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Polycrystalline Materials (polycrystalline + material)
Selected AbstractsExperimental Determination of Fully-Coupled Kinematical and Thermal Fields at the Scale of Grains Under Cyclic LoadingADVANCED ENGINEERING MATERIALS, Issue 9 2009Laurence Bodelot An experimental setup has been developed to measure fully-coupled kinematic and thermal fields at a very fine resolution matching the microstructure size of a heat-treated austenitic stainless steel. In this study, this setup is used in order to investigate the heterogeneous behavior of a polycrystalline material under cyclic loading, as far as the local strain and temperature data are concerned. [source] Technique for Preparing Ultrafine Nanocrystalline Bulk Material of Pure Rare-Earth Metals,ADVANCED MATERIALS, Issue 9 2006X. Song Ultrafine nanocrystalline bulk material of pure rare-earth metals has been prepared using a combination of inert gas condensation and spark plasma sintering (see figure). Some of the bulk properties such as the microhardness and specific heat capacity are remarkably improved compared to the conventional polycrystalline material. This new preparation technique enables the preparation and study of a variety of other nanostructured metal materials. [source] Aspects of a direct homogenization procedure for electro-mechanically coupled problemsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Marc-André Keip The aim of this work is to discuss a micro,macro homogenization procedure for electro,mechanically coupled problems. In this context a two,scale homogenization ansatz for ferroelectric ceramics based on an FE2 -approach is presented. The microscopic discretization of the heterogeneous structure of the polycrystalline material allows for the incorporation of microscopic effects, which are necessary to determine the corresponding overall macroscopic material response. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] On the possibility of using polycrystalline material in the development of structure-based generic assaysACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2009Marc Allaire The discovery of ligands that bind specifically to a targeted protein benefits from the development of generic assays for high-throughput screening of a library of chemicals. Protein powder diffraction (PPD) has been proposed as a potential method for use as a structure-based assay for high-throughput screening applications. Building on this effort, powder samples of bound/unbound states of soluble hen-egg white lysozyme precipitated with sodium chloride were compared. The correlation coefficients calculated between the raw diffraction profiles were consistent with the known binding properties of the ligands and suggested that the PPD approach can be used even prior to a full description using stereochemically restrained Rietveld refinement. [source] Principles of Highly Resolved Determination of Texture and Microstructure using High-Energy Synchrotron Radiation,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Helmut Klein Abstract Diffraction imaging with hard X-rays (high-energy synchrotron radiation) using the detector sweeping techniques allows measurement of the texture and microstructure of polycrystalline materials with high orientation- and location-resolution. These techniques provide continuous two-dimensional images of different sections and projections of the six-dimensional "orientation-location" space. For the high orientation resolution case, it is possible to measure the orientation and location coordinates of up to 105 individual grains simultaneously. From these parameters, the grain size and shape can also be obtained, yielding the complete orientation stereology of the polycrystalline aggregate, which is required for its complete characterization. For the high location resolution case, the intensity at any point of the diagrams corresponds to a pole density as a function of the orientation-location space. [source] Finite element formulation for modelling large deformations in elasto-viscoplastic polycrystalsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 14 2004Karel Matou Abstract Anisotropic, elasto-viscoplastic behaviour in polycrystalline materials is modelled using a new, updated Lagrangian formulation based on a three-field form of the Hu-Washizu variational principle to create a stable finite element method in the context of nearly incompressible behaviour. The meso-scale is characterized by a representative volume element, which contains grains governed by single crystal behaviour. A new, fully implicit, two-level, backward Euler integration scheme together with an efficient finite element formulation, including consistent linearization, is presented. The proposed finite element model is capable of predicting non-homogeneous meso-fields, which, for example, may impact subsequent recrystallization. Finally, simple deformations involving an aluminium alloy are considered in order to demonstrate the algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source] Microstrain and grain-size analysis from diffraction peak width and graphical derivation of high-pressure thermomechanicsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008Yusheng Zhao An analytical method is presented for deriving the thermomechanical properties of polycrystalline materials under high-pressure (P) and high-temperature (T) conditions. This method deals with non-uniform stress among heterogeneous crystal grains and surface strain in nanocrystalline materials by examining peak-width variation under different P,T conditions. Because the method deals directly with lattice d spacing and local deformation caused by stress, it can be applied to process any diffraction profile, independent of detection mode. In addition, a correction routine is developed using diffraction elastic ratios to deal with severe surface strain and/or strain anisotropy effects related to nano-scale grain sizes, so that significant data scatter can be reduced in a physically meaningful way. Graphical illustration of the resultant microstrain analysis can identify micro/local yields at the grain-to-grain interactions resulting from high stress concentration, and macro/bulk yield of the plastic deformation over the entire sample. This simple and straightforward approach is capable of revealing the corresponding micro and/or macro yield stresses, grain crushing or growth, work hardening or softening, and thermal relaxation under high- P,T conditions, as well as the intrinsic residual strain and/or surface strain in the polycrystalline bulk. In addition, this approach allows the instrumental contribution to be illustrated and subtracted in a straightforward manner, thus avoiding the potential complexities and errors resulting from instrument correction. Applications of the method are demonstrated by studies of ,-SiC (6H, moissanite) and of micro- and nanocrystalline nickel by synchrotron X-ray and time-of-flight neutron diffraction. [source] POWTEX , the high-intensity time-of-flight diffractometer at FRM II for structure analysis of polycrystalline materialsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2008Harald Conrad In order to provide the large chemistry and materials science as well as the geosciences communities with a powerful tool for rapid data acquisition, a time-of-flight powder diffractometer to be installed at the new Munich reactor has been designed. The time-of-flight technique is expected to outperform a monochromator instrument by at least an order of magnitude in data acquisition time, particularly on small samples of less than a cubic centimetre. The construction of this innovative type of diffractometer utilizes modern components such as focusing super-mirror neutron guides, a four-unit high-speed disk chopper system and linear position-sensitive detectors covering a solid angle of about 2, steradian. The diffractometer design enables an easy enlargement of the focal spot size and is therefore equally well suited for the texture analysis of large geological and archaeological samples. [source] Synchrotron texture analysis with area detectorsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2003H.