Finite element analysis method for cross-country motorcycle frame in competition-level site

Abstract

The invention provides a finite element analysis method for a competition-level site cross-country motorcycle frame, and belongs to the technical field of crossing of computer-aided engineering and vehicle structure design. The method comprises the following steps: performing parametric modeling on a frame main bearing structure based on CATIA software, and simplifying non-functional characteristics; importing the model into ANSYS Workbench, generating a high-precision finite element model by adopting a grid division strategy of mixing tetrahedron and hexahedron units, and considering the calculation efficiency and precision; defining material characteristics; a limit load working condition is simulated through statics analysis, a displacement cloud picture and a stress cloud picture are combined to be compared with the yield strength of a material, and topological optimization is conducted on a weak area; meanwhile, the inherent frequency of the frame is extracted through modal analysis, and the resonance risk is avoided. According to the method, statics analysis and modal analysis are carried out on the frame through cross-platform co-simulation, the structural reliability is evaluated, and the method is suitable for efficient development and performance optimization of competition-level cross-country motorcycle frames.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of computer-aided engineering (CAE) and vehicle structural design, specifically involving a finite element analysis method for a high-precision racing-grade off-road motorcycle frame based on cross-platform collaborative simulation. Background Technology

[0002] Traditional off-road motorcycle development processes require the manufacture of multiple physical prototypes for testing, resulting in high costs. For complex structures like the frame, solving calculations using traditional mathematical methods is extremely difficult. Because of the frame's complexity, its internal stress and deformation are difficult to analyze accurately using traditional mathematical methods. Therefore, research into using computer tools for the finite element method (FEM) has emerged. The FEM divides the complex frame structure into numerous small elements, analyzes each element individually, and then considers the interactions between elements to obtain a relatively accurate understanding of the stress distribution and deformation of the frame under different load conditions, providing strong support for frame design and optimization.

[0003] The current traditional chassis design methods suffer from three main problems and shortcomings: First, insufficient modeling accuracy. The reliance on a single software platform leads to the loss of geometric features during model conversion, resulting in excessive distortion of key details such as welds and mounting holes. Second, oversimplification of loads. Static analysis often uses standard static loads, which cannot simulate extreme impacts in off-road scenarios. Finally, cost and efficiency bottlenecks. Reliance on physical prototype testing results in high costs for a single bench test, and the inability to obtain full-condition stress distribution data leads to longer design iteration cycles and requires more manpower.

[0004] Finite element method (FEM) simulation technology offers an innovative approach to solving the aforementioned problems. By simulating various operating conditions, it evaluates motorcycle performance and reduces R&D costs. The China Automobile and Motorcycle Sports Federation (CAMF) has formulated relevant competition guidelines and standards, stipulating regulations for the organization of motocross events and vehicle technical standards. These regulations provide a basis and reference for the development of simulation models, ensuring that simulation results conform to the actual competition environment. Motocross motorcycles need to compete in varying terrain and weather conditions; FEM simulation models can simulate different environmental conditions, evaluate motorcycle performance under various environments, and help design more adaptable vehicles. Summary of the Invention

[0005] The core of this invention lies in using finite element analysis technology, combined with structural statics and dynamics simulation, to evaluate the strength, stiffness and vibration characteristics of the chassis under multiple working conditions, and to improve the chassis performance through topology optimization and other means.

