JP2011141237A - Method and for system predicting breakage, program and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable accurate breakage prediction using a breaking limit line of a thin plate made of a metal material by a comparatively simple constitution. <P>SOLUTION: A first breaking limit line at a plate thickness center of a sample is obtained, and bending deformation is given to the sample, and a surface strain quantity when breakage is generated is calculated. A differential value between the surface strain quantity when breakage is generated and a plane strain quantity on the first breaking limit line is calculated, and the differential value is added to the first breaking limit line to obtain a second breaking limit line, and a surface strain quantity of the thin plate is calculated, and existence of breakage of the thin plate is predicted by using the second breaking limit line as a reference based on the calculated surface strain quantity of the thin plate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fracture prediction method, a fracture prediction system, a program, and a recording medium for predicting a fracture of a thin plate made of a metal material.

  In general, the margin for fracture of a thin plate made of a metal material is determined using a plate thickness reduction rate or a forming limit diagram (FLD). FLD is a diagram showing a maximum principal strain that gives a fracture limit for each minimum principal strain, and can also be used in a collision analysis.

As a method for measuring the FLD by experiment, generally, a circle-like or grid-like pattern is drawn in advance on the surface of a metal plate by etching or the like, and after being broken by hydraulic forming or overhang forming with a rigid tool, The fracture limit strain is measured from the deformation amount of the pattern. The fracture limit line (FLC) is obtained by proportionally loading a metal plate for various in-plane strain ratios, plotting the fracture limit strain at each strain ratio on the main strain axis, and connecting them.
Theoretically predicting FLD includes the combined use of Hill's local constriction model and Swift's diffusion constriction model, the Marciniak-Kuczynski method, the Stären-Rice model, and the effect of plate thickness is corrected by Keeler's rule of thumb. Can be obtained.

  The conventional fracture evaluation method compares the positional relationship between the fracture limit line obtained experimentally or theoretically as described above and the strain state of each part obtained from the simulation results of the plastic deformation process by the finite element method. To evaluate. In this case, when the strain in the deformation process reaches the limit strain, it is determined that the fracture occurs, or it is determined that the risk is high.

JP 2007-285832 A

1993, Hosford, Metal Forming, 319 2004, Plasticity and processing 45, 123 2004, CAMP-ISIJ 17, 1063 1988, theory A, 57, 1617

  In contrast to the conventional fracture prediction method using the FLD, Patent Document 1 devises a technique that enables crack prediction even if the deformation path changes, but in the case of a crack caused by a large bending deformation. Is difficult to predict.

  The present invention has been made in view of the above-described problems, and has a relatively simple configuration and a fracture prediction method and a fracture prediction system that enable accurate fracture prediction using a fracture limit line of a thin plate made of a metal material. An object of the present invention is to provide a program and a recording medium.

The fracture prediction method of the present invention is a method for predicting the fracture of a thin plate made of a metal material, a step of obtaining a first fracture limit line at the center of the thickness of the sample, a bending deformation to the sample, Calculating a difference value between a step of calculating a surface strain amount when it occurs, a surface strain amount when the fracture occurs, and a plane strain amount at the first fracture limit line; Adding a first fracture limit line to obtain a second fracture limit line, calculating a surface strain amount of the thin plate,
A step of predicting whether or not the thin plate is broken based on the calculated surface strain amount of the thin plate based on the second breaking limit line.

In one aspect of the fracture prediction method of the present invention, in the step of obtaining the first fracture limit line, Formula (1), which is an approximate expression of a stress-strain curve obtained from a uniaxial tensile test,
σ _eq = Cε _eq ⁿ (1)
Formula (2) which is a local constriction model,

  The first fracture limit line is obtained by using together the expression (3) which is a diffusion constriction model or the expression (3) ′ which is a Stären-Rice model.

  In one aspect of the fracture prediction method of the present invention, in the step of calculating the surface strain amount of the thin plate, the curved surface portion of the sample is divided into five or more elements using a finite element method.

