The high strain rate dependence of the flow stress of metals and alloys is described from a dislocation mechanics viewpoint over a range beginning from conventional tension/compression testing through split Hopkinson pressure bar (SHPB) measurements to Charpy pendulum and Taylor solid cylinder impact tests and shock loading or isentropic compression experiment (ICE) results. Single crystal and polycrystal measurements are referenced in relation to influences of the crystal lattice structures and nanopolycrystal material behaviours. For body centred cubic (bcc) metals, the strain rate sensitivity (SRS) is in the yield stress dependence as compared with the face centred cubic (fcc) case of being in the strain hardening property. An important consequence is that an opposite ductility influence occurs for the tensile maximum load point strain that decreases with strain rate for the bcc case and increases with strain rate for the fcc case. Different hexagonal close packed (hcp) metals are shown to foll...

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High strain rate properties of metals and alloys

Dislocation effected plastic flow stress levels in shock experiments are accounted for in terms of control by defect creation at the shock front: in the fcc case, of a high dislocation density; and, in the bcc case, of deformation twins Isentropic compression experiment (ICE) results differ in that the initially resident, much lower, dislocation density is required to “carry the load” by moving at very high drag‐resisted velocities

Dislocation Mechanics Under Extreme Pressures

A transmission electron microscopy study of quasi‐isentropic high‐pressure loading (peak pressures between 18 GPa and 52 GPa) of polycrystalline and monocrystalline copper was carried out. Deformation mechanisms and defect substructures at different pressures were analyzed. Current evidence suggests a deformation substructure consisting of twinning at the higher pressures and heavily dislocated laths and dislocation cells at the intermediate and lower pressures, respectively. Evidence of stacking faults at the intermediate pressures was also found. Dislocation cell sizes decreased with increasing pressure and increased with distance away from the surface of impact.

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D. Orlikowski

Papers

Dynamic Response of Copper Subjected to Quasi-Isentropic, Gas-Gun Driven Loading