Showing papers on "Viscoplasticity published in 2015"
TL;DR: In this paper, a new Johnson-Cook (JC) constitutive model of 7075-T6 aluminum alloy was obtained by modifying the strain rate hardening term in the Johnson-Coughlin model.
182 citations
TL;DR: In this paper, a model of dry granular flows is proposed that quantitatively reproduce laboratory experiments of granular column collapse over inclined planes, and the rheological parameters are directly derived from the experiments.
Abstract: A mechanical and numerical model of dry granular flows is proposed that quantitatively reproduce laboratory experiments of granular column collapse over inclined planes. The rheological parameters are directly derived from the experiments. The so-called μ ( I ) rheology is reformulated in the framework of Drucker–Prager plasticity with the yield stress and viscosity η ( ‖ D ‖ , p ) depending on both the pressure p and the norm of the strain rate tensor ‖ D ‖ . The granular domain, velocities, stress deviator and pressure fields are calculated using a finite element method based on an iterative decomposition–coordination formulation coupled with the augmented Lagrangian method. 2-D simulations using this model well reproduce the dynamics and deposits of collapsing granular columns. The flow is essentially located in a surface layer behind the front, whereas it is distributed over the whole depth near the front where basal sliding occurs. The computed runout distances and slopes of the deposits agree very well with the values found in the experiments. Using an easily calculated order of magnitude approximation of the mean viscosity during the flow ( η = 1 Pa s here), we show that a Drucker–Prager rheology with a constant viscosity gives results very similar to the μ ( I ) rheology and agrees with experimental height profiles, while significantly reducing the computational cost. Within the range of viscosities 0.1 η 1 Pa s, the dynamics and deposits are very similar. The observed slumping behavior therefore appears to be mainly due to the flow/no-flow criterion and to the associated strain-independent part of the “flowing constitutive relation” (i.e. related to plastic effects). However, the results are very different when an unrealistically large value of viscosity (10 Pa s) is used.
127 citations
TL;DR: In this paper, the mechanical anisotropy of an AA1050 aluminium plate was studied by the use of five crystal plasticity models and two advanced yield functions, and the results were compared with data from tensile tests at every 15° from the rolling direction (RD) to the transverse direction (TD) in the plate.
127 citations
TL;DR: In this article, the time-independent and time-dependent mechanical behavior of electrochemically lithiated silicon was studied with nanoindentation, and the results indicated that Young's modulus of the fully lithiated phase is in fact somewhat larger than reported in some other studies.
115 citations
17 Apr 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a modified Johnson-Cook model was proposed to describe the flow behaviors of the studied alloy based on the correction to the strain rate hardening coefficient, which is a function of strain and strain rate from the tensile experimental results.
Abstract: The uniaxial quasi-static and dynamic tensile tests were conducted at different strain rates (10–3 s−1, 800 s−1, 1900 s−1 and 2900 s−1) for 7050-T7451 aluminum alloy. Then, research of the strain rate hardening coefficient in the original Johnson–Cook model at different strains and strain rates showed that the coefficient is a function of strain and strain rate from the tensile experimental results. Furthermore, a modified Johnson–Cook model was proposed to describe the flow behaviors of the studied alloy based on the correction to the strain rate hardening coefficient. Comparisons between the experimental data and predicted results using the original JC model, Khan–Liu (KL) model and the modified JC model showed that a better agreement can be obtained applying the modified model than the other two models. Verifications for predicting three new high strain rates (1500 s−1, 2500 s−1 and 3500 s−1) experimental data demonstrated the modified JC model can provide an accurate description for the dynamic behaviors of the studied alloy.
109 citations
TL;DR: In this article, the authors derived constitutive equations based on the original Johnson-Cook (JC) model, modified JC model, Arrhenius model, and strain compensated Arrhensius model for homogenized 6026 aluminum alloy under wide range of deformation temperatures and strain rates.
107 citations
TL;DR: In this article, a new anisotropic elastic viscoplastic model is proposed by adopting the concept of anisotropy and isotropy processes, and the determination of model parameters can be determined in a straightforward way requiring the same basic tests as for the Modified Cam Clay model.
