Acoustic emission and acousto-ultrasonic approaches for interface damage monitoring in composites

The surveillance of critical structural components by non-destructive inspection techniques (NDI) to detect the presence of defects and/or damage initiation and growth in composite materials has long been onebf the most beneficial goals of the NDI technologies. This article deals' with damage monitoring 'in' carbon/epoxy cross ply laminates submitted to static and tension-tension fatigue loading. The materials have been exposed to. high' temperature before' being mechanically tested. The purpose of the present study was to investigate the effect of a thermal degradation of the matrix and fiber/matrix interface on the mechanical fatigue behavior of composite material-The onset and development of damage were followed by means of two complementary NDI techniques. Acoustic Emission (AE) and Acousto-Ultrasonics (AU). AU and AE signals were recorded during cyclic testing. Through-an analysis of the signal, contents, the AU technique proved to exhibit a distinction between the thermally exposed and the unexposed laminates. The results obtained indicate that, the identification of the state of degradation of the composite due to overheating and to mechanical loading can be discriminated.