A fatigue analysis calculation method for automobile shock absorber

Abstract

The fatigue analysis calculation method for the automobile shock absorber of the present application comprises the following steps: Step 1: whole vehicle experiment is carried out to obtain the load spectrum at the wheel center and the acceleration spectrum at the wheel center is measured; Step 2: the positions of the hard points of the automobile suspension are measured, and a whole vehicle multi-body dynamics model is built; Step 3: the wheel center load spectrum is input into the Adams software for simulation calculation, and the shock absorber load spectrum and the wheel center acceleration spectrum are extracted; Step 4: the experimental and simulated wheel center acceleration spectrums are verified, and are converted into corresponding frequency spectrum densities for secondary verification, so as to ensure the accuracy of the simulation results; Step 5: the model is secondarily developed in Hypermesh; Step 6: the fatigue calculation block in the Hypermesh software is entered, and the fatigue simulation calculation is carried out in combination with the S-N curve fitted by the software. According to different needs, the fatigue simulation calculation of the automobile shock absorber can be carried out, the action of the road load of the shock absorber can be truly simulated, the fatigue simulation calculation accuracy of the automobile shock absorber is improved, and the research and development period is reduced.

Description

Technical Field

[0001] This invention relates to the field of fatigue analysis of automotive shock absorbers, and more specifically to a fatigue analysis method for automotive shock absorbers. Background Technology

[0002] Shock absorbers are crucial components of a vehicle's suspension system, mitigating impacts from the road surface and absorbing vibrations during driving. Their performance directly affects a vehicle's safety and comfort. Therefore, fatigue research can help identify and prevent cracks that may lead to shock absorber failure, thereby avoiding oil and air leaks, ensuring the long-term stable operation of the shock absorbers, and safeguarding passenger comfort and safety.

[0003] Currently, there are two main methods for fatigue analysis of automotive shock absorbers. The first method relies solely on experiments. While the measured fatigue data is relatively accurate, it suffers from drawbacks such as long development cycles and high costs. The second method combines experiments with simulation. The common process in China involves using a road surface scanner to collect road surface data, establishing a high-precision road surface model, performing virtual road surface simulation on the established vehicle model to obtain the load spectrum, then using simulation software to perform fatigue calculations, and finally comparing the results with experimental data. This method requires significant time, manpower, and resources, resulting in long development cycles, high costs, and uncertain accuracy.

[0004] The key to fatigue analysis and calculation of automotive shock absorbers lies in obtaining an accurate load spectrum, establishing an accurate simulation model of the whole vehicle and shock absorber, shortening the simulation time, and selecting an appropriate fatigue stress correction method. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a fatigue analysis and calculation method for automotive shock absorbers. This method utilizes a six-component force sensor at the wheel center to measure the load spectrum of the actual wheel center, then extracts the load spectrum on the shock absorber in Adams software, and establishes a finite element model of the shock absorber in Hypermesh for strength simulation. The simulation process is then simplified through secondary development, thereby enabling fatigue analysis and calculation of the shock absorber.

[0006] The technical solution of the present invention is as follows:

[0007] A fatigue analysis calculation method for automotive shock absorbers includes the following steps:

[0008] Step 1: Use a wheel center six-component force instrument to conduct a whole vehicle experiment to obtain the load spectrum at the wheel center and simultaneously measure the acceleration spectrum at the wheel center;

[0009] Step 2: Measure the positions of each hard point of the car suspension and build a multibody dynamics model of the whole vehicle in Adams software;

[0010] Step 3: Input the load spectrum at the wheel center into Adams software for simulation calculation, and extract the damper load spectrum and wheel center acceleration spectrum;

[0011] Step 4: Verify the experimental and simulated wheel center acceleration spectra, and convert them into the corresponding frequency spectral density for secondary verification. Observe whether the trends of the two are consistent. If the trends are inconsistent, compare the hard point positions of the actual vehicle suspension and adjust the hard points in Adams software until the trends are basically consistent to ensure the accuracy of the simulation results.

[0012] Step 5: Import the shock absorber assembly model into Hypermesh software, perform structural simplification, simplify the Hypermesh secondary development process, establish the corresponding connection settings, set the corresponding materials and properties and mesh, set the boundaries, and perform strength simulation under inertial release conditions.

