JPH11223580A - Analytical method for strength of structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an analytical method in which the strength of a structure can be analyzed surely and easily by taking into consideration a change in a material due to a working operation by referring to the previously found relationship between the strain amount and the hardness in every part of the measured structure according to the measured hardness in every part of the structure. SOLUTION: Regarding a material whose kind is identical to that of a material constituting a structure, the relationship between its strain amount and its hardness is found in advance. Then, the hardness in every part of the structure is measured, the strain amount in every part of the structure is estimated by referring to the previously found relationship between the strain amount and the hardness according to the measured hardness. On the basis of the estimated strain amount, the thickness of the material in every part of the structure is computed, and the strength of the structure is analyzed on the basis of the computed thickness of the material. For example, the cross section of a front-side frame for an automobile is divided into nine regions in its planes and its corner parts, the mean value in every region is computed regarding Vickers hardness measured values which are measured at intervals of about 5 mm in the circumferential direction of the cross section. The Vickers hardness measured values indicate higher measured values the harder the material is.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of analyzing the strength of a structure, for example, a method of analyzing the strength of various members as a structure constituting a vehicle such as an automobile.

[0002]

2. Description of the Related Art Conventionally, in the design and analysis of a vehicle such as an automobile, for example, various performances such as a collision and strength of the vehicle are analyzed by computer simulation or the like. Further, the applicant of the present application has proposed Japanese Patent Application No. 9-263294 as an example of a vehicle strength analysis technique under the application of the provisions of Article 30, Paragraph 1 of the Patent Act, for example.

In such a vehicle strength analysis technique, it is important to use parameters as close as possible to actual material characteristics in order to perform an accurate analysis.

[0004]

However, the structure (workpiece) to be actually manufactured is formed by press working or the like, so that even if the raw material is a single material (raw material), the material characteristics depend on the part. And the thickness of the material varies in various ways.

[0005] FIG. 1 is a diagram showing a general press working and deformation of a steel plate by the working. Many of the body parts are
It is formed by press working as shown in FIG. At that time, work hardening and a change in the thickness of the steel sheet as a raw material occur, and even if the material is a single material, the material properties and the thickness of the steel sheet are different depending on parts.

Therefore, conventionally, a test piece such as a JIS (Japanese Industrial Standard) No. 5 test piece is cut out from a structure to be analyzed, and a material test such as a tensile test is performed using the test piece. By doing so, the parameters used for analysis are obtained.

[0007] However, in order to cut out the test piece, a flat part having a certain width is required.
For example, it is difficult to grasp the material properties in a place where the area is small or the curvature is large, such as a member twill line portion that is considered to have a large contribution to the collision crushing property.

[0008] Further, since it takes a lot of time to cut out test specimens from many parts of a structure to be analyzed and to carry out a tensile test, the more accurate analysis work is performed, the more the computer is used. The length of the lead time until the analysis is performed becomes a problem.

Accordingly, an object of the present invention is to provide a method for analyzing the strength of a structure which accurately and easily performs a strength analysis in consideration of a change in material due to processing.

[0010]

In order to achieve the above object, a structural strength analysis method according to the present invention is characterized by the following constitution.

That is, in a method for analyzing the strength of a structure formed by processing, a relationship between the amount of strain and hardness is determined in advance for a material of the same type as a material constituting the structure.
The hardness of each part of the structure is measured, and by referring to the relationship between the strain and the hardness according to the measured hardness, the strain of each part of the structure is estimated, and the estimated strain is calculated. The thickness of the material in each part of the structure is calculated based on the calculated thickness of the material, and the strength of the structure is analyzed based on the calculated thickness of the material. Thus, the strength analysis of the structure is accurately and easily performed in consideration of the change in the material due to the processing.

Further, for example, when analyzing the strength of the structure, by further using a characteristic obtained by changing the stress / strain characteristic of the predetermined material in accordance with the estimated strain amount of each part of the structure, Further increase the analysis accuracy.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for analyzing the strength of a structure according to the present invention will be described below in detail with reference to the drawings.

In the present embodiment, as an example of a structure, a work hardening and a change in sheet thickness occurring in a production processing stage are estimated for a front side frame of an automobile, which is a main energy absorbing member at the time of a frontal collision. Then, the influence of the estimated work hardening and the change in plate thickness on the impact crushing characteristics of the member (front side frame) is analyzed using a calculation analysis method.

First, the front side frame to be studied will be described.

