Lightweight design and preparation method of composite material connecting rod for carbon fiber vehicle

Abstract

The invention discloses a lightweight design and preparation method of a carbon fiber vehicle composite material connecting rod, which comprises the following steps: taking PMI foam as a support material, taking thermal expansion foam as an expansion material to coat the surface of the PMI foam, and then coating the surface of the thermal expansion foam with prepreg layer by layer. And meanwhile, the metal rings at the two ends are pre-embedded and coated and then put into a rigid mold to be heated for thermal expansion forming, and finally the foam sandwich carbon fiber composite material connecting rod is integrally prepared. The integrated forming process of the special-shaped tubular structure is innovatively provided, the carbon fiber composite material connecting rod prepared through the forming process is good in surface quality and free of obvious defects and damage, effective preparation of the carbon fiber vehicle composite material connecting rod is achieved firstly, performance indexes meet index requirements, and the carbon fiber vehicle composite material connecting rod is suitable for being used for a vehicle. And after weighing, the weight is reduced by about 55% compared with that of a metal connecting rod, and a remarkable lightweight effect is shown.

Description

Technical Field

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

[0002] With the continuous increase in the number of cars in the world, a series of problems such as energy shortage and environmental pollution are becoming increasingly prominent. Lightweighting of cars can significantly reduce energy consumption and environmental pollution, while effectively increasing the service life of key components and improving the comfort and safety of cars. Therefore, it has become an important development trend in the current automotive industry. Lightweight materials for cars are one of the important ways to achieve lightweight car structures. Carbon fiber reinforced resin-based composite materials (CFRP) have been gradually replacing automotive metal materials with their unique lightweight effects and excellent mechanical properties, and are increasingly widely used in automotive body and chassis structural parts.

[0003] As the positioning element of the automobile suspension system, the automotive connecting rod mainly bears the lateral tensile and compressive loads transmitted to it by the rear steering knuckle and plays a role in positioning and supporting. Therefore, the rear suspension adjustment connecting rod should have sufficient stiffness, strength and service life. At present, major mainstream pure electric platforms around the world have adopted five-link rear suspensions. Due to the axle load of electric vehicles, the strength and stiffness requirements of the connecting rod are higher, which will inevitably lead to a heavier connecting rod. The increase in unsprung mass leads to a decrease in performance and a decrease in 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 of a carbon fiber automotive composite material connecting rod, which can achieve a lightweight design of the rear suspension connecting rod structure while 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 of a carbon fiber vehicle composite connecting rod, comprising the following steps:

[0006] Step S102: taking the steel vehicle connecting rod as a reference, obtaining basic performance indicators of the connecting rod through static analysis and modal analysis;

[0007] Step S104: obtaining a structural design of a carbon fiber composite material connecting rod 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;

[0008] Step S106: performing finite element modeling according to the structural design of the carbon fiber composite material connecting rod, and obtaining index parameters of basic performance using the finite element model. When the index parameters meet preset standards, a lightweight design scheme of the carbon fiber composite material connecting rod is output;

[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 vehicle connecting rod, simplifying and geometrically cleaning the three-dimensional model to establish a geometry and unit set, using shell units to divide the mesh and perform a mesh quality check, and when the mesh quality meets the preset requirements, selecting a preset number of typical working conditions of the steel vehicle 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 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;

[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. 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.

[0014] In this solution, in step S104, the structural design of the carbon fiber composite material connecting rod is performed using the 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 features of the structural form of the steel vehicle 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 features of the structural form, and 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 according to the structural design of the carbon fiber composite material connecting rod to obtain a finite element model of the carbon fiber composite material connecting rod, and the same constraints and loads are applied to the carbon fiber composite material connecting rod based on the established finite element model according to the typical working conditions of the steel vehicle connecting rod to perform performance analysis;

[0019] Obtain index parameters of basic performance, take the performance analysis results of steel automotive connecting rods as a benchmark, compare the index parameters with the benchmark, and when the comparison results of the index parameters meet the preset standards, output a lightweight design scheme for the carbon fiber composite material connecting rod, otherwise, optimize the layup design of the carbon fiber composite material connecting rod.

