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 w ere performed at room temperature on SiC/Ti-6Al-4V specimens, to under stand interface shear failure under fragmentation conditions and to as sess load-sharing behavior in longitudinally loaded composites. Tensil e specimens were instrumented with two acoustic emission sensors and a n extensometer to monitor the strain at which fiber breaks occurred. F ollowing testing, the break locations were determined using a novel ul trasonic 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 av erage shear stress under fragmentation conditions, were determined bas ed 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 prese nted 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 stre ss on the fiber in the immediate vicinity of a fiber break. Experiment s were also performed on multi-fiber single-ply specimens. Comparison with the single-fiber results showed evidence of correlated fracture e ven for the relatively weak interface of the SCS-6 fiber. SBR image an d macroscopic slip bands indicate that localized plasticity plays a do minant role in promoting correlated fiber fractures at room temperatur e, and the mechanism is outlined. (C) 1998 Elsevier Science Limited. A ll rights reserved.