High-precision spring arm fatigue analysis method

Abstract

The invention discloses a high-precision spring arm fatigue analysis method which comprises the following steps: S1, pre-processing a model through grid pre-processing software, and calculating part stress distribution under a fatigue working condition through a finite element analysis method; s2, analyzing the fatigue life through fatigue analysis software; and S3, obtaining a fatigue result through an experiment, and carrying out benchmarking on the fatigue result and an analysis value. The process of simulation constraint and load loading on spring arm motion is closer to actual tests, stress analysis can be better converged, the precision problem caused by complex stress of spring points of the spring arm can be solved, the analysis result and actual experiment verification are high in consistency, risks can be recognized in the early stage of design, the development efficiency is improved, and the development cost is reduced. The development cost is reduced, the universality is high, and the calculation result is accurate.

Description

Technical Field

[0001] The invention relates to the technical field of automobile component fatigue testing, in particular to a high-precision spring arm fatigue analysis method. Background Art

[0002] Fatigue analysis of automobile chassis is widely used, and it can predict the failure risk of parts in the early design stage. For parts with complex motion and force, such as spring arms, the analysis accuracy is lower. Conventional spring points are applied through flexible coupling spring contact surfaces, but this method cannot reflect the uneven force characteristics of the spring arm during the spring jumping process, resulting in extremely poor accuracy in local areas. It is difficult to effectively converge the force analysis in the process of simulating constraints and loads, so the stress results of fatigue conditions are often quite different from actual tests. Summary of the invention

[0003] The present invention provides a high-precision spring arm fatigue analysis method, which can solve the problem that the existing traditional fatigue analysis method cannot meet the fatigue analysis requirements of a part with relatively complex motion and force, such as a spring arm.

[0004] To achieve the above object, the present invention provides the following technical solution: a high-precision spring arm fatigue analysis method, comprising the following steps:

[0005] S1: The model is pre-processed by mesh pre-processing software, and the stress distribution of parts under fatigue conditions is calculated by finite element analysis method;

[0006] S2: Analyze fatigue life through fatigue analysis software;

[0007] S3: Compare the fatigue results obtained through experiments with the analytical values;

[0008] Wherein step S1 comprises the following steps:

[0009] S1.1: including establishing the geometric model of the spring arm and surrounding parts, including the models of the spring arm body, reinforcement plate, spring, spring pad, sleeve and inner bushing, the spring arm body is located at the vehicle position in the static state, the spring pad is assembled to the reinforcement plate, the upper end of the spring is located at the actual position of the vehicle and the spring is in a free state, and a first weld is established between the spring arm body and the reinforcement plate, and a second weld is established between the spring arm body and the sleeve, and the above geometric model is imported into the mesh processing software to perform mesh division of each component part, create coupling, coordinate system, select the contact surface and then export to obtain the final finite element model;

[0010] S1.2: Import the finite element model into the finite element analysis software to apply constraints and loads in the local or vehicle coordinate system, and calculate the stress under the fatigue condition. Specifically, a first local coordinate system is established with the center of the inner bushing as the coordinate center point, the Y axis of the first local coordinate system is the axis of the inner bushing, and the X axis and the Z axis can be arbitrarily specified. A second local coordinate system is established with the center of the spring as the coordinate center point, the center line of the spring is the X axis, and the Y axis and the Z axis can be arbitrarily specified;

[0011] The loading of constraints and loads includes the following five steps:

[0012] Step 1: Fully constrain the inner point of the spring arm based on the first local coordinate system, constrain the outer point of the spring arm based on the three moving directions based on the vehicle coordinate system, fully constrain the upper point of the spring based on the global coordinate system, constrain the lower point of the spring based on the second local coordinate system in the remaining five directions except the X-axis direction, and load the X-direction until the lower end of the spring is above the spring pad. The contact setting is removed in the whole process;

[0013] Step 2: Based on the constraints in the first step, change the loading direction of the lower point of the spring until the spring and the spring pad just touch each other. The whole process includes contact settings.

