Numerical modelling of heat shock‐assisted rock fracture

Abstract

SummaryThis paper presents a numerical investigation on the effects of thermal shock as a pretreatment of rock prior to comminution. More specifically, the effect of heat shock‐induced cracks on the uniaxial compressive strength of rock is numerically studied. The chosen constitutive model of rock employs a (strong) embedded discontinuity finite element formulation to describe cracks. The thermomechanical problem that governs the heat shock pretreatment of rocks is considered as an uncoupled problem because of a highly dominating role of the external heat influx. Two solution methods of the global problem are presented: an explicit‐explicit dynamic scheme and an implicit‐implicit quasi‐static scheme. The model performance is tested in simulations on heterogeneous numerical rock samples subjected first to a heat shock pretreatment and then to a mechanical compression test. According to the results, the compressive strength of intact granite rock having the axial splitting failure mode can be substantially reduced by heat shock pretreatment.

Numerical Modeling of Temperature Effect on Tensile Strength of Granitic Rock

“…It is noted that Equations ( 4)-( 7) have contributions from only the external heat influx, Q int , which simulates heating in an oven. All other heat generation types, such as thermo-elastic (in the bulk material) and thermo-plastic heat generation (at the crack due to opening dissipation), are neglected as insignificant in comparison to the external heat influx [15]. It should be emphasized that this EAS-based formulation results in a simple implementation without the need to explicitly know the exact position of the discontinuity within the element or its length.…”

“…Quartz-bearing rocks are particularly susceptible to temperature effects in their material properties and, consequently, in their response under thermal loading due to the α-β transition of quartz at its Curie point (~573 • C) [4]. Naturally, the temperature effects on rock mechanical properties have been extensively studied, experimentally [1,[5][6][7][8][9][10][11][12][13][14] and numerically [11][12][13][14][15][16][17].…”

Numerical modeling of thermo‐mechanical failure processes in granitic rock with polygonal finite elements

“…The purpose for writing these models in the xy ‐stress space, instead of the principal stress space where their expressions are extremely simple, is to avoid the transformations formulae between the principal and the xy ‐coordinate systems when deriving the tangent stiffness matrix below. It should also be noted that the viscoplastic consistency format allows to use the robust stress return mapping algorithms of computational plasticity 13,28 …”

“…The strong temperature dependence needs to be taken into account in predictive numerical modeling. Many numerical studies have been devoted to thermo‐mechanical failure processes of rocks 11–21 . While these studies have their merits, they do not present a method versatile enough, capable of solving the coupled thermo‐mechanical problem under both mechanical and thermal loadings of short and long duration, while accounting for the rock mesostructure and the heterogeneity thereof.…”

“…It should be noted that the FEM has been enriched to better describe discontinuities. The enrichment methods include the extended FEM 22,23 and the embedded discontinuity FEM 13 . These methods are, however, substantially more challenging from the computational and implementation points of view, especially in problems involving multiple cracks.…”