JP2008155227A - Method and device for fatigue design of member excellent in fatigue durability, computer program and computer readable recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce hydroforming conditions which are optimum to take the variation of thickness and strain into consideration which are generated during forming and to satisfy a desired fatigue life. <P>SOLUTION: The hydroforming conditions are determined by performing repeated calculation of a prescribed number of times of the following step by changing at least one or more among the internal pressure, the amount of shaft pushing and the coefficient of friction of the hydroforming conditions, the step being, after performing hydroforming analysis on the basis of internal pressure, the amount of shaft pushing, the coefficient of friction, etc. as hydroforming conditions, calculating the thickness distribution of formed goods and strain distribution after forming and setting up members on the basis of the formed goods on a computer, the fatigue life of members is calculated by performing elastic analysis on the basis of the thickness distribution, the shapes of the members and fatigue load as the elastic analysis conditions, the stress distribution after forming, the stress distribution after elastic deformation of the members and strain distribution after the elastic deformation are calculated and by performing fatigue analysis on the basis of the strain distribution after forming, stress distribution after the elastic deformation and the fatigue load as fatigue analysis conditions, to calculate the fatigue life of the member. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention predicts and calculates the fatigue life for repeated loads that occur when a vehicle is running in a vehicle, such as exhaust system parts, suspension system parts, body system parts, etc. The present invention relates to a fatigue design method, an apparatus, a computer program, and a computer-readable recording medium for designing an optimum hydroforming molding condition that gives a maximum value or a target fatigue life.

  In the development of vehicles such as automobiles, in order to respond to the problems of weight reduction, development time reduction, and reduction of prototype vehicles, in recent years, prediction of each performance by numerical analysis using a computer is frequently performed at the design site. Regarding the evaluation of vehicle fatigue strength, there is an increasing need for the development of a method that can easily and accurately predict the fatigue life of parts, members, and structures used in a vehicle for limit design.

  Conventionally, static stress analysis under a predetermined fatigue load condition by a finite element method has been widely used in this field. When estimating the fatigue life using the analysis results, first, after determining the initial shape, obtain fatigue test data (SN diagram, EN diagram) of materials and joints used in advance. In addition, the life expectancy is predicted by comparing the diagram with the stress analysis value or strain analysis value, and the member shape, material, joining method, etc. are changed so that the calculated fatigue life becomes the target value. ing.

  After the evaluation by analysis achieves the target value, verification is made by trial manufacture and experiment to determine the design specification. These members are manufactured by plastic working thin plates, pipes or bars of steel or other materials and joining them as necessary. For the plastic working, a forming method such as pressing, hydroforming or extrusion is used. For joining, methods such as spot welding, arc welding, laser welding or rivet joining are used. Recently, fatigue analysis software that automatically refers to the stress calculation result file obtained by the finite element method and the fatigue test data of the materials and joints used in the member in advance and calculates the life of each part is commercially available. .

  Among plastic processing, hydroforming molding technology is attracting particular attention in the automobile field as one of means for reducing costs and weight by reducing the number of parts, and the number of parts applied to actual vehicles is increasing year by year.

  FIG. 8 is a view for explaining general hydroforming. Moreover, FIG. 9 is a figure which shows the process path | route in hydroforming. In the hydroform forming method, a metal pipe 1 that is a metal pipe is placed in a mold 2, the mold 2 is clamped, and then the inner pressure and the pushing force in the pipe axis direction (in this specification, the pipe axis direction) This is a method of forming a predetermined shape by applying an indentation force (referred to as “shaft pushing amount”). In hydroforming, the shape and quality are determined by the combination of the internal pressure and the amount of axial push. Examples of processing failures include bursts that cause the tube to rupture during molding, as well as formation of wrinkles and predetermined corners R. There are things that cannot be done.

  When metals such as steel are used, it is known that changes in sheet thickness and plastic strain occur due to the forming process during member forming, and these plate thickness changes and plastic strain greatly affect the fatigue strength of the member. ing. The conventional fatigue life prediction method does not take into account the effects during molding, and the member fatigue design optimization algorithm for obtaining molding conditions that satisfy the target fatigue life is not applied. Moreover, the fact is that the fatigue design of members cannot be performed quickly.

