Abstract
The response of pultruded glass-graphite/epoxy hybrid composites has been evaluated under two different incident impact energy conditions. A high incident energy (HIE) and a low incident energy (LIE) of impact are chosen to cause either complete fracture or induce delamination, respectively, for assessing the energy absorption characteristics and delamination fracture toughness of these hybrid composites. From the HIE instrumented drop-weight impact tests, the energies required for damage initiation, propagation, as well as total absorbed energies and other parameters necessary for evaluating the impact performance of composites were derived from the load-deformation behavior of each sample. The influence of hybridization on the energy absorption characteristics of pultruded composites was investigated. A parametric study also was performed to correlate the energy absorption characteristics with the energy dissipative mechanisms attributed to the inherent material damping capacity of these composites. The qualitative assessment of the impact performance using inherent damping capacity as a non-destructive testing parameter is highlighted.
The samples that were subjected to LIE impact testing were examined using ultrasonic C-scan tests to ascertain changes in the extent of delamination crack propagation as a result of hybridization. Finite element modeling was performed to simulate delamination crack propagation at various levels through the thickness. The strain energy release rate computed using the virtual crack closure technique was monitored to determine the likelihood of delamination crack propagation with increment in crack growth. The results obtained from LIE impact tests and ultrasonic C-scan tests were used to corroborate the predicted delamination fracture toughness of pultruded hybrids. Graphite-outside hybrids exhibited high flexural stiffness, propagation energy, ductility and failure index, but had lower initiation energy along with a greater tendency to delaminate.