Stress Field in Coated Continuous Fiber-Reinforced Polymeric Composite Due to Hygrothermal Loading

Abstract

Based on a four phase model of the composite, effects of fiber-matrix interphase (coating) on the stresses developed in different constituent phases due to hygrothermal loadings are evaluated. Interphase coating with high, low and the same modulus as that of the matrix have been considered. Obtained stresses, considering degradation in properties of the coating and the matrix due to moisture absorption and temperature rise, have been compared with the corresponding values furnished without properties degradation. Graphite being transversely isotropic and having opposite nature of thermal expansion coefficients in the longitudinal and transverse directions, the bulk of the results are given for the graphite/epoxy composite. The importance of the consideration of coating as a separate phase with its appropriate properties on the stress concentrations in different constituent phases is clearly brought out. It is also suggested that due accounting should be made for the changes in the properties of the matrix and the coating, caused by hygrothermal conditioning, otherwise the stress estimates could be quite misleading and erroneous. Effects of coating thickness and fiber volume fraction are also discussed.