Ceramic fibre reinforced ceramic matrix materials with porous matrix - effect of porosity on mechanical behaviour

Abstract

Ceramic fibre reinforced ceramics (CMC) have been developed to achieve ceramic materials with a high damage tolerance, i.e. high fracture toughness and some remaining load bearing capacity after exceeding the maximum strength. Such damage tolerant behaviour is based on energy dissipation during the damaging and fracturing process by mechanisms like crack deviation and branching, fibre/matrix debonding, crack bridging by fibres and fibbre sliding in the matrix. Crucial is a controlled fibre matrix dedonding, which can be achieved either by introducing fibre coatings providing weak fibre/matrix interphases or by manufacturing a CMC with a highly porous matrix. The effect of porosity on the mechanical behaviour of a CMC will be discussed on the example of the so called WHIPOX, an oxide fibre - oxide matrix CMC developed at the German Aerospace Center in Cologne. Information will be given on processing and characterization of the material as well as numerical approaches for modelling the material with focus on the effects of the porosity.