[0013] Step 6: Enter the fatigue calculation module in Hypermesh software, import the strength simulation results and select the corresponding stress correction method. At the same time, load the load spectrum extracted in Step 3 and align the output channels. Combine the SN curve fitted by the software to perform fatigue simulation calculation.

[0014] Furthermore, in the fatigue analysis and calculation method for automotive shock absorbers of the present invention, step 5 is specifically as follows:

[0015] 5.1 Secondary Development: (1) Material Creation and Attribute Assignment: Use the command *createentity mats cardimage=MAT1 includeid=0name=$matname to create a material card and assign density, Poisson's ratio and elastic modulus to variables such as *setvalue mats name=$matname STATUS=11=$E, *setvalue mats name=$matname STATUS=13=$nu, and *setvalue mats name=$matname STATUS=14=$rho. Use the command if{! [hm_entityinfo exist mats$matname-byname]} to check if there are duplicate materials. Use the command if{[string equal$proptype**]} to judge the selected attribute. According to the attribute, the PSHELL attribute displays "thickness", the PBARL attribute displays "radius", and the PSOLID attribute displays "NO DATA". Finally, use the command *setvalueprops id=$propid materialid={mats$matid} to assign materials and attributes. (2) Mesh generation and inspection module: The selected mesh type is determined by the if{[string equal$element_type"**"]} command, and then each face is meshed by a for loop. After the meshing is completed, the mesh inspection interface is called by the proc**{}{hm_callpanel**} command to adjust the mesh quality. (3) Washer module: The *createmarkpanel comps 1"pleaseselect comps" command selects the components to be added to the washer. First, the node number of each hole is obtained by foreach traversal, and then the first node number of each hole node is obtained by foreach traversal again. These node numbers are defined in a variable. Finally, the *createstringarray 2"layer_number=1uniform_layers=1hole_density=6""0 1.0" and *add_multi_washer_elements 230121200 commands are used to create washer to improve the mesh quality around the hole.(4) Boundary Condition Module: Use the command *collectorcreate loadcols"**"""12 to create Loda Collectors in batches. Use the commands *currentcollector loadcols"***", *createmark nodes 1****, and *loadcreateonentity_curve nodes to create unit forces and unit moments in batches. Finally, use the commands *loadstepscreate"***"1 and *setvalue loadsteps id=1STATUS=14147={Loadcols*} to create Load Steps in batches and assign unit forces and unit moments to them. Then, use the command *feoutputwithdata"D: / ProgramFiles / Altair / 2021 / hwdesktop / tem plates / feoutput / optistruct / optistruct""*: / * / *" to perform strength simulation.

[0016] 5.2 Model Simplification: The valve system model in the shock absorber assembly is simplified into solid parts;

[0017] 5.3 Mesh Generation: In the mesh generation stage, shell elements are used for parts such as sleeves and supports, while solid elements are used for parts such as pistons and piston rods.

[0018] 5.4 Define material properties: Assign the mechanical properties of each component of the shock absorber to isotropic linear elastic materials. The material density, elastic modulus and Poisson's ratio are based on the measured material.

[0019] 5.5 Connection Settings: RBE2 is used to simulate bolted connections between supports, SEAM is used to simulate welding between components, and Spot is used to simulate weld points between outer and inner supports. Contact settings are divided into two types: TIE and CONTACT. The control card can be selected as inertial release or automatic constraint.

[0020] 5.6 Define the load: Set unit force and unit torque in the x, y, and z directions, with the loading point on the simulated bolt, to obtain the complete finite element model of the car shock absorber;

[0021] Furthermore, in the fatigue analysis and calculation method for automotive shock absorbers of the present invention, step 4 is to verify the experimental and simulated wheel center acceleration spectra, and at the same time convert them into the corresponding frequency spectral density for secondary verification, and observe whether the trends of the two are consistent. If the trends are inconsistent, the hard point positions of the actual vehicle suspension are compared, and the hard points are adjusted in Adams software until the trends are basically consistent, so as to ensure the accuracy of the simulation results.

