Effect of Fatigue Testing and Aquatic Environment on the Tensile Properties of Glass

Fiber reinforced polymer composite materials are widely used in several constructions (marine, aerospace and automobile, etc.) due to their various advantages: high stiffness to weight ratio, corrosion resistance, and low maintenance cost. Glass and Kevlar fibers are the most widely used to reinforce composite structures. Indeed, glass fiber has enjoyed widespread popularity to make reinforced composites in every field, because of their competitive cost and relatively good mechanical properties. Kevlar fibers widely used as reinforcement within several advanced composites, which were developed during the 1960s. Their high degree of toughness, associated with the failure mechanism of Kevlar, and damage tolerance promote good impact/ ballistic performance. This is due to the low surface energy and the chemically inert surface of the Kevlar fiber, and consequently to the poor interfacial adhesion between fiber and matrix.

Generally, the mechanical properties of composite materials are well known by engineers, but there are still many concerns about their durability and their performance under severe environmental conditions. In fact, with the use of composite materials in a warm and wet environment, the aggressive actions can appear under several aspects of biological, chemical and physical properties by altering materials and provoking a failure of the residual stiffness and residual strength. The deterioration of a composite material during a wet ageing is, in most cases, the results of a water absorption phenomenon depending on hygrometric and temperature. Indeed, water can penetrate into the composites by three main mechanisms: diffusion of the water through the matrix, capillary along fiber-matrix interface and percolating flow and storage of water in micro-cracks. These diffusion mechanisms generally lead to the following damages in the composites: degradation by a hydrolysis reaction of unsaturated groups within the resin, interfacial fracture, debonding and interlaminar toughness. Beyond these considerations, it is well known that water absorption also affects the mechanical behavior of composite materials globally. In spite of these investigations, few works studied the combined effect of damage mechanics and environmental ageing on the ultimate properties of composite materials.