Numerical modeling of frictional contact between a blunt tool and quasi-brittle rock
Abstract
Frictional contact is an important component of rock cutting with a blunt cutter. There has been a gap in frictional contact between previous theoretical and numerical analyses within the framework of elastoplasticity and laboratory tests conducted on quasi-brittle rocks. By treating the rock as an elastoplastic material, there are three asymptotic regimes: elastic, elastoplastic, and rigid plastic regimes in frictional contact, predominantly depending on a dimensionless parameter that contrasts the magnitude of a characteristic elastic contact stress with a yield strength. These regimes are confirmed by laboratory tests, but the magnitude of contact stress is several times smaller than that based on elastoplasticity. This study interprets the discrepancy by analogy with the bearing capacity problem of a rigid footing resting on a quasi-brittle foundation. The bearing capacity decreases with an increasing brittleness number that is defined as the ratio of a contact length over a material length scale. In frictional contact on quasi-brittle rocks, it is hypothesized that (1) the contact stress is affected by rock damage that is not accounted for by an elastoplastic material model, and (2) the contact stress is also governed by a brittleness number. This study investigates the frictional contact using a coupled elastoplastic damage model within the framework of thermodynamics. The constitutive model is capable of describing the degradation of stiffness and strength under tensile and compressive loadings using different damage criteria. The model is developed based on a previous one that is implemented in ABAQUS as a user-defined material model (UMAT) for plain concrete. Further simplifications and revisions are introduced in the model, by regularizing mesh size sensitivity with a fracture energy based method, and by relating fracture energy to both the elastic and plastic components of Helmholtz free energy. The implemented constitutive model is verified based on both uniaxial tensile and compression tests. The modeling results of frictional contact confirm the two hypotheses that the magnitude of contact stress decreases by considering rock damage and that the decrease is more significant with a larger brittleness number.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMMR31B0070V
- Keywords:
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- 3625 Petrography;
- microstructures;
- and textures;
- MINERALOGY AND PETROLOGYDE: 8004 Dynamics and mechanics of faulting;
- STRUCTURAL GEOLOGYDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICSDE: 8160 Rheology: general;
- TECTONOPHYSICS