A lightweight design and preparation method for a carbon fiber automotive composite connecting rod

Abstract

The present invention discloses a lightweight design and preparation method for a carbon fiber automotive composite connecting rod, comprising: using PMI foam as a supporting material and thermal expansion foam as an expansion material to coat the surface of the PMI foam, and then coating the prepreg layer by layer on the surface of the thermal expansion foam. At the same time, the metal rings at both ends are pre-embedded and coated, and then placed in a rigid mold and heated for thermal expansion molding, and finally a foam sandwich carbon fiber composite connecting rod is prepared in an integrated manner. The present invention innovatively proposes an integrated molding process for a special-shaped tubular structure. The carbon fiber composite connecting rod prepared by this molding process has good surface quality and no obvious defects or damage. It is the first to realize the effective preparation of carbon fiber automotive composite connecting rods, and the performance indicators meet the index requirements. After weighing, it was found that the weight was reduced by about 55% compared with the metal connecting rod, showing a significant lightweight effect.

Description

Technical Field

[0001] The present invention relates to the field of new energy vehicle technology, and more specifically, to a lightweight design and preparation method of a carbon fiber vehicle composite material connecting rod. Background Art

[0002] As the number of cars worldwide continues to increase, energy shortages, environmental pollution, and other issues are becoming increasingly prominent. Lightweighting vehicles can significantly reduce energy consumption and environmental pollution, while effectively extending the service life of key components and improving vehicle comfort and safety, making it a key development trend in the current automotive industry. Lightweight materials are one of the key approaches to achieving lightweight vehicle structures. Carbon fiber reinforced resin-based composites (CFRP), with their unique lightweighting properties and excellent mechanical properties, are gradually replacing metal materials in automotive applications and are becoming increasingly widely used in vehicle body and chassis structures.

[0003] As the positioning element of the vehicle suspension system, the automotive connecting rod primarily bears the lateral tensile and compressive loads transmitted to it by the rear steering knuckle and performs positioning and support functions. Therefore, the rear suspension adjustment link should have sufficient stiffness, strength, and service life. Currently, major global pure electric vehicle platforms have adopted a five-link rear suspension. Due to the axle load of electric vehicles, the strength and stiffness requirements of the connecting rod are higher, which inevitably leads to a heavier connecting rod. The increase in unsprung mass leads to reduced performance and reduced vehicle range. Therefore, developing a further lightweight, high-performance connecting rod while ensuring performance and range is of great significance to improving the competitiveness of pure electric platforms. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a lightweight design and preparation method for a carbon fiber automotive composite material connecting rod. While achieving a lightweight design of the rear suspension connecting rod structure, its related structural performance indicators can meet the performance requirements of current steel parts.

[0005] The present invention provides a lightweight design and preparation method for a carbon fiber vehicle composite connecting rod, comprising the following steps:

[0006] Step S102: Taking a steel automotive connecting rod as a reference, basic performance indicators of the connecting rod are obtained through static analysis and modal analysis;

[0007] Step S104: obtaining a structural design of a carbon fiber composite connecting rod based on the design requirements of the carbon fiber composite material structure, the structural characteristics of the connecting rod main body and the connection parts, and the existing steel automotive connecting rod;

[0008] Step S106: performing finite element modeling based on the structural design of the carbon fiber composite connecting rod, obtaining index parameters of basic performance using the finite element model, and outputting a lightweight design solution for the carbon fiber composite connecting rod when the index parameters meet preset standards;

[0009] Step S108: Based on the lightweight design of the carbon fiber composite material connecting rod, the carbon fiber composite material connecting rod is prepared by using a thermal expansion process, and the obtained carbon fiber composite material connecting rod sample is subjected to tensile and compressive mechanical property tests.

