Framework Of Generalized Plasticity Research Articles

Cyclic response of granular soils evaluated through a strain hardening model incorporated into the generalized plasticity framework

ABSTRACT In this study, constitutive behavior of granular soils is modeled through a generalized plasticity-based theoretical framework. The soil hardening is addressed by a novel relationship proposed to calculate plastic strains and their evolution during loading history. The model is effective in predicting the response and incorporating it into a numerical scheme. Focus is given to stress ratios yielding liquefaction in a few stress cycles. The proposed hardening law is based upon a combined deviatoric-volumetric hardening rule updating the stress-strain relationship and plastic strain vector. Numerous undrained monotonic and cyclic triaxial tests are simulated for verification of the constitutive formulation. Results indicate that the developed model for sand-like cohesionless soils proves to match fairly well with the available experimental data. Plastic strains are calculated accurately and accumulated pore pressures are well captured. Triaxial test simulations exhibit a successfully improved way of capturing the essential static and cyclic behavior of granular soils.

A generalized, computationally versatile plasticity model framework - Part I: Theory and verification focusing on tension‒compression asymmetry

Microstructural characteristics and complex loading conditions in the deformation of metallic materials lead to complexity in mechanical responses. In this study, we propose a generalized constitutive framework that reproduces the plastic anisotropy and asymmetry under various loading conditions. Particularly, the developed model can accurately capture distinctive flow stress, plastic flow and strain hardening between tensile and compressive dominant loadings under a wide range of stress states. The model is based on the stress triaxiality dependence of state variable (or weighting factor) newly incorporated in the existing plasticity theory to keep the computational efficiency and versatility. For example, the new generalized framework can be applied to widely employed Hill48, Yld2k-2d, and Poly6 as a class of associated flow rule-based yield functions, as well as Stoughton-Yoon2009 and Min2016 yield functions for the non-associated flow rule. Also, the model is adaptable when selecting the yield function under tension or compression, which efficiently controls the degree of accuracy in anisotropic modeling under tension and compression. The generalized plasticity framework is validated comprehensively by demonstrating the predictive capability for anisotropy in yield stress and plastic flow of metallic materials with different crystal structures. Moreover, the model can efficiently capture the continuous evolution of asymmetric yield surfaces as functions of strain, temperature, and strain rate. Finally, the identification procedure of the model is discussed by demonstrating the analytical determination of model parameters utilizing the experimental or generic material data obtained from various loading conditions such as tension, compression, plane strain loading, and pure shear.

A Developed Constitutive Model for Sand and Clay under Monotonic and Cyclic Loadings

In this paper, a constitutive model is presented to model the behavior of various soils (sand and clay) in different loading conditions and the minimum required parameters are obtained. Although some practical features (concepts) of the bounding surface framework and modified Cam-Clay have been employed in its formulations, the model is developed mainly based on the generalized plasticity framework. Moreover, some concepts such as dilatancy relation and loading history surface are redefined. Finally, the proposed constitutive model is evaluated using the experimental data related to two different sandy soils and three different clays under different loading conditions. Finally, it is concluded that the proposed constitutive model can easily be calibrated for various clayey and sandy soils. It can depict different behavioral aspects of these soils under different monotonic and cyclic loading conditions.

Meshfree modeling of cyclic behavior of sands within large strain Generalized Plasticity Framework

Abstract In this publication the u - w finite strain formulation is enhanced with a Generalized Plasticity model for sands. The new model is numerically solved using an Optimal Transportation Meshfree approach that is best suited for numerical analysis at finite strains. This new model allows to capture the hydro-mechanical response under large deformations of a saturated sand like soils where acceleration of water with respect the solid skeleton is not negligible. To the authors’ knowledge, no attempt has been previously devoted to include in the u - w finite strain approach an elastoplastic behavior from the Generalized Plasticity theory. In order to assess the validity of the proposed model, four standard laboratory tests are numerically reproduced: i) an undrained triaxial test under monotonic loading, ii) a triaxial consolidation test under monotonic loading with drained boundary conditions, iii) an undrained cyclic triaxial test and iv) a drained cyclic triaxial test. The observed results are qualitatively correct and in agreement with numerical solutions previously obtained by other researchers and with related experimental data.

