Hygrothermal Microstresses in a Unidirectional Composite Exhibiting Inelastic Material Behavior

Abstract

A finite element numerical analysis is presented which models the influ ences of temperature variations and dilatations due to moisture absorption on the local stress state in a unidirectionally-reinforced composite material. These influences are admissible in both fiber and matrix, and all material properties are assumed to be temperature- and moisture-dependent. The fiber is assumed to be elastic and transversely isotropic, the matrix material inelastic and isotropic. A generalized plane strain condition is formulated, which permits the analysis of applied normal loadings in three directions (i.e., longitudinal and biaxial transverse) combined with arbitrary tempera ture and moisture content changes. Numerical results are presented for a typical graphite/epoxy composite, indicating the residual microstresses induced during cooldown from the curing temperature, and how they can be altered by a subsequent moisture absorption at room temperature. Results are also given for predicted microstress states and failure initiation in a graphite/epoxy composite modeled both with and without curing stresses and moisture dilatation, for a transverse normal applied loading continued beyond the elastic limit, to first failure.