Showing papers on "Viscoplasticity published in 2011"
TL;DR: In this article, a physically-based model is developed to address slip in polycrystalline metals and alloys subjected to very high rates of deformation (104−108 s−1).
252 citations
TL;DR: The approach opens the way to the realistic multi-dimensional prediction of complex flows encountered in geophysical, industrial and biological applications, and to the understanding of the link between structure and rheology of soft glassy systems.
Abstract: Foams, gels, emulsions, polymer solutions, pastes and even cell assemblies display both liquid and solid mechanical properties. On a local scale, such “soft glassy” systems are disordered assemblies of deformable rearranging units, the complexity of which gives rise to their striking flow behaviour. On a global scale, experiments show that their mechanical behaviour depends on the orientation of their elastic deformation with respect to the flow direction, thus requiring a description by tensorial equations for continuous materials. However, due to their strong non-linearities, the numerous candidate models have not yet been solved in a general multi-dimensional geometry to provide stringent tests of their validity. We compute the first solutions of a continuous model for a discriminant benchmark, namely the flow around an obstacle. We compare it with experiments of a foam flow and find an excellent agreement with the spatial distribution of all important features: we accurately predict the experimental fields of velocity, elastic deformation, and plastic deformation rate in terms of magnitude, direction, and anisotropy. We analyse the role of each parameter, and demonstrate that the yield strain is the main dimensionless parameter required to characterize the materials. We evidence the dominant effect of elasticity, which explains why the stress does not depend simply on the shear rate. Our results demonstrate that the behaviour of soft glassy materials cannot be reduced to an intermediate between that of a solid and that of a liquid: the viscous, the elastic and the plastic contributions to the flow, as well as their couplings, must be treated simultaneously. Our approach opens the way to the realistic multi-dimensional prediction of complex flows encountered in geophysical, industrial and biological applications, and to the understanding of the link between structure and rheology of soft glassy systems.
241 citations
TL;DR: In this article, constitutive equations for coupled inelastic-damage-healing processes are proposed in a thermodynamic consistent framework and two new yield surfaces for the damage and healing processes were proposed that take into account the isotropic hardening effect.
192 citations
TL;DR: In this paper, a temperature-dependent viscodamage model is proposed and coupled to the temperaturedependent Schapery's nonlinear viscoelasticity and the temperature dependent Perzyna's viscoplasticity constitutive model presented in Abu Al-Rub et al. (2009) in order to model the nonlinear constitutive behavior of asphalt mixes.
187 citations
TL;DR: In this paper, an internal-state-variable based self-consistent constitutive model was proposed for unified prediction of flow stress and microstructure evolution during hot working of wrought two-phase titanium alloys in both single-beta region and twophase region.
186 citations
15 Jun 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the metadynamic recrystallization (MDRX) behavior of 30Cr2Ni4MoV ultra-supercritical (USC) rotor steel during hot deformation was investigated based on the first part of this study, in which the evolution of the dynamically recrystalized structure was studied in detail.
Abstract: The metadynamic recrystallization (MDRX) behavior of 30Cr2Ni4MoV ultra-super-critical (USC) rotor steel during hot deformation was investigated based on the first part of this study, in which the evolution of the dynamically recrystallized structure was studied in detail. Compression tests were performed using double hit schedules at temperatures of 970–1250 °C, strain rates of 0.001–0.1 s−1 and inter-pass time of 1–100 s. Based on the experimental results, the kinetic equations and grain size model were established. Results show that the effects of deformation parameters, including forming temperature and strain rate, on MDRX softening fractions and austenite grain size in the two-pass hot deformed 30Cr2Ni4MoV steel are significant. Results also reveal that the pre-strain (beyond the peak strain) has little influence on the MDRX behaviors in 30Cr2Ni4MoV steel. Comparisons between the experimental and the predicted results were carried out. A good agreement between the experimental and the predicted results was obtained, which verified the developed models.
168 citations
TL;DR: In this paper, the evolution of microstructure and texture during room temperature compression of commercially pure Ti with four different initial orientations were studied under quasi-static and dynamic loading conditions.
161 citations
TL;DR: In this paper, a constitutive model for structured fluids is presented, which is composed of two differential equations, one for the stress and the other for the structure parameter, a scalar quantity that represents the structuring level of the fluid.