[0010] In this solution, step S102 is specifically as follows:

[0011] Obtaining a three-dimensional model of a steel automotive connecting rod, simplifying and geometrically cleaning the three-dimensional model to establish a geometry and element set, meshing the model using shell elements, and performing a mesh quality check. When the mesh quality meets preset requirements, selecting a preset number of typical working conditions of the steel automotive connecting rod to establish a load set;

[0012] In the load concentration, a load condition is constructed by applying loads and boundary conditions, a connecting rod finite element model is constructed, and a static simulation analysis is performed on the steel automotive connecting rod to obtain material properties, stiffness analysis results, and strength analysis results of the steel automotive connecting rod. The material properties include density, Poisson's ratio, elastic modulus, tensile strength, yield strength, and elongation;

[0013] At the same time, modal analysis is performed to obtain the natural frequency and modal vibration shape of the steel automotive connecting rod in different modes, and the modal analysis results are obtained. Based on the material properties, steel quality analysis results, strength analysis results and modal analysis results of the steel automotive connecting rod, the basic performance indicators of the connecting rod are constructed.

[0014] In this solution, in step S104, the structural design of the carbon fiber composite connecting rod is performed using an equivalent design method, specifically:

[0015] Carbon fiber composite materials are used to replace the steel material of the steel vehicle connecting rod structure, and the equal stiffness approximation theory is used to obtain the thickness of the connecting rod structure after the material replacement;

[0016] The key structural features of the steel automotive connecting rod structure are obtained based on the structural characteristics of the connecting rod main body and the metal ring connection part. The geometric structure design of the carbon fiber composite material connecting rod and the structural design of the connection part of the hybrid structure of carbon fiber composite material and steel material are determined based on the thickness of the connecting rod structure and the key structural features. The layup design of the carbon fiber composite material connecting rod is determined through the structural design of the carbon fiber composite material connecting rod.

[0017] In this solution, step S106 is specifically as follows:

[0018] Finite element modeling is performed based on the structural design of the carbon fiber composite connecting rod to obtain a finite element model of the carbon fiber composite connecting rod. Based on the established finite element model, the same constraints and loads are applied to the carbon fiber composite connecting rod according to the typical operating conditions of a steel automotive connecting rod to perform performance analysis;

[0019] Obtain basic performance index parameters, use the performance analysis results of steel automotive connecting rods as a benchmark, and compare the index parameters with the benchmark. When the comparison results of the index parameters meet the preset standards, a lightweight design solution for the carbon fiber composite connecting rod is output; otherwise, the layup design of the carbon fiber composite connecting rod is optimized.

[0020] In this scheme, in the lightweight design of carbon fiber composite connecting rod, the layup sequence [(0°) 10 / (0,90)] to carry out the layup design of carbon fiber composite connecting rod;

[0021] A layup design diagram for each layer of carbon fiber composite material is obtained through layup design. Process notches are set in the layup design diagram according to the curvature change of the connecting rod structure to avoid wrinkles and stress concentration during the layup process;

[0022] When the comparison results of the index parameters do not meet the preset standards, OptiStruct is used to optimize the layup design of the carbon fiber composite connecting rod. The optimal layup thickness and shape at each angle are obtained through free size optimization. The number of layups at each angle is obtained through size optimization. Finally, the optimal layup sequence is obtained through layup sequence optimization.

[0023] In this solution, in step S108, the material selection scheme for the carbon fiber composite connecting rod is determined, specifically:

[0024] PMI foam was selected as the supporting material for the carbon fiber composite connecting rod, and thermal expansion foam was used as the expansion material to coat the surface of the PMI foam. Then, prepreg was coated on the surface of the thermal expansion foam layer by layer.

[0025] At the same time, the metal rings at both ends of the connecting rod are embedded and covered, and then placed in a rigid mold and heated for thermal expansion molding, so as to finally prepare a carbon fiber composite connecting rod, wherein the expansion material and the support material are both retained inside the connecting rod.

[0026] In this solution, in step S108, a carbon fiber composite connecting rod is prepared using a thermal expansion process, specifically:

[0027] Cut or tailor PMI foam, thermal expansion foam and prepreg to preset sizes and quantities;

[0028] The heat expansion foam and prepreg are sequentially laid on the surface of the PMI foam core. The heat expansion foam is laid separately and closely on the four sides of the PMI foam using a single-sided laying method, and the prepreg is laid symmetrically using a double-sided overlapping method.

