Interrogating the Effects of Rate and Orientation on the Dynamic Failure Response of α-Quartz under Uniaxial Stress Compression

The catastrophic failure response of brittle solids is governed by the mechanics of crack nucleation and growth, which have been observed to be rate- and orientation-dependent. One property that is characteristic to this process is the failure strength. At low to intermediate strain rates, the failure strength has been observed to be nearly constant and equal to the strength observed under quasi-static conditions; however, at high-enough strain rates, the failure strength has been observed to become rate-dependent. The main objective of the present work is to interrogate the effects of loading rate and orientation on the failure strength of uniaxially compressed α-quartz at very high strain rates to ascertain the transition into rate sensitivity. For doing this, a miniature Kolsky bar is used to perform dynamic compression experiments on α-quartz at strain rates in the order of 103–104/s, and X-ray phase contrast imaging (XPCI) is used to directly visualize and quantify the cracking process. Experiments are carried out on nominally 1 mm and 2 mm rectangular α-quartz specimens compressed on the {-1,-1,2,0} and {-2,2,0,3} family of planes, resulting in strain rates of approximately 2000 - 5000/s to 20,000/s at the time of failure. The results show no appreciable orientation effects, suggesting that the loading configuration rather than the crystal orientation relative to the loading direction controls the orientation of crack propagation. However, the stress history and XPCI reveal that the failure strength is appreciably rate-sensitive within the present loading rate regimes. The stress history for both configurations exhibits an increasing average failure strength from around 2 GPa to 3 GPa as loading rates increase from 2000 - 5000/s to 20,000/s. The stress history and XPCI data are expected to provide crucial insight into the rate-dependence of the damage mechanisms occurring in this material.