scholarly journals Extension of a basic hypoplastic model for overconsolidated clays

2021 ◽  
Author(s):  
shun wang ◽  
Wei Wu ◽  
Dichuan Zhang ◽  
Jong-Ryeol Kim
Keyword(s):  
Failure Surface ◽  
Asymptotic State ◽  
Stress Criterion ◽  
Hypoplastic Model ◽  
Shear Dilation ◽  
Rate Dependent ◽  
Numerical Predictions ◽  
Overconsolidated Clays ◽  
Limit Stress ◽  
Constitutive Parameters

This paper presents a new rate-dependent hypoplastic constitutive model for overconsolidated clays. The model is developed based on a basic hypoplastic model proposed recently for sand. New density and stiffness factors are introduced to account for history dependence. The Matsuoka-Nakai failure surface is incorporated for the limit stress criterion. With six constitutive parameters, the model is capable of predicting the hardening/softening, shear dilation/contraction, and asymptotic state for overconsolidated clays. Comparison between numerical predictions and experimental results shows this model can properly describe the main features of both reconstituted and undisturbed clays with different overconsolidation ratios.

Asymmetric Shielding Mechanisms in the Mixed-Mode Fracture of a Glass/Epoxy Interface

1998 ◽  
Vol 65 (1) ◽  
pp. 25-29 ◽  
Author(s):  
J. G. Swadener ◽  
K. M. Liechti
Keyword(s):  
Cohesive Zone Model ◽  
Hydrostatic Stress ◽  
Crack Opening ◽  
Shielding Effect ◽  
Mixed Mode Fracture ◽  
Zone Model ◽  
Element Analysis ◽  
Rate Dependent ◽  
Numerical Predictions ◽  
Wide Range

An asymmetric increase in the apparent values of the interfacial fracture toughness with increasing mode II component of loading has been observed by several investigators. In this study, cracks were grown in a steady-state manner along the glass/epoxy interface in sandwich specimens in order to determine the mechanisms responsible for the shielding effect. Finite element analysis using a hydrostatic stress and strain rate dependent plasticity model for the epoxy and a cohesive zone model for the interface shows that plastic dissipation in the epoxy accounts for the asymmetric shielding seen in these experiments which cover a wide range of mode mix. Numerical predictions of normal crack-opening displacements yielded results that were consistent with measured values which were made as close as 0.3 μm from the crack tip.

scholarly journals Confined flow of suspensions modelled by a frictional rheology

2014 ◽  
Vol 759 ◽  
pp. 197-235 ◽  
Author(s):  
Brice Lecampion ◽  
Dmitry I. Garagash
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Normal Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Numerical Predictions ◽  
Dry Granular Flow ◽  
Neutrally Buoyant ◽  
Constitutive Parameters ◽  
Axial Development

AbstractWe investigate in detail the problem of confined pressure-driven laminar flow of neutrally buoyant non-Brownian suspensions using a frictional rheology based on the recent proposal of Boyer et al. (Phys. Rev. Lett., vol. 107 (18), 2011, 188301). The friction coefficient (shear stress over particle normal stress) and solid volume fraction are taken as functions of the dimensionless viscous number $I$ defined as the ratio between the fluid shear stress and the particle normal stress. We clarify the contributions of the contact and hydrodynamic interactions on the evolution of the friction coefficient between the dilute and dense regimes reducing the phenomenological constitutive description to three physical parameters. We also propose an extension of this constitutive framework from the flowing regime (bounded by the maximum flowing solid volume fraction) to the fully jammed state (the random close packing limit). We obtain an analytical solution of the fully developed flow in channel and pipe for the frictional suspension rheology. The result can be transposed to dry granular flow upon appropriate redefinition of the dimensionless number $I$. The predictions are in excellent agreement with available experimental results for neutrally buoyant suspensions, when using the values of the constitutive parameters obtained independently from stress-controlled rheological measurements. In particular, the frictional rheology correctly predicts the transition from Poiseuille to plug flow and the associated particles migration with the increase of the entrance solid volume fraction. We also numerically solve for the axial development of the flow from the inlet of the channel/pipe toward the fully developed state. The available experimental data are in good agreement with our numerical predictions, when using an accepted phenomenological description of the relative phase slip obtained independently from batch-settlement experiments. The solution of the axial development of the flow notably provides a quantitative estimation of the entrance length effect in a pipe for suspensions when the continuum assumption is valid. Practically, the latter requires that the predicted width of the central (jammed) plug is wider than one particle diameter. A simple analytical expression for development length, inversely proportional to the gap-averaged diffusivity of a frictional suspension, is shown to encapsulate the numerical solution in the entire range of flow conditions from dilute to dense.

scholarly journals Validation of a simple hypoplastic constitutive model for overconsolidated clays

2020 ◽  
Author(s):  
Shun Wang ◽  
Wei Wu
Keyword(s):  
Laboratory Tests ◽  
Constitutive Models ◽  
Standard Laboratory ◽  
Hypoplastic Model ◽  
Proposed Model ◽  
Modified Cam Clay ◽  
Overconsolidated Clays ◽  
Hypoplastic Constitutive Model ◽  
Comparison With Experiments ◽  
Cam Clay

