The elevated temperature deformation behavior of interfaces in model single fiber composites was isolated and studied using a fiber push-down approach, whereby the interface is loaded in shear. Two fiber matrix systems. one with no mutual solubility (quartz--lead) and the other with limited mutual solubi- lity (nickel lead), were investigated. In both systems. the matrix and fiber underwent sliding relative to each other. with the interface acting as a high diffusivity path. The mechanism of sliding was inferred to be interface-diffusion-controlled diffusional creep with a threshold stress (Bingham flow). The behavior was modeled analytically using a continuum approach. and an expression for the constitutive creep behavior of the interface was derived. The model provided a physical basis for the observed threshold behavior, which was found to be directly related to the normal (radial) residual stress acting on the fiber--matrix interface. The results are deemed to be significant because: (l) in some instances, interfacial sliding may be instru- mental in determining the overall creep/thermal cycling response of a composite; and (2) they offer an alternative rationalization of threshold behavior during diffusional flow (besides interface reaction control)
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