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

[0021] A layup design diagram of each layer of carbon fiber composite material is obtained through layup design, and a process notch is set in the layup design diagram according to the curvature change of the connecting rod structure to avoid wrinkles and stress concentration during the laying 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, and 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 material connecting rod is determined, specifically:

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

[0025] At the same time, the metal rings at both ends of the connecting rod are embedded and coated, and placed in a rigid mold for heating and thermal expansion molding, and finally a carbon fiber composite connecting rod is prepared, and the expansion material and the supporting material are retained inside the connecting rod.

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

[0027] Cut or trim PMI foam, heat 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, wherein the heat expansion foam is laid separately and closely on the four sides of the PMI foam by single-sided laying, and the prepreg is laid symmetrically by double-sided overlapping;

[0029] Place the laid connecting rod into the rigid mold that has been evenly coated with release agent, and fasten 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 heat-expanding foam begins to expand due to the heat. Under the reserved process gap, due to the spatial constraints of the core material and the mold, the heat-expanding foam generates enough expansion pressure to meet the carbon fiber composite material molding requirements;

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

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

[0033] In the plying of the connecting rod body, the heat expansion foam and prepreg are sequentially laid on the surface of the PMI foam core. Several layers of heat expansion foam are laid using a single-sided plying 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, the prepreg is reinforced and laid in the fillet area of ​​the connecting rod main body to avoid surface defects in the fillet area of ​​the carbon fiber composite material connecting rod, so as to complete the preforming coating of the connecting rod main body;

[0035] In the layup of the metal ring part of the connecting rod, the connection between the metal ring and the main body is achieved by winding the prepreg outside the metal ring, and the prepreg of the main part of the connecting rod 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 position of the interface is dispersed;

[0036] A heat expansion 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 body through surface contact, reducing the gap between the metal ring part and the body part to complete the preforming covering of the connecting rod metal ring part.

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

[0038] The present invention solves the problem that the special-shaped composite connecting rod cannot be integrally formed in the prior art, by using PMI foam as a supporting material, and thermal expansion foam as an expansion material coated on 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 for heating and thermal expansion molding, and finally a foam sandwich composite connecting rod is prepared, and the thermal expansion material and the supporting material are retained inside the connecting rod to achieve integrated molding, wherein the thermal expansion material and the supporting material inside the connecting rod are conducive to improving the energy absorption characteristics of the connecting rod.

[0039] A series of carbon fiber composite connecting rods were prepared by the molding process of the present invention. After multiple optimizations and improvements, the surface quality of the carbon fiber composite connecting rods was good, without obvious defects and damage, indicating that the pressure was relatively uniform during the molding process, the selected process configuration was appropriate, and the effective preparation of carbon fiber composite connecting rods for automobiles was first realized. After weighing, the weight was reduced by about 55% compared with the steel automobile connecting rod, showing a significant lightweight 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 drawings required for use in the embodiments or exemplary descriptions will be briefly introduced below. 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 the drawings without paying creative work.

[0041] Figure 1 A flow chart of a lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles is shown;

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

[0043] Figure 3 A schematic diagram of the layup method of the preformed coating of the carbon fiber composite material connecting rod in the 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 purpose, 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 the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[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 protection scope 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 vehicle composite material connecting rod, comprising:

