A method for fine modeling of a variable-width and variable-height composite leaf spring

Abstract

The application discloses a variable-width and variable-height composite plate spring fine modeling method, and comprises the following steps: introducing a variable-width and variable-height plate spring three-dimensional model into finite element software; adopting a surface mesh to volume mesh idea, and segmenting and separating in the width and height directions to form an equilateral rectangular cross-section strip structure with variable width and height; adopting a Discrete discrete field to define a fiber layer, taking the upper surface of the strip structure as a normal axis, taking a side line as a main direction axis, stacking in a direction parallel to the geometric upper surface, and setting the fiber layer thickness by using ElementRelativeThickness; assigning anisotropic material properties to hundreds of strip structures in batches through a Python subprogram; and adopting an 8-node hexahedral solid element to perform mesh division, so as to capture interlayer stress and evaluate strength. The method considers the continuous change characteristics of the fiber direction with the cross-section width and height by means of discretization and a local coordinate system, the stiffness simulation deviation of the model is within 3% compared with test, and the strength simulation can pass bench and vehicle durability verification at one time.

Description

Technical Field

[0001] This invention belongs to the field of commercial vehicle suspension technology, and particularly relates to a refined modeling method for variable width and height composite material leaf springs. Background Technology

[0002] Against the backdrop of global advocacy for energy conservation and emission reduction, and the automotive industry's pursuit of high performance and low energy consumption, lightweight design has become a key trend in automotive development. Composite materials, with their lightweight, high specific strength, high specific modulus, high specific strain energy, and excellent fatigue performance, show great potential as lightweight materials for automobiles. Compared to traditional steel leaf springs, composite leaf springs offer significant weight reduction, ranging from 30% to 70%. For traditional gasoline-powered vehicles, this helps improve fuel economy and reduce emissions; for new energy vehicles, it effectively increases driving range. The reduced unsprung mass also contributes to improved handling and ride comfort. Therefore, research on the engineering applications of composite leaf springs is of great significance.

[0003] However, the complex characteristics of composite materials, such as anisotropy, fiber orientation variation with cross-sectional structure, and diversity of layup schemes, pose challenges to the characterization of the stiffness and strength of composite leaf springs by the finite element method or theoretical method, affecting the performance optimization of composite leaf springs and the whole vehicle. A refined modeling method for variable-thickness composite leaf springs is disclosed in the prior art (publication number CN202210400136.6). The principle involves importing a geometric model of the composite leaf spring, analyzing the composition of straight and circular segments on the upper and lower surfaces, and selecting a surface with relatively regular geometric features as the base plane for the ply. The variable-thickness composite leaf spring body is geometrically cut according to the ply length of each layer, with the boundary length after cutting encompassing the length of all ply layers. The base plane is meshed using surface element units, ensuring that the normal of the surface elements is consistent with the ply direction. Local coordinate systems are established for each curved segment of the base plane, a rectangular coordinate system for straight segments, and a cylindrical coordinate system for circular segments. A set of elements (SET) is created for each layer to prepare for assigning single-layer attributes. Anisotropic material properties of the composite leaf spring are established, as are the properties of single-layer composite materials and the laminate. The stacking direction of the laminate is defined, and the ply sequence and fiber direction are checked for correctness. This method is applicable to composite leaf springs with constant width and variable thickness, but it cannot reflect the change in fiber direction with the width and height of the leaf spring cross-section for leaf springs with varying width and height; therefore, the modeling method needs further improvement.

[0004] To address the problem that existing technologies for simulating the stiffness, strength, and fatigue damage of composite leaf springs manufactured using variable width and height molding processes suffer from imprecise modeling methods that fail to accurately reflect the characteristics of fiber orientation variations with the width and height of the leaf spring cross-section, leading to discrepancies between simulation and experimental results, this invention provides a refined modeling method for variable width and height composite leaf springs. Summary of the Invention

[0005] To address the problems existing in current technologies, this invention provides a refined modeling method for composite leaf springs with varying width and height. It ensures that the deviation between the stiffness simulation results and experimental results is within 3%. The strength simulation performance meets the standards and passes bench and vehicle durability tests in one go.

