Technical field
[0001]
The present invention, fracture determination apparatus, fracture determination program, and a method thereof.
BACKGROUND
[0002]
Recently, from the request of the collision safety and weight reduction, while the application of high-strength steel sheet is rapidly advanced to the automobile body. High-strength steel sheet used for automobile body, breaking strength is increased to increase the absorption energy at the time of collision without increasing the plate thickness. However, by reducing the ductility of the steel sheet with high strength of a steel sheet, there is a possibility that the steel sheet is broken upon collision deformation of the vehicle at the time of press forming, and an automobile. To determine the state of the steel sheet during press molding and during collision deformation, FEM (Finite Element Method, FEM) there is a growing need for accurate collision deformation simulation and fracture criterion by.
[0003]
　Further, as a method of joining steel sheet in the vehicle assembly process, such as an automobile, spot welding is used. Members assembled by spot welding is known to be referred heat affected zone with HAZ (Heat affected zone) portion around the spot weld is formed. HAZ portion, the strength is lowered due to the influence of heating by spot welding. The strength of the HAZ is lowered, strain is concentrated at the time of collision deformation, it is possible to break the HAZ portion is generated. Therefore, breakage of the HAZ at the time of collision deformation are required to be accurately predicted, thereby making it possible to improve the accuracy of the collision deformation simulation of an automobile.
[0004]
　For example, Patent Document 1, based on the master curve showing the relationship between the strain and the material parameters calculated from such as mechanical properties and chemical composition of the HAZ, a technique for predicting a breakage of the HAZ portion is described . Techniques described in Patent Document 1 can break strain even for members made of steel species is uncalculated, the fracture criterion value accurately predicted without performing the fracture determination value calculation process. However, when predicting the fracture of the HAZ in the collision deformation simulation using the FEM, strain of the HAZ, since different depending on the element size, the timing at which HAZ portion is determined to have broken, differs by the element size there is a problem in that.
[0005]
　To solve such a problem, to create an analysis model for each element size, the breaking strain in each model is calculated, predicted breakage of the HAZ from the relationship between breaking strain and parameters that define the element size technique is known (e.g., see Patent Document 2). Techniques described in Patent Document 2, by obtaining the value of the element size parameter from the relationship between breaking strain and parameters that define the element size, regardless of element size, be accurately calculating the breaking strain of the HAZ it can.
CITATION
Patent Document
[0006]
Patent Document 1: JP 2012-132902 Patent Publication
Patent Document 2: JP 2008-107322 JP
Summary of the Invention
Problems that the Invention is to Solve
[0007]
　However, in the technology described in Patent Document 2, when performing steels fracture prediction of strain at break is not calculated, it is necessary to perform a process for calculating the fracture criterion value before performing fracture prediction, a vehicle such as an automobile it is not easy to apply to the collision deformation simulation. Processing for calculating the fracture criterion value, it takes a great deal of effort, it is impossible to determine the fracture criterion value for all of the spot welding point of up to normal several thousand RBI of a vehicle such as an automobile.
[0008]
　Accordingly, the present invention provides a deformation simulation heat affected zone containing a large amount of member such as a vehicle such as an automobile is used FEM upon collision deformation, suitable predictable fracture of the heat-affected zone regardless of element size and to provide a fracture judgment apparatus.
Means for Solving the Problems
[0009]
　The present invention to solve such problems, fracture determination device described below is intended to break determining program, and the fracture determination method and gist.
　(1) the material properties and thickness of the steel having a heat affected zone, as well as the input information element indicating an element size in the analysis model used for deformation simulation of steel by the finite element method, the reference element size is an element size as a reference a reference forming limit value information indicating a reference molding limits the forming limit value, a storage unit for storing, in the
　element extracting section that extracts elements included in the heat affected zone formed around the steel spot weld If,
　based on the reference forming limit value information, the reference forming limit value generator for generating a reference forming limit value according to the material properties and thickness of the heat-affected zone,
　reference forming limit value using a tensile strength of steel change and a heat-affected zone forming limit value generation unit that generates a heat affected portion forming limit value to predict the forming limit in element size of elements in the heat-affected zone,
　using the input information deformed Run the Interview configuration, a simulation executing unit that outputs modification information including the strain of each element included in the heat-affected zone,
　the main determining respective maximum principal strain and minimum principal strains of elements in the heat-affected zone a strain determining unit,
　each of the maximum main strain and minimum principal strains of principal strain is determined elements, on the basis of the heat-affected zone forming limit line which is defined by the heat-affected zone forming limit value, the elements in the analysis model respectively, and the fracture determination unit that determines whether to break
　fracture judgment apparatus characterized in that it comprises a.
　(2) element extraction unit,
　and the joining element extraction unit for extracting the contact elements defining a joining of two steel
　defining an annular centering point contact between the elements forming the contact elements and steel an annular defining portion,
　the element containing at least a portion in a circular ring, and the element determination unit for determining the elements forming the heat-affected zone,
　having a fracture determination apparatus according to (1).
　(3) reference forming limit value generator
　and the neighbor information acquiring unit for acquiring material properties and thickness of the element adjacent to the contact point between the elements forming the contact elements and steel,
　obtained by the neighbor information acquiring unit material properties a material characteristic estimating unit for estimating the material properties of the heat affected zone from
　the material characteristic estimating section forming limit value for generating a reference forming limit value corresponding to the thickness obtained by material properties and the neighbor information acquiring unit estimated by a generating unit,
　having a fracture determination apparatus according to (2).
　(4) the heat-affected zone forming limit value generation unit,
　and the element size determining unit that determines the element size of the elements included in the heat-affected zone,
　using a tensile strength of the steel material, the reference in accordance with the determined element size and forming limit value changing unit for changing the forming limit value,
　having, (1) fracture judgment apparatus according to any one of the - (3).
　(5) element size determining unit
　and the element size extracting unit for extracting each element size of elements in the heat-affected zone,
　from each of the extracted element size, the element size of the elements included in the heat-affected zone and element size calculating unit for calculating,
　with a break determination apparatus according to (4).
　(6) Modification simulation is collision deformation simulation of the vehicle formed by the steel, (1) fracture judgment apparatus according to any one of - (5).
