Revealing of Failure Modes of FRP Composites by Microscopic Technique.

Abstract

Fiber-reinforced composite materials are used extensively in stiffness critical, weight sensitive structures such as those found in aerospace and motor racing where strength to weight ratio is very much important. They are characterized by high in-plane strength, stiffness and toughness and low density. The environmental effect on the FRP (fiber reinforced polymer) and the subsequent failure has lead to emphasize on the study of different fracture surfaces. The presence of moisture and the stresses associated with the moisture induced expansion may cause lowering of damage tolerance and structural durability. In case of water absorption there are both reversible and irreversible changes in the mechanical properties of the thermoset polymers. Delamination between layers is an important problem in applications of fiber reinforced composite laminates. This paper is an attempt to study the cracked surface and reveal the failure mechanism that has occurred using microscopic techniques. By observing carefully the fracture surface of the composite, the factors affecting their respective failure and the type of environment they were subjected to could be determined. SEM micrographs of the fractured surfaces of glass/epoxy and jute/epoxy composites under various environmental conditions were studied revealing the failure modes (delamination sites, debonding, fiber pullout regions, crack propagation front, striations and bubble bursting in the matrix). AFM micro graphs were studied to give a precise outlook of the behavior of composites to the changing environmental conditions being exposed to such as moisture absorption etc.