Abstract: A constitutive model for structured fluids is presented. Its predictive capability includes thixotropy, viscoelasticity and yielding behavior. It is composed by two differential equations, one for the stress and the other for the structure parameter—a scalar quantity that represents the structuring level of the fluid. The equation for stress is obtained in accordance with a simple mechanical analog composed by a structuring-level-dependent Maxwell element in parallel with a Newtonian element, leading to an equation of the same form as the Jeffreys (or Oldroyd-B) equation. The relaxation and retardation times that arise are functions of the structure parameter. The ideas found in de Souza Mendes, J. Non-Newtonian Fluid Mech., 2009, 164, 66 are employed for the structure parameter equation as well as for the dependencies on the structure parameter of the structural viscosity and structural shear modulus. The model is employed in constant-rate, constant-stress, and oscillatory shear flows, and its predictive capability is shown to be excellent for all cases.
150 citations
TL;DR: In this article, the authors focus on modeling the response of the bond-coat material and its oxidation, and present a new continuum-level thermodynamically-consistent, large-deformation, fully three-dimensional theory which couples high-temperature elastic-viscoplastic deformation of the material with diffusion of oxygen, eventually leading to an oxidation reaction in which the reaction-product causes permanent swelling.
137 citations
TL;DR: It is shown that the time delay for this yielding decreases in two distinct exponential regimes with applied stress, universal and found for a variety of colloidal gel systems.
Abstract: Networks of aggregated colloidal particles are solidlike and can sustain an applied shear stress while exhibiting little or no creep; however, ultimately they will catastrophically fail. We show that the time delay for this yielding decreases in two distinct exponential regimes with applied stress. This behavior is universal and found for a variety of colloidal gel systems. We present a bond-rupture model that quantitatively describes this behavior and highlights the role of mesoscopic structures. Our result gives new insight into the nature of yielding in these soft solid materials.
136 citations
25 Jan 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the deformation characteristics of the 2205 duplex stainless steel were analyzed using constitutive equations and processing maps, and it was realized that dynamic restoration mechanisms could efficiently hinder the occurrence of flow instability at low and medium strain rates.
Abstract: The hot deformation characteristics of the 2205 duplex stainless steel were analyzed using constitutive equations and processing maps. The hot compression tests were performed at temperature range of 950–1200 °C and strain rate of 0.001–1 s−1. Flow stress was modeled by the constitutive equation of hyperbolic sine function. However, the stress exponent and strain rate sensitivity were different at low and high deformation temperatures where austenite and ferrite are dominant, respectively. It was recognized that strain at the peak point of flow curve increases with the Zener–Hollomon parameter, Z, at low temperature deformation while at high temperature deformation it actually decreases with Z. The power dissipation map, instability map and processing map were developed for the typical strain of 0.3. It was realized that dynamic restoration mechanisms could efficiently hinder the occurrence of flow instability at low and medium strain rates. Otherwise, the increase in strain rate at low and high temperatures could increase the risk of flow instability.
TL;DR: In this paper, the hot deformation behavior of Stir cast 7075 alloy was studied using processing map technique and the map has been interpreted in terms of the microstructural processes occurring in situ with deformation, based on the values of a dimensionless parameter η which is an efficiency index of energy dissipation through micro-structural process.
TL;DR: In this article, the authors provide an overview of the main mathematical and computational aspects of viscoplasticity, and discuss Bingham flow in cylinders and cavities, numerical simulation of nonisothermal, compressible, and thixotropic viscplastic flow, which is an augmented Lagrangian finite-volume approach.
Abstract: Publisher Summary This chapter provides an overview of the main mathematical and computational aspects of viscoplasticity. It discusses Bingham flow in cylinders and cavities; the numerical simulation of nonisothermal, compressible, and thixotropic viscoplastic flow, which is an augmented Lagrangian finite-volume approach; the application of fictitious domain; and methods for the numerical simulation of viscoplastic flow. Among the various classes of non-Newtonian materials, those exhibiting viscoplastic properties are particularly interesting in accordance with their ability to strain only if the stress intensity exceeds a minimum value. Many industrial processes involve viscoplastic fluids. The chapter mentions only a few of them—namely, mud, cement slurries, food, waxy crude oils, suspensions, emulsions, foams, etc. In a viscoplastic fluid flow, the flow pattern highlights two kinds of regions: the regions where the stress intensity exceeds the yield stress and the regions where it does not. The former and latter regions are usually called the “yielded” and “unyielded” regions, respectively. The most commonly encountered viscoplastic model is the Bingham fluid.
