Plastic Flow Model Research Articles

Extension of Flow Behaviour and Damage Models for Cast Iron Alloys with Strain Rate Effect

Cast iron alloys with low production cost and quite good mechanical properties are widely used in the automotive industry. To study the mechanical behavior of a typical ductile cast iron (GJS-450) with nodular graphite, uni-axial quasi-static and dynamic tensile tests at strain rates of 10−4, 1, 10, 100, and 250 s−1 were carried out. In order to investigate the influence of stress state on the deformation and fracture parameters, specimens with various geometries were used in the experiments. Stress strain curves and fracture strains of the GJS-450 alloy in the strain rate range of 10−4 to 250 s−1 were obtained. A strain rate-dependent plastic flow model was proposed to describe the mechanical behavior in the corresponding strain-rate range. The available damage model was extended to take the strain rate into account and calibrated based on the analysis of local fracture strains. Simulations with the proposed plastic flow model and the damage model were conducted to observe the deformation and fracture process. The results show that the strain rate has obviously nonlinear effects on the yield stress and fracture strain of GJS-450 alloys. The predictions with the proposed plastic flow and damage models at various strain rates agree well with the experimental results, which illustrates that the rate-dependent plastic flow and damage models can be used to describe the mechanical behavior of cast iron alloys at elevated strain rates. The proposed plastic flow and damage models can be used to describe the deformation and fracture analysis of materials with similar properties.

Johnson–Cook yield functions for cyclotetramethylene-tetranitramine (HMX) and cyclotrimethylene-trinitramine (RDX) derived from single crystal plasticity models

High-fidelity constitutive models are critical for accurate meso-scale continuum modeling and prediction of shock initiation of crystalline energetic materials (EMs). While empirically calibrated or atomistic-guided anisotropic elastoplastic models of EM such as cyclotetramethylene-tetranitramine (HMX) and cyclotrimethylene-trinitramine (RDX) capture important micromechanical phenomena (such as dislocation evolution, slip-resistance, and anisotropic elasticity), the computational cost of using anisotropic single-crystal plasticity models can become prohibitive for meso-scale computations of void-collapse and hotspot formation in microstructures. Thermo-mechanically representative, isotropic, pressure, temperature, and rate-dependent material constitutive models are practical alternatives for meso-scale simulations of the shock response of microstructures. To this end, this work constructs physically consistent isotropic plasticity from anisotropic single-crystal plasticity models for HMX and RDX. State-of-the-art crystal plasticity models for HMX and RDX are used to compute the stress states in single crystals oriented in three different directions relative to shocks generated by impact at velocities ranging from 100 to 1000 m/s. Post-shock von Mises stress fields for the three orientations are then used to calibrate the strain-rate hardening coefficient and the reference strain rate for a rate-dependent Johnson–Cook (JC) yield surface model. We compare the pressures and the post-shock von Mises stresses between the JC and the anisotropic models to show that the isotropic computations closely approximate the averaged deformation response of the three different crystal orientations. We then model the interaction of a shock generated by a 500 m/s impact with a 0.5 μm void and show that the pressures and the deviatoric stresses obtained using the isotropic model closely match those computed from anisotropic models for both HMX and RDX. The resulting isotropic J2 plastic flow model for HMX and RDX can be employed to perform meso-scale simulations for energy localization due to shear bands and void collapse in the two materials.

Synthesis of terpolymer from Helianthus annuus (natural oil) and evaluation as pour point depressant and viscosity reducer on Indian crude oil

Pour Point Depressant is introduced to crude oil at ppm level to overcome transportation problem of crude oil because of its complex chemical structure. Synthesized PPDs improve flow property, viscosity and also improve its numerous parameters to improve performance of crude oil. Low molecular weight and high molecular weight, copolymer having better PPD types. In present work, synthesized Terpolymer, from natural source, was formed from the reaction with Helianthus annuus oil and ester of Erucic Acid with various fatty alcohol. It was evaluated for its properties on Indian waxy crude oils, i.e., From Limbodra well. Structure and molecular weight of synthesized polymer was confirmed by Spectral data and Gel permeation chromatography (GPC). Also its effect on crude oil was evaluated by Rheological studies, SARA Analysis, Pour point depressant effect. Cross–polarizing microscopic studies were performed to study changes in morphology of wax crystals in crude oil with and without additive. A zero friction advanced Rheometer AR-500 was used to determine the viscosity by applying Bingham plastic-flow model.