[0014] Step 3: Based on the constraints in the second step, release the freedom of the inner point to rotate around the Y axis based on the second local coordinate system, and release the constraints and loading of the point under the spring to make it contact naturally with the spring pad;

[0015] Step 4: According to the three-dimensional forces on the external points in the third step, the three-dimensional force constraints of the external points are changed to three-dimensional force loading, with a smooth transition to achieve better convergence of the analysis, in preparation for the fifth step of full loading;

[0016] Step 5: According to the three-dimensional force loaded at the external point in step 4, the force is smoothly transitioned to the actual load required by setting the default amplitude curve;

[0017] S1.3: Through the above five steps of analysis, the stress results of each fatigue condition required are obtained for fatigue analysis.

[0018] Furthermore, when meshing is performed in step S1.1, the mid-surface of the equal-wall thickness parts is extracted for meshing, and the mesh types are S4R and S3, where the S3 mesh accounts for no more than 5% of the shell unit. The mesh of regular solid parts is divided into hexahedral meshes with mesh types of C3D8R and C3D6, and the mesh of irregular solid parts is divided into second-order tetrahedral meshes with mesh type of C3D10M. The mesh type of the weld connection unit is S4R.

[0019] Preferably, the establishment of the weld defined in step S1.1 specifically includes: a first weld model established between the spring arm body and the reinforcement plate is connected by a 90° lap weld, the weld thickness is 3 mm, and the weld mesh type is S4R; a second weld model is established between the spring arm body and the sleeve by a 45° fillet weld, the weld thickness is 3 mm, the weld mesh type is S4R, and the mesh unit normal directions of the first weld and the second weld are outward.

[0020] Preferably, in step S2, the EN module in the nCode software is specifically used to calculate the fatigue of the main body, and step S2 includes the following steps:

[0021] S2.1: Import the fatigue stress results obtained in step S1 into the FEI nput module in the nCode software;

[0022] S2.2: Set parameters, assign materials, and define load cycles in the EN module;

[0023] S2.3: Display the results through the FEdisplay module and export the results through the FEOutput module.

[0024] Preferably, in step S3, a test bench is built according to the same constraints and loading methods as those in the analysis, and cyclic loading of fatigue conditions is performed at a frequency of 2 Hz until the part breaks, and the number of fractures is recorded.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] A new analysis method is adopted, in which the process of simulating constraints and load loading on the spring arm movement is closer to the actual test, the force analysis can converge better, and the accuracy problem caused by the complex force of the spring point of the spring arm can be solved. The analysis results are highly consistent with the actual experimental verification, which can identify risks in the early stage of design, improve development efficiency, and reduce development costs. It has the characteristics of high versatility and accurate calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A grid model diagram of a spring arm of the present invention;

[0028] Figure 2 It is a schematic diagram of fatigue analysis results in the nCode software of the present invention.

[0029] Reference numerals:

[0030] 1. Spring arm body, 2. Spring, 3. Reinforcement plate, 4. Spring pad, 5. Second weld, 6. Inner sleeve, 7. First weld, 8. Sleeve, A. First local coordinate system, B. Second local coordinate system, C. Inner point, D. Outer point. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] like Figure 1-2 As shown, the present invention solves the problem that the existing traditional fatigue analysis method cannot meet the fatigue analysis of a spring arm, a part with relatively complex motion and force, and provides the following technical solutions: a high-precision spring arm fatigue analysis method, comprising the following steps:

[0033] S1: The model is pre-processed by mesh pre-processing software, and the stress distribution of parts under fatigue conditions is calculated by finite element analysis method;

[0034] S2: Analyze fatigue life through fatigue analysis software;

[0035] S3: Compare the fatigue results obtained through experiments with the analytical values;

[0036] Wherein step S1 comprises the following steps:

[0037] S1.1: It includes establishing a geometric model of the spring arm and surrounding parts, including a model of a spring arm body 1, a reinforcing plate 3, a spring 2, a spring pad 4, a sleeve 8 and an inner bushing 6. The spring arm body 1 is located at the position of the vehicle in a stationary state, the spring pad 4 is assembled on the reinforcing plate 3, the upper end of the spring 2 is located at the actual position of the vehicle and the spring 2 is in a free state, and a first weld 7 is established between the spring arm body 1 and the reinforcing plate 3, and a second weld 5 is established between the spring arm body 1 and the sleeve 8. The above geometric model is imported into the mesh processing software to perform mesh division of each component part, create coupling, coordinate system, select the contact surface and then export it to obtain the final finite element model;

[0038] Among them, the central node of the inner point of the inner sleeve 6 is coupled to the inner wall of the sleeve 8 as a constraint point; the upper end of the spring 2 is coupled to any point on the end surface as a constraint point; the center of the lower end plane of the spring 2 cross section is used as the first loading point; the outer point D of the spring arm is coupled to the spring arm body 1 according to the size of the flange area as a loading point.

[0039] S1.2: Import the finite element model into the finite element analysis software to apply constraints and loads in the local or vehicle coordinate system, and calculate the stress under the fatigue condition. Specifically, a first local coordinate system A is established with the center of the inner bushing 6 as the coordinate center point, the Y axis of the first local coordinate system A is the axis of the inner bushing, and the X axis and the Z axis can be arbitrarily specified. A second local coordinate system B is established with the center of the spring 2 as the coordinate center point, the center line of the spring 2 is the X axis, and the Y axis and the Z axis can be arbitrarily specified;

[0040] The loading of constraints and loads includes the following five steps:

[0041] Step 1: Fully constrain the inner point C of the spring arm based on the first local coordinate system A, constrain the outer point D of the spring arm based on the three moving directions based on the vehicle coordinate system, fully constrain the upper point of spring 2 based on the global coordinate system, constrain the lower point of spring 2 based on the second local coordinate system B in the remaining five directions except the X-axis direction, and load the load in the X direction until the lower end of spring 2 is above the spring pad 4. The contact setting is removed in the whole process. The X-axis of the second local coordinate system B is along the central axial direction of spring 2, so the load in the X direction can compress spring 2 until its lower end is above the spring pad 4, but there is no contact with the spring pad 4. The outer point D constrained in three moving directions based on the vehicle coordinate system refers to constraining the movement of the outer point of the car wheel in the three moving directions of front and back, left and right, and up and down, but will not constrain the rotation of the outer point of the wheel;

[0042] Step 2: Based on the constraints in the first step, change the loading direction of the lower point of spring 2 until spring 2 just contacts spring pad 4. The whole process adds contact settings. Changing the loading direction of the lower point of spring 2 means reversing the load direction of spring 2 along the X direction, so that spring 2 is stretched until it just contacts spring pad 4. This can more accurately simulate the installation compression process of spring 2.

[0043] Step 3: Based on the constraints in the second step, release the freedom of the inner point C to rotate around the Y axis based on the second local coordinate system B, and release the constraints and loads on the lower point of the spring 2, so that it can naturally contact with the spring pad 4. Releasing the freedom of the inner point C allows the spring arm body 1 to automatically apply thrust to the spring pad 4 under the conditions of releasing the constraints and loads on the lower point of the spring 2, which is closer to the actual loading state and is more conducive to the convergence of the force analysis, and will not cause the load to be too large and exceed the critical value of the model;

[0044] Step 4: According to the three-dimensional force on the external point D in the third step, the three-dimensional force constraint of the external point D is changed to the three-dimensional force loading method, with a smooth transition, so that the analysis converges better, in preparation for the fifth step of full loading. The constraint is directly converted into the loading, which can simulate the loading force of the spring arm body 1 in the front and back, left and right, and up and down directions during the driving process of the wheel. Moreover, the constraint is directly converted into the loading to avoid starting the loading in these three directions from zero, and the upper limit of the loading is directly set. After the constraint force is converted into the loading, it is loaded to the upper limit, which is more realistic and accurate.

