Damage monitoring of carbon fibre reinforced composites using acoustic emission

Abstract

This work is aimed at practical damage assessment in large composite panels with a view to long-term monitoring of such components. Three sets of experiments have been carried out on a carbon fibre epoxy composite to assess the possibilities for source location and also to characterise the AE associated with impacts and with various damage modes. AE wave propagation was studied using a Hsu-Nielsen source on a one-metre square CFRC plate and a new approach using features of the Gabor Wavelet Transform was developed to determine the resulting wave speeds and modes. Next, a series of tests were carried out with low speed impacts and the time and frequency features identified as a function of the incident energy, size and material of the impacting particle. In particular, it was found that the time difference between two peaks in the Gabor Transform Contour Plot could be used as a measure of the impact contact time. Finally, a set of destructive tests (tension, tearing and bending) were carried out while measuring AE to identify fibre breakage, matrix cracking and fibre/matrix de-bonding. Using a classification scheme based on the modal analysis developed in the propagation studies, the proportions of the various damage modes could be assessed. The research concludes overall that modal AE analysis, aided by the novel signal processing schemes developed here is an efficient way of identifying and locating damage in CFRC panels in a way that reduces the reliance on energy methods and the consequent problems that this raises with calibration.