Abstract: This paper focuses on the rate-dependent yield stress, undrained strength, and long-term undrained strength of clay. Various oedometer and triaxial tests were performed on Wenzhou marine clay. The uniqueness of rate-dependent and long-term yield stress and strength is discussed. A new anisotropic elastic viscoplastic model is proposed by adopting the concept of anisotropy and isotropy processes. The determination of model parameters is discussed, demonstrating how all model parameters can be determined in a straightforward way requiring the same basic tests as for the Modified Cam Clay model. Experimental verifications are carried out using the constant strain-rate and creep tests on the Wenzhou marine clay.
105 citations
TL;DR: In this article, the effects of hot deformation parameters (deformation temperature and strain rate) on flow stress are analyzed, and it is found that the flow stress of the Ni-based superalloy is significantly affected by deformation temperature.
96 citations
TL;DR: In this paper, the authors apply a phenomenological higher-order theory of distortion gradient plasticity to the torsion problem, here assumed as a paradigmatic benchmark of small-scale plasticity.
Abstract: Under small strains and rotations, we apply a phenomenological higher-order theory of distortion gradient plasticity to the torsion problem, here assumed as a paradigmatic benchmark of small-scale plasticity. Peculiar of the studied theory, proposed about ten years ago by Morton E. Gurtin, is the constitutive inclusion of the plastic spin, affecting both the free energy and the dissipation. In particular, the part of the free energy, called the defect energy, which accounts for Geometrically Necessary Dislocations, is a function of Nye's dislocation density tensor, dependent on the plastic distortion, including the plastic spin. For the specific torsion problem, we implement this distortion gradient plasticity theory into a Finite Element (FE) code characterised by implicit (Backward Euler) time integration, numerically robust and accurate for both viscoplastic and rate-independent material responses. We show that, contrariwise to other higher-order theories of strain gradient plasticity (neglecting the plastic spin), the distortion gradient plasticity can predict some strengthening even if a quadratic defect energy is chosen. On the basis of the results of many FE analyses, concerned with (i) cyclic loading, (ii) switch in the higher-order boundary conditions during monotonic plastic loading, (iii) the use of non-quadratic defect energies, and (iv) the prediction of experimental data, we mainly show that (a) including the plastic spin contribution in a gradient plasticity theory is highly recommendable to model small-scale plasticity, (b) less-than-quadratic defect energies may help in describing the experimental results, but they may lead to anomalous cyclic behaviour, and (c) dissipative (unrecoverable) higher-order finite stresses are responsible for an unexpected mechanical response under non-proportional loading.
96 citations
TL;DR: The role of microplasticity effects was additionally explored using a Continuum Dislocation Dynamics Viscoplastic Self-Consistent (CDD-VPSC) model for the first two cycles of the fatigue life.
94 citations
TL;DR: In this article, a multiscale modeling strategy is presented to determine the effective mechanical properties of polycrystalline Ni-based superalloys by computational homogenization of a representative volume element of the microstructure which was built from the grain size, shape and orientation distributions of the material.
TL;DR: In this article, the authors present numerical simulations of punching shear in a reinforced concrete slab-column configuration, using two damage plasticity models; one implemented in FEAP and the second from ABAQUS.
TL;DR: In this paper, the authors show that when the fluid has been cooled at rest it forms a structure that irreversibly collapses during the startup flow, and that the evolution of the apparent viscosity mainly depends on the deformation undergone by the fluid for low or moderate deformation and starts to significantly depend on the shear rate for larger values.