[0022] Furthermore, in the fatigue analysis and calculation method for automotive shock absorbers of the present invention, step 6 is specifically as follows:

[0023] 6.1. Import the calculation results from step 5 into the Hypermesh fatigue calculation module;

[0024] 6.2 Select a suitable stress correction algorithm and fit the SN curve according to the material properties;

[0025] 6.3 Import the load spectrum, align the channels of the load spectrum, and perform fatigue simulation analysis.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention uses the load spectrum measured by a six-component force sensor at the wheel center as a basis to construct a simulation model of the entire vehicle in Adams. To ensure the accuracy of the geometric model and the reliability of motion, the experimental and simulated wheel center acceleration spectra are verified, and simultaneously converted into corresponding frequency spectral densities for secondary verification. The consistency of the trends of the two is observed to ensure the accuracy of the simulation results. The collected load spectrum is input into Adams software for whole-vehicle simulation, and the load spectrum on the shock absorber is extracted. A shock absorber simulation model is built in Hypermesh software, and a simplified Hypermesh secondary development process is performed. This process includes selecting an appropriate mesh type, defining material properties, connection settings, defining loads, and mesh generation. Then, unit force intensity simulation under relational release conditions is performed to ensure the accuracy and reliability of the finite element model and simplify the simulation process. Finally, the simulation results are imported into the fatigue calculation module, Goodman nominal stress correction is selected, the load spectrum is imported and the channels are aligned, and fatigue simulation is performed using the SN curve fitted by the software. This method can realize fatigue simulation analysis of automotive shock absorbers under different parameters according to different needs.

[0028] Compared with existing technologies, this invention establishes a geometric model by measuring the actual dimensions of the vehicle structure and verifies the accuracy of the whole-vehicle simulation results using experimental and simulated wheel center acceleration. Furthermore, it verifies the feasibility and reliability of the load spectrum signals by performing pre-report processing on the collected load spectrum signals in Ncode software. The invention simplifies the valve system components inside the shock absorber, using rbe2 to simulate bolt connections, employing seam welding, and using spot welding for the weld seams. Contact settings are divided into TIE and CONTACT types, resulting in higher computational efficiency, accuracy, and reliability. The use of Hypermsh secondary development code simplifies the simulation process and significantly shortens simulation time. Simultaneously, this invention can also perform simulation evaluation in the early stages of shock absorber design, reducing prototype manufacturing costs, shortening the development cycle, and improving human-machine efficiency. Attached Figure Description

[0029] Figure 1Flowchart of the fatigue analysis method for automotive shock absorbers provided by this invention;

[0030] Figure 2 The six-component force load spectrum of the left front wheel of an automobile provided by the present invention;

[0031] Figure 3 The result of the Ncode software signal pre-reporting processing provided by this invention;

[0032] Figure 4 The full vehicle simulation model in Adams provided by this invention;

[0033] Figure 5 The experimental and simulated wheel center acceleration spectrum comparison verification results provided for this invention;

[0034] Figure 6 The finite element model of the automobile shock absorber is provided in a specific embodiment of the present invention;

[0035] Figure 7 Various modified stress method curves provided for this invention;

[0036] Figure 8 The fatigue life cloud map of the automobile shock absorber fatigue simulation provided in the embodiments of the present invention;

[0037] Figure 9 The image shows the actual failure of the fatigue test structure of the automobile shock absorber provided by this invention. Detailed Implementation

[0038] To make the objectives, advantages, and technical solutions of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the embodiments described below are only for explaining the invention and are not limited to it. The invention will be described in detail below, and through these details, those skilled in the art will fully understand the invention.

[0039] See Figure 1-9 The fatigue analysis and calculation method for automotive shock absorbers of the present invention comprises the following specific steps:

[0040] Step 1: Use a wheel center six-component force instrument to conduct a whole vehicle experiment to obtain the load spectrum at the wheel center and simultaneously measure the acceleration spectrum at the wheel center;

[0041] Step 2: Measure the positions of each hard point of the car suspension and build a multibody dynamics model of the whole vehicle in Adams software;

[0042] Step 3: Input the load spectrum at the wheel center into Adams software for simulation calculation, and extract the damper load spectrum and wheel center acceleration spectrum;

[0043] Step 4: Verify the experimental and simulated wheel center acceleration spectra, and convert them into the corresponding frequency spectral density for secondary verification. Observe whether the trends of the two are consistent. If the trends are inconsistent, compare the hard point positions of the actual vehicle suspension and adjust the hard points in Adams software until the trends are basically consistent to ensure the accuracy of the simulation results.

