Distortion analysis method

Abstract

To provide a distortion analysis method easy to reproduce an actual measurement value using a distortion gauge.SOLUTION: In a fastening step S3, a membrane model 20 set in a membrane setting step S2 to simulate a distortion gauge is fixed to the surface of a shape model 10 set in an object setting step S1. In an analysis step S5 after the fastening step S3, the distortion of the shape model 10 and the membrane model 20 at the time when external force is applied to the shape model 10 are analyzed by the finite element method. In this way, the distortion of the membrane model 20 can be analyzed by simulating the same situation as actual measurement using the distortion gauge in which external force is applied to an object to which the distortion gauge is attached to confirm the distortion of the distortion gauge. As a result, the analysis results of the membrane model 20 can easily reproduce an actual measurement value using the distortion gauge.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a strain analysis method, and more particularly to a strain analysis method that makes it easy to reproduce actual measurements using strain gauges. [Background technology]

[0002] Conventionally, there has been known a method for analyzing the strain that occurs in an object when an external force is applied to the object by computer simulation using the finite element method (FEM). Patent Document 1 discloses a method for estimating the strain (load value) at a specific position on the object by substituting the actual measurement value from a strain gauge attached to the actual object into a relational expression obtained by FEM analysis of the object. This relational expression is calculated from the analysis results of a geometric model of the object divided into multiple meshes, and expresses the relationship between the strain of the mesh at the position where the strain gauge is attached in the actual measurement and the strain of the mesh at the specific position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-57691 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, meshes corresponding to positions where strain gauges will be attached in actual measurements are selected from multiple meshes of a geometric model, which means that there is a high possibility that the selected meshes will differ from the actual strain gauges in terms of shape, size, position, etc. This causes a problem in that the reproducibility of the analysis results for strain at the positions where strain gauges are attached decreases compared to the actual measured values ​​of the strain gauges. This decrease in reproducibility also reduces the accuracy of strain calculations using the relational equation.

[0005] The present invention has been made to solve the above-mentioned problems, and has as its object to provide a strain analysis method that can easily reproduce actual measured values ​​using strain gauges. [Means for solving the problem]

[0006] In order to achieve this object, the strain analysis method of the present invention is a method for analyzing strain occurring in an object when an external force is applied to the object by a finite element method, and includes an object setting step of dividing a shape model simulating the object into a plurality of object meshes and setting analysis conditions for the shape model, a film setting step of dividing a rectangular membrane model simulating a strain gauge for measuring strain on the surface of the object into a plurality of rectangular or square membrane meshes and setting analysis conditions for the membrane model, a fixing step of fixing the membrane model set in the film setting step to the surface of the shape model set in the object setting step, and an analysis step of analyzing strain in the shape model and the membrane model when an external force is applied to the shape model after the fixing step by the finite element method. In the fixing step, the membranous model is fixed to the geometric model without connecting the plurality of nodes of the membranous model to the plurality of nodes of the geometric model. . [Effects of the Invention]

[0007] According to the strain analysis method of claim 1, in the fixing step, a membranous model set in the membrane setting step to imitate a strain gauge is fixed to the surface of the geometric model set in the object setting step. In the analysis step after this fixing step, the distortion of the geometric model and the membranous model when an external force is applied to the geometric model is analyzed using the finite element method. In this way, the distortion of the membranous model can be analyzed by simulating a situation similar to actual measurement using a strain gauge, in which an external force is applied to an object to which a strain gauge is attached and the strain of the strain gauge is confirmed. As a result, the analysis results of the membranous model can easily reproduce actual measurement values ​​using a strain gauge.

[0008] Furthermore, in the membrane setting step, the membrane model is set separately from the geometric model. This prevents the shape, size, position, etc. of the membrane model from being affected by the division method of the target mesh in the geometric model (the shape of the target mesh, mesh spacing, etc.). As a result, the analysis results of the membrane model can be made closer to the actual measured values ​​of the strain gauge.

[0009] solid In the attachment step, the membranous model is fixed to the geometric model without connecting the plurality of nodes of the membranous model to the plurality of nodes of the geometric model, so that the membranous model can be placed regardless of the positions of the nodes of the geometric model. This makes it possible to prevent the position of the membranous model from being affected by the division method of the target mesh in the geometric model, so that the analysis results of the membranous model can be made closer to the actual measured values ​​of the strain gauge.