The fracture prediction system of the present invention is a system for predicting the fracture of a thin plate made of a metal material, and includes a first fracture limit line acquisition unit that acquires a first fracture limit line at the thickness center of a sample,
A first surface strain amount calculation unit that applies a bending deformation to the sample and calculates a surface strain amount when the fracture occurs, a surface strain amount when the fracture occurs, and a plane at the first fracture limit line A second fracture limit line acquisition unit that calculates a difference value from the strain amount, adds the difference value to the first fracture limit line to obtain a second fracture limit line, and a surface strain amount of the thin plate A second surface strain amount calculation unit for calculating
A fracture prediction unit that predicts whether or not the thin plate is broken based on the second fracture limit line based on the surface strain amount of the thin plate calculated by the second surface strain amount calculation unit.

  In one aspect of the fracture prediction system of the present invention, the first fracture limit line acquisition unit obtains the above formula (1) of the stress-strain curve obtained from a uniaxial tensile test when acquiring the first fracture limit line. 1) is combined with the above equation (2), which is a local constriction model, and the above equation (3), which is a diffusion constriction model, or the above equation (3) ′, which is a Stären-Rice model. Determine the fracture limit line.

  In one aspect of the fracture prediction system of the present invention, the second surface strain amount calculation unit uses a finite element method when calculating the surface strain amount of the thin plate, and the curved surface portion of the sample is made to have five or more elements. To divide.

  The program of the present invention is a program for predicting a fracture of a thin plate made of a metal material, a step of obtaining a first fracture limit line at the center of the thickness of the sample, a bending deformation to the sample, and Calculating a difference value between a step of calculating a surface strain amount when it occurs, a surface strain amount when the fracture occurs, and a plane strain amount at the first fracture limit line; Adding the first fracture limit line to obtain a second fracture limit line; calculating the surface strain amount of the thin plate; and calculating the second fracture amount based on the calculated surface strain amount of the thin plate. And causing the computer to execute a step of predicting whether or not the thin plate is broken based on a limit line.

  In one aspect of the program of the present invention, in the step of obtaining the first break limit line, the above-described formula of the stress-strain curve obtained from a uniaxial tensile test when obtaining the first break limit line ( 1) is combined with the above equation (2), which is a local constriction model, and the above equation (3), which is a diffusion constriction model, or the above equation (3) ′, which is a Stären-Rice model. Determine the fracture limit line.

  In one aspect of the program of the present invention, in the step of calculating the surface strain amount of the thin plate, the curved surface portion of the sample is divided into five or more elements using a finite element method.

  The recording medium of the present invention is a computer-readable medium on which the above program is recorded.

  According to the present invention, accurate fracture prediction using a fracture limit line of a thin plate made of a metal material is realized with a relatively simple configuration. According to the present invention, it is possible to accurately evaluate the risk of press forming and fracture at the time of collision, and it is possible to efficiently and highly accurately develop an automobile body considering the material, construction method and structure at the same time.

It is a block diagram which shows schematic structure of the fracture prediction system by this embodiment. It is a flowchart which shows the fracture | rupture prediction method by this embodiment in process order. FIG. 5 is a characteristic diagram showing a relationship between a minimum principal strain (ε ₂ ) and a maximum principal strain (ε ₁ ) for explaining the basic outline of the present embodiment. It is a figure which illustrates a mode that it analyzes using FEM about the sample which made the bending radius 3 mm. It is a characteristic view which shows the 2nd fracture limit line and hair crack limit line which were acquired in Example 1. FIG. In Example 1, it is a schematic diagram which shows the thin plate which is the determination object by FEM analysis. In Example 1, it is a schematic diagram which shows the mode of the thin plate by which FEM analysis was carried out about the case where a bending span was 200 m. In Example 1, it is a schematic diagram which shows the maximum principal strain distribution on the outer surface of the thin plate subjected to FEM analysis by dividing the R portion into 6 parts when the bending span is 200 m. In Example 1, it is a schematic diagram which shows the largest principal-strain distribution by which the thin plate outer surface by which FEM analysis was carried out by R part 4 division | segmentation was carried out when the bending span was 200 m. In Example 1, it is a schematic diagram which shows the mode of the thin plate by which FEM analysis was carried out about the case where a bending span was 600 m. In Example 1, it is a schematic diagram which shows the mode of the thin plate by which FEM analysis was carried out about the case where a bending span was 600 m. In Example 1, it is a schematic diagram which shows the largest principal strain distribution of the thin plate outer surface by FEM analysis by R part 6 division and 4 division about the case where a bending span is 600 m. It is a characteristic view which shows the determination result by the conventional fracture prediction method about No.5-No.7 which made the bending span 200m. It is a characteristic view which shows the determination result by the fracture prediction method of a present Example about No.5-No.7 which made the bending span 200m. It is a characteristic view which shows the determination result by the conventional fracture | rupture prediction method about No.1-No.4 which made the bending span 600m. It is a characteristic view which shows the determination result by the fracture prediction method of a present Example about No.1-No.4 which made the bending span 600m. It is a schematic diagram which shows the internal structure of a personal user terminal device.