FIG. 2 is a perspective view showing the entire front side frame to be examined. The front side frame shown in the figure is a prototype manufactured by press working, and is characterized by having a bead near the end of the frame for stabilizing the deformation behavior at the time of collision. In the present embodiment, as an example, the front side frame (hereinafter, referred to as the front side frame)
3 were manufactured from three types of steel plates (TRIP, SAPH400, SPHC) each having a thickness of 1.6 mm shown in FIG.

<Step 1: Measurement of Vickers Hardness Distribution> As a method of examining the amount of strain generated in a member during molding,
Although the scribed circle method is often used, this method cannot examine a local distortion amount such as a corner. Thus, in the present embodiment, the distribution of Vickers hardness in a plurality of cross sections of the frame is measured, and a change in material properties and a change in plate thickness occurring in each part of the member are estimated based on the measured values.

As shown by arrows in FIG. 2, the measurement of the distribution of Vickers hardness is performed by selecting a bead portion and a basic cross-sectional portion of the frame, and measuring at intervals of about 5 mm in the cross-sectional circumferential direction.

Next, as shown in FIG. 4, the frame cross section was divided into nine regions consisting of a plane portion and a corner portion, and the measured values of Vickers hardness measured at intervals of about 5 mm in the cross section circumferential direction were obtained. An average value is calculated for each area. The results are shown in FIGS. 5 to 7 for each material.

FIG. 5 to FIG. 7 are diagrams showing Vickers hardness distribution for each frame cross-sectional area as one embodiment of the present invention.

As can be seen from the figure, the Vickers hardness is
Higher strength materials show higher measured values. In addition, the Vickers hardness in the cross section has the same distribution for all the materials, and the corners (,,,
,) And the horizontal planes (,) have high hardness, indicating that more work hardening occurs at these sites.

When the hardness increase rates of the respective materials are compared based on the hardness of the vertical surface which is considered to be closest to the base material hardness, the Vickers hardness of the C material (SPH) is the highest, and 33% at the corner. And a 27% increase in hardness in the horizontal plane. The material with the next largest increase in hardness is material A (TRIP) and material B (SAPH).
400) was the smallest result.

As described above, in step 1, the distribution of Vickers hardness of each part of the frame cross section was measured.

<Step 2: Estimation of Material Property Change> Next, based on the Vickers hardness distribution of each material measured in Step 1, the amount of plastic deformation occurring in each part of the frame is estimated.

Specifically, prior to estimating the amount of plastic deformation, first, a tensile test with a different amount of strain was performed using a JIS No. 5 test piece, and a score between scores was determined in accordance with each amount of strain generated by the test. The change in Vickers hardness was measured, and the relationship between plastic strain and Vickers hardness was examined.

FIG. 8 is a diagram showing the relationship between the plastic strain of each material and Vickers hardness as one embodiment of the present invention. As shown in the figure, the higher the strength of the material, the higher the value of Vickers hardness, and any material tends to increase in Vickers hardness with an increase in plastic strain. The Vickers hardness sharply increases in a region where the distortion is small, but with the increase in the distortion, the inclination of the increase in the Vickers hardness becomes gentle. Further, when comparing the increase rates of Vickers hardness based on the hardness at the time of zero strain, there is a tendency that the A material and the C material are large and the B material is small.

The relationship between the plastic strain and Vickers hardness of each material described above (FIG. 8) may be stored in a storage device of a computer or the like in advance as a referenceable database.

Next, using the above relationship between the plastic strain of each material and the Vickers hardness, the results of estimating the plastic strain (the amount of plastic deformation) of each part of the member from the Vickers hardness distribution for the material A are shown. It is shown in FIG. In FIG. 9, similar to the Vickers hardness, the plastic strain shows a low value in the vertical plane and a high value in the corners (particularly at the root of the flange) and in the horizontal plane. It is easy to imagine that the distortion of the corners is high, but it can be seen that approximately the same degree of plastic distortion occurs in the horizontal plane. The plastic strain is estimated to be about 1 to 2% on the vertical plane, and about 10% on the corner (flange root) and the horizontal plane.

As described above, in step 2, based on the Vickers hardness distribution measured in step 1, plastic strain was estimated as a change in material properties occurring in each part of the member. This plastic strain corresponds to work hardening.

<Step 3: Estimation of Change in Sheet Thickness> Next, the change in the sheet thickness of the material is determined by the following method based on the plastic strain (FIG. 9) of each part estimated from the Vickers hardness distribution. Estimate by In the present embodiment, a pulling operation of a plate having an a × b thickness t shown in FIG. 10 is considered.

If the plastic strain is εp and the Poisson's ratio is ν, the length a is (1 + εp) × a and the length b is (1−νεp)
× b.

Assuming that the volume of the steel sheet does not change before and after the pulling operation, the thickness t ′ after deformation is given by the following equation.

