A combined hardening model of anisotropically consolidated cohesive soils

1991 ◽  
Vol 28 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Hiroyoshi Hirai ◽  
Takeshi Kamei
Keyword(s):  
Yield Surface ◽  
Kinematic Hardening ◽  
Strain Curve ◽  
Cohesive Soil ◽  
Stress Path ◽  
Yield Function ◽  
Triaxial Tests ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Cohesive Soils

A model introduced in the present paper is capable of describing the mechanical behaviour of anisotropically consolidated cohesive soils reasonably well. The salient features of the proposed model are summarized as follows: (i) generalized forms of the Cambridge models are given to both yield function and plastic potential; (ii) a combination of isotropic and kinematic hardening is used; (iii) a nonassociated-flow rule is proposed; (iv) the isotropic hardening involves plastic work not only related to volumetric change but also to deviatoric deformation; (v) the translation of the yield surface is specified by extending Ziegler's rule of kinematic hardening; (vi) the constitutive model has versatility and flexibility to describe expansion, translation, and rotation of a yield surface in stress space. Several undrained triaxial tests of anisotropically consolidated cohesive soils are simulated, and good agreement is observed between simulation and experimental data. Key words: anisotropy, dilatancy, cohesive soil, consolidated undrained shear, constitutive equation, stress-strain curve, pore pressure - strain curve, effective-stress path.

Stress update algorithm for non-associated flow metal plasticity

2012 ◽  
Vol 3 (2) ◽  
pp. 106-110
Author(s):  
Mohsen Safaei ◽  
Wim De Waele
Keyword(s):  
Plastic Strain ◽  
Yield Stress ◽  
Kinematic Hardening ◽  
Quadratic Function ◽  
Yield Function ◽  
Plastic Strain Rate ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Strain Rate Tensor ◽  
Incremental Change

. In this paper we present the continuum plasticity model based on non-Associated Flow Rule (nonAFR) for Hill’s48 quadratic yield function. In case of non-AFR, Hill’s quadratic function used as plasticpotential function, makes use of plastic strain ratios to determine the direction of effective plastic strain rate.In addition, the yield function uses direction dependent yield stress data. Therefore more accuratepredictions are expected in terms of both yield stress and strain ratios at different orientations. Weimplemented a modified version of the non-associative flow rule originally developed by Stoughton [1] intothe commercial finite element code ABAQUS by means of a user material subroutine UMAT. The mainalgorithm developed includes combined effects of isotropic and kinematic hardening [2]. This paper assumesproportional loading cases and therefore only isotropic hardening effect is considered. In our model theincremental change of plastic strain rate tensor is not equal to the incremental change of the compliancefactor. The validity of the model is demonstrated by comparing stresses and strain ratios obtained from finiteelement simulations with experimentally determined values for deep drawing steel DC06. A criticalcomparison is made between numerical results obtained from AFR and non-AFR based models.

An Application of Incremental Plasticity Theory to Fatigue Life Prediction of Steels

1991 ◽  
Vol 113 (4) ◽  
pp. 404-410 ◽  
Author(s):  
W. R. Chen ◽  
L. M. Keer
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Kinematic Hardening ◽  
Yield Condition ◽  
Strain Curve ◽  
Fatigue Life Prediction ◽  
304 Stainless Steel ◽  
Flow Rule ◽  
Stress Strain ◽  
Von Mises

An incremental plasticity model is proposed based on the von-Mises yield condition, associated flow rule, and nonlinear kinematic hardening rule. In the present model, fatigue life prediction requires only the uniaxial cycle stress-strain curve and the uniaxial fatigue test results on smooth specimens. Experimental data of 304 stainless steel and 1045 carbon steel were used to validate this analytical model. It is shown that a reasonable description of steady-state hysteresis stress-strain loops and prediction of fatigue lives under various combined axial-torsional loadings are given by this model

