Study And Optimization Of Tensile-shear Static Properties Of Al-CFRP Pre-embedded Joints

Body lightweighting technology has been a long-standing hot topic in the automotive industry.The lightweighting method of using composite materials to replace some metal materials in body parts has received a lot of attention,as a result of which the connecting design of composite and metal materials is one of the key issues in the design of body structures.The common joining processes between carbon fiber reinforced polymer(CFRP)and metal include bonding joints,bolted joints,riveted joints and hybrid joints,etc.In this paper,we propose a pre-embedded joints between aluminum alloy and CFRP,compared with the mechanical joints such as bolted joints and riveted joints between metal and CFRP,the pre-embedded joints can be prepared without destructive behaviors such as drilling of CFRP,and its load-bearing capacity is significantly higher than that of traditional bonding joints,while avoiding the defects such as poor peel resistance and poor sealing of bonding joints.In this paper,the failure modes and damage mechanisms of pre-embedded joints are investigated through a combination of experiments and simulations,and the tensile and shear strengths of the joints are multi-objective optimized based on genetic algorithms to determine their optimal design dimension parameters.The main research of this paper is as follows:Firstly,the material models corresponding to the adhesive and CFRP used to prepare the pre-embedded joints are established.Quasi-static tensile tests were conducted on dumbbelltype specimens and aluminum alloy bonding joints made with LT-5028 epoxy resin adhesive,and the mechanical property parameters of this epoxy resin adhesive were obtained.According to the different failure modes of LT-5028 epoxy resin adhesive,Cohesive model and ductile damage constitutive based on Lin’s constitutive were established to simulate the interfacial failure and cohesive failure of the epoxy resin adhesive,respectively.The improved Hashin failure criterion and the damage evolution mode of linear stiffness degradation were used to establish the damage model of CFRP.The above material models were used in the subsequent simulation analysis of the pre-embedded joints.Subsequently,quasi-static tensile-shear loading tests of the pre-embedded joints were carried out,and the load-displacement curves of the tests showed that the peak loads of the pre-embedded joints were significantly higher than those of the conventional single-lap bonding joints.Ultrasonic nondestructive analysis and SEM electron microscopy were performed on the tested specimens to observe the specific damage of the resin and CFRP inside the joints.A finite element simulation model of the pre-embedded joints was established to study the failure process and damage mode of each component material in the pre-embedded joints.Finally,based on the three dimensional parameters of the pre-embedded depth,the width of joining area and the thickness of adhesive layer,a three-factor and three-level test scheme was designed to establish a second-order polynomial proxy model for the two objectives of tensile strength and shear strength of the pre-embedded joints by response surface method.Sensitivity analysis was performed on the objective function,and the Pareto optimal solution set was obtained by optimizing the tensile strength and shear strength according to the multiobjective genetic algorithm.The better solution in the solution set is compromised by the TOPSIS method to obtain the best design solution for the joint size parameters.In summary,this paper designed a type of Al-CFRP pre-embedded joints,determined the types of each component material required to prepare the joints,and obtained the corresponding material mechanical property parameters through a series of tests.The failure mode and damage mechanism of the pre-embedded joints under tensile-shear loading are investigated through tests and simulations,and the tensile and shear strengths of the preembedded joints are optimized based on genetic algorithm,which provides guidance for the design of hybrid material structures.