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Deformation Mechanisms (deformation + mechanism)
Selected AbstractsDeformation Mechanism of Fine-Grained Magnesium Aluminate Spinel Prepared Using an Alkoxide PrecursorJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2000Takeshi Shiono Polycrystalline MgAl2O4 spinel with high purity and stoichiometric composition was prepared using alkoxide precursors. The average grain size of the polycrystal was fine (1.7 ,m). The deformation mechanism of the polycrystal was investigated in air at temperatures of 1300°,1400°C. At 1300°C, oxygen lattice diffusion controlled the deformation, despite the fine grain size; however, increases in the temperature and applied stress caused cavities to nucleate and grow. Spinel possessed better creep resistance than alumina of comparative grain size. The effective diffusion coefficient was determined as follows: [formula omitted] [source] Hot Deformation Mechanisms and Microstructural Control in High-Temperature Extruded AZ31 Magnesium Alloy,ADVANCED ENGINEERING MATERIALS, Issue 7 2007A Processing map has been developed for Magnesium alloy AZ31 extruded at 450,°C which revealed that the extruded rods may be further processed into components industrially at 400,°C and at a strain rate of 10,s,1. If processed at lower strain rates in the vicinity of 0.1,s,1, unusual grain size variations with temperature and strain rate are observed, suggesting that grain size control will be difficult. [source] Deformation Mechanisms in Compression-Loaded, Stand-Alone Plasma-Sprayed Alumina CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2000Rodney W. Trice Cylindrical, stand-alone tubes of plasma-sprayed alumina were tested in compression in the axial direction at room temperature, using strain gauges to monitor axial and circumferential strains. The primary compression-loading profile used was cyclic loading, with monotonically increased peak stresses. Hysteresis was observed in the stress,strain response on unloading, beginning at a peak stress of 50 MPa. The modulus decreased as the maximum applied stress increased. The stress,strain response was only linear at low stresses; the degree of nonlinearity at high stresses scaled with the stress applied. One-hour dwells at constant stress at room temperature revealed a time-dependent strain response. Using transmission electron microscopy and acoustic emission to investigate deformation mechanisms, the stress,strain response was correlated with crack pop-in, growth, and arrest. It is proposed that the numerous defects in plasma-sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small, nucleated cracks extend under the applied stress, they propagate nearly parallel to the loading direction along interlamellae boundaries. With increasing stress, these cracks ultimately link, resulting in catastrophic failure. [source] Deformation mechanism of polystyrene toughened with sub-micrometer monodisperse rubber particlesPOLYMER INTERNATIONAL, Issue 11 2006Guanghui Gao Abstract Core,shell polybutadiene- graft -polystyrene (PB- g -PS) rubber particles with different ratios of polybutadiene to polystyrene were prepared by emulsion polymerization through grafting styrene onto polybutadiene latex. The weight ratio of polybutadiene to polystyrene ranged from 50/50 to 90/10. These core-shell rubber particles were then blended with polystyrene to prepare PS/PB- g -PS blends with a constant rubber content of 20 wt%. PB- g -PS particles with a lower PB/PS ratio (,70/30) form a homogeneous dispersion in the polystyrene matrix, and the Izod notched impact strength of these blends is higher than that of commercial high-impact polystyrene (HIPS). It is generally accepted that polystyrene can only be toughened effectively by 1,3 µm rubber particles through a toughening mechanism of multiple crazings. However, the experimental results show that polystyrene can actually be toughened by monodisperse sub-micrometer rubber particles. Scanning electron micrographs of the fracture surface and stress-whitening zone of blends with a PB/PS ratio of 70/30 in PB- g -PS copolymer reveal a novel toughening mechanism of modified polystyrene, which may be shear yielding of the matrix, promoted by cavitation. Subsequently, a compression-induced activation method was explored to compare the PS/PB- g -PS blends with commercial HIPS, and the result show that the toughening mechanisms of the two samples are different. Copyright © 2006 Society of Chemical Industry [source] Determination of Activation Volume in Nanocrystalline Cu Using the Shear Punch Test,ADVANCED ENGINEERING MATERIALS, Issue 10 2007K. Guduru Stress relaxation test (SRT) is very useful to study the dislocation dynamics and