JP6175947B2 - Method for predicting fracture limit line of welded portion, prediction system, and method for manufacturing member having welded portion - Google Patents

Description

  The present invention relates to a method for predicting the fracture limit of a weld using a finite element method analysis (Finite Element Method analysis, hereinafter sometimes referred to as “FEM analysis”), a prediction system capable of performing the prediction method, and The present invention relates to a method for manufacturing a member having a welded portion using the prediction method.

  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 order to improve the analysis accuracy of FEM analysis, which is often used for evaluating the impact energy absorption performance of members, it is important to consider the fracture of the spot welded part. There is a need for a method that enables consideration. Moreover, it is desirable that these studies can be performed on various types of steel plates having different mechanical characteristics.

  Non-Patent Document 1 includes a weld metal portion of a spot welded portion and a heat affected zone (Heat Affected Zone; hereinafter referred to as “HAZ portion”) by a tensile test using a microscopic test piece having a smooth parallel portion. )), And a method for individually and quantitatively measuring the stress-strain, tensile strength, elongation at break, and fracture drawing of each base material part, and the relationship between the stress-strain and the fracture drawing, A method of deriving a local breaking strain (hereinafter, also referred to as “smooth breaking strain”) at each site by FEM analysis simulating a tensile test is disclosed. According to such a technique, FEM analysis is performed using local fracture strain as a fracture criterion for each part of the spot welded part, and joint strength and fractured part of the spot welded part can be predicted with high accuracy. Yes.

  In addition to Non-Patent Document 1, in addition to the smooth shape described in Non-Patent Document 1, a weld metal part, a HAZ part, and a mother part of a spot weld are obtained by a tensile test using a new notched micro test piece. A method of individually and quantitatively measuring stress-strain, tensile strength, elongation at break, and fracture drawing of each material part, and FEM simulating a tensile test of a micro test piece from its stress-strain relationship and fracture drawing Deriving local fracture strains (hereinafter, referred to as “notch fracture strains”) of each part having different stress triaxiality by analysis, approximating smooth fracture strain and notch fracture strain by a power function, A method for constructing a fracture limit line (a fracture strain with the stress triaxiality as a parameter) is disclosed. 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.

Eisuke Nakayama and five others, “Measurement of mechanical properties of spot welds and prediction of joint tensile strength”, Automobile Engineering Society Proceedings, Vol. 36, no. 1, (2005), p. 205-210 Hideki Ueda, three others, “Study on spot weld fracture prediction technology based on fracture strain and stress triaxiality”, Automotive Engineering Society academic lecture pre-print, No. 31-12, (2012), p. 11-14

  With the technique described in Non-Patent Document 1, 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 technique, the fracture strain may vary depending on the steel type, and the local fracture strain is obtained from the tensile test result and the FEM analysis result of a smooth micro-sized test piece for each steel type (hereinafter referred to as this The process is sometimes referred to as “local smooth fracture strain derivation process”.)

  In the technique described in Non-Patent Document 2, it is possible to predict the fracture mode and joint strength of tensile shear joints, cruciform joints, and L-shaped joints with different load modes applied to the welds, and study the fracture factors. is there. In this technology, in addition to the smooth shape described in Non-Patent Document 1, local fracture strain is obtained from the tensile test result and FEM analysis result of a micro test piece having a notched shape for each steel type (in the following, This process is sometimes referred to as “local notch fracture strain derivation process”.) In this technology, the fracture limit line may differ depending on the steel type. For each steel type, a local smooth fracture strain derivation process and a local notch fracture strain derivation process are performed, and smooth fracture strain and notch fracture strain are approximated by a power function. The fracture limit line is obtained (hereinafter, this process may be referred to as a “break limit line derivation process”).

  However, for example, when performing fracture prediction FEM analysis for a joint made of a steel type for which the fracture limit line has not been derived, conventionally, since it is necessary to perform a fracture limit line derivation process for the steel type in advance, It required human labor and was a problem.

  Therefore, the present invention is capable of accurately predicting a fracture limit line without performing a fracture limit line derivation process for a metal material that has not been derived from a fracture limit line, and that constitutes a welded part. It is an object of the present invention to provide a method for predicting a line, a prediction system capable of performing the prediction method, and a method for manufacturing a member having a weld using the prediction method.

