In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation

PubMed Central

Gerbig, Y.B; Michaels, C.A.; Bradby, J.E.; Haberl, B.; Cook, R.F.

2016-01-01

Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline β-tin phase within the a-Si network. PMID:26924926

Electrical resistance oscillations during plastic deformation in A Ti-Al-Nb-Zr alloy at 4·2 K

NASA Astrophysics Data System (ADS)

Nikiforenko, V. N.; Lavrentev, F. F.

1986-10-01

The serrated plastic flow in titanium alloy containing 5% Al, 2·5% Zr and 2% Nb has been investigated by measuring its electrical resistance and applying selective chemical etching. The electrical resistance was found to oscillate under active deformation at 4·2 K. Analysis of the possible causes seems to indicate a dominant role of break by dislocation pile-ups through obstacles, viz second phase precipitates and grain boundaries.

Hydrogen-Induced Plastic Deformation in ZnO

NASA Astrophysics Data System (ADS)

Lukáč, F.; Čížek, J.; Vlček, M.; Procházka, I.; Anwand, W.; Brauer, G.; Traeger, F.; Rogalla, D.; Becker, H.-W.

In the present work hydrothermally grown ZnO single crystals covered with Pd over-layer were electrochemically loaded with hydrogen and the influence of hydrogen on ZnO micro structure was investigated by positron annihilation spectroscopy (PAS). Nuclear reaction analysis (NRA) was employed for determination of depth profile of hydrogen concentration in the sample. NRA measurements confirmed that a substantial amount of hydrogen was introduced into ZnO by electrochemical charging. The bulk hydrogen concentration in ZnO determined by NRA agrees well with the concentration estimated from the transported charge using the Faraday's law. Moreover, a subsurface region with enhanced hydrogen concentration was found in the loaded crystals. Slow positron implantation spectroscopy (SPIS) investigations of hydrogen-loaded crystal revealed enhanced concentration of defects in the subsurface region. This testifies hydrogen-induced plastic deformation of the loaded crystal. Absorbed hydrogen causes a significant lattice expansion. At low hydrogen concentrations this expansion is accommodated by elastic straining, but at higher concentrations hydrogen-induced stress exceeds the yield stress in ZnO and plastic deformation of the loaded crystal takes place. Enhanced hydrogen concentration detected in the subsurface region by NRA is, therefore, due to excess hydrogen trapped at open volume defects introduced by plastic deformation. Moreover, it was found that hydrogen-induced plastic deformation in the subsurface layer leads to typical surface modification: formation of hexagonal shape pyramids on the surface due to hydrogen-induced slip in the [0001] direction.

Analysis of fluid-structure interaction in a frame pipe undergoing plastic deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khamlichi, A.; Jezequel, L.; Jacques, Y.

1995-11-01

Water hammer pressure waves of sufficiently large magnitude can cause plastic flexural deformations in a frame pipe. In this study, the authors propose a modelization of this problem based on plane wave approximation for the fluid equations and approximation of the structure motion by a single-degree-of-freedom elastic-plastic oscillator. Direct analytical integration of elastic-plastic equations through pipe sections, then over the pipe length is performed in order to identify the oscillator parameters. Comparison of the global load-displacement relationship obtained with the finite element solution was considered and has shown good agreement. Fluid-structure coupling is achieved by assuming elbows to act likemore » plane monopole sources, where localized jumps of fluid velocity occur and where net pressure forces are exerted on the structure. The authors have applied this method to analyze the fluid-structure interaction in this range of deformations. Energy exchange between the fluid and the structure and energy dissipation are quantified.« less

Discrete dislocation plasticity analysis of loading rate-dependent static friction.

PubMed

Song, H; Deshpande, V S; Van der Giessen, E

2016-08-01

From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length [Formula: see text], the onset of sliding is fully controlled by adhesion while for large contact length [Formula: see text], the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.

Foam rheology at large deformation

NASA Astrophysics Data System (ADS)

Géminard, J.-C.; Pastenes, J. C.; Melo, F.

2018-04-01

Large deformations are prone to cause irreversible changes in materials structure, generally leading to either material hardening or softening. Aqueous foam is a metastable disordered structure of densely packed gas bubbles. We report on the mechanical response of a foam layer subjected to quasistatic periodic shear at large amplitude. We observe that, upon increasing shear, the shear stress follows a universal curve that is nearly exponential and tends to an asymptotic stress value interpreted as the critical yield stress at which the foam structure is completely remodeled. Relevant trends of the foam mechanical response to cycling are mathematically reproduced through a simple law accounting for the amount of plastic deformation upon increasing stress. This view provides a natural interpretation to stress hardening in foams, demonstrating that plastic effects are present in this material even for minute deformation.