thus the deformation behavior. It becomes quite difficult to use conventional testing methods when the material availability is limited. In such instances, miniaturized specimen testing procedures such as shear punch test (SPT) becomes significantly useful for studying the mechanical behavior of materials. Current research deals with a novel SRT method employed on nanocrystalline Cu using SPT to study the deformation mechanism. [source] The Effect of Grain Size on the Deformation Behaviour of Magnesium Alloys Investigated by the Acoustic Emission Technique,ADVANCED ENGINEERING MATERIALS, Issue 5 2006J. Bohlen Extruded round bars from magnesium alloys ZM21, ZK30, ZE10 and ZEK100 with various grain sizes were tested in tension and compression. The effect of grain size on the deformation behaviour of the alloys was investigated through the Hall-Petch relation. In-situ acoustic emission measurements were conducted during testing to evaluate the mechanisms of plastic deformation. The results are discussed with respect to twinning as one important deformation mechanism in magnesium alloys. [source] High-strain-rate Superplasticity in a Nanostructured Al-Mg AlloyADVANCED ENGINEERING MATERIALS, Issue 4 2005B. Q. Han In this work, the authors report high-strain-rate superplasticity in a nanostructured Al-7.5%Mg alloy with a mean grain size of 90 nm processed via consolidation of cryomilled Al-Mg powders. Tensile ductility with an elongation of 291% was observed at a strain rate of 10-1 s-1 and at a temperature of 573 K. Noteworthy is the fact that the microstructure is essentially stable during testing at 573 K. Grain boundary sliding is suggested to be the dominant deformation mechanism in the superplastic deformation of the nanostructured Al-Mg alloy. [source] In situ Mechanical Testing Reveals Periodic Buckle Nucleation and Propagation in Carbon Nanotube BundlesADVANCED FUNCTIONAL MATERIALS, Issue 14 2010Shelby B. Hutchens Abstract Uniaxial compression studies are performed on 50-µm-diameter bundles of nominally vertical, intertwined carbon nanotubes grown via chemical vapor deposition from a photolithographically defined catalyst. The inhomogeneous microstructure is examined, demonstrating density and tube orientation gradients, believed to play a role in the unique periodic buckling deformation mechanism. Through in situ uniaxial compression experiments it is discovered that the characteristic bottom-to-top sequential buckling proceeds by first nucleating on the bundle surface and subsequently propagating laterally through the bundle, gradually collapsing the entire structure. The effects of strain rate are explored, and storage and loss stiffnesses are analyzed in the context of energy dissipation. [source] The preservation of seismic anisotropy in the Earth's mantle during diffusion creepGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009J. Wheeler SUMMARY Seismic anisotropy in the Earth, particularly in the mantle, is commonly interpreted as the result of solid-state deformation by dislocation creep that induces a lattice preferred orientation (LPO). Diffusion creep operates where stress levels are lower and/or grain sizes smaller. It is often assumed that diffusion creep induces grain rotations that eventually destroy any existing LPO. A new numerical test of this assumption shows that it is not necessarily the case: diffusion creep will create some relative grain rotations, but rotation rates decrease through time. Hence, when microstructural change due to diffusion creep dominates that due to grain growth, defined here as ,type P' behaviour (the converse being ,type O' behaviour), the model indicates that LPO will be weakened but preserved (for a variety of strain paths including both pure and simple shear). One measure of anisotropy is the proportional difference in shear wave velocities for different polarization vectors (AVs). A model olivine microstructure with equant grains and initial maximum AVs of 10.0 percent has this value reduced to 6.7 per cent when ,rotational steady state' is attained. Other models with different initial maximum AVs values exhibit final maximum AVs values more than half the initial values. If the grains are initially elongate by a factor of 2, maximum AVs is reduced just slightly, to 8.5 per cent. Thus, when grain growth plays a subordinate role to the deformation, diffusion creep weakens seismic anisotropy by a factor of less than 2 (using maximum AVs as a measure and olivine as an example). Consequently, the link between seismic anisotropy and deformation mechanism in the mantle requires reappraisal: regions with LPO may comprise material which once deformed by dislocation creep, but is now deforming by diffusion creep in a