Experimental and numerical study of sand–steel interfaces

Abstract

SUMMARYExperimental and numerical studies on and sand-steel interfaces are presented. Emphasis is laid on the effect of boundary conditions of the whole system and of localized deformation. The experiments with different roughness of steel surface, sand density, normal stress and grain size are carried out in a plane strain apparatus, a parallely guided direct shear apparatus and in a planar silo model with a movable bottom and parallel steel walls. During the test in the plane strain apparatus the localized zone is observed with the help of X-rays. The results indicate a significant effect of wall roughness and boundary conditions of the whole system on the wall friction angle and the thickness of the localized zone along the steel surface, An elastoplastic constitutive model established within the framework of a Cosserat continuum, capable of describing isotropic hardening, softening and dilatancy, is implemented in a finite element code. The model differs from the conventional theory of plasticity due to the presence of Cosserat rotation and couple stress using the mean grain diameter as the characteristic length. Finite element simulations of simple shear tests are presented. The additional boundary condition along the steel plate, characteristic of the Cosserat continuum, allows for modelling the different roughness of the steel plate with consideration of grain rotations. A comparison between the numerical calculations and the experimental results shows acceptable agreement.

Non‐coaxiality and stress–dilatancy rule in granular materials: FE investigation within micro‐polar hypoplasticity

“…It can vary from about 1.0 at the point of bifurcation to about 0.5 ( = 30 • ) at the residual state [33]. According to Equation (9), the dilatancy angle is first negative (material undergoes contractancy), then the material is subjected to a significant dilatancy which is the highest at the peak friction angle. Next, the dilatancy angle diminishes down to zero in the course of shearing reaching a critical (residual) state.…”

“…Thus, it is of primary importance to take it into account while modeling the behaviour of granulates. Localization under shear occurs either in the interior domain in the form of spontaneous shear zones [1,7] or at interfaces in the form of induced shear zones where structural members are interacting and stresses are transferred from one member to the other [8,9]. The localized shear zones inside the granular material are closely related to its unstable behaviour since they act as a precursor to the ultimate failure.…”

Shearing of a narrow granular layer with polar quantities

“…The behaviour of granular bodies along a wall with di!erent roughness was experimentally studied with a Casagrande shear apparatus [17}19], with an improved direct shear device [1,2], with a torsional ring shear apparatus [20}22], with a ring shear device [23], with a simple shear device by Roscoe [24], with a biaxial apparatus [1,25], with a Couette apparatus [22], with model silo tests [1,26] and with pull-out tests [10].…”

FE-studies on rapid flow of bulk solids in silos

“…They were assumed on the basis of biaxial compression tests [46]. The capability of an elasto-plastic Cosserat model in solving various boundary value problems involving localisation was demonstrated by Tejchman [1], [5], Mühlhaus [34][35][36], de Borst [47], Papanastasiou and Vardoulakis [48], Sluys [38], Tejchman and Wu [40], [49], [50], Tejchman and Gudehus [4], Unterreiner et al [51], Steinmann [52], Murakami and Yoshida [37] and Groen [53]. A satisfactory agreement between theoretical and experimental results was achieved.…”