Diffuse instabilities with transition to localization in loose granular materials

Abstract

International audienceThis paper is concerned with diffuse and other ensuing failure modes in geomaterials when tested under homogeneous states of shearing in various loading programs and drainage conditions. Material instability is indeed the basic property that accounts for the instability of an initially homogeneous deformation field leading to diffuse failure and strain localization in geomaterials. The former is normally characterized by a runaway type of failure accompanied with a sudden and violent collapse of the material in the absence of any localization phenomena. Against this backdrop, we present a brief overview of material instability in elastoplastic solids where one finds a rich source of theoretical concepts including bifurcation, strain localization, diffuse failure and second-order work, as well as a considerable body of experiments. Some compelling laboratory experimental studies of material instability with focus to diffuse failure are then presented and interpreted based on the second-order work. Finally, various material instability analyses using an elastoplastic constitutive and a general finite element analysis of the above-mentioned laboratory experimental tests are presented as a boundary value problem. It is shown that instability can be captured from otherwise uniform stress, density and hydraulic states, whereas uniform deviatoric loads are being applied on the external boundaries of a specimen. Although the numerical simulations reproduce well the laboratory experimental results, they also highlight the hierarchy of failure modes where localization phenomena emerge in the post-bifurcation regime as a result of a degradation of homogeneity starting from a diffuse mode signalled by a zero second-order work

Numerical Simulation of Static Liquefaction of Loose Sand

“…The results indicate that loose sand subjected to fast loading under undrain condition will go through the transition from diffuse instability into shear band instability. Wan et al (2012) draw the same conclusion through numerical simulation of triaxial specimen under undrain condition, which is calculated by using fluid-solid interaction finite element and the loading time is very short. …”

Drained instability analysis of sand under biaxial loading using a 3D material model

“…However, in all the cases localization was the final instability mode. This type of diffused instability modes are different from the diffused failures characterized by a sudden collapse of the material [19,20].…”

Microstructural self-organization in granular materials during failure

“…In some cases, the computed strain field presents a chaotic pattern, with no visible sign of structuring. In other cases, localized deformations develop clearly into a shear band [14,15]. As another goal of this paper, we wish to investigate what are the microstructural ingredients that could explain why the deformation of the material localizes or not.…”