Research on dynamic compressive behaviors of marble under high strain rates with split Hopkinson pressure bar

Abstract

The strain rates can significantly change the mechanical properties of rock materials. In this study, the static and dynamic compressive behaviors of marble under different strain rates were investigated by a series of compressive tests. The highest strain rate reached to1230s⁻¹ by using a split Hopkinson pressure bar (SHPB). A high-speed camera was employed to capture the fracture and failure progress of rock specimens during SHPB tests. The compressive stress-strain response of the tested rock material and the strain rate effects were analyzed. The experimental results showed that the fracture behavior and mechanical properties of marble have a significant correlation with the strain rate. Under quasi-static loading, the failure process of marble was dominated by one main crack. However, under dynamic loadings, there were more micro-cracks were generated within the specimens with the increase of strain rate. Moreover, the predominant failure modes of rock specimens change from intergranular fracture to transgranular fracture. The ultimate compressive strength increased with the increase of strain rate, and the grain size of the rock fragment decreased with the increasing strain rate.

Introduction

Rock materials are widely used in the construction industry. For the conventional machining process such as grinding, cutting and drilling, the materials generally undergo high-strain-rate dynamic loadings during deformation and fracture. Understanding the dynamic mechanical properties of rock materials is significant for its engineering application.

It is well known that rock materials always exhibit quite different mechanical properties under high strain rates in comparison with quasi-static conditions. Many kinds of research have been carried out to investigate the effect of loading conditions on the mechanical properties for rock materials (Li et al., 2008, 2018, 2017; Zhang and Zhao, 2014a, Zhang and Zhao, 2014b; Wong et al., 2014). The experimental results have shown that the strength of rocks under coupled loading was much higher than those in individual static or dynamic loading conditions, and confining pressure can increase the strength of rocks (Li et al., 2008, 2017). Zhang and Zhao, 2014a, Zhang and Zhao, 2014b investigated fracture behaviors of different rock materials and determined that the failure phenomena of rocks were dependent on the loading rate as well as its microstructures.

In order to study the dynamic behaviors of rock materials at a high strain rate, the split Hopkinson pressure bar (SHPB) is considered as the most commonly used experimental method (Li et al., 2000; Xia and Yao, 2015; Zhang and Zhao, 2014a, Zhang and Zhao, 2014b). Many researchers have used SHPB to study the mechanical properties and fracture mechanisms for different rocks. Shan et al. (2000) obtained the dynamic stress-strain response of marble and granite using SHPB tests, and analyzed the failure behavior of specimens. Gong and Zhao (2014), Gong et al. (2019) investigated the dynamic compression strength and indirect tensile strength of sandstone under high strain rates using a modified SHPB system. Zhang and Zhao, 2013a, Zhang and Zhao, 2013b presented a detailed experimental procedure to measure the strain of rocks based on the SHPB system and investigated the deformation characteristics and failure micro-mechanisms of Fangshan marble by a series of dynamic tests. Wang et al. (2009, 2011, 2015) explored the fracture toughness and tensile strength of the marble with a large diameter (100 mm) SHPB and flattened Brazilian disc specimens. Yao et al. (2017) investigated the dynamic mechanical properties of fine-grained Fangshan marble using an SHPB system and applied a dynamic Mohr-Coulomb theory to interpreting the loading rate effect on the strength. Ai et al. (2019) investigated the crack generation and dynamic properties of rocks based on SHPB tension tests. Zhang et al. (2001) and Liu and Xu (2013) studied the effect of temperature on dynamic mechanical property and fracture morphology of marble using a high-temperature SHPB system.

During the SHPB tests, Rock material deformation and failure occurred within a very short time. In the present study, high-speed camera was commonly used to capture the failure progress of rock specimens under impact loadings at high strain rates (Zhang and Zhao, 2013a, Zhang and Zhao, 2013b, 2014; Ai et al., 2019; Khosravani et al., 2018; Guo et al., 2019). In addition, the digital image correlation (DIC) techniques were employed to determine the crack initiation and propagation by measuring the full-field strain fields in rock specimens (Zhang and Zhao, 2013a, Zhang and Zhao, 2013b; Field et al., 2004). Furthermore, some numerical simulation methods such as extended finite element method (XFEM) (Goodarzi et al., 2015; Xie et al., 2016), discrete element method (DEM) (Lisjak and Grasselli, 2014; Du et al., 2018; Li et al., 2014), and combined finite-discrete element method (FDEM) (Gui et al., 2016; Abdelaziz et al., 2018) were also used to explain the deformation and fracture mechanism of rock materials.

Rocks’ mechanical strength and failure mode are sensitive to the strain rate especially in the high strain rate regime (Zwiessler et al., 2017). Though SHPB has been widely used to investigate the strain rate effects on the stress-strain response, most experiments were conducted with a large diameter SHPB. The highest strain rate is limited to 200 s⁻¹ in present studies (Gong et al., 2019; Liu and Xu, 2013; Zwiessler et al., 2017), the response of marble at much higher dynamic strain rates is sparse in the literature.

In this paper, a series of dynamic compressive tests were conducted with a diameter of 20 mm SHPB under the strain rates ranging from 215 s⁻¹ to 1230 s⁻¹. A high-speed camera was employed to capture the failure progress and fracture behavior of rock specimens. The fragment size distribution of rock blasting and fracture surfaces at the microscopic level was comprehensively analyzed. The purpose of this study is to explore the fracture process and failure mechanisms of marble at high strain rates.