The inventor of the present invention has come up with a technique for realizing accurate fracture prediction with a simple configuration in consideration of the influence of bending deformation of a thin plate made of a metal material.
FIG. 1 is a block diagram showing a schematic configuration of a fracture prediction system according to the present embodiment.
FIG. 2 is a flowchart showing the fracture prediction method according to this embodiment in the order of steps.
FIG. 3 is a characteristic diagram showing the relationship between the minimum principal strain (ε ₂ ) and the maximum principal strain (ε ₁ ) for explaining the basic outline of the present embodiment.

As shown in FIG. 1, the fracture prediction system according to the present embodiment includes a first fracture limit line acquisition unit 1, a first surface strain amount calculation unit 2, a second fracture limit line acquisition unit 3, and a second surface. A strain amount calculation unit 4, a fracture prediction unit 5, and a recording unit 6 are provided. The recording unit 6 includes a storage medium such as a CD-ROM, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, and a nonvolatile memory card.
Hereinafter, this fracture prediction system will be described together with the fracture prediction method shown in FIG.

First, for a thin plate sample made of a desired metal material, the first break limit line acquisition unit 1 acquires a first break limit line representing a break limit due to strain at the center of the plate thickness of the sample (step S1). ). Here, the strain at the center of the plate thickness is a strain generated in the central portion in the thickness direction of the thin plate as a sample. The obtained data of the first breaking limit line is stored in the recording unit 6.
In the present embodiment, the first break limit line is obtained by the first break limit line acquisition unit 1 based on theoretical estimation from the mechanical property value of the metal material.

A method for theoretically obtaining the FLC of the strain space as the first fracture limit line based on the mechanical property value of the metal material will be described.
The first fracture limit line acquisition unit 1 uses, for example, an approximate expression of a stress-strain curve obtained from a uniaxial tensile test, a Hill local constriction model, and a Swift diffusion constriction model or a Stären-Rice model. To obtain the first break limit line.

The theoretical estimation methods of FLC include the combined use of Hill's local constriction model and Swift's diffusion constriction model, and the Stären-Rice model (1975, J. Mech. Phys. Solids, 23, 421). Is obtained by correcting the influence of the plate thickness. A specific calculation method will be described below. First, data for obtaining the following formula (4) is collected. As a test method, a uniaxial tensile test is simple and preferable.
σ _eq = f (ε _eq ) (4)

From the stress-strain curve obtained from the uniaxial tensile test, the material parameter may be determined by fitting to a functional equation including an appropriate material parameter as Equation (4).
By using the n-th power hardening law that is highly accurate and often used in numerical simulation of thin steel sheets, the stress-strain curve can be approximately expressed by the above equation (1).

  Using the Mises yield function shown in the following equation (5) for the n-th power hardening law and yield surface, the Hill's local neck model is given by the above equation (2), and the Swift diffusion neck model Is given by equation (3) above.

However, since Hill's theory does not allow local necking in biaxial tension, it is used in the range of the following formula (6), and Swift's diffusion necking model is applied in the range of ρ> 0. The obtained FLC is shown as a _first breaking limit line L _{1 in} FIG.

  Swift's diffusion constriction model tends to estimate the fracture limit in the vicinity of equal biaxial tension, and needs to be improved. Therefore, it is preferable to use the Stälen-Rice model, which is an extension of Hill's local constriction model based on the bifurcation theory. When the Stälen-Rice model uses the n-th power hardening law and the incremental representation of the total strain theory for the yield surface for the yield surface, the fracture limit strain in the range of ρ ≧ 0 is given by the following equation (8): .

