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High Rate Plastic Deformation Of Nanocrystalline Tantalum To Large Strains
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Book Synopsis High-rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains by :
Download or read book High-rate Plastic Deformation of Nanocrystalline Tantalum to Large Strains written by and published by . This book was released on 2009 with total page 19 pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent advances in the ability to generate extremes of pressure and temperature in dynamic experiments and to probe the response of materials has motivated the need for special materials optimized for those conditions as well as a need for a much deeper understanding of the behavior of materials subjected to high pressure and/or temperature. Of particular importance is the understanding of rate effects at the extremely high rates encountered in those experiments, especially with the next generation of laser drives such as at the National Ignition Facility. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum to investigate the processes associated with plastic deformation for strains up to 100%. We use initial atomic configurations that were produced through simulations of solidification in the work of Streitz et al [Phys. Rev. Lett. 96, (2006) 225701]. These 3D polycrystalline systems have typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures.
Book Synopsis Plasticity and Failure in Nanocrystalline BCC Metals Via Molecular Dynamics Simulation by :
Download or read book Plasticity and Failure in Nanocrystalline BCC Metals Via Molecular Dynamics Simulation written by and published by . This book was released on 2010 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in the ability to generate extremely high pressures in dynamic experiments such as at the National Ignition Facility has motivated the need for special materials optimized for those conditions as well as ways to probe the response of these materials as they are deformed. We need to develop a much deeper understanding of the behavior of materials subjected to high pressure, especially the effect of rate at the extremely high rates encountered in those experiments. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum at pressures less than 100 GPa to investigate the processes associated with plastic deformation for strains up to 100%. We focus on 3D polycrystalline systems with typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures. We also present some results on void growth in nanocrystalline BCC metals under tension.
Book Synopsis Plasticity and Failure in Nanocrystalline BCC Metals Via MD Simulation by :
Download or read book Plasticity and Failure in Nanocrystalline BCC Metals Via MD Simulation written by and published by . This book was released on 2010 with total page 3 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in the ability to generate extremely high pressures in dynamic experiments such as at the National Ignition Facility has motivated the need for special materials optimized for those conditions as well as ways to probe the response of these materials as they are deformed. We need to develop a much deeper understanding of the behavior of materials subjected to high pressure, especially the effect of rate at the extremely high rates encountered in those experiments. Here we use large-scale molecular dynamics (MD) simulations of the high-rate deformation of nanocrystalline tantalum at pressures less than 100 GPa to investigate the processes associated with plastic deformation for strains up to 100%. We focus on 3D polycrystalline systems with typical grain sizes of 10-20 nm. We also study a rapidly quenched liquid (amorphous solid) tantalum. We apply a constant volume (isochoric), constant temperature (isothermal) shear deformation over a range of strain rates, and compute the resulting stress-strain curves to large strains for both uniaxial and biaxial compression. We study the rate dependence and identify plastic deformation mechanisms. The identification of the mechanisms is facilitated through a novel technique that computes the local grain orientation, returning it as a quaternion for each atom. This analysis technique is robust and fast, and has been used to compute the orientations on the fly during our parallel MD simulations on supercomputers. We find both dislocation and twinning processes are important, and they interact in the weak strain hardening in these extremely fine-grained microstructures. We also present some results on void growth in nanocrystalline BCC metals under tension.
Book Synopsis High-strain, High-strain-rate Deformation of Tantalum by : Yuejian Chen
Download or read book High-strain, High-strain-rate Deformation of Tantalum written by Yuejian Chen and published by . This book was released on 1998 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Dislocation-drag Contribution to High-rate Plastic Deformation in Shock-loaded Tantalum by :
Download or read book Dislocation-drag Contribution to High-rate Plastic Deformation in Shock-loaded Tantalum written by and published by . This book was released on 1993 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Time-resolved plastic waves in plate-impact experiments give information on relation between applied shear stress and plastic strain rate at low plastic strain. This information is different from that obtained at intermediate strain rates using Hopkinson bar techniques, because the material deformation state is driven briefly into the regime dominated by dislocation drag. Two VISAR records of particle velocity at the tantalum/sapphire (window) interface are obtained for symmetric impact producing peak in-situ longitudinal stresses of 75 and 111 kbar. Rise-times of plastic waves are about l00 and 50 ns, respectively, with peak strain rates of about 2 x l05 and 8.5 x l05/s, respectively, as determined by weak-shock analysis. These data show a much stronger dependence of plastic strain rate on applied shear stress than predicted by linear viscous drag models in combination with thermal activation through a large Peierls barrier. The data also show complex evolution of the mobile dislocation density during early stages of high-rate plastic flow. This measurement and corresponding analysis aid significantly in establishing the fundamental picture of dynamic deformation of metals and the evolution of the internal material state at early times following shock compression.
