Stress calculation device and stress calculation method

Abstract

To enable quick evaluation of the stress distribution generated in a frame of a vehicle.SOLUTION: A stress calculation device calculates the stress distribution generated in a frame for a vehicle having the frame attached with a plurality of wheels. The stress calculation device includes a processor. The processor acquires data of a three-dimensional stress analysis result indicating the stress distribution generated in the frame when a load in one direction is applied to one of the wheels for each combination of the wheel and the load direction. The processor receives the load applied to each wheel. The processor calculates a linear sum of the three-dimensional stress analysis result on the basis of a component in each of the plurality of acquired load directions of the received load applied to each of the plurality of wheels. The processor generates output data for three-dimensional display of the stress distribution generated in the frame on the basis of the linear sum.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to stress calculations for vehicles. [Background technology]

[0002] Patent Document 1 discloses an object management system including a model manager that generates an avatar representing a human operator. The avatar is placed in a three-dimensional environment having a model of an object, and the three-dimensional environment having the model of the object and the avatar is displayed on a display system from the viewpoint of the avatar. Interactions between the avatar and the model of the object are identified in real time, and the interaction changes a group of dimensions in the model of the object. The interaction is displayed on the system, allowing the human operator to make design changes to the model of the object.

[0003] Patent Document 1 discloses performing a finite element analysis on a model based on live information and identifying stresses within the object from the finite element analysis. In an example where the model is an airplane wing, the stresses occurring in the model are displayed on a display using a graphical indicator, with blue indicating low stress and red indicating high stress. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-59213 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned Patent Document 1 discloses that the object or model may be an automobile, etc. However, it does not disclose a specific configuration for specifying stress based on what data in the vehicle.

[0006] The present disclosure has been made in consideration of the above circumstances, and its purpose is to enable quick evaluation of the stress distribution occurring in a vehicle frame. [Means for solving the problem]

[0007] The problem to be solved by the present disclosure is as described above. Next, the means for solving this problem and the effects thereof will be described.

[0008] According to a first aspect of the present disclosure, there is provided a stress calculation device having the following configuration. Specifically, the stress calculation device calculates the stress distribution occurring in a frame of a vehicle having a frame to which multiple wheels are attached. The stress calculation device includes a processor. The processor acquires data of three-dimensional stress analysis results indicating the stress distribution occurring in the frame when a load in a certain direction is applied to one of the wheels, for each combination of wheel and load direction. The processor accepts forces applied to each of the wheels. The processor calculates a linear sum of the three-dimensional stress analysis results based on the components of the load applied to each of the multiple wheels in the acquired multiple load directions. The processor generates output data for three-dimensionally displaying the stress distribution occurring in the frame based on the linear sum.

[0009] According to a second aspect of the present disclosure, there is provided the following stress calculation method. Specifically, this stress calculation method calculates the stress distribution occurring in a frame of a vehicle having a frame to which multiple wheels are attached. Three-dimensional stress analysis results showing the stress distribution occurring in the frame when a load in a certain direction is applied to one of the wheels are stored for each combination of wheel and load direction. The load applied to each of the wheels is input. A linear sum of the three-dimensional stress analysis results is calculated based on the components of the load applied to each of the multiple wheels in each of the multiple load directions. Data for three-dimensionally displaying the stress distribution occurring in the frame is output based on the linear sum.

[0010] This allows the stress distribution in the vehicle frame to be quickly evaluated by combining pre-stored 3D stress analysis results based on the load applied to each wheel. [Effects of the Invention]

[0011] The present disclosure allows for a quick assessment of the stress distribution occurring in a vehicle frame. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing the overall configuration of a stress calculation system including a stress calculation computer according to an embodiment of the present disclosure. [Figure 2] A conceptual diagram showing the preparation work before performing stress calculations. [Figure 3] 10A and 10B are conceptual diagrams illustrating calculation and display of stress. [Figure 4] 10 is a flowchart showing a stress calculation process in a stress calculation computer. [Figure 5] 10 is a flowchart showing a damage degree calculation process in a stress calculation computer. DETAILED DESCRIPTION OF THE INVENTION

[0013] Next, the disclosed embodiments will be described with reference to the drawings. Fig. 1 is a block diagram showing the overall configuration of a stress calculation system 1 including a stress calculation computer 10 according to an embodiment of the present disclosure.

