Characterization of indentation damage resistance of hybrid composite laminates using acoustic emission monitoring

This paper focuses on the experimental investigation of impact damage resistance in hybrid composite laminates. In this case, the low velocity impact behaviour of quasi-isotropic glass/epoxy, glass/basalt/epoxy (G/B/G, B/G/B) and glass/carbon/epoxy (G/C/G, C/G/C) composite laminates was simulated by carrying out quasi-static indentation (QSI) tests with online acoustic emission (AE) monitoring. The dent depth, back surface crack size and load-deflection behaviors were examined and there is no distinct differences could be seen between low velocity impact tests and quasi-static indentation tests. The QSI tests were performed on specimens with rectangular section, of size 150 mm x 100 mm, which were loaded at the centre by a hemispherical steel indenter with 12.7 mm diameter. The indentation response was evaluated by measuring peak force, absorbed energy and linear stiffness. The residual strength of the laminates following indentation was measured by testing them under compression load in a 100 kN universal testing machine, once again with AE monitoring. AE parameters, such as amplitude, rise time, cumulative counts and cumulative energy were considered for monitoring damage progression during quasi-static indentation loading. Also other parameters linked to AE monitoring, such as the rise angle (RA) and Felicity ratio (FR) were measured for evaluating the damage resistance in each cycle of indentation. In addition, sentry function was also computed based on the combination of mechanical strain energy accumulated in the materials and of the acoustic energy propagates by fracture events made it possible to evaluate the amount of induced damage. These results showed that the combination of glass and carbon fibres in glass/carbon/epoxy (C/G/C) laminates improved their interlaminar shear strength at a level well above the other configurations tested.