Investigation of carbon nanotube reinforcement to polyurethane adhesive for improving impact performance of carbon fiber composite sandwich panels

In this study, the development of a polyurethane adhesive by using carbon nanotubes (CNT) to enhance the lowvelocity impact behavior of aluminum honeycomb sandwich composite structures was investigated. The interaction of CNT and polyurethane for the impact behavior of sandwich composite panels is the main originality of this paper. The fabrication of carbon fiber reinforced composite (CFRC) sandwich structures was conducted using different polyurethane (PU) adhesives and different honeycomb cell sizes. CFRC sandwich structures were fabricated with multi-walled carbon nanotube (MWCNT) added and neat PU adhesives, 6.78 and 10.39 mm honeycomb cell sizes, and carbon fiber prepregs. Neat and nanotube added PU adhesives with MWCNT at reinforcement of 0.1% and 0.2% by weight percent were prepared. Sandwich composite panels were manufactured using the hot pressing method. Specimens of 100 x 100 mm were cut from the sandwich panels, and low-velocity impact tests were conducted at 100 J initial impact energy according to ASTM D7136 standard. After experiments, load-deflection curves, load-time, and energy-time histories were acquired. The absorbed energy values at maximum load were evaluated as a function of MWCNT content and honeycomb cell size. Specimens were sectioned from the impacted region and scanned using scanning electron and optical microscopes to analyze the damaged area. Specimens with MWCNT reinforced adhesives carried higher maximum loads compared to neat ones. CFRC sandwich structures with MWCNT added PU adhesives exhibited a 6% higher impact resistance at 100 J energy levels. Experimental results demonstrated that an increase in MWCNT loading and a decrease in PU adhesive cell size increased the maximum load values in CFRC sandwich panels. Among the nanotube added adhesives, 0.1 wt percent showed the best impact performance.