Subsequently, the first surface strain amount calculation unit 2 gives the surface strain ε _B (ε ₂ when ε ₂ = 0 when the thin plate sample made of a desired metal material is subjected to bending deformation and breakage occurs. ₁ ) is calculated (step S2). Here, the surface strain is a strain generated on the surface of a thin plate as a sample, and is considered to have a value that faithfully reflects the strain due to bending deformation.

First, a bending test is performed to give a bending deformation to the sample. As a test method, for example, a V block method (a test method in which a sample is placed on a V block, a metal fitting is applied to the center of the sample, and a load is gradually applied and bent into a specified shape) is used. For example, the plate thickness of the sample is 1.88 mm, the bending angle of the sample is 90 °, and the bending radius of the sample is set to 3 mm, 4 mm, and 5 mm.
An example of the bending test result is shown in Table 1 below.

In the sample having a bending radius of 3 mm, breakage was observed due to bending deformation. In the sample with a bending radius of 4 mm, breakage was not observed, but so-called hair cracks (surface cracks only) were observed. The sample with a bending radius of 5 mm did not break or break even when subjected to bending deformation.
From the above results, the target for calculating the surface strain ε _B at the time of fracture due to bending deformation is a sample having a bending radius of 3 mm. In addition to the surface strain ε _B described above, the surface strain at the time when hair cracks occur due to bending deformation may be calculated. In this case, the calculation target is a sample having a bending radius of 4 mm.

Next, based on the result of the bending test, the first surface strain amount calculation unit 2 calculates the surface strain ε _B of a sample having a bending radius of 3 mm, for example, a finite element when a fracture due to bending deformation occurs. Calculated using the method (FEM). The calculation results are shown in Table 2 below. Table 2 shows the surface strain ε _B and the surface strain of the sample having a bending radius of 4 mm at which hair cracking occurred in the sample. In the present embodiment, the surface of the sample closed at a finite boundary is mesh-divided into finite partial regions by FEM, and simultaneous linear equations relating to values at a finite number of points (nodes) generated by mesh division are derived. By solving this simultaneous linear equation, the surface strain of the sample with bending radii of 3 mm and 4 mm is calculated. FIG. 4 illustrates a state in which a sample having a bending radius of 3 mm is analyzed using FEM.

Subsequently, the second break limit line acquisition unit 3 reads the data of the first break limit line from the recording unit 6, the surface strain amount ε _B when the sample breaks, and the first break limit line. The difference value with respect to the plane strain ε _b (the value of ε ₁ when ε ₂ = 0 in the first breaking limit line) is calculated, and this difference value is added to the first breaking limit line to obtain the second A fracture limit line is acquired (step S3). That is, in FIG. 3, the first break limit line L ₁ is offset upward by the above difference value. The second breaking limit line is FLC in which the first breaking limit line is subjected to bending correction in accordance with the surface strain caused by bending deformation of the sample, and is shown as the second breaking limit line L _{2 in} FIG. The obtained second break limit line data is stored in the recording unit 6.

Here, together with the second break limit line, the amount of surface strain when the cracks occur in the sample and the plane strain ε _{b at} the first break limit line (when ε ₂ = 0 on the first break limit line) And the difference value with respect to ε ₁ ) is added to the first fracture limit line to obtain an FLC corresponding to a hair crack (hereinafter referred to as “hair crack limit line”). You may do it.

  Subsequently, the second surface strain amount calculation unit 4 calculates the surface strain amount of the thin plate that is the target of fracture prediction using, for example, FEM (step S4). In the present embodiment, for example, as described later, FEM analysis is performed using a parameter of Cowper-Symonds and setting mesh division to a predetermined size.

Subsequently, the fracture prediction unit 5 predicts the presence or absence of fracture of the thin plate based on the second fracture limit line based on the surface strain amount of the thin plate calculated by the second surface strain amount calculation unit 4 (step S5). .
Specifically, the fracture prediction unit 5 reads the data of the second fracture limit line from the recording unit 6 and the surface strain amount (minimum principal strain ε ₂₎ obtained by the FEM analysis in the second surface strain amount calculation unit 4. , Maximum principal strain ε ₁ ) is determined with respect to the second fracture limit line. That is, when the surface strain amount obtained by the FEM analysis is equal to or greater than the second fracture limit line (when the obtained surface strain amount is located above the _second fracture limit line L _{2 in} FIG. 3). If there is, it is determined that the thin plate is broken. On the other hand, when the surface strain obtained by the FEM analysis is smaller than the second fracture limit line (when the obtained surface strain is located below the second fracture limit line L ₂ in FIG. 3). Determines that the thin plate does not break. FIG. 3 shows an example of the former as surface strain A and an example of the latter as surface strain B.

