TEMPERATURE DEPENDENCE OF THE PRECURSOR AMPLITUDE IN LITHIUM-FLUORIDE (SHOCK WAVES, STRESS RELAXATION, DYNAMIC LOADING, IMPACTRESPONSE)

Shock impact experiments were performed on single crystals of undoped lithium fluoride (LiF). The shock propagation was chosen to coincide with a crystal direction and the response revealed that elastic precursor amplitude strongly depends on the sample temperature. This dependence shows important similarities to temperature dependence of the critical shear stress required to initiate plastic flow in quasi-static torsion tests perfomed by Gilman. Since the only possible slip system that could be activated in Gilman's and the present experiments is the secondary slip system 100 , it is concluded that activation of the secondary slip system is responsible for the dynamic failure observed in shocked LiF.;The critical shear stress on the secondary slip system at room temperature is 16 kilobars. This compares with 14 kilobars reported by Rosenberg in similar experiments and a limit value of 0.6 kilobars by Gilman in quasi-static experiments.;The decay of the precursor with propagation distance for undoped LiF has been re-examined using the concept of homogeneous nucleation of dislocations on the shock front and the calculated decay curves have been compared with previously published data.;The sample temperature was varied from 151(DEGREES)K to 723(DEGREES)K, and a velocity interferometer method was used to obtain the particle velocity of the back surface of the sample. The LiF disks were impacted with aluminum or copper projectiles to produce impact stresses ranging from 46 to 75 kbars.