George Efremidis - Academia.edu (original) (raw)
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Papers by George Efremidis
Journal of the Mechanical Behavior of Materials
Journal of the Mechanical Behavior of Materials
Journal of the Mechanical Behavior of Materials
It is shown that the phenomenon of strength dependence on size, for otherwise geometrically simil... more It is shown that the phenomenon of strength dependence on size, for otherwise geometrically similar specimens, may be interpreted on the basis of gradient elasticity or multifractal scaling law arguments. This paper compares the predictions of these two different approaches to the scaling properties of the compressive strength in disordered materials. A detailed study for the stress concentration factor and the normalized failure stress of the borehole axisymmetric plane strain problem is presented. This problem has been already solved analytically by using a simple form of gradient elasticity theory. However the solution was not explored sufficiently to illustrate the size effect in a bilogarithmic diagram. By doing this the predictions of gradient elasticity can be related to the predictions of the multifractal scaling law. A comparison between the two mentioned approaches is presented and a common denominator is found.
Computers and Geotechnics, 2017
2015 6th International Conference on Information, Intelligence, Systems and Applications (IISA), 2015
Spring-block models were introduced several years ago to model avalanche-like dynamics for catast... more Spring-block models were introduced several years ago to model avalanche-like dynamics for catastrophic landslides. This article aims to address precursor phenomena in rain-induced landslides through the enrichment of a 2D spring block model with strain gradients. To this end an appropriate stochastic constitutive relation, introducing an effective dissipation parameter (which is related to structural heterogeneity and deformation processes at the failure plane) is used. It is shown that there is definite precursor activity before rain-induced landslides that can be modeled by a process of material yielding at the failure plane (a “weak” plane at a certain depth, parallel to the surface of the soil or rock mass, over which landslide takes place). This activity is related to the exponent b of the power law distribution of the slip events within the failure plane. Cellular automata simulations were used to verify the analytical predictions, which can be useful to geoscientists and eng...
The paper elaborates on an avalanchelike dynamic model for catastrophic landslides introducing th... more The paper elaborates on an avalanchelike dynamic model for catastrophic landslides introducing the effect of water diffusion along the failure plane. The main idea lies on the assumption that the stochastic nature of water diffusion along the failure plane results in a dynamic decrease in time of the shear strength for the entire rock mass parallel to this plane. To
Journal of the Mechanical Behavior of Materials, 2007
Journal of the Mechanical Behavior of Materials, 2004
Journal of the Mechanical Behavior of Materials, 2004
Journal of the Mechanical Behavior of Materials, 2014
ABSTRACT Spring-block models were introduced several years ago to model avalanche-like dynamics f... more ABSTRACT Spring-block models were introduced several years ago to model avalanche-like dynamics for catastrophic landslides. This article aims to address precursor phenomena in rain-induced landslides through the enrichment of a two-dimensional spring-block model with displacement gradients and stochasticity. This approach is along the lines of Aifantis and coworkers, who introduced deterministic gradients to stabilize material behavior in the softening regime and later expanded on it by introducing stochastic terms to model the competition between deterministic gradients and random effects. To this end, an appropriate stochastic constitutive relation, introducing an effective dissipation parameter (which is related to structural heterogeneity and deformation processes at the failure plane) is used. It is shown that there is definite precursor activity before rain-induced landslides that can be modeled by a process of material yielding at the failure plane (a “weak” plane at a certain depth, parallel to the surface of the soil or rock mass, over which landslide takes place). This activity is related to the exponent b of the power-law distribution of the slip events within the failure plane. Cellular automaton simulations were used to verify the analytical predictions, which can be useful to geoscientists and engineers, as an early prediction of the initiation of a landslide can minimize its catastrophic results through proper safety and precautionary measures.
International Journal of Plasticity, 2006
The modest goal of this article -the first in a series of three dedicated to Kirk Valanis -is to ... more The modest goal of this article -the first in a series of three dedicated to Kirk Valanis -is to discuss and compare (in terms of their constitutive and variational formulation, boundary conditions and size-dependent solutions to axially symmetric problems) a class of deformation and flow models of gradient plasticity derived from the same basic assumption of a gradientdependent flow stress: That is, the dependence of the flow or effective stress r on the Laplacian r 2 e of the effective strain e. This assumption is also used to derive, through wavelet analysis, a scale-dependent constitutive model involving a scale or gage length parameter instead of a gradient term. All models exhibit size effects which may differ from one model to another according to the nature of the boundary conditions and the values of the gradient coefficients or the scale parameter used. A weak formulation of stress equilibrium is employed to derive corresponding extra boundary conditions for the deformation and flow models which are then examined in view of their solutions for problems of axial symmetry, and also in connection with the corresponding solutions of the scale-dependent model for which extra boundary conditions are not required. In particular, results for the stress/strain distributions and the description of the associated size effects for internally pressurized thick-walled cylinders are provided. A comparison with some
Journal of the Mechanical Behavior of Materials
Journal of the Mechanical Behavior of Materials
Journal of the Mechanical Behavior of Materials
It is shown that the phenomenon of strength dependence on size, for otherwise geometrically simil... more It is shown that the phenomenon of strength dependence on size, for otherwise geometrically similar specimens, may be interpreted on the basis of gradient elasticity or multifractal scaling law arguments. This paper compares the predictions of these two different approaches to the scaling properties of the compressive strength in disordered materials. A detailed study for the stress concentration factor and the normalized failure stress of the borehole axisymmetric plane strain problem is presented. This problem has been already solved analytically by using a simple form of gradient elasticity theory. However the solution was not explored sufficiently to illustrate the size effect in a bilogarithmic diagram. By doing this the predictions of gradient elasticity can be related to the predictions of the multifractal scaling law. A comparison between the two mentioned approaches is presented and a common denominator is found.
