Preliminary applications of acoustic emission detection systems on composite structures

Acoustic Emission is getting new attention from the scientific and technological community for a number of applications that need a prompt identification of the health status of a certain structure. For instance, they allow getting info on the released energy after a crack event, making it possible to extrapolate indications on its residual life. Such potentialities are interesting for critical structures, like hydrogen tanks, recently recognised as a novel component on-board commercial aircraft, following the Greening wave that is investing all the means of transport, and even all-day life. In this perspective, the widely used piezoelectric ceramics, excellent for their very large bandwidth, are hard to use for the possibility of spark insurgence after being exposed to strain fields. In this view, optical sensors could be a viable means for overcoming those limitations. Within the H2ELIOS, a EU Clean Aviation Project, CIRA is starting to develop its expertise, with the support of the Consortium, to deploy a suitable acoustic emission sensor network for structural health monitoring purposes. In this activity, preliminary results are shown, mainly dealing with the characterisation of typical crack signals by a common piezoelectric sensors network for individuating its main features, in view of replacing it with an optical acoustic system. Different coupons have been tested on a standard mechanical rig. At first, a simple growing damage was imposed, and the strain history was recorded and post-processed in detail, highlighting some peculiar properties of the acquired signal. In a second case, the signals were detected at the event insurgence, irrespective of the magnitude and variability of the quasi-static load therein applied, in the perspective of a full real-time application. A correlation analysis was then performed among the successive acquisitions, and some preliminary conclusions were drafted. Preliminary evidence of the equivalence between optical and piezoelectric systems was explored