Mechanical hysteresis in ceramic matrix composites

Abstract

Ceramic matrix composites (CMCs) are interesting materials for aeronautic applications because of their good mechanical properties at high temperatures even under air. Contrary to bulk ceramics, CMCs have a non-brittle mechanical behaviour due to the high strength of fibres, and due to optimized fibre/matrix interactions after matrix multi-cracking. Interactions between fibres and matrix act mainly at the interface level. When fibres and matrix are debonded in a zone close to a matrix crack, bridging fibres slide with friction in the surrounding matrix. This friction is characterised by the interfacial frictional shear stress ( τ) and is the main phenomenon leading to energy dissipation during cyclic fatigue of CMCs. Internal friction evolutions measured from stress/strain loops during cyclic fatigue or static fatigue can be described by shear-lag models with a variation of the interfacial shear stress. For example to-and-fro slides of bridging fibres can lead to an interfacial wear and a decrease of the interfacial shear stress. For static fatigue, recession of interfaces is also a way to modify the interfacial shear stress during time. Hence internal friction is an interesting parameter to be measured on CMCs because it allows to follow the evolutions of fibre/matrix interactions during fatigue.