A study of elastic precursor decay in FCC, BCC and HCP metals under shock loading
The evolution of the elastic precursor with strain rate and distance contains rich information regarding the origins of yielding under intense dynamic loading. Despite being a topic of study for over 40 years, the lattice and microstructural origins of this behaviour remain obscured and strongly material dependent. Efforts to analytically model the decay of the precursor based upon elementary dislocation theory typically result in an over-prediction of the initial mobile dislocation density of at least 2 orders of magnitude. This phenomenon has been attributed to a number of possible sources, including the high-rate activation of high order slip systems, the rapid nucleation of dislocations during the finite rise of the stress wave, and transonic dislocation velocities. Despite a great many experimental studies of Al and Fe, extension to other FCC or BCC materials, to higher symmetry HCP systems, or indeed materials considering microstructural variation have been few, limiting careful study of the dependence of factors such as Peiriel's stress, thermal activation, and stacking-fault energy. Means to carefully study precursor decay lies in the unique capabilities of the highly instrumented ISP 100 mm bore single stage gas gun. Preliminary experiments performed on single crystal and polycrystalline tantalum, commerically pure aluminium, and Ma2 magnesium alloy have revealed the potential for performing simultaneous loading of multiple targets, allowing direct comparison between samples of differing thickness, composition, or defect density. This PhD seeks to build upon these pilot studies, by extending this research to the study of specific FCC, BCC, and HCP metals of interest.