[0050] Step S102: Taking a steel vehicle 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 the comprehensive performance evaluation of automotive parts requires consideration of both static and dynamic characteristics. Static analysis can 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 is used for pre-processing, and ABAQUS software is used for solving to obtain the three-dimensional model of the steel automotive connecting rod. The three-dimensional model is simplified and geometrically cleaned to establish the geometry and unit set. Since the connecting rod is a sandwich thin-walled structure, shell units are used to divide the mesh and perform mesh quality inspection. The indicators of the mesh quality inspection include the proportion of triangular mesh units, the Jacobian ratio of the mesh unit, 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 is used to evaluate the structural strength and obtain the strength analysis results of the steel vehicle connecting rod. The finite element stiffness analysis of the steel vehicle connecting rod is performed, and the force-displacement curve is obtained by extracting the reaction force at the loading point of the connecting rod in the elastic deformation stage. The slope of the curve is the stiffness of the connecting rod. The bending stiffness K1 and torsional stiffness K2 are 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 mode and constrained mode according to different constraints. The resonance of the suspension system will affect the stability and comfort of the car. In order to avoid the resonance caused by the excitation frequency generated during the driving of the car being close to the natural frequency of the connecting rod, it is necessary to perform modal analysis on the steel automotive connecting rod, obtain parameters such as natural frequency and modal vibration shape, and check 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: obtaining a structural design of a carbon fiber composite material connecting rod 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.

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

[0060] When the stiffness remains unchanged, the thickness calculation formula 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 features of the structural form of the steel vehicle 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 features of the structural form, and 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 should be noted that the following points need to be considered when designing the structure of a carbon fiber composite connecting rod: First, the paving ability of the composite connecting rod structure should be considered, that is, each ply block of the structure must be unfolded into a plane or an approximate plane. For plies that are difficult to unfold into a plane, the process gap should be reasonably designed. In order to achieve the paving ability of the composite connecting rod structure, the structural shape of the connecting rod should be appropriately simplified, and complex spatial curved surfaces should not be used as much as possible. The area with sudden changes in curvature should be smoothly transitioned, and some typical metal structural features should be appropriately deleted if they are not necessary in the composite structure. In order to avoid the warping deformation of the structure caused by inconsistent shrinkage of the resin during the molding process, the thickness of each part of the carbon fiber composite connecting rod structure should be as consistent as possible, and a stepped transition design should be adopted to avoid sudden changes in thickness and reduce warping deformation. Furthermore, in order to avoid resin accumulation, fiber bridging and fiber breakage at the corners of the structure, the fillet radius at the corners should be as large as possible, and the intersection of the two surfaces in the structure should also be designed as a right angle or an obtuse angle, or a circular arc transition should be used. Based on the above requirements, the equivalent design method is used to design the carbon fiber composite connecting rod. Under the condition that the load and constraint environment remain unchanged, the original material is replaced by a carbon fiber composite material with the same shape, retaining the main key features of the original structure. The steel vehicle connecting rod structure and its mechanical properties are used as the design basis, and the strength and stiffness of the new structure are calculated and compared with the original structure.

[0065] Step S106: Perform finite element modeling according to the structural design of the carbon fiber composite material connecting rod, and use the finite element model to obtain index parameters of basic performance indicators. When the index parameters meet preset standards, a lightweight design scheme for the carbon fiber composite material connecting rod is output.