　(7) the subject forming limit value generator generates a target forming limit value using the element size and shaped limits prediction expression which is a function of the tensile strength of the steel,
　forming limit value prediction equation, [rho is the strain is the ratio, M represents an element size indicating the size of the elements of the analysis model used in the simulation by FEM, epsilon 1 is the maximum principal strain in the element size M, epsilon 2 is the minimum principal strain in element size M when, by the first coefficient k1 and the second coefficient k2
[number 1]

is represented by the first coefficient k1 is the tensile strength TS and the material of the steel sheet, the coefficient γ and [delta]
[Equation 2]

is represented by the second coefficient k2, the maximum principal strain ε in the reference element size 1B from and coefficient eta
[number 3]

represented by the fracture judgment apparatus according to (1).
　(8) extracts the elements included in the heat-affected zone formed around the spot weld of the steel,
　the reference forming limit indicating reference molded limits the forming limit value in the reference element size is an element size as a reference based on the value information, it generates a reference forming limit value according to the material properties and thickness of the heat-affected zone,
　and change the reference forming limit value using a tensile strength of element size and steel, contained in the heat-affected zone predicting the forming limits in the size of the element is the element generates a heat affected portion forming limit value,
　modified by using the input information for the deformation simulation of steel by FEM including material properties and thickness of the steel running simulation, it outputs modification information including the strain of each element included in the heat-affected zone,
　to determine the respective maximum principal strain and minimum principal strains of elements in the heat-affected zone,
　the main Zumi is based on the respective the maximum principal strain and minimum principal strain of the determined element, and the heat affected zone forming limit line which is defined by the heat-affected zone forming limit value, whether each element in the analysis model is broken determining, fracture determination method characterized by comprising or.
　(9) to extract the elements included in the heat-affected zone formed around the spot weld of the steel,
　the reference forming limit indicating reference molded limits the forming limit value in the reference element size is an element size as a reference based on the value information, it generates a reference forming limit value according to the material properties and thickness of the heat-affected zone,
　and change the reference forming limit value using a tensile strength of element size and steel, contained in the heat-affected zone predicting the forming limits in the size of the element is the element generates a heat affected portion forming limit value,
　modified by using the input information for the deformation simulation of steel by FEM including material properties and thickness of the steel running simulation, it outputs modification information including the strain of each element included in the heat-affected zone,
　to determine the respective maximum principal strain and minimum principal strains of elements in the heat-affected zone,
　the main Zumi is based on the respective the maximum principal strain and minimum principal strain of the determined element, and the heat affected zone forming limit line which is defined by the heat-affected zone forming limit value, whether each element in the analysis model is broken determining, fracture determination program for causing the execution of the computer or.
Effect of the invention
[0010]
　In one embodiment, the deformation simulation by FEM member containing much heat affected portion, it is possible to appropriately predict the breakage of the heat-affected zone regardless of element size.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
[1] a shaping limit line generated using the forming limit prediction expression is a diagram showing the relationship between the actual measurement value.
2 is a diagram showing a fracture determining apparatus according to the first embodiment.
3 is a flowchart of a fracture determination process by breaking determining apparatus according to the first embodiment.
It is a flowchart showing a detailed processing of the processing of S103 shown in FIG. 4 FIG.
[Figure 5] is a diagram for explaining the processing shown in FIG. 4, (a) and (b) is a diagram for explaining the processing of S201, (c) it is for explaining the processing of S202 a diagram is a diagram for explaining the process of (d), S203.
It is a flowchart showing a detailed processing of the processing of S104 shown in FIG. 6 FIG.
7 is a flowchart showing a detailed process of step S105 shown in FIG.
8 is a diagram showing a fracture determination apparatus according to the second embodiment.
9 is a flowchart of a fracture determination process by breaking determining apparatus according to the second embodiment.
Is a diagram for explaining the process of S103 when the [10] element size differs (a) is a diagram for explaining the processing of S201, (b) is for explaining the processing of S202 a diagram is a diagram for explaining the processing of (c) is S203.
11 is a diagram showing a mold manufacturing system which is an example of application of the fracture determination apparatus according to the embodiment.
[Figure 12] is a view showing a bending test apparatus hat member 3 point used for the measurement, (a) is a side view, a sectional view taken along the A-A'line (b) is (a).
13 is a diagram showing a FEM simulation conditions in the vicinity of the spot welding Examples and Comparative Examples.
[Figure 14] is a diagram showing a comparison of the experimental results of real and Examples 1 and 2, (a) is a diagram showing the real breaking state, (b) is a diagram showing a broken state of Example 1 in and, (c) is a diagram showing a broken state of example 2, it is a graph showing the relationship (d) and the load caused depression distance and hat member pressing member.
[Figure 15] is a diagram showing a comparison between Comparative Example 1 and 2 and the experimental results real, (a) is a diagram showing the real breaking state, (b) is a diagram showing a broken state of Comparative Example 1 in and, (c) is a diagram showing a broken state of Comparative example 2 is a diagram showing the relationship (d) and the load caused depression distance and hat member pressing member.
DESCRIPTION OF THE INVENTION
[0012]
　With reference to the accompanying drawings, fracture determination apparatus, fracture determination program, and its method will be described. However, the technical scope of the present invention is not limited to the embodiments shown.
[0013]
　(Overview of the fracture determination device according to the embodiment)
　fracture determination device according to the embodiment, the reference forming limit value information at the reference element size created by actual measurement or the like, material properties and thickness of the HAZ (heat affected zone) the reference forming limit value determined by changes by a function of the tensile strength of the element size and the steel is the size of the elements in the analysis model forming limit value prediction equation. Implementation fracture judgment apparatus according to the embodiment, by using the an element size and function of the tensile strength of the steel material is sized HAZ forming limit values that have been changed by the forming limit prediction equation is the element in the analysis model, the object forming limit value corresponding to the tensile strength can be used. Break determining apparatus according to the embodiment, tensile Since the object forming limit value corresponding to the intensity can be used, can be predicted in a short time breakage of a number of heat-affected zone that is included in the member. Hereinafter, the principle of breaking determination processing in fracture determination apparatus according to the embodiment before describing fracture determination apparatus according to the embodiment will be described.
[0014]
　The inventors of the present invention, the reference shaping limits on reference element size corresponding to the forming limit curve prepared by actual measurement or the like, O the maximum principal strain in the element size and the reference element size in the analytical model of the steel sheet is used as a judgment target the maximum principal strain in the element size was found molded limits prediction expression for predicting, based on the relationship. That is, the inventors of the present invention, the reference forming limit value corresponding to the reference shaping limit line as a reference, is generated by modifying the forming limit value prediction expression which is a function of the tensile strength and element size steel It was found to determine the presence or absence of fracture using object forming limit value. Depending on the element size, by changing the forming limit value using a forming limit prediction equation allows fracture determination in accordance with the element size.