[0045] Step 5: According to the three-dimensional force loaded at the external point D in the fourth step, the force is smoothly transitioned to the actual load required by setting the default amplitude curve. The amplitude curve is used to load the external point D during the loading process, which is relatively smooth.

[0046] S1.3: Through the above five steps of analysis, the stress results of each fatigue condition required are obtained for fatigue analysis.

[0047] Among them, when meshing is performed in step S1.1, the mid-surface of the equal-wall thickness parts is extracted for meshing, and the mesh types are S4R and S3, among which the S3 mesh accounts for no more than 5% of the shell unit. The regular solid parts are meshed as hexahedral meshes with mesh types of C3D8R and C3D6, and the irregular solid parts are meshed as second-order tetrahedral meshes with mesh type of C3D10M. The mesh type of the weld connection unit is S4R. Different mesh types can be selected for division according to the specific structure of the spring arm, so as to better simulate the actual force of the spring arm.

[0048] In this embodiment, the definition of establishing a weld in step S1.1 specifically includes: a first weld 7 model established between the spring arm body 1 and the reinforcing plate 3 is connected by a 90° lap welding, the weld thickness is 3 mm, and the weld mesh type is S4R; a second weld 5 model is established between the spring arm body 1 and the sleeve 8 with a 45° fillet welding connection, the weld thickness is 3 mm, the weld mesh type is S4R, and the mesh unit normal directions of the first weld 7 and the second weld 5 face outward, so that the actual structure and strength of the first weld 7 and the second weld 5 can be more accurately simulated, making the test more accurate.

[0049] In this embodiment, step S2 specifically uses the EN module in the nCode software to calculate the body fatigue, and step S2 includes the following steps:

[0050] S2.1: Import the fatigue stress results obtained in step S1 into the FE Input module in the nCode software;

[0051] S2.2: Set parameters, assign materials, and define load cycles in the EN module;

[0052] S2.3: Display the results through the FEdisplay module and export the results through the FEOutput module.

[0053] Next, in step S3, a test bench is built according to the constraints and loading methods equivalent to those in the analysis, and cyclic loading of fatigue conditions is performed at a frequency of 2 Hz until the part breaks, and the number of fractures is recorded.

[0054] like Figure 2 As shown in the figure, the results are displayed by the FEdisplay module and exported by the FEOutput module, and the analysis life result is 43837. The cyclic loading of the fatigue condition is carried out at a frequency of 2Hz until the part breaks, and the number of fractures is recorded as 46786. Therefore, the accuracy of the analysis result compared with the test result is 93.7%, which is relatively high.

[0055] It can be seen that the results of the force analysis and online fatigue analysis of the control arm using the analysis method in this embodiment are very close to the results of the actual fatigue test.