[0006] A finite element analysis method for a racing-grade off-road motorcycle frame includes the following steps: A. Model Establishment: Parametric modeling and geometric simplification of the racing motocross frame are performed, including: a1 Parametric Modeling: The chassis is modeled in 3D using CATIA software. The modeling parameters include tube diameter, wall thickness and spatial connection angle, ensuring that the model can be quickly adjusted to meet optimization requirements. a2 Geometry Simplification: The main load-bearing structure is retained and non-functional features are removed to simplify the frame geometry model. The main load-bearing structure includes key load-bearing areas such as the main beam, subframe, and suspension mounting points. The geometric details of the key load-bearing areas are maintained. The non-functional features include decorative holes and non-load-bearing brackets, which are components that do not affect the mechanical performance, thus reducing computational complexity. B. Hybrid Mesh Generation Strategy: Import the model into ANSYS Workbench, and use the ANSYS Mesh module to generate a high-precision finite element model using a hybrid mesh generation strategy of tetrahedral and hexahedral elements. The global mesh size is controlled within 6-8mm. Check the Jacobian determinant and warpage index to ensure that the mesh quality meets the simulation requirements. C. Material property definition: Define the elastic modulus, Poisson's ratio and density according to the frame material. If plastic deformation analysis is involved, input the stress-strain curve and yield strength of the material. D. Static Analysis: Combining structural statics and dynamics simulation, static analysis and modal analysis are performed to comprehensively evaluate the frame strength, stiffness and vibration risk. Structural optimization is carried out based on the analysis results. The static analysis includes ultimate load conditions, which include rider weight load, suspension impact load and ground reaction force. The load application direction is consistent with the actual force direction of the frame. E. Modal Analysis: The modal analysis is used to obtain the natural frequencies and mode shapes of the frame, extract the multi-order natural frequencies of the frame, and perform structural optimization on the parts that do not meet the requirements based on the comparison results between the frame's natural frequencies and the main external excitation frequencies, thereby avoiding the risk of external excitation resonance.

[0007] Preferably, in step A, the welded area of ​​the main load-bearing structure is rigidly connected or contact-bound through equivalent stiffness constraints. This technical feature uses equivalent weld treatment to avoid local stress distortion.

[0008] Preferably, based on the finite element model in step B, rigid body elements are used to connect the contact surfaces of the two parts. Boundary constraints are applied according to the ultimate load condition in step D. Displacement cloud map and stress cloud map are obtained through finite element analysis and compared with the material yield strength. Topology optimization design is performed on the areas that do not meet the strength requirements.

[0009] Preferably, for step D, the boundary constraint conditions are as follows: the front riser mounting base locks the translational degrees of freedom in the X / Y / Z directions, the horizontal pipe limits the rotational degrees of freedom around the axis, the contact interface realizes the load transfer path simulation through rigid elements, the stress concentration area is located using a composite stress cloud map, and when the local equivalent stress exceeds the material yield limit, the topology optimization program is started to generate the weight reduction hole structure or optimize the distribution of the reinforcing ribs.

[0010] Preferably, in step D, the driver weight load in the extreme load condition is a vertical force applied by simulating the driver's weight through the seat and foot pedals; the suspension impact load is a dynamic force calculated based on the suspension stiffness and impact speed, applied to the front and rear suspension connection points; the ground reaction force is the longitudinal force applied to the frame according to the friction coefficient under braking conditions and the lateral centrifugal force applied to the frame under sharp turning conditions.

[0011] Preferably, for step D, the extreme load condition further includes the maximum deceleration condition. The maximum deceleration condition simulates the instantaneous extreme situation of a motorcycle encountering a sudden event and performing emergency braking while traveling straight on a level road. Under this condition, the frame is subjected to a huge reaction force from the braking system and the influence of road friction. The load under this condition includes a horizontal load set to 2.5-3.5 times the vehicle weight, a front wheel braking torque of 800-2000 N·m, and a lateral acceleration of 1.0-1.5g. The maximum equivalent stress is calculated for safety factor assessment. The instantaneous extreme situation of a motorcycle encountering a sudden event and performing emergency braking while traveling straight on a level road is the most common instantaneous sudden event during driving. Load analysis under this condition can significantly improve the safety of the frame. Furthermore, although the motorcycle is traveling normally, in actual situations involving emergency braking, the driver will have an instinctive tendency to swerve to avoid the situation, resulting in a rapid decrease in speed followed by a turn. Therefore, it is necessary to couple the longitudinal braking and lateral acceleration loads on the frame to better reflect real accident conditions.

