Dynamic mechanical properties and constitutive model of red sandstone under different loading rates and high temperatures

Abstract

Dynamic compression experiments were conducted on red sandstone utilizing a split Hopkinson pressure bar (SHPB) to study the loading rate and high temperatures on their mechanically deformed properties and ultimate failure modes, and to analyze the correlation between the strain rate, temperature, peak strength, and ultimate failure modes. The results show that the mass decreases with the increase of treatment temperature, and the pattern of the stress −strain curves is not impacted by the increase of impact velocity. Under a fixed temperature, the higher the impact velocity, the higher the strain rate and dynamical compression strength, indicating a strain rate hardening effect for red sandstone. With an increasing treatment temperature, the strain rate gradually increases when the impact loading remains unchanged, suggesting a rise in the deformability of red sandstone under high-temperature environment. Raise in both impact velocity and treatment temperature leads to an intensification of the damage features of the red sandstone. Similarly, higher strain rates lead to the intensification of the final damage mode of red sandstone regardless of the change in treatment temperature. Moreover, a dynamic damage constitutive model that considers the impacts of strain rate and temperature is proposed based on experimental results.

1. Introduction

Shallow resources are increasingly being depleted following years of heavy exploitation [1−3], there is therefore a need to develop and utilize deeper resources, such as deep resource extraction, deep treatment of highly radioactive nuclear wastes, and the exploration of geothermal resources [4−7]. With the increasing mining thickness, the ambient environment temperature around the rock formation increases progressively. Firstly, the high temperatures result in alterations in the mechanical behavior of the rocks [8]. Secondly, deep excavation subjects the surrounding rock masses to dynamic disturbances, such as explosions and thermal impact [9, 10]. Therefore, it remains important to examine the mechanic behavior of rocks subjected to impact loading and elevated temperatures.

Researchers have conducted a number of experimental studies into the mechanical properties of rock at elevated temperatures. The mechanical properties of deep rocks at elevated temperatures have been investigated using granite rocks [11−15], sandstone [16−18], limestone [19, 20] and other rocks. For instance, QIN et al. [21] performed uniaxial and triaxial studies on granite to investigate their physical and mechanical performances observed prior to and after high-temperature processing respectively. SRINIVASAN et al. [22] studied the influence of heat treatment on the mechanical properties of Gondwana shale samples and determined the influence of temperature change towards the shale fracture destruction areas and damage properties. Fracture toughness of petrogenetic material is a key factor in rock damage characterization. ALNEASAN et al. [23] examined the influence of heat treatment on Mode I and Mode II fracture toughness of rocks and found that the crack velocity and fracture toughness of rocks were markedly increased following Mode I and Mode II heat treatments. HU et al. [24, 25] demonstrated that Mode I fracture ductility first increased and then decreased as the treatment temperature of granite increased. ZHANG et al. [26] studied the impact of high-temperature treatment on the physico-mechanical characteristics of rocks including density, elastic modulus, porosity, P-wave velocity, and compressive strength.

As mentioned above, the deep rock mass may be dynamically disturbed and its dynamic properties are more representative of actual engineering conditions under high strain rate loading. Generally, the split Hopkinson pressure bar (SHPB) is a popular and highly dependable experimental setup for studying the dynamical mechanical performances of rock samples at higher strain rates [27−29]. WEI et al. [30] investigated the energy expenditure during breccia damage and the impact of axial static loading on the dynamical tensile properties using a 3D SHPB system. ZHOU et al. [31] investigated the micro-process and inherent mechanism of rock failure under impact loading.