rotational steady state. [source] Cover Picture: Ductile-to-Brittle Transition in Nanocrystalline Metals (Adv. Mater.ADVANCED MATERIALS, Issue 16 200516/2005) Abstract Uniaxial tensile studies concerning electrodeposited nanocrystalline face-centered cubic Ni and Ni,Fe alloys are reported on p.,1969 by Ebrahimi and Li. The nanograined metals display a transition in the deformation mechanism at a critical grain size. The cover shows that their fracture surfaces exhibited a ductile-to-brittle transition from the "cup,cup" (intragranular, ductile failure, dislocation controlled) (top panels) to "cup,cone" (intergranular, brittle fracture, probably due to breaking of atomic bonds) (bottom panels) characteristics at room temperature across this critical grain size value. [source] Microfabric characteristics and rheological significance of ultra-high-pressure metamorphosed jadeite-quartzite and eclogite from Shuanghe, Dabie Mountains, ChinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2010L. WANG Abstract Quantitative analysis of the structural evolution of jadeite-quartzite, a rare ultra-high pressure (UHP) rock type from the Dabie Mountains of eastern China, sheds light on the formation and evolution of UHP orogenic belts worldwide. Geological mapping of the Shuanghe area, where jadeite-quartzites crop out, was carried out to determine the spatial relationships between different UHP rocks within this orogen. The deformation mechanisms of jadeite-quartzite, geodynamical parameters (stress, strain, strain rate), and microstructure including lattice preferred orientation (LPO) were determined from six jadeite-quartzite samples from the Shuanghe area. LPOs of clinopyroxene (jadeite and omphacite), garnet, rutile and quartz from these jadeite-quartzite samples are compared with those of three eclogites preserving different degrees of deformation from the Shuanghe area. Microstructural LPOs of jadeite, omphacite, garnet, rutile and quartz were determined using electron backscattered diffraction (EBSD) analysis. Quartz fabrics were largely recrystallized during late, low-grade stages of deformation, whereas garnet shows no strong LPO patterns. Rutile fabrics show a weak LS fabric along [001]. Jadeite and omphacite show the strongest eclogite facies LPO patterns, suggesting that they may provide important information about mantle deformation patterns and control the rheology of deeply subducted continental crust. Microstructural data show that the jadeite LPO patterns are similar to those of omphacite and vary between L- and S-types, which correlate with prolate and oblate grain shape fabrics (SPO); quartz LPOs are monoclinic. Microstructural analysis using TEM shows that the dominant slip systems of jadeite in one sample are (100)[001], (110)[001] and (1 1 0)1/2[110], while in another sample, no dislocations are observed. Abundant dislocations in quartz were accommodated by the dominant slip system (0001)[110], indicating basal glide and represents regional shearing during the exhumation process. This suggests that dislocation creep is the dominant fundamental deformation mechanism in jadeite under UHP conditions. The protoliths of jadeite-quartzite, metasedimentary rocks from the northern passive continental margin of the Yangtze craton, experienced the same deep subduction and were deformed under similar rheological conditions as other UHP eclogite, marble and paragneiss. Experimental UHP deformation of quartzo-feldspathic gneiss with a chemical composition similar to the bulk continental crust has shown that the formation of a jadeite,stishovite rock is associated with a density increase of the host rock similar to the eclogite conversion from basaltic protoliths. The resulting rock can be denser than the surrounding mantle pyrolite up to depths of 660 km (24 GPa). Thus, processes of deep continental subduction may be better-understood through understanding the rheology and mechanical behaviour of jadeite. Jadeite-quartzites such as those from the Shuanghe may be exhumed remnants of deeply-subducted slabs of continental crust, other parts of which subducted past the ,depth of no return', and remain in the deep mantle. [source] Experimental Investigation of Eclogite Rheology and Its Fabrics at High Temperature and PressureJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2007J. ZHANG Abstract Eclogite plays an important role in mantle convection and geodynamics in subduction zones. An improved understanding of processes in the deeper levels of subduction zones and collision belts requires information on eclogite rheology. However, the deformation processes and associated fabrics in eclogite are not well understood. Incompatible views of deformation mechanism have been proposed for both garnet and omphacite. We present here deformation behaviour of eclogite at temperatures of 1027,1427 °C, confining pressures of 2.5,3.5 GPa, and strain rates of 1 × 10,5 s,1 to 5 × 10,4 s,1. We obtained a power-law creep for the high temperature and pressure deformation of a ,dry' eclogite (50 vol.