Impact of Environmental and Experimental Parameters on FRP Composites

Abstract

The mechanical performance of a composite material is decisively controlled by the state of fiber-matrix interface or interphase. Its properties influence the integrity of composite behavior because of its role in transferring stress between the fiber and the matrix. The factors affecting the interface are too complex to be precisely concluded. Fibrous composites are increasingly being used in many casual as well as critical applications owing to various desirable properties including high specific strength, high specific stiffness and controlled anisotropy. But unfortunately polymeric composites are susceptible to heat and moisture when operating in changing environmental conditions. They absorb moisture in humid environments and undergo dilatational expansion. The presence of moisture and stresses associated with moisture-induced expansion may cause lowered damage tolerance and structural durability. The structural integrity and life time performance of fibrous polymeric composites are strongly dependent on the stability of the fiber/polymer interfacial region. The low molecular weight impurities may migrate from the bulk of the adhesive to form a weak boundary layer at or near the fiber surface. The active carbon fiber surface can strongly attract polar molecules of the polymer matrix. This may develop a boundary layer of high cross-link density. This micro-structural gradient at the interface may promote crack initiation and propagation through this layer. The environmental and experimental variations, such as moisture, temperature and variation of loading rate can limit the usefulness of polymer composites by deteriorating mechanical properties during service.