2.1.4. Relational expression creation step S14 (step S14)
Step S14 is a step of creating a relational expression that satisfies the cooling rate C _r and the conversion coefficients F _r and N _{r of} equation (3). As described above, the relationship shown in FIG. 2 is established between the cooling rate C _r and the conversion coefficients F _r and N _r . Therefore, the above formulas (4) and (5) can be derived as relational expressions satisfied by the cooling rate C _r and the conversion coefficients F _r and N _r . In step S14, using a cooling rate _{C r} identified in step S13.

2.1.5. Laser welding part cooling rate deriving step S15 (step S15)
In step S15, laser welding is performed on the steel type for which the fracture limit line of the laser weld is not measured (in the description of the derivation method S10, it may be referred to as “evaluation target steel type”) from the laser welding feed speed W _r. This is a step of deriving the cooling rate _{Cr of the} part. In step S15, by using equation (6), it is possible to derive the cooling rate C _r of the laser weld.

2.1.6. Second conversion coefficient calculation step S16 (step S16)
Step S16, the cooling rate C _r of the laser welds evaluated grades derived in the above step S15, equation created in the above step S4 by substituting into (Equation (4) and (5)) This is a step of calculating the conversion coefficient of the steel type to be evaluated.

2.1.7. Break limit line conversion step S17 (step S17)
Step S17 uses the conversion coefficient of the evaluation target steel type calculated in step S16 to calculate the fracture limit line of the spot welded portion of the evaluation target steel type derived by the fracture limit line derivation process, and the laser welded portion of the evaluation target steel type. It is the process of converting into a fracture limit line. As described above, the breaking limit line of spot welds can be represented in the form of the equation (1), if the fracture limit line is derivation of F _s and N _s in the formula (1) Specific figures are known. Therefore, the specific numerical values of F _s and N _s, and a conversion factor to be evaluated grades calculated at step S16, by substituting into the equation (3), the table in the form of the equation (3) It is possible to derive the constitutive equation of the fracture limit line of the laser welded portion of the steel type to be evaluated.

  As described above, according to the derivation method S10 including the steps S11 to S17, it is possible to derive the fracture limit line of the laser welded portion of the evaluation target steel type that has not been derived without performing the fracture limit line derivation process.

2.2. Method for Deriving Fracture Limit Line of Spot Welded Part FIG. 5 shows a method S20 for deriving a fracture limit line for a welded part according to another embodiment of the present invention (hereinafter simply referred to as “derivative method S20”). The derivation method S20 shown in FIG. 5 includes a formulating step S21, a first conversion coefficient calculating step S22, a cooling rate specifying step S23, a relational expression creating step S24, a spot weld cooling rate grasping step S25, 2 conversion coefficient calculation process S26, and fracture | rupture limit line conversion process S27.

2.2.1. Formulation process S21 (process S21)
In step S21, the rupture limit line of the laser welded portion and a plurality of spot welded portion rupture limit lines with different welding cooling speeds derived from the rupture limit line derivation process are ruptured at the spot welded portion. In this step, the limit line is expressed in the form of the above formula (X) and the above formula (Y), and the fracture limit line of the laser weld is expressed in the form of the above formula (Z). Here, the rupture limit line of the steel type from which the rupture limit line is derived can be expressed by an expression in which the coefficients of the above formulas (X) to (Z) are replaced with specific numerical values. That is, “the above formula F ′ (F ′ is represented in the form of (X), (Y), or (Z))” specifically refers to F _s , N _s , F _l , and N _l . This means that it is expressed by an expression that is replaced with a numeric value. In step S21, for example, a base material strength class 590 MPa grade steel plate can be used as a steel type in which the fracture limit lines of the laser weld and the two types of spot welds are known by the fracture limit line derivation process.

2.2.2. First conversion coefficient calculation step S22 (step S22)
Step S22 is a step of calculating the conversion coefficients F _r ′ and N _r ′ of the above formula (Y) for the steel type of step S21 using the formula represented in step S21. From the above formulas (X) and (Y), F _r ′ = F _s / F _l and N _r ′ = N _s / N _l, so substitute numerical values for F _l , F _s , N _l , and N _s. Thus, F _r ′ and N _r ′ can be calculated.

2.2.3. Cooling rate specifying step S23 (step S23)
Reaction process S23 is a process for obtaining the cooling rate C _r of the spot welds and laser welds. Since step S23 is the same as step S13, description thereof is omitted here.

