ABSTRACT
Microstructural damage is a major cause of deterring overall mechanical properties of reinforced composites, resulting in diminished structural integrity. Debonding at the fiber-matrix interface, along with brittle crack propagation in the matrix, are important micromechanical damage phenomena. Experimental studies have shown that these complementary damage mechanisms often co-exist in the material. Damage initiates at the interface with decohesion and can subsequently propagate into the matrix. The damage mechanisms are sensitive to local morphological parameters like volume fraction, size, shape, and spatial distribution of reinforcements, interfacial strength, and process-related defects. Fibers and interfaces in regions of clustering or preferential alignment are subjected to increased local stresses. Consequently, they have a greater propensity to undergo damage nucleation than those in dilute regions. A number of failure prediction models for composite laminates are phenomenological and have been based on empirical methods or ply level fracture mechanics. These macroscopic models are not capable of relating the failure process to local interactions and stress concentrations. Because of limited large-scale testing in the emerging design environment, it is critical that robust failure analysis tools evolve, accounting for details of the microstructure and micromechanics of damage modes.
