Effect of low velocity impact responses on durability of conventional and nanophased CFRP composites exposed to seawater

The effect of nanoclay on the degradation of low velocity impact responses of carbon fiber reinforced polymer (CFRP) composites manufactured by the vacuum assisted resin transfer molding (VARTM) process is experimentally investigated with and without exposure to seawater for marine applications. Nanoclay was dispersed into the matrix by using magnetic stirring. Samples (100 mm by 100 mm) exposed to seawater for 0, 6, and 12 months in laboratory conditions were impacted at 20, 30, and 40 J energy levels using a Dynatup8210. The damage sustained by the samples was evaluated by a thermographic imaging technique. Comparisons between conventional and nanophased CFRP composites both in conditioned and unconditioned cases were made in terms of peak force, absorbed energy, deflection, delamination area, and specific delamination energy. Water absorption was observed to be reduced due to nanoclay infusion. After 12 months of exposure to seawater 2% nanophased samples absorbed 0.39% moisture whereas control samples absorbed 0.67% moisture. Impact strength, toughness, and energy absorption decreased with increasing conditioning time by weakening the bond between the fiber and matrix and softening the matrix materials. However, reduction in properties is significantly extenuated by the incorporation of nanoclay in the matrix. Specific delamination energy (SDE) is observed to be higher in the nanophased CFRP compared to that of the conventional one at different aging periods indicating enhanced fracture toughness in the nanophased composites. The larger and stronger interfacial area produced by the nanoclay inclusion has been found to facilitate more energy absorption in the nanophased sample compared to the conventional one. Furthermore, nanoclay reduced the development of delamination by arresting the crack propagation path or by toughening the matrix. It is concluded that the excellent barrier capacity, higher surface area, and high aspect ratio of nanoclay are responsible for the superior performance of CFRP composites, which in turn, enhances the durability of composites. (C) 2013 Elsevier Ltd. All rights reserved.