Influence of Plastic Deformation on Martensitic Transformation During Hot Stamping of Complex Structure Auto Parts

NASA Astrophysics Data System (ADS)

Shen, Yuhan; Song, Yanli; Hua, Lin; Lu, Jue

2017-04-01

The ultra-high strength steel auto parts manufactured by hot stamping are widely applied for weight reduction and safety improvement. During the hot stamping process, hot forming and quenching are performed in one step wherein plastic deformation and phase transformation simultaneously take place and affect each other. Thereinto, the influence of deformation on martensitic transformation is of great importance. In the present paper, the influence of plastic deformation on martensitic transformation during hot stamping of complex structure auto parts was investigated. For this purpose, a B-pillar reinforced panel in B1500HS steel was manufactured by hot stamping, and the process was simulated by finite element software based on a thermo-mechanical-metallurgical coupled model. Considering various deformation degrees, the microstructures and mechanical properties at four typical locations of the hot stamped B-pillar reinforced panel were detected. The results show that the martensitic content and the microhardness increase with the increase in the deformation amount. There are two reasons causing this phenomenon: (1) the increase in mechanical driving force and (2) the increased probability of the martensitic nucleation at crystal defects. The x-ray diffraction analysis indicates the carbon enrichment in retained austenite which results from the carbon diffusion during the low-carbon martensite formation. Furthermore, the carbon content decreases with the increase in the deformation amount, because the deformation of austenite suppresses the carbon diffusion.

Study of the Micro-Nonuniformity of the Plastic Deformation of Steel

NASA Technical Reports Server (NTRS)

Chechulin, B. B.

1957-01-01

The plastic flow during deformation of real polycrystalline metals has specific characteristics which distinguish the plastic deformation of metals from the deformation of ordinary isotropic bodies. One of these characteristics is the marked micro-nonuniformity of the plastic deformation of metals. P.O. Pashkov demonstrated the presence of a considerable micro-nonuniformity of the plastic deformation of coarse-grained steel wit medium or low carbon content. Analogous results in the case of tension of coarse-grained aluminum were obtained by W. Boas, who paid particular attention to the role of the grain boundaries in plastic flow. The nonuniformit of the plastic deformation in microvolumes was also recorded by T.N. Gudkova and others, on the alloy KhN80T. N.F. Lashko pointed out the nonuniformity of the plastic deformation for a series of pure polycrystalline metals and one-phase alloys. In his later reports, P.O. Pashkov arrives at he conclusion that the nonuniformity of the distribution of the deformation along the individual grains has a significant effect on the strength and plastic characteristics of polycrystalline metals in the process of plastic flow. However, until now there has not existed any systematic investigation of the general rules of the microscopic nonuniformit of plastic deformation even though the real polycrystalline metals are extremely simple with regard to structure. In the present report, an attempt is made to study the micrononuniformity of the flow of polycrystalline metals by the method of statistical analysis of the variation of the frequency diagrams of the nonuniformity of the grains in the process of plastic deformation.

An Auxetic structure configured as oesophageal stent with potential to be used for palliative treatment of oesophageal cancer; development and in vitro mechanical analysis.

PubMed

Ali, Murtaza N; Rehman, Ihtesham Ur

2011-11-01

Oesophageal cancer is the ninth leading cause of malignant cancer death and its prognosis remains poor. Dysphagia which is an inability to swallow is a presenting symptom of oesophageal cancer and is indicative of incurability. The goal of this study was to design and manufacture an Auxetic structure film and to configure this film as an Auxetic stent for the palliative treatment of oesophageal cancer, and for the prevention of dysphagia. Polypropylene was used as a material for its flexibility and non-toxicity. The Auxetic (rotating-square geometry) structure was made by laser cutting the polypropylene film. This flat structure was welded together to form a tubular form (stent), by an adjustable temperature control soldering iron station: following this, an annealing process was also carried out to ease any material stresses. Poisson's ratio was estimated and elastic and plastic deformation of the Auxetic structure was evaluated. The elastic and plastic deformation behaviours of the Auxetic polypropylene film were evaluated by applying repetitive uniaxial tensile loads. Observation of the structure showed that it was initially elastically deformed, thereafter plastic deformation occurred. This research discusses a novel way of fabricating an Auxetic structure (rotating-squares connected together through hinges) on Polypropylene films, by estimating the Poisson's ratio and evaluating the plastic deformation relevant to the expansion behaviour of an Auxetic stent within the oesophageal lumen.

Change and anisotropy of elastic modulus in sheet metals due to plastic deformation

NASA Astrophysics Data System (ADS)

Ishitsuka, Yuki; Arikawa, Shuichi; Yoneyama, Satoru

2015-03-01

In this study, the effect of the plastic deformation on the microscopic structure and the anisotropy of the elastic modulus in the cold-rolled steel sheet (SPCC) is investigated. Various uniaxial plastic strains (0%, 2.5%, 5%, 7.5%, and 10%) are applied to the annealed SPCC plates, then, the specimens for the tensile tests are cut out from them. The elastic moduli in the longitudinal direction and the transverse direction to the direction that are pre-strained are measured by the tensile tests. Cyclic tests are performed to investigate the effects of the internal friction caused by the movable dislocations in the elastic deformation. Also, the movable dislocations are quantified by the boundary tracking for TEM micrographs. In addition, the behaviors of the change of the elastic modulus in the solutionized and thermal aged aluminum alloy (A5052) are measured to investigate the effect on the movable dislocations with the amount of the depositions. As a result in SPCC, the elastic moduli of the 0° and 90° directions decrease more than 10% as 10% prestrain applied. On the other hand, the elastic modulus shows the recovery behavior after the strain aging and the annealing. The movable dislocation and the internal friction show a tendency to increase as the plastic strain increases. The marked anisotropy is not observed in the elastic modulus and the internal friction. The elastic modulus in A5052 with many and few depositions decreases similarly by the plastic deformation. From the above, the movable dislocations affect the elastic modulus strongly without depending on the deposition amount. Moreover, the elastic modulus recovers after the plastic deformation by reducing the effects of them with the strain aging and the heat treatment.