[0010] Claim 2 According to the distortion analysis method described in claim 1 In addition to the effects of the strain analysis method described above, the method also provides the following effects. In the membrane setting step, the membrane model is divided so that multiple membrane meshes are arranged in the long and short side directions of the membrane model, making it possible to bend the membrane model in both the long and short side directions. As a result, the membrane model can be fixed along the curved surfaces and corners of the shape model, and the strain in both the long and short side directions of the membrane model due to deformation (strain) of the shape model can be analyzed more accurately. Therefore, the analysis results of the membrane model can be made closer to the actual measured values ​​of the strain gauge.

[0011] Claim 3 According to the distortion analysis method described in claim 1 or 2 In addition to the effects of the distortion analysis method described in 2., the present invention provides the following effect: In the geometric model and the membranous model of the part fixed to each other in the fixing step, the average distance between the nodes of the vertices of the plurality of membrane meshes is smaller than the average distance between the nodes of the vertices of the plurality of object meshes. This makes it possible to improve the analysis accuracy of the membranous model while suppressing an increase in the analysis time of the geometric model of the part to which the membranous model is fixed.

[0012] Claim 4 According to the distortion analysis method described in claim 1 to claim 2, 3 In addition to the effects of the distortion analysis method described in any one of the above, the following effect is achieved: In the membrane setting step, the stiffness of the membranous model is set to 0.5 N / mm or less. This makes it possible to prevent the stiffness of the membranous model from interfering with the deformation of the shape model in the analysis step. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a flowchart illustrating a distortion analysis method in one embodiment. [Figure 2] FIG. 10 is a perspective view of a shape model to which a membranous model is fixed. [Figure 3] 3A is an enlarged perspective view of the shape model and the membranous model in the area IIIa of FIG. 2, and FIG. 3B is a front view of the membranous model. DETAILED DESCRIPTION OF THE INVENTION

[0014] Preferred embodiments will be described below with reference to the accompanying drawings. Fig. 1 is a flowchart showing a distortion analysis method in one embodiment. Fig. 2 is a perspective view of a shape model 10 to which a membranous model 20 is fixed. Fig. 3(a) is a perspective view of the shape model 10 and the membranous model 20, with an enlarged view of part IIIa in Fig. 2. Fig. 3(b) is a front view of the membranous model 20. Note that Fig. 2 shows the outlines of the shape model 10 and the membranous model 20 in a schematic manner, and omits mesh shapes and the like.

[0015] Strain analysis is a method of analyzing the strain that occurs in an object when an external force is applied to it through computer simulation using the finite element method (FEM). A commercially available FEM analysis program can be used for FEM analysis. More specifically, a simulation program can be used for FEM analysis that can calculate the load and strain on each part of an analytical model when an analytical model of an object divided into multiple meshes is deformed by an external force, for each mesh node. For example, a finite element analysis solver such as NASTRAN can be used.

[0016] Furthermore, in FEM analysis, various conditions are set for the analysis, such as the shape of the analysis model, material properties (Young's modulus, Poisson's ratio, etc.), mesh shape, mesh spacing (number of nodes), position where external force is applied, and magnitude of external force. Mesh shapes mainly include rod-shaped bar elements, shell elements made of triangles or quadrilaterals, and solid elements made of tetrahedrons, pentahedrons, or hexahedrons. Each mesh is connected to another using the vertices of the figure (both ends in the case of bar elements) as nodes. However, it is also possible to set intermediate nodes in the middle of the sides connecting the vertices of each mesh figure.

[0017] The accuracy of FEM analysis of an analytical model that mimics an object can be determined by comparing the measured strain values ​​when the actual object is deformed by applying the same external force as during analysis with the analytical results of the strain at the measured position. The measured strain values ​​of the object are the values ​​measured by the strain gauges attached when the object is deformed.

[0018] A strain gauge is a rectangular sensor used to measure local strain on the surface of an object, converting the deformation (strain) that occurs in the strain gauge itself into an electrical signal. From this electrical signal, the amount of strain in the strain gauge, i.e., the amount of local strain in the part of the object where the strain gauge is attached, is calculated as the strain gauge's measurement value.

[0019] Here, if the reproducibility of the analysis results of the strain at the position measured by the strain gauge is low compared to the actual measurement value using the strain gauge, the accuracy of the FEM analysis cannot be appropriately determined by comparing the actual measurement value with the analysis result. Therefore, the strain analysis method in this embodiment performs FEM analysis of the target object and FEM analysis of the strain gauge attached to the target object at the same time, making it possible to perform an analysis with high reproducibility compared to the actual measurement value using the strain gauge.

