FE-studies on the influence of initial void ratio, pressure level and mean grain diameter on shear localization

Abstract

SUMMARYThe paper is concerned with shear localization in the form of a spontaneous shear zone inside a granular material during a plane strain compression test. The in#uence of an initial void ratio, pressure and a mean grain diameter on the thickness of a shear zone is investigated. A plane strain compression test with dry sand is numerically modelled with a "nite element method taking into account a polar hypoplastic constitutive relation which was laid down within a polar (Cosserat) continuum. The relation was obtained through an extension of a non-polar hypoplastic constitutive law according to Gudehus and Bauer by polar quantities: rotations, curvatures, couple stresses and a characteristic length. It can reproduce the essential features of granular bodies during shear localization. The material constants can be easily calibrated. The FEcalculations demonstrate an increase in the thickness of the shear zone with increasing initial void ratio, pressure level and mean grain diameter. Polar e!ects manifested by the appearance of grain rotations and couple stresses are only signi"cant in the shear zone. A comparison between numerical calculations and experimental results shows a satisfying agreement.

Modeling of textural anisotropy in granular materials with stochastic micro-polar hypoplasticity

“…A predominantly quartz sand of medium grain size with the following index properties: e i0 =1.30, e d0 =0.51, One shear zone occurs inside of the specimen which crosses the specimen and whose location is caused by a stochastic distribution of the initial void ratio. The shear zone thickness and its inclination can be determined by using one of the following indicators: shear deformation, void ratio, modulus of deformation and Cosserat rotation (Tejchman et al 1999). The shear zone thickness is insignificantly influenced by the rotation angle θ (it slightly increases with increasing θ).…”

“…The shear resistance decreases with increasing bedding angle, and the shear zone width increases and its inclination υ decreases with increasing bedding angle. The shear zone width is slightly different for each model (for the same angle θ) due to the various rate of softening influencing the shear zone formation (the smaller rate of softening, the wider the shear zone width, Tejchman et al 1999). The difference is about 1-2 mm.…”

Effect of Heterogeneity on Formation of Shear Zones in Granular Bodies

“…The polar hypoplastic constitutive model [4]- [6] can reproduce essential features of granular bodies during shear localization depending on the void ratio, pressure level, direction of the deformation and curvature rate, mean grain diameter and grain roughness. The material parameters can be found by means of standard element tests and simple index tests.…”

“…The FE-calculations were performed with a polar hypoplastic constitutive model [4]- [6]. In this model, a characteristic length is directly related to the mean grain diameter of the granulate.…”

Finite element study of patterns of shear zones in granular bodies during plane strain compression

“…Numerically, shear localization was studied using enhanced continuum models including a characteristic length of micro-structure within elasto-plasticity [6,11,31,48,62,69] and hypoplasticity [28,54,64,67] based on the micro-polar, non-local, gradient and viscous approach. In addition, the so-called strong discontinuity approaches were used to properly capture shear localization which allow a finite element with a displacement discontinuity [43].…”