A strength and damage model for rock under dynamic loading

AIP Conference Proceedings

Johnson-Holmquist constitutive model for brittle materials, coupled with a crack softening model, is used to describe the deviatoric and tensile crack propagation beneath impact crater in granite. Model constants are determined either directly from static uniaxial strain loading experiments, or indirectly from numerical adjustment. Constants are put into AUTODYN-2D from Century Dynamics to simulate the shock-induced damage in granite targets impacted by projectiles at different velocities. The agreement between experimental data and simulated results is encouraging. Instead of traditional grid-based methods, a Smooth Particle Hydrodynamics solver is used to define damaged regions in brittle media.

AIP Conference Proceedings, 2000

This paper describes the results of a computational study performed to investigate the behavior of granite under shock wave loading conditions. A thermomechanically consistent constitutive model that includes the effects of bulking, yielding, material damage, and porous compaction on the material response was used in the simulations. The model parameters were determined based on experimental data, and the model was then used in a series of onedimensional simulations of PILE DRIVER, a deeply-buried explosion in a granite formation at the Nevada Test Site. Particle velocity histories, peak velocity and peak displacement as a function of slant range, and the cavity radius obtained from the code simulations compared favorably with PILE DRIVER data.

Advances in Materials Science and Engineering, 2016

The dynamic tensile behavior of granite samples, when some preexisting cracks are introduced artificially, is investigated. Spalling tests using a Hopkinson bar are performed and strain rates of ~102 1/s are obtained in both specimen types (with and without initial cracks). This experimental technique is employed being of the same order as strain rates in rock materials during percussive drilling, the application of interest here. The dynamic tensile responses of both sample-sets are compared using the velocity profile measured on the free-end of the sample. Furthermore, an anisotropic damage model based on the concept of obscuration probability describes the response without preexisting cracks. Here, a term of cohesive strength in obscuration zones is added to accurately handle the softening behavior of the material in tension. Results from the spalling tests are used to validate the model prediction of the dynamic tensile strength and also to calibrate the cohesive model parameter...

Journal of Physics of the Earth, 1987

Effects of the strain rate and pressure on various brittle properties of granite under compressional loading are studied experimentally. Granite specimens were tested to failure under various constant strain rates at confining pressures of 0.1 to 200 MPa. The strain rates in these tests varied from 10-4 to 10-8 S s-1. The results show that the strength of granite decreases linearly as the logarithm of the strain rate decreases, and that the strain-rate dependence on the strength is enhanced at high confining pressures. The dilatant strain and elastic wave velocity variations with stress were found to be independent of the strain rate if the stress is normalized by the strength. The dilatant-strain-versus-stress curve is significantly affected by confining pressure but the confining pressure effect on the dilatant strain versus normalized stress is small. The acoustic emission rate is accelerated at a stress level closer to the failure strength as the strain rate decreases. Some of the timedependent properties are explained by a theory based on the concept of subcritical stress-corrosion cracking. But it is also clear that the stress-corrosion cracking theory does not provide reasonable explanations of the variation of acoustic emission rate with stress and the variation of strain with stress at the stage immediately before fracture.

1999

This paper deals with numerical modelling of induced damage in three granites. A continuous anisotropic damage model is proposed in the framework of thermodynamics and fracture mechanics. A second rank tensor is used to describe damage state which is directly related to orientation and density of microcracks. Both time independent and time dependent (or sub-critical) growth of microcracks are taken into account. A simple procedure for the determination of model parameters from standard laboratory tests is proposed. Comparisons between model simulation and experimental data are presented for some basic loading paths. Finally the application of the model to stability analysis of the Mine-by test tunnel of the URL in Manitoba (Canada) is presented. A comparison between numerical predictions and in situ observations makes it possible to evaluate the performance of the proposed model.

International Journal of Rock Mechanics and Mining Sciences, 2003

Dynamic tension tests based on Hopkinson's effect combined with the spalling phenomena were performed on Inada granite and Tage tuff to investigate the strain-rate dependency of the dynamic tensile strength of rock. The static tensile strengths were determined and compared with the dynamic tensile strengths. The fracture processes under various loading conditions were analyzed using a proposed finite element method to verify the differences between the dynamic and static tensile strengths and the strain-rate dependency. These analyses revealed that the differences were due to the stress concentrations and redistribution mechanisms in the rock. The rock inhomogeneity also contributed to the difference between the dynamic and static tensile strengths. An increase in the uniformity coefficient stimulated a reduction in the strain-rate dependency; i.e., the strain-rate dependency of the dynamic tensile strength was caused by the inhomogeneity of the rock. The fracture processes and principal stress fields in the specimens at high and low strain rates were analyzed to investigate fracture formations at various strain rates. Higher strain rates generated a large number of microcracks; the interaction of the microcracks interfered with the formation of the fracture plane. The observed dynamic tensile strength increase at a high strain rate was caused by crack arrests due to the generation of a large number of microcracks.

Rock Mechanics and Rock Engineering, 2014

AIP Conference Proceedings, 2018

The paper deals with a problem of rock finite element modelling and simulation. The main intention of authors was to present possibilities of different approaches in case of rock constitutive modelling. For this purpose granite rock was selected, due to its wide mechanical properties recognition and prevalence in literature. Two significantly different constitutive material models were implemented to simulate the granite fracture in various configurations: Johnson-Holmquist ceramic model which is very often used for predicting rock and other brittle materials behavior, and a simple linear elastic model with a brittle failure which can be used for simulating glass fracturing. Four cases with different loading conditions were chosen to compare the aforementioned constitutive models: uniaxial compression test, notched three-point-bending test, copper ball impacting a block test and small scale blasting test.

International Journal of Impact Engineering, 2006

The mechanical response of rocks to dynamic loading is complex. It is not well understood because of the difficulty of defining an effective shear and tensile strength model. Recently AUTODYN-2D from Century Dynamics is used to simulate the shock-induced damage in granite targets impacted by projectiles at different velocities. The simulated results are compared with experiment data. Johnson-Holmquist shock damage constitutive model for brittle materials is applied to describe the damage and shear strain achieved in a confined volume of granite. A tensile crack softening model is coupled with the JH model to simulate the propagation of radial tensile cracks generated by the principal tensile stress perpendicular to the shock front. The tensile stress is assumed to be equal to the deviatoric stress at radii that experience less than the Hogoniot elastic limit stress. Instead of traditional grid-based methods, a smooth particle hydrodynamics is used to define damaged regions in brittle media.

Materials, 2021

In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperature environments is always a major issue. The discrete element method and Voronoi modeling method were used to study the mechanical characteristics and crack evolution of granite specimens subjected to the high temperature and uniaxial compression test in order to study the internal crack evolution process of granite under the influence of high temperatures. Meanwhile, dependable findings were acquired when compared to experimental outcomes. A modified failure criterion was devised, and a Fish function was built to examine the evolution behavior of tensile and shear cracks during uniaxial compression, in order to better understand the evolution process of micro-cracks in granite specimens. Shear contacts occurred first, and the number of shear cracks reached its maximum value earliest, according to the findings. The number of tensile contacts then rapidly grew, whereas the number of shea...