A numerical and experimental study on the tensile behavior of plasma shocked granite under dynamic loading

Abstract

Summary. This paper presents a numerical and experimental study on the mechanical behavior of plasma shocked rock. The dynamic tensile behavior of plasma shock treated Balmoral Red granite was studied under dynamic loading using the Brazilian disc test and the Split Hopkinson Pressure Bar device. Different heat shocks were produced on the Brazilian disc samples by moving the plasma gun over the sample at different speeds. Microscopy clearly showed that as the duration of the thermal shock increases, the number of the surface cracks and their complexity increases (quantified here as the fractal dimension of the crack patterns) and the area of the damaged surface grows larger as well. At the highest thermal shock duration of 0.80 seconds the tensile strength of the Brazilian disc sample drops by approximately 20%. In the numerical simulations of the dynamic Brazilian disc test, this decrease in tensile strength was reproduced by modeling the plasma shock induced damage using the embedded discontinuity finite element method. The damage caused by the plasma shock was modeled by two methods, namely by pre-embedded discontinuity populations with zero strength and by assuming that the rock strength is lowered and conform to the Weibull distribution. This paper presents a quantitative assessment of the effects of the heat shock, the surface microstructure and mechanical behavior of the studied rock, and a promising numerical model to account for the pre-existing crack distributions in a rock material.

Thermal jet drilling of granite rock: a numerical 3D finite-element study

“…With the friction angle of 50°, this translates into a cohesion, used in the DP criterion, of c 0 = (1 − sinϕ)/(2cosϕ)σ c0 = 32.8 MPa. The viscosity parameter for the pre-peak continuum model,s, is chosen so that the dynamic indirect tensile strength (29 ± 3 MPa) of the Balmoral granite in the experiments reported in [11] dissipated during the uniaxial tension and compression softening processes, i.e. the area under the stress-strain curves in these tests-hence, the relatively large values of mode II energies.…”

“…These shortcomings and the quest for harnessing deep geothermal energy in cold areas, like Scandinavia, have stimulated an intensive search for non-mechanical drilling and comminution methods. These methods include plasma jet drilling [2], electro-pulse drilling [3][4][5], microwave-induced breakage [6], and thermal shock (flame jet)-induced drilling and cracking of rock [7][8][9][10][11][12].…”

“…Moreover, only 3D simulations can provide realistic estimates on the drilling efficiency. It should be mentioned that Mardoukhi et al [11] presented a 3D numerical study on predicting the heat-shock weakening effect on the dynamic tensile strength of granite. However, the thermally induced cracking problem was not properly modelled.…”

“…For these reasons, this paper presents a finite-element-based numerical study on thermal jet drilling in 3D setting. A numerical solution procedure for the underlying thermo-mechanical problem is developed and validated by the experiments in Mardoukhi et al [11]. This means that the mechanical dynamic Brazilian disc (BD) test is also simulated for intact and thermally treated rock samples made of Balmoral granite.…”

Experimental study of the dynamic indentation damage in thermally shocked granite

“…The heat shock method shows a good level of consistency in generating different crack patterns [14,15], which enables experimental testing of the same rock type with different amounts of pre-existing damage. Therefore, it becomes easier to study and analyze the effects and the role of the pre-existing cracks on the dynamic indentation behavior and especially on the material removal of rock materials.…”