Effects of loading modes and temperature on fracture properties of limestone

Abstract

Abstract Studying the fracture properties of rocks under high temperatures is crucial for understanding the laws of crack propagation and fracture mechanisms in deep underground engineering. In this study, based on digital image correlation technique, fracture tests were conducted on heat-treated limestone specimens under monotonic (ML) and cyclic loading (CL). The fracture properties including the peak load (P max), normal stresses (i.e., σ n and σ N) considering and without considering the influence of the crack, critical mid-span deflection (δ c), and critical crack mouth and tip opening displacement (CMODc and CTODc) of the specimens were calculated, and the influences of heat-treated temperature (T) and loading modes (i.e., ML and CL) on the above parameters were studied. In addition, by investigating the changes in fracture process zone (FPZ) of the specimens under CL and ML, the fracture mechanics of the specimens were obtained. The results show that whether under CL or ML, as T increases, P max, σ n and σ N all gradually decrease, while CMODc, CTODc and δ c all gradually increase, indicating that the heat-treated process enhances the deformation performance of limestone, but reduces its bearing capacity. For a specimen after the heat-treated process, as the loading progresses, the FPZ length undergoes an initial increase followed by a decrease. For specimens after different high temperatures, as T increases, the fully developed FPZ length gradually increases, but the change in the fully developed FPZ width is small. This indicates that the heat-treated process can lead to an increase in the nonlinearity of limestone, but has little effect on the volume of mineral particles.

Keywords

• Limestone
• Heat-treated process
• Digital image correlation
• Under cyclic loading
• Fracture properties
• Fracture process zone