A plurality of fracture limit lines are derived in advance and used as the fracture limit line reference data for representative steel grades of the base metal strength class. FIG. 1 shows, as an example, fracture limit lines of welds of tensile strength 590 MPa grade steel plates and 980 MPa grade steel plates. 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).
ε _CR = a · σ _triax ^ b (1)
In the formula (1), ε _CR is failure strain, sigma _TRIAX is stress triaxial degree. Moreover, a and b of Formula (1) are respectively calculated from Formula (2) and Formula calculated from, for example, chemical components (C, Si, Mn, P, S, Mo, Cr, B, Ti, Nb) of the steel type. (3).
_{a = a 0 + a 1 ·} C + a 2 · Si + a 3 · Mn + a 4 · P + a 5 · S + a 6 · Mo + a 7 · Cr + a 8 · B + a 9 · Ti + a ₁₀ · Nb ... (2)
b = b ₀ + b ₁ · C + b ₂ · Si + b ₃ · Mn + b ₄ · P + b ₅ · S + b ₆ · Mo + b ₇ · Cr + b ₈ · B + b ₉ · Ti + b ₁₀ · Nb (3)

As a result of intensive studies, the inventors expressed the constants (a _{0 to} a ₁₀ and b ₀ to b) of the equations (2) and (3) when the coefficients a and b of the equation (1) are expressed by the equations (2) and (3). ₁₀ ) has found that it can be obtained by the method of least squares so that the difference between the coefficients a and b in the rupture limit line constitutive equation of the rupture limit line reference data becomes small. In this way, if the coefficients a and b of the formula (1) can be derived using the chemical component of the steel type, even if the steel type has not yet been derived from the fracture limit line, the chemical component can be used to easily break. Limit lines can be predicted.
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 predicting a fracture limit line of a welded part used when performing fracture prediction of a welded part by a finite element method analysis, wherein the fracture limit line includes a constant and a metal material. Preparation for preparing fracture limit line constitutive equations for a plurality of metal materials, which are approximated by a rupture limit line constitutive equation, including coefficients represented by polynomials using the chemical components of A first coefficient calculating step for calculating a coefficient of each break limit line constitutive equation from the chemical components of the plurality of metal materials, a coefficient of the break limit line constitutive equation prepared in the preparation step, and a first coefficient A constant determining step for determining a constant of the polynomial so that a difference from the coefficient of the rupture limit line constitutive equation calculated in the calculating step is within a predetermined range; and the chemistry of the constant determined in the constant determining step and the metal material Welding to polynomials using components A second coefficient calculating step of calculating a coefficient of a fracture limit line constitutive equation of the metal material constituting the welded portion by inputting a chemical component of the metal material constituting the welded portion, This is a prediction method.

  Here, in the first aspect of the present invention and the other aspects of the present invention described below (hereinafter, these may be collectively referred to as “the present invention”), the “welded portion” particularly refers to a steel material. It is preferable to use a welded portion, which can be roughly divided into a weld metal portion (or nugget portion), a HAZ portion, and a base material portion. Specific examples of the “breaking limit line” include a breaking limit line of a base metal part, a breaking limit line of a HAZ part, a breaking limit line of a weld metal part, and the like. 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 laser welding. Further, in the present invention, the “chemical component” can include mass% concentration, molar concentration, volume% concentration, composition ratio, and the like of the component contained in the metal material.

  In the first aspect of the present invention, when the first metal material and the second metal material different from the first metal material are joined in the welded portion, the fracture limit of the metal material constituting the welded portion. The coefficient of the line constitutive equation is a value obtained by multiplying the volume fraction of the first metal material in the welded portion by the coefficient of the fracture limit line constitutive equation of the first metal material, and the volume fraction of the second metal material in the welded portion. Is preferably represented by the sum of values obtained by multiplying the coefficient of the fracture limit line constitutive equation of the second metal material.

  In the first aspect of the present invention, when the first metal material and the second metal material different from the first metal material are joined in the welded portion, the fracture limit of the metal material constituting the welded portion. The coefficient of the line constitutive equation is obtained by multiplying the chemical component in the polynomial representing the coefficient by the volume fraction of the first metal material in the welded portion and the chemical component in the first metal material, and in the welded portion. It can be calculated through a process of inputting the sum of values obtained by multiplying the volume fraction of the second metal material by the chemical component of the second metal material.

  “A value obtained by multiplying the chemical component in the polynomial representing the coefficient by the volume fraction of the first metal material in the welded portion to the chemical component in the first metal material, and the volume of the second metal material in the welded portion. The meaning of “input the sum of values obtained by multiplying the fraction by the above-mentioned chemical component of the second metal material” will be described later, but the contents thereof will be outlined here by exemplifying the case where the chemical component is C. . For example, when a 1st metal material and a 2nd metal material are joined in a welding part, as a value inputted into chemical component C of a formula (2) showing coefficient a, to mass% of chemical component C in the 1st metal material The value C1 obtained by multiplying the volume fraction of the first metal material in the welded portion (volume of the first metal material in the weld metal portion / total volume of the weld metal portion) and the chemical component C in the second metal material Sum (C = C1 + C2) obtained by multiplying mass% by the volume fraction of the second metal material in the weld zone (volume of the second metal material in the weld metal portion / total volume of the weld metal portion) Can be used. Similarly, C1 + C2 can be used for the chemical component C of the formula (3) representing the coefficient b, and the same can be applied to other chemical components (Si, Mn, etc.).