In addition, when the hair crack limit line is acquired with the 2nd fracture | rupture limit line in step S3, generation | occurrence | production of the hair crack of a thin plate may be estimated in step S5. In this case, if the surface strain amount (minimum principal strain ε ₂ , maximum principal strain ε ₁ ) obtained by the FEM analysis in step S4 is greater than or equal to the hair cracking limit line, it is determined that hair cracking occurs in the thin plate. . On the other hand, when the amount of surface strain obtained by FEM analysis is smaller than the limit line of hair cracking, it is determined that no cracking occurs in the thin plate.

  As described above, in the present embodiment, the first fracture limit line representing the fracture limit due to strain at the center of the plate thickness of the sample is converted to the second fracture limit line corresponding to the surface strain reflecting the bending deformation. Then, using the second fracture limit line as a reference, the surface strain amount calculated for the thin plate to be judged is compared with the second fracture limit line to determine whether or not there is a possibility of fracture or fracture. As described above, according to the present embodiment, the determination of the fracture is based on the surface distortion that sufficiently reflects the bending deformation, not the distortion due to the center of the plate thickness that is insufficiently compatible with the bending deformation. Thus, it is possible to accurately determine the fracture according to the actual fracture.

  Hereinafter, specific examples of the fracture prediction method and the fracture prediction system according to the above-described embodiment will be described as various examples based on a comparison with a conventional fracture prediction method.

Example 1
In this example, a fracture experiment was performed to verify the fracture prediction method of the present embodiment.
As a fracture experiment, a three-point bending drop test was performed. Using a sample having a cross-sectional hat shape with a size of 50 mm × 50 mm and a length of 900 mm, the three-point bending of the sample was evaluated. As for the material, the hat side was a so-called hot stamping material (hot press material), the contact side was JSC590Y, and the plate thickness was 1.4 mm.

  Breaking experiments were conducted on seven types of samples (No. 1 to No. 7) using the above-mentioned samples, with different bending spans, falling weights, initial speeds, and presence or absence of the portal clamp. The experimental results are shown in Table 3 below.

  Thus, Sample No. 3 and No. 4 with a bending span of 600 mm and an initial speed of 3.0 m / s or more and no gate-type press, and a bending span of 200 mm and an initial speed of 4.0 m / s or more. Breakage was confirmed in samples No. 6 and No. 7.

The fracture prediction method of FIG. 2 (fracture prediction system of FIG. 1), perform the steps S1 to S3, obtaining a second fracture limit line L ₂ as shown in FIG. In FIG. 5, the case where the bristle breaking limit line L ₃ is acquired together with the second breaking limit line L ₂ is shown. And after performing step S4 and calculating the surface distortion amount of the thin plate which is the object of fracture prediction, step S5 is performed to determine whether or not the thin plate is broken.

  In step S4, for example, using the Cowper-Symonds parameters shown in Table 4 below, mesh division is set to a predetermined element size, and FEM analysis is performed. Specifically, the element size is set as shown in Table 5 below. As shown in FIG. 6, the thin plate to be determined has a top part, an R part, a vertical wall part, and a flange part. For example, as shown in FIG. A surface from one end to the other end of a portion defined as a curved surface is divided into a plurality of portions. In this example, the element size is set to 6 divisions (division (1)) and 4 divisions (division (2)) according to this criterion. Table 6 shows the FEM analysis results obtained in step S4. Here, No. 1 to No. 7 were analyzed in the divisions (1) and (2) under the same conditions as in Table 3.

For No. 5 to No. 7 when the bending span is 200 m, the state of the thin plate subjected to FEM analysis by the fracture experiment and division (1), (2) of this example is shown in FIG. FIG. 8 shows the maximum principal strain distribution on the outer surface of the thin plate subjected to the FEM analysis according to 1), and FIG. 9 shows the maximum principal strain distribution on the outer surface of the thin plate according to the division (2) of this example.
Moreover, about No.1-No.4 which is a case where a bending span is 600 m, the state of the thin plate by which FEM analysis by the fracture | rupture experiment and division | segmentation (1), (2) of this example was carried out to FIG.10 and FIG.11. The maximum principal strain distributions on the inner surfaces of No. 3 and No. 4 thin plates subjected to FEM analysis according to the divisions (1) and (2) of this example are shown in FIG.