[0006] This invention is implemented as follows: a refined modeling method for variable-width and variable-height composite leaf springs, comprising the following steps: importing the three-dimensional model of the variable-width and variable-height composite leaf spring into finite element software; adopting a meshing approach from surface mesh to volume mesh, segmentally discretizing the width and height directions of the leaf spring to form multiple strip structures with continuously varying widths and heights along the length of the leaf spring; defining fiber layups using a Discrete field, taking the upper surface of each strip structure as the Normal axis and its length edge as the Primary axis, ensuring that the stacking direction of the fiber layers is parallel to the geometric upper surface of the strip structure, and setting the thickness of each fiber layer using the ElementRelativeThickness method; writing a Python subroutine to automatically traverse all strip structures and batch assign anisotropic material properties; and using 8-node hexahedral solid elements to mesh the entire model to capture interlaminar stress states under different working conditions and evaluate strength.

[0007] Further preferably, the fineness of the equal separation in the width and height directions is determined based on the simulation accuracy requirements and computer computing power.

[0008] More preferably, the formation of the strip structure with equal rectangular cross-sectional area makes the internal geometry of each strip structure approximately a regular rectangular cross-section, thereby enabling the precise establishment of a local coordinate system on it to define the fiber direction.

[0009] Furthermore, by employing a Discrete field combined with ElementRelativeThickness, the thickness and orientation in the local coordinate system of each fiber layer within each strip structure with equal rectangular cross-sectional area can be independently and precisely controlled.

[0010] Furthermore, the Python subroutine automatically assigns material properties to all strip structures with equal rectangular cross-sectional areas by reading preset material parameters and ply information, thus solving the problem of low efficiency in manual assignment caused by the large number of strip structures due to structural discretization.

[0011] More preferably, the 8-node hexahedral solid unit can effectively simulate the three-dimensional stress state of composite leaf springs under complex loads, especially the shear and peel stress between layers.

[0012] In a further preferred embodiment, stiffness simulation analysis is performed on the model obtained by mesh generation, and the deviation between the stiffness simulation analysis results and the physical test results is controlled within 3%.

[0013] In a further preferred embodiment, the model obtained by mesh generation is subjected to strength simulation analysis, and the results of the strength simulation analysis can be verified by bench and vehicle durability tests in one go.

[0014] More preferably, the finite element software is Abaqus.

[0015] More preferably, this method is applicable to widened and heightened composite leaf springs formed by compression molding.

[0016] The advantages and technical effects of this invention are as follows: By discretizing the variable-width and variable-height composite leaf spring into strip structures with equal rectangular cross-sectional areas, and using a discrete field to independently establish local material coordinate systems for each structure, this invention achieves a precise description of the continuous variation of fiber direction with cross-sectional width and height. When performing stiffness simulations, the results deviate from experimental results by less than 3%; the strength simulation performance meets the standards and can pass bench and vehicle durability tests in one go. This method effectively improves the engineering practicality of stiffness and strength simulations for composite leaf springs, shortens product development cycles, reduces the cost of repeated testing and verification, and increases the success rate of first-time product design and market acceptance of vehicle performance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a composite material leaf spring front suspension; Figure 2 This is a schematic diagram of a composite material leaf spring with varying width and height. Figure 3 This is an overall rendering of the composite material leaf spring created using the modeling method of this invention; Figure 4 This is a magnified view of a composite material leaf spring and a schematic diagram defining its material properties. Figure 5 It is a graph showing the trend of the uniform rectangular cross-sectional area strip structure along the length of the leaf spring as the cross-sectional width changes; Figure 6 It is a graph showing the trend of the uniform rectangular cross-sectional area strip structure along the length of the leaf spring as the cross-sectional height changes; Figure 7 yes Figure 6 The magnified view on the left shows the trend of fiber orientation as a result of the combined changes in cross-sectional height and width; Figure 8 This is a front view along the fiber layup stacking direction S of the leaf spring length direction; Figure 9 It is a top view showing the perpendicular relationship between the fibers and direction 2 along the length of the leaf spring; Figure 10 It is a partial three-dimensional view along the length of the leaf spring, in the main fiber direction Ref1, Ref2 (perpendicular to the main fiber direction Ref1 along the width direction), and Ref3 (perpendicular to the main fiber direction Ref1 along the height direction). Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] The following is in conjunction with the appendix Figures 1 to 10 The specific implementation method of the fine modeling method for variable width and height composite leaf springs of the present invention will be described in detail. Figure 1 This diagram shows the assembly of a composite leaf spring in a front suspension. Figure 2 This is a structural diagram of a variable width and height leaf spring. Figure 3 This is a schematic diagram of a finite element modeling method that considers the variation of fiber orientation with cross-section. This embodiment uses a single-piece variable-width, variable-height composite leaf spring manufactured using a molding process in a commercial vehicle suspension system as the object, and is implemented in Abaqus finite element software.

