Showing papers in "Mechanics of Cohesive-frictional Materials in 1999"
TL;DR: In this article, the stress-strain behavior of granular materials can be modelled with hypoplastic constitutive relations, and a procedure for the determination of its parameters is described in detail.
Abstract: The stress–strain behaviour of granular materials can be modelled with hypoplastic constitutive relations. A hypoplastic model is briefly introduced for the axially symmetric case, and a procedure for the determination of its parameters is described in detail. It is shown, for several sands and one gravel, that all parameters of the hypoplastic model are closely related to the granulometric properties of grain assemblies. Recalculations of some element tests are presented in order to verify the proposed procedure. Copyright © 1999 John Wiley & Sons, Ltd.
408 citations
TL;DR: In this article, a computational analysis of hygro-thermal and mechanical behavior of concrete structures at high temperature is presented, and the evaluation of thermal, hygral and mechanical performance of this material, including damage effects, needs the knowledge of the heat and mass transfer processes.
Abstract: A computational analysis of hygro-thermal and mechanical behaviour of concrete structures at high temperature is presented. The evaluation of thermal, hygral and mechanical performance of this material, including damage effects, needs the knowledge of the heat and mass transfer processes. These are simulated within the framework of a coupled model where non-linearities due to high temperatures are accounted for. The constitutive equations are discussed in some detail. The discretization of the governing equations is carried out by Finite Elements in space and Finite Differences in time. Copyright © 1999 John Wiley & Sons, Ltd.
335 citations
TL;DR: In this article, a series of biaxial undrained tests on a fine, angular, quartz sand (Hostun FR) were performed using a false relief stereophotogrammetric method, which allows a full field measurement of the incremental strain within a specimen throughout the test.
Abstract: Results from a series of biaxial undrained tests on a fine, angular, quartz sand (Hostun FR) are presented. Both dilative and contractive specimens were tested. Strain localization in the specimen was recorded using a false relief stereophotogrammetric method, which allows a full-field measurement of the incremental strain within a specimen throughout the test. Incremental strain maps are obtained at different states on the stress–strain response. It is shown that shear banding can take place in both contractive and dilative specimens, but for the latter the onset of localization is delayed until cavitation takes place in the pore-fluid. It is concluded that in dilative granular media, non-drainage can preclude localization as long as cavitation in the pore-fluid does not relax the isochoric constraint. Copyright © 1999 John Wiley & Sons, Ltd.
171 citations
TL;DR: In this paper, the scalar damage model is compared to another model where damage-induced orthotropy is described, with the possibility of rotation of the principle axes of orthots.
Abstract: Scalar damage models are very often implemented in computational analyses in order to predict the response and failure modes of concrete and reinforced concrete structures. In most situations, however, damage is not isotropic but has preferential directions. Therefore, there have been many questions about the pertinence and range of applicability of isotropic, scalar, damage models for describing a degradation process which is strongly geometrically oriented. In order to assess what are the limitations of such a simplifying assumption, a comparative study is presented. The constitutive relations used for this purpose derive from the same class of models with a gradual enhancement of the description of damage. The scalar damage model is compared to another model where damage-induced orthotropy is described, with the possibility of rotation of the principle axes of orthotropy. Both models incorporate crack closure effects and a plasticity damage coupling. Structural analyses on bending beams, compression-shear and tension-shear concrete panels are presented. Although it may appear to be simplistic, the scalar damage model provides accurate predictions when failure is mainly due to uniaxial extension. Crack closure introduces an additional anisotropy which is important in compression-shear problems. Finally, damage-induced anisotropy seems important when failure is due to multiaxial extensions, such as in shear-tension problems. Copyright © 1999 John Wiley & Sons, Ltd.
137 citations
TL;DR: In this paper, an isotropic gradient-enchanced damage model is proposed in which the loading function not only depends on the damage value, but also on its Laplacian.
Abstract: To avoid the well-known drawbacks of the classical continuum damage theory when localization occurs, an isotropic gradient-enchanced damage model is proposed in which the loading function not only depends on the damage value, but also on its Laplacian. The initial boundary value problem obtained adopting this model is considered both in statics and in dynamics. In the dynamic context the finite-step problem is formulated according to a Newmark scheme; the constitutive law is integrated by the backward difference rule. An iterative procedure for the finite-step solution is discussed. Finite elements space discretization is carried out in terms of generalized variables on the basis of two variational principles pertinent to the two phases of the iterative process. One- and two-dimensional numerical tests show the regularizing effect of the gradient term and the effectiveness of the proposed discretization technique. Copyright © 1999 John Wiley & Sons, Ltd.
