The inelastic behavior of Bohus granite is studied based on experimental and numerical results. A number of quasi-static indentation tests are carried out. Several small and large load-drops are noticed in the force-penetration responses during those tests. These load drops are probably due to conical, Hertzian cracks initiated at the surface of the rock specimens. Each of these load drops are corresponding to a material removal event in the region with positive hydrostatic stress (negative pressure) state at the rock surface enclosing the growing contact boundary. Moreover, the P-h response after the first large load-drop is highly affected by cracking and fragmentation in this material. Therefore in order to predict the load-drop force levels and the response after the first large load-drop, a pressure-dependent damage criteria seems required.

1 Introduction

A review of the literature reveals that quasi-brittle materials under quasi-static (Q–S) or dynamic loading condition is being widely investigated (Price & Farmer 1979, Cook et al. 1984, Vermeer & De Borst 1984, Detournay 1986). The cracking behavior in Q-S indentation test on rock specimen is studied in (Cook et al. 1984). Several stages of fragmentation are described by the authors and the formation of a crater, a crushed zone and a region with multiple cracks are investigated. A damage-viscoplastic cap constitutive model is considered by Saksala (Saksala 2010) in order to simulate rock behavior during low-velocity impact. In another study, a numerical tool is developed in order to simulate rock fragmentation during indentation in (Wang et al. 2011). Heterogeneity and isotropic damage is considered by Wang et al in that work. More specifically, the fragmentation response of Bohus granite is investigated in (Saadati et al. 2014, 2018). Pressure dependent plasticity (i.e. Krieg, Swenson and Taylor (KST) model), together with an anisotropic damage model (proposed by Denoual, Forquin and Hild (DFH) model) is taken into consideration (Saadati et al. 2014).

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