Static and low-velocity impact response characteristics of pultruded hybrid glass-graphite/epoxy composite beams

The influence of hybridization on the crashworthiness and energy-absorption characteristics of pultruded glass-graphite/epoxy composite beams was inve stigated. Low-velocity drop weight instrumented impact tests were conducted on these hybrid composites to determine the toad-deformation behavior for evaluating the impact performance in terms of the ductility index, damage i nitiation, propagation, and total absorbed energies. Three-point static fle xural tests were also conducted to compare the static load-deformation char acteristics with those of the dynamic low-velocity impact tests. The behavi or under both static and dynamic loading conditions was simulated using fin ite element modeling procedures to identify the failure mechanisms for opti mizing the performance of pultruded hybrid composites. Experimental results show that the load and strain to failure of all-graphi te/epoxy, all-glass/epoxy and other hybrid composites obtained from impact tests are significantly higher as compared to the static test data. The loa d-bearing capability of composites after damage initiation (which is dictat ed by the ductility and failure index) has shown marked improvement for the graphite-outside hybrids when compared with the all-graphite, all-glass, a nd glass-outside hybrids. The high strain to failure glass fibers absorb co nsiderably higher energy before ultimate failure compared to the brittle gr aphite fibers; as a result, the fiber content and geometric placement of ea ch type of fiber significantly influenced the energy-absorption characteris tics of hybrids. Results indicate that the energy-absorption behavior of pu ltruded hybrids predicted using finite element modeling is in close agreeme nt with the behavior characterized from experimental impact tests. The effe ctiveness of hybridization to improve the impact performance of composites was demonstrated.