T ′ = t / {(1 + εp) × (1−νεp)} (1) Sheet thickness distribution calculated for material A based on the above equation (1) Is shown in FIG. As can be seen from the figure, a portion having a larger plastic strain, such as a corner of a frame or a horizontal plane, has a greater reduction in plate thickness. Also, ●
The marks are actually measured values obtained by actually cutting the frame, and these measured values substantially coincide with the values estimated from the plastic strain according to (1), indicating that the present estimation method is valid. .

As described above, in step 3, the thickness change occurring in each part of the member was estimated based on the plastic strain (FIG. 9) estimated in step 2.

<Step 4: Collision analysis of frame alone by calculation analysis (strength analysis)> Next, step 2 described above
By performing a so-called collision crush analysis as a strength analysis of a single frame using computational analysis based on the “plastic strain” obtained by and the estimation result of the “plate thickness distribution” obtained in Step 3, The effect of work hardening and thickness change on the material decompression characteristics is investigated. In the present embodiment, a so-called dynamic explicit method FEM (PAM-CRAS) is used for analysis.
H) is used, but is not limited thereto.

Here, in the calculation analysis of the influence of work hardening, first, a stress-strain curve (curve A) of a base material, which is a stress-strain curve of a JIS No. 5 test piece, is prepared, and the curve is obtained. Is slid according to the amount of plastic strain estimated in step 2, as shown in FIG. Then, material characteristic data represented by a curve B is obtained for each part of the frame cross section. Then, the data is incorporated into a calculation analysis model to perform calculation analysis. At this time, as another analysis condition to be set, in the present embodiment, the collision speed is 9 m / sec, and a mass corresponding to the bogie is added to the rear end of the model.

FIG. 13 is a deformation mode diagram of the material A when uniform characteristics are set as one embodiment of the present invention. FIG. 14 is a deformation mode diagram of the material A in consideration of work hardening and a change in plate thickness as one embodiment of the present invention.

In FIGS. 13 and 14, the deformation in the first half of the crushing (up to the vicinity of the crushing amount of 150 mm) becomes a substantially uniform axial compression mode in any case due to the effect of the bead. In the latter half of the collapse, bending deformation occurs at the center of the frame (contracted section), but when work hardening and changes in plate thickness are considered, the overall collapse amount is reduced, and the amount of bending is reduced. You can see how he is. Although the drawings are omitted, the tendency of the deformation mode is substantially the same for the materials B and C.

FIGS. 15 to 17 are diagrams showing the relationship between the frame crushing load and the amount of crushing for each material according to one embodiment of the present invention, in which work hardening and changes in plate thickness are considered. "Mat. &Thick.change", otherwise "U
niform ”.

As shown in FIGS. 15 to 17, for all materials, the entire frame has uniform characteristics (hereinafter simply referred to as “uniform characteristics”) by considering work hardening and changes in plate thickness. ), The result that the crushing load increased compared to the case where the calculation was performed in ()) was obtained. In particular, A material with high n value /
A remarkable increase in the crushing load is observed in the C material (the average load increase of 8.5% in the A material). Further, the crushing load of the material B is slightly increased.

FIG. 18 is a diagram showing a comparison result of the average value of the frame crushing load for each material according to an embodiment of the present invention. Is “Mat. & Thick.change”, and “Uniform” when the characteristics are uniform.

As shown in FIG. 18, when comparing the average crushing load in the 150 mm section where the deformation mode is substantially constant, the load increases by 8.5% for material A and 6.5% for material C. . Further, the difference is small at 1.4% for the material B, but it is 150%.
A shift occurs in the peak of the crushing load in the vicinity of mm, which indicates that the influence of the deformation mode has occurred. In addition, the crush amount 20
When the average crushing load is 0 mm section, the difference is 3.3%.

<Comparison between Calculation Analysis and Test Results> FIG.
FIG. 3 is a diagram for explaining a comparison result between a calculation analysis and an impact test result using a prototype frame according to an embodiment of the present invention, and shows a result of comparing average crush loads up to a crush amount of 150 mm.

In each of the calculation results, the average crushing load is lower than the experimental result (Test). When the work hardening and the thickness change were taken into consideration (Mat. & Thick. Change), the crushing load increased compared to the case of calculating with uniform characteristics (Uniform), and the results were closer to the experimental results.