Inception of macroscopic shear bands during hot working of aluminum alloys

Macroscopic shear bands (MSB) may develop during hot working of metallic materials. They are well-understood as a physical manifestation of flow instability, and the processing regimes wherein they form are well-charted. However, the microstructural transitions that occur between the onset of flow instability and MSB inception are not fully understood. In order to elucidate them, several aluminum alloy specimens were subjected to strip testing in a thermomechanical simulator (Gleeble™) at 298 K and 573 K. Prominent MSB were observed along the diagonals of the strip volume of only Aluminum-6 wt% Magnesium alloy specimen deformed at 573 K. Comparing the experimental grain morphology and crystallographic textures with those from plastic flow models revealed that MSB inception occurred only after ∼0.20 homogeneous plane strain deformation. However, classical flow instability was predicted at much smaller strain. This ‘delay’ was explained experimentally by showing that clusters of neighbouring severely deforming, fragmenting, mostly soft-oriented grains gradually developed due to lattice rotations along the specimen diagonals, and that MSB inception corresponded to the formation of a percolating network of such grains spanning the specimen. Further, clear experimental evidence revealed that differential dynamic recovery between hard- and soft-oriented grains was essential for MSB formation.

Formability of blanks from hot-rolled microalloyed steel plate with high yield strength

The increase in the carrying capacity of KAMAZ vehicles necessitates the use of heavyduty hot-rolled thick-sheet rolled products made of microalloyed steels with a high yield strength for the production of sheet stamping. The development of the production of such parts faces problems of ensuring stampability, which requires finding ways to increase it both in the metallurgical and machine-building processing of rolled products. Based on expert assessments of specialists, generalization of production experience, modeling of plastic flow in sheet stamping operations, field experiments, the thinning deformations responsible for the appearance of defective signs (cracks excessive refinement) in stamped parts are estimated. The influence of the parameters of the processed material, workpiece, technology on the deformation of thinning is established, the directions of increasing the stampability on a specific part “Bracket” are shown.

Aqueous drilling fluids systems incorporated with green nanoparticles and industrial spent caustic: Optimum rheology and filtration loss properties

Drilling fluids are one of the most significant components of drilling operations for proper functions including fluid loss reduction into the formation and outstanding rheological properties. The drilling fluids according to environmental regulations and governmental rules have to be friendly to the environment to lessen the negative effects on the environment and improve safety. In the current study, a cost-effective industrial alkali waste (spent caustic) was used as a pH controller along with the environmentally friendly uncoated and Chitosan-coated green magnetite nanoparticles (MNPs) in water-based drilling fluid systems. The study focuses on exploring the impact of the alkali waste compared to the conventional alkali (NaOH) on rheology and filtration loss properties. The flow models of the drilling fluid systems were examined. The results proved that the drilling fluid formulated with polymer-coated green MNPs and waste alkali exhibited higher rheological properties and lower mud cake thickness and filtration volume compared to the reference fluid, thus, the waste alkali could replace NaOH as a pH controller. The flow behavior of new fluids could be described precisely using the Herschel-Bulkley flow model. Whereas, the Bingham plastic flow model described the fluid systems incorporated with uncoated and polymer-coated green NPs and NaOH.

New double surface constitutive model of intermittent plastic flow applied to near 0 K adiabatic shear bands

One of the most interesting phenomena that occur in ductile materials strained in the proximity of absolute zero are the adiabatic shear bands. In the stainless steels, massively used to construct superconducting magnets, their occurrence can be detected by various techniques, including magnetometric methods (feritscope). Formation of adiabatic shear bands is strictly correlated to the occurrence of the intermittent plastic flow (IPF), characteristic of stainless steels strained in liquid or superfluid helium. Evidence for the occurrence of the phase transformation during nucleation and formation of the shear bands in the proximity of absolute zero is for the first time given. The rate of shear bands propagation along the sample as well as the amount of secondary phase is measured. In order to describe the intermittent plastic flow, novel double surface model has been developed. It includes type Huber-Mises-Hencky yield surface, and new recovery surface reflecting the lower bound for the stress oscillations. The yield surface can move and expand due to nonlinear mixed (kinematic and isotropic) hardening, resulting from the phase transformation, whereas, the recovery surface remains constant. The serrations occur between the yield surface and the recovery surface, with the yield surface coming back to its initial position after each serration. Each serration corresponds to formation of single shear band there, where the easy slip planes are available, and the mechanism of anchoring the shear bands by the secondary phase is explained. New double surface model has been correlated to the experimental data and applied to explain stress oscillations during the regular stage of the intermittent plastic flow, when the shear bands gradually cover the gauge length of the sample.