  In Patent Document 1, in a method for analyzing the fatigue strength of a welded structure composed of a plurality of members, a direction parallel to the weld line with respect to the position of the weld line based on the shape of the two welded members and the welding method. The fatigue strength diagram for the weld and the fatigue strength diagram for the direction perpendicular to the weld line are selected, respectively, and the stress in the direction perpendicular to and parallel to the weld line is obtained from the stress analysis result of the welded structure. A fatigue strength analysis method for a welded structure is disclosed in which the fatigue strength is evaluated by comparing each with the fatigue strength diagram.

  However, the method disclosed in Patent Document 1 does not take into account the strain applied at the time of molding the member, the thickness distribution after molding, and the optimization algorithm is not applied. There is a problem that life cannot be predicted.

  Further, in Patent Document 2, the stress concentration rate corresponding to the welded shape (finishing process) of the welded portion is grasped by experiments in advance for each joint type, along with fatigue life estimation data (SN diagram) of the front structure, The stress in the weld is calculated by FEM analysis, and the peak stress at the bead toe is calculated by multiplying this stress value by the stress concentration rate corresponding to the weld shape. Therefore, a fatigue life evaluation system that estimates the fatigue life according to the weld shape is disclosed.

  In Patent Document 3, a finite element method analysis shell model is created for a spot welded structure combining flat plates, and a finite element method linear elastic analysis is performed using the created finite element method analysis shell model. Calculate the shared load of the nugget part at the center of the spot welded part, the deflection on the circumference of the diameter D drawn around the nugget part and the inclination in the radial direction, the calculated shared load, the deflection on the circumference and the radiation A method is disclosed in which the nominal structural stress in the nugget portion is obtained based on the inclination of the direction using the elastic disk bending theory, and the fatigue life of the spot welded structure is predicted from the nominal structural stress.

  However, the methods disclosed in Patent Document 2 and Patent Document 3 do not take into account the strain applied at the time of molding the member, the plate thickness distribution after molding, and the optimization algorithm is not applied. Thus, there is a problem that the molding process conditions satisfying the fatigue life cannot be obtained, and the fatigue design of the member cannot be performed accurately and quickly.

  Further, in Patent Document 4, in order to design steel products such as automobile parts using a computer, a step of storing material parameters to be used in advance and at least a material standard, plate thickness, and shape of the steel product are stored. A step of evaluating the formability, rigidity, and strength of the steel product, and if not satisfying at least one of the required specifications of the formability, rigidity, and strength, A design method and a design system including a step of correcting at least one of thickness and shape and a step of reevaluating the formability, rigidity, and strength are disclosed. That is, in the method disclosed in Patent Document 4, after evaluating the formability of a steel product by forming CAE (Computer Aided Engineering), rigidity CAE and strength CAE are individually performed until the required specifications regarding rigidity and strength are satisfied. The material standard, plate thickness, and shape of the steel product are corrected.

  However, in the method disclosed in Patent Document 4, there is a description of a step of re-evaluating by changing the molding conditions when a defect such as a crack occurs in the molding CAE, but the final required characteristics (rigidity, strength) There is no description about a method for presenting the optimum molding process conditions satisfying the above.

JP 2001-116664 A JP 2003-149091 A JP 2003-149130 A JP 2002-297670 A

  The present invention has been made in view of the above points, and takes into account changes in plate thickness and distortion that occur during molding, which greatly affect the fatigue strength of members, parts, and structures, and provides desired fatigue. The objective is to be able to present the optimum hydroforming process conditions to satisfy the service life.