[0029] Place the laid connecting rod into the rigid mold that has been evenly coated with release agent, and tighten the rigid mold with bolts;

[0030] The rigid mold is heated. During the heating process, the viscosity of the resin gradually decreases, the prepreg softens, and the thermal expansion foam begins to expand due to the heat. Within the reserved process gap, due to the spatial constraints of the core material and the mold, the thermal expansion foam generates enough expansion pressure to meet the requirements of carbon fiber composite molding;

[0031] The carbon fiber composite connecting rod sample is obtained by demoulding.

[0032] In this solution, in the preparation of carbon fiber composite connecting rods using a thermal expansion process, the preforming and coating method is specifically as follows:

[0033] In the layup of the connecting rod body, heat-expanding foam and prepreg are sequentially laid on the surface of the PMI foam core. Several layers of heat-expanding foam are laid using a single-sided layup method, and the prepreg is symmetrically laid using a double-sided overlap method to achieve inter-layer slippage during the expansion process.

[0034] In addition, prepreg reinforcement is laid in the fillet area of ​​the connecting rod main body to avoid surface defects in the fillet area of ​​the carbon fiber composite connecting rod, thereby completing the preformed covering of the connecting rod main body;

[0035] In the layup of the connecting rod metal ring, the metal ring is connected to the main body by wrapping prepreg around the metal ring. The prepreg of the connecting rod main body is extended from both sides at the same time. By adjusting the interface distribution position of the prepreg outside the metal ring, the stress concentration at the metal ring is reduced and the weak points of the interface are dispersed.

[0036] A heat-expanding foam layer and a prepreg layer are added between the metal ring and the PMI foam core, so that the metal ring is connected to the prepreg of the connecting rod main body through surface contact, reducing the gap between the metal ring part and the main body part to complete the preformed covering of the connecting rod metal ring part.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] This invention solves the existing problem of irregular composite connecting rods being unable to be integrally molded. By using PMI foam as a support material, thermal expansion foam as an expansion material coated on the PMI foam surface, and then layering prepreg on the thermal expansion foam surface, the invention also pre-embeds and coats metal rings at both ends. The rod is then placed in a rigid mold, heated, and thermally expanded to form a foam-core composite connecting rod. Both the thermal expansion material and support material are retained within the connecting rod, achieving integrated molding. The thermal expansion material and support material within the connecting rod contribute to improved energy absorption characteristics.

[0039] A series of carbon fiber composite connecting rods were produced using the molding process of this invention. After multiple optimizations and improvements, the surface quality of the carbon fiber composite connecting rods was excellent, with no noticeable defects or damage. This demonstrated relatively uniform pressure during the molding process and the appropriate process configuration. This pioneered the effective production of carbon fiber composite connecting rods for automotive applications. After weighing, the rods were approximately 55% lighter than steel automotive connecting rods, demonstrating a significant lightweighting effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments or exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or exemplary descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained according to these drawings without paying any creative work.

[0041] Figure 1 A flow chart of the lightweight design and preparation method of carbon fiber automotive composite connecting rods is shown;

[0042] Figure 2 The PMI foam core and layup design of the carbon fiber composite connecting rod in the embodiment are shown;

[0043] Figure 3 A schematic diagram of a layup method for preforming and wrapping a carbon fiber composite connecting rod in an embodiment is shown;

[0044] Figure 4 A schematic diagram of the preparation process of a carbon fiber composite connecting rod in an embodiment is shown;

[0045] Figure 5 The tensile test load-displacement curve of the carbon fiber composite connecting rod in the embodiment is shown;

[0046] Figure 6 The load-displacement curve of the compression test of the carbon fiber composite connecting rod in the embodiment is shown. DETAILED DESCRIPTION

[0047] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0048] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0049] like Figure 1 As shown, an embodiment of the present invention provides a lightweight design and preparation method for a carbon fiber automotive composite connecting rod, comprising:

[0050] Step S102: Taking a steel automotive connecting rod as a reference, basic performance indicators of the connecting rod are obtained through static analysis and modal analysis.