2.2.4. Relational expression creation step S24 (step S24)
Step S24 is a step of creating a relational expression that satisfies the cooling rate C _r and the conversion coefficients F _r ′ and N _r ′ of the equation (Y). As described above, the relationship shown in FIG. 2 is established between the cooling rate C _r and the conversion coefficients F _r ′ and N _r ′. Therefore, the following formulas (4) ′ and (5) ′ can be derived as relational expressions satisfied by the cooling rate C _r and the conversion coefficients F _r ′ and N _r ′. In step S24, using a cooling rate _{C r} identified in step S23.
F _r ′ = −a 1 ′ · ln (C _r ) + a 2 ′ (4) ′
_Nr ′ = b1 ′ · ln ( _Cr ) −b2 ′ (5) ′
Here, a1 ′, a2 ′, b1 ′, b2 ′ are parameters (> 0).

2.2.5. Spot welding part cooling rate grasping step S25 (step S25)
Step S25 is a step of grasping the cooling rate of the spot welded part for a steel type in which the fracture limit line of the spot welded part is not measured (in the description of the derivation method S20, it may be referred to as “evaluation target steel type”). is there. In spot welding, since the cooling conditions do not change greatly depending on the welding conditions, for example, the representative value can be set as the cooling rate of the spot welded part. Specifically, the cooling rate of the spot welded part of the steel type used in step S21 is set. It can be set as the cooling rate of the spot welding part grasped | ascertained by process S25. In addition, the cooling rate of the spot welded portion of the steel grade to be evaluated is measured in advance using a radiation thermometer or the like, and the measured cooling rate is the cooling rate of the spot welded portion grasped in step S25. You can also

2.2.6. Second conversion coefficient calculation step S26 (step S26)
In step S26, by substituting the cooling rate of the spot welded portion of the evaluation target steel type obtained in step S25 into the relational expressions (formula (4) ′ and formula (5) ′) created in step S24, This is a step of calculating the conversion coefficient of the steel type to be evaluated.

2.2.7. Break limit line conversion step S27 (step S27)
Step S27 uses the conversion coefficient of the evaluation target steel type calculated in the above step S26 to determine the fracture limit line of the laser welded portion of the evaluation target steel type derived by the fracture limit line derivation process, and the spot welded portion of the evaluation target steel type. It is the process of converting into a fracture limit line. As described above, the fracture limit line of the laser weld can be expressed in the form of the above formula (Z), and when the fracture limit line is derived, F ₁ and N ₁ in formula (Z) Specific figures are known. Therefore, the specific numerical values of F _l and N _l, and a conversion factor to be evaluated grades calculated at step S26, by substituting the above equation to (Y), the table in the form of the above formula (Y) It is possible to derive the constitutive equation of the fracture limit line of the spot welded portion of the evaluation target steel type.

  As described above, according to the derivation method S20 including the steps S21 to S27, the fracture limit line of the spot welded portion of the evaluation target steel type that has not been derived can be derived without performing the fracture limit line derivation process.

3. Derivation system for weld fracture limit line 3.1. System for Deriving Fracture Limit Line of Laser Welded Portion FIG. 6 shows a system for deriving a fracture limit line of a welded portion according to another embodiment of the present invention (hereinafter simply referred to as “derivation system 10”). The derivation system 10 shown in FIG. 6 includes data (at least coefficients F _s , N of approximate formulas) regarding the fracture limit line of the spot weld and a plurality of laser weld fracture lines with different cooling rates of the weld. Data relating to _{s 1} , F ₁ , N _{1 (the} same _applies below), and database 1 storing data relating to the cooling rate of the weld zone, and data selected from database 1 are used to convert conversion factors F _r and N using a relational expression creating unit 2 to create a relationship between _r and the cooling rate C _r, steel species fracture limit line of the laser welding portion is not derived in (evaluated grades), the cooling rate C _r of the laser weld Using the conversion coefficients F _r and N _r of the steel grade to be evaluated and the coefficients in the approximate expression of the fracture limit line of the spot weld of the steel grade to be evaluated, And a breakage limit line conversion part 3 for deriving a breakage limit line at the contact portion.

  In the database 1, data on the fracture limit line of the spot welded portion, the fracture limit line of the laser welded portion, and data on the cooling rate of the welded portion measured in the past for a certain steel type are recorded. The form of the database 1 is not particularly limited as long as these data can be recorded.

In addition to the function of calculating the conversion coefficients F _r and N _r using the coefficient selected from the database 1, the relational expression creating unit 2 adds the cooling rate C _r selected from the database 1 and the calculated conversion coefficient F _It has a function of creating a relational expression that _r and Nr satisfy. As the relational expression creating unit 2, an arithmetic device in which spreadsheet software or the like is installed can be used as appropriate. In the relational expression creation unit 2, each coefficient of the constitutive formula of the fracture limit line recorded in the database 1 is input together with the cooling rate of the corresponding welding technique, and the conversion coefficient of the rupture limit line constitutive formula is calculated by spreadsheet software. The above equations (4) and (5), which are equations, are determined. Since the specific calculation content is as described above, the description is omitted here.