[0020] 1, the distortion analysis method first sets a shape model 10 as an analysis model that imitates the shape of an object (object setting step S1). In the object setting step S1, the shape model 10 is divided into a plurality of object meshes 13, and analysis conditions for the shape model 10, such as the shape, mesh spacing, and material properties of the object meshes 13, are set.

[0021] 2 shows a geometric model 10 displayed on the display of a computer on which FEM analysis is performed. The geometric model 10 in this embodiment is modeled after a bracket that connects an engine mount (vibration isolation device) fixed to the body of an automobile to the engine side.

[0022] The geometric model 10 comprises a fixed portion 11 that is fixed to the engine side with a bolt, and an insertion portion 12 that protrudes laterally from the fixed portion 11 and is inserted into an attachment member of the engine mount. In this geometric model 10, the insertion portion 12 vibrates up and down relative to the fixed portion 11 in response to engine vibrations, and distortion is particularly likely to occur at the base of the insertion portion 12. Therefore, when measuring distortion of an actual object with a strain gauge, the strain gauge is attached to the base of the insertion portion 12 of the object where distortion is likely to occur.

[0023] FIG. 3(a) shows an enlarged view of the base of the insertion portion 12 of the shape model 10. The object mesh 13 of the shape model 10 is a tetrahedral solid element. The nodes of this object mesh 13 are referred to as object nodes 14. In the shape model 10 of this embodiment, object nodes 14 are provided only at the vertices of the object mesh 13, and no object nodes 14 are provided as intermediate nodes. It is also possible to provide object nodes 14 as intermediate nodes, in which case the analysis accuracy will improve but the analysis time will increase.

[0024] 1 and 3(b), after the object setting step S1, a membrane model 20 is set as an analysis model imitating the shape of a strain gauge (membrane setting step S2). In the membrane setting step S2, the membrane model 20 is divided into a plurality of membrane meshes 21, and analysis conditions for the membrane model 20, such as the shape of the membrane meshes 21, mesh spacing, and material properties, are set.

[0025] 3(b) shows the membrane model 20 displayed on the display of a computer on which the FEM analysis is performed. The membrane model 20 is set to a rectangular shape, that is, set to have substantially the same shape as an actual strain gauge.

[0026] The rigidity of the membranous model 20 is set to 0.5 N / mm or less. Preferably, the rigidity of the membranous model 20 is set to 0.3 N / mm or less, and more preferably, to 0.1 N / mm or less. The lower the rigidity of the membranous model 20, the more likely it is that the rigidity of the membranous model 20 will prevent deformation of the shape model 10 from being hindered by the rigidity of the membranous model 20 in the analysis step S5 described below.

[0027] The membrane mesh 21 is a quadrilateral membrane element. More specifically, the membrane mesh 21 is set to a square or rectangular shape. The shape and size (lengths of long and short sides) of the plurality of membrane meshes 21 are all set to be the same.

[0028] In the membrane setting step S2, the membrane model 20 is divided so that a plurality of membrane meshes 21 are arranged in each of the long side direction and the short side direction of the membrane model 20, and the membrane meshes 21 approach a square shape. Specifically, for example, after determining the number of divisions in the short side direction of the membrane model 20, the number of divisions in the long side direction of the membrane model 20 can be determined so that the membrane meshes 21 approach a square shape as much as possible. By arranging the membrane meshes 21 in the long side direction and the short side direction, it becomes possible to bend and deform the membrane model 20 in both the long side direction and the short side direction. Furthermore, the closer the membrane meshes 21 approach a square shape, the more the analysis accuracy of the membrane model 20 can be improved.

[0029] In the membrane model 20 of this embodiment, membrane nodes 22 are provided only at the vertices of the membrane mesh 21, and no membrane nodes 22 are provided as intermediate nodes. It is also possible to provide membrane nodes 22 as intermediate nodes, in which case the analysis accuracy improves but the analysis time increases.

[0030] 1, 2, and 3(a), after the object setting step S1 and the film setting step S2, the membranous model 20 is fixed to the surface of the shape model 10 (fixing step S3). In the fixing step S3, the position where the membranous model 20 is fixed to the shape model 10 is set to be the same as the position where a strain gauge is attached to the actual object.

