Acoustic emission for low velocity impact damage characterisation on polymer composites

Acoustic emission is a technique which has shown over the years a significant potential in damage assessment on polymer composite materials. In the specific case of impact damage, the very short time, during which the impact event takes place, does not allow in most cases a direct application of this technique for real time test monitoring. However, specific methods may also be applied for the acquisition of acoustic emission signals in very short time loading events, such as impact, more specifically using embedded piezoelectric sensors, alternative to the usual surface ones. The main limitation in this case is due to the need to prepare specifically every single laminate for the occurrence of the impact events. For this reason, a number of possibilities substitute to the direct approach described above have been explored: a first possibility is AE monitoring of quasi-static indentation loading on composites. This is a test procedure which has its origins in the study of surface properties of ceramics and metals. On polymer composites, it can be used as a simulation for low velocity impact: the difficulties and approximations of this approach are discussed. A second possible approach is the evaluation of acoustic emission during post-impact monotonic and cyclic loading tests: here, the residual properties and acoustic emission detected during the tests show some relation, and are in turn connected with the impact energy applied and therefore the level of damage introduced. This procedure is particularly suitable for the comparison of different configurations and lay-ups which may lead to the optimization of the stacking sequence of the composite, in terms of impact resistance. © 2011 Nova Science Publishers, Inc. All rights reserved.