  A second aspect of the present invention is a system for predicting a fracture limit line of a welded part used when predicting fracture of a welded part by finite element method analysis, wherein the fracture limit line includes a constant and a metal. It is approximated by a rupture limit line constitutive equation including a coefficient represented by a polynomial using a chemical component of the material, an input / output unit, a database storing the rupture limit line constitutive equations of a plurality of metal materials, and the database A first coefficient calculation unit for calculating a coefficient of each break limit line constitutive expression from chemical components of a plurality of metal materials in which the break limit line constitutive expressions are accumulated, and a coefficient of the break limit line constitutive expression accumulated in the database And a constant determining unit that determines a constant of the polynomial so that a difference between the coefficient of the rupture limit line constitutive equation calculated by the first coefficient calculating unit falls within a predetermined range, and a constant determined by the constant determining unit And the chemical composition of the metal material 2nd coefficient calculation which calculates the coefficient of the fracture limit line constitutive formula of the metal material which constitutes the welding part by substituting the chemical composition of the metal material which constitutes the welding part inputted from the input / output part to the polynomial A fracture limit line prediction system for a welded portion.

  According to a third aspect of the present invention, a finite element method analysis is performed using a fracture limit line predicted by the method for predicting a fracture limit line of a weld according to the first aspect of the present invention, and the analysis result is based on the analysis result. Determining the plate assembly of the member, the size and / or welding position of the welded portion, and welding the member according to the determined plate assembly, the size of the welded portion and / or the welding position. It is a manufacturing method of the member provided.

  In the present invention, using the chemical component of the target metal material, the unknown fracture limit is set so that the error between the coefficient of the unknown fracture limit line constitutive equation and the coefficient of the known fracture limit line constitutive formula falls within a predetermined range. Calculate the coefficient of the line constitutive equation. As a result, when it is desired to specify the fracture limit line of the metal material from which the fracture limit line has not been derived, the coefficient of the fracture limit line constitutive equation can be calculated by specifying the chemical component of the metal material. The break limit line constitutive equation can be specified using the coefficient. That is, according to the present invention, it is possible to accurately predict a fracture limit line without performing a conventional fracture limit line derivation process for a metal material for which a fracture limit line has not been derived. A limit line prediction method can be provided. Moreover, according to this invention, the manufacturing method of the member provided with the welding part using the prediction system which can implement this prediction method, and the said prediction method can be provided.

It is a figure which shows the relationship between the fracture | rupture distortion of a weld metal, and stress triaxiality. It is a figure which shows an example of the prediction method of the fracture limit line of the welding part which concerns on this invention. It is a figure for demonstrating the example which applied the prediction method of the fracture limit line which concerns on this invention in the FEM analysis of spot-welded joint tension test conditions. It is a figure for demonstrating the example of the analysis result which applied the prediction method of the fracture limit line which concerns on this invention in the FEM analysis of spot-welded joint tension test conditions. It is a figure which shows an example of the prediction system of the fracture limit line of the welding part which concerns on this invention. It is a figure which shows the fracture limit line of the weld metal part and HAZ part of an evaluation object steel type in an Example. It is a figure which shows the deformation resistance curve of the steel type for evaluation in an Example. It is a figure which shows the joint shape of the spot welded joint tension test model in an Example.

1. Background to the 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. In addition, by performing this process for each weld metal part, HAZ part, and base material part, the smooth fracture strain at each part (weld metal part, HAZ part, and base material part; the same applies hereinafter) and The notch breaking strain and the stress triaxiality at the breaking limit can be derived. And the fracture limit line of each part can be constructed by approximating the relation between the fracture strain and the stress triaxiality by a power function.

  FIG. 1 is a diagram showing the relationship between fracture strain and stress triaxiality of a weld metal. As shown in FIG. 1, the breaking strain of the breaking limit line is more influenced by the stress triaxiality as the strength material is higher, and shows a decreasing tendency. Therefore, the coefficients a and b in the above formula (1) are smaller as the strength material is higher. It is considered to be. In addition, in steel materials, there is an index called carbon equivalent in which the influence of elements other than carbon is converted into carbon content, and there are materials corresponding to the tensile strength of steel materials and materials corresponding to welded portion hardness. Thus, in steel materials, it is considered that there is a correlation between chemical components and mechanical properties. On the other hand, 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 present inventors considered that there is also a correlation between the fracture drawing and the fracture strain derived therefrom and the chemical composition. As a result of intensive studies, the present inventors have found that the coefficients a and b of the fracture limit line constitutive equation (the above equation (1)) can be calculated by using the above equations (2) and (3).

  The present invention has been made based on the above findings. That is, in the present invention, the fracture limit line is used by using the above formulas (2) and (3) for the fracture limit line relating to the fracture site (for example, weld metal part, HAZ part, base metal part) of the welded part. The coefficients a and b of the constitutive formula (the above formula (1)) can be calculated, and the fracture limit line related to the fracture site of the welded portion of the metal material can be appropriately derived and predicted.