Analytical study of the velocity of the lubricating fluid in the hydrodynamic journal bearing with the effect of centrifugal force for short bearing type

The paper aims to obtain the expression of the velocity of lubricating fluid in the hydrodynamic journal bearings by analytical method. In the classical short-bearing theory, the fluid flow was studied by ignoring the effect of centrifugal force of the lubricating fluid film. However, the self-oscillation of the shaft of high-power motors does not follow the rules in classical hydrodynamic lubrication theory. To explain this phenomenon, a modified form of Reynolds equation, in which the influence of centrifugal force of the lubricant is not ignored, is established. The study aims to establish the modified Reynolds equation by including the effect of centrifugal forces for the case of the short bearing type. Integration of the Navier-Stokes equations, yield the expressions for the components of velocity of the lubricating fluid in the gap. The oil’s pressure in the hydrodynamic journal bearing is obtained by solving the modified Reynolds equation. The numerical results are considered in the case of the stable equilibrium position of the motion of the shaft, i.e. the symmetry axis of the shaft does not move. The plots of the velocity components in the tangential axial direction are displayed too. The theoretical results of a parabolic velocity distribution similar to that of a Newtonian fluid, derived from a Bingham plastic flow model. The flow in the gap, which are obtained by analytical method, are completely consistent with its boundary conditions and its physical properties. Further, with these results, the paper as a lemma to solve the dynamics problem in floating ring bearing with the influence of the centrifugal force of the lubricant

Coupled quantitative modeling of microstructural evolution and plastic flow during continuous dynamic recrystallization

Continuous dynamic recrystallization (cDRX) dominates microstructural evolution during the hot working of metallic materials with high stacking fault energy (SFE), such as aluminum alloys. However, in reality, a lack of quantitative and visual modeling of the process hinders its widespread application in the hot working process. In this study, using a recently developed multilevel cellular automaton (MCA) that integrates the newly established cell switching rules and topology deformation technique, a novel mesoscale MCA-cDRX model was constructed to investigate the evolution of both microstructures and macroscopic mechanical response in the hot working of AA7075 aluminum alloy. By considering the evolution of dislocation density and the orientation angle of the local cells as the primary clues, the plastic flow, recrystallization kinetics, features of subgrain size and high-angle grain boundaries, and influence of initial matrix characteristics on the cDRX mechanism were analyzed. The model predictions are consistent with the experimental data. Quantitative analysis confirms that the incubation time for the initiation of subgrain formation is significantly short. The fine-grain matrix and high initial volume fraction of low-angle grain boundaries can significantly accelerate the progress of cDRX owing to a stronger accumulation of dislocations in the dislocation cell walls through the climb and cross-slip mechanisms in the deformed aluminum alloy. The subgrain size is dependent on the Zener-Hollomon parameter. The developed simulation framework offers an effective means to allow the visualization of the cDRX.

Numerical Analysis of a Laminar Transient Flow of a Pseudo-Plastic Fluid

This study is devoted to a numerical modeling of a transient pseudo plastic fluid flow in an elastic pipe. The set partial equations for both the fluid are derived from the law conservations of mass, momentum and energy for the fluid and Hooke’s law for the wall pipe. The system governing this problem is presented and then solved numerically. The non-Newtonian character behavior of the fluid s modeled by the power law. The coupled method of characteristics, finite differences and Runge Kutta are used for spatial and temporal discretization respec-tively. Some results obtained are in good agreement with those found in the literature.

A free volume-based analytical model for plastic flow in thin-walled silicon structures of lithium-ion batteries

A free volume-based analytical model for plastic flow in thin-walled silicon structures of lithium-ion batteries

Effect of SFE on the evolution of crystallographic texture in Cu-Zn alloys subjected to severe plastic deformation

Within the framework of experimental investigations and computer modeling using the viscoplastic self-consistent (VPSC) model of a material plastic flow, the regularities of preferential orientations formation were established, the proportion of certain texture components was estimated, and existing slip systems (SS) and twinning systems (TS) were identified for equal-channel angular pressing (ECAP) of copper alloys depending on the stacking fault energy (SFE).

