However, studies on the effect of nano-reinforcements in repeated impact scenarios are relatively limited. This work investigates the effect of resin nanoclay modification on the impact resistance of glass-fiber reinforced polymer (GFRP) composites subjected to repeated impacts. Three impact energy levels were used in experiments with a minimum of four specimens per case for statistical significance. Each sample was subjected to 40 repeated impacts or was tested up to perforation, whichever happened first. The impact response was evaluated in terms of evolution of the peak force, bending stiffness, visual damage inspection and optical transmission scanning (OTS) at critical stages as a function of number of impacts. Also, the damage degree (DD) was calculated to monitor the evolution of damage in the laminates. As expected, the impact response of the GFRP composites varied based on the presence of nano-clay and the applied impact energy. The modification of the resin with nano-clay introduced novel phenomena that changed the damage progression mechanism under repetitive impacts, which was verified by visual observation and optical transmission scanning. A better understanding of these phenomena (e.g. crack-bridging, tortuosity) and their contributions to enhancements in the impact behavior and modifications of the types of damage propagation can lead to better design of novel structural composites.
Glass fiber reinforced polymer (GFRP) composites constitute nearly 90% of the global composites market and are extensively used in aerospace, marine, automotive and construction industries. While their advantages of lightweight and superior mechanical properties are well explored, non-destructive evaluation (NDE) techniques that allow for damage/defect detection and assessment of its extent and severity are not fully developed. Some of the conventional NDE techniques for GFRPs include ultrasonics, X-ray, IR thermography, and a variety of optical techniques. Optical methods, specifically measuring the transmission properties (e.g. ballistic optical imaging) of specimens, provide noninvasive, safe, inexpensive, and compact solutions and are commonly used in biomedical applications. In this work, this technique is adapted for rapid NDE of GFRP composites. In its basic form, the system for optical transmission scanning (OTS) consists of a light source (laser diode), a photo detector and a 2D translation stage. The proposed technique provides high-resolution, rapid and non-contact OT (optical transmittance)-scans, and does not require any coupling. The OTS system was used for inspection of pristine and low-velocity impacted (damaged) GFRP samples. The OT-scans were compared with conventional ultrasonic C-scans and showed excellent agreement but with better resolution. Overall, the work presented lays the groundwork for cost-effective, non-contact, and rapid NDE of GFRP composite structures.