Effect of thermal and hydrothermal aging on the crashworthiness of carbon fiber reinforced plastic composite tubes

Thin-walled structures constructed of fiber reinforced composites are increasingly being employed in engineering practice. However, there is limited investigation into their residual properties after high temperature and hygrothermal aging. The aim of this experimental investigation is to study how moisture absorption and high temperatures affect the mechanical characteristics of fiber reinforced plastic (FRP) composite tubes. A set of accelerated thermal and hygrothermal aging experiments are designed to imitate the service conditions of carbon fiber reinforced plastic (CFRP) structure in harsh environment. Based on the glass transition temperature ob-tained by dynamic mechanical analysis (DMA), the specimens are divided into two groups for various temper-atures (25 degrees C, 70 degrees C, 100 degrees C, 160 degrees C) and hydrothermal aging (25 degrees C, 70 degrees C). The specimens of hydrothermal aging group are immersed for about 700 h to monitor the water absorption of the specimens in hygrothermal envi-ronments with different aging time. Aged composite tubes subjected to quasi-static axial compression are tested to identify compressive strength, failure modes and structural degradation process. The scanning electron mi-croscope (SEM) is used to explore the microscopic failure mechanism of CFRP tubes. As temperature and moisture absorption rate increase, the crashworthiness characteristics decrease drastically; and the failure modes differ substantially with three different failure types identified. The crashworthiness of CFRP has a nonlinear relationship with temperature, but it is related to the glass transition temperature of the matrix. Furthermore, moisture absorption can be divided into two stages and temperature affects the moisture absorption of CFRP. Microscopically, the morphology and bonding conditions between fiber and resin is found to change significantly on the microscale as a result of various temperatures and hydrothermal aging.