Book Synopsis Large Deformation Plasticity of Polycrystalline Tantalum by :
Download or read book Large Deformation Plasticity of Polycrystalline Tantalum written by and published by . This book was released on 2000 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt: A physical, crystal mechanics-based theory of thermo-elasto-viscoplasticity which is valid for large strains and high strain rates at low homologous temperatures has been formulated. The theory is able to predict the macroscopic anisotropic stress-strain response, the evolution of crystallographic texture, and the macroscopic shape changes for b.c.c. tantalum. The material functions and parameters in the model were determined by calibrating the model against existing experimental results for tantalum. The model reproduces the data of these researchers rather well. The constitutive model has been implemented in the finite element program ABAQUS Explicit by writing a 'user material' subroutine. The ability of the constitutive model and computational procedures to capture the effect of initial texture on the final shape under high strain rates and large strains was evaluated by carrying out a simulation of a Taylor rod-impact experiment and by comparing the predicted final shape to that observed experimentally.
Book Synopsis Investigations and Applications of Severe Plastic Deformation by : Terry C. Lowe
Download or read book Investigations and Applications of Severe Plastic Deformation written by Terry C. Lowe and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Material processing techniques that employ severe plastic deformation have evolved over the past decade, producing metals, alloys and composites having extraordinary properties. Variants of SPD methods are now capable of creating monolithic materials with submicron and nanocrystalline grain sizes. The resulting novel properties of these materials has led to a growing scientific and commercial interest in them. They offer the promise of bulk nanocrystalline materials for structural; applications, including nanocomposites of lightweight alloys with unprecedented strength. These materials may also enable the use of alternative metal shaping processes, such as high strain rate superplastic forming. Prospective applications for medical, automotive, aerospace and other industries are already under development.
Book Synopsis Nanomaterials by Severe Plastic Deformation by : Michael J. Zehetbauer
Download or read book Nanomaterials by Severe Plastic Deformation written by Michael J. Zehetbauer and published by John Wiley & Sons. This book was released on 2006-03-06 with total page 872 pages. Available in PDF, EPUB and Kindle. Book excerpt: These proceedings of the "Second International Conference on Nanomaterials by Severe Plastic Deformation" review the enormous scientific avalanche that has been developing in the field over recent years. A valuable resource for any scientist and engineer working in this emerging field of nanotechnology.
Book Synopsis Severe Plastic Deformation by : Burhanettin Altan
Download or read book Severe Plastic Deformation written by Burhanettin Altan and published by Nova Publishers. This book was released on 2006 with total page 626 pages. Available in PDF, EPUB and Kindle. Book excerpt: It has been already well established that the nanostructured materials (materials with a grain size of 100mm or less) is the future materials. Nanostructured materials possess properties superior to those of conventional, coarse grained materials. Hence designing potentially cost efficient and environmentally friendly products with better performance is a possibility. Among others, nanostructured materials exhibit increased strength, hardness and ductility and provide an opportunity for superplastic forming. When all the procedures in use for the production of nanostructured materials are examined, only severe plastic deformation (SPD) processes exhibit a potential for producing relatively large samples suitable for industrial applications. In this monograph, the state-of-the-art on severe plastic deformation methods is presented in one volume. The monograph is organised into eight chapters, each of which contains papers on different aspect of severe plastic deformation methods prepared by the experts in this field. The topics covered in the monograph are structure formation, phase transformation, superplasticity, mechanical properties of nanostructured materials, electronic and magnetic properties of nanostructured materials, deformation analysis, novel SPD methods, commercialisation of ECAE method.