[0015]
　Equation (1) shown below are forming limit value prediction equation found by the inventors of the present invention.
[0016]
[Formula 4]

[0017]
　Here, [rho is strain ratio, M is an element size (mm) indicating the size of the element of interest in the simulation using the finite element method, epsilon 1 is the maximum principal strain in the element size M, epsilon 2 is the minimum principal strain in element size M. A multiplier element size M k1 is the first coefficient, the maximum strain mainly in reference element size as k2 is an index of the element size M will be described with reference to equation (2) and (4) shown below it is a second coefficient which depends on. Equation (1), the maximum principal strain ε in element size M based on the relationship of the maximum principal strain and the element size M and the reference element size 1 is an equation to predict. In the formula (1), the maximum principal strain ε in element size M 1 is the multiplier of the first coefficient k1, and calculation results calculated by the calculation by the powers operation to the base and element size M and the second coefficient k2 and index It is shown to be generated by multiplying the.
[0018]
　Equation (2) below is an expression indicating the equation (1) in more detail.
[0019]
[Formula 5]

[0020]
　Here, TS denotes the tensile strength [MPa] of the material such as a steel plate, epsilon 1B shows a reference element size, gamma, [delta] and η denotes a coefficient. γ is a negative value, [delta] is a positive value. Coefficient γ and δ may vary depending on the strain ratio [rho. Coefficient η is determined by the reference element size. From equation (1) and (2), the first coefficient k1 is
[0021]
[Number 6]

[0022]
　In shown. In the formula (3), the first coefficient K1 is strain ratio ρ is proportional to the tensile strength TS of the steel at the time of constant, i.e., is shown to be a function of the tensile strength of the strain ratio ρ and steel. Equation (3), the first coefficient k1 has shown that proportional to the tensile strength TS of the steel, according to the tensile strength TS of steel increases, the maximum principal strain epsilon 1 and the minimum principal strain epsilon 2 that is increased It is shown. First coefficient k1 is a positive value, gamma is a negative value, [delta] is because it is a positive value, the first coefficient k1 in accordance with the tensile strength TS of steel increases decreases. Further, from equation (1) and (2), the second coefficient k2 is
[0023]
[Number 7]

[0024]
　In shown. In the formula (4), the second coefficient k2, the maximum principal strain ε in the reference element size 1B it is and function of the first coefficient k1 is shown. More specifically, in the equation (4), the second coefficient k2 together with is shown to be proportional to the maximum principal strain in the logarithmic in the reference element size, the second coefficient k2 is proportional to the logarithm of the reciprocal of the first coefficient k1 it is shown.
[0025]
　Figure 1 shows the formula (1) to (4) forming limit line generated using the target forming limit value changed by the molding limit prediction equation described with reference to the relationship between the actual measurement value it is a diagram. 1, the horizontal axis is the minimum principal strain epsilon 2 and a Y axis minimum principal strain epsilon 1 shows a. Also, circles indicate the measured values when the gauge length of 10 mm. Square marks gauge length indicates the measured value at 6 mm and triangles gauge length is 2 [mm shows the measured value when the]. Curve 101 is the reference forming limit curve prepared using the calculated reference forming limit value from the generated reference forming limit value information and material properties and the sheet thickness from measured data of the gauge length of 10 mm. is there. Curves 102 and 103 were generated using the equation (1) to the target forming limit values that have been changed from the reference forming limit value indicated by the curve 101 by reference to the forming limit line prediction formula described by (4) representing the target forming limit line. Curve 102 shows the forming limit line when the gauge length of 6 mm and a curve 103 represents a forming limit line when the gauge length of 2 mm. Incidentally, was used to generate the actual measurement and the forming limit line shown in FIG. 1, the tensile strength of the material properties of the steel sheet is 1180 [MPa], the plate thickness is 1.6 mm. In general, since the strain at rupture in the vicinity it is localized strain higher closer to the fracture portion has occurred. Therefore, as the gauge length for reading the distortion of the fracture portion is shortened, to read high strain occurring in breaking the vicinity, the value of the forming limit is higher. That is, forming limit line in FIG. 1 is located above a more. Also, when compared to steel other material properties, since in general the tensile strength TS of the steel is the steel ductility is reduced significantly, the value of the strain at break in the vicinity is reduced. Therefore forming limit curve in FIG. 1 will be more positioned below.
[0026]
　As shown in FIG. 1, the object forming limit lines which are modified using the reference forming limit value from the reference forming limit line, and the measured values ​​both in the case of the gauge length of 2 [mm] and 6 mm. accuracy well matched, forming limit value prediction expression according to the present invention is shown to have a high accuracy.
[0027]
　Break determining apparatus according to the embodiment, since the decision whether to break on the basis of the forming limit line corresponding to the element size of the elements included in the HAZ, it is possible to break determination in accordance with the element size. Further, the fracture determination apparatus according to the embodiment, even when the element size of the elements included in the HAZ was different from the element size of other elements in order to improve the analysis accuracy of the HAZ portion, depending on the element size break it is possible to determine.
[0028]
　(Configuration and Function of the fracture determination apparatus according to the first embodiment)
　FIG. 2 is a diagram showing a fracture determining apparatus according to the first embodiment.
[0029]
　Fracture determination apparatus 1 includes a communication unit 11, a storage unit 12, an input unit 13, an output unit 14, a processing unit 20. Communication unit 11, a storage unit 12, input unit 13, output unit 14 and the processor 20 are connected to each other via a bus 15. Fracture determination apparatus 1, by forming limit value prediction formula using the tensile strength of the steel, to generate a target forming limit value showing the molding limit in element size by changing the reference forming limit value, such as an automobile by FEM performing collision deformation simulation of the vehicle. Fracture determination apparatus 1 determines based on the generated object forming limit value, since the strain respective maximum principal strain and minimum elements to be output by the collision deformation simulation, whether each element is broken. In one example, fracture determination apparatus 1 is a personal computer simulations that can be performed by FEM.
[0030]
　The communication unit 11 has a wired communication interface circuit such as Ethernet (registered trademark). The communication unit 11 communicates with the server or the like (not shown) via a LAN.
