A 'Simple' Method for In-Situ Observation of Crack Mechanisms in Ceramic Materials in the Environmental Scanning Electron Microscope

摘要

We have developed a special test fixture in an attempt to study the fracture behaviour of ceramic materials in an Environmental Scanning Electron Microscope (ESEM). The fixture, which can be easily fitted onto any conventional tensile/compression stage, was designed to load a double torsion specimen, thus providing conditions for stable crack growth. This not only allows evaluation of the fracture toughness and R-curve behaviour of a material, but also observation of the propagating crack at high resolutions. In this proof of concept study we have used two methodologies to study the mechanical behaviour of thermal barrier coatings - Constant Displacement Rate Method & Relaxation Method. It was found that the Relaxation Method worked adequately and it was possible to follow the development of a growing crack, whereas the Constant Displacement Rate Method was found to be unsuitable, due to the fact that in most cases the force increased continuously until abrupt failure of the specimen occurred.