A high-precision spring arm fatigue analysis method

Abstract

This invention discloses a high-precision fatigue analysis method for spring arms, comprising the following steps: S1: Preprocessing the model using mesh preprocessing software and calculating the stress distribution of the part under fatigue conditions using finite element analysis; S2: Analyzing the fatigue life using fatigue analysis software; S3: Comparing the fatigue results obtained through experiments with the analyzed values. The method closely approximates actual experiments in simulating the constraints and loads on the spring arm's motion, resulting in better convergence of the force analysis. It addresses the accuracy issues caused by the complex forces at the spring points of the spring arm, and the analysis results show high consistency with actual experimental verification. This allows for early risk identification in the design phase, improving development efficiency and reducing development costs. It features high versatility and accurate calculation results.

Description

Technical Field

[0001] This invention relates to the field of fatigue testing technology for automotive parts, specifically a high-precision fatigue analysis method for spring arms. Background Technology

[0002] Fatigue analysis of automotive chassis is widely used, allowing for the early prediction of component failure risks during the design phase. However, for components with complex motion and stress distribution, such as spring arms, the analysis accuracy is lower. Conventional spring points are achieved by flexibly coupling the spring contact surface and applying loads. However, this method fails to capture the uneven stress distribution on the spring arm during its vertical movement, resulting in extremely poor accuracy in localized areas. Consequently, it is difficult to effectively converge the stress analysis during the simulation of constraints and loads, leading to significant discrepancies between the stress results under fatigue conditions and actual experimental data. Summary of the Invention

[0003] This invention provides a high-precision fatigue analysis method for spring arms, which can solve the problem that existing traditional fatigue analysis methods cannot meet the fatigue analysis requirements of parts such as spring arms with complex motion and stress.

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

[0005] S1: The model is preprocessed using mesh preprocessing software, and the stress distribution of the part under fatigue conditions is calculated using the finite element analysis method.

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

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

[0008] Step S1 includes the following steps:

[0009] S1.1: This includes establishing the geometric model of the spring arm and surrounding parts, including the model of the spring arm body, reinforcing plate, spring, spring pad, sleeve and inner bushing. The spring arm body is located at the vehicle's stationary position. The spring pad is assembled onto the reinforcing plate. The upper end of the spring is located at the actual position of the vehicle and the spring is in a free state. A first weld is established between the spring arm body and the reinforcing plate, and a second weld is established between the spring arm body and the sleeve. After importing the above geometric model into the mesh processing software, the mesh of each component is generated. After creating coupling, coordinate system, and selecting contact surface, the model is exported to obtain the final finite element model.

[0010] S1.2: Import the finite element model into the finite element analysis software, apply constraints and loads in the local or whole vehicle coordinate system, and calculate the stress under fatigue conditions. Specifically, establish a first local coordinate system 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 Z-axis can be arbitrarily specified. Establish a second local coordinate system 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 Z-axis can be arbitrarily specified.

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

[0012] Step 1: Fully constrain the inner point of the spring arm under the first local coordinate system, constrain the outer point of the spring arm under the vehicle coordinate system in three directions of movement, fully constrain the upper point of the spring under the global coordinate system, and constrain the lower point of the spring under the second local coordinate system in the other 5 directions except the X-axis direction. Apply a load in the X-direction until the lower end of the spring is above the spring pad. The contact setting is removed throughout the process.

[0013] Step 2: Based on the constraints of Step 1, change the loading direction of the lower point of the spring until the spring and the spring pad just make contact. Contact settings are added to the whole process.

[0014] Step 3: Based on the constraints of Step 2, release the degree of freedom of the interior point to rotate around the Y-axis in the second local coordinate system, and release the constraints and loading of the lower point of the spring so that it can make natural contact with the spring pad.

[0015] Step 4: Based on the triaxial force on the external point in Step 3, change the triaxial force constraint on the external point to a triaxial force loading method for a smooth transition, so that the analysis converges better and prepares for the full loading in Step 5.

[0016] Step 5: Based on the triaxial force applied at the external point in Step 4, smoothly transition the force to the actual load that needs to be applied by setting the default amplitude curve;

[0017] S1.3: The stress results for each fatigue condition are obtained through the above five steps of analysis, which are used for fatigue analysis.

[0018] Furthermore, in step S1.1, when meshing, the mid-surface of the uniform wall thickness part is extracted for meshing, and the mesh types are S4R and S3. Among them, the proportion of S3 mesh does not exceed 5% of the shell element. The regular solid part is meshed as a hexahedral mesh with mesh types C3D8R and C3D6. The irregular solid part is meshed as a second-order tetrahedral mesh with mesh type C3D10M. The weld connection element mesh type is S4R.

[0019] Preferably, step S1.1 defines the establishment of the weld as follows: the first weld model between the spring arm body and the reinforcing plate is connected by a 90° lap weld, the weld thickness is 3mm, and the weld mesh type is S4R; the second weld model between the spring arm body and the sleeve is connected by a 45° fillet weld, the weld thickness is 3mm, the weld mesh type is S4R, and the normal direction of the mesh elements of the first weld and the second weld is outward.

