Characterization of Indentation Damage on Carbon/epoxy Laminates by Means of Acoustic Emission

Static indentation tests on carbon fibre reinforced laminates have been frequently used in literature to predict the value of penetration energy for the laminate. The mechanical set-up most commonly employed involves the use of indentors of diameter comparable with that of the impactors prescribed from standards for falling weight impact, such as ASTM D3763.The specimen is simply supported using a steel plate, so to leave a variable opening for the indentor to strike the laminate [1]. From indentation tests, empirical relations have been obtained, correlating the penetration energy with the total fibre areal weight (FAW) and indentor diameter [2]. During static indentation tests, the concentration of loading in a small area of the laminate, similarly to what is done during falling weight tests, reduces the flexure of the specimen, especially close to failure. It is to be verified, however, if this gives accurate values of the linear stiffness, a significant parameter in impact tests on composites [3]. With this aim, static indentation tests on carbon/epoxy laminates have been performed in a bending rig, using two different test configurations: in the former, the specimens were simply supported using a steel plate, whilst in the second one the specimens were left free to bend between the flexural rig supports. The comparison of the results obtained with the two configurations would allow clarifying the reliability of simulating falling weight impact test results using static indentation tests. All the tests were monitored by acoustic emission (AE).