[0014] 1 corresponds to a stress calculation device. The stress calculation computer 10 includes a storage unit 11, an input unit 12, a linear sum calculation unit 13, an output unit 14, and a damage degree calculation unit 15.

[0015] Specifically, the stress calculation computer 10 is configured as a known computer and includes a CPU, RAM, SSD, etc. The CPU is a type of processor. Real-time stress calculation software is pre-stored in the SSD. This allows the stress calculation computer 10 to operate as a storage unit 11, an input unit 12, a linear sum calculation unit 13, an output unit 14, and a damage degree calculation unit 15.

[0016] The storage unit 11 stores a stress analysis model created for a vehicle for which stress calculation is to be performed. This model is created as three-dimensional data in accordance with FEM, which stands for finite element modeling. The model can be created using, for example, known software such as three-dimensional CAD.

[0017] In FEM, a model is divided into a large number of elements called meshes and treated discretely. A number is assigned to each mesh to identify it. The relationship between the mesh number and the position and shape of the mesh in the model is stored in advance in the storage unit 11.

[0018] In this embodiment, the object of stress analysis is a frame that forms the skeleton of a four-wheeled vehicle. The created model for stress analysis has the frame and four wheels.

[0019] In this embodiment, the three-dimensional data is created in an XYZ coordinate space defined so that the direction from the front to the rear of the vehicle is the +X direction, the direction from left to right is the +Y direction, and the direction from bottom to top is the +Z direction. However, how the coordinate axes are defined is arbitrary.

[0020] The memory unit 11 stores, as basic data, the stress distribution that occurs in the frame when a load of a predetermined magnitude is applied to the contact point of the wheel for each combination of four wheels and three load directions included in the stress analysis model. This stress distribution is specifically the stress tensor of each mesh. The stress distribution is calculated by the stress analysis computer 20.

[0021] The input unit 12 can input data relating to the loads acting on the four wheels of the vehicle at their contact points. The loads can also be referred to as forces. The input unit 12 can be configured as a communication interface to another computer that implements the driving simulator 30, for example.

[0022] The driving simulator 30 is configured as a known computer. Although not shown, the driving simulator 30 includes an input interface and an output interface. Examples of the input interface include a steering wheel controller, a pedal controller, a lever controller, etc. Examples of the output interface include an appropriate display (including a head-mounted display).

[0023] The traveling simulator 30 and the stress calculation computer 10 are connected by a known network such as a LAN, and can exchange data via communication.

[0024] Appropriate three-dimensional driving simulator software is installed in the driving simulator 30. A driver operates the driving simulator 30 to simulate driving a virtual vehicle on a road surface arranged in a virtual space. This realizes a virtual driving test function. The virtual road surface can be, for example, a durable road surface.

[0025] During the simulation run, the running simulator 30 calculates in real time the load applied from the road surface to each of the four wheels of the virtual vehicle, and outputs the calculated load to the stress calculation computer 10. This load is input to the input unit 12. This information can be input by, for example, known UDP communication.

[0026] The linear sum calculation unit 13 calculates stress distribution data by linearly superimposing basic data of stress distribution based on the load data input to the input unit 12. This will be described in detail later.

[0027] Based on the stress distribution data obtained by the calculation of the linear sum calculation unit 13, the output unit 14 generates output data that three-dimensionally expresses the stress distribution, and outputs the output data.

[0028] The damage calculation unit 15 calculates cumulative damage distribution data based on the stress distribution data obtained by the calculation by the linear sum calculation unit 13. The output unit 14 can generate and output output data that three-dimensionally expresses the cumulative damage distribution based on the cumulative damage distribution data. This will be described in detail later.

[0029] Next, the flow of stress calculation in the real-time stress calculation system will be described in detail.

[0030] First, the preparation work for stress calculation will be described with reference to Fig. 2. In this preparation work, basic data of stress distribution is stored in the storage unit 11 of the stress calculation computer 10.

[0031] As described above, the basic data of the stress distribution is obtained using the stress analysis computer 20 .