  Embodiments of the present invention will be described below. In the following description, the metal material is a steel plate of the base material strength class 270 MPa class to 1500 MPa class, and the case where the fracture limit line of the weld metal part is predicted is mainly exemplified, but the present invention will be described below. The form is not limited.

2. 2. Method for Predicting Fracture Limit Line of Welded Part FIG. 2 shows a method for predicting a fracture limit line of a welded part according to the first embodiment of the present invention (hereinafter referred to as “prediction method S10”). As shown in FIG. 2, the prediction method S10 includes a preparation step S1, a first coefficient calculation step S2, a constant determination step S3, and a second coefficient calculation step S4.

2.1. Preparatory process S1
The preparation step S1 is a step of preparing a rupture limit line constitutive equation of a plurality of metal materials (for example, a plurality of steel plates having a base material strength class of 270 MPa class to 1500 MPa class) specified in advance by a rupture limit line derivation process. . The number of fracture limit line constitutive formulas prepared in the preparation step S1 is not particularly limited as long as it is plural, but from the viewpoint of making the prediction accuracy easy to increase, it is preferably 4 or more, and the strengthening mechanism and the tensile strength 4 to 7 types of steel, for example, 5 types of steel. In the following description, steel plates of the base material strength class 270 MPa class to 1500 MPa class (5 steel types) are used as a plurality of steel types whose fracture limit lines are known by the fracture limit line derivation process, and The example which determined the coefficient is shown.

2.2. First coefficient calculation step S2
In the first coefficient calculation step S2, the coefficient of the fracture limit line constitutive equation of the weld metal portion of each of the five steel types (from the above) is determined from the chemical components of the five steel types for which the rupture limit line constitutive equation is specified in advance by the fracture limit line derivation process. This is a step of calculating the coefficients a and b in the equation (1) (the same applies hereinafter). First, the fracture limit line of the weld metal part of the steel type is expressed by the constitutive formula of Formula (1). Next, the coefficients a and b in the formula (1) are expressed by the formulas (2) and (3) calculated from the chemical components (C, Si, Mn, P, S, Mo, Cr, B, Ti, Nb). This is performed for a plurality of steel types (all five steel types).

2.3. Constant determination step S3
In the constant determination step S3, the difference between the coefficient of the fracture limit line constitutive equation prepared in the preparation step S1 and the coefficient of the fracture limit line constitutive equation calculated in the first coefficient calculation step S2 is within a predetermined range. , Constants (the constants a _{0 to} a _{10 in} the above formula (2) and the constants b _{0 to} b _{10 in} the above formula (3)). In the constant determination step S3, optimized constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) are determined using, for example, a least square method so that the errors of the coefficients a and b are within a predetermined range. . In the constant determination step S3, the “predetermined range” is not particularly limited. For example, the constants (a _{0 to} a ₁₀ and b ₀ to b are set so that the average error of the coefficient a and the coefficient b is less than 5%. ₁₀ ) can be determined. By determining the optimized constant in the constant determining step, it is possible to increase the prediction accuracy of the fracture limit line. Here, the constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) are specifically expressed as a ₀ ≧ 1.0, a _{1 to} a ₁₀ ≦ 0.0, b ₀ ≧ −0.5, b ₁ is a ~b ₁₀ ≦ 0.0.

2.4. Second coefficient calculation step S4
The second coefficient calculation step S4 is a polynomial (the above formulas (2) and (2) using the constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) determined in the constant determination step S3 and the chemical components of the metal material. 3))) By inputting the chemical composition (mass%) of the metal material that constitutes the weld zone (here, the steel type from which the fracture limit line has not been derived), the fracture of the steel type from which the fracture limit line has not been derived. This is a step of calculating the coefficient of the limit line constitutive equation (coefficients a and b in the above equation (1)). Since the fracture limit line constitutive equation can be specified by calculating the coefficients a and b of the rupture limit line constitutive equation, the rupture limit line of the steel type from which the rupture limit line has not been derived can be predicted.

When joining the same kind of metal materials, the fracture limit line can be predicted by the above method. However, this invention is not limited to the said form, It can apply also to the weld metal which joined the metal material of a different material. In this case, the coefficients a and b (a _mix and b _mix ) of the fracture limit line constitutive equation of the weld metal portion in the welded joint obtained by joining a plurality of different metal materials are as shown in the following equations (4) and (5). The volume ratio of the respective metal materials in the weld metal portion is preferably calculated by multiplying the coefficients a and b. In addition, about the chemical component (mass%) of the metal material which comprises a welding part, it can identify from the data of the said metal material, the data of the mill sheet | seat which described the material information of the metal material, etc.
_{a mix = awm s × (V} s / V mix) + awm t × (V t / V mix) ... (4)
_{b mix = bwm s × (V} s / V mix) + bwm t × (V t / V mix) ... (5)
In the formula (4) and (5), awm _s welding the second metal material fracture limit line Constitutive factor a weld metal portion of the first metallic material, awm _t is constituting the weld portion constituting the weld coefficient of fracture limit line structure type metal parts a, bwm _s second metallic material fracture limit line constitutive equation coefficients b of the weld metal portion of the first metallic material, bwm _t is constituting the weld portion constituting the weld The coefficient b, V _s of the fracture limit line constitutive equation of the weld metal part of FIG. 5 is the volume of the first metal material in the weld metal part, V _t is the volume of the second metal material in the weld metal part, and V _mix is the entire weld metal part. Volume.

