Effect of loading rate and peak stress on the elastic limit of dynamically compressed brittle single crystals

To examine the effect of loading rate on the compressive elastic limit of brittle solids, shockless and shock compression experiments were conducted on x-cut and z-cut quartz crystals. A compact pulsed power generator was used to achieve shockless compression at stresses up to 16 GPa in x-cut quartz and 18 GPa in z-cut quartz. Plate impacts generated shock compression to elastic impact stresses up to 16 GPa in x-cut quartz and 37 GPa in z-cut quartz. Transmitted wave profiles were recorded at the interface between the quartz crystals and LiF windows using a velocity interferometer. The shockless (loading rate ∼ 105--106 s-1) elastic limit of x-cut quartz was ∼ 11 GPa, a significant increase over the shock wave (loading rate > 107 s-1) elastic limit of ∼ 6 GPa. The shockless elastic limit of z-cut quartz, ~ 14 GPa, was also higher than the shock wave elastic limit of ~ 12 GPa. The increase in elastic limit with a decrease in loading rate is contrary to the expected loading rate dependence of material strength, and cannot be explained by usual inelastic deformation models. A strain energy localization model is proposed to explain the observed loading rate dependence for the quartz elastic limit. Strain energy localization is incorporated using dynamic stress concentrations in a shear cracking model. Constant loading rate calculations, performed using the model, provided results that were in qualitative agreement with the measured elastic limit-loading rate dependence.;To examine the effect of impact stress on the elastic limit of brittle solids, shock wave experiments were conducted on 3.2 mm thick, [100] and [111] gadolinium gallium garnet (GGG) crystals. Elastic impact stresses ranged from 15 to 50 GPa. Velocity interferometry measurements at the interface between GGG samples and LiF windows, together with impact pins, were used to measure transmitted shock and particle velocities. The measured elastic limits were strongly dependent on the impact stresses for both GGG orientations, and ranged from 13 GPa at an elastic impact stress of 17 GPa to 34 GPa at an elastic impact stress of 50 GPa.