[0032] Focusing on the left front wheel of the stress analysis model, consider the case where a load of 1000 N is applied in the +X direction to the ground contact point of this left front wheel. The stress analysis computer 20 calculates the stress distribution that occurs in the frame in this case. This calculation can be realized by the well-known inertial relief analysis. Inertial relief analysis is an analytical method for determining stress and strain from the forces acting on an object moving with a uniform acceleration, in a state where the object is supported at a support point that serves as the reference for the coordinates of inertial force (free support state).

[0033] The stress analysis computer 20 also calculates the stress distribution in the frame when a load of 1000 N is applied to the left front wheel in the +Y direction and when a load of 1000 N is applied to the left front wheel in the +Z direction. As a result, analysis results of the stress distribution for the left front wheel are obtained for each of the three load directions. In this embodiment, the magnitude of the reference load is set to 1000 N, but this can be changed as desired.

[0034] The stress analysis computer 20 obtains analysis results of the three stress distributions occurring in the frame for each of the right front wheel, left rear wheel, and right rear wheel, so that a total of 12 stress distribution analysis results are obtained.

[0035] The obtained analysis results are output from the stress analysis computer 20 to the stress calculation computer 10 and stored in a storage unit 11 provided in the stress calculation computer 10. The transfer of data from the stress analysis computer 20 to the stress calculation computer 10 can be achieved, for example, by the stress analysis computer 20 saving a file of the analysis results in a removable storage medium and reading this file into the stress calculation computer 10. However, this is not limited to this, and for example, data may be sent from the stress analysis computer 20 to the stress calculation computer 10 via known network communication.

[0036] Hereinafter, a combination of one wheel selected from the four and one load direction selected from the three directions of the X-axis, Y-axis, and Z-axis may be referred to as a "case." The number of cases is 4 x 3 = 12. As described above, the analysis results of stress distribution are obtained for each of the 12 cases and stored in the memory unit 11.

[0037] To identify each case, a number from 1 to 12 is assigned to each case. Figure 2 shows an example in which the number 1 is assigned to the case in which a load of 1000 N is applied to the left wheel in the +X-axis direction.

[0038] The processing of the stress analysis computer 20 is performed by calculating the stress tensor σ mn This is equivalent to asking for

number

[0039] The above-mentioned basic data calculated by the stress analysis computer 20 and stored in the memory unit 11 of the stress calculation computer 10 is substantially the stress tensor σ of all meshes for each case. m1 ,σ m2 ,···,σ m12 is.

[0040] The creation of a model for stress analysis may be performed in either the stress calculation computer 10 or the stress analysis computer 20, or in a computer different from either of them. The stress analysis process may be performed in the stress calculation computer 10 instead of the stress analysis computer 20.

[0041] Next, with reference to FIG. 3, the actual stress calculation flow performed after the preparation work is completed will be described in detail.

[0042] The loads applied to the contact points of each of the four wheels are calculated in the driving simulation performed by the driving simulator 30. The loads calculated by the driving simulator 30 are input to the stress calculation computer 10 in real time.

[0043] When focusing on one wheel, for example the left front wheel, the load applied to this wheel at the contact point can be expressed by the magnitudes of the force components in three axial directions, i.e., the X direction, the Y direction, and the Z direction (Fx, Fy, Fz). In this embodiment, the vehicle has four wheels, so 12 values ​​are input to the input unit 12.

[0044] The 12 values ​​input to the input unit 12 correspond one-to-one to the 12 cases described above. For example, the X-direction component Fx of the load applied to the left front wheel corresponds to case 1 of the 12 cases described above.

[0045] When 12 values ​​representing the loads applied to the four wheels are input to the input unit 12, the linear sum calculation unit 13 of the stress calculation computer 10 calculates the linear sum of the stress tensors for each mesh of the stress analysis model, thereby obtaining the stress distribution in the current situation.

[0046] Linear sum of stress tensors σ m,TOTAL can be calculated using the following formula (2).

number

[0047] The linear sum calculation unit 13 calculates the linear sum σ obtained for each mesh. m,TOTAL is output to the output unit 14.

[0048] The output unit 14 outputs the linear sum σ of the stress tensors obtained for all the meshes. m,TOTAL Based on this, data is generated and output to graphically display the stress distribution occurring in the frame in three dimensions.

