Study of damage behavior and repair effectiveness of patch repaired carbon fiber laminate under quasi-static indentation loading

Abstract

Damage caused due to low-velocity impacts in composites leads to substantial deterioration in their residual strength and eventually provokes structural failure. This work presents an experimental investigation on the effects of different patch and parent laminate stacking sequences on the enhancement of impact strength of Carbon Fiber Reinforced Polymers (CFRP) composites by utilising the adhesively bonded external patch repair technique. Damage evolution study is also performed with the aid of Acoustic Emission (AE). Two different quasi-isotropic configurations were selected for the parent laminate, viz., [45°/45°/0°/0°]s and [45°/0°/45°/0°]s. Quasi Static Indentation (QSI) test was performed on both the pristine laminates, and damage areas were detected by using the C-scan inspection technique. Damaged laminates were repaired by using a single-sided patch of two different configurations, viz., [45°/45°/45°/45°] and [45°/0°/0°/45°], and employing a circular plug to fill the damaged hole. Four different combinations of repaired laminates with two configurations of each parent and patch laminate were produced, which were further subjected to the QSI test. The results reveal the effectiveness of the repair method, as all the repaired laminates show higher impact resistance compared to the respective pristine laminates. Patches of [45°/0°/0°/45°] configuration when repaired by taking [45°/45°/0°/0°]s and [45°/0°/45°/0°]s as parents exhibited 68% and 73% higher peak loads, respectively, than the respective pristine laminates. Furthermore, parent and patch of configuration [45°/0°/45°/0°]s and [45°/0°/0°/45°], respectively, attain the highest peak load, whereas [45°/45°/0°/0°]s and [45°/45°/45°/45°] combinations possess the most gradual decrease in the load.