[0031] In the fixing step S3, the membrane model 20 is fixed to the surface of the shape model 10 by an "adhesion definition" that structurally joins surfaces of different mesh patterns as if they were glued together. In other words, the "adhesion definition" means fixing the membrane model 20 to the surface of the shape model 10 without connecting the plurality of object nodes 14 of the shape model 10 with the plurality of membrane nodes 22 of the membrane model 20. However, when fixing the membrane model 20 to the shape model 10 by the "adhesion definition", some of the plurality of object nodes 14 and some of the plurality of membrane nodes 22 may coincide with each other.

[0032] After the fixing step S3, other analysis conditions are set (condition setting step S4), such as constraint conditions for the shape model 10, the position where an external force is applied to the shape model 10, and the magnitude of the external force. Next, since all analysis conditions have been set, an FEM analysis is performed to analyze distortions of the shape model 10 and the membranous model 20 when an external force is applied to the shape model 10 after the fixing step S3 (analysis step S5).

[0033] According to the strain analysis method described above, it is possible to analyze the strain of the membranous model 20 fixed to the shape model 10 by simulating a situation similar to actual measurement using a strain gauge, in which an external force is applied to an object to which a strain gauge is attached and the strain of the strain gauge is confirmed. As a result, the analysis results of the membranous model 20 make it easy to reproduce the actual measurement values ​​using a strain gauge.

[0034] In particular, in the membrane setting step S2, a membranous model 20 simulating a strain gauge is set separately from the shape model 10. That is, in the membrane setting step S2, some surfaces of the plurality of object meshes 13 of the shape model 10 are not set as equivalent to strain gauges (membrane models 20). This makes it possible to prevent the shape, size (dimensions in the short side direction and long side direction), position, etc. of the membranous model 20 from being affected by the division method of the object mesh 13 in the shape model 10 (shape of the object mesh 13, mesh spacing, etc.). As a result, the analysis results of the membranous model 20 can be made closer to the actual measured values ​​of the strain gauge.

[0035] Furthermore, in the fixing step S3, the membrane model 20 is fixed to the surface of the shape model 10 by "adhesion definition" that makes it appear as if faces of different mesh patterns are glued together, so the membrane model 20 can be placed regardless of the positions of the object nodes 14. From this point of view, the position of the membrane model 20 can be prevented from being affected by the division method of the object mesh 13 in the shape model 10, so the analysis results of the membrane model 20 can be made closer to the actual measured values ​​of the strain gauge.

[0036] The strain analysis method of this embodiment makes it possible to analyze the membranous model 20 with high reproducibility relative to the actual measured values ​​of the strain gauge, and therefore by comparing the actual measured values ​​of the strain gauge with the analysis results of the membranous model 20, the analysis accuracy of the membranous model 20 and the shape model 10 can be appropriately determined.

[0037] When comparing the actual measured values ​​of the strain gauge with the analysis results of the membranous model 20, it is preferable to set the size of the membranous model 20 so that it is approximately the same as the size of the actual strain gauge. This allows the analysis results of the membranous model 20 to be closer to the actual measured values ​​of the strain gauge.

[0038] Furthermore, since the membrane meshes 21 are arranged in the long and short side directions, the membranous model 20 can be bent and deformed in both directions, and therefore the membranous model 20 can be fixed along the curved surfaces and corners of the surface of the shape model 10. Furthermore, the strain in both the long and short side directions of the membranous model 20 that accompanies the deformation (strain) of the shape model 10 can be analyzed more accurately. As a result, the analysis results of the membranous model 20 can be brought closer to the actual measured values ​​of the strain gauge.

[0039] In the part of the shape model 10 and the part of the membranous model 20 that are fixed to each other in the fixing step S3, the average interval between the membrane nodes 22 consisting of the vertices of the plurality of membrane meshes 21 is smaller than the average interval between the object nodes 14 consisting of the vertices of the plurality of object meshes 13. This makes it possible to improve the analysis accuracy of the membranous model 20 while suppressing an increase in the analysis time of the part of the shape model 10 to which the membranous model 20 is fixed.

[0040] Furthermore, it is relatively easy to analyze a membrane model 20 having a simple shape formed in a rectangular shape by a plurality of rectangular or square membrane meshes 21. Therefore, even if the intervals between the membrane nodes 22 are reduced to improve the analysis accuracy of the membrane model 20, an increase in the analysis time of the membrane model 20 can be suppressed.