[0049] This process can be performed, for example, as follows: That is, for each mesh, the von Mises stress, which is a known scalar quantity, is calculated. This calculation is performed by calculating the linear sum σ of stress tensors. m,TOTAL The output unit 14 generates three-dimensional model data that is color-coded according to stress from data that associates mesh numbers with the magnitude of the von Mises stress.

[0050] The stress calculation computer 10 is electrically connected to, for example, a display 3. The display 3 can be, for example, a liquid crystal display, an organic EL display, or the like, but is not limited to these. The output unit 14 can graphically display the stress distribution on the display 3 by two-dimensionally rendering the three-dimensional model data including color information indicating the stress. In this example, the two-dimensionally rendered data corresponds to the data for three-dimensionally displaying the stress distribution.

[0051] An example of a rendering display is shown in Figure 3 at 50. For convenience of illustration, the display data 50 in Figure 3 shows color differences in shades of gray. The colors used to represent the magnitude of stress are arbitrary, and the format of the display data 50 is also arbitrary.

[0052] The output unit 14 can be realized by using, for example, a three-dimensional view function provided by a known library for developing 3D games. The user can change the viewpoint of the three-dimensional model data representing stress by operating an operation device (e.g., the mouse 2) of the stress calculation computer 10.

[0053] Instead of the display 3, a head-mounted display may be connected to the stress calculation computer 10. This configuration enables a virtual reality (VR) function. Specifically, an appropriate three-dimensional virtual space is constructed in the stress calculation computer 10, and three-dimensional model data, colored differently according to stress, is placed in the virtual space as a virtual reality object. The position and orientation of the head-mounted display are detected using a known tracking technique, and the obtained position and orientation are input to the stress calculation computer 10 in real time. A virtual camera is placed in the three-dimensional virtual space, and the position and orientation of this virtual camera are changed to track the detected position and orientation of the head-mounted display. The output unit 14 of the stress calculation computer 10 renders a virtual reality object based on the position and orientation of the virtual camera and outputs the rendering result to the head-mounted display in real time. In this example, the rendered data corresponds to data for displaying the stress distribution in three dimensions. This allows the user to understand, with a sense of realism close to reality, which parts of the vehicle are likely to experience large stress.

[0054] The stress calculation computer 10 may function as a server for other client computers, which may be portable or stationary.

[0055] When the client computer is a portable computer such as a tablet computer, an augmented reality (AR) function may be implemented. Specifically, the tablet computer includes a display with a touch panel. Furthermore, the tablet computer includes a camera capable of continuously capturing images of its surroundings. The camera can capture images of a real vehicle placed at an appropriate location. The vehicle has a shape corresponding to the three-dimensional model described above. A plurality of markers are installed on or around the vehicle.

[0056] The tablet computer acquires the position and orientation of the camera relative to the actual vehicle in real time based on the positions of the multiple markers captured by the camera. This processing can be realized by known image recognition technology. The tablet computer transmits the detected position and orientation of the camera to the stress calculation computer 10 in real time. Communication between the stress calculation computer 10 and the tablet computer can be realized by known wireless communication means.

[0057] The output unit 14 of the stress calculation computer 10 changes the viewpoint to follow the position and orientation of the received camera, and then generates a 2D rendering result of the stress color-coded 3D model data. This rendering result is sent in real time from the stress calculation computer 10 to a tablet computer. The tablet computer displays the received 2D rendering result on its display by combining it with the image captured by the camera. In this example, the 2D rendered data corresponds to the data for displaying the stress distribution in 3D. This allows the user to easily understand, based on the combined image, which parts of the actual vehicle are likely to experience large stresses.

[0058] The above-described augmented reality function can also be realized by a see-through head-mounted display instead of a tablet computer. The head-mounted display may be an optical see-through type or a video see-through type.

[0059] Rendering may be performed on the client computer side. In this case, three-dimensional model data and the like are transmitted from the stress calculation computer 10 to the client computer. In this example, the three-dimensional model data corresponds to data for three-dimensionally displaying the stress distribution.

[0060] Next, the above flow will be specifically described with reference to the flowchart in FIG.