[0031]
　Storage unit 12 includes, for example, a semiconductor memory device, a magnetic tape unit, a magnetic disk device, or at least one of the optical disk apparatus. Storage unit 12 stores an operating system program used for processing in the processing unit 20, a driver program, an application program, stores the data, and the like. For example, the storage unit 12 as an application program, stores the break determining program for executing the fracture determination process for determining the respective breakage of elements of the element or the like included in the HAZ. Further, the storage unit 12 as an application program, stores the collision deformation simulation program for performing a collision deformation simulation using FEM. Break determining program and a collision deformation simulation program, etc., for example, a CD-ROM, a computer readable portable recording medium such as a DVD-ROM, or may be installed in the storage unit 12 using such as a known setup program.
[0032]
　The storage unit 12 stores various data used in fracture determination process and the collision deformation simulation. For example, the storage unit 12 stores the input information 120 and the reference forming limit value information 121 or the like is used in fracture determination process and the collision deformation simulation.
[0033]
　Input information 120 includes material properties and thickness of the steel, and the element size indicating the size of the elements in the collision deformation simulation by the finite element method. Material properties of the steel comprises stress-strain (stress-strain, S-S) curve, each coefficient in equation Swift used for fitting S-S curve, Young's modulus, Poisson's ratio and density or the like. Reference forming limit value information 121 is used to define the reference forming limit value indicating a forming limit value corresponding to the forming limit line in the reference element size indicating the element size to be a reference for each material properties and thickness. In one example, the reference forming limit value information 121 includes a forming limit value corresponding reference shaping limit line is measured for each material properties and thickness. In another example, the reference shaping limit line information 121, forming limit curve obtained from the theoretical formula of Storen-Rice is, corresponding reference shaping limit line corrected to match the actually measured reference forming limit line including a shaped limits.
[0034]
　The storage unit 12 stores the input data of the collision deformation simulation by FEM.
[0035]
　Also, it stores the HAZ characteristic table 122 showing a correlation between the material properties of the HAZ formed by spot welding. In one example, to implement the micro-tensile test the HAZ in various steel materials, and materials grade steel base metal, and obtain the relation of the material properties of the HAZ, and stores the HAZ portion characteristic table 122. Material properties of the HAZ portion, the stress strain curves or can be obtained by fitting the stress-strain curve by the formula Swift, stored in Swift factor like. HAZ portion characteristic table 122 by storing the relationship between the material properties of the material grade and the HAZ of the steel base material, the material properties of the HAZ in accordance with the material grade of the steel of the base material are defined correctly. Further, the storage unit 12 may temporarily store temporary data associated with a predetermined processing.
[0036]
　The input unit 13 may be any device as long as possible input data, for example, a touch panel, a keyboard or the like. Operator uses the input unit 13 can input characters, numbers, symbols, or the like. The input unit 13, when operated by the operator, generates a signal corresponding to the operation. The generated signal, as an indication of the operator, is supplied to the processing unit 20.
[0037]
　The output unit 14 may be any device as long as capable of displaying such video or image, for example, a liquid crystal display or an organic EL (Electro-Luminescence) display or the like. The output unit 14, and video corresponding to the video data supplied from the processing unit 20, and displays an image or the like in accordance with image data. The output unit 14, the display medium such as paper, the image may be an output device for printing images or characters, and the like.
[0038]
　Processor 20 has one or a plurality of processors and their peripheral circuitry. Processing unit 20, which centrally controls the overall operation of the fracture judgment apparatus 1, for example, a CPU. Processor 20, programs stored in the storage unit 12 (driver program, an operating system program and application programs) executes processing based on the. The processing unit 20 can execute a plurality of programs (application programs) in parallel.
[0039]
　Processor 20 includes an information acquisition unit 21, an element extracting section 22, a reference forming limit value generator 23, a heat affected zone forming limit value generation unit 24, a simulation executing unit 25, a determining unit 26 principal strain, a fracture determining unit 27, and a simulation result outputting unit 28. Element extracting section 22 includes a joining element extraction unit 221, an annular defining portion 222, and a element determination unit 223. Reference forming limit value generation unit 23 includes a neighboring information acquisition unit 231, a material characteristic estimating unit 232, and a forming limit value generation unit 233. HAZ forming limit value generating section 24 includes an element size extracting unit 241, an element size calculation unit 242, and a forming limit value changing section 243. These units are functional modules implemented by a program executed by the processor of the processing unit 20 is provided. Alternatively, these units may be implemented to break determination device 1 as firmware.
[0040]
　(Fracture judgment apparatus fracture determination process by which the first embodiment)
　FIG. 3 is a flow chart of determining fracture determination process whether or not each broken element of the fracture determination device 1 is a collision deformation simulated HAZ portions is there. Break determination process shown in FIG. 3, in advance based on the program stored in the storage unit 12, are executed in cooperation with the elements of the fracture determination apparatus 1 mainly by the processor 20.
[0041]
　First, the information acquisition unit 21 acquires the material properties such as tensile strength, acquires the input information 120 including the thickness and element size from the storage unit 12 (S101), the reference forming limit value information 121 from the storage unit 12 (S102).
[0042]
　Then, the element extracting section 22 extracts the elements included in the HAZ portion formed around the steel spot weld (S103).
[0043]
　Then, the reference forming limit value generator 23, based on the reference forming limit value information 121 obtained by the processing of S102, and generates a reference forming limit value according to the material properties and thickness of the HAZ portion (S104).
[0044]
　Then, the heat affected zone forming limit value generating section 24, the forming limit value predicting equation shown in equation (1) to (4), by changing the reference forming limit value generated by the processing in S104, the elements of the HAZ produce heat affected zone forming limit value showing the molding limit in size (S105).
[0045]
　Then, the simulation execution unit 25, based on the acquired input information in the process of S101, by using the mesh data stored in the storage unit 12, the collision deformation simulation of a vehicle such as an automobile formed by steel FEM executed by (S106). Simulation execution unit 25, as the execution result of the simulation, the displacement of the contact point, and sequentially outputs the modification information including the stress strain and elements of the element for each element.
[0046]
　Then, the main strain determination unit 26, each of the maximum principal strain epsilon elements of the HAZ 1 and the minimum principal strain epsilon 2 to determine (S107). In one example, principal strain determination unit 26, each of the distortion components each element of the maximum principal strain epsilon of elements in the modification information outputted in the process of S106 1 and the minimum principal strain epsilon 2 to determine.
