Simulation And Experimental Investigation On Adhesive Bonding Process And Mechanical Behavior Of Steel/CFRP Joint

Currently, there is a series of environmental problems, owing to the rapid growth of automobile productions and sales such as energy shortages, excessive emissions, environmental pollution, and so on. In order that automotive industry can be sustainable development, lightweight technology has become a key way to develop new energy vehicles. Therefore, Carbon Fiber Reinforced Polymer(CFRP) is gaining more and more attention,due to the advantages of light weight, high strength, fatigue resistance, corrosion resistance and design-versatility. In addition, high-strength steel has been applied to automobile manufacturing instead of ordinary medium and low carbon steel, to reduce the weight by thinning the thickness of the body structure. The above two mainstream lightweight materials used in the same body structure will inevitably bring secure and reliable connectivity problems of heterogeneous materials, which plays a vital role in improving the performance and prolonging lifetime of the structures.This paper, based on the local hot stamping technique, put forward adhesive bonding process of Steel/CFRP joint with additional geometric features, to research the connectivity performance of joints. Failure load, shear and peel stress distribution, fracture energy and process stability of joints under different geometric features were analyzed through finite element simulation, process test and tensile shear test, which provided the basis of optimizing the additional geometric distribution and size and controlling process of Steel/CFRP adhesively bonded joints, to improve the mechanical properties and carrying capacity of the joint. The main conclusions are as follows:(1) Based on the basic theories of adhesively bonded, mechanics of composite materials, the cohesive force of constitutive equations, etc, different geometric features of the Steel/CFRP joints were designed, such as flat, rectangular groove, arc-shaped groove, cylindrical and spherical pit with different distributions. The performance, carrying capacity and stress distribution of Steel/CFRP joints were studied by ABAQUS, to optimize additional geometric features and size of the joints that can improve the mechanical properties of joint.(2) Failure load of Steel/CFRP joint increased linearly with the bond length, while it exceeded the optimal effective bond length. The increase in the bond length not only had a little contribution to improve the performance of joint, but also increased bond area, structure weight, the complex degree of process, the difficulty of controlling adhesive layer uniformity, and make the bubbles, gaps and other defects easier to appear, which have an impact on the performance of the joints.(3) The stress distributions of Steel/CFRP joints under different additional geometric features are different from the flat joint, due to the function of mechanical interlock between connecting members. Compared to the flat joint, the mechanical properties of joints under additional geometric features were improved with different degrees, in which the distributed spherical pit geometric feature is most advantageous.(4) Stress distribution and performance, carrying capacity and fracture damage models of Steel/CFRP joints are significantly affected by the local additional geometric features and distributions, which existed obvious spring back and size effect. It is necessary to further optimize the condition of hybrid hot stamping local deformation adhesive bonding process, additional geometric distribution and size, in order to improve performance and load carrying capacity of Steel/CFRP joint.(5) By comparing the numerical simulation results with experiment results, the carrying capacity of Steel/CFRP joints under different additional geometric features is strikingly different, due to the fact that the more complex of additional geometric feature becomes, the greater simulation error is. In fact, the simulation analysis about carrying capacity of the joints is overestimated in varying degrees. The main reasons for the above phenomenon are the redistribution of residual stress in the bonding interfaces because of the spring back of steel, the size effect of geometric features and the coupling effect between and two, which reduced the real contact area and the performance of joint.(6) Based on the hybrid hot stamping local deformation adhesive bonding process, Steel/CFRP joint with local additional geometric features of the samples was acquired. It is feasible and effective to improve the performance and load carrying capacity of the joint by using the function of mechanical interlocking between Steel and CFRP, work hardening effect of steel sheet. However, it still needs to strictly control the implementation process of the process and amend the corresponding material models, which could improve the reliability of the process conditions and the additional geometric features optimization through simulation.