[0044] Step 5: Import the shock absorber assembly model into Hypermesh software, simplify the structure, perform secondary development of Hypermesh software to simplify the simulation process, establish corresponding connection settings, set corresponding materials and properties, mesh, set boundaries, and perform strength simulation under inertial release conditions; Step 5 specifically includes: simplifying the valve system model in the shock absorber assembly into solid parts; in the mesh generation stage, shell elements are used for parts such as sleeves and brackets, and solid elements are used for parts such as pistons and piston rods; assigning isotropic linear elastic materials to the mechanical properties of each component of the shock absorber, with material density, elastic modulus, and Poisson's ratio based on measured material values; connection settings: rbe2 is used to simulate bolt connections between brackets, seam is used to simulate welding between components, spot is used to simulate weld points between outer and inner brackets, contact settings are divided into TIE and CONTACT, and the control card is selected for inertial release and automatic constraint; define loads: set unit force and unit torque in the x, y, and z directions, with the loading point being the simulated bolts, to obtain a complete finite element model of the automotive shock absorber;

[0045] Step 6: Enter the fatigue calculation module in Hypermesh software, import the strength simulation results and select the corresponding stress correction method. At the same time, load the extracted load spectrum and align the output channels. Combine the SN curve fitted by the software to perform fatigue simulation calculation.

[0046] Example:

[0047] Road spectrum collection experiments were conducted on Belgian roads, and the sensor placement locations are shown in Table 1. The collected load spectra are as follows: Figure 2 As shown, the collected load spectra are input into Ncode software for pre-report analysis, such as... Figure 3 As shown, the amplitude, power spectral density, and rainflow count data are analyzed to improve the reliability and feasibility of the signal data. Hard point locations are extracted from the suspension model, thereby establishing a full vehicle model in Adams software, such as... Figure 4 As shown. The load spectrum obtained from the experiment was input into Adams software for whole-vehicle simulation. The load spectrum on the shock absorber was extracted from the simulation results. At the same time, the wheel center acceleration was extracted and compared with the wheel center acceleration obtained from the experiment. Simultaneously, it was converted into the corresponding frequency spectral density for secondary verification, such as... Figure 5As shown, the trends of the acceleration frequency spectral density obtained from the experiment and simulation are basically consistent, which can demonstrate the accuracy of the simulation results. (When implementing this invention, if the trends are inconsistent, the hard point positions of the actual vehicle suspension are compared, and the hard points are adjusted in Adams software until the trends are basically consistent.)

[0048] Table 1 Sensor Settings

[0049]

[0050] Finite element models are built based on geometric models. The geometric model of an automotive shock absorber device is relatively complex. In order to improve the model calculation efficiency and reduce the workload of building the finite element model, the geometric cleanup tool in Hypermesh is used to remove geometric features that have little impact on the analysis results, such as positioning holes and chamfers. The structure of the geometric model that is difficult to mesh is simplified, reducing the modeling difficulty, such as the scale used for model positioning.

