1,721,014 research outputs found
On stress integration of coupled viscodamage-viscoplasticity models with separate yield/loading surfaces
No full textThis paper deals with numerical integration of stresses, inelastic strains and internal variables related to coupled viscodamage-viscoplasticity models. The class of models considered here is the one where the viscodamage and viscoplasticity parts are described independently based on their specific loading/yield criteria and evolutions laws. Moreover, in the viscodamage part, an anisotropic compliance damage formulation is adopted. Both the viscodmage and the viscoplasticity components are formulated in terms of the consistency model by Wang (1997). Two methods for coupling the damage and the plasticity parts are presented. In the first more traditional method, both models are solved simultaneously returning the trial stress onto the intersection of the criteria while updating the internal variables. The second, nonstandard method exploits the damage strain to impose iteratively the stress equality on the stress vectors returned independently on the respective, viscodamage and viscoplasticity surfaces. A special emphasis is laid on the treatment of the corner point plasticity case. After the general treatment, the two methods are illustrated with an application to the Mohr-Coulomb viscoplasticity model combined with Rankine viscodamage model.  
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Numerical modelling of pore-fluid-enhanced thermal spallation in granitic rock
No full textThis paper considers numerically the effect of pore-fluid on thermal spallation of granitic rock. For this end, a numerical model based on the embedded discontinuity finite element approach to rock fracture and an explicit scheme to solve the underlying thermo-mechanical problem is developed. In the present implementation, a displacement discontinuity (crack) is embedded perpendicular to the first principal direction in a linear triangle element upon violation of the Rankine criterion. In the thermo-mechanical problem, the heating due to mechanical dissipation is neglected as insignificant in comparison to the external heat flux. This leads to an uncoupled thermo-mechanical problem where the only input from the thermal part to the mechanical part is thermal strains. This problem is solved with explicit time marching using the mass scaling to speed up the solution. Finally, the fluid trapped into the micro-pores is modelled as a material that can bear only volumetric compressive stresses. A thermal spallation problem of a rock sample under axisymmetry is simulated as a numerical example
Numerical prediction of thermal weakening effects on granite rock
No full textThis paper presents a numerical method to predict the temperature weakening effects on granite rock. Thermally induced cracking is modelled in the continuum sense by using a damage-viscoplasticity model based on the rounded Rankine surface. The governing thermo-mechanical problem is solved with an explicit staggered method. Rock heterogeneity is described as random <br/>clusters of finite elements assigned with the constituent mineral, here Quartz, Feldspar, and Biotite, material properties. The temperature dependence of the minerals is accounted for up to 800 °C, i.e. well beyond the Curie point (573 °C) of Quartz. The simulations demonstrate that the present approach can accurately predict the experimental weakening effects on the rock strength and stiffness as well as the macroscopic failure modes in tension. Moreover, it does so in a noncircular way, i.e. not using the laboratory data on rock strength as an input data in the constitutive description.Peer reviewe
On modelling quasi-static uniaxial tension and compression tests on rock with explicit time stepping
No full textModelling rock failure in engineering applications, such as blasting and percussive drilling, involve stress wave propagation, high stress rates, and substantial fracturing/fragmentation during extremely short time spans. Such circumstances dictate using explicit time stepping in solving the global system of problem governing equations. The material model development requires validation under dynamic loadings, especially in uniaxial tension and compression tests. However, the failure model must also be able to predict the quasi-static uniaxial tensile and compressive strengths as well as the failure modes of the rock type involved. Unfortunately, the explicit time stepping is only conditionally stable and, thus, modelling quasi-static tests of a laboratory sample size numerical rock sample becomes a computationally laborious task. It is, therefore, tempting to increase the loading rate as much as possible when performing these validation simulations. Notwithstanding, using too high strain rates leads to strain rate hardening effects and affect the failure mode, triggering even a transition from a single (few) macro-failure plane(s) to multiple fracture/fragmentation beyond certain loading rate depending on the loading type and sample size. However, there seems to be no guiding lines in the literature as to how high a loading rate can be used in uniaxial tension and compression tests, to save the CPU time, so that the simulation results can still be considered valid. The present study addresses this gap of knowledge by performing a series of numerical tests on brittle rock under uniaxial tests using an explicit (in time) finite element code. The rock failure is described in the continuum sense based on a damage-viscoplasticity model. The 2D simulations demonstrate that with a sample of size 25*50 (mm), strain rates up to 1 s-1 can be used in both tension and compression without significant deviations from the quasi-static case.Peer reviewe
On the Strain Rate Sensitivity of Coarse-Grained Rock: A Mesoscopic Numerical Study
No full textA numerical study on the strain rate sensitivity of coarse-grained rock fracture under dynamic loading is presented. For this purpose, the embedded discontinuity finite element method is employed as a numerical tool. Moreover, a mesoscopic description of grain boundary-grain interior structure of rock is given. Thereby, the present approach is able to account for inter- and intragranular failure types of rock. The numerical simulations carried out here corroborate the conception that in direct tension the dynamic increase of tensile strength of rock is a real material property. Moreover, the simulations agree <br/>with the hypothesis that in uniaxial compression the dynamic increase of compressive strength is a structural effect due to lateral inertia. Finally, the numerical simulations of the dynamic Brazilian disc test suggest that structural effects also contribute to the dynamic increase in the apparent indirect tensile strength.Peer reviewe
A thermo-mechanical numerical method for modelling heating due to frictional sliding
No full textHeating due to frictional sliding is an important phenomenon in tribological applications. The present study develops a numerical method based on the finite elements (FE) for modelling frictional sliding induced heating. More specifically, the method is designed for applications where the behavior of the tool part of the frictional contact couple is not critical so that it can be idealized as a rigid body. The contact between the tool and the target, assuming linear elastic material, is modelled with the penalty method. The FE-discretized balance of linear momentum is time discretized with the Newmark scheme, and the FE-discretized heat equation is time discretized with the backward Euler scheme. The global coupled thermo-mechanical problem is solved with a globally iterative staggered approach. The frictional contact model is verified against analytical solution of a rotating blade pressed against a plane. Finally, a validation simulation of a pin-on-disc tribology test is carried out
Piezoelectric effect does not contribute in thermal drilling of quartz bearing rocks
No full textThis paper presents a numerical study on a possible piezoelectric effect in thermal drilling of Quartz bearing rocks. For this end, the governing piezoelectro-thermo-mechanical problem is solved with the finite element method. The granitic rock material, consisting of Quartz, Feldspar and Biotite minerals, is taken as linear elastic but heterogeneous and anisotropic. Temperature dependence of material properties is neglected. The simulation demonstrates that the secondary stresses arising from converse piezoelectric effect are three orders of magnitude smaller than the primary thermal stresses, which means that the piezoelectric effect is negligible.Peer reviewe
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