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American Society for Testing and Materials

羟氨苄青霉素引起大疱性类天疱疮样疹

In comparing a material's resistance to distort under mechanical load rather than to alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by ½ and -1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt.

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Poisson's ratio and modern materials

The size and shape of soil particles reflect the formation history of the grains. In turn, the macroscale behavior of the soil mass results from particle level interactions which are affected by particle shape. Sphericity, roundness, and smoothness characterize different scales associated with particle shape. New experimental data and results from published studies are gathered into two databases to explore the effects of particle shape on packing density and on the small-to-large strain mechanical properties of sandy soils. In agreement with previous studies, these data confirm that increased angularity or eccentricity produces an increase in emax and emin. Furthermore, the data show that increasing particle irregularity causes a decrease in stiffness yet heightened sensitivity to the state of stress; an increase in compressibility under zero-lateral strain loading; an increase in the critical state friction angle cs; and an increase in the intercept of the critical state line there is a weak effect on the slope . Therefore, particle shape emerges as a significant soil index property that needs to be properly characterized and documented, particularly in clean sands and gravels. The systematic assessment of particle shape will lead to a better understanding of sand behavior.

Particle Shape Effects on Packing Density, Stiffness, and Strength: Natural and Crushed Sands

Quasi-static shear deformation of granular media is examined by performing numerical simulations on polydisperse systems of elastic spheres in a periodic cell. Results of axisymmetric compression test simulations are reported for both a dense and a loose system. At the macroscopic scale, the simulated stress–strain–dilation responses are in excellent qualitative agreement with the mechanical behaviour of sand observed in real experiments. Numerical simulation permits a detailed examination of the evolution of internal variables associated with the micromechanical processes occurring at the particle scale. In this context, the evolution of the induced structural anisotropy, the percentage of sliding contacts, the average coordination number and the normal and tangential contact force contributions to the stress tensor are presented and discussed. Further simulations are reported which illustrate the effect of interparticle friction on both the macrocopic and microscopic mechanical behaviour. Finally, the v...

Numerical simulations of deviatoric shear deformation of granular media

Development of induced anisotropy during shear deformation of plane granular assemblies is investigated by introducing statistical characteristics of fabric and contact forces. The introduced microstructural parameters are explicitly related to the measure of deviatoric load by considering conditions of static equilibrium. Verification of the relationship between parameters of anisotropy, average forces and external loads is presented based on numerical simulation of tests on plane granular assemblies. The physical significance of introduced parameters of microstructure and their evolution during shear deformations is discussed.

Analytical study of induced anisotropy in idealized granular materials

The paper presents a micromechanical analysis of plane granular assemblies of discs with a range of diameters, and interacting according to linear contact force-interparticle compliance relationships. Contacts are assumed to be fixed and indestructible. Macroscopically, the system is described in terms of a two-dimensional analogue of generalized Hooke’s law. Explicit expressions for elastic constants in terms of microstructure are derived for dense isotropic assemblies. It is shown that Poisson’s ratio for dense systems depends on the ratio of tangential to normal contact stiffnesses. The derived expression for Poisson’s ratio is verified by numerically simulating plane assemblies comprising 1000 particles. The effect of density on Poisson’s ratio is investigated using numerical simulations. The theory of dense plane systems is extended to dense three-dimensional systems comprising spheres. Finally, it is shown that Poisson’s result ν=1/4 is recovered for spherical particles with central interactions.

Micromechanical Aspects of Isotropic Granular Assemblies With Linear Contact Interactions

This Paper presents the results of numerical simulations of planar assemblies of elliptical particles. Qualitative features of these systems that are similar to real sand behaviour are identified a...

Micromechanical features of granular assemblies with planar elliptical particles

The paper describes a numerical model that was developed to simulate the response of three instrumented, full-scale, geosynthetic-reinforced soil walls under working stress conditions. The walls we...

Development and verification of a numerical model for the analysis of geosynthetic-reinforced soil segmental walls under working stress conditions

The construction and surcharge loading response of four full-scale reinforced-soil segmental retaining walls is simulated using the program FLAC. The numerical model implementation is described and constitutive models for the component materials (i.e., modular block facing units, backfill, and four different reinforcement materials) are presented. The influence of backfill compaction and reinforcement type on end-of-construction and surcharge loading response is investigated. Predicted response features of each test wall are compared against measured boundary loads, wall displacements, and reinforcement strain values. Physical test measurements are unique in the literature because they include a careful estimate of the reliability of measured data. Predictions capture important qualitative features of each of the four walls and in many instances the quantitative predictions are within measurement accuracy. Where predictions are poor, explanations are provided. The comprehensive and high quality physical data reported in this paper and the lessons learned by the writers are of value to researchers engaged in the development of numerical models to extend the limited available database of physical data for reinforced soil wall response.

Richard J. Bathurst

Papers

Analytical study of induced anisotropy in idealized granular materials

Micromechanical Aspects of Isotropic Granular Assemblies With Linear Contact Interactions

Micromechanical features of granular assemblies with planar elliptical particles

Development and verification of a numerical model for the analysis of geosynthetic-reinforced soil segmental walls under working stress conditions

Numerical Model for Reinforced Soil Segmental Walls under Surcharge Loading