Elastic-plastic deformation of a metal-matrix composite coupon with a center slot

NASA Technical Reports Server (NTRS)

Post, D.; Czarnek, R.; Joh, D.; Jo, J.; Guo, Y.

1985-01-01

A comprehensive experimental analysis of deformations of the surface of a metal-matrix specimen is reported. The specimen is a 6-ply 0 + or - 45 sub s boron-aluminum tensile coupon with a central slot. Moire interferometry is used for high-sensitivity whole-field measurements of in-plane displacements. Normal and shear strains are calculated from displacement gradients. Displacement fields are analyzed at various load levels from 15% to 95% of the failure load. Deformations of the boron fibers could be distinguished from those of the matrix. Highly localized plastic slip zones occur tangent to the ends of the slot. Shear strains and concurrent transverse compressive strains in the slip zones reach approximately 10% and 1%, respectively. Upon unloading, elastic recovery in surrounding regions causes a reverse plastic shear strain in the slip zone of about 4%. Longitudinal normal strains on the unslotted ligament peak at the slot boundary at about 1% strain. The strain concentration factor at the end of the slot decreases with load level and the advance of plasticity.

Experimental stress analysis of large plastic deformations in a hollow sphere deformed by impact against a concrete block

NASA Technical Reports Server (NTRS)

Morris, R. E.

1973-01-01

An experimental plastic strain measurement system is presented for use on the surface of high velocity impact test models. The system was used on a hollow sphere tested in impact against a reinforced concrete block. True strains, deviatoric stresses, and true stresses were calculated from experimental measurements. The maximum strain measured in the model was small compared to the true failure strain obtained from static tensile tests of model material. This fact suggests that a much greater impact velocity would be required to cause failure of the model shell structure.

Effect of deformation on the structural state of piracetam

NASA Astrophysics Data System (ADS)

Kanunnikova, O. M.; Mikhailova, S. S.; Karban', O. V.; Mukhgalin, V. V.; Aksenova, V. V.; Sen'kovskii, B. V.; Pechina, E. A.; Lad'yanov, V. I.

2016-04-01

The effect of various deformation actions on the structure-phase transformations in piracetam of modifications I and II with a sodium acetate addition is studied. Mechanical activation and pressing are shown to cause the polymorphic transformation of modification I into modification II, and modification III forms predominantly during severe plastic deformation by torsion. The structural difference between the piracetam molecules of modifications I and II is found to be retained in aqueous solutions.

Elastic and plastic strain measurement in high temperature environment using laser speckle

NASA Technical Reports Server (NTRS)

Chiang, Fu-Pen

1992-01-01

Two laser speckle methods are described to measure strain in high temperature environment and thermal strain caused by high temperature. Both are non-contact, non-destructive and remote sensing techniques that can be automated. The methods have different but overlapping ranges of application with one being more suitable for large plastic deformation.

Polycrystal-Plasticity Simulation of Roping in AA 6xxx Automotive Sheet Alloys

NASA Astrophysics Data System (ADS)

Engler, O.; Schäfer, C.; Brinkman, H.-J.

The occurrence of roping in AA 6xxx series sheet for car body applications is caused by the collective deformation of band-like clusters of grains with similar crystallographic orientation. In this study large-scale orientation maps obtained by electron back-scattered diffraction (EBSD) are input into a visco-plastic self-consistent polycrystal-plasticity model to analyze the strain anisotropy caused by the topographic arrangement of the recrystallization texture orientations and, in turn, the occurrence of roping. At variance to earlier studies, the measurements were carried out in the short transverse section of the sheets so as to get information on distribution and morphology of orientation clusters through the sheet thickness. Then, narrow bands in the EBSD maps aligned parallel to the ridges on the sheet surface are considered, and the variation in macroscopic strain response from band to band is determined. For a given deformation of the sample these simulations yield quantitative information on the level of roping of Al-alloy sheet for car body applications.

Optimisation and Validation of the ARAMIS Digital Image Correlation System for Use in Large-scale High-strain-rate Events

DTIC Science & Technology

2013-08-01

enamel paint. Under extreme plastic deformation, the relative deformation of the coating could cause the coating to separate resulting in loss of...point for one to be found. If a discontinuity, such as a crack , occurs through the object separating speckle pattern, then the strain data will only

Reduced partitioning of plastic strain for strong and yet ductile precipitate-strengthened alloys.

