Energy dissipation and dynamic fragmentation of dry and water-saturated siltstones under sub-zero temperatures

This paper outlines the experimental results of the energy dissipation characteristics and fractal dimensions of fragmentation based on the comparison of dry and saturated siltstone specimens. The specimens were first frozen to five different levels of sub-zero temperatures (from -10 degrees C to -50 degrees C) and then were tested at those temperatures using an SHPB apparatus with strain rates of 60-225 s(-1). The energy dissipation density of the specimens for each test scenario was calculated. The debris of the failed specimens was collected and dry-sieved to obtain the fragmentation size distribution and fractal dimensions. The results indicated that at all sub-zero temperatures, the energy dissipation density of the dry and saturated specimen increases with the increase in strain rate. Under the same strain rate, the energy dissipation density of saturated specimens reaches the maximum value at the temperature of -30 degrees C, indicating that the most energy is needed for rock fragmentation when the saturated specimen is frozen to -30 degrees C. The average fragment size of the dry and saturated specimens after failure is negatively correlated with the strain rate and energy dissipation density. Furthermore, for both the dry and saturated specimens, the fractal dimension first decreases with the decrease in the temperature from 18 degrees C to -30 degrees C, and then increases with a further drop in the temperature from -30 degrees C to -50 degrees C. The fractal dimension of the saturated specimen is slightly higher than that of the dry specimen for the same test scenario, indicating that the saturated specimens are more fragmented after the dynamic impact. Finally, the microcracking mechanism of the saturated specimens upon the subzero temperatures was illustrated based on the SEM observations.