The break limit line conversion unit 3 only needs to be able to execute the above steps S15 to S17, and an arithmetic device in which spreadsheet software or the like is installed can be used as appropriate. In the fracture limit line conversion unit 3, the conversion coefficients F _r and N _r of the evaluation target steel type are substituted into the above formulas (4) and (5) by using the cooling rate C _r of the evaluation target steel type as a parameter value. Is calculated. The calculated conversion coefficients F _r and N _r and each coefficient of an equation that approximates the fracture limit line of the spot welded portion of the steel grade to be evaluated, which is recorded in the database 1 and is derived in the fracture limit line derivation process ( By substituting specific numerical values of F _s and N _s ) into the above equation (3), a constitutive equation for the fracture limit line of the laser welded portion of the steel type to be evaluated is derived. Since the specific calculation content in the break limit line conversion part 3 is as above-mentioned, description is abbreviate | omitted here.

  Thus, the derivation method S10 can be performed by the derivation system 10. Therefore, according to the present invention, the derivation system capable of deriving the fracture limit line of the laser welded portion of the evaluation target steel type that has not been derived without performing the fracture limit line derivation process according to the present invention. 10 can be provided.

3.2. FIG. 7 shows a system for deriving a fracture limit line of a welded portion according to another embodiment of the present invention (hereinafter, simply referred to as “derivation system 20”). 7, components similar to those of the derivation system 10 are denoted by the same reference numerals as those used in FIG. 6, and description thereof is omitted as appropriate. The derivation system 20 shown in FIG. 7 creates a relational expression that creates a relational expression between the conversion coefficients F _r ′ and N _r ′ and the cooling rate C _r by using the database 1 and data selected from the database 1. The conversion factors F _r ′ and N _r ′ of the evaluation target steel type calculated using the cooling rate of the spot welded part of the steel type (evaluation target steel type) for which the fracture limit line of the spot welded part is not derived. And a fracture limit line conversion part 3 ′ for deriving a fracture limit line of a spot welded part of the evaluation target steel type using a coefficient in a fracture limit line of the laser welded part of the evaluation target steel type.

In addition to the function of calculating the conversion coefficients F _r ′ and N _r ′ using the coefficients selected from the database 1, the relational expression creating unit 2 ′ calculates the cooling rate C _r selected from the database 1 and It has a function of creating a relational expression satisfying the conversion coefficients F _r ′ and N _r ′. As the relational expression creating unit 2 ′, an arithmetic device in which spreadsheet software or the like is installed can be used as appropriate. In the relational expression creation unit 2 ′, each coefficient of the constitutive equation of the fracture limit line recorded in the database 1 is input together with the cooling rate of the corresponding welding method, and the conversion coefficient of the rupture limit line constitutive equation is calculated by spreadsheet software. The above formulas (4) ′ and (5) ′, which are calculation formulas, are determined. Since the specific calculation content is as described above, the description is omitted here.

The break limit line conversion unit 3 ′ is only required to be able to execute the above steps S25 to S27, and an arithmetic device in which spreadsheet software or the like is installed can be used as appropriate. In the fracture limit line conversion unit 3 ′, the conversion rate F _r of the evaluation target steel type is substituted into the above formula (4) ′ and formula (5) ′ by assigning the cooling rate C _r of the evaluation target steel type as a parameter value. 'And N _r ' are calculated. Each of the equations for approximating the calculated conversion coefficients F _r ′ and N _r ′ and the fracture limit line of the laser welded portion of the steel grade to be evaluated, which is recorded in the database 1 and derived in the fracture limit line derivation process. By substituting specific numerical values of the coefficients (F _l and N _l ) into the above equation (Y), a constitutive equation for the fracture limit line of the spot welded portion of the steel type to be evaluated is derived. Since the specific calculation contents in the fracture limit line conversion unit 3 ′ are as described above, the description thereof is omitted here.

  Thus, the derivation method S20 can be performed by the derivation system 20. Therefore, by adopting such a configuration, according to the present invention, a derivation system capable of deriving the fracture limit line of the spot welded portion of the evaluation target steel type that has not been derived without performing the fracture limit line derivation process. 20 can be provided.

  In the above description regarding the derivation systems 10 and 20, the relational expression creating unit 2 and the breakage limit line conversion unit 3 or the relational expression creation unit 2 ′ and the breakage limit line conversion unit 3 ′ are provided separately. However, the system for deriving the fracture limit line of the weld according to the present invention is not limited to this form. One arithmetic unit may function as a relational expression creation unit and a break limit line conversion unit.

4). Method for Manufacturing Member with Welded Portion The method for manufacturing a member with a welded portion according to another embodiment of the present invention (hereinafter referred to as “the manufacturing method of the present invention”) is the fracture limit of the present invention described above. The finite element method analysis is performed using the fracture limit line predicted by the line derivation method, and the plate assembly of the member, the size of the weld, and / or the welding position are determined based on the analysis result. And the step of welding the members in accordance with the determined plate assembly, the size of the welded portion, and / or the welding position.