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

[0067] In the lightweight design of carbon fiber composite connecting rod, the ply sequence [(0°) 10 / (0,90)] to carry out the layup design of the carbon fiber composite connecting rod; the layup design drawing of each layer of carbon fiber composite material is obtained through the layup design, and the process notch is set in the layup design drawing according to the curvature change of the connecting rod structure to avoid wrinkles and stress concentration during the laying process; in addition, the process notch position between the upper and lower prepreg layup design drawings should be as far away from each other as possible to avoid stress concentration. After the thermal expansion foam and prepreg are cut according to the size of the layup design drawing, they can be preformed and coated. When the comparison result of the index parameters does not meet the preset standard, the layup design of the carbon fiber composite connecting rod is optimized by OptiStruct. In the field of composite material optimization, OptiStruct software has significant advantages. It provides full-process layup optimization function based on the finite element method, and can consider the strength, stiffness and process manufacturing constraints of the structure, and has powerful structural optimization function. OptiStruct software is used to optimize the layup design of the composite connecting rod. The pre-processing is carried out in HyperMesh, and the optimization results are 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 of the carbon fiber composite connecting rod, the heat expansion foam is coated on the surface of the PMI foam as the expansion material, and then the prepreg is coated on the surface of the heat expansion foam layer by layer, and effective molding is achieved through the 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, and 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 FIG. 1 , in the plying of the connecting rod main body, several layers of heat expansion foam are laid on the main body, and the heat expansion foam is laid in a full circle, that is, each layer is connected end to end; the prepreg is symmetrically laid in a double-sided overlap manner to achieve inter-layer sliding during the expansion process, as shown in FIG. Figure 3As shown. At the same time, the problem of mold closing difficulties encountered during the production process and wrinkles on the surface of the carbon fiber composite connecting rod body after molding was 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 part is reinforced. After increasing the number of thermal expansion foam layers, the prepreg is fully extruded and 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 enough 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 can be reduced, such as Figure 3 As shown. The prepreg of the main body is extended from both sides at the same time, and the interfaces of the prepreg are staggered by calculation. This can not only reduce the stress concentration at the connection between the ring and the main body, but also disperse the weak positions of these interfaces. The connection tightness of the ring rod is improved by adjusting the layer structure between the metal ring and the main body. 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 prepreg of the main body 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 trimmed to preset sizes and quantities; the thermal expansion foam and prepreg are layered on the surface of the PMI foam core in turn, 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 by single-sided laying method, and the prepreg is symmetrically laid by 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. Under 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 carbon fiber composite material molding requirements; the carbon fiber composite connecting rod sample is obtained by demolding.

[0073] It should be noted that in order to ensure the accuracy and efficiency of the preparation process, corresponding bosses are set at the positions where the metal rings are embedded 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 such as mold cleaning, foam core cutting, prepreg and thermal expansion foam cutting, material laying, mold closing, heating molding, demolding and polishing. In order to simplify the production process and improve production efficiency, after many tests and adjustments, the process parameters finally selected were 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 initial stage of stretching, the load rises rapidly and linearly, and the outermost layer of prepreg fibers on the outer side of the upper sleeve breaks. In the subsequent tensile process, the prepreg is broken from the outside to the inside until it breaks completely when the peak load is reached, accompanied by a loud and crisp sound, and the load drops drastically. The maximum peak load of the connecting rod is 61.2kN. The mechanical response of the crushing failure process of the carbon fiber composite connecting rod can be divided into two stages. The first stage is defined as the elastic deformation stage. Since the yield limit of the material has not been reached, the load increases almost linearly, the sample undergoes inconspicuous elastic deformation, and no macroscopic damage occurs on the surface. The second stage is defined as the plastic deformation stage. During this process, the resin matrix breaks and the fibers on the surface of the main body bend have slight cracks. The load fluctuates and the growth rate gradually slows down, indicating that the stiffness continues to decrease. When the load increases to the peak load, due to the lateral fiber breakage of the carbon fiber reinforced plastic and the shear cracking of the PMI foam and the thermal expansion foam, the load suddenly drops significantly, accompanied by a loud and crisp sound, but with the support of the carbon fiber reinforced plastic tube wall and the core layer, the load does not drop to a very low value. The mechanical properties test data of the carbon fiber composite connecting rod specimens are summarized in Table 1.

[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 found that the tensile and compressive properties of the carbon fiber composite connecting rod specimen prepared in this embodiment have met the index requirements.

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

Claims

1. A lightweight design and preparation method for a carbon fiber composite material connecting rod for a vehicle, characterized in that: The following steps are involved: Step S102: taking the steel vehicle connecting rod as a reference, obtaining basic performance indicators of the connecting rod through static analysis and modal analysis; Step S104: obtaining a structural design of a carbon fiber composite material connecting rod 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; Step S106: performing finite element modeling according to the structural design of the carbon fiber composite material connecting rod, and obtaining index parameters of basic performance indicators using the finite element model, and outputting a lightweight design scheme of the carbon fiber composite material connecting rod when the index parameters meet preset standards; 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.