[0056] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0057] In addition, in the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0058] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0059] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A high-precision spring arm fatigue analysis method, characterized in that: The steps include: S1: The model is pre-processed by mesh pre-processing software, and the stress distribution of parts under fatigue conditions is calculated by finite element analysis method; S2: Analyze fatigue life through fatigue analysis software; S3: Compare the fatigue results obtained through experiments with the analytical values; Wherein step S1 includes the following steps: S1.1: It includes establishing a geometric model of the spring arm and surrounding parts, including a model of the spring arm body (1), a reinforcing plate (3), a spring (2), a spring pad (4), a sleeve (8) and an inner bushing (6), wherein the spring arm body (1) is located at the position of the whole vehicle when the vehicle is stationary, the spring pad (4) is assembled on the reinforcing plate (3), the upper end of the spring (2) is located at the actual position of the whole vehicle and the spring (2) is in a free state, and a first weld (7) is established between the spring arm body (1) and the reinforcing plate (3), and a second weld (5) is established between the spring arm body (1) and the sleeve (8), and the above geometric model is imported into a mesh processing software to perform mesh division of each component, and then a coupling, a coordinate system, and contact surfaces are created and exported to obtain a final finite element model; S1.2: Import the finite element model into the finite element analysis software to apply constraints and loads in the local or whole vehicle coordinate system, and calculate the stress under the fatigue condition. Specifically, a first local coordinate system (A) is established with the center of the inner bushing (6) as the coordinate center point, the Y axis of the first local coordinate system (A) is the axis of the inner bushing, and the X axis and Z axis can be arbitrarily specified. A second local coordinate system (B) is established with the center of the spring (2) as the coordinate center point, the center line of the spring (2) is the X axis, and the Y axis and Z axis can be arbitrarily specified; The loading of constraints and loads includes the following five steps: Step 1: Fully constrain the inner point (C) of the spring arm based on the first local coordinate system (A), constrain the outer point (D) of the spring arm based on the three moving directions based on the vehicle coordinate system, fully constrain the upper point of the spring (2) based on the global coordinate system, constrain the lower point of the spring (2) based on the second local coordinate system (B) in the remaining five directions except the X-axis direction, and apply the load in the X direction until the lower end of the spring (2) is located above the spring pad (4). The contact setting is removed in the whole process; Step 2: Based on the constraints in the first step, change the loading direction of the lower point of the spring (2) until the spring (2) and the spring pad (4) are just in contact. The whole process includes contact settings. Step 3: Based on the constraints in the second step, release the freedom of the inner point (C) to rotate around the Y axis based on the second local coordinate system (B), and release the constraints and loads on the points under the spring (2) to make it naturally contact with the spring pad (4); Step 4: According to the three-dimensional force on the external point (D) in the third step, the three-dimensional force constraint of the external point (D) is changed to the three-dimensional force loading method, with a smooth transition to achieve better convergence of the analysis, in preparation for the full loading in the fifth step; Step 5: According to the three-dimensional force loaded at the external point (D) in step 4, the force is smoothly transitioned to the actual load required by setting the default amplitude curve; S1.3: Through the above five steps of analysis, the stress results of each fatigue condition required are obtained for fatigue analysis.

2. The high-precision spring arm fatigue analysis method according to claim 1 is characterized in that: When meshing is performed in step S1.1, the mid-surface of the parts with equal wall thickness is extracted for meshing, and the mesh types are S4R and S3, where the S3 mesh accounts for no more than 5% of the shell unit. The mesh of regular solid parts is divided into hexahedral meshes with mesh types of C3D8R and C3D6, and the mesh of irregular solid parts is divided into second-order tetrahedral meshes with mesh type of C3D10M. The mesh type of the weld connection unit is S4R.

3. The high-precision spring arm fatigue analysis method according to claim 2 is characterized in that: The welds defined and established in step S1.1 specifically include: a first weld (7) model established between the spring arm body (1) and the reinforcing plate (3) is connected by 90° lap welding, the weld thickness is 3 mm, and the weld mesh type is S4R; a second weld (5) model is established between the spring arm body (1) and the sleeve (8) by 45° fillet welding, the weld thickness is 3 mm, the weld mesh type is S4R, and the mesh unit normal directions of the first weld (7) and the second weld (5) face outwards.

4. The high-precision spring arm fatigue analysis method according to claim 1 is characterized in that: In step S2, the EN module in the nCode software is specifically used to calculate the fatigue of the main body. Step S2 includes the following steps: S2.1: Import the fatigue stress results obtained in step S1 into the FEInput module in the nCode software; S2.2: Set parameters, assign materials, and define load cycles in the EN module; S2.3: Display the results through the FEdisplay module and export the results through the FEOutput module.

5. The high-precision spring arm fatigue analysis method according to claim 1, characterized in that: In step S3, a test bench is built according to the constraints and loading methods equivalent to those in the analysis, and cyclic loading of fatigue conditions is performed at a frequency of 2 Hz until the part breaks, and the number of fractures is recorded.

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