% garnet, 40% omphacite and 10% quartz) with A = 103.3 ± 1.0, n = 3.5 ± 0.4, ,E =403 ± 30 KJ mol,1 and ,V = 27.2 cm3 mol,1. The two principal minerals of eclogite have greatly different strengths. Progressive increase of garnet results in a smooth increase in strength. Analysis by electron back-scattered diffraction shows that: (1) garnet displays pole figures with near random distributions of misorientation angle under both dry and wet conditions; (2) omphacite shows pronounced lattice preferred orientations (LPOs), suggesting a dominant dislocation creep mechanism. Further investigation into the water effects on eclogite show: (3) water content does not influence the style of omphacite fabric but increases slightly the fabric strength; (4) grain boundary processes dominate the deformation of garnet under high water fugacity or high shear-strain conditions, yielding a random LPO similar to that of non-deforming garnet, despite the strong shape preferred orientation (SPO) observed. {110} [001] slip may dominate the deformation of rutile. Quartz displays complicated and inconsistent LPOs in eclogite. These results are remarkably similar to observations from deformed eclogites in nature. [source] Metamorphism and microstructures along a high-temperature metamorphic field gradient: the north,eastern boundary of the Královský hvozd unit (Bohemian Massif, Czech Republic)JOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2002D. Scheuvens Abstract A metamorphic field gradient has been investigated in the Moldanubian zone of the central European Variscides encompassing, from base to the top, a staurolite,kyanite zone, a muscovite,sillimanite zone, a K-feldspar,sillimanite zone, and a K-feldspar,cordierite zone, respectively. The observed reaction textures in the anatectic metapsammopelites of the higher grade zones are fully compatible with experimental data and petrogenetic grids that are based on fluid-absent melting reactions. From structural and microstructural observations it can be concluded that the boundary between the kyanite,staurolite zone and the muscovite- and K-feldspar,sillimanite zones coincides with an important switch in deformation mechanism(s). Besides minor syn-anatectic shearing (melt-enhanced deformation), microstructural criteria point (a) to a switch in deformation mechanism from rotation recrystallization (climb-accommodated dislocation creep) to prism Dynamic Compressive Failure of AlON Under Controlled Planar ConfinementJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Bhasker Paliwal An experimental technique is developed to impose a planar lateral confinement in a prismatic specimen (with a rectangular cross section); the setup enabled a controlled and homogeneous stress state with high lateral compressive stresses. A transparent polycrystalline aluminum oxynitride (AlON) specimen was used for the study. The statically precompressed specimen was then subjected to axial dynamic compressive loading using a modified compression Kolsky bar setup. Experimental design was performed using 3D computational modeling. Initial exploratory experiments were conducted on AlON at an average planar confinement of 400,410 MPa; the results suggested a higher compressive strength and a nonlinear stress evolution in AlON due to the confinement. A high-speed camera was used to observe the damage evolution in the specimen during the course of loading. The photographs and stress evolution are suggestive of an additional inelastic deformation mechanism, whose evolution is slower than the typical brittle-cracking type of damage apparent in the unconfined case. The TEM and high-resolution electron microscope analysis indicated dislocation plasticity in some fragments; dislocations in the slip bands were characterized to be dissociated ,110, dislocations on {111} planes. The width between two partial dislocations was about 15 nm, suggesting low stacking fault energy of AlON. Microscopic characterization also shows that the eventual fragmentation of AlON is by cleavage mainly along low-index {111} planes. [source] Contact Damage of Silicon Carbide/Boron Nitride NanocompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2007Takafumi Kusunose To investigate the deformation mechanism of silicon carbide (SiC)/boron nitride (BN) nanocomposites, Hertzian contact tests were performed on monolithic SiC, and nanocomposite and microcomposite SiC/BN. Monolithic SiC