  As a specific form of the manufacturing method of the present invention, for example, a finite element method analysis is performed using the fracture limit line predicted by the derivation method S10 or the derivation method S20, and the joint plate is based on the analysis result. Determine the assembly, weld bead width, and / or spacing. And the form which manufactures the joint provided with the welding part can be mentioned by welding a member according to the determined board assembly, the width | variety of a weld bead, and / or a space | interval. According to the manufacturing method of the present invention, it is possible to manufacture a welded member in which the plate assembly, the size of the welded portion, and the welding position are appropriate. By reflecting this in the design of, for example, an automobile member or the like, it is possible to manufacture an automobile structural member that can suppress welding portion breakage during collision deformation of the automobile and appropriately absorb energy.

  In the said description, although the form applied when this invention uses a steel material as a welding material was illustrated, this invention is not limited to the said form. The present invention can be applied even when analyzing a welded member made of another metal material such as titanium or aluminum.

  Moreover, in the said description regarding the derivation | leading-out method of the fracture limit line of the welding part of this invention, the form which has seven processes (process S11-process S17 or process S21-process S27) from a numerical formula process to a fracture limit line conversion process. However, the present invention is not limited to this form. For example, using the relational expression created in the past from the formulating process to the relational expression creating process, the laser welding part cooling rate derivation process to the fracture limit line conversion process, or the spot welded part cooling rate grasping process to fracture It is also possible to adopt an embodiment in which only the limit line conversion step is performed. Even in such a form, the same effect as the derivation method S10 or the derivation method S20 can be achieved.

5. In the present invention, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various recording media. A configuration in which the computer (or CPU, MPU, etc.) of the apparatus reads and executes the program is also included. That is, such a program and a computer-readable recording medium on which the program is recorded are included in the present invention.

When the program of the present invention is a program for causing the computer to derive the fracture limit line of the laser welded portion of the evaluation target steel type that has not been derived, without performing the fracture limit line derivation process, the formulating step includes the above step S11, The first conversion coefficient calculation step is the step S12, the cooling rate specifying step is the step S13, the relational expression creation step is the step S14, the laser weld cooling rate derivation step is the step S15, and the second conversion coefficient is calculated. The step is a step for causing the computer to execute the step S16, and the fracture limit line converting step is to execute the step S17.
Further, when the program of the present invention is a program for causing the computer to derive the fracture limit line of the spot welded portion of the evaluation target steel type that has not been derived, without performing the fracture limit line derivation process, the formulating step is the step S21 described above. The first conversion coefficient calculating step is the above step S22, the cooling rate specifying step is the above step S23, the relational expression creating step is the above step S24, the spot welding portion cooling rate grasping step is the above step S25, and the second conversion. The coefficient calculation step is a step for causing the computer to execute step S26, and the fracture limit line conversion step is for causing the computer to execute step S27.
The explanation about each step in the program of the present invention and the explanation about the computer-readable recording medium on which the program of the present invention is recorded are the explanation of the corresponding process in the above-mentioned “2. The contents of “3. Derivation system of fracture limit line of welded part” and the contents overlap. Therefore, description of the program of the present invention and a computer-readable recording medium recording the program is omitted here.

  The present invention will be further described with reference to examples.

The above-mentioned formula (1) shows the break limit line of the spot welded part of the steel type in which the break limit line is derived in advance by the process of deriving the break limit line, and the break limit line of the laser welded part at two welding cooling rates. -It represented with the form of Formula (3). The relationship between the conversion coefficients F _r and N _r and the cooling rate C _r of the welded part is expressed in the form of the above formulas (4) and (5), and constants (a1, a2, b1, b2) of these formulas are expressed. ) Was identified. Further, the relationship between the feed rate of laser welding and the cooling rate of the laser welded part is expressed by the above formula (6), and the constants (d1 and d2) were specified. Furthermore, in calculating the cooling rate of the laser welded portion to be evaluated, the feed rate was specified as 2 m / min from the welding conditions.
The cooling rate of the laser welded part was calculated by substituting the feed rate specified in this way into the above equation (6). The calculated cooling rate of the laser weld was C _r = 347 ° C./s. Next, the conversion coefficients F _r and N _r were calculated by substituting this C _r into the above formulas (4) and (5). The calculated conversion coefficients were F _r = 1.046 and N _r = 0.836.
Each coefficient (F _s and N _s ) in an equation that approximates the fracture limit line of the spot welded portion of the steel grade to be evaluated, which has been derived in the fracture limit line derivation process, and the calculated conversion coefficient (F _r = 1.046). , N _r = 0.836) is substituted into the above equation (3) to identify an equation that approximates the fracture limit line of the laser weld.

