Models for evaluating craters morphology, relation of indentation hardness and uniaxial compressive strength via a flat-end indenter

Abstract

In this work, the intensive theoretical study and laboratory tests are conducted to evaluate the craters morphology via the flat-ended indenter test, relationship of indentation hardness (HRI) and uniaxial compressive strength (UCS). Based on the stress distribution, failure process and Mohr–Coulomb failure criterion, the mathematical mechanical models are presented to express the formation conditions of “pulverized zone” and “volume break”. Moreover, a set of equations relating the depth and apex angle of craters, the ratio of indentation hardness and uniaxial compressive strength, the angle of internal friction and Poisson’s ratio are obtained. The depth, apex angle of craters and ratio of indentation hardness and uniaxial compressive strength are all affected by the angle of internal friction and Poisson’s ratio. The proposed models are also verified by experiments of rock samples which are cored from Da Qing oilfield, the percentage error between the test and calculated results for depth, apex angle of craters and the ratio of HRI and UCS are mainly in the range of –1.41%–8.92%, –5.91%–3.94% and –8.22%–13.22% respectively for siltstone, volcanic tuff, volcanic breccia, shale, sand stone and glutenite except mudstone, which demonstrates that our proposed models are robust and effective for brittle rock.

Calculation of Stress Intensity Factors at Both Ends of the Indenter under Eccentric Loads

“…In drilling engineering, the interface of the rock and bit interface process is very complex. In order to describe the rock failure and mechanism, many scholars usually select a simplified indention test using the flat-end indenter [24,25], and the indentation hardness is also usually used to assess the drillability of rocks [26][27][28]. Figure 2(a) shows a typical flat-tipped indenter, and the saw tooth of the drill is composed of a cylindrical shell periodic array flat-end diamond indenter.…”