[0012] Preferably, for step E, modal analysis, the risk of overlap between the natural frequency and the excitation frequency is determined by comparing the main external excitation sources; when the frequency difference between the two is less than 10Hz, the structure is optimized to generate a frequency shift of 5-15Hz in the resonant frequency, ensuring that the natural frequency of the frame is misaligned with the external excitation frequency by more than 20%, thereby effectively avoiding the risk of fatigue failure caused by structural resonance.

[0013] Preferably, the main external excitation frequencies include the motorcycle's excitation frequency, the excitation frequency caused by wheel imbalance, and the engine's idling frequency. This invention also innovatively calculates the road surface excitation frequency. By ensuring that the natural frequency > excitation frequency and the frequency difference > 20%, the design criterion is more stringent than the conventional 10Hz safety margin. This is especially true considering the extreme conditions of off-road conditions with wavelengths of 0.32-6.3m.

[0014] Preferably, the methods for improving the rigidity of the frame include adding high-damping alloy bushings and optimizing the cross-sectional shape of the tube beam. For example, changing the circular tube to a variable cross-section elliptical tube or locally reinforcing the welded area can improve rigidity.

[0015] Preferably, it also includes F, structural optimization and iterative verification: Based on the high-stress area data output by static analysis, the material distribution of the frame is reconstructed using the ANSYS topology optimization module to achieve a minimum mass design while ensuring that the structural strength meets the yield limit; then, through multiple rounds of parameter iteration, the core dimensional parameters such as the main beam diameter and the wall thickness of key nodes are systematically adjusted, and the entire process of modeling, mesh generation, and loading simulation is executed cyclically until the overall stress distribution of the frame is uniform and the safety factor is ≥1.5, finally forming an optimized scheme that balances lightweight and high reliability.

[0016] Compared with traditional techniques, the finite element analysis method for the frame of this competition-grade off-road motorcycle has the following advantages: 1. This invention utilizes cross-platform collaboration (CATIA + ANSYS) and structural statics and dynamics co-simulation to comprehensively evaluate the strength, load-bearing capacity, stiffness, and vibration response characteristics of a chassis under different operating conditions. This creates conditions for subsequent multi-objective optimization or topology optimization techniques to achieve precise performance enhancement and efficient structural improvement of the chassis. First, a three-dimensional model is established using CATIA software. Then, ANSYS finite element analysis is used to analyze the strength, stiffness, and modal characteristics of the chassis, providing a theoretical basis for structural improvement design. Based on the calculated parameters of the chassis, such as torsional stiffness and bending stiffness, the basic parameter model is obtained through performance analysis and optimization calculations of the chassis structure using the finite element method. This can solve problems that cannot be solved by manual calculations in previous experiments, enabling experiments that are difficult or impossible to perform in reality, improving the accuracy of optimization analysis, and reducing experimental costs.

[0017] 2. Compared to the previous step-by-step design, testing, improvement and optimization of off-road motorcycle frames, the secondary design is faster and more effective, shortening the frame design cycle. Moreover, this enclosed structure has excellent safety.

[0018] 3. Pure hexahedral meshes typically offer higher quality but are difficult to mesh, while pure tetrahedral meshes lack sufficient precision. Therefore, a hybrid mesh combining hexahedral and tetrahedral elements is used to mesh the vehicle frame. This invention experimentally determined this 6-8mm mesh size range, controlling the number of elements to the order of 100,000 while ensuring stress and modal accuracy. This is crucial for subsequent rapid iterations. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a three-dimensional model of the vehicle frame provided in an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the grid division of the vehicle frame provided in an embodiment of the present invention.

[0021] Figure 3 This is a cloud map showing the maximum deformation displacement of the vehicle frame under extreme working conditions, provided in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of the maximum equivalent stress cloud of the chassis under extreme working conditions provided in the embodiments of the present invention.

[0023] Figure 5 This is the first-order mode shape diagram of the first six modes of the vehicle frame provided in the embodiment of the present invention.

[0024] Figure 6 This is the second-order mode shape diagram of the first six modes of the vehicle frame provided in this embodiment of the invention.

