scholarly journals A Framework for Versatile Shape of Yield Surfaces for Structured Aniso-tropic Soft Soils

2016 ◽  
Author(s):  
Nallathamby Sivasithamparam ◽  
Jorge Castro
Keyword(s):  
Yield Surface ◽  
Earth Pressure ◽  
Type Model ◽  
Flow Rule ◽  
Lateral Movement ◽  
Plastic Potential ◽  
Yield Surfaces ◽  
Anisotropic Clays ◽  
Associated Flow Rule ◽  
Cam Clay

A framework based on logarithmic contractancy is proposed to produce versatile shapes of yield surfaces for structured anisotropic clays. The recently proposed constitutive model (E-SCLAY1S) is an extension of existing model called S-CLAY1S, which is a Cam Clay type model that accounts for anisotropy and structure. A new parameter called contractancy parameter is introduced to control the shape of the yield surface as well as the plastic potential (as an associated flow rule is applied). This new parameter can be used to fit the coefficient of earth pressure at rest, the undrained shear strength or the stiffness under shearing stress paths predicted by the model. The model predicts the uniqueness of the critical state line and its slope is independent of the contractancy parameter. The effect of the shape of the yield surface was investigated on computed results of a benchmark embankment constructed on Bothkennar (Scotland) clay by employing the E-SCLAY1S model as a user-defined soil model into the PLAXIS finite element code. The results demonstrate that the contribution of the shape of yield surface (logarithmic contractancy parameter) have a relatively large effect on lateral movement of subsoil beneath the toe of the embankment compared to the settlement of subsoil at the centre of the embankment.

scholarly journals Plastic Dissipation of the Fractional Plasticity using Modified Cam-Clay Yielding Function

2020 ◽  
Vol 36 (3) ◽  
pp. N1-N7
Author(s):  
P. Tai ◽  
Y. Sun
Keyword(s):  
Flow Rule ◽  
State Dependent ◽  
Plastic Dissipation ◽  
Modified Cam Clay ◽  
Plastic Potential ◽  
Classical Plasticity ◽  
Material State ◽  
Associated Flow Rule ◽  
Fractional Plasticity ◽  
Cam Clay

ABSTRACTSoils usually exhibit state-dependent frictional behaviour that undergoes plastic volumetric deformation. To correctly capture such response under the framework of classical plasticity, a non-associated flow rule using additional plastic potential is inevitably needed. Recently, a novel fractional plasticity (FP) without using plastic potential has been developed, and successfully applied in modelling the state-dependent nonassociated behaviour of soils. However, the energy dissipation characteristics of FP has not been probed in depth. This note examines the plastic dissipation behaviour of FP, when modelling the constitutive behaviour of soils. It is found that the plastic dissipation of FP increases continuously with the shear strain. However, the rate of plastic dissipation depends on the initial material state in relation to the critical state line.

A Simple Constitutive Model for Overconsolidated Clays

2011 ◽  
Vol 243-249 ◽  
pp. 2283-2286
Author(s):  
Yang Liu ◽  
Xian De Zhu ◽  
Zhi Gong
Keyword(s):  
Constitutive Model ◽  
Soil Mechanics ◽  
Flow Rule ◽  
Hardening Law ◽  
Proposed Model ◽  
Overconsolidated Clays ◽  
Strain Relationship ◽  
As Stress ◽  
Associated Flow Rule ◽  
Cam Clay

In the framework of critical state soil mechanics, a simple constitutive model for overconsolidated clays is proposed based on subloading surface and normal consolidation yield surface. A more rational hardening law is used to describe the change between subloading surface and the normal consolidation surface with plastic deformation and an associated flow rule is adopted. The model can describe many characteristics of overcaonsolidated clays, such as stress-strain relationship, strain hardening and softening, and stress dilatancy. Compared with the Cam-clay model, two more parameters are required which represents specific physical meanings. Numerical simulation is compared with data from triaxial drained compression test, indicating that the proposed model can rationally describe overconsolidated properties.