[0051] Secondary development of Hypermesh software was carried out. (1) Material creation and attribute assignment: The material card was created using the command *createentitymats cardimage=MAT1 includeid=0name=$matname. The density, Poisson's ratio and elastic modulus were assigned by the variables *setvalue mats name=$matname STATUS=1 1=$E、*setvalue mats name=$matnameSTATUS=13=$nu、*setvalue mats name=$matname STATUS=14=$rho. The if{! [hm_entityinfo exist mats$matname-byname]} command was used to check if there were materials with the same name. The if{[string equal$proptype**]} command was used to judge the selected attribute. According to the attribute, the PSHELL attribute showed "thickness", the PBARL attribute showed "radius", and the PSOLID attribute showed "NO DATA". Finally, the material and attribute were assigned by the command *setvalue props id=$propid materialid={mats$matid}. (2) Mesh generation and inspection module: The selected mesh type is determined by the if{[string equal$element_type"**"]} command, and then each face is meshed by a for loop. After the meshing is completed, the mesh inspection interface is called by the proc**{}{hm_callpanel**} command to adjust the mesh quality. (3) Washer module: The *createmarkpanel comps1"please select comps" command selects the components to be added to the washer. First, the node number of each hole is obtained by foreach traversal, and then the first node number of each hole node is obtained by foreach traversal again. These node numbers are defined in a variable. Finally, the *createstringarray 2"layer_number=1uniform_layers=1hole_density=6""01.0" and *add_multi_washer_elements 230121200 commands are used to create washer to improve the mesh quality around the hole.(4) Boundary Condition Module: Use the command *collectorcreate loadcols"**"""12 to create LodaCollectors in batches. Use the commands *currentcollector loadcols"***", *createmark nodes 1****, and *loadcreateonentity_curve nodes to create unit forces and unit moments in batches. Finally, use the commands *loadstepscreate"***"1 and *setvalue loadsteps id=1STATUS=14147={Loadcols*} to create Load Steps in batches and assign unit forces and unit moments to them. Then, use the command *feoutputwithdata"D: / ProgramFiles / Altair / 2021 / hwdesktop / tem plates / feoutput / optistruct / optistruct""*: / * / *" to perform strength simulation.

[0052] The model mesh was generated in the Optistruct environment. For components with simple geometry in the main body of the shock absorber model, the midsurface was extracted using Geom's midsurface method for mesh generation, with quadrilateral meshes. The mesh sizes for the outer cylinder, inner cylinder, upper support, lower support, and stabilizer bar support were 2mm, 1.5mm, 2.5mm, 2.3mm, and 3.2mm, respectively. For components with complex structures such as the spring disc, outer support, and inner support, the midsurface was extracted using the offset method, i.e., the component surface was extracted first, and then offset by half the thickness. Shell elements were used for mesh generation, with quadrilateral meshes selected. The mesh sizes for the spring disc, outer support, and inner support were 3mm, 2.3mm, and 2.3mm, respectively. The control mass was controlled according to the element conditions shown in Table 2, and the remaining solid components were meshed using hexahedral meshes.

[0053] Table 2. Cell Grid Quality Control Conditions

[0054] category Quadrilateral unit Triangular unit hexahedral unit wedge unit Tetrahedral unit Aspect Ratio ≤5.0 ≤5.0 ≤5.0 ≤5.0 ≤5.0 Warp ≤16° ≤18° ≤18° Skewness ≤60° ≤60° ≤60° ≤60° ≤60° inner angle 40°～135° 20°～120° 40°～135° 20°～120° 20°～120°

[0055] Welding connections between components are defined using the `SEAM` keyword, while weld points between the outer and inner supports are defined using the `SPORT` keyword. Contact settings are divided into two types: `TIE` and `CONTACT`. `TIE` connections are used to fix two components, such as between the outer support and the outer cylinder; `CONTACT` connections are used between components that move relative to each other, such as between the piston and the inner cylinder. To prevent element penetration, a `PCONT` attribute needs to be created. The bolted connections of the supports are simulated using `reb2`. Unit forces and unit moments in the x, y, and z directions are applied at the simulated bolts. An inertial release control card is set, with `AUTOSPC` set to `Yes` and `INREL` set to `-2` for strength simulation.

[0056] This embodiment establishes a complete finite element model of an automotive shock absorber, and the final finite element model is as follows: Figure 6 As shown. Open the FatigueProcess tool in Hypermesh software to create a new fatigue analysis process, import the strength simulation results from the previous steps, and apply the material properties and the formula conclusions of the modified stress method, such as... Figure 7 As shown. The Goodman method was selected for calculation. The yield strength and tensile strength of the material were input into the software for fitting to obtain the SN curve of the material. The properties of the component to be calculated and the material were set in the software. The load spectrum of the vibration damper extracted from the simulation was imported and matched one-to-one with the force and moment channels set in the strength simulation to perform fatigue simulation analysis of the vibration damper. The results are as follows. Figure 8 As shown.