AbstractHypoplastic constitutive models are able to describe history dependence using a single nonlinear tensorial function with a set of parameters. A hypoplastic model including a structure tensor for consolidation history was introduced in our previous paper (Wang and Wu in Acta Geotechnica, 2020, 10.1007/s11440-020-01000-z). The present paper focuses mainly on the model validation with experiments. This model is as simple as the modified Cam Clay model but with better performance. The model requires five parameters, which are easy to calibrate from standard laboratory tests. In particular, the model is capable of capturing the unloading behavior without introducing loading criteria. Numerical simulations of element tests and comparison with experiments show that the proposed model is able to reproduce the salient features of normally consolidated and overconsolidated clays.

scholarly journals Extension of a basic hypoplastic model for overconsolidated clays

2020 ◽  
Vol 123 ◽  
pp. 103486 ◽  
Author(s):  
Shun Wang ◽  
Wei Wu ◽  
Dichuan Zhang ◽  
Jong Ryeol Kim
Keyword(s):  
Hypoplastic Model ◽  
Overconsolidated Clays

Evaluations of failure initiation criteria for predicting damages of composite structures under crushing loading

2018 ◽  
Vol 37 (21) ◽  
pp. 1279-1303 ◽  
Author(s):  
Hongyong Jiang ◽  
Yiru Ren ◽  
Zhihui Liu ◽  
Songjun Zhang ◽  
Xiaoqing Wang
Keyword(s):  
Composite Structures ◽  
Maximum Stress ◽  
Failure Modes ◽  
Damage Model ◽  
Axial Loading ◽  
Failure Criteria ◽  
Quantitative Relation ◽  
Stress Criterion ◽  
Failure Initiation ◽  
Numerical Predictions

The crushing behaviors of thin-walled composite structures subjected to quasi-static axial loading are comparatively evaluated using four different failure initiation criteria. Both available crushing tests of composite corrugated plate and square tube are used to validate the stiffness degradation-based damage model with the Maximum-stress criterion. Comparatively, Hashin, Maximum-stress, Stress-based Linde, and Modified criteria are respectively implemented in the damage model to predict crush behaviors of corrugated plate and square tube. To develop failure criteria, effects of shear coefficients and exponents in the Modified and Maximum-stress criteria on damage mechanisms of corrugated plate are discussed. Results show that numerical predictions successfully capture both of experimental failure modes and load–displacement responses. The Modified criterion and particularly Maximum-stress criterion are found to be more appropriate for present crush models of corrugated plate and square tube. When increasing the failure index, the crushing load is decreased, which also causes premature material failure. The shear coefficient and exponents have dramatic influence on the crushing load. Overall, an insight into the quantitative relation of failure initiation is obtained.

Theoretical and Numerical Predictions of Burst Pressure of Pipelines

2007 ◽  
Vol 129 (4) ◽  
pp. 644-652 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Equivalent Stress ◽  
Failure Criteria ◽  
Burst Pressure ◽  
Isotropic Hardening ◽  
Flow Rule ◽  
Strain Criterion ◽  
Stress Criterion ◽  
Numerical Predictions ◽  
Yield Theory ◽  
Von Mises

To accurately characterize plastic yield behavior of metals in multiaxial stress states, a new yield theory, i.e., the average shear stress yield (ASSY) theory, is proposed in reference to the classical Tresca and von Mises yield theories for isotropic hardening materials. Based on the ASSY theory, a theoretical solution for predicting the burst pressure of pipelines is obtained as a function of pipe diameter, wall thickness, material hardening exponent, and ultimate tensile strength. This solution is then validated by experimental data for various pipeline steels. According to the ASSY yield theory, four failure criteria are developed for predicting the burst pressure of pipes by the use of commercial finite element softwares such as ABAQUS and ANSYS, where the von Mises yield theory and the associated flow rule are adopted as the classical metal plasticity model for isotropic hardening materials. These failure criteria include the von Mises equivalent stress criterion, the maximum principal stress criterion, the von Mises equivalent strain criterion, and the maximum tensile strain criterion. Applications demonstrate that the proposed failure criteria in conjunction with the ABAQUS or ANSYS numerical analysis can effectively predict the burst pressure of end-capped line pipes.

scholarly journals A simple hypoplastic model for overconsolidated clays

2021 ◽  
Author(s):  
shun wang ◽  
Wei Wu
Keyword(s):  
Constitutive Model ◽  
Structure Tensor ◽  
History Dependence ◽  
Hypoplastic Model ◽  
Clay Model ◽  
Modified Cam Clay ◽  
Overconsolidated Clays ◽  
Independent Parameters ◽  
Hypoplastic Constitutive Model ◽  
Cam Clay

This paper presents a simple hypoplastic constitutive model for overconsolidated clays. The model needs five independent parameters and is as simple as the modified Cam Clay model but with better performance. A structure tensor is introduced to account for the history dependence. Simulations of various elementary tests show that the model is capable of capturing the salient behavior of overconsolidated clays.

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