Modelling the mechanical behaviour of a natural unsaturated pyroclastic soil within Generalized Plasticity framework

The paper deals with the mechanical behaviour of a natural volcanic silty soil sampled from steep slopes. This soil is very loose and unsaturated over most of the year due to climate conditions. Thus so-called wetting collapse and static liquefaction may occur during rainfall. Major issues are posed once the slides turn into flows with high destructive potential. However, the modelling of the constitutive behaviour is challenging and not yet available in the literature for this soil. A recent Generalized Plasticity Model was selected as it is capable to adequately take into account the effects of change in soil porosity, bonding related to the matric suction normalized versus soil porosity, and static liquefaction proneness. The model is calibrated for 37 saturated/unsaturated laboratory tests, and the performance of the model is assessed quantitatively. It is newly shown that the model – with one single set of constitutive parameters – is capable to well describe the soil mechanical response, in unsaturated and saturated conditions, experienced by the soil in different laboratory devices and along different stress paths. Those insights provide a theoretical framework for designing further laboratory tests, improving the understanding of this complex natural soil, and implementing better modelling of landslides of the flow-type.

Discussion of “Associated Generalized Plasticity Framework for Modeling Gravelly Soils Considering Particle Breakage” by Huabei Liu and Degao Zou

Discussion of “Associated Generalized Plasticity Framework for Modeling Gravelly Soils Considering Particle Breakage” by Huabei Liu and Degao Zou

Closure to “Associated Generalized Plasticity Framework for Modeling Gravelly Soils Considering Particle Breakage” by Huabei Liu and Degao Zou

Closure to “Associated Generalized Plasticity Framework for Modeling Gravelly Soils Considering Particle Breakage” by Huabei Liu and Degao Zou

A modelling framework for marine structure foundations with example application to vertical breakwater seaward tilt mechanism under breaking wave loads

A theoretical and numerical framework to model the foundation of marine structures is presented. The theoretical framework includes two main components: (i) a mathematical model to properly represent soil skeleton–pore fluids interaction based on the Generalized Biot formulation, (ii) an advanced constitutive model to reproduce the nonlinear soil behavior based on the Generalized Plasticity framework. Apart from these two main components, suitable boundary conditions are of paramount importance. The proposed theoretical framework includes: (i) hydraulic boundary conditions to simulate the interaction between waves, sea bed and maritime structures, (ii) soil–structure interaction conditions to reproduce accurately the principal loads transmitted to the foundation, and (iii) radiation boundary conditions to make the computational domain finite. The finite element method is adopted in order to achieve accurate and robust approximate solutions of the governing equations. The proposed theoretical and numerical framework is applied to the analysis of the seaward tilt mechanism induced by the action of breaking waves over a vertical breakwater. The results numerically attained are in agreement with the main conclusions drawn from the literature associated with this failure mechanism.

Associated Generalized Plasticity Framework for Modeling Gravelly Soils Considering Particle Breakage

Gravelly soils are used extensively for a wide range of engineering applications. One example is railway ballast, and another is the fill for rock-filled dams. These soils are usually subjected to complicated loading, including high pressure, repeated loading from trains, and earthquake loading. Depending on the natural characteristics of soil particles and the level of external loading, gravelly soils may undergo particle breakage, which modifies the strength and deformation properties of the soils. To better estimate the response of earth structures with gravelly soils, it is necessary to describe particle breakage properly, its relation with external loading, and its effect on soil properties. In this study, a generalized plasticity framework, based on critical-state soil mechanics and following the associated flow rule, was developed based on the unique responses of gravelly soils. Particle breakage and its effects were described by a translating critical-state line that was related to dissipated plastic energy through a hyperbolic function. The responses of six gravelly soils along different stress paths were simulated using the proposed model. It was shown that with 12 parameters, the constitutive model was capable of describing the responses of gravelly soils over a wide range of initial void ratios and initial confining pressures, as well as along different stress paths. The model parameters, most of which have definite physical meanings, can be calibrated through conventional triaxial compression tests. This framework will provide a basis for simulating the cyclic responses of gravelly soils.

A uniaxial model for shape-memory alloys

We present a uniaxial model for shape-memory alloys, cast within the generalized plasticity framework, previously developed. The model is based on two internal variables (the single-variant martensite fraction and the multiple-variant martensite fraction), for which evolution equations in rate form are proposed. The model reproduces the shape-memory effect and the superelastic behavior; moreover, for loading-unloading cycles, without completion of the phase transition, it presents a cyclic response with internal loops.