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Plastic Flow (plastic + flow)

Distribution by Scientific Domains

Engineering	57%
Polymers and Materials Science	38%

Selected Abstracts

Effects of Temperatures on Inhomogeneous Plastic Flows of a Bulk-Metallic Glass,

ADVANCED ENGINEERING MATERIALS, Issue 11 2008
H. Jiang
The effects of temperatures on plastic flow and shear banding of a bulk-metallic glass in compression were investigated. Temperature significantly affects the plastic-flow and shear-banding behaviors. With increasing temperatures from the ambient, the plastic deformation tends to become homogeneous both in time and space; while decreasing temperature from the ambient, it tends to be less inhomogeneous in time, but more inhomogeneous in space. Plastic flow is related to shear banding. [source]

Image analysis to reveal crack development using a computer simulation of wear and rolling contact fatigue

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 10 2003
D. I. FLETCHER
ABSTRACT Plastic flow of near-surface rail material under contact loading is a feature of rail,wheel contact, and severe flow typically leads to both wear, and the initiation and development of small surface-breaking cracks. This paper presents results from a ratcheting based computer simulation, which has been developed to allow the simultaneous investigation of wear, crack initiation and early crack propagation. To identify repeatably small crack-like flaws, image analysis is applied to the visual representation of the wearing surface generated by the model. This representation shows a good similarity to traditional micrographs taken from sections of worn surfaces. The model clearly reveals the interaction of wear with crack development, processes which are linked because wear truncates surface-breaking cracks, and can completely remove small surface-breaking cracks. [source]

A discrete thermodynamic approach for anisotropic plastic,damage modeling of cohesive-frictional geomaterials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 12 2010
Q. Z. Zhu
Abstract A discrete plastic,damage model is developed for cohesive-frictional geomaterials subjected to compression-dominated stresses. Macroscopic plastic strains of material are physically generated by frictional sliding along weakness planes. The evolution of damage is related to the evolution of weakness planes physically in connection with the propagation of microcracks. A discrete approach is used to account for anisotropic plastic flow and damage evolution, by introducing two stress invariants and one plastic hardening variable for each family of sliding weakness planes. Plastic flow in each family is coupled with damage evolution. The proposed model is applied to typical geomaterials and comparisons between numerical predictions and experimental data are presented. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Effects of Temperatures on Inhomogeneous Plastic Flows of a Bulk-Metallic Glass,

Incremental model for fatigue crack growth based on a displacement partitioning hypothesis of mode I elastic,plastic displacement fields

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007
S. POMMIER
ABSTRACT The mode I displacement field in the near crack tip region is assumed to be depicted by its partition into an elastic field and a plastic field. Then, each part of the displacement field is also assumed to be the product of a reference field, a function of space coordinates only, and of an intensity factor, function of the loading conditions. This assumption, classical in fracture mechanics, enables one to work at the global scale since fracture criteria can be formulated as a function of the stress intensity factors only. In the present case, the intensity factor of the plastic part of the displacement field measures crack tip plastic flow rate at the global scale. On the basis of these hypotheses, the energy balance equation and the second law of thermodynamics are written at the global scale, i.e. the scale of the K-dominance area. This enables one to establish a yield criterion and a plastic flow rule for the crack tip region. Then, assuming a relation between plastic flow in the crack tip region and fatigue crack growth allows an incremental model for fatigue crack growth to be built. A few examples are given to show the versatility of the model and its ability to reproduce memory effects associated with crack tip plasticity. [source]

A discrete thermodynamic approach for anisotropic plastic,damage modeling of cohesive-frictional geomaterials

Numerical simulations of simple shear with non-coaxial soil models

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2006
Yunming Yang
Abstract This paper investigates the effects of a non-coaxial model on simulated stress,strain behaviour of granular materials subject to simple shearing under various initial conditions. In most cases, a significant difference of predictions between coaxial and non-coaxial modelling is found during the early stage in shearing. With the increase in shearing, non-coaxial simulations approach and tend to coincide with coaxial simulations. It is also found that the roles of non-coaxial modelling in simulating simple shear behaviour are considerably influenced by hardening rules, flow rules, initial static lateral pressure coefficients. In some cases, the non-coaxial modelling gives a similar simulation as the coaxial modelling. In other cases, the non-coaxial modelling decreases the hardening response or softening response of materials, compared with the coaxial modelling. Under certain conditions, the predicted peak strength of materials with non-coaxial modelling is larger than that for coaxial modelling. Some of these observations can be attributed to the amount of principal stress rotation in various cases analysed. Others can be attributed to the difference between the directions of the non-coaxial plastic flow and those for coaxial plastic flow. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Incrementalization of a single hardening constitutive model for frictional materials