PubMed

Jones, R D; Di Gioacchino, F; Lim, H; Edwards, T E J; Schwalbe, C; Battaile, C C; Clegg, W J

2018-06-06

When a material that contains precipitates is deformed, the precipitates and the matrix may strain plastically by different amounts causing stresses to build up at the precipitate-matrix interfaces. If premature failure is to be avoided, it is therefore essential to reduce the difference in the plastic strain between the two phases. Here, we conduct nanoscale digital image correlation to measure a new variable that quantifies this plastic strain difference and show how its value can be used to estimate the associated interfacial stresses, which are found to be approximately three times greater in an Fe-Ni 2 AlTi steel than in the more ductile Ni-based superalloy CMSX-4 ® . It is then demonstrated that decreasing these stresses significantly improves the ability of the Fe-Ni 2 AlTi microstructure to deform under tensile loads without loss in strength.

Studying plastic shear localization in aluminum alloys under dynamic loading

NASA Astrophysics Data System (ADS)

Bilalov, D. A.; Sokovikov, M. A.; Chudinov, V. V.; Oborin, V. A.; Bayandin, Yu. V.; Terekhina, A. I.; Naimark, O. B.

2016-12-01

An experimental and theoretical study of plastic shear localization mechanisms observed under dynamic deformation using the shear-compression scheme on a Hopkinson-Kolsky bar has been carried out using specimens of AMg6 alloy. The mechanisms of plastic shear instability are associated with collective effects in the microshear ensemble in spatially localized areas. The lateral surface of the specimens was photographed in the real-time mode using a CEDIP Silver 450M high-speed infrared camera. The temperature distribution obtained at different times allowed us to trace the evolution of the localization of the plastic strain. Based on the equations that describe the effect of nonequilibrium transitions on the mechanisms of structural relaxation and plastic flow, numerical simulation of plastic shear localization has been performed. A numerical experiment relevant to the specimen-loading scheme was carried out using a system of constitutive equations that reflect the part of the structural relaxation mechanisms caused by the collective behavior of microshears with the autowave modes of the evolution of the localized plastic flow. Upon completion of the experiment, the specimens were subjected to microstructure analysis using a New View-5010 optical microscope-interferometer. After the dynamic deformation, the constancy of the Hurst exponent, which reflects the relationship between the behavior of defects and roughness induced by the defects on the surfaces of the specimens is observed in a wider range of spatial scales. These investigations revealed the distinctive features in the localization of the deformation followed by destruction to the script of the adiabatic shear. These features may be caused by the collective multiscale behavior of defects, which leads to a sharp decrease in the stress-relaxation time and, consequently, a localized plastic flow and generation of fracture nuclei in the form of adiabatic shear. Infrared scanning of the localization zone of the plastic strain in situ and the subsequent study of the defect structure corroborated the hypothesis about the decisive role of non-equilibrium transitions in defect ensembles during the evolution of a localized plastic flow.

Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

NASA Astrophysics Data System (ADS)

Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

2018-02-01

This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems <100>{010} and < 1 bar 10>{110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system <100>{001} and rotation axis [010]. The slip system < 1 bar 10>{110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of deformation, if the isotopic systems of deformed zircon were reset.

Finite Element Analysis of Plastic Deformation During Impression Creep

NASA Astrophysics Data System (ADS)

Naveena; Ganesh Kumar, J.; Mathew, M. D.

2015-04-01

Finite element (FE) analysis of plastic deformation associated with impression creep deformation of 316LN stainless steel was carried out. An axisymmetric FE model of 10 × 10 × 10 mm specimen with 1-mm-diameter rigid cylindrical flat punch was developed. FE simulation of impression creep deformation was performed by assuming elastic-plastic-power-law creep deformation behavior. Evolution of the stress with time under the punch during elastic, plastic, and creep processes was analyzed. The onset of plastic deformation was found to occur at a nominal stress about 1.12 times the yield stress of the material. The size of the developed plastic zone was predicted to be about three times the radius of the punch. The material flow behavior and the pile-up on specimen surface have been modeled.

The notion of a plastic material spin in atomistic simulations

NASA Astrophysics Data System (ADS)

Dickel, D.; Tenev, T. G.; Gullett, P.; Horstemeyer, M. F.

2016-12-01

A kinematic algorithm is proposed to extend existing constructions of strain tensors from atomistic data to decouple elastic and plastic contributions to the strain. Elastic and plastic deformation and ultimately the plastic spin, useful quantities in continuum mechanics and finite element simulations, are computed from the full, discrete deformation gradient and an algorithm for the local elastic deformation gradient. This elastic deformation gradient algorithm identifies a crystal type using bond angle analysis (Ackland and Jones 2006 Phys. Rev. B 73 054104) and further exploits the relationship between bond angles to determine the local deformation from an ideal crystal lattice. Full definitions of plastic deformation follow directly using a multiplicative decomposition of the deformation gradient. The results of molecular dynamics simulations of copper in simple shear and torsion are presented to demonstrate the ability of these new discrete measures to describe plastic material spin in atomistic simulation and to compare them with continuum theory.

Mechanisms of Plastic Deformation in Collagen Networks Induced by Cellular Forces.

