An Experimental Study of Dynamic Tensile Failure of Rocks Subjected to Hydrostatic Confinement

Abstract

It is critical to understand the dynamic tensile failure of confined rocks in many rock engineering applications, such as underground blasting in mining projects. To simulate the in situ stress state of underground rocks, a modified split Hopkinson pressure bar system is utilized to load Brazilian disc (BD) samples hydrostatically, and then exert dynamic load to the sample by impacting the striker on the incident bar. The pulse shaper technique is used to generate a slowly rising stress wave to facilitate the dynamic force balance in the tests. Five groups of Laurentian granite BD samples (with static BD tensile strength of 12.8 MPa) under the hydrostatic confinement of 0, 5, 10, 15, and 20 MPa were tested with different loading rates. The result shows that the dynamic tensile strength increases with the hydrostatic confining pressure. It is also observed that under the same hydrostatic pressure, the dynamic tensile strength increases with the loading rate, revealing the so-called rate dependency for engineering materials. Furthermore, the increment of the tensile strength decreases with the hydrostatic confinement, which resembles the static tensile behavior of rock under confining pressure, as reported in the literature. The recovered samples are examined using X-ray micro-computed tomography method and the observed crack pattern is consistent with the experimental result. Keywords Dynamic tensile strength Á Hydrostatic confinement Á Brazilian disc Á SHPB Á Rate dependence Á X-ray CT Abbreviations SHPB Split Hopkinson pressure bar BD Brazilian disc CT Computed tomography LG Laurentian granite ISRM International Society for Rock Mechanics List of SymbolsA b Cross-sectional area of the bars (mm 2 ) A s Contact area between the sample and the transmitted bar (mm 2 ) r 0 Pump oil pressure (MPa) r 1 Stresses of the sample at the transmitted bar end (MPa) r 2 Stresses of the sample at the incident bar end (MPa) e i Incident strain wave e r Reflected strain wave e t Transmitted strain wave P 1 Force on incident end of the Brazilian disc specimen (N) P 2 Force on transmitted end of the Brazilian disc specimen (N) E b Young's modulus of the bars (GPa) B Thickness of the Brazilian disc specimen (mm) D Diameter of the Brazilian disc specimen (mm) r Tensile stress at the center of the Brazilian disc specimen (MPa) S Dynamic tensile strength of the Brazilian disc specimen (MPa) S 0 Static Brazilian tensile strength of Laurentian granite (MPa) & Kaiwen Xia

Compression-Induced Tensile Mechanical Behaviors of the Crystalline Rock under Dynamic Loads

“…In this study, we investigated the compression-induced tensile mechanical behaviors of the crystalline rock, combining the SHPB test and the GBM simulation. The experimental results showed that the macro tensile strength of the SJK granite depended on the loading rate, which was similar to findings obtained in previous studies [ 25 , 26 , 27 ]. However, previous studies rarely characterized the dynamic compression-induced tensile mechanical behaviors of the crystalline rock from the micromechanical viewpoint.…”

“…Out of the quasi-static case, the Brazilian test was extended to the dynamic case by making full use of the split Hopkinson pressure bar (SHPB) system [ 25 , 26 , 27 ]. Besides the internal heterogeneous microstructure, the loading rate significantly influenced the tensile behaviors of the rock materials.…”

“…Besides the internal heterogeneous microstructure, the loading rate significantly influenced the tensile behaviors of the rock materials. It was found that the Brazilian tensile strength increased with the loading rate increasing [ 26 ]. Near two loading points on the sample, there were two obvious crushing zones with a “V” shape, of which the areas increased as the loading rate increased.…”

Energy Dissipation Characteristic of Red Sandstone in the Dynamic Brazilian Disc Test with SHPB Setup

“…Dai and Xia [13] conducted dynamic Brazilian disc tests on Barre granite and confirmed the dependence between the tensile strength and loading rate. Wu et al [14] carried out the dynamic tensile tests of rock under the hydrostatic confinement.…”

Review of the Validity of the Use of Artificial Specimens for Characterizing the Mechanical Properties of Rocks

“…Natural rock has a high degree of variability, making it difficult to generate consistent results from tests that need a number of different samples even if they are taken from the same rock body. In addition, rocks normally being brittle materials, specimens are usually destroyed in most mechanical tests (Wu et al 2016), meaning that repeat tests or investigation of other properties cannot be carried out.…”