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 7 2002
P. V. Lade
Abstract The governing equations for an elasto-plastic constitutive model for frictional materials such as soil, rock, and concrete are presented, and the incremental form is indicated in preparation for implementation of the model in a user-defined module for finite element calculations. This isotropic, work-hardening and -softening model employs a single yield surface, it incorporates non-associated plastic flow, and its capability of capturing the behaviour of different types of frictional materials under various three-dimensional conditions has been demonstrated by comparison with measured behaviour, as presented in the literature. The incrementalization procedure is indicated and the resulting equations for the single hardening model are presented together with parameters for a dense sand. Following the implementation of the model, these parameters are used for evaluation of different integration schemes as presented in a companion paper by Jakobsen and Lade (Int. J. Numer. Anal. Meth. Geomech. 2002; 26:661). Copyright © 2002 John Wiley & Sons, Ltd. [source]

A note on formulas for localized failure of frictional materials in compression and biaxial loading modes

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 10 2001
Matthias Lambrecht
Abstract The paper investigates aspects of the localization analysis of frictional materials. We derive closed formulas and diagrams for the inclination angle of critical discontinuity surfaces which develop in homogeneous compression and biaxial loading tests. The localization analysis is based on a Drucker,Prager-type elastoplastic hardening model for non-associated plastic flow at small strains, which we represent in spectral form. For this type of constitutive model, general analytical formulas for the so-called critical hardening modulus and the inclination angle of critical discontinuity surfaces are derived for the plane strain case. The subsequent treatment then specializes these formulas for the analysis of compression and biaxial loading modes. The key contribution here is a detailed analysis of plane strain deformation modes where the localized failure occurs after subsequent plastic flow. The derived formulas and diagrams can be applied to the checking of an accompanying localization analysis of frictional materials in finite-element computations. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Computational issues in large strain elasto-plasticity: an algorithm for mixed hardening and plastic spin

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2005
Francisco Javier Montáns
Abstract In this paper an algorithm for large strain elasto-plasticity with isotropic hyperelasticity based on the multiplicative decomposition is formulated. The algorithm includes a (possible) constitutive equation for the plastic spin and mixed hardening in which the principal stress and principal backstress directions are not necessarily preserved. It is shown that if the principal trial stress directions are preserved during the plastic flow (as assumed in some algorithms) a plastic spin is inadvertently introduced for the kinematic/mixed hardening case. If the formulation is performed in the principal stress space, a rotation of the backstress is inadvertently introduced as well. The consistent linearization of the algorithm is also addressed in detail. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Finite volume method for simulation of extrusion processes

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2005
H. Ba
Abstract In this paper, the development of a finite volume method for prediction of plastic flow of metals during cold and hot extrusion processes is described. The method solves the equations governing mass, momentum and heat balance in their integral form, using discretization elements of an arbitrary polyhedral shape. Comparisons of the numerical and experimental results show a very good agreement, implying that the proposed numerical method can be used as a useful tool in designing extrusion processes. Copyright © 2005 John Wiley & Sons, Ltd. [source]

A novel approach to the analysis of distributed shear banding in polymer blends

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003
K. G. W. Pijnenburg
Abstract The toughness of glassy polymers can be enhanced by blending with rubber particles. The consensus is that this toughening is due to massive plastic deformation of the matrix that takes place once the particles have cavitated. Micromechanical studies of regular stackings of particles in a polymer matrix have provided much insight into the localized plastic flow in blends at the microscale of individual particles (or voids, once cavitated). Even some steps towards macroscopic constitutive models have been made. However, at intermediate length scales (i.e. larger than several particles, but smaller than the scale at which the material may be regarded as homogeneous) the situation is unclear. It is this length scale that becomes important around crack tips, for example, where a thorough understanding of the toughening effect has to be derived from. In this paper, we therefore present a novel approach to the analysis of distributed shear banding in polymer,rubber blends. A coarse-grain description, in which much of the morphology is retained but the local shear banding is idealized into ,shear surfaces', will enable us to analyse ensembles with large numbers of particles. The parameters of this model will be validated with results from detailed cell analyses. Copyright © 2003 John Wiley Sons, Ltd. [source]

