Model for shear stress relaxation around fiber break in unidirectional composites and creep rupture analysis
Ohno Nobutada; Kawabe Hirokazu; Miyake Takushi; Mizuno Mamoru
Abstract:This paper describes a relaxation model of interfacial shear stress acting on broken fibers in unidirectional metal matrix composites reinforced with long brittle fibers. A cylindrical cell with a broken fiber embedded in power law creeping matrix is considered, and the broken fiber is assumed to have a bilinear distribution of axial stress. Then, on the basis of energy balance in the cell, a relaxation equation of interfacial shear stress is derived in a simple form. Under overall constant strain the relaxation equation is integrated to give an analytical solution, which is shown to agree fairly well with the numerical analysis of Du and McMeeking. Moreover, the relaxation equation is combined with Curtin's model, so that rupture time in long term creep is evaluated analytically on the assumption of global load sharing. It is shown that the resulting relation represents well the dependence of creep rupture time on applied stress observed experimentally on SCS-6/Beta21S at 500 degree. Key Words:composite material, continuous fiber, fiber break, interfacial shear stress, stress relaxation, creep rupture