[0020] Step 1: Import and Discretize the Geometric Model: Import the 3D model of the variable-width, variable-height leaf spring into Abaqus. Using a meshing approach from surface to volume, the spring is segmented along its length. Within each segment, equal discretization is performed in both the width and height directions, resulting in multiple strip structures with continuously varying widths and heights along the length. The fineness of the discretization in the width and height directions can be determined based on the simulation accuracy requirements and the computer's computing power; the finer the discretization, the closer the fiber orientation within each strip structure is to the actual flow direction. This step transforms the complex variable-section continuum into a series of approximately regular rectangular cross-section strip structures, laying the foundation for independently defining the local fiber orientation on each strip structure, achieving a balance between computational accuracy and efficiency.

[0021] Step 2: Define fiber layup using a discrete field: For each rectangular cross-sectional strip structure obtained by discretization, define the fiber layup using the Discrete field in Abaqus. Specify the upper surface of the strip structure as the normal axis and its length edge as the primary axis, ensuring the fiber layer stacking direction is parallel to the geometric upper surface of the strip structure. Simultaneously, set the thickness of each fiber layer within the strip structure using ElementRelativeThickness. Since each strip structure is approximately a regular rectangular cross-section, the local material coordinate system established on it can be continuously adjusted according to the structure's width and height, thus accurately reflecting the characteristics of fiber orientation variation with the leaf spring's cross-sectional width and height. Furthermore, the relative thickness method allows for independent and precise control of each fiber layer thickness, realistically reproducing the variable thickness layup process.

[0022] Please see Figures 3 to 10 This exemplifies the core ideas and specific details of the aforementioned refined modeling. Figures 5 to 7 The red lines in the diagram represent the direction of the fibers. Figure 3 This is an overall effect diagram of the composite material leaf spring established using the method of the present invention. Figure 4 This diagram shows a partial magnification of the leaf spring and the definition of its material properties. Each color in the diagram represents a discrete set of strip structures with equal rectangular cross-sectional areas. These strip structures serve as the smallest unit that imparts material properties. The geometric upper surface of each strip structure is taken as the normal axis, and its length direction edge is taken as the primary axis, so that the stacking direction of the fiber layers is parallel to the upper surface. Figure 5 The rectangular cross-sectional area strip structure shows a continuous change as the width of the leaf spring cross-section varies, representing the characteristic that the fiber direction changes continuously with the width direction. Figure 6 This demonstrates the continuous change of the strip structure as the cross-sectional height of the leaf spring changes, representing the characteristic that the fiber direction changes continuously with the height direction. Figure 7 This reflects the trend that the fiber orientation changes together with the height and width of the leaf spring section, indicating that the fiber orientation changes continuously with changes in height and width. Figure 8 The S-direction represents the fiber layup stacking direction, which is 180° to the 3-direction and the fiber orientation is perpendicular to the 3-direction. Figure 9 The fiber orientation is shown to be perpendicular to direction 2. Figure 10The marker "Ref1" clearly indicates the main direction of the fiber. As can be seen from the above series of figures, the method of the present invention, through discretization and the definition of independent local coordinate systems, accurately describes the correspondence between fiber orientation and cross-sectional geometric features in each local region. Thus, the simulation model realistically reproduces the flow characteristics of the fiber continuously deflecting as the width and height of the leaf spring cross-section changes under the molding process. This allows the deviation between the stiffness simulation results and the experimental results to be controlled within 3%, and the strength simulation can pass the bench and vehicle durability tests in one go.

[0023] Step 3: Write a Python subroutine to batch assign material properties: For the hundreds of strip structures generated by discretization, write a Python subroutine to automatically traverse all strip structures and batch assign material properties to them by reading preset anisotropic material parameters and layup information. This subroutine effectively solves the problem of extremely low efficiency in manually assigning values ​​one by one due to the high degree of discretization of the structure, making fine modeling feasible within the engineering time limit.