[0025] Figure 7 This is the third-order mode shape diagram of the first six orders of the vehicle frame provided in the embodiment of the present invention.

[0026] Figure 8 This is the fourth-order mode shape diagram of the first six orders of the vehicle frame provided in the embodiment of the present invention.

[0027] Figure 9 This is the fifth-order mode shape diagram of the first six orders of the vehicle frame provided in the embodiment of the present invention.

[0028] Figure 10 This is a diagram showing the first six and middle six modal vibration modes of the vehicle frame provided in an embodiment of the present invention. Detailed Implementation

[0029] The following will refer to the appendix Figure 1-10 Various exemplary embodiments, features, and aspects of this disclosure are described in detail. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0030] Furthermore, to better illustrate the present invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In some instances, methods well-known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0031] This invention provides a finite element analysis method for a racing motocross motorcycle frame, comprising the following steps: A. Model Establishment: Parametric modeling and geometric simplification of the racing motocross frame are performed, including: A1 Parametric Modeling: When constructing a 3D parametric model of the vehicle frame in CATIA software, the frame model includes structures such as the front riser tube, main beam tube, upper tube, cross tube, front suspension beam, lower tube, side plates, bolts, reinforcing plates, shock absorber mounts, and side leg plates. Using tube diameter, wall thickness, and spatial connection angles as core driving parameters, dynamic linkage of geometric features is achieved through variable association technology. This allows the model to directly trigger topology reconstruction through the parameter input window, effectively supporting multi-condition optimization design requirements.

[0032] a2 Geometric Simplification: The main load-bearing structure is retained while non-functional features are removed to simplify the chassis geometry model. Specifically, the complete geometric features of key load-bearing components such as the main beam, subframe, and suspension mounting points are preserved, while non-load-bearing components such as decorative holes are removed to reduce the model size. Equivalent stiffness treatment is applied to weld areas using rigid connections or bonded contacts to eliminate local stress distortion effects. Frictional contact relationships at bolted connection interfaces are defined based on measured friction coefficients, while nonlinear contact algorithms are introduced to simulate potential separation behavior in pipe joint areas.

[0033] B. Meshing: Import the model into ANSYS Workbench and use the ANSYS Mesh module to generate a high-precision finite element model with a mixed tetrahedral and hexahedral element meshing strategy. The model is 8mm in size, balancing computational accuracy and efficiency, and generates 187,874 nodes and 92,925 elements.

[0034] C. Material Properties: Typical parameters of chromium-molybdenum steel are: density 7850 kg / m³, elastic modulus 210 GPa, Poisson's ratio 0.3, tensile strength 930 MPa, and yield strength 1080 MPa. Advantages of this material: high strength, excellent impact resistance, suitable for high-load off-road applications; low cost, and mature welding technology.

[0035] D. Static Analysis: In structural analysis, the rider load is applied vertically through the seat support surface and foot pedals. The suspension impact load is derived based on the mapping relationship between suspension stiffness characteristics and impact velocity, and is applied to the front and rear suspension hard points respectively. During braking, a longitudinal load based on the friction coefficient μ is applied tangentially along the wheel, while during cornering, a centrifugal force field corresponding to lateral acceleration is applied. Regarding boundary constraints, the front seat tube mounting locks the translational degrees of freedom in the X / Y / Z directions, and the cross tube restricts the rotational degrees of freedom around the axis. The contact interface uses rigid elements to simulate the load transfer path, and a composite stress cloud map is used to locate stress concentration areas. When the local equivalent stress exceeds the material yield limit, a topology optimization program is initiated to generate weight-reducing hole structures or optimize the distribution of reinforcing ribs. The maximum deceleration condition simulates an instantaneous extreme situation where a motorcycle encounters a sudden event and performs emergency braking while traveling in a straight line on a level road. Under this condition, the motorcycle needs to rapidly reduce its speed to cope with the sudden situation; therefore, the frame is affected by the huge reaction force generated by the braking system and the road friction. The horizontal load was set to 3.5 times the vehicle weight, i.e., 3675 N; the front wheel braking torque was 2000 N·m; and the lateral acceleration was 1.5 g. Software analysis results showed that the maximum equivalent stress was 362.87 MPa. Calculations indicated that the safety factor was much greater than 1, indicating that the frame had an extremely high safety margin under static load. The maximum deformation was 0.33 mm, located on the side leg plate.

