Damage assessment of oxide fibre reinforced oxide ceramic matrix composites using acoustic emission

The damage mechanisms of woven mullite fibre (Nextel 720™) reinforced alumina ceramic matrix composites (CMCs) were monitored during tensile tests using acoustic emission (AE) technique. The effects of microstructural characteristics, such as porosity and pore size as well as the nature of interfacial zone between fibre and matrix on the type of damage were also examined and correlated with the microstructural observations. It is shown that based on the energy level of acoustic events, during the tensile tests, delamination of the fibres from the matrix takes place first then multiple matrix cracks form and finally reinforcement fibres break before the composite's final failure. It is also shown that porosity content of the composite samples influences the acoustic emission response during the tensile loading, as both amplitude and the energy values are higher for the composites with low porosity level and smaller pore diameter.