[0061] In the flow of stress calculation, first, the load applied to each wheel is input to the input unit 12 of the stress calculation computer 10 (step S101).

[0062] Next, the linear sum calculation unit 13 calculates the stress tensor of each mesh by linear summation based on the load value input to the input unit 12 (step S102).

[0063] Next, the output unit 14 renders a three-dimensional model that expresses, for example, the distribution of the Mises stress in color based on the linear sum calculated in step S102, and outputs the rendering result to the display 3 (step S103). After that, the process returns to step S101.

[0064] The series of processes described in steps S101 to S103 is performed substantially in real time. This allows the user to quickly understand the trend of stresses occurring in the vehicle. Therefore, strength evaluation, which usually requires a long period of time, can be completed in a significantly shorter time.

[0065] Next, the calculation of the cumulative damage level of the vehicle frame performed by the damage level calculation unit 15 will be described.

[0066] In this embodiment, a mesh corresponding to a welded portion of a frame member is specified in advance in the stress analysis model stored in the storage unit 11. The damage calculation unit 15 calculates a linear sum σ of stress tensors related to the mesh. m,TOTAL The stress perpendicular to the weld is calculated based on the following equation: This stress can be easily calculated using well-known transformation formulas for the stress tensor.

[0067] The damage calculation unit 15 calculates the stress in the direction perpendicular to the weld in real time and determines its time transition. Next, the damage calculation unit 15 determines the maximum and minimum values ​​of the stress based on the time transition and counts the components effective for fatigue life in real time using the known rainflow method. The damage calculation is performed based on the counting results. The damage calculation can be performed, for example, based on the known modified Miner's rule.

[0068] The output unit 14 can render three-dimensional model data that is color-coded according to the degree of damage calculated by the damage degree calculation unit 15, instead of stress, and output it to a display or the like. This allows the user to understand the tendency of damage occurring to the frame in real time.

[0069] Next, the above flow will be specifically described with reference to the flowchart of FIG.

[0070] The processing in steps S201 and S202 is the same as the processing in steps S101 and S102 in FIG. 4, and therefore a description thereof will be omitted.

[0071] When the process of step S202 is completed, the damage calculation unit 15 calculates the stress in the direction perpendicular to the weld for the mesh of the frame weld (step S203). This calculation is performed based on the linear sum of the stress tensors calculated by the linear sum calculation unit 13.

[0072] Next, the damage level calculation unit 15 counts the stress frequency based on the time transition of the stress calculated in step S203 (step S204).

[0073] Next, the damage calculation unit 15 calculates the damage degree of the welded portion based on the count result of the stress frequency (step S205).

[0074] Next, the output unit 14 outputs data obtained by rendering a three-dimensional model in which the distribution of the damage level of the welded portion is expressed in color to the display 3 (step S206). After that, the process returns to step S201.

[0075] The series of processes described in steps S201 to S206 are performed substantially in real time, allowing the user to quickly understand the trend in the degree of damage to the vehicle.

[0076] As described above, the stress calculation computer 10 of this embodiment calculates the stress distribution occurring in a frame of a vehicle having a frame to which four wheels are attached. The stress calculation computer 10 includes a processor. The processor acquires data of three-dimensional stress analysis results indicating the stress distribution occurring in the frame when a load in a certain direction is applied to one of the four wheels, for each combination of wheel and load direction. The processor receives the load applied to each wheel. The processor calculates a linear sum of the three-dimensional stress analysis results based on the components of the load applied to each of the received wheels in the acquired multiple load directions. The processor generates output data for a three-dimensional display of the stress distribution occurring in the frame based on the linear sum.

[0077] This allows the stress distribution in the vehicle frame to be quickly evaluated by combining pre-stored 3D stress analysis results based on the load applied to each wheel.

[0078] In the stress calculation computer 10 of this embodiment, the processor outputs the generated output data in real time in response to the reception of the load.

[0079] This allows a very rapid assessment of the stress situations encountered by the vehicle under evaluation.

[0080] In the stress calculation computer 10 of this embodiment, the processor receives the result of calculation by the driving simulator 30 as the load applied to the wheel.

[0081] This allows the stress conditions that arise as a result of vehicle operation to be quickly grasped without actually running the vehicle.

