Role of interfacial sliding on the longitudinal creep response of continuous fiber reinforced metal-matrix composites

Abstract

Experiments have been conducted on a model single Ni fiber reinforced Pb-matrix composite in order to detect the effect of interfacial sliding during creep under axial tension. This was achieved by separately measuring the axial fiber and matrix strains during creep deformation. The fiber and matrix were observed to strain differentially, this being accommodated by interfacial sliding near the ends of the fiber where the interfacial shear stress is large. Prior work on single fiber push-down creep of Ni fiber-Pb matrix composites has shown that the interface slides by diffusional creep with a threshold stress (Bingham flow). Based on this constitutive law for interfacial sliding, a unidimensional micro-mechanical model for thermo-mechanical deformation of continuous fiber reinforced metal-matrix composites is developed. The results show that during tensile creep, interfacial sliding is typically confined to the extremities of the tensile sample, allowing the isostrain condition to be valid over the tested gauge length. However, with increasing fiber diameter and decreasing gauge length, significant interfacial shear stresses may develop well away from the extremities of the sample, allowing differential matrix and fiber strains (and hence interfacial sliding) even within the gauge length. When interfacial sliding occurs within the gauge length, the composite creep rate is finite even after long times, whereas in the absence of interfacial sliding, the composite creep rate continuously decreases and eventually vanishes with time. These effects are considered to be of particular importance during deformation in the absence of end-constraints, e.g. during thermal cycling or flexural creep of composites.