JP3609600B2 - Structural strength analysis method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure strength analysis method, for example, a strength analysis method of various members as a structure constituting a vehicle such as an automobile.
[0002]
[Prior art]
Conventionally, for example, in designing and analyzing a vehicle such as an automobile, various performances with respect to the collision and strength of the vehicle are analyzed by computer simulation or the like. In addition, the applicant of the present application has proposed Japanese Patent Application No. 9-263294 as an example of a vehicle strength analysis technique in response to the application of the provisions of Article 30, Paragraph 1 of the Patent Law.
[0003]
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 accurate analysis.
[0004]
[Problems to be solved by the invention]
However, the structures (workpieces) that are actually manufactured are molded by pressing, etc., so that even if the raw material is a single material (material), the material properties and material thickness vary depending on the part. doing.
[0005]
FIG. 1 is a diagram showing general press working and deformation of a steel plate by the working. Many body parts are formed by press working as shown in FIG. At that time, work hardening and plate thickness change occur in the steel plate, which is a raw material, and even if it is a single material, the material characteristics and plate thickness vary depending on the part.
[0006]
Therefore, conventionally, from a structure to be analyzed, a test piece such as that found in a JIS (Japanese Industrial Standard) No. 5 test piece is cut out, and a material test such as a tensile test is performed using the test piece. The parameters used for analysis are obtained.
[0007]
However, in order to cut out the above-mentioned test piece, a flat portion having a certain size is required. For example, the area of the member cross-line portion that is considered to have a large contribution to the impact crushing characteristics may be small. In the part where the curvature is large, it is difficult to grasp the material characteristics.
[0008]
In addition, it takes a lot of time to cut out test pieces from many parts of the structure to be analyzed and to conduct a tensile test. The length of the lead time to do is a problem.
[0009]
Therefore, an object of the present invention is to provide a structure strength analysis method for accurately and easily performing a strength analysis in consideration of a change in material due to processing.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a structure strength analysis method according to the present invention is characterized by the following configuration.
[0011]
That is, a method for analyzing the strength of a structure formed by processing, wherein the relationship between the amount of strain and the hardness is obtained in advance for the same type of material that constitutes the structure, and the hardness of each part of the structure is determined. Measure and estimate the strain amount of each part of the structure by referring to the relationship between the strain amount and the hardness according to the measured hardness, and based on the estimated strain amount, each part of the structure The thickness of the material is calculated, and the strength of the structure is analyzed based on the calculated thickness of the material.
Thereby, the strength analysis of the structure is performed accurately and easily in consideration of the material change due to processing.
[0012]
Further, for example, when analyzing the strength of the structure, the analysis accuracy can be further increased by using the characteristics obtained by changing the stress / strain characteristics of the predetermined material in accordance with the estimated amount of strain of each part of the structure. do.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a structure strength analysis method according to the present invention will be described in detail with reference to the drawings.
[0014]
In the present embodiment, as an example of a structure, the work hardening and the plate thickness change that occur in the production processing stage are estimated for a front side frame of an automobile that is a main energy absorbing member at the time of a frontal collision. The influence of the estimated work hardening and plate thickness change on the impact crush characteristics of the member (front side frame) is analyzed using a calculation analysis method.
[0015]
First, the front side frame to be studied will be described.
[0016]
FIG. 2 is a perspective view showing the entire front side frame to be studied. The front side frame shown in the figure is a prototype manufactured by press working, and is characterized in that there is a bead for stabilizing the deformation behavior at the time of collision near the front end of the frame. In this embodiment, as an example, the material of the front side frame (hereinafter referred to as a frame) is manufactured from three types of steel plates (TRIP, SAPH400, SPHC) each having a thickness of 1.6 mm shown in FIG. did.
[0017]
<Step 1: Measurement of Vickers hardness distribution>
The scribed circle method is often used as a method for examining the amount of strain generated in a member during molding, but this method cannot examine the amount of local strain such as a corner. Therefore, in this embodiment, the distribution of Vickers hardness in a plurality of cross sections of the frame is measured, and the material property change and the plate thickness change that occur in each part of the member are estimated based on the measured values.