In order to solve this problem, the gist of the present invention is as follows.
(1). Computer based on hydroform molding conditions based on material shape before processing, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness Hydroform molding analysis is performed to calculate the thickness distribution and post-molding strain distribution of the molded product, and after assembling the members based on the molded product on the computer, the plate thickness distribution, member shape, and The computer performs elastic analysis based on the fatigue load, calculates the post-elastic deformation stress distribution and post-elastic deformation distribution of the member, and the post-molding strain distribution, post-elastic deformation stress distribution and post-elastic deformation strain as fatigue analysis conditions. The computer performs a fatigue analysis based on the distribution and the fatigue load, and calculates the fatigue life of the member. Excellent fatigue durability, characterized in that, by changing at least one of the friction coefficients, a computer repeatedly calculates a predetermined number of times to obtain hydroforming molding conditions that give the maximum fatigue life or the target fatigue life Fatigue design method for members.
(2). Hydroform that inputs material shape before molding, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness as hydroform molding conditions Molding condition input means;
Hydroform molding analysis means for performing hydroform molding analysis based on the hydroform molding conditions input to the hydroform molding condition input means, and calculating a plate thickness distribution and a post-molding strain distribution of the molded product;
Elastic analysis condition input means for inputting the plate thickness distribution, member shape, and fatigue load calculated by the hydroform molding analysis means,
An elastic analysis means for performing an elastic analysis based on the elastic analysis conditions input to the elastic analysis condition input means, and calculating a post-elastic deformation stress distribution and a post-elastic deformation strain distribution of the member;
Fatigue analysis condition input means for inputting the post-molding strain distribution calculated by the hydroform molding analysis means, the post-elastic deformation stress distribution and post-elastic deformation strain distribution of the member calculated by the elastic analysis means, and a fatigue load;
Fatigue analysis means for performing fatigue analysis based on the fatigue analysis conditions input to the fatigue analysis condition input means, and calculating a fatigue life of the member;
Iterative calculation control for automatically executing a predetermined number of calculations from the hydroform molding condition input means to the fatigue analysis means by changing at least one of the internal pressure, axial push amount, and friction coefficient of the hydroform molding conditions Means,
An apparatus for designing a fatigue of a member having excellent fatigue durability, comprising: an optimum molding condition output means for outputting a hydroforming molding condition that gives a maximum fatigue life or a target fatigue life.
(3). Based on material shape, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness input as hydroform molding conditions Hydroform molding analysis means for calculating the thickness distribution and post-molding strain distribution of the molded product,
Elasticity analysis is performed based on the plate thickness distribution, member shape, and fatigue load calculated by the hydroform molding analysis means as the elastic analysis condition, and the elasticity distribution for calculating the stress distribution after elastic deformation and the strain distribution after elastic deformation of the member is calculated. Analysis means;
As fatigue analysis conditions, fatigue analysis is performed based on the strain distribution after molding calculated by the hydroforming molding analysis means, the stress distribution after elastic deformation and the strain distribution after elastic deformation of the member calculated by the elastic analysis means, and the fatigue load. And a fatigue analysis means for calculating a fatigue life of the member,
Iterative calculation control for automatically executing a predetermined number of calculations from the hydroform molding condition input means to the fatigue analysis means by changing at least one of the internal pressure, axial push amount, and friction coefficient of the hydroform molding conditions Means,
An apparatus for designing a fatigue of a member having excellent fatigue durability, comprising: an optimum molding condition output means for outputting a hydroforming molding condition that gives a maximum fatigue life or a target fatigue life.
(4). A computer program that causes a computer to function as each means of the fatigue design apparatus according to (2) or (3).
(5). A computer-readable recording medium on which the computer program according to (4) is recorded.
In the present invention, the design parameter is hydroforming molding conditions, and is at least one of internal pressure, axial push amount, and friction coefficient.
In the present invention, the “molded product” refers to an intermediate product after molding, and an assembly of the “molded product” is defined as a “member”, that is, a final product.

  According to the present invention, the hydroforming molding conditions for setting the fatigue life under a fatigue load condition in accordance with the actual use environment of the member to a desired value while taking into account the plastic strain and the change in the plate thickness that occur during molding. It is possible to obtain an optimum member accurately and quickly.

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a flowchart for explaining a fatigue design method to which the present invention is applied.
First, the hydroform molding conditions are: material shape before processing, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness. Input data 101 is set, and hydroforming molding analysis 102 is performed using this as input data.

  Next, the computer performs hydroform molding analysis 102 based on the hydroform molding conditions 101, calculates the thickness distribution and post-molding strain distribution of the molded product, and outputs the result as output data 103 of the hydroform molding analysis.

