In this study, investigation was performed to comprehend the influence of hybridization on the impact performance in terms of the energy absorption characteristics and delamination fracture toughness of pultruded uni-directional composite materials. In order to evaluate the improvements/changes in the impact performance as a result of hybridization, apart from considering mono-fiber reinforced all-graphite and all-glass composites, several types of sandwich hybrid composites comprising of both graphite as well as glass fibers were included in the investigation. By keeping a constant overall fiber content, the lay-up sequence and the volume fraction of each type of fiber are altered in these pultruded composites to determine the trend in the mechanical behavior as a result of hybridization.; The response of pultruded all-graphite, all-glass and glass-graphite hybrid composites is 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 (crashworthiness) and delamination fracture toughness of these composites.; Finite element modeling is performed under static as well as dynamic loading conditions to simulate the stress distribution and to predict the energy absorption behavior of composites. Progressive damage due to sequential ply failure was modeled by utilizing the failure strain data obtained from static and HTE impact tests for analyzing the post-initial ply failure characteristics of pultruded composites. Finite element modeling was also 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 for the pultruded composites under consideration.; Experimental results indicate that the strain to failure of glass fibers is comparatively higher than graphite fibers and a significant influence of this effect has been observed on the energy absorption characteristics. The ductility and failure index have shown marked improvement for the graphite outside hybrids. On the other hand, the incipient and initiation energies are higher for glass-outside hybrids. An increase in the fiber content of high stain to failure glass fibers has shown a corresponding increase in the total energy absorption capability. A significant reduction in the failure strain of glass fibers is observed under static loading conditions when compared with the results obtained from HIE impact tests. As a result, the energy absorption characteristics and associated parameters under static and low-velocity HIE impact loading conditions indicated different trends in the mechanical behavior. Results from LIE impact tests, ultrasonic C-scan tests indicated that the graphite-outside hybrids have shown a greater tendency to delaminate. (Abstract shortened by UMI.)
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