TL;DR: In this paper, a physically-based hyperelastic-viscoplastic approach was adopted to develop a pertinent model for describing the mechanical behaviour of polyethylene (PE) materials under finite strains.
TL;DR: In this paper, the authors developed a nonlinear viscoelastic-viscoplastic constitutive model to represent the response of asphalt mixtures under different temperatures and rates of loading.
Abstract: The writers recently developed a nonlinear viscoelastic-viscoplastic constitutive model, in order to represent the response of asphalt mixtures under different temperatures and rates of loading. This model has been implemented in the finite-element (FE) code Abaqus via the user material subroutine UMAT, and it was verified through comparisons with experimental data of asphalt mixtures at various stress levels and temperatures. This research develops a three-dimensional FE model using Abaqus to represent a three-layer pavement structure and to simulate the viscoelastic and viscoplastic responses under repeated loading at different temperatures. The results demonstrate the capability of the model in simulating the influence of temperature on permanent deformation and in predicting viscoelastic and viscoplastic strain distributions in the asphalt layer. The simulations show that tensile viscoplastic strain accumulates at the pavement surface, a phenomenon that could be associated with cracking of asphalt pavements. In addition, the results show that at high pavement temperature (40°C), tensile viscoplastic strain develops at the sides of the applied load due to asphalt mixture heave associated with permanent deformation and dilation.
TL;DR: In this article, a viscoplastic approach using the Fast Fourier Transform (FFT) method for obtaining local mechanical response is utilized to study microstructure-property relationships in composite materials.
TL;DR: In this article, the authors propose a generalized solution based on a viscoplastic approximation, in such a way that the plastic strain is uniformly Lipschitz with respect to the rescaled time, and the limit of these rescaled solutions, as the viscosity parameter tends to zero, is characterized through an energy-dissipation balance.
Abstract: Cam-Clay nonassociative plasticity exhibits both hardening and softening behaviour, depending on the loading. For many initial data the classical formulation of the quasistatic evolution problem has no smooth solution. We propose here a notion of generalized solution, based on a viscoplastic approximation. To study the limit of the viscoplastic evolutions we rescale time, in such a way that the plastic strain is uniformly Lipschitz with respect to the rescaled time. The limit of these rescaled solutions, as the viscosity parameter tends to zero, is characterized through an energy-dissipation balance, that can be written in a natural way using the rescaled time. As shown in Dal Maso and DeSimone (Math Models Methods Appl Sci 19:1–69, 2009) and Dal Maso and Solombrino (Netw Heterog Media 5:97–132, 2010), the proposed solution may be discontinuous with respect to the original time. Our formulation allows us to compute the amount of viscous dissipation occurring instantaneously at each discontinuity time.
TL;DR: A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity and predicts strengthening of materials when a gradient in stress acts over dislocation source–obstacle configurations.
Abstract: A new model, stress-gradient plasticity, is presented that provides unique mechanistic insight into size-dependent phenomena in plasticity. This dislocation-based model predicts strengthening of materials when a gradient in stress acts over dislocation source–obstacle configurations. The model has a physical length scale, the spacing of dislocation obstacles, and is validated by several levels of discrete-dislocation simulations. When incorporated into a continuum viscoplastic model, predictions for bending and torsion in polycrystalline metals show excellent agreement with experiments in the initial strengthening and subsequent hardening as a function of both sample-size dependence and grain size, when the operative obstacle spacing is proportional to the grain size.
25 Jan 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a physically-based macroscopic model for deformation twinning in face-centered cubic austenitic steels is proposed. But the model is not suitable for the case of steel and it cannot be used in finite element-based metal forming simulations.