  Next, the plate thickness distribution in the hydroform molding analysis output data 103, the member shape assembled based on the molded product, and the fatigue load are set as the elastic analysis condition input data 104, and the computer is based on the condition 104. The elastic analysis 105 of the member is performed, the stress distribution after elastic deformation and the strain distribution after elastic deformation of the member are calculated, and output as elastic analysis output data 106.

  Next, the post-molding strain distribution in the hydroform molding analysis output data 103, the post-elastic deformation stress distribution and the post-elastic strain distribution in the elastic analysis output data 106, and the fatigue load are set as fatigue analysis condition input data 107. Then, the computer performs fatigue analysis 108 based on the condition 107, calculates the fatigue life of the member, and outputs it as fatigue analysis output data 109. Then, an evaluation step 110 is performed to determine whether the fatigue life satisfies the target fatigue life or is the maximum value.

  Next, when the fatigue life of the member does not reach a desired value, at least one of the internal pressure, the shaft pressing amount, and the friction coefficient of the hydroform molding condition 101 is changed, and the computer again performs the above 101 to 109. The above process is repeated a predetermined number of times for calculation.

  Next, the steps from 101 to 109 are repeated, and the flow is terminated when the fatigue life of the member reaches a desired value. Thereby, the optimum hydroforming molding condition 111 that gives the maximum fatigue life or the target fatigue life can be obtained.

  For hydroforming molding analysis, static elasticity analysis, and fatigue (lifetime) analysis, an analysis program such as a commercially available finite element method or a self-made program may be used. As a program for hydroforming molding analysis, there are commercially available solvers such as PAM-STAMP, LS-DYNA, and ABAQUS using the finite element method. In addition, there are commercially available solvers that use finite element methods such as NASTRAN, MARC, and ABAQUS for elastic analysis programs. In addition, there are commercially available software such as MSC.Fatigue, FEMFAT, and FE-Fatigue for fatigue analysis programs.

  In addition, a commercially available program or a self-made program may be used to transfer data from the hydroform molding analysis result to fatigue analysis and to change analysis conditions. Commercial optimization software such as iSIGHT, OPTIMUS, and AMDESS is available as an optimization tool that automatically changes analysis conditions and performs iterative calculations to obtain optimal results. Can be automated.

  Note that the input data 101, 104, and 107 may be input from an external input unit each time, or may be automatically captured in a program.

  In FIG. 2, the example of the member which assembled the hydrofoam molded article is shown. The member (hydroform molded member) assembled with the hydroform of this example is obtained by welding a metal tube 4 to a hydroform molded product 3 expanded in a rectangular cross section, and welded portions 5 on both sides of the hydroform molded product 3. Have

  FIG. 3 shows an example of hydroform molding analysis executed by the hydroform molding analysis program 102. A finite element mesh model is created from the shape data of the base tube 1 and the mold 2 which is a tool, and a molding analysis is performed based on hydroforming molding conditions. Obtain the strain distribution after molding.

  Using the molded product in which the plate thickness distribution and the post-molding strain distribution of the molded product obtained by the hydroform molding analysis are mapped, the components are assembled on a computer. Data on the shape and plate thickness distribution of the assembled member is added with data on predetermined restraint conditions and load conditions, and an elastic analysis is performed by the elastic analysis program 105 to obtain a stress distribution after elastic deformation and a strain distribution after elastic deformation of the member. Ask.

  Next, an example of the fatigue life calculation taking into account the post-molding strain distribution performed in the fatigue analysis program 108 is shown. The post-molding strain distribution obtained by the hydroforming molding analysis is set as a pre-strain distribution of the member, and based on the value, the reference SN diagram and EN diagram are selected for fatigue life calculation. Here, the EN diagram indicates a fatigue life diagram showing the relationship between the strain value and the number of repetitions. For the SN diagram and EN diagram, commercially available data or data of known literature may be used, or data created by conducting a fatigue test in advance using a steel material equivalent to the steel material used for the design may be used. It is known that a pre-strained metal material generally has an increased fatigue strength in a high cycle region.