Book Synopsis Thermally Activated Mechanisms in Crystal Plasticity by : D. Caillard
Download or read book Thermally Activated Mechanisms in Crystal Plasticity written by D. Caillard and published by Elsevier. This book was released on 2003-09-08 with total page 453 pages. Available in PDF, EPUB and Kindle. Book excerpt: KEY FEATURES: A unified, fundamental and quantitative resource. The result of 5 years of investigation from researchers around the world New data from a range of new techniques, including synchrotron radiation X-ray topography provide safer and surer methods of identifying deformation mechanisms Informing the future direction of research in intermediate and high temperature processes by providing original treatment of dislocation climb DESCRIPTION: Thermally Activated Mechanisms in Crystal Plasticity is a unified, quantitative and fundamental resource for material scientists investigating the strength of metallic materials of various structures at extreme temperatures. Crystal plasticity is usually controlled by a limited number of elementary dislocation mechanisms, even in complex structures. Those which determine dislocation mobility and how it changes under the influence of stress and temperature are of key importance for understanding and predicting the strength of materials. The authors describe in a consistent way a variety of thermally activated microscopic mechanisms of dislocation mobility in a range of crystals. The principles of the mechanisms and equations of dislocation motion are revisited and new ones are proposed. These describe mostly friction forces on dislocations such as the lattice resistance to glide or those due to sessile cores, as well as dislocation cross-slip and climb. They are critically assessed by comparison with the best available experimental results of microstructural characterization, in situ straining experiments under an electron or a synchrotron beam, as well as accurate transient mechanical tests such as stress relaxation experiments. Some recent attempts at atomistic modeling of dislocation cores under stress and temperature are also considered since they offer a complementary description of core transformations and associated energy barriers. In addition to offering guidance and assistance for further experimentation, the book indicates new ways to extend the body of data in particular areas such as lattice resistance to glide.
Book Synopsis Bulk Nanostructured Materials by : Michael J. Zehetbauer
Download or read book Bulk Nanostructured Materials written by Michael J. Zehetbauer and published by John Wiley & Sons. This book was released on 2009-06-10 with total page 736 pages. Available in PDF, EPUB and Kindle. Book excerpt: The processing and mechanical behaviour of bulk nanostructured materials are one of the most interesting new fields of research on advanced materials systems. Many nanocrystalline materials possess very high strength with still good ductility, and exhibit high values of fatigue resistance and fracture toughness. There has been continuing interest in these nanomaterials for use in structural and biomedical applications, and this has led to a large number of research programs worldwide. This book focuses on the processing techniques, microstructures, mechanical and physical properties, and applications of bulk nanostructured materials, as well as related fundamental issues. Only since recently can such bulk nanostructured materials be produced in large bulk dimensions, which opens the door to their commercial applications.
Book Synopsis Influence of Large-strain Deformation on the Microstructure, Texture, and Mechanical Response of Tantalum Bar by :
Download or read book Influence of Large-strain Deformation on the Microstructure, Texture, and Mechanical Response of Tantalum Bar written by and published by . This book was released on 1996 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Numerous studies have established the influence of impurities, crystallographic texture, temperature, and strain rate separately or collectively on the constitutive response of annealed tantalum, in particular plate Ta-stock. However, fewer detailed studies have examined the evolution of crystallographic texture and the mechanical response of tantalum bar or rod material following prestraining to large strains [epsilon]> I. In this paper the influence of large plastic prestraining on the microstructure evolution, texture evolution, and mechanical response of high-purity tantalum bar material is presented. Tantalum cylinders annealed at 1200 °C were quasi-statically upset forged, with intermediate lubrication, to true strains of 0.4, 0.95, and 1.85. Microstructural and textural banding within the starting Ta-bar was characterized in detail. It was found that different oriented bands evolved differently during large-strain forging leading to significant scatter in the mechanical response. Aspects of defect storage, work-hardening response, and texture evolution in Ta-bar as a function of forging strain are discussed.