126 citations
TL;DR: In this paper, Sols Reference LMS-ARTICLE-1999-004View record in Web of Science Record created on 2006-11-09, modified on 2016-08-08
Abstract: Note: Sols Reference LMS-ARTICLE-1999-004View record in Web of Science Record created on 2006-11-09, modified on 2016-08-08
114 citations
TL;DR: In this article, a general framework for the formulation of constitutive models that incorporate a localized dissipative mechanism is presented, allowing for the decoupling of the constitutive characterization of the continuum and localized responses of the material.
Abstract: This paper presents a general framework for the formulation of constitutive models that incorporate a localized dissipative mechanism. The formalism of strong discontinuities is employed, allowing for the decoupling of the constitutive characterization of the continuum and localized responses of the material. A procedure for incorporating the localized small-scale effects of the material response in the large-scale problem characterized by the standard local continuum is described in detail. The resulting large-scale model is able to capture objectively the localized dissipation observed in localized failures of solids and structures. A localized viscous slip model is presented as a model example. The finite element implementation of the proposed formulation arises naturally as a local element enhancement of the finite element interpolations, with no regularization of the discontinuities. The above considerations are formulated first in the infinitesimal range, and then extended to the finite strain regime. Furthermore, it is shown that the proposed framework allows for the development of effective finite element methods capturing in the large scale the localized dissipation observed in the failure of rate-dependent materials, avoiding the resolution of small length scales associated to the localization bands in these regularized models. Several representative numerical simulations are presented to illustrate these ideas. Copyright © 1999 John Wiley & Sons, Ltd.
84 citations
TL;DR: In this paper, the mechanical behavior of a weak sandstone (Red Wildmoor sandstone) is analyzed and modelled within the frame of the theory of elastoplasticity.
Abstract: On the basis of an extensive experimental program of axisymmetric triaxial compression and extension tests, the mechanical behaviour of a weak sandstone (Red Wildmoor sandstone) is analysed and modelled within the frame of the theory of elastoplasticity. Stress-dependent elasticity and damage are incorporated into the model. Pressure sensitivity of the plastic behaviour is described through a non-linear Mohr–Coulomb model with friction hardening and cohesion softening. Emphasis is given on the calibration procedure. Validation of the model is done through back analysis of the experimental tests. Shear-band analysis is performed on the basis of the extension of the constitutive model to non-coaxial plasticity. Copyright © 1999 John Wiley & Sons, Ltd.
77 citations
62 citations
TL;DR: In this paper, a consutitutive model for compaction of granular media, with account for deformation induced anisotropy, is proposed, which is based on a model for the deformation-induced anisotropic deformation.
Abstract: A consutitutive model for compaction of granular media, with account for deformation induced anisotropy
59 citations
TL;DR: In this article, a method based on the Markov estimation procedure is proposed to evaluate the accuracy and the well-posedness of the identification problem, characterized by the uniqueness and identifiability of the estimated values.
Abstract: Non-local and gradient enhanced damage models are able to properly model localization phenomena in quasi-brittle materials. By the introduction of an internal length scale they avoid mesh-size sensitivity in finite element calculations and are capable of describing size effects. To experimentally determine the internal length scale and other damage model parameters, indirect identification methods have to be used. The method presented is based on the Markov estimation procedure, which also permits to evaluate the accuracy and the well-posedness of the identification problem, characterized by the uniqueness and identifiability of the estimated values. This information offers the possibility to compare and optimize the designs of laboratory tests in order to minimize the effect of errors on the estimated values. The indirect determination of the gradient damage parameters based on global response measurements far from the crack on one-size specimens is sensitive to the problem of ill-posedness due the high correlation between the gradient damage parameters, which dominate the localization process. The size effect method can be used as an accurate identification method for the gradient damage parameters, when information on the tensile behaviour is included and a sufficient size range is considered. Local displacement analysis close to the crack provides sufficient information with respect to the identification problem independent of the size of the specimen and gives the most accurate parameter estimations. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: In this article, the authors considered the problem of how to represent a regularized strong discontinuity in the finite element environment within the context of large deformation multiplicative elasto-plasticity theory.