[0018]
As the measurement points of the distribution of Vickers hardness, as indicated by arrows in FIG. 2, the bead portion and the basic cross-sectional portion of the frame are selected and measured at intervals of about 5 mm in the circumferential direction of the cross-section.
[0019]
Next, as shown in FIG. 4, the frame cross section is divided into nine regions from (1) to (9) at the plane portion and the corner portion, and the measured value of Vickers hardness measured at intervals of about 5 mm in the circumferential direction of the cross section. The average value is calculated for each region. The results are shown for each material in FIGS.
[0020]
5 to 7 are diagrams showing Vickers hardness distribution for each frame cross-sectional area as one embodiment of the present invention.
[0021]
As can be seen from the figure, the Vickers hardness indicates a higher measurement value as the strength material increases. In addition, the Vickers hardness in the cross section has the same distribution for any material, and the corners (2), (4), (6), (8) compared to the frame vertical surface (5). ) And the horizontal surface ((3), (7)) are high, and it can be seen that a lot of work hardening occurs in these parts.
[0022]
In addition, when the hardness increase rate of each material is compared on the basis of the hardness of the vertical surface that seems to be the closest to the base material hardness, the Vickers hardness of the C material (SPH) is the highest, 33% at the corner, and at the horizontal plane A 27% increase in hardness is seen. Next, A material (TRIP) has the largest hardness increase rate, and B material (SAPH400) has the smallest result.
[0023]
As described above, in Step 1, the distribution of Vickers hardness at each part of the frame cross section was measured.
[0024]
<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.
[0025]
Specifically, prior to estimating the amount of plastic deformation, first, a JIS No. 5 test piece was used to conduct a tensile test with different strain amounts, and the Vickers hardness between the scores according to each strain amount generated by the test. The relationship between plastic strain and Vickers hardness was investigated.
[0026]
FIG. 8 is a diagram showing the relationship between plastic strain and Vickers hardness of each material as one embodiment of the present invention. As shown in the figure, the higher the strength of the material, the higher the Vickers hardness, and all the materials tend to increase in Vickers hardness as the plastic strain increases. The Vickers hardness increases rapidly in a region where the distortion is small, but the inclination of the increase in the Vickers hardness becomes gentle as the distortion increases. Further, when the rate of increase in Vickers hardness is compared using the hardness at the time of zero strain as a criterion, the tendency is that the A material and the C material are large and the B material is conversely small.
[0027]
The above-described relationship between the plastic strain and Vickers hardness of each material (FIG. 8) may be stored in advance as a referenceable database in a storage device of a computer or the like.
[0028]
Next, FIG. 9 shows the result of estimating the plastic strain (plastic deformation amount) of each part of the member from the Vickers hardness distribution with respect to the material A using the relationship between the plastic strain of each material and the Vickers hardness. . In FIG. 9, like the Vickers hardness, the plastic strain is low in the vertical plane and has a high value in the corner (particularly the root portion of the flange) and the horizontal plane. It can be easily imagined that the corner is highly strained, but it can be seen that substantially the same level of plastic strain occurs on the horizontal plane. Further, 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.
[0029]
As described above, in step 2, based on the distribution of Vickers hardness measured in step 1, the plastic strain was estimated as the material property change occurring in each part of the member. This plastic strain corresponds to work hardening.
[0030]
<Step 3: Estimation of plate thickness change>
Next, the change in the plate thickness of the material is estimated by the following method based on the plastic strain (FIG. 9) of each part of the member estimated from the Vickers hardness distribution. In the present embodiment, a pulling operation of a plate having a × b and a plate thickness t shown in FIG. 10 is considered.
[0031]
If the plastic strain is εp and the Poisson's ratio is ν, the length a can be set to (1 + εp) × a and the length b can be set to (1−νεp) × b.
[0032]
If the volume of the steel plate does not change before and after the pulling operation, the thickness t ′ after deformation is given by the following equation.