-R. Wenk The wide availability of X-ray area detectors provides an opportunity for using synchrotron radiation based X-ray diffraction for the determination of preferred crystallite orientation in polycrystalline materials. These measurements are very fast compared to other techniques. Texture is immediately recognized as intensity variations along Debye rings in diffraction images, yet in many cases this information is not used because the quantitative treatment of texture information has not yet been developed into a standard technique. In special cases it is possible to interpret the texture information contained in these intensity variations intuitively. However, diffraction studies focused on the effects of texture on materials properties often require the full orientation distribution function (ODF) which can be obtained from spherical tomography analysis. In cases of high crystal symmetry (cubic and hexagonal) an approximation to the full ODF can be reconstructed from single diffraction images, as is demonstrated for textures in rolled copper and titanium sheets. Combined with area detectors, the reconstruction methods make the measurements fast enough to study orientation changes during phase transformations, recrystallization and deformation in situ, and even in real time, at a wide range of temperature and pressure conditions. The present work focuses on practical aspects of texture measurement and data processing procedures to make the latter available for the growing community of synchrotron users. It reviews previous applications and highlights some opportunities for synchrotron texture analysis based on case studies on different materials. [source] Mapping of unstressed lattice parameters using pulsed neutron transmission diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2002Javier Roberto Santisteban Stress measurement by neutron diffraction depends critically on knowledge of the unstressed lattice parameter (a0) of the specimen under study. As a result, measurement of stress profiles in components where a0 is not homogeneous throughout the sample, such as welds or carburized surfaces, can be particularly difficult. An efficient solution to this problem is proposed based on the pulsed neutron transmission diffraction technique. This technique exploits the sharp steps in intensity, the so-called Bragg edges, appearing in the transmitted neutron spectra of polycrystalline materials, such steps being produced by coherent scattering from lattice planes. The position of these Bragg edges as defined by the time-of-flight technique is used to determine precisely local interplanar distances. In this work it is shown that the unstressed lattice parameter of thin specimens subjected to plane stress fields can be defined by recording transmission spectra at different sample inclinations, in complete analogy with the sin2, technique used in X-ray diffraction. Moreover, by using an array of detectors it is possible to produce a radiographic `image' of a0 for plane specimens or thin sections out of three-dimensional ones. The capability of the technique is exemplified by mapping the changes in a0 for a ferritic weld that was used as a round robin sample in an international program for standardization of stress measurements by neutron diffraction. [source] Application of quantitative texture analysis to Rietveld profile refinement of neutron diffraction patterns of a zircaloy sampleJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3 2001Y. C. Kim The possibility of extending the Rietveld method to incorporate textured polycrystalline materials is demonstrated with a zircaloy sample. By assigning the pole densities obtained by separate texture analysis to the preferred orientation factors (POFs) in the mathematical model of the Rietveld method, good profile refinement results are achieved with the neutron diffraction patterns. The approach of predetermining the individual POF values from quantitative texture information can be used to improve refinement of other parameters related to the analysis of composite phases as well as to crystal structure refinement. [source] Prediction of intragranular strains in metallic polycrystals with a two-level homogenisation approach: Influence of dislocation microstructure on the mechanical behaviourPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2006D. Gloaguen Abstract A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multiscale simulation of polycrystal mechanics of textured ,-Ti alloys using ab initio and crystal-based finite element methodsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008D. Ma Abstract Crystal-based finite element methods (FEM) are versatile continuum approaches for predicting mechanical properties and deformation-induced crystallographic textures. They can be applied to both, elastic,plastic and elastic problems. The methodology is based on (i) a detailed understanding of the underlying crystal deformation mechanisms and (ii) a number of constitutive material parameters that are often difficult to measure. First principle calculations, that take into account the discrete nature of matter at the atomic scale, are an alternative way to study mechanical properties of single crystals without using empirical parameters. In this study we demonstrate how to combine these two well-established modeling tools, viz., ab initio modeling and crystal mechanical FEM, for an improved approach to design of polycrystalline materials. The combination is based on (i) the determination of basic thermodynamic and elastic parameter trends in metallurgical alloy design using density-functional (DFT) calculations (P. Hohenberg and W. Kohn, Phys. Rev. 136, B864 (1964), W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965) [1, 2], respectively) and (ii) the up-scale transfer of these results into crystal-based finite element simulations which take into account the anisotropic nature of the elastic,plastic deformation of metals. The method is applied to three body-centered cubic (bcc, ,) Ti,Nb alloys for bio-medical applications. The study addresses two technological processes, namely, the prediction of texture evolution during cold rolling (elastic-plastic problem) and elastic bending of textured polycrystals (elastic problem). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||