Abstract: TWinning Induced Plasticity (TWIP) steel is a typical representative of the 2nd generation advanced high strength steels (AHSS) which exhibits a combination of high strength and excellent ductility due to the deformation twinning mechanisms. This paper discusses the principal features of deformation twinning in faced-centered cubic austenitic steels and shows how a physically based macroscopic model can be derived from microscopic-level considerations. In fact, a dislocation-based phenomenological model, with internal state variables including dislocation density and micro-twins volume fraction describing the microstructure evolution during deformation process, is proposed to model the deformation behavior of TWIP steels. The originality of this work lies in the incorporation of a physically based model on twin nucleation and volume fraction evolution in a conventional dislocation-based approach. Microstructural level experimental observations with scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques together with the macroscopic quasi-static tensile test, for the TWIP steel Fe–17.5 wt.% Mn–1.4 wt.% Al–0.56 wt.% C, are used to validate and verify the modeling assumptions. The model could be regarded as a semi-phenomenological approach with sufficient links between microstructure and the overall mechanical properties, and therefore offers good predictive capabilities. Its simplicity also allows a modular implementation in finite element-based metal forming simulations.
01 Jan 2011
TL;DR: In this paper, the effect of viscoelasticity on fatigue and deformation of polymer matrix composites is investigated. And the authors propose an accelerated testing methodology for predicting long-term deformation and fatigue in polymer matrix composite structures.
Abstract: Part 1 Viscoelastic and viscoplastic modelling: Viscoelastic constitutive modeling of creep and stress relaxation in polymers and polymer matrix composites Time-temperature-age superposition principle for predicting long-term response of linear viscoelastic materials Time-dependent behaviour of active/intelligent polymer matrix composites incorporating piezoceramic fibers Predicting the elastic-viscoplastic and creep behaviour of polymer matrix composites using the homogenization theory Measuring fiber strain and creep behaviour in polymer matrix composites using Raman spectroscopy Predicting the viscoelastic behaviour of polymer nanocomposites Constitutive modelling of viscoplastic deformation of polymer matrix composites Creep analysis of polymer matrix composites using viscoplastic models Micromechanical modeling of viscoelastic behaviour of polymer matrix composites undergoing large deformations. Part 2 Creep rupture: Fiber bundle models for creep rupture analysis of polymer matrix composites Micromechanical modelling of time-dependent failure in off-axis polymer matrix composites Time-dependent failure criteria for lifetime prediction of polymer matrix composite structures. Part 3 Fatigue modelling, characterisation and monitoring: Testing the fatigue strength of fibers used in fiber-reinforced composites using fiber bundle tests Continuum damage mechanical modelling of creep damage and fatigue in polymer matrix composites Accelerated testing methodology for predicting long-term creep and fatigue in polymer matrix composites Fatigue testing methods for polymer matrix composites The effect of viscoelasticity on fatigue behavior of polymer matrix composites Characterization of vicoelasticity, viscoplasticity and damage in composites Structural health monitoring of composite structures for durability.
25 Feb 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors investigated the dynamic recrystallization of austenite in the Cu-bearing HSLA-100 steel and found that at high temperatures, flow stress exhibited a linear relation with temperature while at temperatures below 950°C the behavior changed to non-linear.
Abstract: Dynamic recrystallization of austenite in the Cu-bearing HSLA-100 steel was investigated by hot compression testing at a temperature range of 850–1150 °C and a strain rate of 0.001–1 s −1 . The obtained flow curves at temperatures higher than 950 °C were typical of DRX while at lower temperatures the flow curves were associated with work hardening without any indication of DRX. At high temperatures, flow stress exhibited a linear relation with temperature while at temperatures below 950 °C the behavior changed to non-linear. Hence, the temperature of 950 °C was introduced as the T nr of the alloy. All the flow curves showed a yield point elongation like phenomenon which was attributed to the interaction of solute atoms, notably carbon, and moving dislocations. The maximum elongation associated with the yield point phenomenon was observed at about 950 °C. Since the maximum yield point elongation was observed about the calculated T nr , it was concluded that carbon atoms were responsible for it. It was also concluded that the temperature at which the yield point elongation reaches the maximum value increases as strain rate rises. The stress and strain of the characteristic points of DRX flow curves were successfully correlated to the Zener–Hollomon parameter, Z , by power-law equations. The constitutive exponential equation was found more precise than the hyperbolic sine equation for modeling the dependence of flow stress on Z . The apparent activation energy for DRX was determined as 377 kJ mol −1 . The kinetics of DRX was modeled by an Avrami-type equation and the Avrami's exponent was determined around 1.1.
