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.

At the conceptual design phase of a large-scale underwater structure, a small-scale model in a water tank is often used for the experimental verification of kinematic principles and structural safety. However, a general scaling law for structure-fluid interaction (FSI) problems has not been established. In the present paper, the scaling laws for three typical FSI problems under the water, rigid body moves at a given kinematic equation or is driven by time-dependent fluids with given initial condition, as well as elastic-plastic body moves and then deforms subject to underwater impact loads, are investigated, respectively. First, the power laws for these three types of FSI problems were derived by dimensional analysis method. Then, the laws for the first two types were verified by numerical simulation. In addition, a multipurpose small-scale water sink test device was developed for numerical model updating. For the third type of problem, the dimensional analysis is no longer suitable due to its limitation on identifying the fluid pressure and structural stress, a simulation-based procedure for dynamics evaluation of large-scale structure was provided. The results show that, for some complex FSI problems, if small-scale prototype is tested safely, it doesn’t mean the full-scale product is also safe if both their pressure and stress are the main concerns, it needs further demonstration, at least by numerical simulation.