Toughening Behavior of a Two‐Dimensional SiC/SiC Woven Composite at Ambient Temperature: II, Stress‐Displacement Relationship in the Crack Process Zone

Abstract

In this paper insight into the origin of the JR‐curve of a SiC/SiC woven composite was obtained by experimental characterization of the closure stress‐crack opening displacement, sigma(u), relationship in the process zone of the crack. This process zone included both a crack frontal zone and a crack wake damage zone so that quantitative estimates could be obtained of the magnitudes of toughening associated with these two separate zones. The research indicated that the closure stress‐crack opening displacement curve has a positive slope in the crack frontal zone and a negative slope in the wake zone with a maximum stress capability on the order of 350 MPa. The toughness contributions from the crack wake and from the crack front were consistent with the JR‐curve results obtained in the previous paper. The stresses supported locally in the crack frontal zone were almost twice as large as those supported by tensile specimens even though this zone was considerably damaged by matrix cracks. This appears to be the result of stabilization of matrix cracks by arrest at fiber bundles. Application of a previously derived theoretical function, sigmab(u), solely based on crack bridging by continuous unidirectional fibers, suggested that the efficacy of bridging in the woven composite may in part be related to the woven fiber architecture. Such an architecture apparently induces greater sliding resistance of the SiC bundles against the surrounding SiC matrix.