As another method of applying to a weld metal in which metal materials of different materials are joined, as shown in the following formula (6), the chemical component (mass%) to be input is changed to the chemical component of each metal material in the weld metal portion. It can also be calculated by multiplying the volume ratio of each metal material. In formula (6), as an example, a calculation method of C _mix that is a chemical component (mass%) of C in a weld metal portion in a welded joint obtained by joining a plurality of different metal materials is shown.
_{C mix = C s × (V} s / V mix) + C t × (V t / V mix) ... (6)
In the formula (6), C _s chemical composition (mass%) of C in the first metallic material forming the weld, C _t is C chemical component of the second metal material constituting the weld (wt%) is there. Si, Mn, etc. are also calculated by the same formula, and the calculated chemical composition (mass%) is input to the above formula (2) and formula (3), thereby welding in a welded joint in which a plurality of different metal materials are joined. The coefficient of the fracture limit line constitutive equation of the metal part (coefficients a and b in the above equation (1)) is calculated.

  As described above, in the prediction method S10, the fracture limit line can be predicted with high accuracy for the welded portion of the metal material from which the fracture limit line has not been derived, through the preparation step S1 to the second coefficient calculation step S4. It becomes possible.

  FIG. 3 shows a method for predicting a fracture limit line of a weld according to the first embodiment of the present invention in FEM analysis under the spot weld joint tensile test conditions (hereinafter, also referred to as “prediction method of the present invention”). An application example is shown. Here, a conventional example is also shown for comparison. FIG. 3A shows a spot welded joint to be evaluated. In the prior art shown in FIG. 3 (b), the fracture strain is calculated by a tensile test of an ultra-small test piece taken from a spot weld welded under the same conditions as the joint to be evaluated and FEM analysis simulating the tensile strain. The fracture limit line is derived by approximating the relationship between stress and triaxiality by a power function. In the tensile test, a spot welding work and a micro work piece processing work are required, and in the FEM analysis, a series of analysis work such as creation of analysis mesh and material property data, setting of boundary conditions, and the like are required. Further, in order to derive the fracture limit line, a tensile test and FEM analysis of a plurality of test pieces with notches having different notch shapes are performed, which requires work time and human labor.

  On the other hand, as shown in FIG. 3C, in the prediction method of the present invention, the fracture limit line is calculated with high accuracy only by calculating the coefficient of the fracture limit line constitutive equation by, for example, the preparation step S1 to the second coefficient calculation step S4. Can be predicted. In addition, since the prediction method of the present invention is a method of predicting the fracture limit line based on the chemical composition of the material constituting the welded portion, it can respond flexibly to material strengthening mechanisms and chemical component minor changes. The fracture limit line can be predicted with high accuracy. FIG. 3D shows mesh data of FEM analysis under the spot welded joint tensile test condition, which is modeled in a ½ symmetry with respect to the z-axis direction. FIG. 3E is an enlarged view around the spot welded portion. The material property data and the fracture limit line are set in the weld metal portion 11, the HAZ portion 12, and the base material portion 13, respectively.

  In FIG. 4, the example of the analysis result which applied the prediction method of this invention to the FEM analysis of spot-welded joint tensile test conditions is shown. FIG. 4 (f) shows the result of FEM analysis using the mesh data of FIG. 3 (d). 4 (g) to 4 (j) are analysis results showing the fracture process, in which the equivalent plastic strain of the weld vicinity element reaches the fracture limit line, and the element is deleted. In this example, the damage function is simulated by applying the damage function of the commercially available general-purpose solver Abaqus to delete the fractured element. However, other solvers having equivalent functions may be used. 4 (g) is the displacement 5mm, FIG. 4 (h) is the displacement 6mm, FIG. 4 (i) is the displacement 9mm, and FIG. 4 (j) is the analysis result at the displacement 11mm. Can be confirmed. FIG. 4 (k) shows the test results and the FEM analysis results, comparing the load histories. The FEM analysis results are compared between the conventional method (FEM (no fracture)) and the fracture consideration method according to the present invention (FEM (fracture consideration)), assuming that the metal material for which the fracture limit line has not been derived will not break. doing. As is clear from this result, the conventional method estimates the maximum load larger than the test result, but the FEM analysis result to which the prediction method of the present invention is applied agrees with the test result. From this result, it can be seen that according to the prediction method of the present invention, the fracture limit line of the steel type from which the fracture limit line has not been derived can be predicted with high accuracy. In this way, by using the prediction method of the present invention, it is possible to appropriately examine the site that is the starting point of the fracture and the fracture path. Therefore, the prediction method of the present invention can be used for examination of a plate assembly, a size of a welded portion, a welding position, and the like for reducing a load drop due to fracture.