PubMed

Ban, Ehsan; Franklin, J Matthew; Nam, Sungmin; Smith, Lucas R; Wang, Hailong; Wells, Rebecca G; Chaudhuri, Ovijit; Liphardt, Jan T; Shenoy, Vivek B

2018-01-23

Contractile cells can reorganize fibrous extracellular matrices and form dense tracts of fibers between neighboring cells. These tracts guide the development of tubular tissue structures and provide paths for the invasion of cancer cells. Here, we studied the mechanisms of the mechanical plasticity of collagen tracts formed by contractile premalignant acinar cells and fibroblasts. Using fluorescence microscopy and second harmonic generation, we quantified the collagen densification, fiber alignment, and strains that remain within the tracts after cellular forces are abolished. We explained these observations using a theoretical fiber network model that accounts for the stretch-dependent formation of weak cross-links between nearby fibers. We tested the predictions of our model using shear rheology experiments. Both our model and rheological experiments demonstrated that increasing collagen concentration leads to substantial increases in plasticity. We also considered the effect of permanent elongation of fibers on network plasticity and derived a phase diagram that classifies the dominant mechanisms of plasticity based on the rate and magnitude of deformation and the mechanical properties of individual fibers. Plasticity is caused by the formation of new cross-links if moderate strains are applied at small rates or due to permanent fiber elongation if large strains are applied over short periods. Finally, we developed a coarse-grained model for plastic deformation of collagen networks that can be employed to simulate multicellular interactions in processes such as morphogenesis, cancer invasion, and fibrosis. Copyright © 2017 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Two Back Stress Hardening Models in Rate Independent Rigid Plastic Deformation

NASA Astrophysics Data System (ADS)

Yun, Su-Jin

In the present work, the constitutive relations based on the combination of two back stresses are developed using the Armstrong-Frederick, Phillips and Ziegler’s type hardening rules. Various evolutions of the kinematic hardening parameter can be obtained by means of a simple combination of back stress rate using the rule of mixtures. Thus, a wide range of plastic deformation behavior can be depicted depending on the dominant back stress evolution. The ultimate back stress is also determined for the present combined kinematic hardening models. Since a kinematic hardening rule is assumed in the finite deformation regime, the stress rate is co-rotated with respect to the spin of substructure obtained by incorporating the plastic spin concept. A comparison of the various co-rotational rates is also included. Assuming rigid plasticity, the continuum body consists of the elastic deformation zone and the plastic deformation zone to form a hybrid finite element formulation. Then, the plastic deformation behavior is investigated under various loading conditions with an assumption of the J2 deformation theory. The plastic deformation localization turns out to be strongly dependent on the description of back stress evolution and its associated hardening parameters. The analysis for the shear deformation with fixed boundaries is carried out to examine the deformation localization behavior and the evolution of state variables.

Numerical Modeling of Exploitation Relics and Faults Influence on Rock Mass Deformations

NASA Astrophysics Data System (ADS)

Wesołowski, Marek

2016-12-01

This article presents numerical modeling results of fault planes and exploitation relics influenced by the size and distribution of rock mass and surface area deformations. Numerical calculations were performed using the finite difference program FLAC. To assess the changes taking place in a rock mass, an anisotropic elasto-plastic ubiquitous joint model was used, into which the Coulomb-Mohr strength (plasticity) condition was implemented. The article takes as an example the actual exploitation of the longwall 225 area in the seam 502wg of the "Pokój" coal mine. Computer simulations have shown that it is possible to determine the influence of fault planes and exploitation relics on the size and distribution of rock mass and its surface deformation. The main factor causing additional deformations of the area surface are the abandoned workings in the seam 502wd. These abandoned workings are the activation factor that caused additional subsidences and also, due to the significant dip, they are a layer on which the rock mass slides down in the direction of the extracted space. These factors are not taken into account by the geometrical and integral theories.

Strength evolution of simulated carbonate-bearing faults: The role of normal stress and slip velocity

NASA Astrophysics Data System (ADS)

Mercuri, Marco; Scuderi, Marco Maria; Tesei, Telemaco; Carminati, Eugenio; Collettini, Cristiano

2018-04-01

A great number of earthquakes occur within thick carbonate sequences in the shallow crust. At the same time, carbonate fault rocks exhumed from a depth < 6 km (i.e., from seismogenic depths) exhibit the coexistence of structures related to brittle (i.e., cataclasis) and ductile deformation processes (i.e., pressure-solution and granular plasticity). We performed friction experiments on water-saturated simulated carbonate-bearing faults for a wide range of normal stresses (from 5 to 120 MPa) and slip velocities (from 0.3 to 100 μm/s). At high normal stresses (σn > 20 MPa) fault gouges undergo strain-weakening, that is more pronounced at slow slip velocities, and causes a significant reduction of frictional strength, from μ = 0.7 to μ = 0.47. Microstructural analysis show that fault gouge weakening is driven by deformation accommodated by cataclasis and pressure-insensitive deformation processes (pressure solution and granular plasticity) that become more efficient at slow slip velocity. The reduction in frictional strength caused by strain weakening behaviour promoted by the activation of pressure-insensitive deformation might play a significant role in carbonate-bearing faults mechanics.

