Effects of wet aging on the damage progress in multidirectional GFRP composites under fatigue loading

Abstract

The impact of harsh environments with variable temperatures, high humidity, or direct water contact poses a challenge for lightweight construction materials, such as polymer composites, because of their hydrophilic and temperature-dependent properties. Since the most widely used glass fiber reinforced polymers are known to suffer from the above-mentioned conditions, precise knowledge of their long-term durability is of high interest. In addition to the pure change of mechanical properties due to water absorption or temperature, damage evolution and lifetime performance are important. This is what the present study addresses, bringing together the initiation and development with the effects on fatigue life. In contrast to what is regularly reported in the literature, a lifetime increase was found for a specific multidirectional (quasi-isotropic), epoxy-based laminate after short- and long-term wet-aging. The reasons for this outcome were investigated using interrupted fatigue tests, microscopy, and residual strength analysis. As a result, significant differences in damage initiation and progress could be identified and related to the quasi-static and fatigue result. The main reason for the increase in lifetime is expected to be the distributed energy dissipation in the wet-aged condition. Here, damage occurs simultaneously in several regions, which leads to the fact that the introduced energy is divided among numerous defects at the same time. In the dry case, on the contrary, the growth of the few, individual damages terminates in an early catastrophic failure