Numerical Evaluation of Crashworthiness of Automotive Sheets

2007 ◽  
Vol 345-346 ◽  
pp. 1537-1540
Author(s):  
Han Sun Ryou ◽  
Myoung Gyu Lee ◽  
Chong Min Kim ◽  
Kwan Soo Chung
Keyword(s):  
Crystal Structures ◽  
Yield Surface ◽  
Numerical Evaluation ◽  
Kinematic Hardening ◽  
Sheet Thickness ◽  
Back Stress ◽  
Yield Function ◽  
Chaboche Model ◽  
Simulation Results ◽  
Function Shape

Crash simulations were performed for automotive sheets. To understand the influence of crystal structures in sheet materials on crashworthiness, the effect of the yield function shape was studied by adopting the recently developed non-quadratic anisotropic yield surface, Yld2004-18p. The effect of the back-stress was also investigated by comparing simulation results obtained for the isotropic, kinematic and combined isotropic-kinematic hardening laws based on the modified Chaboche model. In addition, the effects of anisotropy and sheet thickness on crashworthiness were evaluated.

Significance of Lu¨der’s Plateau on Pipeline Fault Crossing Assessment

2010 ◽  
Author(s):  
Lanre Odina ◽  
Robert J. Conder
Keyword(s):  
Finite Element ◽  
Compressive Strain ◽  
Strain Curve ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Pipe Material ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Integrity Assessment ◽  
Analytical Approaches

When subjected to permanent ground deformations, buried pipelines may fail by local buckling (wrinkling under compression) or by tensile rupture. The initial assessment of the effects of predicted seismic fault movements on the buried pipeline is performed using analytical approaches by Newmark-Hall and Kennedy et al, which is restricted to cases when the pipeline is put into tension. Further analysis is then undertaken using finite element methods to assess the elasto-plastic response of the pipeline response to the fault movements, particularly the compressive strain limits. The finite element model is set up to account for the geometric and material non-linear parameters. The pipe material behaviour is generally assumed to have a smooth strain hardening (roundhouse) post-yield behaviour and defined using the Ramberg-Osgood stressstrain curve definition with the plasticity modelled using incremental theory with a von Mises yield surface, associated flow rule and isotropic hardening. However, material tests on seamless pipes (X-grade) show that the stress-strain curve typically displays a Lu¨der’s plateau behaviour (yield point elongation) in the post-yield state. The Lu¨der’s plateau curve is considered conservative for pipeline design and could have a significant impact on strain-based integrity assessment. This paper compares the pipeline response from a roundhouse stress-strain curve with that obtained from a pipe material exhibiting Lu¨der’s plateau behaviour and also examines the implications of a Lu¨der’s plateau for pipeline structural integrity assessments.

A Generalized Anisotropic Hardening Rule Based on the Mroz Multi-Yield-Surface Model

2008 ◽  
Author(s):  
K. S. Choi ◽  
J. Pan
Keyword(s):  
Cyclic Loading ◽  
Yield Surface ◽  
Kinematic Hardening ◽  
Constitutive Relations ◽  
Yield Function ◽  
Surface Model ◽  
Loading Conditions ◽  
Anisotropic Hardening ◽  
Hardening Rule ◽  
Strain Data

In this paper, a generalized anisotropic hardening rule based on the Mroz multi-yield-surface model is derived. The evolution equation for the active yield surface is obtained by considering the continuous expansion of the active yield surface during the unloading/reloading process. The incremental constitutive relation based on the associated flow rule is then derived for a general yield function. As a special case, detailed incremental constitutive relations are derived for the Mises yield function. The closed-form solutions for one-dimensional stress-plastic strain curves are also derived and plotted for the Mises materials under cyclic loading conditions. The stress-plastic strain curves show closed hysteresis loops under uniaxial cyclic loading conditions and the Masing hypothesis is applicable. A user material subroutine based on the Mises yield function, the anisotropic hardening rule and the constitutive relations was then written and implemented into ABAQUS. Computations were conducted for a simple plane strain finite element model under uniaxial monotonic and cyclic loading conditions based on the anisotropic hardening rule and the isotropic and nonlinear kinematic hardening rules of ABAQUS. The results indicate that the plastic response of the material follows the intended input stress-strain data for the anisotropic hardening rule whereas the plastic response depends upon the input strain ranges of the stress-strain data for the nonlinear kinematic hardening rule.

