Transient hygrothermal stresses in fiber reinforced composites: A heterogeneous characterization approach

Transient hygrothermal stresses induced in fiber-reinforced composites are studied in detail by adopting a novel heterogeneous characterization approach. This approach incorporates two distinct features: transient moisture absorption analysis of actual composite materials exposed to a humid environment, and highly detailed computational analyses that capture the actual heterogeneous microstructure of the composite. The latter feature is carried out by modeling a uniaxial laminate having more than one thousand individual carbon fibers that are randomly distributed within an epoxy matrix. Results indicate that these computational models are essential in capturing the accurate moisture absorption process of the actual specimen. In the analysis, the evolutions of thermal residual stresses and moisture-induced stresses within the humidity and thermal exposed composites have been analyzed. It was observed that high stress concentration develops in the epoxy phase where high fiber density or fiber clustering exists and its magnitude increases as the moisture content saturates. Large stresses can potentially initiate epoxy damage or delamination of epoxy and fibers. Furthermore, due to opposing effects of thermal and moisture exposure, lower stresses are found in the laminate when both are considered simultaneously.