Improving and predicting the strengths of fiber-reinforced composites using a graphene-based self-healing system and finite element analysis
Patlolla, Vamsidhar Reddy
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A new method for self-healing is developed by incorporating graphene nanoparticles into the microcapsules to improve the healing efficiency after initial failure and to extend the service life of a composite. Graphene is used for this study because of its single atomic layer structure and excellent physical properties. The microcapsules were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) to confirm the encapsulation of nanoparticles along with the healing agent. Finite element analysis (FEA) models for the microcapsules were developed to determine the optimum physical characteristics of the capsules. FEA models using cohesive element technology were also developed for the mode 1 critical energy release rate (G1C) test of the composites. The models were validated by experimental testing results. After the first failure, the elastic properties of self-healing microcapsules were incorporated into the model. Analysis results suggest that 20% of the load-carrying capability can be recovered for dicyclopentadiene (DCPD) capsules and by 42% when graphene microcapsules were used. Furthermore, four-point bend test coupons were fabricated and tested for their interlaminar tensile (ILT) strength, the objective here to suppress failure due to free-edge effects. This was achieved by using metal clamps, wrapping, and self-healing methods. FEA models developed for ILT strength measurements correlated to the mechanical test results. These models were used to simulate the performance of self-healing capsules under four-point bending. Results suggested that 43% ILT strength could be recovered for self-healing capsules without nanoparticles, and 79% ILT strength could be recovered for selfhealing capsules with graphene.
Thesis (Ph.D.)-- Wichita State University, College of Engineering, Dept. of Mechanical Engineering