[0020] Preferably, step S2 specifically uses the EN module in the nCode software to calculate the body fatigue. 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: Parameter settings, material assignment, and load cycle definition are performed in the EN module;

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

[0024] As a preferred option, in step S3, an experimental rig is built with the same constraints and loading methods as the analysis, and fatigue conditions are cyclically loaded at a frequency of 2Hz until the part breaks, and the number of fractures is recorded.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] A new analysis method is adopted, which is closer to the actual test in simulating the constraint and load of the spring arm motion. The force analysis can converge better, which can solve the accuracy problem caused by the complex force of the spring arm spring point. The analysis results are highly consistent with the actual experimental verification. It can identify risks in the early stage of design, improve development efficiency, reduce development costs, and has the characteristics of high versatility and accurate calculation results. Attached Figure Description

[0027] Figure 1 This is a mesh model diagram of the spring arm of the present invention;

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

[0029] Figure label:

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

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

[0032] like Figure 1-2 As shown, this invention addresses the problem that existing traditional fatigue analysis methods cannot meet the fatigue analysis requirements of components like spring arms with complex motion and stress, and provides the following technical solution: A high-precision fatigue analysis method for spring arms, comprising the following steps:

[0033] S1: The model is preprocessed using mesh preprocessing software, and the stress distribution of the part under fatigue conditions is calculated using the finite element analysis method.

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

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

[0036] Step S1 includes the following steps:

[0037] S1.1: This includes establishing the geometric model of the spring arm and surrounding parts, including the models of the spring arm body 1, reinforcing plate 3, spring 2, spring pad 4, sleeve 8, and inner bushing 6. The spring arm body 1 is located at the vehicle's stationary position. The spring pad 4 is assembled onto 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. 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. After importing the above geometric model into the mesh processing software, the mesh of each component is generated. After creating coupling, coordinate system, and selecting contact surface, the model is exported to obtain the final finite element model.

[0038] Specifically, the inner center node of the inner bushing 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 face as a constraint point; the center of the lower plane of the spring 2 section is used as the first loading point; and the outer point D of the spring arm is coupled to the spring arm body 1 according to the flange area as a loading point.

[0039] S1.2: Import the finite element model into the finite element analysis software, apply constraints and loads in the local or whole vehicle coordinate system, and calculate the stress under fatigue conditions. Specifically, establish a first local coordinate system A 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. Establish a second local coordinate system B 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.

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

[0041] Step 1: Fully constrain the inner point C of the spring arm under the first local coordinate system A, constrain the outer point D of the spring arm in three directions under the vehicle coordinate system, fully constrain the upper point of spring 2 under the global coordinate system, and constrain the lower point of spring 2 in the other five directions except the X-axis under the second local coordinate system B. Apply a load in the X-direction until the lower end of spring 2 is above 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 axis of spring 2, so the load in the X-direction can compress spring 2 until its lower end is above spring pad 4, but without contacting spring pad 4. The constraint of the outer point D in three directions under the vehicle coordinate system refers to constraining the movement of the outer point of the car wheel in the three directions of front-back, left-right and up-down, but does not constrain the rotation of the outer point of the wheel.

[0042] Step 2: Based on the constraints of Step 1, change the loading direction of the lower point of spring 2 until spring 2 just contacts spring pad 4. The entire process incorporates 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 and compression process of spring 2.

[0043] Step 3: Based on the constraints of Step 2, release the degree of freedom of the interior point C to rotate around the Y-axis in the second local coordinate system B, and release the constraints and loads on the lower point of spring 2 so that it can naturally contact the spring pad 4. Releasing the degree of freedom of the interior point C allows the spring arm body 1 to apply a pushing force to the spring pad 4 on its own under the condition that the constraints and loads on the lower point of spring 2 are released, which is closer to the actual loading state and is more conducive to the convergence of the force analysis. It will not cause the load to be too large and exceed the critical value of the model.

[0044] Step 4: Based on the triaxial force on the external point D in Step 3, change the triaxial force constraint on the external point D to a triaxial force loading method. This smooth transition makes the analysis converge better and prepares for the full loading in Step 5. Directly converting the constraint into a loading method can simulate the loading force on the spring arm body 1 in the front-back, left-right, and up-down directions during the wheel's movement. Moreover, directly converting the constraint into a loading method avoids starting the loading in these three directions from zero. Instead, the upper limit of the loading is set directly, and the constraint force is converted into a loading method before loading to the upper limit, which is more realistic and accurate.

[0045] Step 5: Based on the triaxial force applied at point D in step 4, the force is smoothly transitioned to the actual load by setting a default amplitude curve. Applying the load at point D using the amplitude curve method results in a smoother loading process.

[0046] S1.3: The stress results for each fatigue condition are obtained through the above five steps of analysis, which are used for fatigue analysis.

