Hopkinson Bar Perforation of Laminated Graphite/Epoxy Composite

摘要

A Dillard University split Hopkinson pressure bar (SHPB) test apparatus wasdeveloped for dynamic quantification of energy expenditure in the perforation process of composite laminates. This report describes the basic features of the Hopkinson bar system for wave propagation and perforation experiments to characterize the perforation process, the nature of energy absorption process, and to explain and predict the extent of damage sustained during high strain rate perforation. Preliminary results for graphite/epoxy laminates show that the nature of energy expended in the perforation process depends on the thickness of the laminate, the fiber lay-up, the impact parameters and the incident stress delivered to the composite. The mode of laminate failure can be characterized by the level of energy absorption. The average impact energy per ply needed for damage initiation in graphite/epoxy were 7 plus or minus 1 J/ply, 10 J/ply and 11 plus or minus 3 J/ply for crack initiation on the rear surface, perforation and plug push-out, respectively. The reflected stress waves show the presence of multiple peaks, possibly caused by reflection from the incident bar/indentor interface (due to the impedance mis-match at the interface). Although such reflection has a negligible effect on the results, the indentor will be modified to eliminate this anomaly.