scholarly journals Simulation of the micro Single Point Incremental forming process of very thin sheets

2021 ◽  
Author(s):  
Stéphanie Thuillet ◽  
Pierre-Yves Manach ◽  
Fabrice Richard ◽  
Sébastien Thibaud
Keyword(s):  
Incremental Forming ◽  
Single Point ◽  
Small Diameter ◽  
Flow Rule ◽  
Single Point Incremental Forming ◽  
Shear Tests ◽  
Forming Process ◽  
Punch Force ◽  
Plastic Potential ◽  
Associated Flow Rule

The purpose of this paper is to simulate a complex forming process with parameters identified from tensile and shear tests. An elastic-plastic model is retained which combines a Hill’s 1948 anisotropic criterion and plastic potential using a non-associated flow rule. Firstly, a mechanical characterization is made with homogenous tests like tensile and shear tests [1]. On the other hand a process of micro Single Point Incremental forming is simulated [2]. It consists in deforming a clamped blank using a hemispherical punch which has a small diameter compared to the blank dimensions. From a small-size sheet of 0.2 mm thick, a square-based pyramid is obtained incrementally, with a define height path and advanced speed, by a tool instrumented to measure the forming force, which deforms locally the material. It is shown that the non-associated flow plasticity model leads to a good agreement between experimental and numerical results for the evolution of the punch force during the process.

Application of Associated and Non-Associated Flow Metal Plasticity for F.S.S Sheet

2021 ◽  
Vol 406 ◽  
pp. 473-480
Author(s):  
Oualid Chahaoui ◽  
Houssem Soltani ◽  
Nadjoua Matougui
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Mechanical Anisotropy ◽  
Flow Rule ◽  
Plastic Behavior ◽  
Sheet Plane ◽  
Yield Criteria ◽  
Plastic Potential ◽  
Associated Flow Rule

In the last decade, several phenomenological yield criteria for anisotropic material has been proposed to improve the modeling predictions about sheet metal-forming processes. In regard to this engineering application, two proprieties of models have been used. If the yield function and the plastic potential are not same (not equal), the normality rule is non associative flow rule (NAFR), otherwise, when the stresses yield has been completely coupled to the anisotropic strain rate ratio (plastic potential), is called the associated flow rule (AFR). The non-associated flow rule is largely adopted to predict a plastic behavior for metal forming, accurately about à strong mechanical anisotropy presents in sheet metal forming processes. However, various studies described the limits of the AFR concept in dealing with highly anisotropic materials. In this study, the quadratic Hill1948 yield criteria is considered to predict mechanical behavior under AFR and NAFR approach. Experiment and modeling predictions behaviour of normalized anisotropic coefficient r (θ) and σ (θ) evolved with θ in sheet plane. and the equibiaxial yield stress σb was assumed σb=1 but the rb-values was computed from Yld96 [15].

scholarly journals An Evolutionary Yield Function Model Based on Plastic Work and Non-Associated Flow Rule

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 611 ◽  
Author(s):  
Taejoon Park ◽  
Fadi Abu-Farha ◽  
Farhang Pourboghrat
Keyword(s):  
Yield Stress ◽  
Stress Function ◽  
Biaxial Tension ◽  
Yield Function ◽  
Plastic Work ◽  
Constitutive Law ◽  
Flow Rule ◽  
Tension Tests ◽  
Plastic Potential ◽  
Associated Flow Rule

A constitutive law was developed based on the evolutionary yield function to account for the evolution of anisotropy induced by the plastic deformation. For the effective description of anisotropy, the yield stress function and plastic potential were separately defined based on the non-associated flow rule. In particular, for the description of the equivalent status, the accumulated plastic work was employed as an alternative to the accumulated plastic strain. Numerical formulations based on the plastic work were also derived in case the hardening rule, as well as the evolution of the plastic potential and yield stress function, were defined in terms of the plastic work. The developed constitutive law was characterized using the mechanical properties of the multi-phase BAO QP980 steel and niobium sheets at room temperature. From the uniaxial tension tests and the balanced biaxial tension test, separate sets of anisotropic coefficients for each of the plastic potential and yield stress functions were obtained as a function of the plastic work. By comparing with non-evolving yield functions, the importance of the developed constitutive law to properly describe the evolution of the plastic potential and yield function were validated.