Non-uniform plastic deformation of micron scale objects

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2003
Christian F. Niordson
Abstract Significant increases in apparent flow strength are observed when non-uniform plastic deformation of metals occurs at the scale ranging from roughly one to ten microns. Several basic plane strain problems are analysed numerically in this paper based on a new formulation of strain gradient plasticity. The problems are the tangential and normal loading of a finite rectangular block of material bonded to rigid platens and having traction-free ends, and the normal loading of a half-space by a flat, rigid punch. The solutions illustrate fundamental features of plasticity at the micron scale that are not captured by conventional plasticity theory. These include the role of material length parameters in establishing the size dependence of strength and the elevation of resistance to plastic flow resulting from constraint on plastic flow at boundaries. Details of the finite element method employed in the numerical analysis of the higher order gradient theory will be discussed and related to prior formulations having some of the same features. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Stabilized finite element method for viscoplastic flow: formulation with state variable evolution

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2003
Antoinette M. Maniatty
Abstract A stabilized, mixed finite element formulation for modelling viscoplastic flow, which can be used to model approximately steady-state metal-forming processes, is presented. The mixed formulation is expressed in terms of the velocity, pressure and state variable fields, where the state variable is used to describe the evolution of the material's resistance to plastic flow. The resulting system of equations has two sources of well-known instabilities, one due to the incompressibility constraint and one due to the convection-type state variable equation. Both of these instabilities are handled by adding mesh-dependent stabilization terms, which are functions of the Euler,Lagrange equations, to the usual Galerkin method. Linearization of the weak form is derived to enable a Newton,Raphson implementation into an object-oriented finite element framework. A progressive solution strategy is used for improving convergence for highly non-linear material behaviour, typical for metals. Numerical experiments using the stabilization method with hierarchic shape functions for the velocity, pressure and state variable fields in viscoplastic flow and metal-forming problems show that the stabilized finite element method is effective and efficient for non-linear steady forming problems. Finally, the results are discussed and conclusions are inferred. Copyright © 2002 John Wiley & Sons, Ltd. [source]

POTENTIAL STRUCTURAL TRAPS ASSOCIATED WITH LOWER CARBONIFEROUS SALT IN THE NORTHERN TARIM BASIN, NW CHINA

JOURNAL OF PETROLEUM GEOLOGY, Issue 1 2004
Jiangyu Zhou
In the Aixieke-Santamu area of the northern Tarim Basin (NW China), 45 relatively low amplitude structures related to the plastic flow of Lower Carboniferous salt have been discovered in the Lower Carboniferous Kalashayi Formation and the Middle-Upper Triassic Akekule and Halahatan Formations. Three small hydrocarbon accumulations have so far been located at the margins of a Lower Carboniferous salt body (measuring about 55km x 75km and 115,225m thick, controlled by wells and 2D and 3D seismic sections). In this paper, we consider the development of this salt body and discuss possible reasons why vertical diapirs are absent from the study area. We attempt to develop a model of salt flow and we investigate the relationship between salt flow and the occurrence of oil and gas traps. Using recently-acquired high-resolution 2D and 3D seismic profiles, we show that the Lower Carboniferous salt has undergone three separate phases of plastic flow. At the end of the Early Permian, the salt flowed southwards by 2.0,2.8 km; then, during the Late Triassic,Early Jurassic, it flowed in the same direction by 1.0,1.8 km; and finally at the end of the Tertiary, it flowed northwards by 0.6,1.5 km. These movements resulted in the formation of various types of structural trap in the Kalashayi, Akekule and Halahatan Formations including salt ridge anticlines, domes and marginal troughs. Salt ridge and salt edge low-amplitude anticlines are probably the most important targets for future hydrocarbon exploration. [source]

