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The present work aims to understand the stress–strain response of an igneous rock, granite, under high loading rate through detailed experimental and numerical analyses. The high-strain-rate characterization of granite rock was performed for two different diameters and five different slenderness ratios of the rock specimens using a 76-mm-diameter split Hopkinson pressure bar (SHPB) device in an effort to determine the appropriate specimen dimension for granite to be used in an SHPB test. The stress–strain response of the rock specimens was studied by systematically varying the length of the striker bars and the gas gun pressure values of the SHPB device. The petrological and static characterization of the granite rock was also carried out to assess the response of the rock specimens. Finally, a methodology was proposed to characterize granite rock specimens under high loading rate. Further, a numerical simulation of the SHPB test on granite rock was performed using the strain rate–dependent Johnson-Holmquist 2 (JH-2) model available in the finite-element software LS-DYNA. The simulation results were compared with the experimental data; thus, the parameters of the JH-2 model for granite rock were determined. The determined parameters were then used in blast analysis of a tunnel subjected to 20-kg TNT explosive. [ABSTRACT FROM AUTHOR]

In the present work, the dynamic stress-strain responses of three types of rock, compact basalt, metadolerite, and granite, are tested under high loading rates using the 38-mm-diameter split Hopkinson pressure bar (SHPB) device for the first time in the literature. The static characterization of the rocks, i.e., the physical and static mechanical properties of the three types of rock, was also determined. Petrological studies of the rocks were carried out through scanning electron microscope and X-ray diffraction tests. In the dynamic tests using the SHPB device, the stress-strain response, dynamic peak stress, and dynamic elastic modulus were studied. The effect of the mineralogy of the rock on peak stress and the dynamic elastic modulus was also studied under varying strain rates. Two correlation equations for the dynamic strength increase factor of compact basalt and granite are proposed herein. [ABSTRACT FROM AUTHOR]

The present study focuses on the performance of basalt fiber reinforced concrete (BFRC) lining in tunnel situated in sandstone rock when subjected to internal blast loading. The blast analysis of the lined tunnel is carried out using the threedimensional (3-D) nonlinear finite element (FE) method. The stress-strain response of the sandstone rock is simulated using a crushable plasticity model which can simulate the brittle behavior of rock and that of BFRC lining is analyzed using a damaged plasticity model for concrete capturing damage response. The strain rate dependent material properties of BFRC are collected from the literature and that of rock are taken from the authors' previous work using split Hopkinson pressure bar (SHPB). The constitutive model performance is validated through the FE simulation of SHPB test and the comparison of simulation results with the experimental data. Further, blast loading in the tunnel is simulated for 10 kg and 50 kg Trinitrotoluene (TNT) charge weights using the equivalent pressure-time curves obtained through hydrocode simulations. The analysis results are studied for the stress and displacement response of rock and tunnel lining. Blast performance of BFRC lining is compared with that of plain concrete (PC) and steel fiber reinforced concrete (SFRC) lining materials. It is observed that the BFRC lining exhibits almost 65% lesser displacement as compared to PC and 30% lesser displacement as compared to SFRC tunnel linings. [ABSTRACT FROM AUTHOR]

In the present work, dynamic stress–strain response of five sedimentary and three metamorphic rocks from different regions of India, e.g. Kota sandstone, Dholpur sandstone, Kota limestone, Himalayan limestone, dolomite, quartzite, quartzitic gneiss and phyllite have been investigated through split Hopkinson pressure bar test at different strain rates. The dry density, specific gravity, static compressive strength and tensile strength values of the rocks have also been determined. Petrological studies of the rocks have been carried out through X-ray diffraction test and scanning electron microscope test. It is observed from the stress–strain response of the rocks that the peak stress increases with increasing strain rate. Dynamic increase factors for the strength of these rocks have been determined by comparing the dynamic and the static peak compressive stresses and correlation equations are proposed. [ABSTRACT FROM AUTHOR]

In the present work, dynamic stress-strain response of Himalayan quartzite is tested under high loading rates using split Hopkinson pressure bar (SHPB) device for the first time in the literature. The physical and static mechanical properties of quartzite e.g. dry and saturated density, specific gravity, static compressive strength and elastic modulus values are also determined. Petrological studies of quartzite are carried out through X-ray diffraction (XRD) test and scanning electron microscope (SEM) test. In the SHPB tests, it is observed from the stress-strain response that the dynamic peak stress increases with increasing strain rate whereas the elastic modulus does not show any clear trend with increase in strain rate. Dynamic force equilibrium at the incident and transmission bar ends of the rock samples is attained in all tests till the failure of the rock samples. Dynamic increase factor ( DIF ) for the rock is determined at a particular strain rate by comparing the dynamic to static peak compressive stress. Correlation equation for dynamic strength increase factor with respect to strain rate has been proposed herein. [ABSTRACT FROM AUTHOR]

The present work investigates the dynamic mechanical behavior of transversely isotropic Jhiri shale at five anisotropy angles (0°, 30°, 45°, 60°, and 90°) using a large diameter (76 mm) split Hopkinson pressure bar. Jhiri shale, a type of Vindhyan shale, is collected from the Rewa region in the Madhya Pradesh state of India. Samples are loaded at strain rates of ∼150/s, ∼230/s, and ∼320/s under compression. It is found that the strength is rate-dependent and increases as the strain rate rises. At elevated strain rates, U-type anisotropy is noted. The anisotropy ratio lowers from 3.50 to 3.37 when the strain rate changes from quasi-static to ∼320/s, indicating that the influence of bedding planes diminished at higher strain rates. All the samples subjected to dynamic compressive loading are pervasively fragmented and undergo complete pulverization. As the strain increases, the degree of fragmentation intensifies, and the mean fragment size reduces. Samples with intermediate anisotropy angles (30°, 45°, 60°) are subjected to a higher degree of fragmentation than those with 0° and 90°. The rock fragments exhibit fractal distribution, which can be described using a power-law relationship. The dynamic experiments are numerically simulated using the discrete element method. The grains of the rock are generated as randomly sized and distributed polygonal blocks using Voronoi tessellation. The initiation and propagation of micro-cracks and failure mechanisms are explored via numerical simulations. It is found that samples mainly undergo shear failure dynamically. As the strain rate increases, the number of cracks increases. For samples with intermediate anisotropy angles, shear cracks begin along the bedding planes and then spread internally. At any given strain rate, they have a higher number of cracks than 0° and 90° samples, indicating a higher degree of fragmentation, as noted experimentally. • Dynamic tests on Jhiri shale are conducted in a 76 mm split Hopkinson pressure bar (SHPB). • High strain rates up to ∼320/s are achieved for a transversely isotropic rock. • SHPB tests are modeled numerically using Voronoi based discrete element method. • Experiments show that at high strain rates, anisotropy decreases and varies as U-type. • Numerical simulations reveal that mainly shear failure occurs at high strain rates. [ABSTRACT FROM AUTHOR]