The effect of cyclic hygrothermal conditions on the stresses near the surface of a thick composite pipe

It is necessary to estimate the moisture concentration and the hygrothermal internal stress fields to evaluate the durability of thick composite pipes submitted to cyclic environmental conditions. After some time, the moisture concentration, induced by temperature and relative-humidity cycles, is permanent within the pipe and periodic close to the inner and outer surfaces. The hygrothermal stresses induced are computed by using the classical equations of solid mechanics and assuming a hygrothermoelastic orthotropic behaviour for every ply. The aim of this paper is to model the effects of the periodic boundary conditions on the hygrothermal stresses.