Impact Damage and Residual Strength of Composite Joints in Car Bodies

Abstract

With the weight reduction requirements for vehicles and the cost reduction tendency for carbon fibers, carbon fiber reinforced plastics (CFRPs) will be applied more and more in automobile bodies in place of some steel materials. However, the structural design method using CFRPs is much different from that using steel. For example, the anisotropic material properties and the brittle plastics matrix need to be considered, and the connection between components is through adhesive joints, which is possibly weaker than the traditional spot welding. These features make CFRPs sensitive to impact loads, especially the repeated low-energy impact. This paper presents a damage-based residual modulus and strength prediction method, which may be utilized in the design of composites components subject to repeated impact loads. First, the CFRPs samples were impacted repeatedly by the pendulum hammer at a constant kinetic energy, 2J, and then, the residual bending modulus and strength were measured by static three-point bending machine. According to the test data, the relationship between impact number and residual stiffness and residual strength were established, and the damage factors after each impact were calculated. In subsequent numerical simulation, the damage accumulation effect was included in the one-step prediction model through replacing the initial modulus by the degradation modulus, and this method was verified numerically by comparison with N-step prediction results after N-times impact calculations. Finally, two kinds of composite joints were analyzed numerically, which provides theoretical guide for the design of composite joints in automobile body.