scholarly journals Non-orthogonal elastoplastic constitutive model with the critical state for clay

2021 ◽  
Author(s):  
Jingyu Liang ◽  
Dechun Lu ◽  
Xin Zhou ◽  
Xiuli Du ◽  
Wei Wu
Keyword(s):  
Plastic Flow ◽  
Critical State ◽  
Flow Direction ◽  
Volumetric Strain ◽  
Yield Function ◽  
Triaxial Tests ◽  
Flow Rule ◽  
Model Framework ◽  
Plastic Strain Increment ◽  
Plastic Flow Rule

A non-orthogonal elastoplastic model for clay is proposed by combining the non-orthogonal plastic flow rule with the critical state concept, and the model framework is presented from the perspective of the magnitude and direction of the plastic strain increment. The magnitude is obtained based on the improved elliptical yield function and the plastic volumetric strain dependent hardening parameter. The direction is determined by ap-plying the non-orthogonal plastic flow rule with the Riemann-Liouville fractional derivative to the yield function without the necessity of additional plastic potential function. The presented approach gives rise to a simple model for soil with five parameters. All parameters have clear physical meaning and can be easily identified by triaxial tests. The model performance is shown by analyzing the evolution process of the yield surface, the hardening rule and the plastic flow direction. The capability of the proposed model to capture the mechanical behaviours of clay with different stiffness is also confirmed by predicting test results from the literature.

UNDRAINED SHEAR STRENGTH OF K0 CONSOLIDATED SOFT CLAYS UNDER TRIAXIAL AND PLANE STRAIN CONDITIONS

2014 ◽  
Vol 06 (03) ◽  
pp. 1450032 ◽  
Author(s):  
QIUSHENG WANG ◽  
XIULI DU ◽  
QIUMING GONG
Keyword(s):  
Shear Strength ◽  
Plane Strain ◽  
Yield Surface ◽  
Critical State ◽  
Volumetric Strain ◽  
Stress Path ◽  
Undrained Shear Strength ◽  
Triaxial Tests ◽  
Soft Clays ◽  
Undrained Shear

Theoretical formulas for predicting the undrained shear strength of K0 consolidated soft clays under the stress path related to triaxial and plane strain tests are presented within the framework of critical state soil mechanics. An inclined elliptical yield surface is adopted to take account of the initial anisotropic stress state. The undrained strength is determined by combining the undrained stress path in the volumetric stress–strain space and the initial yield surface in the deviator-mean stress space. The derived mathematical expressions are functions of the critical state frictional angle, the plastic volumetric strain ratio and the overconsolidation ratio, which can be simplified into the solutions for isotropically consolidated clays under triaxial tests or under plane strain tests. The results calculated by using the theoretical formulas obtained in this paper are in good agreement with the available collected test results. It indicates that these new formulas are applicable to triaxial and plane strain tests on normally and lightly to moderately overconsolidated soft clays.

scholarly journals Influence of Load Frequency on Cohesive Soil Respond

Geosciences ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 468 ◽  
Author(s):  
Krystian Kucharczyk ◽  
Andrzej Głuchowski ◽  
Maciej Miturski ◽  
Wojciech Sas
Keyword(s):  
Water Pressure ◽  
Cohesive Soil ◽  
Triaxial Tests ◽  
Soil Reaction ◽  
Cohesive Soils ◽  
Cyclic Tests ◽  
Degradation Index ◽  
Complex Behaviour ◽  
Load Frequency ◽  
Cycling Loading