3. FIG. 5 shows an example of a prediction system 10 (hereinafter referred to as “prediction system 10”) of a fracture limit line of a weld according to a second embodiment of the present invention. As shown in FIG. 5, the prediction system 10 includes a constant when the database 1, the first coefficient calculation unit 2 that calculates the coefficient of the break limit line constitutive equation, and the coefficient of the break limit line constitutive expression are expressed by a polynomial. A constant determining unit 3 for determining, a second coefficient calculating unit 4 for calculating a coefficient of a rupture limit line constitutive equation of a metal material from which a rupture limit line has not been derived, and an input / output unit 5 are provided.

  The database 1 stores fracture limit line constitutive equations for a plurality of metal materials. In the prediction system 10, the form of the database 1 is not particularly limited. It is preferable that the database 1 records the chemical composition of the metal material and the fracture limit line constitutive equation in association with each other.

  The first coefficient calculation unit 2 is a part that calculates coefficients (coefficients a and b) of each fracture limit line constitutive equation from the chemical components of a plurality of metal materials whose fracture limit line constitutive equations are stored in the database 1. is there. As long as such a function can be realized, the form of the first coefficient calculation unit 2 is not particularly limited, and a known arithmetic device in which spreadsheet software or the like is installed can be used. The first coefficient calculation unit 2 receives a plurality of the break limit line constitutive coefficients recorded in the database 1 together with the corresponding chemical components, and calculates the break limit line constitutive coefficients.

The constant determining unit 3 is configured so that the difference between the coefficient of the break limit line constitutive equation stored in the database 1 and the coefficient of the break limit line constitutive formula calculated by the first coefficient calculating unit 2 falls within a predetermined range. This is a part for determining constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) used for the polynomial representing the coefficient of the fracture limit line constitutive equation. As long as such a function can be realized, the form of the constant determination unit 3 is not particularly limited, and a known arithmetic device in which spreadsheet software or the like is installed can be used. The constant determination unit 3 receives the coefficient of the fracture limit line constitutive equation stored in the database 1 and the coefficient of the break limit line constitutive equation calculated by the first coefficient calculation unit 2 together with the corresponding chemical components, The constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) are determined by the spreadsheet software so that these errors fall within a predetermined range. Since the specific calculation method is as described above, the description is omitted here.

The second coefficient calculation unit 4 is a polynomial (the above formulas (2) and (3) using the constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) determined by the constant determination unit 3 and the chemical components of the metal material. )), By substituting the chemical composition of the metal material constituting the welded portion inputted from the input / output portion 5, the coefficients (coefficients a and b) of the fracture limit line constitutive equation of the metal material constituting the welded portion are obtained. This is the part to be calculated. As long as such a function can be realized, the form of the second coefficient calculation unit 4 is not particularly limited, and a known arithmetic device installed with spreadsheet software or the like can be used. The second coefficient calculation unit 4 sends the equations (2) and (3) using the constants (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) determined by the constant determination unit 3 from the input / output unit 5. By substituting the chemical composition of the metal material constituting the welded portion as a parameter value, the coefficients a and b of the fracture limit line constitutive equation are calculated. Since the specific calculation contents are as described above, description thereof is omitted here.

  As described above, the prediction system 10 performs the database 1 storing data used in the preparation step S1 in the prediction method S10, the first coefficient calculation unit 2 capable of performing the first coefficient calculation step S2, and the constant determination step S3. Since the possible constant determination unit 3 and the second coefficient calculation unit 4 capable of performing the second coefficient calculation step S4 are provided, the prediction method S10 can be performed. Therefore, by adopting such a configuration, according to the present invention, the prediction system 10 is provided that can predict the fracture limit line with high accuracy for the welded portion of the metal material from which the fracture limit line has not been derived. be able to.

  In the above description regarding the prediction system 10, an example in which the first coefficient calculation unit 2, the constant determination unit 3, and the second coefficient calculation unit 4 are provided separately has been described, but the second embodiment of the present invention. The system for predicting the fracture limit line of a welded part according to the present invention is not limited to this form. One arithmetic unit may function as the first coefficient calculation unit 2, the constant determination unit 3, and the second coefficient calculation unit 4.

4). Manufacturing method of member provided with welded portion A manufacturing method of a member provided with a welded portion according to the third embodiment of the present invention (hereinafter, also referred to as “manufacturing method of the present invention”) is the first of the present invention. The finite element method analysis is performed using the fracture limit line predicted by the prediction method of the fracture limit line of the welded portion according to the embodiment, and based on the analysis result, the plate assembly of the member, the size of the welded portion, and / or The welding position is determined, and the member is welded according to the plate assembly determined in this way, the size of the welded portion, and / or the welding position.