Mechanically Stable Monoclinic Zirconia,Nickel Composite

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2002
José S. Moya
A dense (>98% theoretical density), residual-stress-free m-ZrO2/40 vol% nickel composite with K IC, 5.4 MPa·m1/2 and ,f, 225 MPa has been obtained using a simple wet processing route and subsequent sintering at 1430°C in a 90% argon/10% hydrogen atmosphere. The mechanism for release of internal stresses by the composite developed during the t , m transformation on cooling is explained in terms of plastic flow in the infinite nickel cluster formed at the percolation threshold. [source]

Lubricants under high local pressure: Liquids act like solids

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 10-11 2004
M. H. MüserArticle first published online: 21 OCT 200
Schmierstoff; Druck; plastisches Fliessen; Reibungsgesetz Abstract A lubricant layer solidifies when it is confined between two walls at large normal pressures. The atomic scale motion that occurs when the two confining surfaces slide past each other induces flow in the lubricant layer that is akin of plastic flow. This results in friction-velocity relationships similar to Coulomb's law of friction. Moreover, the lubricant layer does not necessarily melt, even when the two solids are in stick slip motion. In this paper, atomic-scale details of the plastic flow mechanism are investigated by means of molecular dynamics simulations. Schmierstoffe unter hohem lokalem Druck: Flüssigkeiten verhalten sich wie Feststoffe Eine molekular dünne Schicht Schmierstoff verfestigt sich, wenn sie zwischen zwei Festkörpern großen Drücken ausgesetzt ist. Die atomaren Bewegungsmechanismen, die in dem Schmierstofffilm auftreten, wenn die Festkörper gegeneinander verschoben werden, können als plastisches Fliessen verstanden werden. Dieser Mechanismus führt zu einer Kraft-Geschwindigkeitsrelation, die dem Coulomb'schen Reibungsgesetz ähnlich ist. Selbst wenn die beiden Wände in Stick-Slip Bewegung sind, verflüssigt sich der Schmiermittelfilm nicht automatisch. In dieser Arbeit werden die Details des angesprochenen plastischen Fliessens anhand von Molekular-Dynamik Simulationen im Detail untersucht. [source]

Verschleißmechanismen bei moderater und extremer Grenzreibung

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 10-11 2004
M. Scherge
wear mechanisms; continuous wear measurement; surface analysis Abstract Mit einem Stift-Scheibe-Tribometer wurden für das System Stahlstift/Stahlscheibe Versuche durchgeführt, die drastisch unterschiedliche Verschleißraten zur Folge hatten. Durch Wahl der Normalkraft wurde die Energiedissipation so eingestellt, dass im ersten Versuch Verschleißraten in der Größenordnung von Nanometern pro Stunde erreicht wurden, während im zweiten Versuch Mikrometer pro Stunde erzielt wurden. Die Proben wurden nach dem Experiment hinsichtlich Struktur und chemischer Zusammensetzung analysiert. Im Bereich der kleinen Verschleißraten dominierten plastisches Fließen und mechanische Vermischung während die hohen Verschleißraten mit starker Topographieänderung und Oxidation einher gingen. Wear mechanisms at moderate and extreme friction conditions Using a pin-on-disk tribometer drastically different wear rates were obtained in experiments running a steel pin against a steel disk. By tuning the normal force the energy dissipation was varied resulting in either mild wear in the range of nanometers per hour or severe wear with a wear rate of micrometers per hour. After the tribological tests the samples were analyzed with respect to structure and chemical composition. Whereas small wear rates are accompanied by plastic flow and mechanical intermixing, severe wear results in significant topography changes and oxidation. [source]

Optimal transportation meshfree approximation schemes for fluid and plastic flows

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2010
B. Li
Abstract We develop an optimal transportation meshfree (OTM) method for simulating general solid and fluid flows, including fluid,structure interaction. The method combines concepts from optimal transportation theory with material-point sampling and max-ent meshfree interpolation. The proposed OTM method generalizes the Benamou,Brenier differential formulation of optimal mass transportation problems to problems including arbitrary geometries and constitutive behavior. The OTM method enforces mass transport and essential boundary conditions exactly and is free from tension instabilities. The OTM method exactly conserves linear and angular momentum and its convergence characteristics are verified in standard benchmark problems. We illustrate the range and scope of the method by means of two examples of application: the bouncing of a gas-filled balloon off a rigid wall; and the classical Taylor-anvil benchmark test extended to the hypervelocity range. Copyright © 2010 John Wiley & Sons, Ltd. [source]