Hygrothermal and Strain Rate Effects on Properties of Graphite/Epoxy Composites

Abstract

A unidirectional graphite/epoxy material was characterized at strain rates ranging from 5 × 10−6 to 5 s−1 under various hygrothermal conditions. A time-temperature-moisture equivalence principle was applied to obtain master curves for the longitudinal, transverse and in-plane shear moduli and corresponding strengths and ultimate strains of the unidirectional graphite/epoxy. It was found that, except for the longitudinal modulus which shows a slight increase with strain rate, temperature and moisture, all other longitudinal properties in general remain unchanged. All matrix dominated properties, i.e., transverse and intralaminar properties, decrease with increasing temperature and moisture content for a fixed strain rate. The transverse and in-plane shear moduli increase with strain rate. Transverse ultimate properties show a trend reversal with a local maximum. The in-plane shear strength increases noticeably, but the ultimate shear strain decreases slightly with strain rate. The time-temperature-moisture shift function is expressed as a function of two variables, temperature and moisture, allowing interchangeability of the three parameters, time, temperature and moisture content.