Mechanics of Cohesive-frictional Materials最新文献

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.

Many geotechnical problems are conditioned by the coupling effects between the solid matrix and fluid transport, in particular in unsaturated zones: construction of embankments, cyclic loading of road foundations, environmental engineering, etc. An understanding of the behaviour of saturated/unsaturated soils is therefore important for the design and analysis of those geostructures. In this paper, the Svendsen–Hutter thermodynamic theory of a mixture of isotropic visco-elastic materials is summarized and applied to the formulation of field equations for saturated/unsaturated, compressible/incompressible soils. Emphasis is on the presentation of differences in the formulation, the roles of thermodynamics and configurational as well as saturation pressures. The theory is illustrated by studying (1) viscous mixtures (saturated binary/ternary mixtures and unsaturated binary mixtures) and (2) the statics of elastic soils. Several variants of this modern thermodynamic theory are presented. We establish a thermodynamic basis for well-known concepts of effective stress in saturated and unsaturated soils. Copyright © 1999 John Wiley & Sons, Ltd.

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.

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.

A constitutive model is proposed for the cold compaction of metal powders. It relies on classical concepts for elasto-plastic materials. For cemented carbides, which is the current application of the model, it is shown by experimental data that there develops significant anisotropy during a non-isostatic compaction. The model encompasses anisotropy through a kinematic hardening mechanism. For a certain state of hardening the back stress magnitude depends on the mean stress, such that there is a rotation (around the origin) of the yield surface. The need for a two-dimensional hardening parameter set, the relative density and a measure of the intensity of the anisotropy, is demonstrated. A compactness tensor P that holds the current relative density as det(P) and the directionality of the compaction history is conceived. The flow direction is derivable from a non-associated flow potential, but is more easily represented as the ratio of magnitude of deviatoric plastic increment to magnitude of volumetric plastic increment. The basic assumption of a flow potential is needed only to establish the form of the deviatoric flow component. Various functions of the model are mapped by series expansions from irregularly spaced experimental data in the sense of least-square fits. Copyright © 1999 John Wiley & Sons, Ltd.