Environmental Durability of Fibrous Polymeric Composites

Abstract

Durability of fiber reinforced polymer composites (FRP) are controlled by the durability of their constituents: reinforcement fibers, resin matrices, and the status of interfaces. It is at the interfacial area where stress concentration develops because of differences in the thermal expansion coefficients between the reinforcement and matrix phase. A significant mismatch in the environmentally induced degradation of matrix and fiber leads to the evolution of localized stress and strain fields in the FRP composite. The bond strength of composites, deteriorate during service periods depending on the environmental conditions. Both short-term and long-term properties of a composite depend decisively on the microstructure, and the properties of the interface or inter-phase between the fiber and the matrix. A strong interface displays an exemplary strength and stiffness, but is very brittle in nature with easy crack propagation through the interface. A weaker interface reduces the stress transmissibility and consequently decreases the strength and stiffness. Here a crack is more likely to deviate and grow at the weak interface resulting in de-bonding and/or fiber pull-out and contributes to improved fracture toughness. Most polymers lose their ductile properties below their glass transition temperature. The factors affecting the mechanical response of composites are fiber–matrix interfacial properties, volume ratios, load transfer mechanisms, and fabrication techniques. As the volume fraction of reinforced fiber in composites increases, more fiber–matrix interfacial area is created and more energy may be absorbed by the interface.