Granite rock fragmentation at percussive drilling – experimental and numerical investigation

Abstract

International audienceThe aim of this study is to numerically model the fracture system at percussive drilling. Due to the complex behavior of rock materials, a continuum approach is employed relying upon a plasticity model with yield surface locus as a quadratic function of the mean pressure in the principal stress space coupled with an anisotropic damage model. In particular, Bohus granite rock is investigated and the material parameters are defined based on previous experiments. This includes different tests such as direct tension and compression, three point bending and quasi-oedometric tests to investigate the material behavior at both tension and confined compression stress states. The equation of motion is discretized using a FE approach and the explicit time integration method is employed. EOI (Edge-On Impact) tests are performed and the results are used to validate the numerical model. The percussive drilling problem is then modeled in 3D and the bit-rock interaction is considered using contact mechanics. The fracture mechanism in the rock and the bit penetration- resisting force response are realistically captured by the numerical model

Experimental and numerical study of Kuru granite under confined compression and indentation

“…In addition, the combined effect of the strain rate and confining pressure is an important and challenging aspect in rock mechanics and mining sciences 6 . However, the range of strain rates involved in percussive drilling is often considered small 7 and can be obtained by complementary dynamic laboratory tests 8,9 . Moreover, the velocities applied during percussive drilling are low enough to avoid shock regimes 10 , and it has been reported that the failure modes of rock under quasi-static and dynamic (at percussive drilling ranges) indentation are similar 11 .…”

A numerical study of the influence from pre‐existing cracks on granite rock fragmentation at percussive drilling

“…The stress state around the cracks does not increase considerably, indicating that the material in this region is shielded from fracturing. It should be mentioned that these results are more realistic than the preliminary simulation results with structural cracks . In ref.…”

“…This model was used to describe the fragmentation of two grades of limestone subjected to edge‐on impact (EOI) tests and the strength improvement and failure pattern of a microconcrete and a standard concrete during spalling tests and EOI experiments. Saadati et al applied the KST‐DFH model on granite and investigated the rock fragmentation process and the force‐penetration response at percussive drilling. It was shown that the KST‐DFH model is an appropriate tool for this purpose as it deals with both dynamic fragmentation as a result of tensile stress and also plasticity‐like deformation in compression.…”

Brittle materials at high-loading rates: an open area of research

“…The EOI technique has been widely used to investigate the damage modes produced by impact loadings of ceramic materials [12,46,47], ultra-high-strength concrete [48] and rocks [3,15,49]. An ultra-high-speed camera is used in the so-called open experimental configuration to observe the growth of damage at recording frequencies of approximately 1 Mfps (million frames per second).…”