[0082] In the stress calculation computer 10 of this embodiment, the processor calculates the damage level distribution of the frame based on the stress distribution occurring in the frame. The processor generates output data for three-dimensionally displaying the calculated damage level distribution.

[0083] This allows for quick assessment of frame damage caused by vehicle operation.

[0084] Although the preferred embodiment of the present disclosure has been described above, the above configuration can be modified, for example, as follows. A single modification may be made, or multiple modifications may be made in any combination.

[0085] As the stress distribution occurring in the frame, for example, the distribution of the magnitude of the principal stress may be output instead of the distribution of the von Mises stress.

[0086] Instead of or in addition to the stress generated in the frame, the displacement generated in the frame may be calculated as a linear sum and output as a displacement distribution. For ease of visual understanding, the displacement may be displayed exaggerated by an appropriate magnification.

[0087] The damage level calculation unit 15 can be omitted.

[0088] Instead of the simulation calculation results of the driving simulator 30, load values ​​based on information collected by an appropriate sensor when a real vehicle is driven may be input to the input unit 12. For example, an acceleration sensor is mounted on the real vehicle, and the acceleration of the vehicle while it is driving is measured by this sensor. Based on this acceleration, the load applied to each wheel is calculated using an appropriate model and input to the input unit 12.

[0089] The load data may be input to the input unit 12 in non-real time. For example, a wheel load history file is created by the simulation calculation performed by the driving simulator 30, in which the time and the magnitude of the force corresponding to 12 cases are associated with each other. The stress calculation computer 10 then reads the file, generates a transition of the stress distribution occurring in the frame, and outputs it to the display 3.

[0090] The cumulative damage may be calculated and displayed on a mesh other than the mesh corresponding to the frame weld.

[0091] At least one of the stress distribution and the cumulative damage distribution may be calculated in non-real time.

[0092] The number of wheels provided on the vehicle to be subjected to stress analysis may be two, three, five or more.

[0093] The functions of each element disclosed in this disclosure, including the stress calculation computer 10, the stress analysis computer 20, and the driving simulator 30, can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor includes transistors and other circuits, and is therefore considered a processing circuit or circuit. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions or hardware that is programmed to perform the enumerated functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the enumerated functions. When the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor. [Explanation of symbols]

[0094] 1 Stress calculation system 10 Stress calculation computer 11 Storage section 12 Input section 13 Linear sum calculation section 14 Output section 15 Damage degree calculation section 20 Stress analysis computer 30 Driving Simulator

Claims

1. 1. A stress calculation device comprising a processor, for calculating a stress distribution occurring in a frame of a vehicle having a frame to which a plurality of wheels are attached, the device comprising: The processor: obtaining data of three-dimensional stress analysis results showing a stress distribution generated in the frame when a load in a certain direction is applied to one of the wheels, for each combination of wheel and load direction; Accepting a load applied to each of the wheels; calculating a linear sum of the three-dimensional stress analysis results based on the received components of the loads applied to each of the plurality of wheels in the respective load directions; generating output data for three-dimensionally displaying a stress distribution occurring in the frame based on the linear sum; Stress calculation device.

2. 2. The stress calculation device according to claim 1, The processor outputs the generated output data in real time in response to reception of a load.

3. 3. The stress calculation device according to claim 1, The processor receives, as the load applied to the wheel, a simulation result calculated by a simulator or a calculation result based on a sensor provided on an actual vehicle.

4. The stress calculation device according to any one of claims 1 to 3, The processor: calculating a damage distribution of the frame based on a stress distribution occurring in the frame; A stress calculation device that generates output data for three-dimensionally displaying the calculated damage distribution.

5. 1. A stress calculation method for calculating a stress distribution occurring in a frame of a vehicle having a frame to which a plurality of wheels are attached, comprising: storing a three-dimensional stress analysis result showing a stress distribution generated in the frame when a load in a certain direction is applied to one of the wheels, for each combination of wheel and load direction; Input the load applied to each of the wheels; calculating a linear sum of the results of the three-dimensional stress analysis based on components of the loads applied to each of the plurality of wheels in each of the plurality of load directions; outputting data for three-dimensionally displaying the stress distribution occurring in the frame based on the linear sum; Stress calculation method.

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