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Showing papers on "Viscoplasticity published in 2003"


Journal ArticleDOI
TL;DR: In this paper, a continuum theory for the elastic-viscoplastic deformation of amorphous solids such as polymeric and metallic glasses is proposed. But the authors do not consider the elasticity of polymeric solids and instead focus on the dependence of the Helmholtz free energy on the deformation in a thermodynamically consistent manner.

228 citations


Journal ArticleDOI
TL;DR: In this article, a micromechanically based constitutive model for the elasto-viscoplastic deformation and texture evolution of semi-crystalline polymers is developed.
Abstract: A micromechanically based constitutive model for the elasto-viscoplastic deformation and texture evolution of semi-crystalline polymers is developed. The model idealizes the microstructure to consist of an aggregate of two-phase layered composite inclusions. A new framework for the composite inclusion model is formulated to facilitate the use of finite deformation elasto-viscoplastic constitutive models for each constituent phase. The crystalline lamellae are modeled as anisotropic elastic with plastic flow occurring via crystallographic slip. The amorphous phase is modeled as isotropic elastic with plastic flow being a rate-dependent process with strain hardening resulting from molecular orientation. The volume-averaged deformation and stress within the inclusions are related to the macroscopic fields by a hybrid interaction model. The uniaxial compression of initially isotropic high density polyethylene (HDPE) is taken as a case study. The ability of the model to capture the elasto-plastic stress–strain behavior of HDPE during monotonic and cyclic loading, the evolution of anisotropy, and the effect of crystallinity on initial modulus, yield stress, post-yield behavior and unloading–reloading cycles are presented.

214 citations


Journal ArticleDOI
TL;DR: In this paper, a general theory for small deformation viscoplasticity based on a system of microforces consistent with its own balance was developed, including a mechanical version of the second law that includes, via the microforces, work performed during viscoplastic flow; a constitutive theory that allows for dependences on plastic strain gradients.

210 citations


Journal ArticleDOI
TL;DR: In this article, the inelastic deformation behaviors of metals and polymers are discussed with the aim of finding a common base that would simplify academic and engineering analyses, and only monotonic loading conditions at room temperature are considered.

179 citations


Journal ArticleDOI
TL;DR: Shear yielding and steady state flow of glassy materials with molecular dynamics simulations of two standard models: amorphous polymers and bidisperse Lennard-Jones glasses show that rate dependence is nearly independent of temperature.
Abstract: We study shear yielding and steady state flow of glassy materials with molecular dynamics simulations of two standard models: amorphous polymers and bidisperse Lennard-Jones glasses. For a fixed strain rate, the maximum shear yield stress and the steady state flow stress in simple shear both drop linearly with increasing temperature. The dependence on strain rate can be described by either a logarithm or a power law added to a constant. In marked contrast to predictions of traditional thermal activation models, the rate dependence is nearly independent of temperature. The relation to more recent models of plastic deformation and glassy rheology is discussed, and the dynamics of particles and stress in small regions is examined in light of these findings.

153 citations


Journal ArticleDOI
TL;DR: In this paper, a viscoplastic model was used to simulate a reinforced concrete beam submitted to impact, and the model was applied to simulate the rate effect of impact on the beam.
Abstract: This paper deals with a viscoplastic model which is the natural way to take into account the rate effect. Consideration of viscosity averts the habitual mesh sensitivity when strain softening is introduced by preserving the well-posedness of the initial boundary value problem. Modeling can constitute an alternative to experimentation not in order to predict the material response, but to try to understand and to evaluate the rate effect. Numerical simulation of the split test Hopkinson pressure bar gives an idea of dynamic concrete behaviour: forces of inertia, inertial confinement, structural effect and rate effect. Finally, the model is used to simulate a reinforced concrete beam submitted to impact.

146 citations


Journal ArticleDOI
TL;DR: In this article, a set of mechanism-based unified viscoplastic constitutive equations were developed to model the evolution of dislocation density, recrystallisation and grain size during and after hot plastic deformation.