had the typical microstructure of hot-pressed SiC with Y2O3 and Al2O3 additives, composed of slightly large grains in small matrix grains. The microcomposite comprised large BN grains dispersed along the grain boundaries of elongated SiC grains, while the nanocomposite showed a finer microstructure with fine BN particles and small matrix grains. These microstructural differences led to differences in the mechanism of contact damage. The damage of the monolithic SiC and the SiC/BN microcomposite exhibited classical Hertzian cone fracture and many large cracks, whereas the damage observed in the nanocomposites appeared to be quasi-plastic deformation. [source] Internal Structure of a relict rock glacier, ,l,,a Massif, Southwest PolandPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2002Roman, urawek Abstract The sediments of a large accumulation landform, interpreted as one of six Pleistocene rock glaciers occurring in the ,l,,a Massif, southwest Poland, are described. The sediments have been subject to strong compression and the main deformation mechanism is that of shearing. The similar angle of shear in sediments of extremely different lithology is inferred from the geometry of failure surfaces and indicates that ice was necessary for the debris transport. Because the geomorphological setting excludes a glacigenic origin, the sediments are interpreted to result from the creep of permafrost, i.e. the landform is a relict rock glacier. The movement of the rock glacier, at least in its terminal stage, is associated with a dense pattern of shear planes and would have occurred even in the presence of a small amount of interstitial ice. Copyright © 2002 John Wiley & Sons, Ltd. [source] Flexural creep of all-polypropylene composites: Model analysisPOLYMER ENGINEERING & SCIENCE, Issue 5 2008K. Banik In this article, simple viscoelastic and empirical models are presented to predict and analyze the flexural creep behavior of all-poly(propylene) (all-PP) composites. Results of the successful application of these models to the actual creep behavior of unidirectional (UD) and cross-ply (CP) all-PP composites tested by short-term flexural creep measurements over a temperature range of 20,80°C are presented. Analysis of the momentary creep behavior of all-PP composites with different tape lay-ups are made to understand their deformation mechanism. Further to the main theme of the article, an interesting discrepancy while predicting the long-term creep behavior of these composites based on the time-temperature superposition (TTS) principle and Findley power law model is visualized which has also been illustrated here. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Effect of mold temperature on the long-term viscoelastic behavior of polybutylene terepthalatePOLYMER ENGINEERING & SCIENCE, Issue 5 2008K. Banik The effect of mold temperature variation during injection molding on the long-term viscoelastic behavior of polybutylene terepthalate (PBT) was studied by dynamic mechanical thermal analysis (DMTA) and flexural creep tests. The time,temperature superposition (TTS) principle was applied to the experimental data and the master curves were created to predict their long-term behavior. The WLF and Arrhenius models were verified for the shift data in the investigating temperature range and the activation energies for the deformation process were calculated based on the Arrhenius equation. Further a four-element Burger model was applied to the creep results to represent the creep behavior of the PBT processed at two different mold temperatures and to better understand the deformation mechanism. Differential scanning calorimetry (DSC) and density measurements were accomplished to characterize the process-dependent microstructures. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source] Discontinuous deformation in an elastic material.POLYMER ENGINEERING & SCIENCE, Issue 10 2007Part 1. The concept of energy or work dissipation from a perfectly elastic material, due to a discontinuous deformation mechanism, is developed in this study. Dissipation occurs even from a perfectly elastic material, preferably an elastomer, when subjected to a discontinuous "jump" stretch or "jump" contraction. Stretching an elastomeric member through free extension requires a large amount of work. Such a sudden jump stretch of an elastic material is difficult to accomplish and is equivalent to thermodynamic free compression of a gas. The amount of work required can greatly exceed the strain energy stored in the material if the extension were applied without the jump or "shock" process. Interestingly, only part of the stored energy is recovered on unloading the elastomer the same way (through