  Fig. 4 is an SN diagram showing the effect of pre-strain on a certain steel material. Prepare a molded product with a predetermined strain applied in advance by hydroforming, cut out a fatigue test piece from the molded product, and conduct a fatigue test. This figure can be obtained. For example, in the figure, when a stress of 300 MPa is generated at a node position due to a 30% pre-strain at a node position in the finite element mesh model of the member and a fatigue load is applied. As indicated by the dotted line arrow, an SN line with a pre-strain of 30% is selected, and the predicted fatigue life (number of repetitions) at that node can be calculated as 630,000 times. By the same calculation method, the fatigue life is calculated at all nodes of the finite element mesh model of the member, and the smallest value among the calculated results is the predicted fatigue life of the member.

  This completes the description of the method or apparatus to which the present invention is applied. FIG. 5 is a diagram showing a configuration example of a computer system that can function as the fatigue design apparatus of the present invention. In the figure, reference numeral 1200 denotes a computer PC. The PC 1200 includes a CPU 1201, executes device control software recorded in the ROM 1202 or the hard disk (HD) 1211 or supplied from the flexible disk drive (FD) 1212, and collects all devices connected to the system bus 1204. To control. Each functional unit of the present invention is realized by a program recorded in the CPU 1201, the ROM 1202, or the hard disk (HD) 1211 of the PC 1200.

  Reference numeral 1203 denotes a RAM which functions as a main memory, work area, and the like for the CPU 1201. Reference numeral 1205 denotes a keyboard controller (KBC), which controls to input a signal input from the keyboard (KB) 1209 into the system main body. Reference numeral 1206 denotes a display controller (CRTC) which performs display control on the display device (CRT) 1210. A disk controller (DKC) 1207 is a hard disk that records a boot program (startup program: a program for starting execution (operation) of hardware and software of a personal computer), a plurality of applications, editing files, user files, a network management program, and the like. Controls access to the (HD) 1211 and the flexible disk (FD) 1212. Reference numeral 1208 denotes a network interface card (NIC) that performs bidirectional data exchange with a network printer, another network device, or another PC via the LAN 1220.

  The fatigue design device of the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device.

  Another object of the present invention is to supply a recording medium in which a program code of software realizing the functions of the above-described embodiments is recorded to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus stores the recording medium in the recording medium. Needless to say, this can also be achieved by reading and executing the programmed program code. In this case, the program code itself read from the recording medium realizes the functions of the above-described embodiments, and the recording medium on which the program code is recorded constitutes the present invention. As a recording medium for supplying the program code, for example, a flexible disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like can be used.

  As mentioned above, although this invention was demonstrated with various embodiment, this invention is not limited only to these embodiment, A change etc. are possible within the scope of the present invention.

(Example)
Examples of the present invention are shown below.
1. Design object As an embodiment of the present invention, as shown in FIG. 6, a member (hydroform molded member) in which a metal tube 4 is welded to both ends of a hydroformed molded product 3 having a central portion expanded into a rectangular cross section by hydroforming. Design the optimum hydroforming molding conditions. The hydroforming molded member is supported by the end plate 6 for fixing the pipe end. The fatigue load is repeatedly applied to the center of the rectangular cross section by the load-loading jig 7, and the fatigue life (number of repetitions) is maximized. As an appropriate molding condition, the internal pressure is obtained. The repeated fatigue load is a complete double swing load of 20 kN.

  The hydroforming molded member has a total length of 640 mm, a central rectangular section height of 95 mm, a rectangular sectional section width of 63 mm, a rectangular section length of 200 mm, and a horizontal length (one side) of the transition section from the rectangular section to the metal tube 4 of 80 mm. It is. The outer diameter of the metal tube 4 welded to both ends is 63.5 mm, the wall thickness is 2.3 mm, and the length is 140 mm. About the tool shape, the shape dimension of the punch die and the die mold was set from the shape dimension of the hydroform molded member. The material shape before processing used for hydroforming, that is, the shape of the raw tube, is 63.5 mm in outer diameter, 2.3 mm in wall thickness, and 400 mm in length.

