Rock strength determination from scratch tests

Richard, Thomas; Dagrain, Fabrice; Poyol, E.; Detournay, Emmanuel

doi:10.1016/j.enggeo.2012.07.011

Cited by 203 publications

(103 citation statements)

References 23 publications

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“…The ductile to brittle failure transition of rock subjected to cutting has attracted many researchers' attention and the pioneering work was done by Detournay and his collaborators (Detournay and Defourny 1992;Huang et al 2013;Nicodème 1997;Richard 1999;Richard et al 2012;Richard et al 1998;Lin 2013, 2014). In the case of rock engineering, such as strength estimation of core samples, it is important to make sure that only data from ductile failure mode cutting are used (Richard et al 2012).…”

Section: Introductionmentioning

confidence: 98%

“…In the case of rock engineering, such as strength estimation of core samples, it is important to make sure that only data from ductile failure mode cutting are used (Richard et al 2012). Therefore, ensuring the removal of rock materials via cutting only in ductile-dominant failure is crucial and this can be achieved by the help of the proper identification of the cutting depth threshold that separates ductile-regime cutting from brittle-regime cutting.…”

Section: Introductionmentioning

confidence: 99%

“…As most studies cited in this study use a constant vertical load and the depth of cut falls within a moderately wide range of values, the two terms are used interchangeably in this article. Application examples of scratch tests include the measurement of strength and fracture properties of various materials such as rocks (Akono et al 2011;Richard et al 2012), the damage analysis of ceramics (Klecka and Subhash 2008;Tan et al 2012), the assessment of tool wear (Ersoy et al 2005;Tönshoff et al 2002) and the performance measurement of thin films and coatings (Barletta et al 2008;Randall et al 2001). During the cutting process, there is a critical depth beyond which rock failure shifts from the ductile-dominated to the brittle-dominated regime.…”

Section: Introductionmentioning

confidence: 99%

“…1a, 2a) whilst brittle-mode cutting, as shown in Figs. 1b and 2b, is characterised with chippings formed by macro-scale fracturing (Richard et al 2012). The current study aims to develop a quantitative empirical model to predict the critical transition depth using the evolvement of specific energy for different rocks subjected to various cutting arrangements with different operational parameters such as cutting velocity, depth of cut and back rake angle.…”

Section: Introductionmentioning

confidence: 99%

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Specific Energy as an Index to Identify the Critical Failure Mode Transition Depth in Rock Cutting

2015

Rock Mech Rock Eng

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Rock cutting typically involves driving a rigid cutter across the rock surface at certain depth of cut and is used to remove rock material in various engineering applications. It has been established that there exist two distinct failure modes in rock cutting, i.e. ductile mode and brittle mode. The ductile mode takes precedence when the cut is shallow and the increase in the depth of cut leads to rock failure gradually shifted to brittle-dominant mode. The threshold depth or the critical transition depth, at which rock failure under cutting changes from the ductile to the brittle mode, is associated with not only the rock properties but also the cutting operational parameters and the understanding of this threshold is important to optimise the tool design and operational parameters. In this study, a new method termed the specific cutting energy transition model is proposed from an energy perspective which is demonstrated to be much more effective in identifying the critical transition depth compared with existing approaches. In the ductile failure cutting mode, the specific cutting energy is found to be independent of the depth of cut; but in the brittle failure cutting mode, the specific cutting energy is found to be dependent on the depth of cut following a power-law relationship. The critical transition depth is identified as the intersection point between these two relationships. Experimental tests on two types of rocks with different combinations of cutting velocity, depth of cut and back rake angle are conducted and the application of the proposed model on these cutting datasets has demonstrated that the model can provide a very effective tool to analyse the cutting mechanism and to identify the critical transition depth. AbbreviationsA c Cross-sectional area normal to the cutting direction A f Contact area between wear flat and rock surface A s Cracked surface area, A s ¼ ð2pC l þ 2C m Þc s Dl C l Size of lateral crack C m Size of median crack d Depth of cut d c Critical transition depth at which cutting changes from ductile to brittle mode E Elastic modulus of rock E b f Energy consumed for creating cracked surfaces in brittle-mode cutting E b p Energy consumed for plastic deformation in brittlemode cutting E b Energy consumed in ductile-mode cutting, including E b p and E b f E d p Energy consumed for plastic deformation in ductile-mode cutting E d s Energy consumed in overcoming sliding friction in ductile-mode cutting E d Energy consumed in ductile-mode cutting, including E d p and E d s E s Specific cutting energy calculated as F t Dl ð Þ=ðWdDlÞ E s b

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Specific Energy as an Index to Identify the Critical Failure Mode Transition Depth in Rock Cutting

2015

Rock Mech Rock Eng

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“…A bit/rock interaction law for such a bit, i.e., a set of relationships between the dynamical variables W and T and the kinematical variables U t and Φ t , can be constructed from experimental results obtained from single cutter tests [11,21,22].…”

Section: Bit/rock Interaction Lawmentioning

confidence: 99%

Instability regimes and self-excited vibrations in deep drilling systems

Depouhon

Detournay

2014

Journal of Sound and Vibration

Self Cite

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This paper analyzes the stability of the discrete model proposed by Richard et al. [1,2] to study the self-excited axial and torsional vibrations of deep drilling systems. This model, which relies on a rate-independent bit/rock interaction law, reduces to a coupled system of state-dependent delay differential equations governing the axial and angular perturbations to the stationary motion of the bit. A linear stability analysis indicates that, although the steady-state motion of the bit is always unstable, the nature of the instability depends on the nominal angular velocity Ω 0 of the drillstring imposed at the rig. On the one hand, if Ω 0 is larger than a critical velocity Ω c , the angular dynamics is responsible for the instability. However, on the timescale of the resonance period of the drillstring viewed as a torsional pendulum, the system behaves like a marginally stable one, provided that exogenous perturbations are of limited magnitude. The instability then only appears on a much larger timescale, in the form of slowly growing oscillations that ultimately lead to an undesired drilling regime such as bit-bouncing or stick-slip vibrations. On the other hand, if Ω 0 is smaller than Ω c , the instability manifests itself on the timescale of the bit motion due to a dominating unstable axial dynamics; perturbations to the steady-state motion then rapidly degenerate into stick-slip limit cycles or bit-bouncing. For typical deep drilling field conditions, the critical angular velocity Ω c is virtually independent of the axial force acting on the bit and of the bit bluntness. It can be approximated by a power law monomial, a function of known parameters of the drilling system and of the intrinsic specific energy (a quantity characterizing the energy required to drill a particular rock). This approximation holds on account that the dissipation in the drilling structure is negligible with respect to that taking place through the bit/rock interaction, as is typically the case. These findings are further illustrated on an example of deep drilling and shown to match the trends observed in the field.

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Geomechanics of Gas Shales

Rasouli

2015

Fundamentals of Gas Shale Reservoirs

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Rock strength determination from scratch tests

Cited by 203 publications

References 23 publications

Specific Energy as an Index to Identify the Critical Failure Mode Transition Depth in Rock Cutting

Specific Energy as an Index to Identify the Critical Failure Mode Transition Depth in Rock Cutting

Instability regimes and self-excited vibrations in deep drilling systems

Geomechanics of Gas Shales

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