Abstract: In the present paper, we consider the problem of how to represent a regularized strong discontinuity in the finite element environment within the context of large deformation multiplicative elasto-plasticity theory; An issue that has been addressed quite extensively for the geometrically linear theory in recent years to establish cohesive zone models in the finite element setting Our method, which is based on the enhanced assumed strain method, is designed such that the (mixed) element interpolation allows for a regularized discontinuity within the finite elements As a result, we obtain traction continuity across the embedded band in an automatic fashion for the proposed ‘enhanced constant strain triangle’, whereby the magnitude and mode of the internal discontinuity are obtained for the elastic/plastic loading assumption of the element It appears that the condition for onset of discontinuity development within the elements is identical to the classical localization condition for the continuum We present numerical results for the ductile failure of a plane strain specimen Copyright © 1999 John Wiley & Sons, Ltd
TL;DR: In this paper, it is hypothesized that the mechanism underlying this behaviour is related to the formation of a particle structure between the large and small grains which creates a highly compressible soil fabric.
Abstract: Most historic cases of liquefaction have been found to occur in alluvial (water) deposited silty sands. Currently, the effect of non-plastic fines (particles smaller than No. 200 sieve) on the liquefaction behaviour of sands is viewed to be either negligible or its presence actually inhibits liquefaction. Undrained triaxial compression test results performed on silty sands clearly indicate a direct correlation between the quantity of finer, non-plastic constituents and the liquefaction potential of granular soils. Increasing the fines content increases the liquefaction potential, even though the density increases. Complete static liquefaction occurs at low confining pressures. As confining pressures increase, the liquefaction potential decreases resulting in increased stability. Thus, silty sands exhibit a ‘reverse’ pattern of soil behaviour with confining pressure. Drained tests indicate both a large contractive volume change and a suppressed friction angle at low confining pressures, and this explains the undrained behaviour. It is hypothesized that the mechanism underlying this behaviour is related to the formation of a particle structure between the large and small grains which creates a highly compressible soil fabric. This ‘reverse’ behaviour pattern makes predictions of static liquefaction of silty sands difficult. However, simple modifications to the Single Hardening Model yield surface formulation enables predictions of this behaviour pattern. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors proposed a Cosserat-type theory for large deformation analysis of layered materials. But this theory suffers from certain difficulties associated with interface slip and internal instabilities, which can be remedied by considering the bending stiffness of the layers.
Abstract: Methods employing continuum approximation in describing the deformation of layered materials possess a clear advantage over explicit models, However, the conventional implicit models based on the theory of anisotropic continua suffers from certain difficulties associated with interface slip and internal instabilities. These difficulties can be remedied by considering the bending stiffness of the layers. This implies the introduction of moment (couple) stresses and internal rotations, which leads to a Cosserat-type theory. In the present model, the behaviour of the layered material is assumed to be linearly elastic; the interfaces are assumed to be elastic perfectly plastic. Conditions of slip or no slip at the interfaces are detected by a Coulomb criterion with tension cut off at zero normal stress. The theory is valid for large deformation analysis. The model is incorporated into the finite element program AFENA and validated against analytical solutions of elementary buckling problems in layered medium. A problem associated with buckling of the roof and the floor of a rectangular excavation in jointed rock mass under high horizontal in situ stresses is considered as the main application of the theory. Copyright (C) 1999 John Wiley & Sons, Ltd.
TL;DR: In this paper, a plasticity model for bond between ribbed, steel bars and concrete is discussed, which relates local slip and radial dilation to bond stress and radial confinement stress, and provides an interface characterization of the behaviour of a finite-thickness region around the bar.
Abstract: The validation of a plasticity model for bond between ribbed, steel bars and concrete is discussed. The model relates local slip and radial dilation to bond stress and radial confinement stress, i.e. it provides an interface characterization of the behaviour of a finite-thickness region around the bar—the bond zone. The validation study considers experimental results from six independent investigations. The specimens are all pull-out specimens but differ significantly in size and configuration. Models for each specimen, based on a single bond model calibration, reproduce the experimental results with acceptable accuracy. The response over the full range of slip and the mode of failure are examined. Some of the model's strengths, weaknesses, and potential improvements are discussed. For the most part, the models predicts the experimental bond strength within 20 per cent and exhibits the potential to predict both pull-out and splitting failures. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors address the modelling of the incremental behavior of an idealized granular material and its link with the distribution of contact forces within the representative volume, based on the results obtained from a series of numerical DEM experiments, a discussion of the different operations used in a micro mechanical modelling framework is proposed.
