ABSTRACT
Innovative NDE methodologies based on linear and nonlinear acoustics are of outmost importance for developing damage tolerance approaches in aerospace materials by monitoring the accumulation of damage under cyclic loading. High strength titanium alloys, as well as fibre reinforced metal matrix composite materials, are being considered for a number of applications because of their improved mechanical properties in high temperature applications. In applications where cyclic loading is expected and where life management is required, consideration must be given to the behaviour of the material in the vicinity of stress risers such as notches and holes. It is in these regions that damage initiation and accumulations are expected. In the case of metal matrix composites for aircraft structural and engine components, several damage modes near stress risers have been identified [1]. One important damage mode under cyclic loading is the nucleation and growth of matrix cracks perpendicular to the fibre direction. In some composite systems, the matrix crack growth occurs without the corresponding failure of the fibres. This process results in the development of relatively large matrix cracks that are either fully or partially bridged by unbroken fibres. The presence of bridging fibres can significantly influence the fatigue crack growth behaviour of the composite.