Failure Surface and Plastic Potential in Deviatoric Plane of Bangkok Clay

2012 ◽  
Vol 256-259 ◽  
pp. 256-260
Author(s):  
Wanwarang Ratananikom ◽  
Siam Yimsiri ◽  
Fumihiko Fukuda ◽  
Suched Likitlersuang
Keyword(s):  
Principal Stress ◽  
Constitutive Modeling ◽  
Failure Surface ◽  
Intermediate Principal Stress ◽  
Triaxial Tests ◽  
Flow Rule ◽  
Plastic Potential ◽  
Stress Directions ◽  
Deviatoric Plane ◽  
Associated Flow Rule

This paper presents an experimental investigation on the failure surface and plastic potential in deviatoric plane of Bangkok Clay. The results of torsional shear hollow cylinder and triaxial tests with various principal stress directions and magnitudes of intermediate principal stress on undisturbed Bangkok Clay specimens are presented. The obtained stress-strain behaviors assert clear evidences of anisotropic characteristics of Bangkok Clay. Both failure surface and plastic potential in deviatoric plane of Bangkok Clay are demonstrated as isotropic and of circular shape (Drucker-Prager type) which implies an associated flow rule. Concerning the behavior of Bangkok Clay found from this study, the discussions on the effects of employed constitutive modeling approach on the resulting numerical analysis are made.

scholarly journals Plasticity and non-Schmid effects

2014 ◽  
Vol 470 (2161) ◽  
pp. 20130440 ◽  
Author(s):  
Stefan C. Soare
Keyword(s):  
Plastic Deformation ◽  
Yield Surface ◽  
Stress Gradient ◽  
Flow Rule ◽  
Slip Systems ◽  
Metal Plasticity ◽  
Overall Response ◽  
Associated Flow Rule

The structure of the overall response of a metal polycrystal is analysed under the assumption that activity on the slip systems of its constituents is governed by a generalized Schmid law. In the resulting macromodel of metal plasticity, the overall rate of plastic deformation is related to the stress gradient of the yield surface via a generalized, but still associated, flow rule. While the overall rate of plastic deformation is no longer collinear with the stress gradient of the yield surface, its deviation is characterized by an additional macrovariable, representative of the rate of the non-Schmid effects taking place at constituent level.

scholarly journals Significance of flow rule for the passive earth pressure problem

2021 ◽  
Author(s):  
Christoph Schmüdderich ◽  
Franz Tschuchnigg ◽  
Helmut F. Schweiger
Keyword(s):  
Finite Element ◽  
Earth Pressure ◽  
Flow Rule ◽  
Passive Earth Pressure ◽  
Element Analysis ◽  
Pressure Coefficients ◽  
Earth Pressures ◽  
Numerical Instabilities ◽  
Associated Flow Rule

AbstractDetermination of earth pressures is one of the fundamental tasks in geotechnical engineering. Although many different methods have been utilized to present passive earth pressure coefficients, the influence of non-associated plasticity on the passive earth pressure problem has not been discussed intensively. In this study, finite-element limit analysis and displacement finite-element analysis are applied for frictional materials. Results are compared with selected data from literature in terms of passive earth pressure coefficients, shape of failure mechanism and robustness of the numerical simulation. The results of this study show that passive earth pressure coefficients determined with an associated flow rule are comparable to the Sokolovski solution. However, comparison with a non-associated flow rule reveals that passive earth pressure coefficients are significantly over predicted when following an associated flow rule. Moreover, this study reveals that computational costs for determination of passive earth pressure are considerably larger following a non-associated flow rule. Additionally, the study shows that numerical instabilities arise and failure surfaces become non-unique. It is shown that this problem may be overcome by applying the approach suggested by Davis (Soil Mech 341–354, 1968).

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