[0047]
　Then, breaking determination section 27, each of the maximum principal strain epsilon of the determined element in the process of S107 1 and the minimum principal strain epsilon 2 and the heat affected zone which is defined by the target forming limit value generated by the processing of S104 based on the forming limit line, determines whether each element of the HAZ breaks (S108). Break determining section 27, the maximum principal strain epsilon 1 and the minimum principal strain epsilon 2 when it does not exceed the threshold value is given in the heat affected zone forming limit line, it is determined that the element is not broken, the maximum principal strain epsilon 1 and minimum principal strain epsilon 2 when the difference exceeds a threshold value is given in the heat affected zone forming limit line, it is determined that the element is broken. In one example, the heat affected zone forming limit line is calculated as an approximation expression of the target molding limit.
[0048]
　Then, breaking the determination unit 27 determines the elements of the HAZ is broken and (S108-YES), the element outputs the element breaking information indicating that broke the simulation execution unit 25 (S109). Simulation execution unit can also be removed from the data for ie collision deformation simulation erasing the determined elements and breaking.
[0049]
　Reference forming limit value generator 23, the heat affected zone forming limit value generator 24, the processing corresponding to the processing of the main strain determining section 26 and the fracture determining unit 27, is performed for the elements of the steel sheet except for the HAZ. That is, the reference forming limit value generator 23 generates a reference forming limit value according to the material properties and thickness of the elements other than HAZ portion based on the reference forming limit value information 121. In the object-forming limit value generation unit (not shown) generates a target forming limit value showing the molding limit in element size of elements other than HAZ portion by changing the reference forming limit value by forming limit prediction equation. The main distortion determining unit 26, each of the maximum principal strain epsilon elements other than HAZ portion 1 and the minimum principal strain epsilon 2 to determine. The break determining section 27, each of the maximum principal strain epsilon elements other than HAZ portion 1 and the minimum principal strain epsilon 2 and, on the basis of the target forming limit value generated by the processing of S103, other than HAZ portion elements each determines whether breakage.
[0050]
　Simulation result output unit 28, a simulation execution unit 25 outputs the modification information are sequentially output (S110). Then, the simulation execution unit 25 determines whether a predetermined simulation end condition is satisfied (S 111). Simulation end time is obtained from the input data. Until the simulation end condition is determined to be satisfied, the process is repeated.
[0051]
　Figure 4 is a flowchart showing a detailed processing of the processing of S103. Figure 5 is a diagram for explaining the processing shown in FIG. 4, FIG. 5 (a) and (b) is a diagram for explaining the processing of S201, explaining the process of FIG. 5 (c) S202 a diagram for FIG. 5 (d) is a diagram for explaining the processing of S203.
[0052]
　First, joining element extraction unit 221 extracts the contact elements defining a joining two steel (S201).
[0053]
　As shown in FIG. 5 (a) and (b), the first steel 401 formed of a plurality of first shell elements 410, the first steel 401 formed of a plurality of second shell elements 420, bar They are joined through the element 403. Bar element 403, also referred to as beam element, a joining element that binds a first steel 401 and a second steel material 402. Bar element 403 is joined at a first end point 431 to the first steel 401, they are joined at the second end point 432 to a second steel 402.
[0054]
　Then, as shown in FIG. 5 (c), the annular defining portion 222, circle the first end point 431 which is one end and the contact between the first shell element 410 of the first steel 401 bar element 403 and the center point defining a ring 440 (S202). The inner diameter of the ring 440 is shown in the input information, corresponding to the nugget diameter of the nugget is a weld by spot welding. Definition Therefore, the inner diameter of the ring 440 is preferably to nugget diameter ~ nugget diameter + 0.1-2.0 mm in extent, thereby, a region intersecting the ring 440 and the HAZ caused by spot welding can do. In one example, the width of the HAZ portion is about 2 mm and 0.1 mm.
[0055]
　Then, as shown by hatching in FIG. 5 (d) determining, element determination unit 223, a first shell element 410 that includes at least a portion in a circular ring 440, the shell element 450 to form the HAZ portion to (S203).
[0056]
　Figure 6 is a flowchart showing a detailed processing of the processing of S104.
[0057]
　First, the neighbor information acquiring unit 231, the material of the first shell element 411 adjacent the first end point 431 is a contact point between the first shell element 410 which forms one end and a first steel 401 bar element 403 is a joining element It acquires characteristics and plate thickness (S301).
[0058]
　Neighbor information acquiring unit 231, a first shell element 411 hatched in FIG. 5 (b), it is determined that the first shell element 411 adjacent the first end point 431, the first shell element 411 adjacent obtained from the input information 120 stored the material properties and thickness in the storage unit 12. In one example, the neighbor information acquiring unit 231, the stress strain curve included in the input information 120 or, based on the Swift coefficients shown in equation Swift, to calculate the tensile strength TS of the first steel 401 theoretically, adjacent It acquires the material grade of the first shell element 410.
[0059]
　Then, the material characteristic estimating unit 232 refers to the HAZ portion characteristic table 122 stored in the storage unit 12, the material properties of the material properties to be obtained by the neighbor information acquiring unit 231, the shell element 450 to form the HAZ portion to estimate (S302).
[0060]
　Then, forming limit value generation unit 233 generates a reference forming limit value corresponding to the thickness obtained by the material properties and the neighbor information acquiring unit 231 estimated by the material characteristic estimating unit 232 (S303). Specifically, reference shaping limit value generator 22 may, for example, based on the material properties and thickness of the combinations included in the input information 120 from the reference forming limit values ​​of groups stored in the storage unit 12, by selecting a group of reference forming limit value, generating a reference forming limit value corresponding to the material properties and thickness. In this case, the reference forming limit value of plurality of groups included in the reference forming limit value information 121 is actually measured values. The reference forming limit value generator 22 may, for example, correspond to the material properties and thickness by correcting the set of reference forming limit value stored in the storage unit 12 in material properties and the measured value according to the thickness generating a reference molding limit. In this case, forming limit line generating unit 233 first generates a forming limit value corresponding to the forming limit line from the theoretical formula of Storen-Rice. Then, forming limit value generation unit 233, based on the measured value stored in the storage unit 12 as a shift amount according to the material properties and thickness, found a forming limit value generated from the theoretical formula of Storen-Rice by shifting the forming limit value to generate a reference forming limit value corresponding to the material properties and thickness according to.
[0061]
　Figure 7 is a flowchart showing a detailed processing of the processing of S105.
[0062]
　First, element size extracting unit 241, the mesh data stored in the storage unit 12, and extracts each of the element size of the shell element 450 included in the HAZ portion (S401).