contraction). Excess work lost in contraction dissipates as heat but is not due to the common viscoelastic/plastic losses associated with internal friction in solids. Dissipation is possible even from a perfectly elastic material. Energy values associated in this jump deformation process are independent of the stress,strain curve path, and depend only on initial and final states for the material. Heat dissipation from an elastic rubber belt is examined and some applications extended from the developed principle are enunciated. POLYM. ENG. SCI., 47:1511,1520, 2007. © 2007 Society of Plastics Engineers [source] Subsurface sediment remobilization and fluid flow in sedimentary basins: an overviewBASIN RESEARCH, Issue 4 2010Mads Huuse ABSTRACT Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mud volcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the re-charge dynamics of their fluid source. Future research should aim to provide spatio-temporal ,injectite' stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data-driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena. [source] Structural Analysis of the Multi-layer Detachment Folding in Eastern Sichuan ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2010Zongxiu WANG Abstract: A serial of "comb-like and trough-like" folds developed in eastern Sichuan, controlled by the multi-layer detachment folding, is different from the classical Jura-type structure in their development. The key factor resulting in the development of these structures is the occurrence of detachment layers in different parts of Neoprotozoic to Mesozoic stratigraphy of study area, which, from the bottom to the top, are the lower part of Banxi Group, Lower Cambrian (Niutitang Formation), Lower Silurian (Longmaxi Formation and Luoreping Formation), Upper Permian (Wujiaping Formation) and Lower Triassic (Daye Formation). On the basis of field survey combined with sand-box modeling, this study argued that the detachment layer of the lower part of Banxi Group controlled the development of the "comb-like" folds, and the lower part of Cambrian detachment layer controlled the development of "trough-like" folds. Because of several detachment layers occurring in the study area, the development of duplex structures different scales is an important deformation mechanism, and the duplexes are the important structures distinguished from the typical detachment folding structures. Due to these duplexes, the surface structures and structural highs may not be the structural highs in the depth. Meanwhile, the detachment layers are good channels for oil/gas migration benefiting the understanding of accumulation and migration of oil and gas. [source] A Polycrystalline Approach to the Cyclic Behaviour of f.c.c. Alloys , Intra-Granular HeterogeneityADVANCED ENGINEERING MATERIALS, Issue 9 2009Xavier Feaugas For several decades, the plastic deformation mechanisms of f.c.c. metals under cyclic loading have received considerable attention. The extensive work on this subject has gradually lead to the identification of the physical processes to be included in a formal scheme of fatigue behavior. Accordingly, we propose a review of the physical mechanisms of plastic deformation in f.c.c. metals and alloys to define the state-of-the-art and motivate future studies. The aim is to demonstrate the importance of a good knowledge of the heterogeneous nature of deformation at the intra-granular scale in defining a physical model of cyclic behavior. A large characterization of the different stages associated with the evolution of heterogeneous dislocation structures during tensile and cyclic loadings is given for an austenitic stainless steel AISI 316L. A unified view of these various structures is proposed in the form of a modified Pedersen's map [,max,=,f(,pcum), where ,max is the maximum plastic strain and ,pcum the cumulative plastic strain] in the case of tensile loading and different kinds of cyclic loading: uni-axial and multi-axial tests under stress or strain amplitude control. The specificities of each domain defined in the map are discussed in terms of long-range internal stresses in order to formalize, in a simple composite scheme, the intra-granular stress,strain field. The importance of taking into account this scheme and the nature of the different dislocations populations in a polycrystalline model is illustrated. [source] Tensile-Compressive Creep Asymmetry of Recent Die Cast Magnesium Alloys,ADVANCED ENGINEERING MATERIALS, Issue 9 2007S. Xu The tensile-compressive creep asymmetry of die cast magnesium alloys is experimentally explored and the possible deformation mechanisms are discussed. Creep tests were performed under tension and compression at 125,°C and 