A new calculation method of viscoplastic heat production generated by plastic flow of friction stir welding process

Friction stir welding (FSW) is a solid phase welding method. The weld forming and welding quality are related to the heat production generated by plastic flow during FSW process. Therefore, it is of great importance to measure the viscoplastic heat production during FSW process. In this paper, firstly, taking the welding system during quasi-steady state welding stage as a rotary viscosity measuring meter, the relationship between viscous moment and viscosity is deduced. Secondly, the analysis model for plastic flow around welding pin in FSW process is established by applying the principle of fluid dynamics. The relationship between the temperature gradient on the surface of welding pin, the rotation rate of the FSW machine and viscous torque is obtained. Lastly, a new calculation method for viscoplastic heat production in FSW process is proposed with the help of numerical simulation. To verify the validity of the new calculation method, several groups of friction stir welding experiments are carried on. • The welding system during quasi-steady state welding stage is taken as a rotary viscosity measuring meter. • The analysis model for plastic flow around welding pin in FSW process is established. • A calculation method only related to rotation rate for viscoplastic heat is proposed.

Conceptual Progress for Explaining and Predicting Self-Organization on Anodized Aluminum Surfaces.

Over the past few years, researchers have made numerous breakthroughs in the field of aluminum anodizing and faced the problem of the lack of adequate theoretical models for the interpretation of some new experimental findings. For instance, spontaneously formed anodic alumina nanofibers and petal-like patterns, flower-like structures observed under AC anodizing conditions, and hierarchical pores whose diameters range from several nanometers to sub-millimeters could be explained neither by the classical field-assisted dissolution theory nor by the plastic flow model. In addition, difficulties arose in explaining the basic indicators of porous film growth, such as the nonlinear current–voltage characteristics of electrochemical cells or the evolution of hexagonal pore patterns at the early stages of anodizing experiments. Such a conceptual crisis resulted in new multidisciplinary investigations and the development of novel theoretical models, whose evolution is discussed at length in this review work. The particular focus of this paper is on the recently developed electroconvection-based theories that allowed making truly remarkable advances in understanding the porous anodic alumina formation process in the last 15 years. Some explanation of the synergy between electrode reactions and transport processes leading to self-organization is provided. Finally, future prospects for the synthesis of novel anodic architectures are discussed.

Development of a Mathematical Model for a Workpiece Heating and Cooling in a Protective Medium while Treatment under Pressure

The paper reviews and develops the mathematical model of plastic flow during the hot-forming processes. A flat non-stationary temperature problem for a cross-section of a long solid (rolled product) of arbitrary shape with different heat transfer conditions along the perimeter of the cross-section was considered. Equations for calculation of the thermal conductivity coefficient and heat capacity of tungsten billets were obtained in the temperature range of 700 - 1500°C, based on the literature data. Analytical dependences in form of regression equations were obtained, allowing for computer calculations of physical specifications of 11x11 mm VA grade tungsten billets in form of temperature functions with accuracy sufficient for practical calculations.

(Invited) Recent Advances in the Modeling of ZnSySe1-y / GaAs (001) Heterostructures with Application to Dislocation Sidewall Gettering

In this talk we will describe state-of-the-art approaches to the modeling of strain relaxation and dislocations in ZnSySe1-y/GaAs (001) heterostructures, with applications to dislocation sidewall gettering (DSG) in devices. Current modeling approaches are based on the extension of the original Dodson and Tsao plastic flow model [B. W. Dodson and J. Y. Tsao, Appl. Phys. Lett., 51, 1325 (1987); Appl. Phys. Lett., 52, 852 (1988)] to include compositional grading and multilayers, dislocation interactions, and differential thermal expansion. Important recent breakthroughs have greatly enhanced the utility of these modeling approaches in three respects: i) pinning interactions have been included in graded and multilayered structures, providing a better description of the rate of strain relaxation as well as the limiting strain; ii) a refined model describing the interaction length for dislocation-dislocation interactions was formulated to include jogging in compositionally-graded and step-graded layers; and iii) inclusion of back-and-forth weaving of dislocations provides a more accurate description of heterostructures containing strain reversals, such as strained-layer superlattices or overshoot graded layers. We will describe these three key advances and use reasonable estimates of the kinetic parameters for ZnSySe1-y to explain and illustrate practical features of dislocation sidewall gettering in II-VI heterostructures.