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response

PubMed Central

Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-01-01

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process. PMID:29027925

Multiscale Modeling of Polycrystalline NiTi Shape Memory Alloy under Various Plastic Deformation Conditions by Coupling Microstructure Evolution and Macroscopic Mechanical Response.

PubMed

Hu, Li; Jiang, Shuyong; Zhou, Tao; Tu, Jian; Shi, Laixin; Chen, Qiang; Yang, Mingbo

2017-10-13

Numerical modeling of microstructure evolution in various regions during uniaxial compression and canning compression of NiTi shape memory alloy (SMA) are studied through combined macroscopic and microscopic finite element simulation in order to investigate plastic deformation of NiTi SMA at 400 °C. In this approach, the macroscale material behavior is modeled with a relatively coarse finite element mesh, and then the corresponding deformation history in some selected regions in this mesh is extracted by the sub-model technique of finite element code ABAQUS and subsequently used as boundary conditions for the microscale simulation by means of crystal plasticity finite element method (CPFEM). Simulation results show that NiTi SMA exhibits an inhomogeneous plastic deformation at the microscale. Moreover, regions that suffered canning compression sustain more homogeneous plastic deformation by comparison with the corresponding regions subjected to uniaxial compression. The mitigation of inhomogeneous plastic deformation contributes to reducing the statistically stored dislocation (SSD) density in polycrystalline aggregation and also to reducing the difference of stress level in various regions of deformed NiTi SMA sample, and therefore sustaining large plastic deformation in the canning compression process.

How tough is bone? Application of elastic-plastic fracture mechanics to bone.

PubMed

Yan, Jiahau; Mecholsky, John J; Clifton, Kari B

2007-02-01

Bone, with a hierarchical structure that spans from the nano-scale to the macro-scale and a composite design composed of nano-sized mineral crystals embedded in an organic matrix, has been shown to have several toughening mechanisms that increases its toughness. These mechanisms can stop, slow, or deflect crack propagation and cause bone to have a moderate amount of apparent plastic deformation before fracture. In addition, bone contains a high volumetric percentage of organics and water that makes it behave nonlinearly before fracture. Many researchers used strength or critical stress intensity factor (fracture toughness) to characterize the mechanical property of bone. However, these parameters do not account for the energy spent in plastic deformation before bone fracture. To accurately describe the mechanical characteristics of bone, we applied elastic-plastic fracture mechanics to study bone's fracture toughness. The J integral, a parameter that estimates both the energies consumed in the elastic and plastic deformations, was used to quantify the total energy spent before bone fracture. Twenty cortical bone specimens were cut from the mid-diaphysis of bovine femurs. Ten of them were prepared to undergo transverse fracture and the other 10 were prepared to undergo longitudinal fracture. The specimens were prepared following the apparatus suggested in ASTM E1820 and tested in distilled water at 37 degrees C. The average J integral of the transverse-fractured specimens was found to be 6.6 kPa m, which is 187% greater than that of longitudinal-fractured specimens (2.3 kPa m). The energy spent in the plastic deformation of the longitudinal-fractured and transverse-fractured bovine specimens was found to be 3.6-4.1 times the energy spent in the elastic deformation. This study shows that the toughness of bone estimated using the J integral is much greater than the toughness measured using the critical stress intensity factor. We suggest that the J integral method is a better technique in estimating the toughness of bone.

Core Characteristics Deterioration due to Plastic Deformation

NASA Astrophysics Data System (ADS)

Kaido, Chikara; Arai, Satoshi

This paper discusses the effect of plastic deformation at core manufacturing on the characteristics of cores where non-oriented electrical steel sheets are used as core material. Exciting field and iron loss increase proportionally to plastic deformation in the case of rP<10, where rP is a ratio of plastic deformation to that at yield point. In this region, anomalous eddy currents increase because plastic deformations of crystalline grains are distributed and then the flux distribution is induced. In the case of rP>20, the deterioration tend to saturate, and the increases in magnetic field and iron loss are 1000 to 1500A/m and 2 to 4W/kg. They are related to grain size, and high grade with larger grain may have lager field increase and smaller iron loss increase. Anomalous eddy current losses scarcely increase in this region. In actual motors, the plastic deformation affects iron loss increase although exciting current increases a little.

Plastic strain is a mixture of avalanches and quasireversible deformations: Study of various sizes

NASA Astrophysics Data System (ADS)

Szabó, Péter; Ispánovity, Péter Dusán; Groma, István

2015-02-01

The size dependence of plastic flow is studied by discrete dislocation dynamical simulations of systems with various amounts of interacting dislocations while the stress is slowly increased. The regions between avalanches in the individual stress curves as functions of the plastic strain were found to be nearly linear and reversible where the plastic deformation obeys an effective equation of motion with a nearly linear force. For small plastic deformation, the mean values of the stress-strain curves obey a power law over two decades. Here and for somewhat larger plastic deformations, the mean stress-strain curves converge for larger sizes, while their variances shrink, both indicating the existence of a thermodynamical limit. The converging averages decrease with increasing size, in accordance with size effects from experiments. For large plastic deformations, where steady flow sets in, the thermodynamical limit was not realized in this model system.

