Abstract
In this study, the dynamic mechanical properties of red sandstone at low temperatures were studied by performing SHPB dynamic impact tests. According to damage and energy theories, the influences of different low temperatures on the dynamic strength, damage variable, and energy dissipation of red sandstone were analyzed. Combined with a fracture morphology analysis, the deterioration mechanism of the dynamic mechanical strength of red sandstone was deduced at lower negative temperatures. The research results showed that lower negative temperatures (<−30 °C) caused “frostbite” in red sandstone, which resulted in a sharp reduction in the macroscopic, dynamic mechanical strength of rock under high strain. Transient engineering disasters can easily occur under such a dynamic disturbance. According to the fracture morphology analysis, low temperatures generated a large number of cracks at the interface between the components of red sandstone. The plastic deformation ability of the crack tip was poor, and stability loss and expansion under high strain rate were readily achieved, resulting in low-stress brittle failure. However, due to the complex mineral composition of the cementitious materials, they were more susceptible to low temperature. Therefore, under the double action of dynamic load and low temperatures, it was found that damage occurred in the cementitious materials first, and then fracture of the red sandstone as a whole resulted.
Highlights
The dynamic compressive strength and failure strain of water-saturated red sandstone at different temperatures were obtained according to the measured voltage value, and the curves of corresponding characteristic parameters changing with temperature were drawn, as shown in Figures 3 and 4
Under high strain rate, we found that low negative temperatures caused “frostbite” effects in rocks, that is, large numbers of microcracks and intermedium spaces were produced in rocks due to the differences in shrinkage rates and degrees of solid ice, minerals, and other media under low negative temperatures
The values of damage variable of water-saturated red sandstone under dynamic imimpact do not change continuously in the temperature range from 25 to −5 ◦ C, but their pact do not change continuously◦in the temperature range from 25 to −5 °C, but their varvariation in the range from −5 C to −40 ◦ C has regularity, the values of damage iation in the range from −5 °C to −40 °C has regularity, the values of damage variable variable and temperature in this negative temperature range can be fitted as the following and temperature in this negative temperature range can be fitted as the following EquaEquation (4): tion (4): d = −5.04739e−5 T 2 − 0.00846T + 0.28345 (4)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. It is key to solve the problem of mineral resource exploitation and geotechnical engineering construction in cold regions to reveal and understand the mechanical properties of rocks, especially the dynamic properties under low negative temperatures. As compared with the numerous studies in the field of rock statics [13,14,15,16,17,18,19], dynamic studies are relatively scarce, and most of them have focused on −20 ◦ C temperature conditions, which are not low enough to fully reflect the influence of negative temperature changes on rock dynamic characteristics, let alone to explore the dynamic. On characteristics of frozen rock are accurately characterized by fracture morphology analybasis, the effects of low temperatures and water-ice phase transformation on dynamic mebasis, the effects of low temperatures and water-ice phase transformation on dynamic mesis. Chanical strength and deformation characteristics of are dynamic mechanical strength and deformation characteristics of rock are studied
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