  In the manufacturing method of the present invention, for example, the finite element method analysis is performed using the fracture limit line predicted by the prediction method S10, and based on the analysis result, the joint plate assembly, the size of the weld nugget diameter, and / or Determine the dot interval. And it can be set as the form which manufactures the joint provided with the spot weld part by carrying out spot welding of the member according to the determined board assembly, the magnitude | size of a welding nugget diameter, and / or a hitting point 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 / or the welding position are appropriately adjusted in order to reduce the load drop due to breakage. 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 above description regarding the present invention, the form in which the present invention is applied to the analysis of spot welds is mainly exemplified, but the present invention is not limited to this form. The present invention can also be applied when analyzing a member welded by other welding means such as laser welding. Moreover, in the said description, although mentioned mainly about the form applied when this invention uses steel materials as welding material, 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.

  The prediction method of the present invention will be further described with reference to the examples.

Prepare rupture limit line constitutive equations for five steel types with different strengthening mechanisms and tensile strengths identified by the rupture limit line derivation process. Coefficients (coefficients a and b) of rupture limit line constitutive equations from the chemical components of these five steel types Was calculated. After that, it was optimized so that the difference between the calculated coefficients (coefficients a and b) and the coefficients (coefficients a and b) of the rupture limit line constitutive equation specified by the rupture limit line derivation process was within a predetermined range. Constants (a ₀ -a ₁₀ and b ₀ -b ₁₀ ) were determined.

From the constants determined in this way (a _{0 to} a ₁₀ and b _{0 to} b ₁₀ ) and the chemical composition (% by mass) of the metal material for which the fracture limit line constitutive formula is not specified, the rupture limit line constitutive formula. The coefficients (coefficients a and b) of the rupture limit line constitutive equation of the metal material for which no is specified were calculated. In addition, the chemical component of the metal material in which the fracture limit line constitutive formula is not specified was as follows.
C: 0.09 mass%
Si: 0.72 mass%
Mn: 1.5% by mass
P: 0.018 mass%
S: 0.004 mass%
Cr: 0.02 mass%
The coefficients of the fracture limit line constitutive equation calculated by substituting these chemical components were a = 0.43 and b = −1.59.

  By substituting the coefficients a and b into the above equation (1), the fracture limit line constitutive equation of the weld metal portion of the metal material was specified. Next, the fracture limit line constitutive equation of the HAZ portion of the metal material was specified in the same manner except that the weld metal portion was changed to the HAZ portion. FIG. 6 shows the fracture limit line of the weld metal portion represented by the rupture limit line constitutive equation of the identified weld metal portion and the fracture limit line of the HAZ portion represented by the rupture limit line constitutive equation of the identified HAZ portion. Show. As shown in FIG. 6, in the present metal material, the fracture limit line of the weld metal portion and the fracture limit line of the HAZ portion almost overlapped.

  The metal material whose fracture limit line is predicted by the prediction method of the present invention is a steel type having a tensile strength of 590 MPa, Young's modulus of 206 GPa, and Poisson's ratio of 0.3. The deformation resistance curve of this steel type is shown in FIG. The material property data shown in FIG. 7 and the fracture limit line data shown in FIG. 6 were applied to the tensile test model of the spot welded joint shown in FIG. 8, and FEM analysis was performed. In FIG. 8, (l) indicates a tensile shear joint, (m) indicates an L-shaped joint tension, and (n) indicates a cruciform joint tension. Table 1 shows a comparison between the experimental results and the FEM analysis results.

  As shown in Table 1, in the FEM analysis results using the fracture limit line predicted by the prediction method of the present invention, the maximum load and the fracture mode corresponded well with the experimental results in any joint. That is, according to the present invention, even if the conventional fracture limit line derivation process (tensile test and finite element method analysis for deriving the fracture limit line) is omitted for the metal material from which the fracture limit line has not been derived, It was found that the fracture limit line can be predicted with high accuracy.

  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 FEM analysis for studying the plate assembly and weld nugget diameter of spot welded joints, and the results should be reflected in the design of automobile parts. Can do.