Deformation partitioning provides insight into elastic, plastic, and viscous contributions to bone material behavior.

PubMed

Ferguson, V L

2009-08-01

The relative contributions of elastic, plastic, and viscous material behavior are poorly described by the separate extraction and analysis of the plane strain modulus, E('), the contact hardness, H(c) (a hybrid parameter encompassing both elastic and plastic behavior), and various viscoelastic material constants. A multiple element mechanical model enables the partitioning of a single indentation response into its fundamental elastic, plastic, and viscous deformation components. The objective of this study was to apply deformation partitioning to explore the role of hydration, tissue type, and degree of mineralization in bone and calcified cartilage. Wet, ethanol-dehydrated, and PMMA-embedded equine cortical bone samples and PMMA-embedded human femoral head tissues were analyzed for contributions of elastic, plastic and viscous deformation to the overall nanoindentation response at each site. While the alteration of hydration state had little effect on any measure of deformation, unembedded tissues demonstrated significantly greater measures of resistance to plastic deformation than PMMA-embedded tissues. The PMMA appeared to mechanically stabilize the tissues and prevent extensive permanent deformation within the bone material. Increasing mineral volume fraction correlated with positive changes in E('), H(c), and resistance to plastic deformation, H; however, the partitioned deformation components were generally unaffected by mineralization. The contribution of viscous deformation was minimal and may only play a significant role in poorly mineralized tissues. Deformation partitioning enables a detailed interpretation of the elastic, plastic, and viscous contributions to the nanomechanical behavior of mineralized tissues that is not possible when examining modulus and contact hardness alone. Varying experimental or biological factors, such as hydration or mineralization level, enables the understanding of potential mechanisms for specific mechanical behavior patterns that would otherwise be hidden within a more complex set of material property parameters.

Seismic cycle feedbacks in a mid-crustal shear zone

NASA Astrophysics Data System (ADS)

Melosh, Benjamin L.; Rowe, Christie D.; Gerbi, Christopher; Smit, Louis; Macey, Paul

2018-07-01

Mid-crustal fault rheology is controlled by alternating brittle and plastic deformation mechanisms, which cause feedback cycles that influence earthquake behavior. Detailed mapping and microstructural observations in the Pofadder Shear Zone (Namibia and South Africa) reveal a lithologically heterogeneous shear zone core with quartz-rich mylonites and ultramylonites, plastically overprinted pseudotachylyte and active shear folds. We present evidence for a positive feedback cycle in which coseismic grain size reduction facilitates active shear folding by enhancing competency contrasts and promoting crystal plastic flow. Shear folding strengthens a portion of a shear zone by limb rotation, focusing deformation and promoting plastic flow or brittle slip in resulting areas of localized high stress. Using quartz paleopiezometry, we estimate strain and slip rates consistent with other studies of exhumed shear zones and modern plate boundary faults, helping establish the Pofadder Shear Zone as an ancient analogue to modern, continental-scale, strike-slip faults. This feedback cycle influences seismicity patterns at the scale of study (10s of meters) and possibly larger scales as well, and contributes to bulk strengthening of the brittle-plastic transition on modern plate boundary faults.

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

NASA Astrophysics Data System (ADS)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

Effects of Fine Particle Peening Conditions on the Rotational Bending Fatigue Strength of a Vacuum-Carburized Transformation-Induced Plasticity-Aided Martensitic Steel

NASA Astrophysics Data System (ADS)

Sugimoto, Koh-ichi; Hojo, Tomohiko; Mizuno, Yuta

2018-02-01

The effects of fine particle peening conditions on the rotational bending fatigue strength of a vacuum-carburized transformation-induced plasticity-aided martensitic steel with a chemical composition of 0.20 pct C, 1.49 pct Si, 1.50 pct Mn, 0.99 pct Cr, 0.02 pct Mo, and 0.05 pct Nb were investigated for the fabrication of automotive drivetrain parts. The maximum fatigue limit, resulting from high hardness and compressive residual stress in the surface-hardened layer caused by the severe plastic deformation and the strain-induced martensite transformation of the retained austenite during fine particle peening, was obtained by fine particle peening at an arc height of 0.21 mm (N). The high fatigue limit was also a result of the increased martensite fraction and the active plastic relaxation via the strain-induced martensite transformation during fatigue deformation, as well as preferential crack initiation on the surface or at the subsurface.