Abstract: The solidification of waxy components during the cool down of waxy crude oils in pipelines may provide complex yield stress fluid behavior with time-dependent characteristics, which has a critical impact for predicting flow restart after pipeline shut-in. Here, from a previous set of data at a local scale with the help of Magnetic Resonance Imaging and a new full set of data for various flow and temperature histories, we give a general picture of the rheological behavior of waxy crude oils. The tests include start flow tests at different velocities or creep tests at different stress levels, abrupt changes of velocity level, steady flow, after cooling under static or flowing conditions. We show that when the fluid has been cooled at rest it forms a structure that irreversibly collapses during the startup flow. Under these conditions, the evolution of the apparent viscosity mainly depends on the deformation undergone by the fluid for low or moderate deformation and starts to significantly depend on the shear rate for larger values. Even the (apparent) flow curve of statically cooled waxy crude oils was observed to be dependent on the flow history, more specifically on the maximum shear rate experienced by the material. After being sufficiently sheared, i.e., achieving an equilibrium state, the rheological behavior is that of a simple liquid for shear rates lower than the maximum historical one. A model is proposed to represent those trends experimentally observed. In contrast with most previous works in that field, the model is built without any a priori assumption based on classical behavior of a class of fluids. Finally, it is shown that this model predicts the flow characteristics of these materials under more complex flow histories (sweep tests, sudden shear rate decrease) much better than the so far most often used (Houska) model.
TL;DR: In this article, the authors present a computationally efficient, multi-scale model based on crystal plasticity theory for simulations of heterogeneous plastic deformation of metallic components in commercial finite element (FE) codes.
TL;DR: In this article, a simple nonlinear creep formulation is proposed accounting for the effect of volumetric packing of soil assemblies, which is then incorporated into a newly developed elastic-viscoplastic model to take into account the non-linear creep of natural soft clays.
Abstract: This paper focuses on nonlinear creep behavior with a consecutively decreasing creep coefficient Cαe fully related to the soil density. Conventional oedometer tests on reconstituted samples of several natural soft clays are selected to clarify the evolution of creep coefficient throughout testing. On this basis, a simple nonlinear creep formulation is proposed accounting for the effect of volumetric packing of soil assemblies. The formulation is then incorporated into a newly developed elastic-viscoplastic model to take into account the nonlinear creep of natural soft clays. One additional parameter is added that can be determined in a straightforward way from an oedometer test without additional experimental cost. The enhanced nonlinear creep model is examined by simulating a conventional oedometer test on reconstituted Haarajoki clay. The improvement of predictions by the nonlinear creep formulation is highlighted by comparing predictions with constant Cαe. The enhanced model is further applied ...
TL;DR: In this article, a semi-empirical approach based on the analysis of convergence measurements and a numerical model that takes into account the time-dependent and the anisotropic response of the rock mass to investigate the squeezing behavior of the Saint-Martin-la-Porte access gallery, excavated within the Lyon-Turin railway project is presented.
Abstract: Most of the viscoplastic models used to describe the constitutive behavior of squeezing grounds assume isotropic deformation. However, it is commonly observed that squeezing behavior is characterized not only by large time-dependent but also often by anisotropic deformations. This study uses a semi-empirical approach based on the analysis of convergence measurements and a numerical model that takes into account the time-dependent and the anisotropic response of the rock mass to investigate the squeezing behavior of the Saint-Martin-la-Porte access gallery, excavated within the Lyon–Turin railway project. We first show how the semi-empirical convergence law of Sulem et al. (Int J Rock Mech Min Sci Geomech Abstr 24(3):155–164, 1987a; Int J Rock Mech Min Sci Geomech Abstr 24(3):145–154, 1987b) can be extended to anisotropic tunnel closure by considering an elliptical deformation of the rock mass and by fitting the convergence data along the principal axes of deformation. A new anisotropic time-dependent constitutive model is then proposed. This model includes ubiquitous joints of specific orientation embedded in an isotropic viscoplastic medium. This model is implemented in FLAC3D and numerical simulations are performed to back-analyze the anisotropic closure of the Saint-Martin-la-Porte access gallery. An efficient two-step procedure for calibrating the model parameters is proposed: the parameters of the isotropic solid matrix are first estimated by performing axisymmetric numerical simulations. The parameters of the ubiquitous joints are then calibrated by performing 3D computations. It is shown that the numerical results reproduce very well the convergence measurements of the studied sections of Saint-Martin-la-Porte gallery.
TL;DR: In this article, the authors investigated the mechanical behavior of multi-phase steels using a continuum dislocation dynamic model (CDD) coupled with a viscoplastic self-consistent (VPSC) model that accounts for both the effect of dislocations evolution inside the grain as well as grain-grain interactions.
TL;DR: In this paper, a viscoplastic self-consistent (VPSC) polycrystal model and a macroscopic plasticity model based on an yield criterion were used to explain and accurately predict the room temperature torsional response of a strongly textured AZ31 Mg material.
TL;DR: In this paper, the authors improved the elastic viscoplastic self-consistent (EVPSC) model by adding thermal strain to allow study of the behavior of a Zircaloy-2 slab under moderately large strains.
TL;DR: In this paper, the dependences of true stress on true strain under dynamic loading for titanium alloys VT6, OT4, OT 4-0 are constructed, and parameters for Johnson-Cook model are determined.
TL;DR: In this paper, a continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading, where the total strain is decomposed into elastic and plastic parts, and an anisotropic hardening law with a kinematic effect is particularly adopted to capture the complex stress-strain hysteresis typically observed in polymeric materials.
Abstract: A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic solid model expressed in terms of Boltzmann hereditary integral form, which is coupled to a rate-dependent viscoplastic formulation to describe the irreversible plastic part of the overall strain. An anisotropic hardening law with a kinematic effect is particularly adopted in order to capture the complex stress–strain hysteresis typically observed in polymeric materials. In addition, the present model accounts for the effects of material densification associated with through-thickness compression, which are captured using an exponential law typically applied in the continuum description of elasticity in porous media. Material parameters used in the present model are calibrated to the experimental data for high-density (press)boards. The experimental characterization procedures as well as the calibration of the parameters are highlighted. The results of the model simulations are systematically analyzed and validated against the corresponding experimental data. The comparisons show that the predictions of the present model are in very good agreement with the experimental observations for both stationary and transient load cases.
TL;DR: In this article, an azobenzene dye-containing polymer (p4VP(DY7)0.50) by nanoindentation shows a significant photo-softening effect under visible irradiation at 532 nm.
Abstract: Mechanical characterization of an azobenzene dye-containing polymer (p4VP(DY7)0.50) by nanoindentation shows a significant photo-softening effect under visible irradiation at 532 nm. Both strong rate-dependent plastic softening, as well as a rate-independent elastic modulus decrease are observed. Indentation at elevated, sub-glass transition temperatures results in only a rate-independent decrease in hardness however. These findings indicate, from a mechanics standpoint, for the first time a distinct mechanism for the photomechanical softening in azo-materials that is different from a simple thermal effect. The main hallmark of the photosoftening effect was significant viscoplastic flow with strong rate dependence. The presence of the viscoplastic softening in azo-polymers was accounted for in analysis of nanoindentation data to obtain an accurate elastic modulus unaffected by the presence of creep in the unloading curves. These results provide considerable insight into the long-observed and long-debated mechanism of all-optical surface patterning below Tg.
TL;DR: In this article, an experimental device was developed to detect and estimate dissipated energy during very high cycle fatigue tests (VHCF) at high loading frequency (20 kHz) and low stress (i.e. far below the yield stress).
Abstract: This paper presents an experimental device developed to detect and estimate dissipated energy during very high cycle fatigue tests (VHCF) at high loading frequency (20 kHz) and low stress (i.e. far below the yield stress). Intrinsic dissipation is computed using local expressions of the heat diffusion equation and thermal data fields provided by an infrared focal plane array camera. The results obtained from tests performed on pure copper specimens show that dissipated energy exists whatever the attainable stress range and show that the dissipated energy rate is not constant throughout the test. Both findings are respectively incompatible with the concepts of fatigue limit based on elastic shakedown or on stabilized cyclic state associated with the mechanical hysteresis loop (viscoplastic shakedown).
TL;DR: Based on the effective stress concept in continuum damage mechanics and the large deformation theory, a viscodamage model, coupled with Schapery-type nonlinear viscoelasticity and Perzyna-type viscoplasticity constitutive models, is used in order to simulate and predict the inelastic and time-dependent damage behavior of polymeric materials and their composites as mentioned in this paper.
Abstract: Based on the effective stress concept in continuum damage mechanics and the large deformation theory, a viscodamage model, coupled with Schapery-type nonlinear-viscoelasticity and Perzyna-type viscoplasticity constitutive models, is used in order to simulate and predict the inelastic and time-dependent damage behavior of polymeric materials and their composites. The thermo-viscodamage model is presented as a function of temperature, total effective strain, damage history, and a damage-driving force expressed in terms of the deviatoric stress invariants in the undamaged configuration. This expression for the damage force allows for the distinction between the influence of compression and extension loading conditions on damage nucleation and growth. Also, the ability of the constitutive model for predicting the tertiary creep, which shows the nonlinear behavior of polymers during damage growth and nucleation, is presented. The numerical algorithm for integrating the coupled constitutive model is implemented...
TL;DR: In this paper, finite element procedures combined with microstructure development modeling are integrated to quantitatively predict the viscoelastic/viscoplastic relaxation of cement paste due to intrinsic calcium silicate hydrate visco-elasticity and micro-structure evolution associated with the hydration process.
Abstract: Finite element procedures combined with microstructure development modeling are integrated to quantitatively predict the viscoelastic/viscoplastic relaxation of cement paste due to intrinsic calcium silicate hydrate viscoelasticity and microstructure evolution associated with the hydration process. The combined models are implemented in a computational routine to predict time-dependent stress and strain fields in cement paste. The model simulations suggest that inherent viscoelastic deformation caused by calcium silicate hydrate is not necessarily the primary mechanism leading to the overall early-age viscoelastic/viscoplastic behavior of cement paste. The effect of time-dependent dissolution of cement grains occurring during the hydration process is substantial and should be considered as a significant mechanism for the apparent viscoelasticity/viscoplasticity of cement paste.
TL;DR: Rate-dependent plasticity is employed to regularize, for the scope of mesh independency, the numerical solution in strain localization process of multiphase geomaterials, and the capabilities and shortcomings of each regularization technique are compared.
Abstract: Summary
In this paper, rate-dependent plasticity is employed to regularize, for the scope of mesh independency, the numerical solution in strain localization process of multiphase geomaterials. Towards this goal, the viscoplastic Duvaut–Lions and the viscoplastic Perzyna models are implemented in an existing finite element code for multiphase porous media. Perzyna's model is then extended according to the non-local approach, allowing for handling weakly rate-sensitive materials for which viscoplasticity is not sufficient to meet numerical requirements. Assuming quasi-static and isothermal conditions, the models are validated and applied in the numerical simulation of an undrained plane strain biaxial compression test on initially water-saturated dense sand taken from the existing literature. An overview of the significant factors such as loading velocity and soil permeability in conjunction with viscosity on the formation of localization pattern is presented. The interaction of the two internal lengths introduced by non-locality and viscosity is also discussed. Finally, the obtained results are analysed and compared emphasizing the capabilities and shortcomings of each regularization technique. Copyright © 2015 John Wiley & Sons, Ltd.
TL;DR: In this article, a cyclic elastoviscoplastic constitutive model for clayey soils is proposed based on the nonlinear kinematic hardening rules and considering the structural degradation.
Abstract: A cyclic elastoviscoplastic constitutive model for clayey soils is proposed based on the nonlinear kinematic hardening rules and considering the structural degradation. The performance of the model is verified through the undrained triaxial test simulation of soft clay samples under cyclic and monotonic loading conditions and the cyclic compression test. The simulated results are compared with the experimental data through stress-strain relations and stress paths. The simulated results have shown a good agreement with the experimental data, which indicates the capability of the proposed model to reproduce the cyclic behavior of soft clayey soils.
TL;DR: In this paper, a new constitutive relation is developed to model the behavior of face-centred cubic polycrystals, especially aluminum alloys, at elevated temperatures, taking into account the temperature dependence of the single crystal elastic coefficients, single slip hardening parameters, thermal softening, rate sensitivity, and the total deformation.
TL;DR: In this paper, a new approach based on the equivalent plastic strain averaged over the impact particle (PEEQ ) was employed to analyze the deformation and a rate parameter REQ, the steady rate of change of PEEQ, was introduced.