As a comparative example of the fracture prediction method of this example, the presence or absence of fracture of the thin plate was determined by a conventional fracture prediction method. In the conventional fracture prediction method, first, an experimental method such as the Nakajima method or the same process as step S1 of the fracture prediction method of this example is performed. Here, a fracture limit line representing the fracture limit due to strain at the center of the plate thickness is obtained by the latter method.
Next, the amount of strain at the center of the thickness of the thin plate that is the target of fracture prediction is calculated by FEM analysis. Here, as in Table 6 of this example, No. 1 to No. 7 were analyzed by division (1) and (2).
Then, using the fracture limit line as a reference, the amount of strain at the center of the plate thickness obtained by FEM analysis is compared with the fracture limit line to determine whether or not the thin plate is broken.

  For No. 5 to No. 7 with a bending span of 200 m, the determination results of whether or not the thin plate is broken are shown in FIGS. FIG. 13 is a characteristic diagram showing a determination result by a conventional fracture prediction method, and shows a result of FEM analysis in divisions (1) and (2). FIG. 14 is a characteristic diagram showing the determination result by the fracture prediction method of this example, where (a) shows the result of FEM analysis in division (1), and (b) shows the result of FEM analysis in division (2), respectively. Show.

  In the conventional fracture prediction method, as shown in FIG. 13, for No. 6 and No. 7 in which breaks were observed in the fracture experiments for both divisions (1) and (2), No. Similar to .5, it was below the fracture limit line and it was determined that no fracture occurred. Since the determination results of No. 6 and No. 7 are different from the results of the fracture experiment, it was confirmed that the conventional fracture prediction method cannot accurately predict the fracture due to bending deformation.

In the fracture prediction method of this example, as shown in FIG. 14, accurate prediction results were obtained for both the divisions (1) and (2). That is, for No. 5 in which no rupture was found in the rupture experiment, both divisions (1) and (2) were below the second break limit line L ₂ and the crack limit line L ₃ , and no breakage occurred. It was judged. On the other hand, for No. 6 and No. 7 in which breakage was observed in the break experiment, both the divisions (1) and (2) exceeded the second break limit line L ₂ and the crack limit line L ₃ , and breakage occurred. It was determined to do. Since all of these determination results agree with the results of the fracture experiment, it was confirmed that the fracture prediction method of this example can accurately predict the fracture due to bending deformation.

  FIG. 15 and FIG. 16 show the determination results of whether or not the thin plate is broken for No. 1 to No. 4 with a bending span of 600 m. FIG. 15 is a characteristic diagram showing a determination result by a conventional fracture prediction method, and shows a result of FEM analysis in divisions (1) and (2). FIG. 16 is a characteristic diagram showing the determination result by the fracture prediction method of this example, where (a) shows the result of FEM analysis in division (1), and (b) shows the result of FEM analysis in division (2), respectively. Show.

  In the conventional fracture prediction method, as shown in FIG. 15, No. 3 and No. 4 in which breaks were recognized in the fracture experiments in both divisions (1) and (2), No fracture was not found in the fracture experiments. Similar to .1 and No. 2, it was below the fracture limit line and it was determined that no fracture occurred. Since the determination results of No. 3 and No. 4 are different from the results of the fracture experiment, it was confirmed that the conventional fracture prediction method cannot accurately predict the fracture due to bending deformation.

In the fracture prediction method of this example, as shown in FIG. 16A, an accurate prediction result was obtained in the division (1). That is, in the division (1) of the fracture prediction method of this example, No. 1 and No. 2 in which no fracture was observed in the fracture experiment were below the second fracture limit line L ₂ and the crack limit line L ₃ . It was determined that no breakage occurred. On the other hand, No. 3 and No. 4 in which rupture was recognized in the rupture experiment exceeded the second break limit line L ₂ and the crack limit line L ₃ , and it was determined that the break occurred. Since these determination results all agree with the result of the fracture experiment, it was confirmed that the fracture due to bending deformation can be accurately predicted according to the division (1) of the fracture prediction method of this example.

