Abstract
Graphene nanoplatelets (GNPs) are multi-layer stacks of a single layer graphene that has two-dimensional and honeycomb-like structure. Due to its excellent mechanical and physical properties, graphene has become the reinforcement of polymer composites that is worthy of being studied and investigated. Although there have been many researches indicating that the toughness of polymer composites could be greatly enhanced by the addition of GNPs, no research mentioned about the toughening effect of adding GNPs into carbon fiber reinforced polymer (CFRP). This study is based on the foundation of a former graduate student in our laboratory. The preliminary results show that the amount of 0.25wt% GNPs/Epoxy has the most significant enhancement in mechanical properties. Then with the more precise range of 0wt%, 0.25wt%, 0.5wt% and 0.75wt% GNPs/CFRP, this study investigates the impact strength, static torsion strength, mode I interlaminar fracture toughness and torsion fatigue life. In order to agree with the real application conditions, a temperature of 25℃ with 85% relative humidity and a temperature of 85℃ with 85% relative humidity are also taken into account and discussed. The experimental results specify that the mode I interlaminar fracture toughness has the most significant enhancement with the addition of 0.75wt% GNPs, resulting in about 81.67% and 93.30% improvement in the mode I interlaminar fracture toughness for crack initiation and crack propagation, respectively. The results also indicate that GNPs can bridge the micro-crack, debonding and delamination layer of matrix and fiber, and also have very good toughening effect under room temperature with high humidity and high temperature with high humidity. The torsion fatigue life has the most significant improvement when adding 0.25wt% GNPs, dramatically increasing 4.64 times longer than neat CFRP at small angle of twist, while the static torsion strength slightly increases only about 15.23%. The results also show that it has pretty good enhancement due to its ability to prevent from intrusion of external moisture and hygrothermal aging under room temperature with high humidity and high temperature with high humidity. Furthermore, the torsion fatigue lifes for neat CFRP under different axial tensile loadings are also investigated. The results show the fatigue life under larger axial loading can be drastically improved about 17.34 times longer than the life under the small one, having the ability to prevent from delamination.