[0057] After fatigue simulation analysis of the vibration damper, the fatigue simulation results are compared with experimental results (such as...). Figure 9 The results (as shown) were compared and verified. The comparison showed that the fatigue simulation results for areas with shorter lifespans largely matched the failure locations of the experimental dampers, verifying the accuracy of the simulation method. For dampers that did not meet fatigue requirements during simulation, the model's morphology parameters and material performance parameters can be directly modified during the design phase, followed by simulation tests. Compared to the traditional design process, which involves fabricating damper prototypes for evaluation and then making modifications, this method can significantly shorten the design cycle.

[0058] The fatigue analysis and calculation method for automotive shock absorbers provided by this invention can extract the load spectrum on the shock absorber by inputting the load spectrum obtained from the whole vehicle test into the simulation software, and build a finite element model of the shock absorber for simulation calculation, thereby achieving the purpose of evaluating the fatigue life of the shock absorber.

[0059] The foregoing general description of the invention and its specific embodiments should not be construed as a limitation on the technical solution of the invention. Those skilled in the art, based on the disclosure of this application, can add, reduce, or combine the disclosed technical features in the foregoing general description and / or specific embodiments (including examples) without departing from the constituent elements of the invention, to form other technical solutions within the scope of protection of this application.

Claims

1. A fatigue analysis calculation method for an automobile shock absorber, characterized by, It comprises the following steps: Step 1: Obtain the load spectrum at the wheel center by using the wheel center six-component force instrument to conduct a whole vehicle experiment, and measure the acceleration spectrum at the wheel center; Step 2: Measure the positions of the hard points of the automobile suspension, and build a whole vehicle multi-body dynamics model in Adams software; Step 3: Input the load spectrum at the wheel center into Adams software to perform simulation calculation, and extract the shock absorber load spectrum and the wheel center acceleration spectrum; Step 4: Verify the experimental wheel center acceleration spectrum and the simulation wheel center acceleration spectrum, and convert them into corresponding frequency spectrum densities for secondary verification, observe whether the trends of the two are consistent, if the trends are inconsistent, compare the hard point positions of the actual vehicle suspension, adjust the hard points in the Adams software until the trends are basically consistent, so as to ensure the accuracy of the simulation results; Step 5: Import the shock absorber assembly model into Hypermesh software, perform structure simplification processing, develop a simplified process in Hypermesh, set up corresponding connection settings, set corresponding materials and properties and divide the mesh, set the boundary, and perform strength simulation under the condition of inertia release; Step 6: Enter the fatigue calculation block of Hypermesh software, import the strength simulation results and select the corresponding stress correction method, load the load spectrum extracted in step 3 and align the output channels, and perform fatigue simulation calculation combined with the S-N curve fitted by the software; The step 6 is specifically as follows: 6.1, import the calculation results in step 5 into the fatigue calculation module of Hypermesh; 6.2, select a suitable stress correction algorithm, and fit the S-N curve according to the material properties; 6.3, import the load spectrum, align the channels of the load spectrum, and perform fatigue simulation analysis.

2. The fatigue analysis calculation method for an automobile shock absorber according to claim 1, characterized by, The step 5 is specifically as follows: 5.1, secondary development: develop a simplified simulation process of Hypermsh software; 5.2, model simplification: simplify the valve system model in the shock absorber assembly into a solid part; 5.3, mesh division: in the mesh division stage, the sleeve and the bracket are divided into shell elements, and the piston and the piston rod are divided into solid elements; 5.4, define material properties: the mechanical properties of each component of the shock absorber are assigned to isotropic linear elastic material, and the material density, elastic modulus and Poisson's ratio are all based on the measured material quality; 5.5, connection setting: rbe2 is used to simulate the bolt connection between the brackets, seam is used to simulate the welding between the components, spot is used to simulate the welding point between the outer bracket and the inner bracket, contact setting is divided into TIE and CONTACT, and the control card selects inertia release and automatic constraint; 5.6, define load: set x, y and z three direction unit force and unit moment loading, and the loading place is above the simulated bolt, to obtain a complete automobile shock absorber finite element model.

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