Effects of Strain Rate and Temperature Dependency on Damage Initiation Behavior of Unidirectional Carbon Fiber Reinforced Plastic

Abstract

Carbon fiber reinforced plastic (CFRP) is composed of carbon fiber and a polymer material, which is a matrix resin. Resin-dependent damage initiation behaviors, such as matrix cracking and interfacial debonding, are affected by the viscoelasticity of the resin (effects of temperature and strain rate), and the strength of the entire CFRP is also affected. In situ observation is required to investigate the effects of viscoelasticity on the damage initiation behaviors. Therefore, in this study, the effects of temperature and strain rate on the damage initiation behaviors of unidirectional CFRP were investigated using the acoustic emission (AE) technique. To understand the details of AE information, frequency analysis was performed. In the frequency analysis, the resonant frequency of AE sensors affects the frequency properties of the detected signals, so we attempted to eliminate the effect of the sensors by deconvolution of the AE sensor frequency properties from the detected signals. As a result of the deconvolution, we could distinguish the failure modes as matrix cracking, fiber/matrix interfacial debonding, and fiber breaking. From these results, matrix cracking and fiber/matrix interfacial debonding were affected by temperature and strain rate; however, fiber breaking was not affected. Scanning electron microscope observation of the fracture surface confirmed that the resin around the fiber was affected by temperature and strain rate. From this damage initiation behavior of the matrix resin, which was affected by the viscoelasticity, it became clear that the behavior influenced the strength of the entire composite material.