[0036] E. Modal Analysis: The first six natural frequencies of the frame are calculated. By comparing with the main external excitation sources, the risk of overlap between the natural frequency and the excitation frequency is judged. When the frequency difference between the two is less than 10Hz, the structure is optimized to generate a frequency shift of 5-15Hz in the resonant frequency, ensuring that the frame natural frequency is misaligned with the external excitation frequency by more than 20%, thereby effectively avoiding the risk of fatigue failure caused by structural resonance.

[0037] Table 1 First Six Modes order 1 2 3 4 5 6 Frequency / Hz 218.25 246.67 274.32 295.36 355.55 363.3 During actual off-road motorcycle operation, uneven road surfaces cause various random vibrations, which are the main source of external excitation. Therefore, the natural frequency of the motorcycle frame should be minimized in its coupling with the external excitation frequency to avoid resonance, ensure the motorcycle's comfort and safety, and prevent damage to the off-road motorcycle frame due to resonance. In actual driving, it is essential to ensure that the natural frequency is not within the vibration frequency range.

[0038] The vibration frequency is calculated using the following formula.

[0039] v —Driving speed, km / h L—The wavelength corresponding to the unevenness of the road surface, in meters. If the two frequencies coincide, it will cause resonance in the off-road motorcycle. If ν is taken as the maximum design speed (120km / h) of the off-road motorcycle studied in this paper, and L is taken into full consideration in conjunction with the actual road conditions, it is selected as the wavelength of the minimum possible unevenness. In this way, a reasonable analysis of various different road conditions can be carried out, thereby obtaining the maximum road excitation frequency that may actually occur.

[0040] Table 2 Calculation results of maximum excitation frequency under different road conditions pavement Unpaved roads gravel road washboard road flat road Road surface unevenness wavelength (m) 0.77-2.5 0.32-6.3 0.74-5.6 1-6.3 Maximum road surface excitation frequency (Hz) 43.29 104.17 45.05 33.33 Modal analysis results show that the modal natural frequencies of the frame structure are higher than the excitation frequency of the frame load, and the frame will not resonate under working conditions.

[0041] It should be noted that the methods described in the embodiments in this article correspond to the methods described in the embodiments. The methods described in the embodiments are used to implement the process steps described in the methods described in the embodiments. Therefore, other undescribed contents of the system described in the embodiments can be obtained by referring to the contents of the methods described in the embodiments, and will not be repeated here.

[0042] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A finite element analysis method for a racing-grade off-road motorcycle frame, characterized in that, Includes the following steps: A. Model Establishment: Parametric modeling and geometric simplification of the racing motocross frame are performed, including: a1 Parametric Modeling: The frame is modeled in 3D using CATIA software. The modeling parameters include tube diameter, wall thickness, and spatial connection angle. a2 Geometry Simplification: The main load-bearing structure is retained and non-functional features are removed to simplify the frame geometry model. The main load-bearing structure includes the main beam, subframe, and suspension mounting points. The non-functional features include decorative holes and non-load-bearing brackets. B. Hybrid Mesh Generation Strategy: Import the model into ANSYS Workbench, and use the ANSYS Mesh module to generate a high-precision finite element model using a hybrid mesh generation strategy of tetrahedral and hexahedral elements. The global mesh size is controlled within 6-8mm. Check the Jacobian determinant and warpage index to ensure that the mesh quality meets the simulation requirements. C. Material property definition: Define the elastic modulus, Poisson's ratio and density according to the frame material. If plastic deformation analysis is involved, input the stress-strain curve and yield strength of the material. D. Static Analysis: Combining structural statics and dynamics simulation, static analysis and modal analysis are performed to comprehensively evaluate the frame strength, stiffness and vibration risk. Structural optimization is carried out based on the analysis results. The static analysis includes ultimate load conditions, which include rider weight load, suspension impact load and ground reaction force. The load application direction is consistent with the actual force direction of the frame. E. Modal Analysis: The modal analysis is used to obtain the natural frequencies and mode shapes of the frame, extract the multi-order natural frequencies of the frame, and perform structural optimization on the parts that do not meet the requirements based on the comparison results between the frame's natural frequencies and the main external excitation frequencies, thereby avoiding the risk of external excitation resonance.

2. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: For step A, the welded areas of the main load-bearing structure are rigidly connected or contact-bound through equivalent stiffness constraints.

3. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: Based on the finite element model in step B, rigid body elements are used to connect the contact surfaces of the two parts. Boundary constraints are applied according to the ultimate load condition in step D. Displacement cloud map and stress cloud map are obtained through finite element analysis and compared with the material yield strength. Topology optimization design is performed on the areas that do not meet the strength requirements.

4. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 3, characterized in that: For step D, the boundary constraints are as follows: the front riser mounting base locks the translational degrees of freedom in the X / Y / Z directions, the horizontal tube limits the rotational degrees of freedom around the axis, the contact interface realizes the load transfer path simulation through rigid elements, the stress concentration area is located using a composite stress cloud map, and when the local equivalent stress exceeds the material yield limit, the topology optimization program is started to generate the weight reduction hole structure or optimize the distribution of the reinforcing ribs.

5. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: For step D, the driver weight load in the extreme load condition is a vertical force applied by simulating the driver's weight through the seat and foot pedals; the suspension impact load is a dynamic force calculated based on the suspension stiffness and impact speed, applied to the front and rear suspension connection points; the ground reaction force is the longitudinal force applied to the frame according to the friction coefficient under braking conditions and the lateral centrifugal force applied to the frame under sharp turning conditions.

6. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: For step D, the extreme load condition also includes the maximum deceleration condition. The maximum deceleration condition simulates the instantaneous extreme situation when a motorcycle encounters a sudden situation and performs emergency braking while traveling in a straight line on a level road. Under this condition, the frame will be affected by the huge reaction force generated by the braking system and the road friction. The load under this condition includes a horizontal load set to 2.5-3.5 times the vehicle weight, a front wheel braking torque of 800-2000 N·m, and a lateral acceleration of 1.0-1.5g. The maximum equivalent stress is calculated to evaluate the safety factor.

7. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: For step E, modal analysis, the risk of overlap between the natural frequency and the excitation frequency is judged by comparing the main external excitation sources. When the frequency difference between the two is less than 10Hz, the structure is optimized to generate a frequency shift of 5-15Hz in the resonant frequency, ensuring that the natural frequency of the frame is misaligned with the external excitation frequency by more than 20%, thereby effectively avoiding the risk of fatigue failure caused by structural resonance.

8. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 7, characterized in that: The main external excitation frequencies include the motorcycle's excitation frequency, the excitation frequency caused by wheel imbalance, and the engine's idling frequency.

9. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: The methods for improving the rigidity of the frame include adding high-damping alloy bushings and optimizing the cross-sectional shape of the tube beam.

10. The finite element analysis method for a racing-grade off-road motorcycle frame according to claim 1, characterized in that: It also includes F, structural optimization and iterative verification: Based on the high-stress area data output by static analysis, the material distribution of the frame is reconstructed using the ANSYS topology optimization module to achieve a minimum mass design while ensuring that the structural strength meets the yield limit; then, through multiple rounds of parameter iteration, the core dimensional parameters such as the main beam diameter and the wall thickness of key nodes are systematically adjusted, and the entire process of modeling, mesh generation, and loading simulation is executed cyclically until the overall stress distribution of the frame is uniform and the safety factor is ≥1.5, finally forming an optimized scheme that balances lightweight and high reliability.

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