Strength of lithium fluoride under shockless compression to 114 GPa

A magnetic loading technique was used to ramp load single-crystal [100] lithium fluoride specimens to peak stresses of 5-114 GPa. Wave analysis of in situ particle velocity profiles was used to estimate the compressive strength of LiF at peak stress. It was found that the strength increased with peak stress and showed two distinct regions of hardening; the first is believed to be governed by strain hardening and the second by pressure hardening. The quasielastic strain obtained from the initial part of the unloading was shown to saturate at about 1.3% for peak stresses greater than approximately 30 GPa. Over the studied pressure range, the measured strength of LiF varied from its initial value of 0.08 to about 1.1 GPa at the highest compressed state of 114 GPa. Comparison of the measured strength to results from two strength models showed good agreement. It was demonstrated that the strength of LiF introduces systematic error of about 10% when used as an interferometer window for measurements of material strength in isentropic compression experiments. (C) 2009 American Institute of Physics. [doi:10.1063/1.3259387]