[0051] It should be noted that a comprehensive performance evaluation of automotive parts requires consideration of both static and dynamic characteristics. Static analysis can more accurately obtain the strength and stiffness performance of the structure under typical working conditions, and the solution is efficient. As the basis of dynamic analysis, modal analysis can be used to determine whether the structure is reasonable. Taking the steel automotive connecting rod as a reference, HyperMesh software was used for pre-processing, and ABAQUS software was used for solving to obtain a three-dimensional model of the steel automotive connecting rod. The three-dimensional model was simplified and geometrically cleaned to establish the geometry and unit set. Since the connecting rod is a sandwich thin-walled structure, shell elements are used to divide the mesh and perform mesh quality inspection. The mesh quality inspection indicators include the proportion of triangular mesh elements, the Jacobian ratio of the mesh elements, the aspect ratio and warpage, etc. When the mesh quality meets the preset requirements, a preset number of typical working conditions of steel automotive connecting rods are selected to establish a load set; in the load set, load conditions are constructed by applying loads and boundary conditions, a connecting rod finite element model is constructed, and a static simulation analysis is performed on the steel automotive connecting rod to obtain the material properties of the steel automotive connecting rod, which include density, Poisson's ratio, elastic modulus, tensile strength, yield strength and elongation.

[0052] In addition, the Von Mises yield criterion was used to evaluate the structural strength and obtain the strength analysis results of the steel automotive connecting rod. Finite element stiffness analysis was performed on the steel automotive connecting rod. By extracting the reaction force at the loading point during the elastic deformation stage of the connecting rod, a force-displacement curve was obtained. The slope of the curve is the stiffness of the connecting rod. The bending stiffness K1 and torsional stiffness K2 were calculated as follows:

[0053]

[0054] Where P is the load acting on the connecting rod, δ is the deformation of the connecting rod caused by the force, M is the torque acting on the connecting rod, and θ is the torsion angle of the connecting rod caused by the torque.

[0055] Mode is an inherent property of a mechanical structure and can be divided into free modes and constrained modes depending on the constraints. Resonance in the suspension system will affect the stability and comfort of the vehicle. To prevent the excitation frequency generated during vehicle operation from approaching the natural frequency of the connecting rod, which would cause resonance, it is necessary to perform modal analysis on the steel automotive connecting rod to obtain parameters such as the natural frequency and modal vibration shape, and to verify whether the mode meets the requirements. Finally, the basic performance indicators of the connecting rod are constructed based on the material properties, steel quality analysis results, strength analysis results, and modal analysis results of the steel automotive connecting rod.

[0056] Step S104: Based on the design requirements of the carbon fiber composite material structure, combined with the structural characteristics of the connecting rod main body and the connection part, and based on the existing steel vehicle connecting rod, a structural design of the carbon fiber composite material connecting rod is obtained.

[0057] It should be noted that in the lightweight design of the structure, carbon fiber composite materials are used to replace the steel materials of the steel vehicle connecting rod structure. The equal stiffness approximation theory is used to obtain the thickness of the connecting rod structure after the material replacement. The stiffness and thickness of the structure are nonlinearly related, which can be approximately expressed as:

[0058] k=λEt η

[0059] Where k is the structural stiffness, λ is the geometric coefficient of the structure, E is the elastic modulus of the material, t is the thickness of the structure, and η is the thickness index coefficient, which is usually 1 to 3;

[0060] When the stiffness remains unchanged, the calculation formula for the thickness of the carbon fiber composite connecting rod is expressed as:

[0061]

[0062] where t c and t0 are the thickness of the carbon fiber composite connecting rod and the thickness of the steel automotive connecting rod, respectively. c and E0 are the equivalent elastic modulus of carbon fiber composite material and the elastic modulus of steel material, respectively.

[0063] The key structural features of the steel automotive connecting rod structure are obtained based on the structural characteristics of the connecting rod main body and the metal ring connection part. The geometric structure design of the carbon fiber composite material connecting rod and the structural design of the connection part of the hybrid structure of carbon fiber composite material and steel material are determined based on the thickness of the connecting rod structure and the key structural features. The layup design of the carbon fiber composite material connecting rod is determined through the structural design of the carbon fiber composite material connecting rod.