[0063]
　Then, element size calculation unit 242, from each of the extracted element size by element size extracting unit 241 calculates the element size of the shell element 450 included in the HAZ portion (S402). In one example, element size computation unit 242, the average value of the element size extracting unit 241 element size extracted by, calculating the element size of the shell element 450 included in the HAZ.
[0064]
　Element size extracting unit 241 and the element size calculation unit 242 functions as an element size determining unit that determines the element size of the shell element 450 included in the HAZ.
[0065]
　Then, forming limit value changing section 243, by forming limit value predicting equation, change the reference forming limit value according to the calculated element size by element size calculation unit 242, generates a heat affected portion molding limit ( S403).
[0066]
　(Effect of the fracture determination apparatus according to the first embodiment)
　or fracture determination apparatus 1, HAZ portion using the modified HAZ forming limit value in accordance with the element size is broken by the forming limit prediction expression to determine whether it is possible to perform accurate fracture prediction in the HAZ portion without depending on the element size.
[0067]
　It is possible to perform the fracture prediction accurate HAZ portion by fracture determining apparatus 1, it is possible to significantly reduce the number of crash tests in actual automobile member. Furthermore, in some cases, it is possible to omit the crash test of an actual automobile parts.
[0068]
　Further, by performing fracture prediction of a correct HAZ portion by fracture judgment apparatus 1, it is possible to design a member for preventing breakage at the time of collision on a computer, to contribute to the reduction of the significant cost savings, development time can.
[0069]
　(Configuration and Function of the fracture determination apparatus according to the second embodiment)
　FIG. 8 is a diagram showing a fracture determination apparatus according to the second embodiment.
[0070]
　Fracture judgment apparatus 2, processing unit 30 is different from the fracture judgment apparatus 1 that is arranged instead according to the first embodiment of the processor 20. Processing unit 30, to have a heat-affected zone forming limit stress generator 34 and strain stress converter 35, as well as breaking the determination unit 36 ​​is different from the processing unit 30 to be arranged in place of the fracture determining unit 27. HAZ forming limit stress generating unit 34, configuration and functions of the components of the strain stress converter 35 and the break determining section 36 except the break judgment apparatus 2, the configuration of the components of the fracture determination apparatus 1 of the same reference numerals are attached and so functions and identical, a detailed description thereof will be omitted.
[0071]
　(Second fracture determination process by breaking determination device according to the embodiment)
　FIG. 9 is a flow chart of determining fracture determination process whether or not each broken element of the fracture judgment apparatus 2 collides modified simulated HAZ portions is there. Break determination process shown in FIG. 9, in advance based on the program stored in the storage unit 12, are executed in cooperation with the elements of the fracture judgment apparatus 2 mainly by the processor 30.
[0072]
　Processing of S501 ~ S505 is the same as the processing of S101 ~ S105, and a detailed description thereof will be omitted. HAZ forming limit stress producing unit 34 changes the reference forming limit value generated by the processing in S505 to generate heat affected zone forming limit stress (S506).
[0073]
　Then, the simulation execution unit 25 uses the finite element method, using the mesh data stored in the storage unit 12, performed by FEM collision deformation simulation when a predetermined collision has occurred (S507). Then, the main strain determination unit 26, each of the maximum principal strain epsilon elements of the HAZ 1 and the minimum principal strain epsilon 2 to determine (S508).
[0074]
　Then, the strain stress converter 35 is outputted determined each element of the HAZ maximum principal strain epsilon in the processing of S508 1 and the minimum principal strain epsilon 2 converts to maximum principal stress and the minimum principal stress (S509 ).
[0075]
　Then, breaking the determination unit 36 ​​based on the respective and maximum principal stress and the minimum principal stress of the transformed elements in the process of S509, and the heat-affected zone forming limit stress generated in the process of S506, the HAZ portion elements each element including a determines whether the fracture (S510). Break determining section 36, when the maximum principal stress and the minimum principal stress does not exceed the heat-affected zone forming limit stress, it is determined that the element is not broken, the maximum principal stress and the minimum principal stress exceeds the heat-affected zone forming limit stress when and determines an element is broken. Processing of S511 ~ S513 is the same as the processing of S109 ~ S 111, and a detailed description thereof will be omitted.
[0076]
　(Modification of the fracture determination device according to the embodiment)
　fracture judgment apparatus 1 and 2, executes the break determination process in collision deformation simulation of the vehicle, breaking determining apparatus according to the embodiment, deformation during press-molding a steel plate in another simulation simulation or the like may execute the break determination process. Further, in the example described, the case element size of the analysis model is uniform has been described as an example, fracture determination device according to embodiments may use the analytical model element size differs depending on the site. That is, element model fracture judgment apparatus used according to the embodiment may include a plurality of element size.
[0077]
　Further, the fracture judgment apparatus 1 and 2, although the bar element is used as a joining element coupling the first steel 401 and the second steel 402, in fracture determination apparatus according to the embodiment, the shell elements, other such solid element the element may be used as a bonding element for bonding a pair of steel.
[0078]
　Further, the fracture judgment apparatus 1 and 2, each of the first shell element 410 and second shell elements 420, have the same element size, the fracture determination apparatus according to the embodiment, the element size element, each element it may be different from one.
[0079]
　Figure 10 is a diagram for explaining a process of S103 when the element size is different. 10 (a) is a diagram for explaining the processing of S201, FIG. 10 (b) is a diagram for explaining the processing of S202, FIG. 10 (c) for explaining the processing of S203 it is a diagram.
[0080]
　As shown in FIG. 10 (a), the first end 531 of the joining element extracted by the joining element extraction unit 221 by the processing in S201 is located at the center of the octagon formed by four shell elements 510. Trapezoidal four shell elements 510 located outside the octagon formed by four shell elements 510, so as to correspond to the HAZ portion is arranged by a designer, not shown.
[0081]
　As shown in FIG. 10 (b), the annular defining portion 222 by the processing in S202, the trapezoidal four shell elements 510 located outside the octagonal ring 540 is formed by four shell elements 510 It is arranged to be included.
[0082]
　Then, as shown in FIG. 10 (c), the shell element 550 to form the HAZ portion by element determination unit 223 is determined by the processing of S202.
[0083]
　(Application Example of the fracture determination device according to the embodiment)
　FIG. 11 is a diagram showing a mold manufacturing system which is an example of application of the fracture determination apparatus according to the embodiment.
