20 - Improving the performance of advanced fiber-reinforced polymer (FRP) composites using nanoclay

Abstract

In this chapter, we discuss the flexural fatigue life and fracture toughness of nanoclay incorporated carbon fiber reinforced polymer composites (CFRPCs). The flexural fatigue test were carried out at three stress levels (0.9, 0.8, 0.75, and 0.7) along with the Mode I interlaminar fracture tests. Further, the fatigue life data was analyzed and validated using a two-parameter Weibull distribution function and Kolmogorov-Smirnov goodness-of-fit test. The fatigue life was also reliably predicted by means of combined Weibull and Sigmoidal model. Finally, the critical Mode I interlaminar fracture toughness (GIc) was calculated using four different data reduction schemes according to ASTM D5528–13 standard. Results of nanoclay added samples showed 327% increase in the mean fatigue life and 352% improvement in the predicted fatigue life (Pf=0.5), compared to the control samples. At 0.7 stress level, all the nanoclay added samples passed the ‘run-out’ fatigue criteria (106cycles), whereas, majority of the control samples failed much earlier. Stiffness degradation model and static test after a predetermined number of fatigue cycles showed that addition of nanoclay significantly improves the residual fatigue properties of the CFRPCs. Interlaminar fracture toughness of nanoclay added samples was found to be 71% higher than the control samples. Based on these results and fracture surface analysis by scanning electron microscope (SEM), it was concluded that addition of nanoclay toughened the polymer matrix and improved fiber-matrix interface and interlaminar properties, and thus, significantly improved the flexural fatigue performance and fracture toughness of the CFRPCs.