Hydroform molding conditions are: axial push amount 30 mm, initial hydrofoam internal pressure 20 MPa, friction coefficient 0.14, material tensile strength 470 MPa, material yield strength 400 MPa, and stress-strain relationship is a value calculated by the following equation. . Here, σ is the true stress and ε is the true strain.
σ = 750 × (ε + 0.0006) ^0.17

2. Hydroform Molding Analysis Enter the above hydroform molding conditions and perform molding analysis of Hydroform Molded Product 3 using the commercially available finite element method program LS-DYNA to determine the shape, thickness distribution, and molding of the molded product. Post-strain distribution was calculated.

3. Elastic analysis After the hydroform molded product 3 and metal pipes 4 welded to both ends are attached on a computer and assembled as a hydroform molded member, the plate thickness distribution of the hydroform molded product 3, the member shape, and Based on the fatigue load of 20 kN, an elastic analysis was performed using a commercially available finite element method program NASTRAN, and the post-elastic deformation stress distribution and post-elastic deformation strain distribution of the member were calculated.

4). Fatigue analysis As fatigue analysis conditions, strain distribution after molding of hydroformed molded product 3 calculated by hydroforming molding analysis, stress distribution after elastic deformation and strain distribution after elastic deformation of hydroformed molded member calculated by elastic analysis, and fatigue load Based on 20 kN, the fatigue life (number of repetitions) of the hat-shaped cross-section member under a torsional fatigue load was calculated using a commercially available fatigue analysis program FE-Fatigue. In addition, about the fatigue strength data (SN diagram) of the material used for the member, the SN diagram shown in FIG. 4 was used.

5. Change of hydroforming molding conditions For the optimization tool, the commercially available program iSIGHT was used, the internal pressure of hydroforming molding conditions was changed in the range of 20-80 MPa, and the steps from 101 to 110 in FIG. Repeated calculations were performed to find the optimal hydroforming conditions that maximize the fatigue life.

6). Results Regarding the relationship between the fatigue life and the hydrofoam internal pressure, if the internal pressure is too small, the cross-sectional shape of the central portion is small and sufficient cross-sectional rigidity cannot be obtained, resulting in a decrease in fatigue life. On the other hand, when the internal pressure is excessive, the plate thickness decrease in the central part of the member increases, and the local stress increases, so that the fatigue life tends to decrease. Furthermore, if the internal pressure is increased, bursts may occur during hydroforming molding, and molding may not be possible.

  FIG. 7 shows a representative example of the stress distribution after elastic analysis of the member. At a relatively low internal pressure, a sufficient rectangular cross section is not formed and the cross section rigidity is low, so that the generated stress is high (see FIG. 7A). When the internal pressure is gradually increased, a rectangular cross section starts to be formed, the cross section rigidity is improved, and the generated stress is reduced (see FIG. 7B). When the internal pressure is further increased, the generated stress increases again due to the reduction of the plate thickness due to the pipe expansion (see FIG. 7C).

  As a result of iterative calculation according to the fatigue design method of the present invention and searching for the optimum hydroform molding conditions, it was found that the internal pressure was 55 MPa and the maximum fatigue life (number of repetitions) was 1.5 million. A member is manufactured based on a molded product that has been subjected to hydroform molding under these conditions, using a hydraulic servo type fatigue tester with a repeated fatigue load of 20 kN with a full swing load and a repetition frequency of 3 Hz, with a maximum load of 100 kN. When a fatigue test was performed, the occurrence of initial cracks was confirmed at the corners of the rectangular cross section at the center when the number of repetitions reached 2 million times, and a fatigue life exceeding the target was obtained.