[0041] The average interval between membrane nodes 22 consisting of the vertices of the membrane mesh 21 is preferably equal to or less than half the average interval between object nodes 14 consisting of the vertices of the object mesh 13 at the position where the membrane mesh 21 is at least partially fixed. This can further improve the analytical accuracy of the membranous model 20.

[0042] Furthermore, the average interval between the membrane nodes 22 consisting of the vertices of the membrane mesh 21 is preferably at least ¼ of the average interval between the object nodes 14 consisting of the vertices of the object mesh 13 at the positions to which the membrane mesh 21 is at least partially fixed. If the difference between the average interval between these membrane nodes 22 and the average interval between the object nodes 14 becomes too large, there is a risk that the rigidity of the fixing surface between the shape model 10 and the membrane model 20 will be over-analyzed. Therefore, by setting the average interval between the membrane nodes 22 to at least ¼ of the average interval between the object nodes 14, it is possible to prevent the rigidity of the fixing surface from being over-analyzed, and to prevent the fixing surface from hindering the deformation of the shape model 10.

[0043] The present invention has been described above based on an embodiment, but the present invention is not limited to the above embodiment, and it can be easily inferred that various improvements and modifications are possible within the scope of the present invention.

[0044] In the above embodiment, a bracket that connects an automobile engine mount to the engine side is used as the object, and a geometric model 10 that imitates the object is set. However, the type of object is not limited and may be changed as appropriate. Furthermore, the position at which the membrane model 20 is fixed to the geometric model 10 and the size of the membrane model 20 are not limited to those described in the above embodiment and may be changed as appropriate depending on the shape of the geometric model 10 that imitates the object. Furthermore, the type of object mesh 13 may be changed as appropriate depending on the shape of the geometric model 10.

[0045] 3(a) and 3(b) in the above embodiment show an example in which two membrane meshes 21 are arranged in the short side direction of the membranous model 20 and six membrane meshes 21 are arranged in the long side direction, but three or more membrane meshes 21 may be arranged in the short side direction, or five or less or seven or more membrane meshes 21 may be arranged in the long side direction. Depending on the shape of the shape model 10 at the position where the membranous model 20 is fixed, it is not necessary to arrange multiple membrane meshes 21 in the short side direction of the membranous model 20.

[0046] In the above embodiment, the case where the film setting step S2 is performed after the target setting step S1 has been described, but the target setting step S1 may be performed after the film setting step S2. Also, the condition setting step S4 for setting the position where an external force is applied to the shape model 10 may be performed before the film setting step S2 or the fixing step S3, as long as it is performed after the target setting step S1. [Explanation of symbols]

[0047] 10 Shape Model 13 Target Mesh 14 Target nodes (nodes of the geometric model) 20 Membrane model 21 Membrane mesh 22 Membrane nodes (membrane model nodes) S1 Target setting step S2 Membrane setting step S3 Fixation step S5 Analysis step

Claims

1. A strain analysis method for analyzing strain occurring in an object when an external force is applied to the object by a finite element method, comprising: an object setting step of dividing a shape model simulating the object into a plurality of object meshes and setting analysis conditions for the shape model; a membrane setting step of dividing a rectangular membrane model simulating a strain gauge for measuring strain on the surface of the object into a plurality of rectangular or square membrane meshes and setting analysis conditions for the membrane model; a fixing step of fixing the membrane model set in the membrane setting step to a surface of the shape model set in the target setting step; an analysis step of analyzing distortions of the shape model and the membranous model by a finite element method when an external force is applied to the shape model after the fixing step, A distortion analysis method, characterized in that in the fixing step, the membranous model is fixed to the geometric model without connecting the plurality of nodes of the membranous model to the plurality of nodes of the geometric model.

2. 2. The distortion analysis method according to claim 1, wherein said membrane setting step divides said membrane model so that a plurality of said membrane meshes are arranged in each of the long side direction and the short side direction of said rectangular membrane model.

3. 3. The distortion analysis method according to claim 1, wherein in the shape model and the membrane model of the parts fixed to each other in the fixing step, an average distance between nodes of the vertices of the plurality of membrane meshes is smaller than an average distance between nodes of the vertices of the plurality of target meshes.

4. 4. The distortion analysis method according to claim 1, wherein the stiffness of the membrane model is set to 0.5 N / mm or less in the membrane setting step.

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