TL;DR: In this paper, the authors applied crystal plasticity to model the cyclic constitutive behavior of a polycrystalline nickel-based superalloy at elevated temperature using finite element analyses.
TL;DR: In this article, a triaxial creep experiment of artificially frozen soil in deep alluvium was performed by a self-developed machine of triaxially creep frozen soil, applying parabolic yield criterion for improved viscoplasticity in the Nishihara model, a new creep constitutive model was established for describing frozen soil's creep characteristics under high confining pressures.
TL;DR: In this article, an incremental large strain formulation additively decomposes the inelastic strain rate into components along the octahedral and cubic slip planes, and a crystallographic-based creep constitutive model is developed to predict sigmoidal creep behavior of Ni base superalloys.
TL;DR: In this paper, a coupled viscoelastic-viscoplastic (VE-VP) model is implemented and studied, where the total strain is the sum of VE and VP parts, and the Cauchy stress is given by a linear VE model as a Boltzmann integral of the history of VEs strains.
TL;DR: In this article, the authors propose constitutive models for polycrystalline aggregates with intergranular cavities and test them against full-field numerical simulations, where the dilatational effects associated with the presence of cavities must be accounted for.
Abstract: We propose constitutive models for polycrystalline aggregates with intergranular cavities and test them against full-field numerical simulations. Such conditions are prevalent in many engineering applications and failure of metallic components (e.g. HIPing and other forming processes, spallation under dynamic loading conditions, etc.), where the dilatational effects associated with the presence of cavities must be accounted for, and standard polycrystalline models for incompressible plasticity are not appropriate. On the other hand, it is not clear that the use of porous plasticity models with isotropic matrix behavior is relevant, particularly, when large deformations can lead to significant texture evolution and therefore to strong matrix anisotropy. Of course, finite strains can also lead to significant changes in the porosity and pore shape, resulting in additional anisotropy development. In this work, we make use of ‘variational linear-comparison’ homogenization methods to develop constitutive models...
TL;DR: In this paper, a non-local and finite deformation-based constitutive model using thermodynamic principles and the theory of micro-force balance was developed to study the causes for the observed observations.
Abstract: Some recent experiments on sub-micron and nano-sized metallic glass (amorphous alloy) specimens have shown that the shear localization process becomes more stable and less catastrophic when compared to the response exhibited by large sample sizes This leads to the discovery that the shear localization process and fracture can be delayed by decreasing sample volume In this work we develop a non-local and finite-deformation-based constitutive model using thermodynamic principles and the theory of micro-force balance to study the causes for the aforementioned observations The constitutive model has also been implemented into a commercially available finite-element program by writing a user-material subroutine With the aid of finite-element simulations, our constitutive model predicts that metallic glass samples have the intrinsic ability to exhibit: (a) the delaying of (catastrophic) shear localization with decreasing sample size, and (b) homogeneous deformation behavior for sample volumes smaller than the shear band nucleus The cause for the observations listed above is the increasing influence of a non-local interaction stress with decreasing sample volume This interaction stress has energetic origins and it affects plastic deformation due to the strong coupling between plastic shearing and free-volume generation Akin to strain-gradient plasticity theory, the role of the interaction stress is to strengthen the material at locations where the defect density/free volume is higher compared to the rest of metallic glass sample
TL;DR: The constitutive model was found to successfully quantitatively predict the loading behavior and its dependence on biaxiality of the loading conditions and to underestimate the gradual nature of both the forward and reverse plastic deformation processes as well as the strain recovery at zero load.
TL;DR: In this article, a tensile relaxation test with various strains, tensile creep tests with various stresses, and cyclic tests with a stress-controlled program (ratcheting with a fixed maximum stress and various minimum stresses) were performed on polyamide-6 reinforced with short glass fibers.
TL;DR: In this paper, the authors investigated the influence of material properties and loading conditions on the recovery performance of amorphous shape memory polymers using a recently developed thermoviscoelastic model.