128 citations


Journal ArticleDOI
TL;DR: In this paper, a finite element (FE) implementation of a stress-dependent elastoviscoplastic constitutive model with damage for asphalt is described, which includes elastic, delayed elastic, and viscoplastic components.
Abstract: The development and finite element (FE) implementation of a stress-dependent elastoviscoplastic constitutive model with damage for asphalt is described. The model includes elastic, delayed elastic, and viscoplastic components. The strains (and strain rates) for each component are additive, whereas they share the same stress (i.e., a series model). This formulation was used so that a stress-based nonlinearity and sensitivity to confinement could be introduced into the viscoplastic component without affecting the behavior of the elastic and delayed elastic components. A simple continuum damage mechanics formulation is introduced into the viscoplastic component to account for the effects of cumulative damage on the viscoplastic response of the material. The model is implemented in an incremental formulation into the CAPA-3D FE program developed at Delft University of Technology in the Netherlands. A local strain compatibility condition is utilized such that the incremental stresses are determined explicitly from the incremental strains at each integration point. The model is demonstrated by investigating the response of a semirigid industrial pavement structure subjected to container loading. Results show that the permanent vertical strains in the non-stress-dependent case are significantly lower than the permanent vertical strains in the stress-dependent case. Results also show that in the stress-dependent case, there is a more localized area of high permanent vertical compressive strain directly under the load at approximately half-depth in the asphalt compared with the non-stress-dependent case, in which the distribution is more even.

123 citations


Journal ArticleDOI
TL;DR: In this paper, a comprehensive constitutive model for asphalt concrete was calibrated that included viscoelasticity, viscoplasticity and irreversible microstructural damage in unconfined compression.
Abstract: A comprehensive constitutive model for asphalt concrete was calibrated that included viscoelasticity, viscoplasticity, and irreversible microstructural damage in unconfined compression. Three different types of laboratory tests were designed and performed to calibrate each of these response components. Small-strain dynamic modulus tests were used to calibrate the undamaged linear viscoelastic properties. Cyclic creep and recovery tests to failure were performed to calibrate the viscoplastic properties. Constant-rate-of-strain tests to failure were used to calibrate the damage behavior. These tests were performed at a wide range of temperatures, loading rates, and stress levels. Upon calibration of each individual response, the model was validated by predicting the results of other constant-rate-of-strain tests at temperatures and strain rates different from those used in the calibrations. The predictions for these different conditions indicate that the comprehensive model can realistically simulate a wide range of asphalt concrete behavior.

107 citations


Journal ArticleDOI
TL;DR: In this paper, the problem of dynamic growth of a single spherical void in an elastic-viscoplastic medium, with a view towards addressing a number of problems that arise during the dynamic failure of metals, was examined.
Abstract: We have examined the problem of the dynamic growth of a single spherical void in an elastic-viscoplastic medium, with a view towards addressing a number of problems that arise during the dynamic failure of metals. Particular attention is paid to inertial, thermal and rate-dependent effects, which have not previously been thoroughly studied in a combined setting. It is shown that the critical stress for unstable growth of the void in the quasistatic case is strongly affected by the thermal softening of the material (in adiabatic calculations). Thermal softening has the effect of lowering the critical stress, and has a stronger influence at high strain hardening exponents. It is shown that the thermally diffusive case for quasistatic void growth in rate-dependent materials is strongly affected by the initial void size, because of the length scale introduced by the thermal diffusion. The effects of inertia are quantified, and it is demonstrated that inertial effects are small in the early stages of void growth and are strongly dependent on the initial size of the void and the rate of loading. Under supercritical loading for the inertial problem, voids of all sizes achieve a constant absolute void growth rate in the long term. Inertia first impedes, but finally promotes dynamic void growth under a subcritical loading. For dynamic void growth, the effect of rate-hardening is to reduce the rate of void growth in comparison to the rate-independent case, and to reduce the final relative void growth achieved.

98 citations


01 Jan 2003
TL;DR: In this article, the authors developed an accurate and advanced material characterization procedure to be incorporated in the Superpave performance models system, including the theoretical models and its supporting experimental testing protocols necessary for predicting responses of asphalt mixtures subjected to uniaxial tension loading.
Abstract: The objective of the research presented in this paper is to develop an accurate and advanced material characterization procedure to be incorporated in the Superpave performance models system. The procedure includes the theoretical models and its supporting experimental testing protocols necessary for predicting responses of asphalt mixtures subjected to uniaxial tension loading. The model encompasses the elastic, viscoelastic, plastic and viscoplastic components of asphalt concrete behavior. Some of the major factors affecting asphalt concrete response, such as rate of loading, loading time, stress/strain amplitude, temperature, and damage, are addressed. The modeling strategy is based on developing separate models for strain components and then integrating those models to form a viscoelastoplastic continuum damage (VEPCD) model. The developed model accurately predicts responses up to localization when microcracks start to coalesce and grow. After that, fracture process zone strains detected using digital image correlation are used to extend the model's ability in predicting responses in the post-localization stage. However, once major macrocracks develop and propagate, the currently developed model ceases to predict responses accurately. At that state, fracture mechanics needs to be integrated with the current continuum damage-based model to predict the response.

Journal ArticleDOI
TL;DR: In this paper, the authors proposed a model that relates the structure of a fractal particle network to its yield stress, and the model predicts the yield stress to be a function of particle size, solid-liquid surface free energy, the amount of network material and the fractal dimension of the network.
Abstract: The apparent yield stress is a fundamental rheological characteristic of a plastic material. In this work, we propose a model that relates the structure of a fractal particle network to its yield stress. The model predicts the yield stress to be a function of particle size, solid-liquid surface free energy, the amount of network material, and the fractal dimension of the network. The predicted yield stress corresponded to the stress at the limit of linearity in fat crystal networks. Moreover, a structural definition for the yield stress is proposed.

Journal ArticleDOI
Weihua Li1, Hejun Du1, G. Chen1, S H Yeo1, Ningqun Guo1 
TL;DR: In this article, the nonlinear viscoelastic properties of the MR fluid, MRF-132LD, under large-amplitude oscillatory shear were investigated using a rheometer with parallel-plate geometry.
Abstract: Nonlinear viscoelastic properties of the MR fluid, MRF-132LD, under large-amplitude oscillatory shear were investigated. This was accomplished by carrying out the experiments under the amplitude sweep mode and the frequency sweep mode, using a rheometer with parallel-plate geometry. Investigations under the influence of various magnetic field strength and temperatures were also conducted. MR fluids behave as nonlinear viscoelastic or viscoplastic materials when they are subjected to large-amplitude shear, where the storage modulus decreases rapidly with increasing strain amplitude. Hence, MR fluid behaviour ranges from predominantly elastic at small strain amplitudes to viscous at high strain amplitudes. Large-amplitude oscillatory shear measurements with frequency sweep mode reveal that the storage modulus is independent of oscillation frequency and approaches plateau values at low frequencies. With increasing frequency, the storage modulus shows a decreasing trend before increasing again. This trend may be explained by micro-structural variation. In addition, the storage modulus increases gradually with increasing field strength but it shows a slightly decreasing trend with temperature.

Journal ArticleDOI
TL;DR: In this article, the viscoelastic behavior of a polymer is modelled as thermally-induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network) The viscoplastic response reflects mutual displacement of mesodomains driven by macro-strains.

Journal ArticleDOI
TL;DR: In this article, numerical simulations were carried out to determine the flow characteristics of a Herschel-Bulkley viscoplastic fluid around a cylinder in an infinite medium, and the location, dimension and kinematics of the rigid zones were determined.
Abstract: The purpose of the numerical simulations carried out in this study is to determine the flow characteristics of a Herschel–Bulkley viscoplastic fluid around a cylinder in an infinite medium. Inertia is assumed to be negligible. Two types of boundary conditions are considered: the fluid adheres or slips (zero tangential stress) on the cylinder wall. Finite-element modelling involves regularising the Herschel–Bulkley model, as proposed by Papanastasiou [J. Rheol. 31 (1987) 385]. The effect of the yield stress value and shear-thinning index on the kinematic field and drag exerted on the cylinder were explored systematically. The location, dimension and kinematics of the rigid zones were determined. The results are compared with available theoretical data.

Journal ArticleDOI
TL;DR: A thermomechanical fatigue life prediction model based on the theory of damage mechanics is presented in this article, where the damage evolution, corresponding to the material degradation under cyclic thermOMEchanical loading, is quantified thermodynamic framework.
Abstract: A thermomechanical fatigue life prediction model based on the theory of damage mechanics is presented. The damage evolution, corresponding to the material degradation under cyclic thermomechanical loading, is quantified thermodynamic framework. The damage, as an internal state variable, is coupled with unified viscoplastic constitutive model to characterize the response of solder alloys. The damage-coupled viscoplastic model with kinematic and isotropic hardening is implemented in ABAQUS finite element package to simulate the cyclic softening behavior of solder joints. Several computational simulations of uniaxial monotonic tensile and cyclic shear tests are conducted to validate the model with experimental results. The behavior of an actual ball grid array (BGA) package under thermal fatigue loading is also simulated and compared with experimental results. @DOI: 10.1115/1.1536171# With the increasing use of surface mount bonding technology in microelectronics industry, the reliability concerns for solder joints are increasing exponentially. Eutectic solder alloys are most commonly used bonding materials in electronic packaging, which provide electrical and thermal interconnection, as well as mechanical support. The temperature fluctuations due to device internal heat dissipation and ambient temperature changes, along with the coefficient of thermal expansion ~CTE! mismatch between the soldered layers, result in thermo-mechanical fatigue of the solder joints. Progressive damage in solder balls eventually leads to device failure. Fatigue life prediction of solder joints is critical to the reliability assessment of electronic packaging. Standard state of practice in the electronic industry for the number of cycles to failure prediction is based on using empirical relations, such as Coffin-Manson approach. Typically, using the CTE differential between the bonded components, the maximum elastic and plastic strain in the solder joint is calculated. Most of the time, using the plastic strain value, Coffin-Manson curves are used to predict the fatigue life of solder joints. Usually this approach yields very conservative results for BGA packages, Zhao et al. @1#. Recently, numerous physics-of failure based models have been developed for the evaluation of reliability of solder alloys under thermo-mechanical fatigue loading, such as Busso

Journal ArticleDOI
TL;DR: In this article, a general framework for the analysis of heterogeneous media that assesses a strong coupling between viscoplasticity and anisotropic viscodamage evolution is formulated for impact related problems within the framework of thermodynamic laws and nonlinear continuum mechanics.
Abstract: A general framework for the analysis of heterogeneous media that assesses a strong coupling between viscoplasticity and anisotropic viscodamage evolution is formulated for-impact related problems within the framework of thermodynamic laws and nonlinear continuum mechanics. The proposed formulations include thermo-elasto-viscoplastici- ty with anisotropic thermo-elasto-viscodamage, a dynamic yield criterion of a von Mises type and a dynamic viscodamage criterion, the associated flow rules, non-linear strain hardening, strain-rate hardening, and temperature softening. The constitutive equations for the damaged material are written according to the principle of strain energy equivalence between the virgin material and the damaged material. That is, the damaged material is modeled using the constitutive laws of the effective undamaged material in which the nominal stresses are replaced by the effective stresses. The evolution laws are impeded in a finite deformation framework based on the multiplicative decomposition of the deformation gradient into elastic, viscoplastic, and viscodamage parts. Since the material macroscopic thermomechanical response under high-impact loading is governed by different physical mechanisms on the macroscale level, the proposed three-dimensional kinematical model is introduced with manifold structure accounting for discontinuous fields of dislocation interactions (plastic hardening), and crack and void interactions (damage hardening). The non-local theory of viscoplasticity and viscodamage that incorporates macroscale interstate variables and their higher-order gradients is used here to describe the change in the internal structure and in order to investigate the size effect of statistical inhomogeneity of the evolution-related viscoplasticity and viscodamage hardening variables. The gradients are introduced here in the hardening internal state variables and are considered to be independent of their local counterparts. It also incorporates the thermomechanical coupling effects as well as the internal dissipative effects through the rate-type covariance constitutive structure with a finite set of internal state variables. The model presented in this paper can be considered as a framework, which enables one to derive various non-local and gradient viscoplasticity and viscodamage theories by introducing simplifying assumptions.

Journal ArticleDOI
Laszlo S. Toth1
TL;DR: In this paper, the evolution of texture in Equal Channel Angular Extrusion (ECAE) is discussed in detail, and a more precise flow field which uses an analytical flow function is proposed.
Abstract: The majority of the techniques of severe plastic deformation calls for simple shear deformation mode. This is why a special interest is given in this paper to textures that develop in simple shear. The evolution of texture in Equal Channel Angular Extrusion (ECAE) is also discussed in detail. The classical “simple shear model” of ECAE is examined as well as a new, more precise flow field which uses an analytical flow function. The proposed function is inspired from finite element calculations. The velocity gradient that follows from the analysis is incorporated into the self consistent viscoplastic polycrystal code. The evolution of deformation texture is predicted up to two passes in the A-route ECAE deformation of copper polycrystal when the extrusion angle is 90°.

Journal ArticleDOI
TL;DR: In this article, a non-linear viscoelastic viscoplastic model is proposed for the tensile behaviour of aramid fibres, based on an analysis of the deformation mechanism of these materials.
Abstract: A non-linear viscoelastic viscoplastic model is proposed for the tensilebehaviour of aramid fibres, based on an analysis of the deformationmechanisms of these materials. This model uses the macroscopicformulation developed by Schapery together with the plasticity conceptof Perzyna. A simple identification procedure for the model parametershas been developed using creep/recovery cycles at different load levels.The identification reveals that two of the four parameters of theviscoelastic model (g 1 and a σ) are independent of stresslevel. This may be due to the simple and regular nature of the fibrestructure. The model enables the parameters which characterise thenon-linear reversible viscoelasticity to be identified independentlyfrom those which characterise the viscoplasticity. The model predictionsare compared to experimental data for a more complex load sequence andreasonable correlation is obtained.

Journal ArticleDOI
TL;DR: In this paper, three different assumptions for averaging the single crystal responses over the polycrystal were used: a Taylor hypothesis, a self-consistent viscoplastic model, and a finite element methodology.

Journal ArticleDOI
TL;DR: In this article, the authors check the validity of the time-temperature superposition principle for hot-mix asphalt (HMA) with growing damage and viscoplastic strain in the compression state.
Abstract: The objective in this study was to check the validity of the time-temperature superposition principle for hot-mix asphalt (HMA) with growing damage and viscoplastic strain in the compression state, which is essential for the permanent deformation characterization of HMA. Constant crosshead rate compression tests were conducted at temperatures between 25° and 55°, and data were analyzed to construct the stresslog reduced-time master curves for various strain levels. Research results indicate that HMA with growing damage remains thermorheologically simple in the temperature range used in this study and that the time-temperature shift factor is only a function of temperature and is independent of the strain level. Two types of tests, the repeated creep and recovery test and the cyclic sinusoidal loading test, were performed in this study to validate the time-temperature superposition in loading histories commonly used in asphalt mixture testing. The results further confirm that the time-temperature superposi...

Journal ArticleDOI
TL;DR: In this paper, a phenomenological viscoplastic model based on thermodynamics has been extended for material behavior that deviates from classical metal plasticity by including all three stress invariants in the threshold function.