The mechanism of cohesive soils response to cycling loading is less investigated compared to cohesionless soils. Multiple load-unload cycles cause significant changes in the structure of cohesive soils, which result in complex behaviour under the given load. The aim of the paper was to investigate and study the influence of load frequency on cohesive soil reaction. In order to obtain results, tests were conducted using the cyclic triaxial apparatus. Three cyclic tests were carried out, each for different frequency −0.5 Hz, 1.0 Hz, 2.0 Hz and one static triaxial test. The maximal value of deviator stress qmax, used in the cyclic tests, was set to 40 kPa. Afterwards samples were unloaded to qmin = 30 kPa. Cyclic loading triaxial tests were performed in a consolidated-undrained (CU) one-way loading manner, a sinusoidal waves were used. After the cycling loading was completed, a static triaxial shear test was conducted. Changes in the cohesive soil responses depending on cycling load frequency were presented in the paper. Differences in the accumulation of plastic strains were noticed, as well as changes of degradation index values, resilient degradation index values and differences in the excess pore water pressure development.

A Constitutive Model of Sandstone Considering the Post Peak Behavior

2017 ◽  
Vol 35 (1) ◽  
pp. 13-25 ◽  
Author(s):  
F. S. Jeng ◽  
M. C. Weng ◽  
F. H. Yeh ◽  
Y. H. Yang ◽  
T. H. Huang
Keyword(s):  
Constitutive Model ◽  
Nonlinear Elasticity ◽  
Strain Curve ◽  
Shear Loading ◽  
Triaxial Tests ◽  
Flow Rule ◽  
Plastic Behavior ◽  
Softening Behavior ◽  
Proposed Model ◽  
Confining Pressures

AbstractIn rock engineering, evaluating the post-peak strength and deformation of rock is necessary. To explore the elasto-plastic behavior of sandstone in the post-peak stage, a series of strain-controlled triaxial tests were conducted under different confining pressures. According to the post-peak characteristics, a constitutive model based on nonlinear elasticity and generalized plasticity is proposed. This proposed model is characterized by the following features: (1) Nonlinear elasticity is observed under hydrostatic and shear loading; (2) the associated flow rule is followed; (3) substantial plastic deformation occurs during shear loading; and (4) post-peak softening behavior is accurately predicted. This model requires twelve material parameters, three for elasticity and nine for plasticity. The proposed model was validated by comparing the triaxial test results of Mushan sandstone at different hydrostatic pressures under dry and saturated conditions. In addition, the model is versatile; it can simulate the deformational behavior of two other sandstones. In summary, the proposed model can reasonably predict the complete stress–strain curve of sandstone.

Effect of Yield Surface Curvature on Local Necking in Biaxially Stretched Sheets in Porous Materials

1992 ◽  
Vol 114 (2) ◽  
pp. 196-200 ◽  
Author(s):  
Xiangqiao Yan
Keyword(s):  
Porous Materials ◽  
Yield Surface ◽  
Kinematic Hardening ◽  
Material Model ◽  
Isotropic Hardening ◽  
Material Models ◽  
Hardening Model ◽  
Local Necking ◽  
Highly Sensitive ◽  
Isotropic Expansion

In this paper, a recently proposed material model (Sun model) that is based on the lower bound approach of plasticity is extended by introducing a family of dilatant plasticity theories. The yield surfaces change by a combination of isotropic expansion and kinematic translation. The sensitivity of the local necking predictions in biaxially stretched sheets to the curvature of the yield surface in porous materials is addressed. The results of the present analysis obtained by using four material models, the isotropic hardening version of Sun, the kinematic hardening version suggested in this paper, the Gurson model, and the Mear and Hutchinson model, indicate that the local necking predictions are highly sensitive to the curvature of the yield surface, and the predictions given by the kinematic hardening model are more reasonable for local necking analysis than those by the isotropic hardening model.

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