[0064] It's important to note that the following points must be considered when designing a carbon fiber composite connecting rod. First, the composite connecting rod's shape must be paved. Specifically, each ply must be able to unfold into a flat or nearly flat surface. For plies that are difficult to unfold into a flat surface, appropriate process gaps should be designed. To ensure paved composite connecting rod structure, the connecting rod's shape should be appropriately simplified, minimizing the use of complex spatial curves. Areas with sudden changes in curvature should have smooth transitions, and typical metal structural features should be omitted if they are no longer necessary in the composite structure. To prevent warping caused by inconsistent resin shrinkage during the molding process, the thickness of each part of the carbon fiber composite connecting rod should be as uniform as possible. Stepped transitions should be employed to avoid sudden changes in thickness and minimize warping. Furthermore, to prevent resin accumulation, fiber bridging, and fiber breakage at corners, the corner radius should be as large as possible. The intersections between two surfaces should be designed as right angles, obtuse angles, or arc transitions. Based on these requirements, the carbon fiber composite connecting rod design was conducted using the equivalent design method. Under the same operating conditions as loads and constraints, the original material was replaced with a carbon fiber composite material of the same shape, retaining the key features of the original structure. The design was based on the structural form and mechanical properties of a steel automotive connecting rod, and the strength and stiffness of the new structure were calculated and compared with the original structure.

[0065] Step S106: performing finite element modeling based on the structural design of the carbon fiber composite connecting rod, obtaining index parameters of basic performance indicators using the finite element model, and outputting a lightweight design solution for the carbon fiber composite connecting rod when the index parameters meet preset standards.

[0066] It should be noted that finite element modeling is performed based on the structural design of the carbon fiber composite connecting rod to obtain a finite element model of the carbon fiber composite connecting rod. According to the typical working conditions of the steel automotive connecting rod, the same constraints and loads are applied to the carbon fiber composite connecting rod based on the established finite element model to perform performance analysis; the index parameters of the basic performance indicators are obtained, and the performance analysis results of the steel automotive connecting rod are used as a benchmark to compare the index parameters with the benchmark. When the comparison results of the index parameters meet the preset standards, the lightweight design scheme of the carbon fiber composite connecting rod is output; otherwise, the layup design of the carbon fiber composite connecting rod is optimized.

[0067] In the lightweight design of carbon fiber composite connecting rod, the layering sequence [(0°) 10 / (0,90)] to perform layup design for a carbon fiber composite connecting rod. This layup design generates a layup design diagram for each layer of carbon fiber composite material. Process notches are set within the layup design diagram based on the curvature of the connecting rod structure to avoid wrinkles and stress concentration during the layup process. Furthermore, the process notches between the upper and lower prepreg layup designs should be positioned as far apart as possible to avoid stress concentration. After the thermal expansion foam and prepreg are cut to the dimensions of the layup design diagram, they can be preformed and wrapped. If the comparison results of the aforementioned parameters do not meet the preset criteria, the carbon fiber composite connecting rod layup design is optimized using OptiStruct. OptiStruct software offers significant advantages in the field of composite material optimization. Based on the finite element method, it provides full-process layup optimization capabilities, taking into account structural strength, stiffness, and manufacturing constraints, offering powerful structural optimization capabilities. OptiStruct software was used for the composite connecting rod layup optimization design. Preprocessing was performed in HyperMesh, and the optimization results were viewed in HyperView. The optimal ply thickness and shape at each angle are obtained through free size optimization, the number of plies at each angle is obtained through size optimization, and finally the optimal ply sequence is obtained through ply sequence optimization.

[0068] Step S108: Based on the lightweight design of the carbon fiber composite material connecting rod, the carbon fiber composite material connecting rod is prepared by using a thermal expansion process, and the obtained carbon fiber composite material connecting rod sample is subjected to tensile and compressive mechanical property tests.

[0069] It should be noted that PMI foam is selected as the supporting material for the carbon fiber composite connecting rod, and the thermal expansion foam is coated on the surface of the PMI foam as the expansion material. Then the prepreg is coated on the surface of the thermal expansion foam layer by layer, and effective molding is achieved through interlayer slippage between the prepregs; at the same time, the metal rings at both ends of the connecting rod are pre-embedded and coated, and placed in a rigid mold and heated for thermal expansion molding, and finally a carbon fiber composite connecting rod is prepared. The expansion material and the supporting material are retained inside the connecting rod to improve the energy absorption characteristics of the carbon fiber composite connecting rod.