DESCRIPTION OF SYMBOLS 1 ... Database 2 ... 1st coefficient calculation part 3 ... Constant determination part 4 ... 2nd coefficient calculation part 5 ... Input-output part 10 ... Prediction system of the fracture limit line of a welding part 11 ... Weld metal part 12 ... HAZ part 13 ... Mother Material part

Claims (5)

A method for predicting a fracture limit line of a welded portion, which is used when performing fracture prediction of a welded portion by a finite element method analysis,
The break limit line is approximated by a break limit line constitutive equation, which is expressed by the following formula (1) to formula (3):
Preparing a rupture limit line constitutive equation of a plurality of metal materials specified in advance by a rupture limit line derivation process;
A first coefficient calculating step of calculating the coefficient of each rupture limit line constitutive equation from chemical components of the plurality of metal materials;
The difference between the coefficient of the rupture limit line constitutive equation prepared in the preparation step and the coefficient of the rupture limit line constitutive equation calculated in the first coefficient calculating step is within a predetermined range. A constant determining step for determining a constant of the polynomial;
By inputting the chemical component of the metal material constituting the welded portion into the polynomial using the constant determined in the constant determining step and the chemical component of the metal material, the fracture limit of the metal material constituting the welded portion A second coefficient calculating step of calculating the coefficient of the line constitutive equation;
A method for predicting a fracture limit line of a welded portion.
ε _CR = a · σ _triax ^ b (1)
a = a ₀ + a ₁ · C + a ₂ · Si + a ₃ · Mn + a ₄ · P + a ₅ · S + a ₆ · Mo + a ₇ · Cr + a ₈ · B + a ₉ · Ti + a ₁₀ · Nb (2)
_{b = b 0 + b 1 ·} C + b 2 · Si + b 3 · Mn + b 4 · P + b 5 · S + b 6 · Mo + b 7 · Cr + b 8 · B + b 9 · Ti + b 10 · Nb (3)
However, epsilon _CR is failure strain, sigma _TRIAX stress three _Jikudo, a 0 _{~a 10} and _b 0 _{~b 10} is Ri constant der, a and b are the chemical components of the constant and the metal material C, It is a coefficient represented by a polynomial expression using Si, Mn, P, S, Mo, Cr, B, Ti, and Nb. When the second metal material different from the first metal material and the first metal material is joined at the weld,
The coefficient of the fracture limit line constitutive equation of the metal material constituting the welded portion is multiplied by the volume fraction of the first metal material in the welded portion to the coefficient of the fracture limit line constitutive equation of the first metal material. 2, and a sum of values obtained by multiplying the volume fraction of the second metal material in the weld by the coefficient of the fracture limit line constitutive equation of the second metal material. Method for predicting the fracture limit line of welded parts. When the second metal material different from the first metal material and the first metal material is joined at the weld,
The coefficient of the fracture limit line constitutive equation of the metal material constituting the weld is the chemical component in the polynomial representing the coefficient,
The value obtained by multiplying the volume fraction of the first metal material in the weld by the chemical component of the first metal material and the volume fraction of the second metal material in the weld are the second metal material. The method of predicting a fracture limit line of a welded portion according to claim 1, wherein the fracture limit line is calculated through a process of inputting a sum of values obtained by multiplying the chemical component of. A system for predicting a fracture limit line of a welded part used when performing fracture prediction of a welded part by finite element method analysis,
The break limit line is approximated by a break limit line constitutive equation, which is expressed by the following formula (1) to formula (3):
An input / output unit;
A database that stores rupture limit line constitutive equations for multiple metal materials;
A first coefficient calculating unit that calculates the coefficient of each of the breaking limit line constitutive formulas from the chemical components of the plurality of metal materials for which the breaking limit constitutive formula is accumulated in the database;
The polynomial so that a difference between the coefficient of the break limit line constitutive equation stored in the database and the coefficient of the break limit line constitutive equation calculated by the first coefficient calculation unit is within a predetermined range. A constant determining unit for determining a constant of
By substituting the chemical component of the metal material constituting the weld input from the input / output unit into the polynomial using the constant determined by the constant determination unit and the chemical component of the metal material, A second coefficient calculation unit for calculating the coefficient of the fracture limit line constitutive equation of the metal material constituting
A system for predicting a fracture limit line of a welded portion.
ε _CR = a · σ _triax ^ b (1)
a = a ₀ + a ₁ · C + a ₂ · Si + a ₃ · Mn + a ₄ · P + a ₅ · S + a ₆ · Mo + a ₇ · Cr + a ₈ · B + a ₉ · Ti + a ₁₀ · Nb (2)
_{b = b 0 + b 1 ·} C + b 2 · Si + b 3 · Mn + b 4 · P + b 5 · S + b 6 · Mo + b 7 · Cr + b 8 · B + b 9 · Ti + b 10 · Nb (3)
However, epsilon _CR is failure strain, sigma _TRIAX stress three _Jikudo, a 0 _{~a 10} and _b 0 _{~b 10} is Ri constant der, a and b are the chemical components of the constant and the metal material C, It is a coefficient represented by a polynomial expression using Si, Mn, P, S, Mo, Cr, B, Ti, and Nb.   A finite element method analysis is performed using the fracture limit line predicted by the method of predicting the fracture limit line of a welded portion according to any one of claims 1 to 3, and a plate assembly of members based on the analysis result, A method of manufacturing a member having a welded portion, comprising: determining a size and / or a welding position of the welded portion, and welding the member according to the determined plate assembly, the size of the welded portion and / or the welded position. .