Dynamic direct tensile behaviours of small-scale marble under sub-zero temperatures and high strain rate loading

Abstract

Understanding the dynamic tensile behaviour of frozen rock is essential for the design and stability of engineering structures in cold regions, where tensile cracking is the predominant failure mode in brittle rocks frequently subjected to dynamic disturbances and low temperatures. This paper presents a novel dynamic direct tension setup based on a dogbone-shaped rock specimen and a Hopkinson tensile bar system, which is integrated with a specialized environmental chamber and high-speed Digital Image Correlation (DIC). This setup enables precise investigation of rock tensile behaviour across a range of strain rates and temperatures, including sub-zero conditions. The method of characteristics is proposed to decouple the superimposed incident and reflected waves caused by the extended length of the striker bar. Pixel-based virtual extensometers from DIC confirm the validity of dynamic tensile tests by detecting misalignment or bending waves and capture the real-time cracking process as well as dynamic tensile strain with high precision. Dynamic direct tensile tests of small-scale specimen were performed at 20, -25, −55 and −70 °C using dry and saturated marble with a dogbone shape. The dynamic tensile strength of saturated marble increased from 6.10 MPa to 11.62 MPa, corresponding to an enhancement factor of 1.90. The results show significant temperature and rate dependencies in dynamic tensile strength, which increases as both ambient temperature decreases and strain rate increases. This behaviour is attributed to the transition of unfrozen water into ice, emphasizing the role of ice in filling pores and strengthening ice-rock interfaces. Intergranular microcracks are predominant during high-rate tensile testing at each low temperature. Furthermore, compared to dry marble, the fracture surface of saturated marble shows a number of transgranular cracks, resulting in the accumulation of debris. The findings hold valuable implications for blasting designs and dynamic disaster prevention in cold regions, such as high-altitude or deep space mining.