  Here, the steel type to be evaluated has a tensile strength of 590 MPa class, Young's modulus 206 GPa, Poisson's ratio 0.3, the deformation resistance curve of the steel type is as shown in FIG. 8, and the fracture limit line of the steel type is shown in FIG. As shown. For reference, analysis with the spot weld fracture limit line set without applying this technology is also performed, analysis A (invention example) when this technology is applied, and analysis B (comparison) when this technology is not applied Example). Further, FIG. 9 also plots the actual measurement values of the fracture limit line of the laser welded portion of the evaluation target steel type. As shown in FIG. 9, the fracture limit line of Analysis A, which is an example of the present invention, coincided with the actual measurement value. On the other hand, the fracture limit line of Analysis B, which is a comparative example, did not match the actual measurement value.

  These material property data were applied to the tensile test model of the laser welded joint shown in FIG. 10, and FEM analysis was performed. FIG. 10A is a diagram showing a symmetrical model of tensile shear in the plate width direction, and FIG. 10B is an enlarged view of a part (welded metal portion) of the model indicated by a dotted line in FIG. FIG. Reference numeral 11 shown in FIG. 10B is a base material, reference numeral 12 is HAZ, reference numeral 13 is a weld metal, and a break limit line is set for each of them. For HAZ, data obtained by averaging the base metal data and the weld metal data is set. FIG. 10 (c) shows a fracture form of the analysis result. This is an example in which a fracture limit line is set and an element that has reached the fracture limit line is deleted to reproduce a reduction in rigidity due to fracture. Table 1 shows an error between the maximum load of the test result and the maximum load of the analysis result.

  As shown in Table 1, the error of analysis A, which is an example of the present invention, is smaller than the error of analysis B, which is a comparative example, and the error of analysis A is less than ¼ of the error of analysis B. From this result, it was found that according to the present invention, the fracture limit line deriving process can be omitted and the fracture limit line can be accurately predicted even for a steel type whose fracture limit line of the laser weld is not measured.

  ADVANTAGE OF THE INVENTION According to this invention, the fracture limit line of the welding part used at the time of FEM analysis of the various members provided with the welding part can be estimated with sufficient accuracy. As a result, it is not necessary to perform the process of deriving the fracture limit line individually during the FEM analysis, and labor can be reduced. The fracture limit line predicted by the present invention can be used, for example, in the FEM analysis for examining the plate assembly and weld bead width of a laser welded joint, and the result is reflected in the member design of the automobile. Can do.

DESCRIPTION OF SYMBOLS 1 ... Database 2, 2 '... Relational expression preparation part 3, 3' ... Breaking limit line conversion part 10, 20 ... Derivation system of fracture limit line of welding part 11 ... Base material 12 ... HAZ
13 ... weld metal

Claims (18)