[0033]
t ′ = t / {(1 + εp) × (1−νεp)} (1)
FIG. 11 shows the estimation result of the plate thickness distribution calculated for the material A based on the above equation (1). As can be seen from the figure, the plate thickness decrease is greater at locations where the plastic strain is greater, such as the corners of the frame and the horizontal plane. The ● marks are actually measured values obtained by actually cutting the frame, and these actually measured values substantially coincide with the values estimated from plastic strain in (1), and this estimation method is appropriate. I understand that.
[0034]
As described above, in Step 3, the plate thickness change occurring in each part of the member is estimated based on the plastic strain estimated in Step 2 (FIG. 9).
[0035]
<Step 4: Collision analysis of frame by calculation analysis (strength analysis)>
Next, based on the estimation result of the “plastic strain” obtained in step 2 and the “plate thickness distribution” obtained in step 3, a so-called collision analysis is performed as a strength analysis of a single frame using calculation analysis. By performing the crush analysis, the influence of work hardening and plate thickness change on the member disintegration characteristics is examined. In the present embodiment, a so-called dynamic explicit method FEM (PAM-CRASH) is used for the analysis, but the present invention is not limited to this.
[0036]
Here, for the calculation analysis of the effect 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. As shown in FIG. 12, the curve B is obtained by sliding according to the amount of plastic strain estimated in Step 2. Then, material characteristic data as represented by the curve B is obtained for each part of the frame cross section. Then, those data are incorporated into a calculation analysis model and a calculation analysis is performed. 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 carriage is added to the rear end of the model.
[0037]
FIG. 13 is a deformation mode diagram for the material A in the case of uniform characteristics as an embodiment of the present invention. Moreover, FIG. 14 is a deformation mode diagram of the material A when considering work hardening and plate thickness change as one embodiment of the present invention.
[0038]
13 and 14, the deformation in the first half of the crush (up to a crushing amount of about 150 mm) becomes a substantially uniform axial compression mode in any case due to the bead effect. In the second half of the collapse, bending deformation occurs at the center of the frame (cross-sectional shrinkage). However, when work hardening and plate thickness change are taken into account, the overall collapse amount decreases and the bending amount decreases. You can see how they are. Although the drawings are omitted, the tendency of the deformation mode is substantially the same for the B material and the C material.
[0039]
FIGS. 15 to 17 are diagrams showing the relationship between the frame crushing load and the amount of crushing for each material as one embodiment of the present invention. .. & Thick. Change ”, and“ Uniform ”otherwise.
[0040]
As shown in FIGS. 15 to 17, the entire frame is calculated with uniform characteristics (hereinafter simply referred to as “uniform characteristics”) by taking into account work hardening and plate thickness change for any material. Compared with the case, the result that the crush load increased was obtained. In particular, a significant increase in crushing load is observed with the A / C material having a high n value (up to an average load of 8.5% at maximum for the A material). Further, the crushing load is also increasing slightly for the B material.
[0041]
FIG. 18 is a diagram showing a comparison result of the average value of the frame crushing load for each material as one embodiment of the present invention, and also in this diagram, the case where work hardening and plate thickness change are taken into consideration. “Mat. & Thick. Change” and “Uniform” are cases where the characteristics are uniform.
[0042]
As shown in FIG. 18, when comparing the average crushing load in the crushing amount 150 mm section in which the deformation mode is substantially constant, a load increase of A material: 8.5% and C material: 6.5% is observed. Further, although the difference in the B material is as small as 1.4%, there is a shift in the peak of the crush load near 150 mm, and it can be seen that the influence of the deformation mode is generated. In addition, when it is set as the average crush load of the crushing amount 200 mm section, it becomes a difference of 3.3%.
[0043]
<Comparison between calculation analysis and test results>
FIG. 19 is a diagram for explaining a comparison result between a calculation analysis as one embodiment of the present invention and a collision test result using a prototype frame, and shows a result of comparing an average crush load up to a crush amount of 150 mm. .
[0044]
In all the calculation results, the average crushing load is lower than the experimental result (Test). When work hardening and plate thickness change were taken into account (Mat. & Thick. Change), the crushing load increased compared to the case of calculation with uniform characteristics (Uniform), and a result closer to the experimental result was obtained.
