The Mechanism of Stable Crack Growth in FRP

Abstract

In this paper, stable crack growth is examined in both experimental and analytical ways to establish a test method to evaluate the fracture toughness of FRP. The mechanism of stable crack growth is considered from observations of vicinity of the crack tip. There is always a damage zone in which debonding between the fibers and the matrix occurs ahead of the crack tip. Crack growth occurs by breaking the fibers at the crack tip. Stress analysis is carried out to find out how much stress is applied to the fibers in the damage zone. A line spring model is used to express the mechanical behavior of the fibers in the damage zone, and infinitesimal dislocation distribution theory is used in the numerical stress analysis. It is concluded that stable crack growth in a fracture toughness test of FRP is inherently different from that in metallic materials induced by plastic deformation near the crack tip ; that it results from the stress relaxation by debonding between the fibers and the matrix ; and that the stress intensity at the point of instability in the fracture toughness test is the material property.