150,°C on die cast Mg alloys AM50, AE44 and AJ62A. Higher tensile than compressive creep strengths were observed for all alloys except for low pressure die cast AM50 at a low creep stress of 35 MPa at 125,°C. An aging treatment of 250 hours at 180,°C was employed for AM50 samples to obtain an over-aged microstructure that would minimize the effects of dynamic precipitation of ,-Mg17Al12 on creep. The creep data for the aged samples showed significant scatter, and the trend in tensile-compressive creep asymmetry of the aged samples is not clear for the short-term creep tests under high creep stresses. [source] Boundary characteristics in Heavily Deformed Metals,ADVANCED ENGINEERING MATERIALS, Issue 5 2003G. Winther Abstract The potential of creating nanostructured metals by plastic deformation to very high strains is currently the subject of intensive research. An important part of this research concerns evolution of the characteristics of deformation induced boundaries, in particular boundary spacing and boundary misorientation. The aim of this paper is to give an overview of the present understanding of the relations between these characteristics, the microscopic deformation mechanisms and the macroscopic deformation mode. [source] Constraints on deformation mechanisms during folding provided by rock physical properties: a case study at Sheep Mountain anticline (Wyoming, USA)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010K. Amrouch SUMMARY The Sheep Mountain anticline (Wyoming, USA) is a well-exposed asymmetric, basement-cored anticline that formed during the Laramide orogeny in the early Tertiary. In order to unravel the history of strain during folding, we carried out combined anisotropy of magnetic susceptibility (AMS), anisotropy of P -wave velocity (APWV) and Fry strain analyses. The results are compared to previously published stress,strain data from calcite twins at the microscopic scale and from fracture sets at the mesoscopic scale, and are used to discuss the kinematics and mechanics of forced folding. The results obtained in sandstone and carbonate lithologies demonstrate a good agreement between (1) the principal axes of the AMS and APWV tensors, (2) stress,strain tensors derived from calcite twins, (3) Fry strain axes and mesoscopic fracture sets. Furthermore, these tensors are coaxial with the main structural trends of the anticline. The differences between AMS and APWV fabrics on one hand, and the differential stress values of the forelimb and the backlimb on the other hand, emphasize how the macroscopic asymmetry of Sheep Mountain anticline affects the strain pattern at the microscopic scale. The data set presented in this paper offers a consistent mechanical scenario for the development of Sheep Mountain anticline. [source] Plastic Dissipation Mechanisms in Periodic Microframe-Structured PolymersADVANCED FUNCTIONAL MATERIALS, Issue 9 2009Lifeng Wang Abstract Novel lightweight micro- and nanostructured materials are being used as constituents in hierarchically structured composites for providing high stiffness, high strength, and energy absorbing capability at low weight. Three dimensional SU-8 periodic microframe materials with submicrometer elements exhibit unusual large plastic deformations. Here, the plastic dissipation and mechanical response of polymeric microframe structures is investigated using micromechanical modeling of large deformations. Finite element analysis shows that multiple deformation domains initiate, stabilize, and then spread plasticity through the structure; simulated deformation mechanisms and deformation progression are found to be in excellent agreement with experimental observation. Furthermore, the geometry can be used to tailor aspects of 3D behavior such as effective lateral contraction ratios (elastic and plastic) during tensile loading as well as negative normal stress during simple shear deformation. The effects of structural geometry on mechanical response are also studied to tailor and optimize mechanical performance at a given density. These quantitative investigations enable simulation-based design of optimal lightweight material microstructures for dissipating energy. [source] High Plasticity and Substantial Deformation in Nanocrystalline NiFe Alloys Under Dynamic LoadingADVANCED MATERIALS, Issue 48 2009Sheng Cheng A nanocrystalline (NC) NiFe alloy is presented, in which both highly improved plasticity and strength are achieved by the dynamic-loading-induced deformation mechanisms of de-twinning (that is, reduction of twin density) and significant grain coarsening (see figure). This work highlights potential ingenious avenues to exploit the superior behavior of NC materials under extreme conditions. [source] On