Analysis of interfacial sliding in brittle-matrix composites during push-out and push-back tests

The aim of this work was to study the friction mechanisms in single-filament model composites (SiC/Pyrex), as the fibre slides into the matrix, and to analyse the modification of friction conditions as interface degradation proceeds. Results obtained by push-out and push-back tests on thin sheets of a single-filament model composite are presented and discussed. The push-out set-up used was classical in principle, except that the stiffness of the device can be easily changed. When this stiffness is high, the pushing force is steady (friction under steady regime) and exhibits a well pronounced seating drop, during push-back, as the fibre reaches its original position. When the stiffness becomes low, the load–displacement curve exhibits large serrations because the friction is now in the stick-slip regime. The dependence of the serration characteristics on specimen thickness is described and discussed. The bifurcation between steady sliding and stick-slip regimes is discussed with respect to the jerky nature of the slip at the microscopic scale, because slip needs to break contacts between asperities of the rough surfaces. As the number of push-out/push-back cycles increases, these serrations progressively disappear. This phenomenon can be explained by the progressive degradation of the sliding surfaces. A simple model describing the degradation kinetics was proposed.