Effect of patch hybridisation on indentation resistance and residual performance of patch repaired glass/epoxy laminates using acoustic emission monitoring

This research work focuses on investigating the effect of external patch repair and its sequence on quasi-static indentation (QSI) response of glass/epoxy laminates. The parent woven glass/epoxy laminates (Type-I) was repaired by using woven (W) and chopped (C) fibres with different patch sequence such as W/W/W/W (Type II), W/C/C/W (Type III), C/W/W/C (Type IV) and C/C/C/C (Type V). The aim of using hybrid patches was to combine the higher load resistance of woven glass fibres and stable crack propagation of chopped fibres. The evolution of damage in different repair patches was observed and their damage mechanisms associated during loading were characterised with online acoustic emission (AE) monitoring. The results noticed that the Type III and Type IV samples exhibited higher peak force by an average of 37% compared to Type II and Type V samples. Moreover, the Type III and Type IV samples showed higher contact stiffness by 3.77 and 2.74 times than the Type II samples. Correspondingly, the Type III and Type IV samples indicated higher damage onset load by an average of 80% compared to the Type II samples. Overall, the Type III samples revealed superior indentation performance with higher peak load and minor residual dent. In contrast, the indentation resistance of Type IV samples was better for lower indentation depths. However, the Type III laminates have greater ability to resist crack progression through crack diversion and debonding of fibre at the repair patch interface.