[0070] The PMI foam core and layup design of the carbon fiber composite connecting rod is shown in the figure below. Figure 2 As shown in the figure, in the ply of the connecting rod main body, several layers of thermal expansion foam are laid on the main body. The thermal expansion foam is laid in a full circle, that is, each layer is connected end to end; the prepreg is laid symmetrically in a double-sided overlap manner to achieve inter-layer sliding during the expansion process, as shown in the figure. Figure 3As shown. At the same time, the problems of difficulty in closing the mold during the production process and wrinkles on the surface of the carbon fiber composite connecting rod body after molding are solved. Considering that the distance between the fillet and the mold is farther than the distance between the flat edge and the mold, a cavity will be formed at the fillet during the molding and curing process, resulting in uneven transmission of thermal expansion pressure, which may further form a local low-pressure area on the surface of the fillet, and ultimately cause a resin-deficient area on the surface. Therefore, when laying the prepreg, the fillet is reinforced with emphasis. After increasing the number of thermal expansion foam layers, the prepreg is fully extruded more evenly. At the same time, after the fillet is reinforced, the thickness of the prepreg at the fillet is thicker, so that it is sufficient to fill the gap and fit tightly with the mold, making the connecting rod surface flat and smooth without obvious surface defects.

[0071] In the winding of the connecting rod metal ring connection part, the metal ring is connected to the main body by winding the prepreg outside the metal ring. By adjusting the distribution position of the carbon fiber reinforced plastic interface outside the ring, the stress concentration at the metal ring is reduced, such as Figure 3 As shown. The main body's prepreg is extended from both sides at the same time, and the interfaces of the prepreg are staggered through calculation. This can not only reduce the stress concentration at the connection between the ring and the main body, but also disperse the weak points of these interfaces. By adjusting the layer structure between the metal ring and the main body, the connection tightness of the ring rod is improved. A thermal expansion foam layer and a prepreg layer are added between the PMI inner core and the metal ring. At this time, the metal ring can be connected to the main body's prepreg through surface contact, which improves the stability between the metal ring and the main body, and the gap defects after molding are also reduced.

[0072] like Figure 4 As shown, the automotive composite connecting rod is prepared by thermal expansion molding technology, and the carbon fiber composite connecting rod is prepared by thermal expansion process, specifically: first, the PMI foam, thermal expansion foam and prepreg are cut or tailored to preset sizes and quantities; the thermal expansion foam and prepreg are sequentially layered on the surface of the PMI foam core, and the tight contact between the materials should be ensured as much as possible during the coating process, wherein the thermal expansion foam is laid separately and tightly according to the four sides of the PMI foam using a single-sided laying method, and the prepreg is symmetrically layered using a double-sided overlap method; the laid connecting rod is placed in a rigid mold that has been evenly coated with a release agent, and the rigid mold is fastened with bolts; the rigid mold is heated, and during the heating process, the viscosity of the resin gradually decreases, the prepreg softens, and the thermal expansion foam begins to expand due to the heat. In the reserved process gap, due to the spatial constraints of the core material and the mold, the thermal expansion foam generates expansion pressure sufficient to meet the requirements of carbon fiber composite molding; by demolding, a sample of the carbon fiber composite connecting rod is obtained.

[0073] It should be noted that in order to ensure the accuracy and efficiency of the preparation process, corresponding bosses are set at the pre-embedded positions of the metal rings in the rigid mold to facilitate the positioning of the metal rings at both ends. The carbon fiber composite connecting rod is prepared according to a series of processes including mold cleaning, foam core cutting, prepreg and thermal expansion foam cutting, material laying, mold closing, thermoforming, demolding and polishing. In order to simplify the production process and improve production efficiency, after many tests and adjustments, the final process parameter selected was heating at 150°C for 2 hours. The prepared carbon fiber composite connecting rod sample was weighed, and the weight was reduced by about 55% compared with the steel automotive connecting rod, showing a significant lightweight effect.

