Precursor amplitudes in LiF from shocks propagating in 〈111〉 directions

Precursor amplitudes have been measured for impact-produced shock waves traveling in 〈111〉 directions in LiF. Impact pressures range from 30 to 98 kbars and precursor amplitudes for the larger pressures are about 60 kbars for crystals containing approximately 100 ppm Mg and about 50 kbars for undoped crystals. The greatest impact pressure at which elastic response is preserved is about 40 kbars. No precursor decay is evident from the measurements, which include sample thicknesses between 0.3 and 5 mm. Mean precursor decay rates inferred for the first 1/2 mm of travel range up to about 100 kbars/mm. Primary slip systems are not active in this geometry and the shear stress on secondary systems ranges up to 38 kbars at the highest impact pressure. This is still well below theoretical shear strength. Mechanisms for the inferred decay are not identified.