Preliminary Development of a Fundamental Analysis Model for Crack Growth in a Fiber Reinforced Composite Material

This paper describes the preliminary development of a mathematical model for the strength of fiber reinforced composites containing specific flaws. The approach is to embed a local heterogeneous region (LHR) surrounding the crack tip into an anisotropic elastic continuum. By direct consideration of the individual failure events that are activated near the flaw tip, a strength prediction can be made from the basic properties of the composite's constituents. Computations for arbitrary flaw size and orientation have been performed for unidirectional composites with linear elastic-brittle constituent behavior. The mechanical properties were nominally those of graphite epoxy. With the rupture properties arbitrarily varied to test the capability of the model to reflect real fracture modes in fiber composites, it is shown in this paper that fiber breakage, matrix crazing, crack bridging, matrix-fiber debonding, and axial splitting all can occur during a period of (gradually) increasing load prior to catastrophic fracture. Qualitative comparisons with experimental results on edgenotched unidirectional graphite epoxy specimens have also been made.