A method for deriving a fracture limit line, which is used when performing fracture prediction of a welded portion by a finite element method analysis,
For the steel types from which the fracture limit line of the spot welded portion and the fracture limit lines of a plurality of laser welded portions with different welding cooling rates were derived by the fracture limit line derivation process, the fracture limit line of the spot welded portion, and , Expressing the fracture limit line of the laser weld by a formula,
Calculates the conversion coefficient in the steel type from which the fracture limit line was derived, used when expressing the formula of the fracture limit line of the laser weld using the coefficient used in the formula of the fracture limit line of the spot weld. A first conversion coefficient calculation step;
A cooling rate specifying step for determining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression that satisfies the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which the fracture limit line is derived;
For the steel types for which the fracture limit line of the laser weld is not derived, a laser weld cooling rate deriving step for deriving the cooling rate of the laser weld from the laser welding feed rate;
By substituting the cooling rate of the laser welding part derived in the laser welding part cooling rate deriving step into the relational expression created in the relational expression creating step, the fracture limit line of the laser welded part is derived. A second conversion coefficient calculation step of calculating a conversion coefficient in the steel type that is not,
Using the conversion coefficient calculated in the second conversion coefficient calculation step, the previously determined fracture limit line of the spot welded part in the steel type from which the fracture limit line of the laser welded part has not been derived is laser-welded. Breaking line conversion process for converting to the breaking line of the part,
A method for deriving a fracture limit line of a welded portion. In the formulating step, the fracture limit line of the spot welded part is represented by the following formula (1), and the fracture limit line of the laser welded part is represented by the following formula (2) and the following formula (3),
The method for deriving a fracture limit line for a weld according to claim 1, wherein the conversion coefficients calculated in the first conversion coefficient calculation step are F _r and N _r in the following formula (3).
ε _p = F _s · σ _triax ^ N _s (1)
_{ε p = F l · σ triax} ^ N l ... (2)
ε _p = F _s · F _r · σ _triax ^ (N _s · N _r ) (3)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A method for deriving a fracture limit line, which is used when performing fracture prediction of a welded portion by a finite element method analysis,
For the steel types in which the fracture limit line of the laser welded part and the fracture limit lines of the spot welded part with different welding cooling rates are derived in advance by the process of deriving the fracture limit line, the fracture limit line of the laser welded part is obtained. And a formulating step for expressing the break limit line of the spot welded part by a formula,
The conversion factor in the steel type from which the fracture limit line was derived is used to represent the formula of the fracture limit line of the spot welded portion using the coefficient used in the formula of the fracture limit line of the laser weld. A first conversion coefficient calculation step;
A cooling rate specifying step for determining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression that satisfies the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which the fracture limit line is derived;
For steel types for which the fracture limit line of the spot weld has not been derived, the spot weld cooling rate grasping process for grasping the cooling rate of the spot weld,
By substituting the cooling rate of the spot welded part grasped in the spot welded part cooling rate grasping process into the relational expression created in the relational expression creating step, the fracture limit line of the spot welded part is derived. A second conversion coefficient calculation step of calculating a conversion coefficient in the steel type that is not,
Using the conversion coefficient calculated in the second conversion coefficient calculation step, spot break welding is performed in advance on the laser welding part of the steel grade from which the fracture limit line of the spot welding part has not been derived. Breaking line conversion process for converting to the breaking line of the part,
A method for deriving a fracture limit line of a welded portion. In the formulating step, the fracture limit line of the spot weld is represented by the following formula (X) and the following formula (Y), and the fracture limit line of the laser weld is represented by the following formula (Z),
The method for deriving a fracture limit line of a weld according to claim 3, wherein the conversion coefficients calculated in the first conversion coefficient calculation step are F _r 'and N _r ' in the following formula (Y).
ε _p = F _s · σ _triax ^ N _s (X)
_{ε p = F l · F r} '· σ triax ^ (N l · N r') ... (Y)
ε _p = F _l · σ _triax ^ N _l (Z)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A method for deriving a fracture limit line, which is used when performing fracture prediction of a welded portion by a finite element method analysis,
For the steel types from which the fracture limit line of the spot welded portion and the fracture limit lines of a plurality of laser welded portions with different welding cooling rates were derived by the fracture limit line derivation process, the fracture limit line of the spot welded portion, and , Expressing the fracture limit line of the laser weld by a formula,
Calculates the conversion coefficient in the steel type from which the fracture limit line was derived, used when expressing the formula of the fracture limit line of the laser weld using the coefficient used in the formula of the fracture limit line of the spot weld. A first conversion coefficient calculation step;
A cooling rate specifying step for determining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression that satisfies the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which the fracture limit line is derived;
And prepare the relational expression created in the relational expression creating step in advance,
For the steel types for which the fracture limit line of the laser weld is not derived, a laser weld cooling rate deriving step for deriving the cooling rate of the laser weld from the laser welding feed rate;
By substituting the cooling rate of the laser welding part derived in the laser welding part cooling rate deriving step into the relational expression prepared in the relational expression preparing step prepared in advance, the fracture limit line of the laser welded part is obtained. A second conversion coefficient calculation step of calculating a conversion coefficient in the steel type that has not been derived;
By using the conversion coefficient calculated in the second conversion coefficient calculation step, a laser welding portion is used as a laser welded portion of a spot welded portion that has been derived in advance in the steel grade from which the fracture limit line of the laser welded portion has not been derived. Breaking line conversion process for converting to the breaking line of