Book Synopsis Plastic Deformation of Metals at High Strain Rates. Part I. The Effects of Temperature on the Static and Dynamic Stress-Strain Characteristics in Torsion of 1100-0 Aluminum by : A. M. Eleiche
Download or read book Plastic Deformation of Metals at High Strain Rates. Part I. The Effects of Temperature on the Static and Dynamic Stress-Strain Characteristics in Torsion of 1100-0 Aluminum written by A. M. Eleiche and published by . This book was released on 1973 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: A series of tests is described in which tubular specimens of a commercially pure polycrystalline aluminum were loaded in torsion up to shear strains of about 2 and 4% respectively, over the temperature range -180C to 250C. The experimental results give the flow stress in shear, the strain and the strain rate against time. They also give stress-strain curves which are compared to the corrresponding static curves obtained by testing similar specimens in torsion at about 0.001/sec. A graph showing the dependence of flow stress on temperature indicates that there are three different temperature ranges for polycrystalline aluminum within each of which a different deformation mechanism presumably dominates the flow process. (Modified author abstract).
Book Synopsis Dynamic Behavior of Polycrystalline Tantalum by :
Download or read book Dynamic Behavior of Polycrystalline Tantalum written by and published by . This book was released on 1997 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: A description for the strain-rate and temperature-dependent behavior of pure tantalum (Ta) at large strains is developed. An integral part of the model incorporates the kinematics of crystallographic slip, and thus, the rotation of single crystals within the material, so as to reflect the evolution of anisotropy resulting from applied mechanical deformation. Such deformation is accommodated via bulk dislocation motion and governed by interactions that may or may not be thermally assisted. The model represents each discrete slip system as a single facet in a multisurface plasticity theory, which is well suited to high-rate numerical methods (explicit integration schemes). A formulation of this type allows for the complete kinematic decomposition of macroscopic material rotations and the rotations of single crystals due to motion through the lattice. Applications to high-rate deformation in polycrystals is conducted within a finite element implementation by invoking a Taylor criterion for interaction between the macroscopic and the mesoscopic (single-crystal) length scales. The model behavior is examined in application to high-rate problems with increasingly complex geometries (homogeneous uniaxial compression, the impact of a textured cylindrical bar into a rigid anvil, and the explosive deep-drawing of a Ta disk).
Book Synopsis Mechanical Properties and Constitutive Relations for Tantalum and Tantalum Alloys Under High-rate Deformation by :
Download or read book Mechanical Properties and Constitutive Relations for Tantalum and Tantalum Alloys Under High-rate Deformation written by and published by . This book was released on 1996 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tantalum and its alloys have received increased interest as a model bcc metal and for defense-related applications. The stress-strain behavior of several tantalums, possessing varied compositions and manufacturing histories, and tantalum alloyed with tungsten, was investigated as a function of temperature from -196 C to 1,000 C, and strain rate from 10−3 s−1 to 8,000 s−1. The yield stress for all the Ta-materials was found to be sensitive to the test temperature, the impurity and solute contents; however, the strain hardening remained very similar for various ''pure'' tantalums but increased with alloying. Powder-metallurgy (P/M) tantalum with various levels of oxygen content produced via different processing paths was also investigated. Similar mechanical properties compared to conventionally processed tantalums were achieved in the P/M Ta. This data suggests that the frequently observed inhomogeneities in the mechanical behavior of tantalum inherited from conventional processes can be overcome. Constitutive relations based upon the Johnson-Cook, the Zerilli-Armstrong, and the Mechanical Threshold Stress models were evaluated for all the Ta-based materials. Parameters were also fit for these models to a tantalum-bar material. Flow stresses of a Ta bar stock subjected to a large-strain deformation of {var_epsilon} = 1.85 via multiple upset forging were obtained. The capabilities and limitations of each model for large-strain applications are examined. The deformation mechanisms controlling high-rate plasticity in tantalum are revisited.
Book Synopsis Deformation Mechanisms During Compressive Loading of Tantalum and Tantalum-2.5 Weight % Tungsten by : Rajeev Kapoor
Download or read book Deformation Mechanisms During Compressive Loading of Tantalum and Tantalum-2.5 Weight % Tungsten written by Rajeev Kapoor and published by . This book was released on 1998 with total page 418 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Atom-to-Continuum Analysis of Plastic Deformation of Nanocrystalline Tantalum Thin Films by :
Download or read book Atom-to-Continuum Analysis of Plastic Deformation of Nanocrystalline Tantalum Thin Films written by and published by . This book was released on 2012 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:
