Experiments and analysis of fiber fragmentation in single and multiple-fiber SiC/Ti-6Al-4V metal matrix composites

Single-fiber and multiple-fiber single-ply fragmentation experiments were performed at room temperature on SiC/Ti-6Al-4V specimens, to understand interface shear failure under fragmentation conditions and to assess load-sharing behavior in longitudinally loaded composites. Tensile specimens were instrumented with two acoustic emission sensors and an extensometer to monitor the strain at which fiber breaks occurred. Following testing, the break locations were determined using a novel ultrasonic shear-wave back reflection (SBR) technique. Data analysis was performed using Curtin's exact fiber fragmentation model, wherein the in situ Weibull strength and Weibull modulus of the fiber, and the average shear stress under fragmentation conditions, were determined based on best fit with two essentially independent sets of data from the experiments, i.e. the breaking stress of the fibers, and the fragment length distribution. Results for the SCS-6/Ti-6Al-4V samples are presented in this paper, and they are compared with results from other SiC fibers in the same Ti-alloy matrix. The average shear stress from the fragmentation test was significantly higher than that obtained by push-out tests, and is explained on the basis of high radial clamping stress on the fiber in the immediate vicinity of a fiber break. Experiments were also performed on multi-fiber single-ply specimens. Comparison with the single-fiber results showed evidence of correlated fracture even for the relatively weak interface of the SCS-6 fiber. SBR image and macroscopic slip bands indicate that localized plasticity plays a dominant role in promoting correlated fiber fractures at room temperature, and the mechanism is outlined. (C) 1998 Elsevier Science Limited. All rights reserved.