Contact acoustic nonlinearity phenomenon caused by the acoustic wave propagating in the composite material

Due to the massive applications of multilayered composite materials (for example carbon fiber material, glass fiber material etc.) in material industry, aviation industry, medical enterprise and other consumer industries, it becomes an important work to carry on the non-destructive evaluation to the long-term characteristic and the security of the composite materials in use. The reliability of a composite material is mainly decided by the quality of its bonded interfaces. In the bonded interface, the weak bonding region is possibly the initial spot of the entire equipment's failure. Therefore the examination technology of the bonding state at the interface becomes the hot spot of the current research and application. Actually, in the bonded interface, micro-cracks or micro-flaws will be formed during the solidification of bonding material or after the composite material have been used for a period of time. When a longitudinal acoustic wave propagates through the interface with micro-cracks, it will drive the two surfaces of the micro-cracks to pop each other and the contact acoustic nonlinearity (CAN) phenomenon will happen. In this paper, we analysis the CAN phenomenon in the interface and propose a CAN parameter to describe the bonding state. Also an experiment is stated in the paper to scan the bonding state at the interface using the CAN parameter. The results show that the region with weak bonding strength can be easily distinguished from the scanning contour.