Abstract: This paper addresses the modelling of the incremental behaviour of an idealized granular material and its link with the distribution of contact forces within the representative volume. Based on the results obtained from a series of numerical DEM experiments, a discussion of the different operations used in a micro mechanical modelling framework is proposed. First, the relevance of the usual description of the contact forces distribution through its average value for a given contact orientation is evaluated. Next, this description is implemented in a complete homogenization process. The derived stress–strain relationship acceptably predicts the anisotropic elastic properties of the material provided that the particles do not rotate but fails to if this constraint is removed. Therefore, in the last section, a more refined description of the contact forces distribution is invoked, considering the actual scatter from the average values through the standard deviation. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: In this paper, a flow theory describing the yielding of anisotropic frictional materials is discussed, and conditions at failure are defined by invoking a set of scalar-valued functions representing spatial variation of the basic material parameters.
Abstract: A flow theory describing the yielding of anisotropic frictional materials is discussed. The formulation incorporates directional distribution of voids as a measure of the material microstructure. The conditions at failure are defined by invoking a set of scalar-valued functions representing spatial variation of the basic material parameters. The flow rule is generalized to incorporate the effect of the initial fabric of the material. The formulation is illustrated by some numerical examples demonstrating the directional dependence of the load-deformation characteristics. Copyright © 1999 John Wiley & Sons, Ltd.
TL;DR: A systematic numerical investigation of the efficiency of Newton iterations, that employ the Algorithmic Tangential Stiffness (ATS) tensor, as compared to various approximations, is carried out for a cohesive-frictional model with non-linear isotropic hardening.
Abstract: Algorithmic issues for the two thermodynamically consistent viscoplastic formulations of Perzyna and Duvaut–Lions are discussed. It is shown that it is simple to avoid the numerical problems associated with a small relaxation time without resorting to elaborate perturbation techniques, as suggested in the literature. A systematic numerical investigation of the efficiency of Newton iterations, that employ the Algorithmic Tangential Stiffness (ATS) tensor, as compared to various approximations, is carried out for a cohesive-frictional model with non-linear isotropic hardening. Generally, the ATS-tensor is formulated in such an explicit fashion that its tensorial structure resembles that of the underlying rate-independent continuum stiffness. For both the Perzyna and the Duvaut–Lions format, it appears that the ATS-tensor is obtained by a proper augmentation of the corresponding rate-independent ATS-tensor. (Less)
Journal Article•
TL;DR: In this paper, the authors present a synthesis of a number of axisymmetric compres- sion tests to extract a detailed implementation of the constitutive framework used by Rudnicki and Rice, which is then used to predict the response for plane strain.
Abstract: Shear bands and faults are ubiquitous features of brittle rock deformation at a variety of length scales. Despite the prevalence of these features, understandhg of their inception remains rudimentary. Laboratory experiments suggest a casual association of localization of deformation (faulting) with peak stress, but more detailed examination reveals that localization can precede or follow the peak. Rudnicki and Rice (1975, hereafter abbreviated as RR) have suggested a the- ory of the inception of localization as a bifurcation or nonuniqueness of the so- lution for homogeneous deformation. They predict a strong dependence of local- ization on deformation state. In particular, they predict that localization can occur prepeak for deformation states near deviatoric pure shear and does not occur until well after peak for axisymmetric compression. This prediction is roughly in ac- cord with the true triaxial experiments of Mogi (1967, 1971). More recently, Ord et al. (1991) and Wwersik et al. (1991) have reported observations of localization prior to peak stress in plane strain experiments. The predictions of RR depend strongly on the constitutive properties of the rock and detailed comparison has been impeded by inadequate knowledge of those properties. Even the idealized constitutive model used by RR requires knowledge ofmore » the evolution of the constitutive properties with inelastic deformation that is not readily obtainable from the typical axisymmetric compression test. Although it is conceptually advantageous to consider inelastic deformation at fixed mean stress, the mean stress changes throughout the axisymmetric compression test. In this paper, we present a synthesis of a number of axisymmetric compres- sion tests to extract a detailed implementation of the constitutive framework used by RR. The resulting constitutive relation is then used to -predict the response for plane strain. Conditions for localization of deformation derived by RR are evalu- ated for both plane strain and axisymmetric compression.« less