Mechanics of Cohesive-frictional Materials最新文献

The factors affecting the onset of unstable behaviour in saturated loose sand loaded under drained stress-controlled conditions are not as well known as those involved in its undrained behaviour, which has been analysed in detail.

This paper is intended as a first step towards a better understanding of the onset of instability in drained stress-controlled tests and reports on the analysis of certain factors affecting the unstable behaviour of saturated loose sand samples subjected to drained stress-controlled triaxial compression tests. The samples are loaded continuously at a constant loading rate and the results are compared with those obtained by other authors who discontinuously applied a load using finite increments.

A special experimental apparatus was designed so that the axial load could be applied in various proportions by a dead weight and by a pneumatic cylinder in a triaxial cell with no friction on the loading ram.

The paper focuses first on the influence of the load application method (i.e. by dead weights and by a pneumatic cylinder), which proves important, since the sample always collapses at a more or less constantly low mobilized friction angle when loaded with dead loads, whereas it may have unstable strain jumps starting from a high value of the mobilised friction angle, but may even be stable up to the steady state of deformation, when the axial load is applied by a pneumatic cylinder.

Then the influence of the loading rate and loading path is examined and found to be negligible, at least in a first approximation. On the other hand, the effects of preshear and initial density are shown to have a major role in the onset of collapse: both the preshear and the increase in density lead to an increase in the resistance of the loose sand to collapse under drained stress-controlled conditions. Copyright © 2000 John Wiley & Sons, Ltd.

This paper is concerned with the theoretical analysis of a stationary shock in cohesive-frictional plastic materials. The shock is defined as a thin layer of localized deformation through which material particles travel during plastic flow, as opposed to a shear band where material particles neither enter nor leave the layer. Mathematically, the shock is regarded as a strong discontinuity in velocity and density. Shocks may occur in cohesive-frictional materials in the problem of indentation of soils and rocks, flow of granular materials in bins and hoppers, rock cutting, etc. In the paper we formulate equations on the stationary shock in rigid-plastic materials with or without hardening or softening. The analysis incorporates the effect of inertia of material crossing the shock. The solution and the necessary condition for the existence of a shock are studied under the assumption that the same flow rule is valid for the material within and the material outside the shock. Three regimes of solution are identified, depending on the ratio of specific kinetic energy and cohesion. Using particular forms of constitutive equations it is demonstrated that a stationary shock cannot exist without some hardening of the material. An example of application of the theoretical framework developed to the problem of wedge indentation is considered for one type of material behavior. Copyright © 2000 John Wiley & Son, Ltd.

The aim of the paper is to present a study of strain localization in Fontainebleau sandstone. To detect strain inhomogeneity, comparisons between measurements of strain and displacement at multiple locations have been done. A first series of tests have been performed on cylindrical samples. However, the results obtained show that the procedure followed is not systematically efficient. Thus, it was decided to use prismatic samples. In order to control the initiation of strain localization and follow the shear banding up to the macroscopic failure, a last series of tests were performed on prismatic specimens containing a small hole. The shear band characteristics (onset, orientation, width) are given for all these tests on prismatic specimens. Their variation with confining pressure is emphasized. Finally, some details on the deformation mechanisms inside the bands are provided by means of visual observations. Copyright © 2000 John Wiley & Sons, Ltd.

This paper analyses the link between local kinematics and strain tensor defined at a macroscale. The aim of the first part is to analyse the local kinematics variables obtained in a numerical simulation using the DEM. The second part is focused on the analysis of two different approaches to define the strain tensor from local variables. The first approach which only considers relative displacements at the contacts is well known. It is shown that this approach is not usually valid. The second approach is based on the Delaunay triangulation. A decomposition of the local strain is then proposed and it allows the influence of the different mechanisms of the local kinematics (kinematics at contact and displacement of neighbouring particles) to be demonstrated. Copyright © 2000 John Wiley & Sons, Ltd.

Using an asymptotic homogenization method, the effect of the porous medium microstructure on the values of poroelastic coefficients is studied in this paper. First, the Biot’s poroelasticity theory and general relations linking the macroscopic poroelastic coefficients with the averaged micromechanical solutions are recalled. Considering a variational formulation of appropriate boundary values problems stated for the representative volume element, microstructural parameters affecting the values of poroelastic coefficients are identified. In order to clarify specific roles of some relevant microstructure parameters, numerical investigations for some simplified pores geometries are presented. The numerical results obtained clearly show a strong dependence of the poroelastic coefficients on the internal geometry of pores as well as on the global porosity of the medium. In the last part, based on the micromechanics analysis, the definition of initial plastic yield condition for saturated porous media is introduced and a new interpretation of the effective stress concept in inelastic domain is proposed. Copyright © 2000 John Wiley & Sons, Ltd.

Conditions for a consistent description of stationary states within the framework of a certain class of hypoplastic constitutive models are presented. The constitutive equation is of the rate type and incrementally non-linear. Casagrande's critical state concept is embedded in the model, which is also apt to describe contractant and dilatant behaviour. The adaptation of various predefined limit conditions with smooth and conical critical stress surfaces is outlined in detail. For large deformations with rotations of the principal axes, the objective stress rate given by Green and Naghdi is proposed instead of the objective stress rate given by Zaremba and Jaumann. Finally, the response of the constitutive equation for large shearing is compared with experimental results. Copyright © 2000 John Wiley & Sons, Ltd.