Experimental investigation of multi-orientation low-velocity impact damage in quasi-isotropic woven GFRP composite

This study investigates low-velocity impact damage in quasi-isotropic Glass Fibre Reinforced Polymer (GFRP) composites subjected to both normal and oblique impact loading using Local Defect Resonance (LDR)-based low-power vibro-thermography. The GFRP laminates were fabricated using the Vacuum Assisted Resin Transfer Moulding (VARTM) process. The specimens were impacted using a portable spring energy based in-house developed low velocity impact testing macine. Low-velocity impacts were introduced by varying the spring compression (10, 15, 20, and 25 mm), base plate angle (0° and 15°) and impactor body orientation (45°, 90°, 135°, and 180°), simulating real-life non-vertical impact conditions. These tests produced visible, barely visible and invisible impact damage on the sample. Damage characterization was initially performed using Phased Array Ultrasonic Testing (PAUT) to evaluate defect size, shape, and depth. Subsequently, Local Defect Resonance (LDR) based low power vibro-thermography (LVT) was performed using wideband excitation, and thermal responses were recorded with an uncooled infrared camera to obtain frequency specific defect mapping. A comparative evaluation demonstrated that LDR-LVT is more effective in detecting physical delamination and provides significantly faster inspection than PAUT for impact damage assessment. The results demonstrate the strong potential of LDR-LVT as a rapid and reliable non-destructive evaluation technique for impact-induced damage in composite structures. Furthermore, the experimental observations indicate that, below a threshold impact energy of approximately 8 Joule, the induced damage remains confined closer to the impacted surface.