It is a flowchart for demonstrating the fatigue design method to which this invention is applied. It is a figure which shows the example of the member which assembled the hydroform molded article. It is a figure which shows an example of a hydroform shaping | molding analysis. It is a SN diagram which shows the influence of the pre-strain of a certain steel material. It is a figure which shows the structural example of the computer system which can function as a fatigue design apparatus of this invention. It is a figure which shows the hydrofoam shaping | molding member in an Example. It is a figure which shows the example of the stress distribution after the elastic analysis of the member in an Example. It is a figure for demonstrating hydroform molding. It is a characteristic view which shows the relationship between the amount of axial pushing and internal pressure in hydroforming molding.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base pipe 2 Mold 3 Hydroform molded article 4 Metal pipe 5 Welded part 6 Fixing end plate 7 Load loading jig

Claims (5)

  Computer based on hydroform molding conditions based on material shape before processing, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness Hydroform molding analysis is performed to calculate the thickness distribution and post-molding strain distribution of the molded product, and after assembling the members based on the molded product on the computer, the plate thickness distribution, member shape, and The computer performs elastic analysis based on the fatigue load, calculates the post-elastic deformation stress distribution and post-elastic deformation distribution of the member, and the post-molding strain distribution, post-elastic deformation stress distribution and post-elastic deformation strain as fatigue analysis conditions. The computer performs a fatigue analysis based on the distribution and the fatigue load, and calculates the fatigue life of the member. Excellent fatigue durability, characterized in that, by changing at least one of the friction coefficients, a computer repeatedly calculates a predetermined number of times to obtain hydroforming molding conditions that give the maximum fatigue life or the target fatigue life Fatigue design method for members. Hydroform that inputs material shape before molding, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness as hydroform molding conditions Molding condition input means;
Hydroform molding analysis means for performing hydroform molding analysis based on the hydroform molding conditions input to the hydroform molding condition input means, and calculating a plate thickness distribution and a post-molding strain distribution of the molded product;
Elastic analysis condition input means for inputting the plate thickness distribution, member shape, and fatigue load calculated by the hydroform molding analysis means,
An elastic analysis means for performing an elastic analysis based on the elastic analysis conditions input to the elastic analysis condition input means, and calculating a post-elastic deformation stress distribution and a post-elastic deformation strain distribution of the member;
Fatigue analysis condition input means for inputting the post-molding strain distribution calculated by the hydroform molding analysis means, the post-elastic deformation stress distribution and post-elastic deformation strain distribution of the member calculated by the elastic analysis means, and a fatigue load;
Fatigue analysis means for performing fatigue analysis based on the fatigue analysis conditions input to the fatigue analysis condition input means, and calculating a fatigue life of the member;
Iterative calculation control for automatically executing a predetermined number of calculations from the hydroform molding condition input means to the fatigue analysis means by changing at least one of the internal pressure, axial push amount, and friction coefficient of the hydroform molding conditions Means,
An apparatus for designing a fatigue of a member having excellent fatigue durability, comprising: an optimum molding condition output means for outputting a hydroforming molding condition that gives a maximum fatigue life or a target fatigue life. Based on material shape, shape of molded product, tool shape, internal pressure, axial push amount, friction coefficient, material tensile strength, yield strength, stress-strain relationship, and plate thickness input as hydroform molding conditions Hydroform molding analysis means for calculating the thickness distribution and post-molding strain distribution of the molded product,
Elasticity analysis is performed based on the plate thickness distribution, member shape, and fatigue load calculated by the hydroform molding analysis means as the elastic analysis condition, and the elasticity distribution for calculating the stress distribution after elastic deformation and the strain distribution after elastic deformation of the member is calculated. Analysis means;
As fatigue analysis conditions, fatigue analysis is performed based on the strain distribution after molding calculated by the hydroforming molding analysis means, the stress distribution after elastic deformation and the strain distribution after elastic deformation of the member calculated by the elastic analysis means, and the fatigue load. And a fatigue analysis means for calculating a fatigue life of the member,
Iterative calculation control for automatically executing a predetermined number of calculations from the hydroform molding condition input means to the fatigue analysis means by changing at least one of the internal pressure, axial push amount, and friction coefficient of the hydroform molding conditions Means,
An apparatus for designing a fatigue of a member having excellent fatigue durability, comprising: an optimum molding condition output means for outputting a hydroforming molding condition that gives a maximum fatigue life or a target fatigue life.   A computer program for causing a computer to function as each means of the fatigue design device according to claim 2.   The computer-readable recording medium which recorded the computer program of Claim 4.

Images