Dynamic Mechanical Characteristics of Impact Rock under the Combined Action of Different Constant Temperatures and Static and Dynamic Loads

Abstract

The complex mechanical environment of deep coal and rock masses leads to obvious changes on their dynamic mechanical properties. However, there are few reports on the dynamic mechanical properties of rocks under the combined action of medium temperature (normal temperature ∼100°C) and static and dynamic loads. In this paper, a dynamic load and temperature combined action Hopkinson pressure bar experimental system is used to experimentally study the impact type of a fine sandstone under temperature conditions of 18°C, 40°C, 60°C, 80°C, and 100°C, an axial static load of 3 MPa, a gas chamber pressure of 0.06 MPa, and a constant temperature time of 4 h. The dynamic characteristics of the change law of the fine sandstone and the energy dissipation characteristics of the load process are analyzed, and the characteristic law of the fine sandstone surface response is analyzed using digital image correlation technology. Our results indicate the following. (1) Under conditions in which the other experimental conditions remain unchanged, the dynamic stress-strain of the fine sandstone presents a bimodal shape with a “rebound” phenomenon. Increasing temperature causes the peak strength of the fine sandstone to increase; however, the relative strength can increase or decrease. The relative increase in the strength is 1.14 MPa (°C) when the temperature increases from 40°C to 60°C, 0.15 MPa (°C) when the temperature increases from 60°C to 80°C, and 0.62 MPa (°C) when the temperature increases from 80°C to 100°C. (2) The digital image correlation results show that, under the action of a dynamic load stress wave, the fine sandstone experiences a displacement vector change on the sample surface; furthermore, under the combined action of the temperature and dynamic and static loads, the fine sandstone experiences macroscopic shear failure. The surface strain in the propagation direction of the stress wave is obviously higher and can even reach values of more than 10 times that of the strain in other directions. (3) From the perspective of energy dissipation, the incident energy, reflected energy, and dissipated energy of the fine sandstone under an impact load have the same change law. After being affected by a dynamic load, the energy rapidly increases to a certain value and then remains relatively stable. The transmitted energy is relatively small and can be approximated as a horizontal line. As the temperature increases, the incident energy, reflected energy, and dissipated energy tend to first decrease and then increase, and most of the incident energy in the fine sandstone is dissipated in the form of reflected waves.

Experiments on the Coal Measures Sandstone’s Dynamic Mechanical Parameter Characteristics under the Combined Action of Temperature and Dynamic Load

“…In this experiment, the SHPB experimental system developed by the China University of Mining and Technology, which is composed of SHPB test system, ultra high-speed strain acquisition system, DIC image analysis system, and temperature control system [36]. The high-speed strain acquisition system consists of an ultra-dynamic strain gauge (LK2107 B, 16 bit, 8-channel), strain gauge junction boxes, and strain gauges, with a sampling rate of 40 MHz.…”

“…The preset bullet incidence velocity was 1.0 m/s, and the gas chamber pressure setting was 0.06 MPa. The density of fine sandstone was between 2.32 g/cm 3 and 2.42 g/cm 3 , and the bullet incidence velocity during the experiment was 1.00 to 1.31 m/s [36]. Figure 3 characterizes the variation of fine sandstone's dynamic stress and strain under seismic loading and different temperature conditions.…”

Experimental study on the quasi-static and dynamic tensile behaviour of thermally treated Barakar sandstone in Jharia coal mine fire region, India

“…In the context of dynamic loading, the mechanical properties of thermally treated rocks, such as compressive strength and tensile strength, are also influenced by the rate at which they are subjected to strain or load. During the last five years, several researchers have made efforts to comprehend how rocks behave dynamically under high-temperature conditions 7 – 10 . An et al 7 explored the dynamic testing of marble to ascertain both its uniaxial compressive strength and Brazilian tensile strength under varying temperatures.…”

“…Their conclusions highlighted the increasing brittleness of sandstone up to 400 °C, followed by a slight transition toward ductility up to 800 °C. In a related context, Zhao et al 10 studied the dynamic compressive strength of sandstone under high-temperature conditions. Their research revealed that the peak strength of sandstone exhibited an increase up to 100 °C.…”

“…Their research revealed that the peak strength of sandstone exhibited an increase up to 100 °C. Although these diverse studies 7 – 10 collectively contribute to understanding the complex behaviour of rocks under changing thermal and loading conditions, they also leave several open questions that need to be answered. Lindholm et al 11 established a correlation between the dynamic compressive strength, strain rate, and treated temperature of Dresser basalt.…”