Computers and Geotechnics, 2017
2015 6th International Conference on Information, Intelligence, Systems and Applications (IISA), 2015
Spring-block models were introduced several years ago to model avalanche-like dynamics for catast... more Spring-block models were introduced several years ago to model avalanche-like dynamics for catastrophic landslides. This article aims to address precursor phenomena in rain-induced landslides through the enrichment of a 2D spring block model with strain gradients. To this end an appropriate stochastic constitutive relation, introducing an effective dissipation parameter (which is related to structural heterogeneity and deformation processes at the failure plane) is used. It is shown that there is definite precursor activity before rain-induced landslides that can be modeled by a process of material yielding at the failure plane (a “weak” plane at a certain depth, parallel to the surface of the soil or rock mass, over which landslide takes place). This activity is related to the exponent b of the power law distribution of the slip events within the failure plane. Cellular automata simulations were used to verify the analytical predictions, which can be useful to geoscientists and eng...
The paper elaborates on an avalanchelike dynamic model for catastrophic landslides introducing th... more The paper elaborates on an avalanchelike dynamic model for catastrophic landslides introducing the effect of water diffusion along the failure plane. The main idea lies on the assumption that the stochastic nature of water diffusion along the failure plane results in a dynamic decrease in time of the shear strength for the entire rock mass parallel to this plane. To
Journal of the Mechanical Behavior of Materials, 2007
Journal of the Mechanical Behavior of Materials, 2004
Journal of the Mechanical Behavior of Materials, 2004
Journal of the Mechanical Behavior of Materials, 2014
ABSTRACT Spring-block models were introduced several years ago to model avalanche-like dynamics f... more ABSTRACT Spring-block models were introduced several years ago to model avalanche-like dynamics for catastrophic landslides. This article aims to address precursor phenomena in rain-induced landslides through the enrichment of a two-dimensional spring-block model with displacement gradients and stochasticity. This approach is along the lines of Aifantis and coworkers, who introduced deterministic gradients to stabilize material behavior in the softening regime and later expanded on it by introducing stochastic terms to model the competition between deterministic gradients and random effects. To this end, an appropriate stochastic constitutive relation, introducing an effective dissipation parameter (which is related to structural heterogeneity and deformation processes at the failure plane) is used. It is shown that there is definite precursor activity before rain-induced landslides that can be modeled by a process of material yielding at the failure plane (a “weak” plane at a certain depth, parallel to the surface of the soil or rock mass, over which landslide takes place). This activity is related to the exponent b of the power-law distribution of the slip events within the failure plane. Cellular automaton simulations were used to verify the analytical predictions, which can be useful to geoscientists and engineers, as an early prediction of the initiation of a landslide can minimize its catastrophic results through proper safety and precautionary measures.
International Journal of Plasticity, 2006
The modest goal of this article -the first in a series of three dedicated to Kirk Valanis -is to ... more The modest goal of this article -the first in a series of three dedicated to Kirk Valanis -is to discuss and compare (in terms of their constitutive and variational formulation, boundary conditions and size-dependent solutions to axially symmetric problems) a class of deformation and flow models of gradient plasticity derived from the same basic assumption of a gradientdependent flow stress: That is, the dependence of the flow or effective stress r on the Laplacian r 2 e of the effective strain e. This assumption is also used to derive, through wavelet analysis, a scale-dependent constitutive model involving a scale or gage length parameter instead of a gradient term. All models exhibit size effects which may differ from one model to another according to the nature of the boundary conditions and the values of the gradient coefficients or the scale parameter used. A weak formulation of stress equilibrium is employed to derive corresponding extra boundary conditions for the deformation and flow models which are then examined in view of their solutions for problems of axial symmetry, and also in connection with the corresponding solutions of the scale-dependent model for which extra boundary conditions are not required. In particular, results for the stress/strain distributions and the description of the associated size effects for internally pressurized thick-walled cylinders are provided. A comparison with some