Researches On The Plastic Strain Gradient-Dependent Generalized Plasticity Theory For Geo-Materials' Strain Localization Analysis

In order to explore the strength and deformation mechanism of the geo-materials, some researches on the deformation and failure process in meso-scope must be performed. Many experiments have shown that the strain localization is caused by asymmetrical of the sample in micro-scope occurred during failure. In fact, the purpose to investigate the strain localization is to describe the actual failure process of geo-materials. It is expected that some new revelations will be obtained if the Generalized Plastic Mechanics is combined with strain-gradient theory to establish the Gradient-dependent Generalized Plasticity Mechanics by which the strain localization characteristics and the basic mechanics characteristics of geo-materials can be described at the same time.The progress in this paper can be summarized as:1,Based on the results of macro-experiment and some CT-experiment for geo-materials, A new plasticity gradient volume unit is proposed, which can describle the local deformation. The startup mechanism of strain localization is analysised: when the hardening Modulus (or sofftting Modulus) change from positive to negative, the deformation pattern will change from uniformity pattern to localization pattern.2,Based on the theoretical frame of the Generalized Plastic Mechanics and the plastic strain gradient-dependent in the double yield functions, the differential expressions of plastical strains are constructed, then the frame of the Generalized Gradient-dependent Plastic Mechanics is established sequentially to describe the strain localization characteristics andthe basic mechanics characteristics of geo-materials. The model parameters, especially the parameters reflecting localization are also discussed and determined.3,Both the displacement and the plastic factor are discretized by interpolation function with C 1 continuity in space. A set of non-linear equations taking the displacements and the plastic factors of nodes as the unknown variables are obtained to solve the new proposed mechanic model, the border condition and the increment algorithm are also gived in this paper.4,A Fortran90 code with Post-processr in Visual Basic for the numerical modeling is given, after that, some numerical examples are implemented and the results demonstrate the development of plastic strain as well as the failure process with a localized strain in a narrow band, which reveal the failure mechanism of the samples in micro-scope.