[0074] In this embodiment, the mechanical properties of the carbon fiber composite connecting rod sample are tested to obtain the tensile and compressive load-displacement curves, such as Figure 5 、 Figure 6 As shown in the figure, during the initial tensile stage, the load increases linearly and rapidly, leading to the fracture of the outermost layer of prepreg fibers on the outer side of the upper sleeve. During the subsequent tensile crushing process, the prepreg breaks sequentially from the outside to the inside, until it completely breaks at the peak load. This is accompanied by a resounding thud, and the load then drops dramatically. The maximum peak load of the connecting rod is 61.2 kN. The mechanical response of the carbon fiber composite connecting rod during crush failure can be divided into two stages. The first stage is defined as the elastic deformation stage. Because the material's yield limit has not been reached, the load increases almost linearly, resulting in subtle elastic deformation and no surface macroscopic damage. The second stage is defined as the plastic deformation stage. During this process, the resin matrix fractures and minor cracks appear on the fibers at the bend of the main body. The load fluctuates, and the rate of increase gradually slows, indicating a continuous decrease in stiffness. Once the load reaches its peak, the load suddenly drops significantly, accompanied by a resounding thud, due to transverse fiber fracture in the CFRP and shear cracking in the PMI foam and thermal expansion foam. However, the support provided by the CFRP tube wall and core prevents the load from dropping to a very low value. The mechanical properties test data of the carbon fiber composite connecting rod specimens are summarized in Table 1 below.

[0075] Table 1 Summary of mechanical properties test data

[0076]

[0077]

[0078] The tensile and compressive mechanical properties of the carbon fiber composite connecting rod were tested. By analyzing the load-displacement curves of the compression and tensile tests, it was concluded that the tensile and compressive properties of the carbon fiber composite connecting rod specimen prepared in this embodiment met the index requirements.

[0079] The above are only specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the scope of protection of the present invention.

Claims

1. A lightweight design and preparation method for a carbon fiber composite material connecting rod for automobiles, characterized in that: The following steps are involved: Step S102: Taking a steel automotive connecting rod as a reference, basic performance indicators of the connecting rod are obtained through static analysis and modal analysis; Step S104: obtaining a structural design of a carbon fiber composite connecting rod based on the design requirements of the carbon fiber composite material structure, the structural characteristics of the connecting rod main body and the connection parts, and the existing steel automotive connecting rod; Step S106: performing finite element modeling based on the structural design of the carbon fiber composite connecting rod, obtaining index parameters of basic performance indicators using the finite element model, and outputting a lightweight design solution for the carbon fiber composite connecting rod when the index parameters meet preset standards; Step S108: Based on the lightweight design of the carbon fiber composite connecting rod, the connecting rod is prepared by using a thermal expansion process, and the obtained carbon fiber composite connecting rod sample is subjected to tensile and compressive mechanical property tests; In step S108, the material selection scheme for the carbon fiber composite connecting rod is determined, specifically: PMI foam was selected as the supporting material for the carbon fiber composite connecting rod, and thermal expansion foam was used as the expansion material to coat the surface of the PMI foam. Then, prepreg was coated on the surface of the thermal expansion foam layer by layer. At the same time, the metal rings at both ends of the connecting rod are embedded and covered, and then placed in a rigid mold and heated for thermal expansion molding, so as to finally prepare a carbon fiber composite connecting rod, wherein the expansion material and the support material are both retained inside the connecting rod.

2. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 1, characterized in that: The step S102 is specifically as follows: Obtaining a three-dimensional model of a steel automotive connecting rod, simplifying and geometrically cleaning the three-dimensional model to establish a geometry and element set, meshing the model using shell elements, and performing a mesh quality check. When the mesh quality meets preset requirements, selecting a typical working condition of the steel automotive connecting rod to establish a load set; In the load concentration, a load condition is constructed by applying loads and boundary conditions, a connecting rod finite element model is constructed, and a static simulation analysis is performed on the steel vehicle connecting rod to obtain material properties, stiffness analysis results, and strength analysis results of the steel vehicle connecting rod, wherein the material properties include density, Poisson's ratio, elastic modulus, tensile strength, yield strength, and elongation; At the same time, modal analysis is performed to obtain the natural frequency and modal vibration shape of the steel automotive connecting rod in different modes, and the modal analysis results are obtained. Based on the material properties, steel quality analysis results, strength analysis results and modal analysis results of the steel automotive connecting rod, the basic performance indicators of the connecting rod are constructed.

3. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 1, characterized in that: In step S104, the structural design of the carbon fiber composite connecting rod is performed using an equivalent design method, specifically: Carbon fiber composite materials are used to replace the steel material of the steel vehicle connecting rod structure, and the equal stiffness approximation theory is used to obtain the thickness of the connecting rod structure after the material replacement; The key structural features of the steel automotive connecting rod structure are obtained based on the structural characteristics of the connecting rod main body and the metal ring connection part. The geometric structure design of the carbon fiber composite material connecting rod and the structural design of the connection part of the hybrid structure of carbon fiber composite material and steel material are determined based on the thickness of the connecting rod structure and the key structural features. The layup design of the carbon fiber composite material connecting rod is determined through the structural design of the carbon fiber composite material connecting rod.

4. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 1, characterized in that: The step S106 is specifically as follows: Finite element modeling is performed based on the structural design of the carbon fiber composite connecting rod to obtain a finite element model of the carbon fiber composite connecting rod. Based on the established finite element model, the same constraints and loads are applied to the carbon fiber composite connecting rod according to the typical operating conditions of a steel automotive connecting rod to perform performance analysis; Obtain basic performance index parameters, use the performance analysis results of steel automotive connecting rods as a benchmark, and compare the index parameters with the benchmark. When the comparison results of the index parameters meet the preset standards, a lightweight design solution for the carbon fiber composite connecting rod is output; otherwise, the layup design of the carbon fiber composite connecting rod is optimized.

5. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 4, characterized in that: In the lightweight design of carbon fiber composite connecting rod, the layup sequence is adopted To carry out the layup design of carbon fiber composite connecting rod; A layup design diagram for each layer of carbon fiber composite material is obtained through layup design. Process notches are set in the layup design diagram according to the curvature change of the connecting rod structure to avoid wrinkles and stress concentration during the layup process; When the comparison results of the index parameters do not meet the preset standards, OptiStruct is used to optimize the layup design of the carbon fiber composite connecting rod. The optimal layup thickness and shape at each angle are obtained through free size optimization. The number of layups at each angle is obtained through size optimization. Finally, the optimal layup sequence is obtained through layup sequence optimization.

6. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 1, characterized in that: In step S108, a carbon fiber composite connecting rod is prepared by using a thermal expansion process, specifically: Cut or tailor PMI foam, thermal expansion foam and prepreg to preset sizes and quantities; The heat expansion foam and prepreg are sequentially laid on the surface of the PMI foam core. The heat expansion foam is laid on one side, and is laid separately and closely on the four sides of the PMI foam. The prepreg is laid symmetrically using a double-sided overlap method. Place the laid connecting rod into the rigid mold that has been evenly coated with release agent, and tighten the rigid mold with bolts; The rigid mold is heated. During the heating process, the viscosity of the resin gradually decreases, the prepreg softens, and the thermal expansion foam begins to expand due to the heat. Within the reserved process gap, due to the spatial constraints of the core material and the mold, the thermal expansion foam generates enough expansion pressure to meet the requirements of carbon fiber composite molding; The carbon fiber composite connecting rod sample is obtained by demoulding.

7. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 6, characterized in that: In the preparation of carbon fiber composite connecting rods using a thermal expansion process, the preforming and coating method is specifically as follows: In the layup of the connecting rod body, heat-expanding foam and prepreg are sequentially layered on the surface of the PMI foam core. Several layers of heat-expanding foam are laid using a single-sided layup method, and the prepreg is symmetrically laid using a double-sided overlap method to achieve inter-layer slippage during the expansion process. In addition, prepreg reinforcement is laid in the fillet area of ​​the connecting rod main body to avoid surface defects in the fillet area of ​​the carbon fiber composite connecting rod, thereby completing the preformed covering of the connecting rod main body; In the layup of the connecting rod metal ring, the metal ring is connected to the main body by wrapping prepreg around the metal ring. The prepreg of the connecting rod main body is extended from both sides at the same time. By adjusting the interface distribution position of the prepreg outside the metal ring, the stress concentration at the metal ring is reduced and the weak points of the interface are dispersed. A heat-expanding foam layer and a prepreg layer are added between the metal ring and the PMI foam core, so that the metal ring is connected to the prepreg of the connecting rod main body through surface contact, reducing the gap between the metal ring part and the main body part to complete the preformed covering of the connecting rod metal ring part.

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