[0045]
In addition, between the materials, the increase in the crushing load of material A / material C is large, and when calculated with uniform characteristics, the difference from the experimental result of 8 to 10% is that work hardening and plate thickness change. In consideration, it has decreased to about 3%. On the other hand, although the material B is in the direction approaching the experimental result, the amount of change is only reduced from 8% to 7% as seen from the average value up to the crushing amount of 150 mm. When compared with an average load up to a crushing amount of 200 mm, the difference from the experimental result is 5%.
[0046]
As described above, in the present embodiment described above, the work hardening and the plate thickness change occurring in the production processing stage are estimated for the front side frame of the automobile, and the estimated work hardening and the plate thickness change are the members (front side frame). The impact of the frame on the impact crush characteristics was analyzed using a computational analysis technique.
[0047]
As described above, when comparing the calculation analysis with the test results, the load characteristics closer to the experimental results are obtained when the work hardening and the plate thickness change are taken into consideration than when the calculation is performed with uniform characteristics. It is done. Therefore, using the analysis method of the present embodiment, based on the Vickers hardness measured for the processed structure having a complex shape, work hardening and thickness change can be easily estimated, It is possible to omit the trouble of actually measuring by cutting the structure as in the prior art. Moreover, since the estimated work hardening and the plate thickness change are accurate, the strength analysis of the structure can be performed in accordance with the actual situation (experimental result) by using the parameters obtained by the estimation.
[0048]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a structure strength analysis method for accurately and easily performing a strength analysis in consideration of a material change due to processing.
[0049]
[Brief description of the drawings]
FIG. 1 is a diagram showing general press working and 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 mechanical properties of materials used for examination 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: TRIP).
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: SAPH400).
FIG. 7 is a diagram showing a Vickers hardness distribution for each frame cross-sectional area as one embodiment of the present invention (C material: SPHC).
FIG. 8 is a diagram showing the relationship between plastic strain and Vickers hardness of each material as one embodiment of the present invention.
FIG. 9 is a diagram showing a result of estimating plastic strain of each part of a member from a Vickers hardness distribution as one embodiment of the present invention (A material: TRIP).
FIG. 10 is a diagram showing a flat plate used for estimating a plate thickness change of a material.
FIG. 11 is a diagram showing an estimation result of a plate thickness distribution as one embodiment of the present invention (A material: 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 the material A in the case of uniform characteristics as an embodiment of the present invention.
FIG. 14 is a deformation mode diagram of the material A in consideration of work hardening and plate thickness change as one embodiment of the present invention.
FIG. 15 is a diagram showing a relationship between a frame crushing load and a crushing amount for each material as one 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 as one embodiment of the present invention (B material: SAPH400).
FIG. 17 is a diagram 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 average values of frame crush loads for each material as one embodiment of the present invention.
FIG. 19 is a diagram illustrating a comparison result between a calculation analysis and a collision test result using a prototype frame as one embodiment of the present invention.

Claims (5)

A strength analysis method for a structure formed by processing,
For the same type of material that constitutes the structure, the relationship between the strain amount and the hardness is obtained in advance.
Measure the hardness of each part of the structure,
By referring to the relationship between the strain amount and the hardness according to the measured hardness, estimate the strain amount of each part of the structure,
Based on the estimated strain amount, calculate the thickness of the material in each part of the structure,
A structure strength analysis method, comprising: analyzing the strength of the structure based on the calculated thickness of the material. 2. The characteristic according to claim 1, wherein when analyzing the strength of the structure, a stress / strain characteristic of a predetermined material is further changed according to the estimated amount of strain of each part of the structure. Structural strength analysis method. The structure analysis method according to claim 1, wherein the structure is a vehicle member formed by press working. The structural strength analysis method according to claim 3, wherein the strength analysis is a collision crush analysis of the vehicle member. 2. The structural strength analysis method according to claim 1, wherein a Vickers hardness distribution is used for the hardness of each part of the structural body.

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