Microscale model for fiber breaking displacement in ceramic-matrix composites

Abstract

In this paper, the fiber breaking displacements (FBDs) of ceramic-matrix composites (CMCs) under tensile loading were systematically investigated using a micromechanical approach. The micro strain fields of fibers before and after breaking were analyzed for five different damage states, i.e., isolated fiber breakage away from matrix cracking, as well as fiber breakage surrounding single, long, medium, and short multiple cracks. The FBDs and corresponding fiber slip lengths associated with different damage states were determined. Effects of stress levels, constitutive properties, damage state and fiber breakage location on FBDs and fiber sliding were comprehensively analyzed. Relationships between FBDs, fiber slip length, stress levels and damage states were established. Experimental FBDs of fiber breakages away from matrix crack or at the center of medium/short matrix crack spacing in unidirectional SiC/SiC composite under in-situ tensile loading were predicted using the developed microscale models. The FBDs increase with applied stress and decrease with interface shear stress. When the fiber breakage position away from the matrix cracking plane, the FBD decreases for single matrix cracking; when the fiber breakage position away from the matrix cracking center, the FBD remains constant for long matrix cracks, decreases for mediums matrix cracks, and increases for short matrix cracks.