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: Obtain a three-dimensional model of a steel automotive connecting rod, simplify and clean the three-dimensional model to establish a geometry and unit set, divide the mesh using shell elements and perform a mesh quality check, and when the mesh quality meets the preset requirements, select 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. 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.

3. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobile according to claim 1, characterized in that: In step S104, the structural design of the carbon fiber composite material 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 features of the structural form of the steel vehicle 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 features of the structural form, and 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 automobile according to claim 1, characterized in that: The step S106 is specifically as follows: Finite element modeling is performed according to the structural design of the carbon fiber composite material connecting rod to obtain a finite element model of the carbon fiber composite material connecting rod, and the same constraints and loads are applied to the carbon fiber composite material connecting rod based on the established finite element model according to the typical working conditions of the steel vehicle connecting rod to perform performance analysis; Obtain index parameters of basic performance, take the performance analysis results of steel automotive connecting rods as a benchmark, compare the index parameters with the benchmark, and when the comparison results of the index parameters meet the preset standards, output a lightweight design scheme for the carbon fiber composite material connecting rod, otherwise, optimize the layup design of the carbon fiber composite material connecting rod.

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 ply sequence [(0°) 10 / (0,90)] to carry out the layup design of carbon fiber composite connecting rod; A layup design diagram of each layer of carbon fiber composite material is obtained through layup design, and a process notch is set in the layup design diagram according to the curvature change of the connecting rod structure to avoid wrinkles and stress concentration during the laying 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, and 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, the material selection scheme for the carbon fiber composite material connecting rod is determined, specifically: PMI foam is selected as the supporting material of the carbon fiber composite connecting rod, thermal expansion foam is used as the expansion material to coat the surface of the PMI foam, and then the prepreg is coated layer by layer on the surface of the thermal expansion foam; At the same time, the metal rings at both ends of the connecting rod are embedded and coated, and placed in a rigid mold for heating and thermal expansion molding, and finally a carbon fiber composite connecting rod is prepared, and the expansion material and the supporting material are retained inside the connecting rod.

7. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobile according to claim 1, characterized in that: In the step S108, the carbon fiber composite material connecting rod is prepared by using a thermal expansion process, specifically: Cut or trim PMI foam, heat 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, wherein the heat expansion foam is laid on one side, and laid separately and closely on the four sides of the PMI foam, and the prepreg is laid symmetrically by overlapping on both sides; Place the laid connecting rod into the rigid mold that has been evenly coated with release agent, and fasten 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 heat-expanding foam begins to expand due to the heat. Under the reserved process gap, due to the spatial constraints of the core material and the mold, the heat-expanding foam generates enough expansion pressure to meet the carbon fiber composite material molding requirements; The carbon fiber composite connecting rod sample is obtained by demoulding.

8. The lightweight design and preparation method of a carbon fiber composite material connecting rod for automobiles according to claim 7, 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 plying of the connecting rod body, the heat expansion foam and prepreg are sequentially laid on the surface of the PMI foam core. Several layers of heat expansion foam are laid using a single-sided plying method, and the prepreg is symmetrically laid using a double-sided overlap method to achieve inter-layer slippage during the expansion process. In addition, the prepreg is reinforced and laid in the fillet area of ​​the connecting rod main body to avoid surface defects in the fillet area of ​​the carbon fiber composite material connecting rod, so as to complete the preforming coating of the connecting rod main body; In the layup of the metal ring part of the connecting rod, the connection between the metal ring and the main body is achieved by winding the prepreg outside the metal ring, and the prepreg of the main part of the connecting rod 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 position of the interface is dispersed; A heat expansion 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 body through surface contact, reducing the gap between the metal ring part and the body part to complete the preforming covering of the connecting rod metal ring part.

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