double shearing in frictional materialsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2007J. A. M. Teunissen Abstract This paper evaluates the mechanical behaviour of yielding frictional geomaterials. The general Double Shearing model describes this behaviour. Non-coaxiality of stress and plastic strain increments for plane strain conditions forms an important part of this model. The model is based on a micro-mechanical and macro-mechanical formulation. The stress,dilatancy theory in the model combines the mechanical behaviour on both scales. It is shown that the general Double Shearing formulation comprises other Double Shearing models. These models differ in the relation between the mobilized friction and dilatancy and in non-coaxiality. In order to describe reversible and irreversible deformations the general Double Shearing model is extended with elasticity. The failure of soil masses is controlled by shear mechanisms. These shear mechanisms are determined by the conditions along the shear band. The shear stress ratio of a shear band depends on the orientation of the stress in the shear band. There is a difference between the peak strength and the residual strength in the shear band. While peak stress depends on strength properties only, the residual strength depends upon the yield conditions and the plastic deformation mechanisms and is generally considerably lower than the maximum strength. It is shown that non-coaxial models give non-unique solutions for the shear stress ratio on the shear band. The Double Shearing model is applied to various failure problems of soils such as the direct simple shear test, the biaxial test, infinite slopes, interfaces and for the calculation of the undrained shear strength. Copyright © 2006 John Wiley & Sons, Ltd. [source] Microstructural deformation mechanisms of unsaturated granular soilsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2002J. A. Gili Abstract A discrete model for unsaturated granular soils has been developed. Three discrete entities have been defined: particles, water menisci and pores. Local interaction forces and water transfer mechanisms have been integrated into a model through the appropriate equilibrium and balance equations. The results of several numerical tests using this model have been described and discussed. Simulations include wetting and drying under load tests, the application of suction cycles and the effect of a deviatoric stress ratio on wetting-induced collapse. The model reacts just as true granular soil samples behave in laboratory tests. The model provides a new insight into the internal mechanisms leading to large-scale features of behaviour such as wetting-induced collapse or the increase in soil strength provided by suction. The paper also stresses that matric suction changes acting on a granular structure are capable of explaining most of the macroscopic features of stress,strain behaviour. Copyright © 2002 John Wiley & Sons, Ltd. [source] Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysisJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2008P. HASALOVÁ Abstract A detailed field study reveals a gradual transition from high-grade solid-state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular, foliation-parallel bodies of nebulitic migmatite within the eastern part of the Gföhl Unit (Moldanubian domain, Bohemian Massif). The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well-equilibrated banded microstructure by crystallization of new interstitial phases (Kfs, Pl and Qtz) along feldspar boundaries and by resorption of relict feldspar and biotite. The grain size of all felsic phases decreases continuously, whereas the population density of new phases increases. The new phases preferentially nucleate along high-energy like,like boundaries causing the development of a regular distribution of individual phases. This evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases. To explain these data, a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation. In this model, infiltrating melt passes pervasively along grain boundaries through the whole-rock volume and changes completely its macro- and microscopic appearance. It is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation. The melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding, indicating that the melt distribution was controlled by the deformation of the solid framework. The microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms. The migmatite microstructures developed by granular flow accompanied by melt-enhanced diffusion and/or melt flow. However, an AMS study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains. 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