However, as shown in FIG. 16 (b), in the division (2) of the fracture prediction method of this example, the fracture was not observed in the fracture experiment as in No. 1 and No. 2 where the fracture was not observed in the fracture experiment. The recognized No. 3 and No. 4 were also below the second break limit line L ₂ and the hair crack limit line L ₃ , and it was determined that no break occurred.

From the above, in the fracture prediction method of this example, if the bending span is not so large, for example, about 200 mm, the element size of the FEM analysis when calculating the surface strain amount of the thin plate that is the target of fracture prediction is 4 It can be seen that a sufficiently accurate fracture prediction of bending deformation is possible even with the division (based on the R portion of the thin plate).
On the other hand, when the bending span is large, for example, about 600 mm, the element size of the FEM analysis may not be sufficient for about four divisions. When the bending span is larger than 200 mm and smaller than 600 mm, for example, if it is about 5 divisions, it is considered possible to accurately predict the bending deformation. Even in the case of a large bending span of 600 mm or more, a sufficiently accurate fracture prediction of bending deformation is possible if it is about 6 divisions.
From the above, in the fracture prediction method of the present example, the appropriate element size of the FEM analysis when calculating the surface strain amount of the thin plate that is the target of the fracture prediction is 5 divisions (based on the R portion of the thin plate) or more. In consideration of securing a certain size of element size, it can be concluded that it is preferably about 6 divisions.

  As described above, according to the present embodiment, accurate fracture prediction using the fracture limit line of a thin plate made of a metal material, here, the second fracture limit line, which is a bending-corrected FLC, is realized. According to the present embodiment, it is possible to accurately evaluate the risk of press forming and fracture at the time of collision, and it is possible to efficiently and highly accurately develop an automobile body considering the material, construction method and structure at the same time.

(Other embodiments to which the present invention is applied)
The function of each component (excluding the recording unit 6) constituting the fracture prediction system of FIG. 1 according to the above-described embodiment can be realized by operating a program stored in a RAM or ROM of a computer. Similarly, each step (steps S1 to S5 in FIG. 2) of the fracture limit acquisition method can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable storage medium storing the program are included in the present invention.

  Specifically, the program is recorded on a recording medium such as a CD-ROM or provided to a computer via various transmission media. As a recording medium for recording the program, a flexible disk, a hard disk, a magnetic tape, a magneto-optical disk, a nonvolatile memory card, and the like can be used in addition to the CD-ROM. On the other hand, a communication medium in a computer network system for propagating and supplying program information as a carrier wave can be used as the program transmission medium. Here, the computer network is a WAN such as a LAN or the Internet, a wireless communication network, or the like, and the communication medium is a wired line such as an optical fiber or a wireless line.

  Further, the program included in the present invention is not limited to the one in which the functions of the above-described embodiments are realized by the computer executing the supplied program. For example, such a program is also included in the present invention when the function of the above-described embodiment is realized in cooperation with an OS (operating system) or other application software running on the computer. Further, when all or part of the processing of the supplied program is performed by the function expansion board or function expansion unit of the computer and the functions of the above-described embodiment are realized, the program is also included in the present invention.

  For example, FIG. 17 is a schematic diagram illustrating an internal configuration of a personal user terminal device. In FIG. 17, reference numeral 1200 denotes a personal computer (PC) having a CPU 1201. The PC 1200 executes device control software stored in the ROM 1202 or the hard disk (HD) 1211 or supplied from the flexible disk drive (FD) 1212. The PC 1200 generally controls each device connected to the system bus 1204.

  By the program stored in the CPU 1201, the ROM 1202, or the hard disk (HD) 1211 of the PC 1200, the procedure of steps S1 to S5 in this embodiment is realized.

  Reference numeral 1203 denotes a RAM which functions as a main memory, work area, and the like for the CPU 1201. A keyboard controller (KBC) 1205 controls instruction input from a keyboard (KB) 1209, a device (not shown), or the like.