[0024] Step 4: Element Selection and Solution Evaluation: The entire model is meshed using 8-node hexahedral solid elements (e.g., C3D8 or C3D8I elements) and the calculation is submitted. These solid elements can accurately capture the three-dimensional interlaminar stress state of composite leaf springs under different load conditions, especially interlaminar shear and peel stresses, thus achieving accurate assessment of stiffness and strength. Based on the refined model established using this method, the deviation between the stiffness simulation results and physical test results can be controlled within 3%, and the strength simulation results can be verified by bench and vehicle durability tests in one go, without repeated model modifications.

[0025] The above steps describe a complete modeling process, which is particularly suitable for widened and heightened composite leaf springs manufactured by molding.

[0026] The modeling method provided by this invention solves the problem of accurately representing the fiber orientation in composite leaf springs with varying width and height by organically combining a "converting curves into straight lines" discretization strategy with a local conformal coordinate system. In principle, during the molding of a real leaf spring, the fiber bundles deflect according to the varying width and height contour of the mold cavity, and the axes of its local coordinate system change with the cross-sectional geometry. This method cuts the leaf spring into strip structures with equal rectangular cross-sectional areas along its length, width, and thickness. Each strip structure is microscopically approximated as a segment of a prism with equal cross-section, and its geometric upper surface and length-direction edges can serve as natural references for defining the local material coordinate system. Through a Discrete field, with the upper surface of the strip structure as the normal, the edges as the principal fiber directions, and the stacking direction parallel to the upper surface, an independent fiber coordinate system conforming to its actual geometric characteristics is established for each local region. As the discretization density increases, the set of these local coordinate systems tends to change continuously, accurately approximating the true fiber orientation within the varying width and height curved surface. Meanwhile, the ElementRelativeThickness method allows the ply thickness to be automatically adjusted according to the element geometry, ensuring the simulation fidelity of variable thickness features. Finally, the assignment of properties to a large number of strip structures is completed automatically by a Python program, ensuring the efficiency of the method.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for refined modeling of composite leaf springs with variable width and height, characterized in that, Includes the following steps: Import the 3D model of the variable width and height composite leaf spring into the finite element software; By adopting a division approach from surface mesh to volume mesh, the width and height directions of the leaf spring are equally separated in segments, thereby forming multiple strip structures with continuously varying widths and heights along the length of the leaf spring. The fiber layup is defined using a discrete field, with the upper surface of each strip structure with equal rectangular cross-sectional area as the normal axis and its length side as the primary axis, so that the stacking direction of the fiber layers is parallel to the geometric upper surface of the strip structure, and the thickness of each fiber layer is set using the ElementRelativeThickness method. Write a Python subroutine to automatically traverse all strip structures and batch assign anisotropic material properties; The entire model was meshed using 8-node hexahedral solid elements to capture the interlayer stress state under different working conditions and to evaluate the strength.

2. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, The fineness of the equal separation in the width and height directions is determined based on the simulation accuracy requirements and the computing power of the computer.

3. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, The formation of the strip structure with equal rectangular cross-sectional area makes the internal geometry of each strip structure approximately a regular rectangular cross-section, thereby enabling the precise establishment of a local coordinate system on it to define the fiber direction.

4. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, By employing a Discrete field combined with ElementRelativeThickness, the thickness and orientation in the local coordinate system of each fiber layer within each strip structure with equal rectangular cross-section can be independently and precisely controlled.

5. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, The Python subroutine automatically assigns material properties to all strip structures with equal rectangular cross-sectional areas by reading preset material parameters and ply information, thus solving the problem of low efficiency in manual assignment caused by the large number of strip structures due to structural discretization.

6. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, The 8-node hexahedral solid element can effectively simulate the three-dimensional stress state of composite leaf springs under complex loads, especially the shear and peel stress between layers.

7. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, Stiffness simulation analysis was performed on the model obtained by mesh generation, and the deviation between the stiffness simulation analysis results and the physical test results was controlled within 3%.

8. The refined modeling method for variable width and height composite leaf springs according to claim 1, characterized in that, The model obtained by mesh generation is subjected to strength simulation analysis, and the results of the strength simulation analysis can be verified by bench and vehicle durability tests in one go.

9. The method for refined modeling of variable-width and variable-height composite leaf springs according to any one of claims 1 to 8, characterized in that, The finite element software used is Abaqus.

10. The method for refined modeling of variable width and height composite leaf springs according to claim 9, characterized in that, This method is applicable to variable width and height composite leaf springs formed by compression molding.

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