Experimental and theoretical assessment of the longitudinal tensile strength of unidirectional SiC-fiber/titanium-matrix composites

The tensile strength of unidirectional SiC-fiber/titanium composites (SCS-6/Ti-1100) of varying fiber volume fraction (0.15-0.35) was measured in the as-produced condition. Additionally, fibers were etched from the panels and tensile tested to determine their strength distribution, interface properties were measured with fiber push-out tests, and the tensile properties of the matrix (without fiber) were also determined. From the measured constituent properties, the composite strength was predicted by using both global load-sharing (GLS and LLS) models, predictions were compared with the measured values. The composite strength was lower than predicted by Curtin's GLS model, but greater than predicted if it is assumed that the first fiber failure initiates composite failure (i.e. severe LLS). Metallographic examination of the fractured specimens revealed that the failure was consistent with a non-cumulative (localized damage) failure mode, which, as suggested by previous theoretical and experimental studies, is promoted by matrix plasticity. (C) 1997 Elsevier Science Limited.