(Invited) Recent Advances in the Modeling of ZnSySe1-y / GaAs (001) Heterostructures with Application to Dislocation Sidewall Gettering

In this paper we describe state-of-the-art approaches to the modeling of strain relaxation and dislocations in ZnSSe/GaAs (001) heterostructures, with applications to dislocation sidewall gettering (DSG) in devices. Current modeling approaches are based on the extension of the original Dodson and Tsao plastic flow model [B. W. Dodson and J. Y. Tsao, Appl. Phys. Lett., 51, 1325 (1987); Appl. Phys. Lett., 52, 852 (1988)] to include compositional grading and multilayers, dislocation interactions, and differential thermal expansion. Important recent breakthroughs have greatly enhanced the utility of these modeling approaches in three respects: i) pinning interactions have been included in graded and multilayered structures, providing a better description of the rate of strain relaxation as well as the limiting value; ii) a refined model describing the interaction length for dislocation-dislocation interactions was formulated to include jogging in compositionally-graded and step-graded layers; and iii) inclusion of back-and-forth weaving of dislocations provides a more accurate description of heterostructures containing strain reversals, such as strained-layer superlattices or overshoot graded layers. We will describe these three key advances and use reasonable estimates of the kinetic parameters for ZnSSe to explain and illustrate practical features of dislocation sidewall gettering in II-VI heterostructures.

Mechanical Properties Test of Butt Welds of Corroded Q690 High Strength Steel under the Coupling of Damp-heat Cycle Dipping

In order to study the mechanical property degradation rule of butt welds of Q690 high strength steel in the marine environment, high strength steel specimens under different corrosion cycles were obtained through indoor artificial acceleration tests, and uniaxial tensile and cyclic loading tests were performed to analyze the different degrees of corrosion affects the Elastic Modulus, yield strength, ductility, and hysteretic energy dissipation performance of the specimen. Based on the secondary plastic flow model and the Ramberg-Osgood model, a constitutive model for butt welds of corroded Q690 high strength steel was established. The results show that with the increase of the corrosion cycle, reddish-brown layered rust products are formed on the surface of the steel, and the metal luster is basically lost. The size of the pits continues to increase, and the maximum depth reaches 440 μm at 100 days of corrosion. Under the action of unidirectional tensile load, the yield strength and elastic modulus of the test specimens decreased by 8.28% and 7.8% after 100 days of corrosion. Based on the quadratic plastic flow model, the stress-strain curve was fitted. The curve shape parameters k1 and k2 were reduced by 26.5% and 19.3%, respectively. Under reciprocating load, the hysteresis energy of the test piece after 100d corrosion was reduced by 10.2%, the cyclic strengthening coefficient K’ and the cyclic strengthening index n’ were reduced by 13.4% and 37.3%, respectively. The research provided basic data and theoretical basis for the mechanical property degradation and reliability evaluation of high strength steel in the low-lying areas of the ocean.

Discontinuous plastic flow in stainless steels subjected to combined loads at extremely low temperatures

In the present paper, the question of the mechanism of discontinuous plastic flow (DPF) occurring at extremely low temperatures (in the proximity of absolute zero), is for the first time raised in the context of kinematically controlled combined loads (independent control of displacement and rotation) and non-proportional loading paths. In order to identify the multiaxial stress state during DPF, a unique set-up for testing tubular samples under kinematically controlled traction and torsion in liquid helium (4.2 K) has been developed. The results of tests performed on grade 304 stainless steel thin-walled tubular samples subjected to combined loads (traction and torsion) in the proximity of absolute zero are for the first time reported. These novel results confirm the assumptions accepted when building the multiaxial constitutive model of discontinuous plastic flow, namely, the production of lattice barriers, the pile-ups of dislocations and the criterion of their collective failure, as well as the assumption that the serrations may be recorded by force and torque transducers independently. Thus, the numerically implemented model allows to reproduce the observed serrations, and to redistribute them between the loading directions.

Plasticity: from Crystal Lattice to Macroscopic Phenomena

New representations concerning plasticity physics in crystals are discussed. The model of plastic flow is suggested, which can describe its main regularities. With the use of the experimental investigation, it is shown that the plastic flow localization plays the role in the evolution of plastic deformation. Obtained data are explained with the application of the principles of nonequilibrium-systems’ theory. The quasi-particle is introduced for the description of plasticity phenomenon. It is established the relation between plasticity characteristics of metals and their position in Periodic table of the elements. A new model is elaborated to address localized plastic-flow evolution in solids. The basic assumption of the proposed model is that the elementary plasticity acts evolving in the deforming of medium would generate acoustic emission pulses, which interact with the plasticity carriers and initiate new elementary shears. As found experimentally, the macrolocalization of plastic flow involves a variety of autowave processes. To address the phenomenon of localized plastic-flow autowaves, a new quasi-particle called ‘autolocalizon’ is introduced; the criterion of validity of the concept is assessed.