Strength of SCS-6 fibers in a Tiβ21s/SCS-6 composite before and after fatigue

The strength distributions of SCS-6 fibers extracted from both as-received (AR) and fatigued Tiβ21s/SCS-6 composite specimens have been characterized by single-fiber-tension tests and have then been analyzed statistically. With the assistance of fractography, the whole population of SCS-6 fibers in the composite can be cataloged into three subpopulations with fracture strengths, σ _F , of <2000, 2000 ≤ σ _F <3700, and ≥ 3700 MPa, respectively. Each subpopulation has distinctive statistical parameters, which do not appear to change markedly after fatigue. However, cyclic loading can reduce the average strength of the whole population by decreasing the percentage of high-strength fibers present. In addition, cyclic loading can also break some of the low-strength fibers. By using a trimodal Weibull function, the degradation of the strength of the fibers after fatigue, as well as the influence of such degradation of fiber strength on the fiber-bundle strength and then on the predicted fatigue crack growth resistance of the composite, have been analyzed.