[0084]
　Mold manufacturing system 100 includes a fracture judgment apparatus 1, the mold design apparatus 111, and a mold manufacturing apparatus 112. Mold design apparatus 111 is, for example, a device for designing a mold for manufacturing a car body, is an electric machine that is connected through the fracture judgment apparatus 1 and LAN 113. Mold design apparatus 111 uses the fracture determination by breaking determination apparatus 1 generates the mold data indicating the desired mold. In Figure 8, the mold design apparatus 111 is arranged as break determination device 1 and the separate device may be integrated with the fracture determination apparatus 1 in another embodiment.
[0085]
　Mold manufacturing device 112, electric discharge machine (not shown), has a mold manufacturing equipment such as milling and grinding machines, mold design apparatus via the communication network 114 is a wide area communication network by the switch (not shown) 111 It is connected to. Mold manufacturing apparatus 102, based on the mold data transmitted from the die design device 111, for producing a mold corresponding to the die data.
Example
[0086]
　Figure 12 is a diagram showing a hat member 3 point bending test apparatus used for the measurement, a 12 (a) is a side view, FIG. 12 (b) along the A-A'line shown in FIG. 12 (a) it is a cross-sectional view.
[0087]
　Hat member 3 point bending test apparatus 600 includes a hat member 601 is to be tested member, a pressing jig 602, a first support jig 603, and a second support jig 604. Hat member 601 includes a hat panel 611 having a flange portion which is pressed into hat, and a closing plate 612 which is bonded via a spot weld 613 with the flange portion of the hat panel 611. Hat panel 611, and the thickness tensile strength of the material is 1.5 [GPa] is a hot stamp material is 1.6 mm. Closing plate 612, and plate thickness are made tensile strength 440 [MPa] is 1.2 mm. The height of the hat member 60 mm and a width, a 80 mm. A flange portion and a closing plate 612 hat panel 611 in the longitudinal direction 50 mm and a pitch by spot welding, spot welds 613, placed at 50 mm and a pitch in the longitudinal direction of the flange portion of the hat member 601 It is.
[0088]
　Pressing jig 602, the radius is a cylindrical member 150 mm and a hat member 601, and presses the surface of the closing plate 612 facing the hat panel 611. First support jig 603 and the second support jig 604 is placed 300 mm and spaced apart from, supports the hat member 601 at the rear surface of the closing plate 612.
[0089]
　Figure 13 is a diagram showing a FEM simulation conditions in the vicinity of the spot welding Examples and Comparative Examples.
[0090]
　In Example 1, the mesh shape is webbed, the definition of the HAZ is defined material properties after extracting elements corresponding to the HAZ by the present invention. Average element size of the HAZ is 1.1 mm and forming limit line is by prediction equation of the present invention.
[0091]
　In Example 2, the mesh shape is lattice-like, the definition of the HAZ is defined material properties after extracting elements corresponding to the HAZ by the present invention. Average element size of the HAZ portion is 1.3 mm and forming limit line is by prediction equation of the present invention.
[0092]
　In Comparative Example 1, the mesh shape is webbed, HAZ portion is not defined, forming limit line is by prediction equation of the present invention.
[0093]
　In Comparative Example 2, the mesh shape is webbed, the definition of the HAZ is defined material properties after extracting elements corresponding to the HAZ by the present invention. Average element size of the HAZ is 1.1 mm and forming limit line is by the theoretical equation of the conventional Storen-Rice.
[0094]
　In Examples 1 and 2 and Comparative Examples 1 and 2, Swift coefficient of the base material portion of the hat member 601, K = 2000 [MPa], n = 0.05, epsilon 0 is == 0.0001. Meanwhile, Swift coefficient of the HAZ of the hat member 601, K = 1400 [MPa], n = 0.04, epsilon 0 is == 0.0002.
[0095]
　Figure 14 is a diagram showing a comparison between the experimental results and the FEM simulation of Example 1 and 2 result by real. 14 (a) is a diagram showing the hat member after real experiment, and FIG. 14 (b) is a diagram showing the FEM simulation results of Example 1, FEM simulation of FIG. 14 (c) Example 2 It shows the results, FIG. 14 (d) is a diagram showing the relationship between the pressing distance that the depression reaction force of the pressing jig 602. In FIG. 14 (d), the horizontal axis represents the depressed distance of the pressing member 602, i.e., it indicates the stroke [mm], the vertical axis represents the reaction force generated in the pressing jig, i.e. the load [kN].
[0096]
　As shown by the arrows A and B in FIG. 14 (a), the Experimental results by the real breaking occurs in two HAZ portion. Further, as shown by the arrows C and D in FIG. 14 (b), the Example 1, breaking the same two HAZ portion and experimental results of real occurred. Further, as indicated by arrows E and F in FIG. 14 (c), the Example 2, the fracture in the same two HAZ portion and experimental results of real occurred. Further, as shown in FIG. 14 (d), in experiments, the load immediately after the rupture occurs has been found to decrease slightly, the timing of rupture occurs in Examples 1 and 2, break in experiments with real There is substantially the same as the timing for generating and slightly load immediately after the fracture occurred was also reproduced the phenomenon to be reduced.
[0097]
　Examples 1 and 2 were able to accurately predict the fracture position and breaking generation timing of the HAZ portion generated in experiments with real. Further, as a method of mesh cutting around the spot welding, Example 1 was cut into web-like, and in any of the second embodiment cut in a grid pattern, it was confirmed that it was possible accurately predict the experimental results.
[0098]
　Figure 15 is a diagram showing a comparison between Comparative Example 1 and 2 of FEM simulation and experimental results by real. 15 (a) is a diagram showing the hat member after real experiment, and FIG. 15 (b) is a diagram showing the FEM simulation results of Comparative Example 1, FEM simulation shown in FIG. 15 (c) Comparative Example 2 It shows the results, Figure 15 (d) is a diagram showing the relationship between the pressing distance that the depression reaction force of the pressing member 602. The view shown in FIG. 15 (a) is identical to the diagram shown in FIG. 14 (a). In FIG. 15 (d), the horizontal axis represents the depressed distance of the pressing member 602, i.e., it indicates the stroke [mm], the vertical axis represents the reaction force generated in pressing jig that is, shows a load [kN].
[0099]
　As shown by the arrows A and B in FIG. 15 (a), the Experimental results by the real breaking occurs in two HAZ portion. Further, as shown in FIG. 15 (b), in Comparative Example 1, in the range of pressed distance in experiments with actual machine, rupture did not occur. Further, as shown by arrow C ~ F in FIG. 15 (c), the Comparative Example 2, breaking the four HAZ portion is greater than the experimental result by the actual generated. Further, as shown in FIG. 15 (d), Comparative Example 1, since the fracture does not occur, the load increases with increasing pressing distance (stroke). Meanwhile, the timing of rupture is generated in Comparative Example 2 is earlier than the timing at which rupture occurs in experiments with real. In Comparative Example 2, the decrease of the load after fracture is greater than the decrease in load after fracture in experiments with real.