[0047] In step S1.1, when meshing, the mid-surface of the uniform wall thickness part is extracted for meshing, and the mesh types are S4R and S3. The proportion of S3 mesh does not exceed 5% of the shell element. The regular solid part is meshed as a hexahedral mesh with mesh types C3D8R and C3D6. The irregular solid part is meshed as a second-order tetrahedral mesh with mesh type C3D10M. The weld connection element mesh type is S4R. Different mesh types can be selected for meshing according to the specific structure of different spring arms, so as to better simulate the actual force of the spring arm.

[0048] In this embodiment, the definition of establishing the weld in step S1.1 specifically includes: establishing a first weld 7 model between the spring arm body 1 and the reinforcing plate 3 with a 90° lap weld connection, a weld thickness of 3mm, and a weld mesh type of S4R; establishing a second weld 5 model between the spring arm body 1 and the sleeve 8 with a 45° fillet weld connection, a weld thickness of 3mm, and a weld mesh type of S4R. The normal direction of the mesh unit of the first weld 7 and the second weld 5 faces outward, which can more accurately simulate the actual structure and strength of the first weld 7 and the second weld 5, making the test more accurate.

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

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

[0051] S2.2: Parameter settings, material assignment, and load cycle definition are performed in the EN module;

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

[0053] Next, in step S3, an experimental platform is built using the same constraints and loading methods as the analysis, and fatigue conditions are cyclically loaded at a frequency of 2Hz until the part breaks, and the number of fractures is recorded.

[0054] like Figure 2 As shown, the results are displayed through the FE module and exported through the FEOutput module. The lifespan analysis result is 43837. Furthermore, cyclic loading under fatigue conditions at a frequency of 2Hz was applied until the part fractured, recording 46786 fractures. Therefore, the accuracy of the analysis results compared to the experimental results is 93.7%, which is relatively high.

[0055] It is evident that the results of force analysis and online fatigue analysis of the control arm using the analysis method in this embodiment are very close to the results of actual fatigue tests.

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

[0057] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0058] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A high-precision fatigue analysis method for spring arms, characterized in that, Includes the following steps: S1: The model is preprocessed using mesh preprocessing software, and the stress distribution of the part under fatigue conditions is calculated using the finite element analysis method. S2: Analyze fatigue life using fatigue analysis software; S3: Compare the fatigue results obtained through experiments with the analytical values; Step S1 includes the following steps: S1.1: This includes establishing a geometric model of the spring arm and surrounding parts, including the spring arm body (1), reinforcing plate (3), spring (2), spring pad (4), sleeve (8) and inner bushing (6). The spring arm body (1) is located at the vehicle position 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 vehicle and the spring (2) is in a free state. 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 generation of each component, create coupling, coordinate system, select contact surface and export to obtain the final finite element model. S1.2: Import the finite element model into the finite element analysis software and apply constraints and loads in the local or whole vehicle coordinate system to calculate the stress under fatigue conditions. Specifically, establish a first local coordinate system (A) 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. Establish a second local coordinate system (B) 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 application 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 vehicle coordinate system in three directions of movement, 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 other 5 directions except the X-axis direction, and apply a load in the X-direction until the lower end of the spring (2) is above the spring pad (4). The contact setting is removed throughout the process. Step 2: Based on the constraints of Step 1, change the loading direction of the lower point of spring (2) until spring (2) and spring pad (4) just come into contact. Contact setting is added to the whole process. Step 3: Based on the constraints of Step 2, release the degree of freedom of the interior point (C) to rotate around the Y-axis in the second local coordinate system (B), and release the constraint and loading of the lower point of the spring (2) so that it can naturally contact the spring pad (4); Step 4: Based on the triaxial force on the external point (D) in Step 3, change the triaxial force constraint on the external point (D) to a triaxial force loading method for a smooth transition, so that the analysis converges better and prepares for the full loading in Step 5. Step 5: Based on the triaxial force applied at the external point (D) in step 4, smoothly transition the force to the actual load required by setting the default amplitude curve; S1.3: The stress results for each fatigue condition are obtained through the above five steps of analysis, which are used for fatigue analysis.

2. The high-precision fatigue analysis method for spring arms according to claim 1, characterized in that: In step S1.1, when meshing, the mid-surface of the uniform wall thickness part is extracted for meshing, and the mesh types are S4R and S3. The proportion of S3 mesh does not exceed 5% of the shell element. The regular solid part is meshed as a hexahedral mesh with mesh types C3D8R and C3D6. The irregular solid part is meshed as a second-order tetrahedral mesh with mesh type C3D10M. The weld connection element mesh type is S4R.

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

4. The high-precision fatigue analysis method for spring arms according to claim 1, characterized in that: Step S2 specifically uses the EN module in the nCode software to calculate the fatigue of the body. Step S2 includes the following steps: S2.1: Import the fatigue stress results obtained in step S1 into the FEInput module of the nCode software; S2.2: Parameter settings, material assignment, and load cycle definition are performed in the EN module; S2.3: Display the results using the FEdisplay module and export the results using the FEOutput module.

5. The high-precision fatigue analysis method for spring arms according to claim 1, characterized in that: In step S3, an experimental platform is built using the same constraints and loading methods as the analysis. The fatigue condition is cyclically loaded at a frequency of 2Hz until the part breaks, and the number of fractures is recorded.

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