Some New Insights of Rock Failure under Dynamic Loading

International Journal of Rock Mechanics and Mining Sciences, 2012

Journal of the South African Institute …, 2006

In this paper the effects of oblique impact loading of brittle rocks are investigated. The drilling process in hard rocks is simulated using particles dynamics (PD). The rock sample and impactor are described by particles with different bond strength. Impact is generated by applying a dynamical force to the impactor. The results are compared with the predictions obtained according to a simple analytical model of a drifting oscillator [1]. It is shown that the models correspond to each other reasonably well but there are a number of differences in their predictions. The results of the computer simulations aim to provide a valuable insight into the brittle fracture of rocks subjected to impact loading and eventually improve analytical model of this process.

1998

Fracture is the main reason for the non-linear behaviour of hard rocks. The fracture mechanics of rock is studied in this article by analysis of the fracture process under compression. A constitutive model that describes the relationship between the macro deformation of rock and the micro fracture within rock is developed. The propagation of microcracks, the non-linearity of deformation, the loading-and-unloading hysteresis and the variation of the apparent Young's modulus and Poisson's ratio are studied using the developed model. The model simulations demonstrate that: (1) the fracture toughness, initial crack length, crack density, and Young's modulus are four crucially important parameters that affect the deformation behaviour of rock; (2) the elastic parameters (E and v) of the rock matrix should be measured in triaxial tests. If they are measured in uniaxial tests, the upper straight unloading portion of the stress-strain curve is suggested to be used for the purpose, unless the closure effect of open cracks will be included in the estimations. In addition (3), the slope of the reloading stress-strain curve is a measure of the damage in material.

The initiation and propagation of failure in intact rock are a matter of fundamental importance in rock engineering. At low confining pressures, tensile fracturing initiates in samples at 40%e60% of the uniaxial compressive strength and as loading continues, and these tensile fractures increase in density, ultimately coalescing and leading to strain localization and macro-scale shear failure of the samples. The Griffith theory of brittle failure provides a simplified model and a useful basis for discussion of this process. The HoekeBrown failure criterion provides an acceptable estimate of the peak strength for shear failure but a cutoff has been added for tensile conditions. However, neither of these criteria adequately explains the progressive coalition of tensile cracks and the final shearing of the specimens at higher confining stresses. Grain-based numerical models, in which the grain size distributions as well as the physical properties of the component grains of the rock are incorporated, have proved to be very useful in studying these more complex fracture processes.

Journal of Mining and Environment, 2020

The dynamic fracture characteristics of rock specimens play an important role in analyzing the fracture issues such as blasting, hydraulic fracturing, and design of supports. Several experimental methods have been developed for determining the dynamic fracture properties of the rock samples. However, many used setups have been manufactured for metal specimens, and are not suitable and efficient for rocks. In this work, a new technique is developed to measure the dynamic fracture toughness of rock samples and fracture energy by modifying the drop weight test machine. The idea of wave transmission bar from the Hopkinson pressure bar test is applied to drop weight test. The intact samples of limestone are tested using the modified machine, and the results obtained are analyzed. The results indicate that the dynamic fracture toughness and dynamic fracture energy have a direct linear relationship with the loading rate. The dynamic fracture toughness and dynamic fracture energy of limesto...

IOP Conference Series: Earth and Environmental Science, 2016

In the work the problem of directed chipping of facing stone material by means of managing of explosion process is considered. The technology of the mining of decorative stone by the use of explosion energy means the very rapid transfer of potential energy of elastic deformations to kinetic energy. As a result, the explosion impulse, in the expanse of the inertia of rock massive, does not cause the increase of existing cracks. In the course of explosion, the shock wave is propagated by ultrasonic velocity and in this case the medium parameters (pressure, density, temperature, velocity) increase in spurts. In spite of this fact the all three conservation laws of mechanics remain valid on basis of three laws the equations are derived by which the parameters of shock wave may be defined by means of the rock physical-mechanical properties. The load on the body volume at breaking under explosion acts over very small period of the time. Therefore, stressed-deformed state of the rock was studied when the impulse load acts on the boundary. It was considered that the mining of the blocks of facing stone is performed from the hard rocks. This means that the breaking proceeds in the zone of elastic deformation. In the conditions of mentioned assumptions, the expression of the stress tensor and displacement of vector components initiated by stressed-deformed state in the rock are written.

2019

Understanding the rock failure mechanism under dynamic loading is of high importance in rock engineering projects. It requires a model to address a coupling effect between plastic flow caused by sliding along micro-crack faces and damage evolution due to nucleation and growth of wing-cracks. The goal of this paper is to develop a self-consistent based micromechanical model by taking into account the coupling process between frictional sliding and damage under dynamic compressive loading. To achieve this goal, the developed model algorithm was programmed in the commercial finite difference software environment to investigate the relationship between the mechanical behavior and microstructure. The simulation results demonstrate that the developed micromechanical model can present many features of the rock behavior such as hardening prior to the peak strength, softening in post-peak region, damage induced by wing-cracks and irreversible deformations caused by frictional sliding along micro-cracks.

Hittite Journal of Science and Engineering, 2019

The Charpy impact test, a widely applied impact strength determination test for various materials such as metals, polymers and cementitious materials was performed to evaluate the crack propagation energy of 13 different granite type rock materials under the impact load condition. Additionally, crack propagation energies of the granite materials were determined under the static load condition to compare the results with those of the Charpy impact test. The energy levels measured from static load tests were significantly lower than those obtained from the dynamic load test that the ratio of energy level under the dynamic loading to energy level under static loading condition was measured to change between 39 and 200 for different 13 type of granite materials tested in this study. The crack propagation time for the chevron-notched specimens under static loading was also measured using professional sound recording systems. As results of this study have not indicated that the crack propagation speed and energy values measured from different granite materials have a direct relationship, energy-dependent crack propagation speed was found to be an inherent property of rock materials. The Charpy impact test was assessed usable for being a sensitive crack propagation energy determination method for rock materials. In the context of improvement of the Charpy impact test for rock materials, some issues were pointed out in this study.

International Journal of Rock Mechanics and Mining Sciences, 2005