[0100]
　In Comparative Example 1, since the definitions of extraction and material properties of the HAZ portion is not performed, it is impossible to predict the fracture from the HAZ generated in experiments, it is quite fracture does not occur a result, excessive compared with the experiment It was the result to generate a load. In Comparative Example 2, although the characteristics of the HAZ and can be defined, because it uses the limit line by the theoretical equation of the conventional Storen-Rice, results in predicting excessive breakage compared to experiment, fracture occurs the number is doubled, was the result of the experiment and compared a significant load decrease occurs.

The scope of the claims
[Requested item 1]
　Material properties and thickness of the steel having a heat affected zone, and forming an input information element indicating an element size in the analysis model used for deformation simulation of the steel according to the finite element method, in the reference element size is an element size as a reference a storage unit for storing the reference forming limit value information indicating a reference forming limit value as a limit value, a,
　and element extraction unit for extracting the elements contained in the heat-affected zone formed around the spot weld of the steel ,
　based on the reference forming limit value information, the reference forming limit value generation section that generates the reference forming limit value according to the material properties and thickness of the heat affected zone,
　using said tensile strength of said steel change the reference forming limit value, and the heat-affected zone forming limit value generation unit predicts the forming limits in the element size of the elements included in the heat-affected zone to generate heat affected zone forming limit value
　Run the deformation simulation using the input information, a simulation executing unit to output the deformation information including each strain of elements included in the heat affected zone,
　of each element included in the heat affected zone principal strain determination unit that determines the maximum principal strain and minimum principal strains and,
　the respective maximum main strain and minimum principal strains of principal strain is determined elements, the heat affected zone which is defined by the heat-affected zone forming limit value based on the forming limit line, each element in the analysis model, a break determining section determines whether or not to break
　fracture judgment apparatus characterized in that it comprises a.
[Requested item 2]
　The element extracting section,
　and the joining element extraction unit for extracting the contact elements defining a joining of two steel
　defining an annular centering point contact between the elements forming the steel and the joining element an annular defining portion,
　the element containing at least a portion the circular ring, and determining element determination unit elements forming the heat-affected zone
　having a fracture determination apparatus according to claim 1.
[Requested item 3]
　The reference forming limit value generator
　and the neighbor information acquiring unit for acquiring material properties and thickness of the element adjacent to the contact point between the elements forming the steel and the joining element,
　obtained by the neighbor information acquiring unit a material characteristic estimating unit for estimating the material properties of the heat affected zone of the material characteristics,
　the material characteristic estimating section estimating material properties and the said reference corresponding to the thickness obtained by the neighbor information acquiring unit forming limit value by a forming limit value generation unit for generating a
　having a break determination device according to claim 2.
[Requested item 4]
　HAZ forming limit value generation unit,
　and the element size determining unit that determines the element size of the elements included in the heat-affected zone,
　using a tensile strength of the element size and the steel, the determined element size the reference forming limit value to change the forming limit value changing unit, in response to
　having the fracture determination apparatus according to any one of claims 1 to 3.
[Requested item 5]
　The element size determining unit
　and the respective element size extracting unit that extracts an element size of elements in the heat affected zone,
　from each of the extracted element size, element size of elements in the heat affected zone the element size calculator for calculating a
　having a fracture determination apparatus according to claim 4.
[Requested item 6]
　The deformation simulation is collision deformation simulation of the vehicle formed by the steel, fracture determination apparatus according to any one of claims 1 to 5.
[Requested item 7]
　The object forming limit value generation unit uses the element size and shaped limits prediction expression which is a function of the tensile strength of the steel material to produce the target forming limit value,
　the forming limit value prediction equation, [rho is a strain ratio, M is an element size indicating the element size indicating the size of the elements of the analysis model used in the simulation by FEM, epsilon 1 is the maximum principal strain in the element size M, epsilon 2 is in element size M when the minimum is the predominant strain, the first coefficient k1 and the second coefficient k2
[number 1]

is represented by the first coefficient k1 is the tensile strength TS as well as the material of the steel sheet, the coefficient γ and [delta]
[Equation 2]

in indicated, the second coefficient k2, the maximum principal strain ε in the reference element size 1B and from the coefficient eta
[number 3]

represented by the fracture judgment apparatus according to claim 1.
[Requested item 8]
　Extract the elements included in the heat-affected zone formed around the spot weld of the steel,
　the reference forming limit value information indicating a reference molding limits the forming limit value in the reference element size is an element size as a reference based on, to generate the reference forming limit value according to the material properties and thickness of the heat-affected zone,
　using a tensile strength of the element size and the steel to change the reference forming limit value, the heat affected predicting a molding limits on element size of elements in the section generates a heat affected portion forming limit value,
　the input information for the deformation simulation of the steel according to the finite element method comprising material properties and thickness of the steel run the deformation simulation using outputs modification information including each strain of elements included in the heat affected zone,
　each of the top of the elements included in the heat affected zone Determine the principal strain and minimum principal strains,
　based the respective maximum main strain and minimum principal strains of principal strain is determined elements, in the heat-affected zone forming limit line which is defined by the heat affected zone forming limit value Te, each element in the analysis model for determining whether to break
　fracture determination method, characterized in that it comprises.
[Requested item 9]
　Extract the elements included in the heat-affected zone formed around the spot weld of the steel,
　the reference forming limit value information indicating a reference molding limits the forming limit value in the reference element size is an element size as a reference based on, to generate the reference forming limit value according to the material properties and thickness of the heat-affected zone,
　using a tensile strength of the element size and the steel to change the reference forming limit value, the heat affected predicting a molding limits on element size of elements in the section generates a heat affected portion forming limit value,
　the input information for the deformation simulation of the steel according to the finite element method comprising material properties and thickness of the steel run the deformation simulation using outputs modification information including each strain of elements included in the heat affected zone,
　each of the top of the elements included in the heat affected zone Determine the principal strain and minimum principal strains,
　based the respective maximum main strain and minimum principal strains of principal strain is determined elements, in the heat-affected zone forming limit line which is defined by the heat affected zone forming limit value Te, it is determined whether each element in the analysis model is broken,
　the fracture criterion program characterized by executing the process to the computer.