Mechanical behavior of a notched oxide/oxide ceramic matrix composite in combustion environment: Experiments and simulations

This paper is focused on understanding the role of combustive environment on thermal fatigue of Nextel™ 720/alumina CMCs. The role of pre-existing flaws in thermal monotonic and fatigue failure of the CMCs is also computationally and experimentally investigated. A notch (hole) was fabricated on the samples to study the effect of defects on the mechanical behavior of CMCs in combustion environment. Fatigue life in the combustion condition for notched samples was lower by an order of magnitude in comparison to the unnotched samples in combustion environment and notched samples in isothermal furnace results across the range of applied stress. The different fatigue performance is attributed to the thermal gradient stresses and increased rate of oxidation due to a high moisture level in the combustion rig test condition. The former will be further verified using finite element analysis and the latter from finite element analysis and microscopic analysis of the fracture surfaces.