A method for deriving a fracture limit line of a welded portion. In the formulating step, the fracture limit line of the spot welded part is represented by the following formula (1), and the fracture limit line of the laser welded part is represented by the following formula (2) and the following formula (3),
The method for deriving a fracture limit line for a weld according to claim 5, wherein the conversion coefficients are F _r and N _r in the following formula (3).
ε _p = F _s · σ _triax ^ N _s (1)
_{ε p = F l · σ triax} ^ N l ... (2)
ε _p = F _s · F _r · σ _triax ^ (N _s · N _r ) (3)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A method for deriving a fracture limit line, which is used when performing fracture prediction of a welded portion by a finite element method analysis,
For the steel types in which the fracture limit line of the laser welded part and the fracture limit lines of the spot welded part with different welding cooling rates are derived in advance by the process of deriving the fracture limit line, the fracture limit line of the laser welded part is obtained. And a formulating step for expressing the break limit line of the spot welded part by a formula,
The conversion factor in the steel type from which the fracture limit line was derived is used to represent the formula of the fracture limit line of the spot welded portion using the coefficient used in the formula of the fracture limit line of the laser weld. A first conversion coefficient calculation step;
A cooling rate specifying step for determining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression that satisfies the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which the fracture limit line is derived;
And prepare the relational expression created in the relational expression creating step in advance,
For steel types for which the fracture limit line of the spot weld has not been derived, the spot weld cooling rate grasping process for grasping the cooling rate of the spot weld,
By substituting the cooling rate of the spot welded part grasped in the spot welded part cooling rate grasping process into the relational expression created in the relational expression creating step prepared in advance, the fracture limit line of the spot welded part is obtained. A second conversion coefficient calculation step of calculating a conversion coefficient in the steel type that has not been derived;
Using the conversion coefficient calculated in the second conversion coefficient calculation step, the previously determined break limit line of the laser welded part in the steel type from which the break limit line of the spot welded part has not been derived is used as the spot welded part. A break limit line conversion step for converting to a break limit line of
A method for deriving a fracture limit line of a welded portion. In the formulating step, the fracture limit line of the spot weld is represented by the following formula (X) and the following formula (Y), and the fracture limit line of the laser weld is represented by the following formula (Z),
The method for deriving a fracture limit line for a weld according to claim 7, wherein the conversion coefficients are F _r 'and N _r ' in the following formula (Y).
ε _p = F _s · σ _triax ^ N _s (X)
_{ε p = F l · F r} '· σ triax ^ (N l · N r') ... (Y)
ε _p = F _l · σ _triax ^ N _l (Z)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A finite element method analysis is performed using the fracture limit line derived by the method for deriving a fracture limit line of a welded portion according to any one of claims 1 to 8, and based on the analysis result, a plate assembly of members Determining the size of the weld and / or the welding position, and welding the member according to the determined plate assembly, the size of the weld and / or the welding position. The manufacturing method of the member provided. A program for deriving a fracture limit line used when performing fracture prediction of a welded part by finite element analysis,
For the steel types from which the fracture limit line of the spot welded portion and the fracture limit lines of a plurality of laser welded portions with different welding cooling rates were derived by the fracture limit line derivation process, the fracture limit line of the spot welded portion, and , Expressing the fracture limit line of the laser weld by a formula,
Calculates the conversion coefficient in the steel type from which the fracture limit line was derived, used when expressing the formula of the fracture limit line of the laser weld using the coefficient used in the formula of the fracture limit line of the spot weld. A first conversion coefficient calculation step;
A cooling rate specifying step for obtaining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression satisfying the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which a fracture limit line is derived;
A laser welding part cooling rate deriving step for deriving a cooling rate of the laser welding part from a feed rate of laser welding for a steel type for which the fracture limit line of the laser welding part is not derived,
By substituting the cooling rate of the laser welded part derived in the laser welded part cooling rate deriving step into the relational expression created in the relational expression creating step, the fracture limit line of the laser welded part is derived. A second conversion coefficient calculating step of calculating a conversion coefficient in the steel type not having
Using the conversion coefficient calculated in the second conversion coefficient calculation step, the previously determined fracture limit line of the spot welded part in the steel type from which the fracture limit line of the laser welded part has not been derived is laser-welded. Breaking limit line conversion step for converting to the breaking limit line of the part,
A program that causes a computer to execute. The break limit line of the spot welded part represented by the formulating step is the following formula (1), and the break limit line of the laser welded part is the following formula (2) and the following formula (3). ,
The program according to claim 10, wherein the conversion coefficients calculated in the first conversion coefficient calculation step are F _r and N _r in the following equation (3).
ε _p = F _s · σ _triax ^ N _s (1)
_{ε p = F l · σ triax} ^ N l ... (2)
ε _p = F _s · F _r · σ _triax ^ (N _s · N _r ) (3)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A program for deriving a fracture limit line used when performing fracture prediction of a welded part by finite element analysis,
For the steel types in which the fracture limit line of the laser welded part and the fracture limit lines of the spot welded part with different welding cooling rates are derived in advance by the process of deriving the fracture limit line, the fracture limit line of the laser welded part is obtained. And a formulating step for expressing the break limit line of the spot weld by a formula,
The conversion factor in the steel type from which the fracture limit line was derived is used to represent the formula of the fracture limit line of the spot welded portion using the coefficient used in the formula of the fracture limit line of the laser weld. A first conversion coefficient calculation step;