Further, the crushing load of the material A / C greatly increases between the materials, and is 8 to 1 when calculated with uniform characteristics.
The difference from the experimental result of 0% is reduced to about 3% when the work hardening and the change in the plate thickness are considered. On the other hand, although the material B is in the direction approaching the experimental results, the change amount is 8% to 7% as viewed from the average value up to the crush amount of 150 mm.
It has only been reduced to%. In addition, when compared with the average load up to the crush amount of 200 mm, the difference from the experimental result is 5%.
Becomes

In the present embodiment described above, work hardening and sheet thickness change occurring in the production processing stage are estimated for the front side frame of an automobile, and the estimated work hardening and sheet thickness change are used as members. The effect of the (front side frame) on the crash characteristics was analyzed using a computational analysis method.

As described above, when the calculation analysis is compared with the test results, the load when the work hardening and the change in the plate thickness are considered is closer to the experimental result than when the calculation is performed with uniform characteristics. Characteristics are obtained. Therefore, using the analysis method of the present embodiment, it is possible to easily estimate the work hardening and the thickness change based on the Vickers hardness measured for the processed structure having a complicated shape, It is possible to omit the trouble of cutting the structure and performing actual measurement as in the related art. Further, since the estimated work hardening and the change in plate thickness are accurate, by using the parameters obtained by the estimation, it is possible to perform the strength analysis of the structure more in accordance with the actual condition (experimental result).

[0048]

As described above, according to the present invention,
It is possible to provide a structural strength analysis method for accurately and easily performing a strength analysis in consideration of a change in material due to processing.

[0049]

[Brief description of the drawings]

FIG. 1 is a view showing a general press working and a deformation of a steel plate by the working.

FIG. 2 is a perspective view showing the entire front side frame to be studied.

FIG. 3 is a diagram showing the mechanical properties of the materials used for the study in the present embodiment.

FIG. 4 is a diagram showing a cross section of a frame divided into a plurality of regions.

FIG. 5 is a diagram showing a Vickers hardness distribution for each frame cross-sectional area as one embodiment of the present invention (A material: TRI)
P).

FIG. 6 is a diagram showing a Vickers hardness distribution for each frame cross-sectional area as one embodiment of the present invention (material B: SAPH40).
0).

FIG. 7 is a view showing a Vickers hardness distribution for each frame cross-sectional area as one embodiment of the present invention (C material: SPH);
C).

FIG. 8 is a diagram showing a relationship between plastic strain of each material and Vickers hardness as one embodiment of the present invention.

FIG. 9 is a view showing a result of estimating a plastic strain of each member from a Vickers hardness distribution as one embodiment of the present invention (A material: TRIP).

FIG. 10 is a view showing a flat plate used for estimating a change in the thickness of a material.

FIG. 11 is a view showing a result of estimating a plate thickness distribution as one embodiment of the present invention (material A: TRIP).

FIG. 12 is a diagram showing stress-strain characteristics as one embodiment of the present invention.

FIG. 13 is a deformation mode diagram of a material A when uniform characteristics are set as an embodiment of the present invention.

FIG. 14 is a deformation mode diagram of a material A in consideration of work hardening and a change in plate thickness as an embodiment of the present invention.

FIG. 15 is a diagram showing a relationship between a frame crushing load and a crush amount for each material according to an embodiment of the present invention (A material:
TRIP).

FIG. 16 is a diagram showing a relationship between a frame crushing load and a crushing amount for each material according to an embodiment of the present invention (material B:
SAPH400).

FIG. 17 is a view showing a relationship between a frame crushing load and a crushing amount for each material as one embodiment of the present invention (C material:
SPHC).

FIG. 18 is a diagram showing a comparison result of an average value of a frame crushing load for each material as one embodiment of the present invention.

FIG. 19 is a diagram illustrating a result of comparison between calculation analysis and a collision test result using a prototype frame according to an embodiment of the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Seiichi Ando 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd.

Claims (5)

[Claims] 1. A method for analyzing the strength of a structure formed by processing, wherein a material of the same type as a material constituting the structure is
The relationship between the amount of strain and the hardness is determined in advance, the hardness of each part of the structure is measured, and the relationship between the amount of strain and the hardness is referred to according to the measured hardness. Estimating the thickness, calculating the thickness of the material in each part of the structure based on the estimated strain amount, and analyzing the strength of the structure based on the calculated thickness of the material. The strength analysis method for the structure. 2. When analyzing the strength of the structure,
2. The structural strength analysis method according to claim 1, further comprising using a characteristic obtained by changing a stress / strain characteristic of the predetermined material in accordance with the estimated amount of distortion of each part of the structure. 3. The structural strength analysis method according to claim 1, wherein the structure is a vehicle member formed by press working. 4. The structural strength analysis method according to claim 3, wherein the strength analysis is a crash crush analysis of the vehicle member. 5. The strength analysis method for a structure according to claim 1, wherein a Vickers hardness distribution is used as the hardness of each part of the structure.