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damage model  damage  john wiley  john  materials  mechanics  model  paper  sintering  states  strain  stress  unstable  wiley sons  wiley 
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Preview: Mechanics of Cohesive-frictional Materials

Mechanics of Cohesive-frictional Materials



Wiley Online Library : Mechanics of Cohesive-frictional Materials



Published: 2000-11-01T00:00:00-05:00

 



Damage model for concrete-like materials coupling cracking and friction, contribution towards structural damping: first uniaxial applications

2000-11-13T00:00:00-05:00

This paper is concerned with the development of a damage model for concrete materials exhibiting a residual hysteretic behaviour at a fixed level of damage. This feature is obtained by coupling damage mechanics and friction phenomena. In its complete form, the damage variable by means of which the stiffness decrease is obtained in an orthotropic second-order tensor. Its evolution is governed by the tensile part of the strain tensor. The sliding between the crack lips is assumed to have a plasticity-like behaviour with non-linear kinematic hardening. The sliding stress depends on the level of damage. Such a model assumes the evolution of two yield surfaces: a fracture one and a sliding one. If unilateral effects need to be taken into account for cyclic loading analysis (crack closure modelling), the damage evolution remains isotropic. The effectiveness of this model in reproducing a part of damping when subjected to dynamic loading is exemplified through two structural case studies. Copyright © 2000 John Wiley & Sons, Ltd.



Instabilities in granular materials and application to landslides

2000-11-13T00:00:00-05:00

Landslides or questions related to slope stability are usually considered in the framework of plastic limit analyses. Recent progress has made it possible to describe some failure modes in the framework of the theories of bifurcation of the strain mode by plastic strain localization and the shear-banding phenomenon. We propose in this paper to reconsider the question of landslide analysis by taking into account an appropriate instability criterion. As soils are strongly non-associated materials, unstable states can be reached strictly inside the plastic limit condition (which defines the set of admissible stresses). In the first part of this paper, we describe the constitutive model. Then Lyapunov's definition of stability allows us to detect unstable stress–strain states from experimental evidence. These unstable states are analysed by considering the sign of the second-order work. The stability analysis, performed for loose and dense sands under plane strain conditions, shows a large domain of instabilities in the stress space. This method is applied to some boundary-value problems by finite elements computations. It is shown finally by examples that such unstable stress–strain states are observed in our FEM modelling of slope problems. Copyright © 2000 John Wiley & Sons, Ltd.



Modelling of solid-phase sintering of hardmetal using a mesomechanics approach

2000-11-13T00:00:00-05:00

The mesomechanics approach presented in this paper aims at enhancing the understanding of, as well as providing a predicting capability for, the densification process in cemented carbides due to solid-phase sintering. The major mesostructural constituents are tungsten carbide (WC) particles and large pores, which are embedded in a contiguous cobolt (Co) matrix. A preprocessor code, which is based on Voronoi polygonization, was developed to generate the morphology with prescribed area fraction and size distribution of the constituents. In a continuum model, the ‘driving force’ that brings about the densification is the sintering stress, which is given a rational thermodynamic definition in the paper. This stress represents the boundary loading of a representative volume element (RVE) at free sintering, i.e. in the absence of macroscopic stresses. In such a volume element (or unit cell) the constituents WC and Co are assumed as viscoplastic non-porous solids. A generalized Bingham model (of Norton-type with hardening) seems to be sufficient to represent the creep properties, which are assumed to be of dislocation as well as of diffusion type. The temperature dependence of certain material parameters is discussed. Thermal expansion is accounted for. The developed algorithm was implemented in the commercial FE-code ABAQUS. Finally, the simulation results are compared with experimental results from the sintering of free as well as uniaxially loaded specimens. Copyright © 2000 John Wiley & Sons, Ltd.