A cooling rate specifying step for obtaining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression satisfying the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which a fracture limit line is derived;
For steel types for which the fracture limit line of the spot weld is not derived, the spot weld cooling rate grasping step for grasping the cooling rate of the spot weld,
By substituting the cooling rate of the spot welded part grasped in the spot welding part cooling rate grasping step into the relational expression created in the relational expression creating step, the fracture limit line of the spot welded part is derived. A second conversion coefficient calculating step of calculating a conversion coefficient in the steel type not having
Using the conversion coefficient calculated in the second conversion coefficient calculation step, the previously determined fracture limit line of the laser welded part in the steel type from which the fracture limit line of the spot welded part has not been derived is spot welded. Breaking limit line conversion step for converting to the breaking limit line of the part,
A program that causes a computer to execute. The fracture limit line of the spot welded part represented by the formulating step is the following formula (X) and the following formula (Y), and the fracture limit line of the laser welded part is the following formula (Z). ,
The program according to claim 12, wherein the conversion coefficients calculated in the first conversion coefficient calculation step are F _r ′ and N _r ′ in the following formula (Y).
ε _p = F _s · σ _triax ^ N _s (X)
_{ε p = F l · F r} '· σ triax ^ (N l · N r') ... (Y)
ε _p = F _l · σ _triax ^ N _l (Z)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A program for deriving a fracture limit line used when performing fracture prediction of a welded part by finite element analysis,
For the steel types from which the fracture limit line of the spot welded portion and the fracture limit lines of a plurality of laser welded portions with different welding cooling rates were derived by the fracture limit line derivation process, the fracture limit line of the spot welded portion, and , Expressing the fracture limit line of the laser weld by a formula,
Calculates the conversion coefficient in the steel type from which the fracture limit line was derived, used when expressing the formula of the fracture limit line of the laser weld using the coefficient used in the formula of the fracture limit line of the spot weld. A first conversion coefficient calculation step;
A cooling rate specifying step for obtaining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression satisfying the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which a fracture limit line is derived;
By preparing the relational expression created in the relational expression creating step in advance,
A laser welding part cooling rate deriving step for deriving a cooling rate of the laser welding part from a feed rate of laser welding for a steel type for which the fracture limit line of the laser welding part is not derived,
By substituting the laser welding part cooling rate derived in the laser welding part cooling rate deriving step into the relational expression created in the relational expression creating step prepared in advance, the fracture limit line of the laser welded part is obtained. A second conversion coefficient calculating step of calculating a conversion coefficient in the steel type that has not been derived;
Using the conversion coefficient calculated in the second conversion coefficient calculation step, the previously determined fracture limit line of the spot welded part in the steel type from which the fracture limit line of the laser welded part has not been derived is laser-welded. Breaking limit line conversion step for converting to the breaking limit line of the part,
A program that causes a computer to execute. The break limit line of the spot welded part represented by the formulating step is the following formula (1), and the break limit line of the laser welded part is the following formula (2) and the following formula (3). ,
The program according to claim 14, wherein the conversion coefficients calculated in the first conversion coefficient calculation step are F _r and N _r in the following expression (3).
ε _p = F _s · σ _triax ^ N _s (1)
_{ε p = F l · σ triax} ^ N l ... (2)
ε _p = F _s · F _r · σ _triax ^ (N _s · N _r ) (3)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A program for deriving a fracture limit line used when performing fracture prediction of a welded part by finite element analysis,
For the steel types in which the fracture limit line of the laser welded part and the fracture limit lines of the spot welded part with different welding cooling rates are derived in advance by the process of deriving the fracture limit line, the fracture limit line of the laser welded part is obtained. And a formulating step for expressing the break limit line of the spot weld by a formula,
The conversion factor in the steel type from which the fracture limit line was derived is used to represent the formula of the fracture limit line of the spot welded portion using the coefficient used in the formula of the fracture limit line of the laser weld. A first conversion coefficient calculation step;
A cooling rate specifying step for obtaining a cooling rate of the spot weld and the laser weld; and
A relational expression creating step for creating a relational expression satisfying the cooling rate obtained in the cooling rate specifying step and the conversion coefficient in the steel type from which a fracture limit line is derived;
By preparing the relational expression created in the relational expression creating step in advance,
For steel types for which the fracture limit line of the spot weld is not derived, the spot weld cooling rate grasping step for grasping the cooling rate of the spot weld,
By substituting the cooling rate of the spot welded part grasped in the spot welded part cooling rate grasping step into the relational expression prepared in the relational expression creating step prepared in advance, the fracture limit line of the spot welded part is obtained. A second conversion coefficient calculating step of calculating a conversion coefficient in the steel type that has not been derived;
Using the conversion coefficient calculated in the second conversion coefficient calculation step, the previously determined fracture limit line of the laser welded part in the steel type from which the fracture limit line of the spot welded part has not been derived is spot welded. Breaking limit line conversion step for converting to the breaking limit line of the part,
A program that causes a computer to execute. The fracture limit line of the spot welded part represented by the formulating step is the following formula (X) and the following formula (Y), and the fracture limit line of the laser welded part is the following formula (Z). ,
The program according to claim 16, wherein the conversion coefficients calculated in the first conversion coefficient calculation step are F _r ′ and N _r ′ in the following formula (Y).
ε _p = F _s · σ _triax ^ N _s (X)
_{ε p = F l · F r} '· σ triax ^ (N l · N r') ... (Y)
ε _p = F _l · σ _triax ^ N _l (Z)
Here, ε _p is the fracture strain, and σ _triax is the stress triaxiality (0.7 <σ _triax <2.0). A computer-readable recording medium on which the program according to claim 10 is recorded.