Investigation of the residual tensile behavior of fiber bundles after static fatigue: Implications for the prediction of durability of composites

Abstract

Several brittle inorganic fibers (including glass, SiC- or alumina- based fibers) are sensitive to slow crack growth activated by environment (water, high temperature air, etc.) in fatigue, so that failure can occur under stresses much smaller than the fracture stress. The delayed fracture of glass fibers has been investigated in a previous paper, on multifilament tows loaded under constant deformation in water. This tow testing technique was shown to be powerful for the estimation of the intrinsic crack growth law and the determination of the statistical distribution of rupture times pertinent to filaments. The present paper focuses on the residual behavior of filaments and tows after static fatigue (under constant deformation). It is aimed at assessing this tow-based approach to slow crack growth in filaments, i.e. demonstrating validity of the model, of the values of slow crack growth constants and of the equation of residual strength. For this purpose, E-glass fiber tows that comprised 2000 single filaments were subjected to interrupted static fatigue tests under constant deformation in water in a first step, and, then to residual tensile tests in inert environment in a second step. The residual behavior of tows was predicted using the slow crack growth constants that have been extracted from the static fatigue tests, and the fast fracture statistical parameters estimated from tensile tests on as-received tows. Validity of the approach was established by comparing experimental and predicted results. Then, the equations of residual strength and residual behavior were used for the investigation of residual behavior of filaments and tows.