A high strain-rate investigation of a zirconium-based bulk metallic glass and an HTPB polymer composite.

摘要

High strain-rate tests are performed on LM-1 using a Split-Hopkinson Pressure Bar (SHPB) to investigate effects of L/D ratio and annealing. An ultra high-speed camera was also employed to record the deformation and failure processes of LM-1. The amorphous specimens exhibit a reduction in peak stress with reduced L/D ratio and failure at the specimen-insert interface, indicative of stress concentrations due to the difference in the specimen and insert diameters, while the annealed specimens exhibited extensive fragmentation.;The stress concentrations in the specimen motivated simulations using LS-DYNA to design new inserts. A tapered insert design was chosen to reduce stress concentrations on amorphous and annealed specimens. Strain gages were also attached to as-cast specimens to determine the elastic stress-strain response. As-cast and annealed specimens with tapered inserts exhibit failure in the gage section, and a comparison of the peak stresses from quasi-static and pressure-shear plate-impact experiments to those in the current study indicate a negligible strain-rate sensitivity of LM-1.;Additional experiments are carried out using a modified SHPB to investigate the loading-rate sensitivity of notched LM-1 specimens. An ultra high-speed camera is employed to provide images synchronized with load-displacement traces from a high-bandwidth oscilloscope. No loading-rate sensitivity on the fracture toughness was observed. Experiments are also conducted to induce damage into notched LM-1 specimens without causing catastrophic failure; a damage zone is present in the specimens and slip-line fields are created which are consistent with those expected in an elastic-perfectly plastic material. Finally, experiments conducted to load previously damaged LM-1 samples indicate an increase in the fracture toughness and energy required to induce catastrophic failure.;Finally, high strain-rate compression experiments are conducted on a hydroxy-terminated polybutadiene (HTPB) polymer and its composite using another modified SHPB for testing of soft materials. Results from the experiments on HTPB polymer indicate a transition in the polymer between low and high strain-rate sensitivity at 2100/s, along with axial splitting at strain-rates above 3000/s. On the other hand, reduced rate-sensitivity is observed in the HTPB composite, most likely due to the presence of numerous interfaces between the glass beads and the polymer binder.