Journal ArticleDOI
TL;DR: In this paper, an approximate analytical dispersion relationship for elastic-plastic acceleration-driven instability growth is presented, where the accelerated solid behaves like a viscoplastic after its elastic yield strength is exceeded, with the viscosity inversely proportional to the strain rate.
Abstract: We present an approximate analytical dispersion relationship for elastic–plastic acceleration-driven instability growth. In this model, the accelerated solid behaves like a viscoplastic after its elastic yield strength is exceeded, with the viscosity inversely proportional to the strain rate. We have applied this model, or a 1993 model of shock-driven viscous instability growth, where applicable, to perturbation growth measurements made in three separate types of experiments: High-explosive (HE)-driven planar Al plates, HE-driven implosions of steel cylinders, and planar Al foils driven indirectly by Lawrence Livermore National Laboratory’s Nova laser. We have also compared the analytical modeling of these experiments with simulations done with a two-dimensional Lagrangian radiation-hydrodynamics computer code containing an elastic–plastic constitutive model. We find that for the moderate strain rates of the HE experiments, the simulations and analytical modeling of perturbation growth agree with each oth...

Journal ArticleDOI
TL;DR: In this paper, a comparison of five different material models applied to the simulation of a combined welding and heat treatment process for a fabricated martensitic stainless steel component is presented, where the simulation is performed early in the product development process and more sophisticated models are used to obtain more accurate predictions of deformations and residual stresses.

Journal ArticleDOI
TL;DR: In this article, a unified non-linear kinematic hardening model for nickel-based superalloy, waspaloy, is described using a unified constitutive model representing plasticity and creep using a single inelastic strain variable within the same set of equations.

Journal ArticleDOI
TL;DR: Schapery's nonlinear viscoelastic, viscoplastic material model was used to characterize the inelastic response of glass fiber epoxy composite (Vicotex NVE 913/28%/192/EC9756 300MM produced by HEXCEL Composites Ltd) as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, a phenomenological model for the evolution of the elastic and viscoplastic properties of cubic polycrystals was developed, which predicts the axial effects in torsion experiments.

Journal ArticleDOI
TL;DR: In this article, a constitutive model for the time and rate-dependent responses of a semicrystalline polymer at isothermal deformation with small strains is derived, where a polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical cross-links and lamellar blocks).

Journal ArticleDOI
TL;DR: In this paper, a generalized material model is presented for inelastic materials incorporating classical elastic, viscoelastic, plastic and viscoplastic material description, all operating in the finite strain regime.
Abstract: This work is concerned with the computational modelling of non‐linear solid material behaviour in the finite strain regime. Based on the recent computational formulations for modelling of inelastic material behaviour, a generalized material model is presented for inelastic materials incorporating classical elastic, viscoelastic, plastic and viscoplastic material description, all operating in the finite strain regime. The underlying rheological model corresponds to the combined action of several rheological components, such as Hooke, Maxwell and Prandtl elements, arranged in parallel. This work summarizes the theoretical basis of the material model and presents the computational treatment in the framework of a finite element solution procedure. Numerical examples are provided to illustrate the scope of the described computational strategy.

Journal ArticleDOI
TL;DR: In this article, a viscoplastic constitutive model is proposed that can reproduce both strain rate dependence of natural soft clay behaviour and destruction processes (DPs) induced by strain or stress increments.
Abstract: A viscoplastic constitutive model is proposed that can reproduce both strain rate dependence of natural soft clay behaviour and destruction processes (DPs) induced by strain or stress increments. The model tracks changes in the yield locus from the initial position (INYL), which reflects the presence of metastable structures, to the intrinsic position (IRYL), which represents structurally stable conditions, where DPs are almost complete. The model is able to simulate in oedometric conditions Bjerrum's 1967 framework, and makes a clear distinction between the vertical effective yield stress, σ′vy, above which significant irrecoverable time-dependent strains are irreversibly activated, and the preconsolidation pressure, σ′vp, from Casagrande's construction, helping to avoid possible sources of error in consolidation settlement predictions. Notwithstanding some simplifications, the model fits well the experimental results of oedometric tests on a natural soft clay with distinct σ′vy and σ′vp for which viscop...