  Reference numeral 1206 denotes a CRT controller (CRTC), which controls display on a CRT display (CRT) 1210. Reference numeral 1207 denotes a disk controller (DKC). The DKC 1207 controls access to a hard disk (HD) 1211 and a flexible disk (FD) 1212 that store a boot program, a plurality of applications, an editing file, a user file, a network management program, and the like. Here, the boot program is an activation program, that is, a program for starting execution (operation) of hardware and software of a personal computer.

  Reference numeral 1208 denotes a network interface card (NIC) that exchanges data bidirectionally with a network printer, another network device, or another PC via the LAN 1220.

DESCRIPTION OF SYMBOLS 1 1st fracture limit line acquisition part 2 1st surface strain amount calculation part 3 2nd fracture limit line acquisition part 4 2nd surface strain amount calculation part 5 Breaking prediction part 6 Recording part

Claims (10)

A method for predicting the breakage of a thin plate made of a metal material,
Obtaining a first break limit line at the thickness center of the sample;
A step of applying bending deformation to the sample and calculating the amount of surface strain when the fracture occurs;
A difference value between a surface strain amount when the rupture occurs and a plane strain amount in the first rupture limit line is calculated, and the difference value is added to the first rupture limit line to obtain a second rupture. Obtaining a limit line; and
Calculating a surface strain amount of the thin plate;
A step of predicting the presence or absence of breakage of the thin plate based on the calculated amount of surface strain of the thin plate with reference to the second break limit line. In the step of obtaining the first break limit line,
An approximate expression σ _eq = Cε _eq ⁿ of a stress-strain curve obtained from a uniaxial tensile test,
Local constriction model

When,
Diffusion constriction model

Or
Stalen-Rice model

The fracture prediction method according to claim 1, wherein the first fracture limit line is obtained by using together.   2. The fracture prediction method according to claim 1, wherein in the step of calculating the surface strain amount of the thin plate, a finite element method is used to divide the curved surface portion of the sample into five or more elements. A system for predicting fracture of a thin plate made of a metal material,
A first breaking limit line acquisition unit for acquiring a first breaking limit line at the thickness center of the sample;
A first surface strain amount calculation unit that applies a bending deformation to the sample and calculates a surface strain amount when a fracture occurs;
A difference value between a surface strain amount when the rupture occurs and a plane strain amount in the first rupture limit line is calculated, and the difference value is added to the first rupture limit line to obtain a second rupture. A second break limit line acquisition unit for acquiring a limit line;
A second surface strain amount calculation unit for calculating the surface strain amount of the thin plate;
A fracture prediction unit that predicts whether or not the thin plate is broken based on the second fracture limit line based on the surface strain amount of the thin plate calculated by the second surface strain amount calculation unit. A fracture prediction system. The first fracture limit line acquisition unit obtains an approximate expression σ _eq = Cε _eq ⁿ of a stress-strain curve obtained from a uniaxial tensile test when acquiring the first fracture limit line,
Local constriction model

When,
Diffusion constriction model

Or
Stalen-Rice model

The rupture prediction system according to claim 4, wherein the first rupture limit line is obtained in combination with and.   The said 2nd surface strain amount calculation part divides | segments the curved-surface part of the said sample into five or more elements using a finite element method, when calculating the surface strain amount of the said thin plate. Described fracture prediction system. A program for predicting breakage of a thin plate made of a metal material,
Obtaining a first break limit line at the thickness center of the sample;
A step of applying bending deformation to the sample and calculating the amount of surface strain when the fracture occurs;
A difference value between a surface strain amount when the rupture occurs and a plane strain amount in the first rupture limit line is calculated, and the difference value is added to the first rupture limit line to obtain a second rupture. Obtaining a limit line; and
Calculating a surface strain amount of the thin plate;
A program for causing a computer to execute a step of predicting the presence or absence of breakage of the thin plate based on the calculated surface strain amount of the thin plate with reference to the second break limit line. In the step of obtaining the first break limit line,
An approximate expression σ _eq = Cε _eq ⁿ of a stress-strain curve obtained from a uniaxial tensile test,
Local constriction model

When,
Diffusion constriction model

Or
Stalen-Rice model

The program according to claim 7, wherein the first fracture occurrence limit is obtained using both of and.   8. The program according to claim 7, wherein in the step of calculating the surface strain amount of the thin plate, the curved surface portion of the sample is divided into five or more elements using a finite element method.   The computer-readable recording medium which recorded the program of any one of Claims 7-9.

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