Mechanical Deformation of a Lithium-Metal Anode Due to a Very Stiff Separator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrese, A; Newman, J

2014-05-21

This work builds on the two-dimensional model presented by Ferrese et al. [J. Electrochem. Soc., 159, A1615 (2012)1, which captures the movement of lithium metal at the negative electrode during cycling in a Li-metal/LiCoO2 cell. In this paper, the separator is modeled as a dendrite-inhibiting polymer separator with an elastic modulus of 16 GPa. The separator resists the movement of lithium through the generation of stresses in the cell. These stresses affect the negative electrode through two mechanisms altering the thermodynamics of the negative electrode and deforming the negative electrode mechanically. From this analysis, we find that the dendrite-inhibiting separatormore » causes plastic and elastic deformation of the lithium at the negative electrode which flattens the electrode considerably when compared to the liquid-electrolyte case. This flattening of the negative electrode causes only very slight differences in the local state of charge in the positive electrode. When comparing the magnitude of the effects flattening the negative electrode, we find that the plastic deformation plays a much larger role than either the pressure-modified reaction kinetics or elastic deformation. This is due to the low yield strength of the lithium metal, which limits the stresses such that they have only a small effect on the reaction kinetics. (C) 2014 The Electrochemical Society. All rights reserved.« less

Defects with Deep Levels in GaAs Induced by Plastic Deformation and Electron Irradiation

NASA Astrophysics Data System (ADS)

Haga, Toru; Suezawa, Masashi; Sumino, Koji

1988-10-01

Defects with deep electronic energy levels induced by plastic deformation at 450°C or electron irradiation at room temperature in boat-grown GaAs crystals are investigated by means of optical absorption. The optical absorption spectra associated with the induced defects are compared with that of grown-in defects EL2. Thermal stabilities of the defects are studied by tracing the changes in the absorption spectra due to isochronal annealing of the specimens. The defects induced by the above two procedures are identified not to be EL2, even though some part of the defects gives rise to absorption similar to that caused by EL2 in the spectral shape. The absorptions in both the deformed and the irradiated samples are mostly photo-unquenchable. Deformation-induced defects responsible for this absorption are found to be AsGa antisite-related defects which are less thermally stable than EL2. Irradiation-induced defects giving rise to this kind of absorption are far more unstable in comparison with the deformation-induced defects, and are mostly eliminated by annealing at temperatures lower than 300°C.

Experimental Study on Tensile Properties of a Novel Porous Metal Fiber/Powder Sintered Composite Sheet

PubMed Central

Zou, Shuiping; Wan, Zhenping; Lu, Longsheng; Tang, Yong

2016-01-01

A novel porous metal fiber/powder sintered composite sheet (PMFPSCS) is developed by sintering a mixture of a porous metal fiber sintered sheet (PMFSS) and copper powders with particles of a spherical shape. The characteristics of the PMFPSCS including its microstructure, sintering density and porosity are investigated. A uniaxial tensile test is carried out to study the tensile behaviors of the PMFPSCS. The deformation and failure mechanisms of the PMFSCS are discussed. Experimental results show that the PMFPSCS successively experiences an elastic stage, hardening stage, and fracture stage under tension. The tensile strength of the PMFPSCS is determined by a reticulated skeleton of fibers and reinforcement of copper powders. With the porosity of the PMFSS increasing, the tensile strength of the PMFPSCS decreases, whereas the reinforcement of copper powders increases. At the elastic stage, the structural elastic deformation is dominant, and at the hardening stage, the plastic deformation is composed of the structural deformation and the copper fibers’ plastic deformation. The fracture of the PMFPSCS is mainly caused by the breaking of sintering joints. PMID:28773833

Characterization of a cold-rolled 2101 lean duplex stainless steel.

PubMed

Bassani, Paola; Breda, Marco; Brunelli, Katya; Mészáros, Istvan; Passaretti, Francesca; Zanellato, Michela; Calliari, Irene

2013-08-01

Duplex stainless steels (DSS) may be defined as a category of steels with a two-phase ferritic-austenitic microstructure, which combines good mechanical and corrosion properties. However, these steels can undergo significant microstructural modification as a consequence of either thermo-mechanical treatments (ferrite decomposition, which causes σ- and χ-phase formation and nitride precipitation) or plastic deformation at room temperature [austenite transformation into strain-induced martensite (SIM)]. These secondary phases noticeably affect the properties of DSS, and therefore are of huge industrial interest. In the present work, SIM formation was investigated in a 2101 lean DSS. The material was subjected to cold rolling at various degrees of deformation (from 10 to 80% thickness reduction) and the microstructure developed after plastic deformation was investigated by electron backscattered diffraction, X-ray diffraction measurements, and hardness and magnetic tests. It was observed that SIM formed as a consequence of deformations higher than ~20% and residual austenite was still observed at 80% of thickness reduction. Furthermore, a direct relationship was found between microstructure and magnetic properties.

Primary combination of phase-field and discrete dislocation dynamics methods for investigating athermal plastic deformation in various realistic Ni-base single crystal superalloy microstructures

NASA Astrophysics Data System (ADS)

Gao, Siwen; Rajendran, Mohan Kumar; Fivel, Marc; Ma, Anxin; Shchyglo, Oleg; Hartmaier, Alexander; Steinbach, Ingo

2015-10-01

Three-dimensional discrete dislocation dynamics (DDD) simulations in combination with the phase-field method are performed to investigate the influence of different realistic Ni-base single crystal superalloy microstructures with the same volume fraction of {γ\\prime} precipitates on plastic deformation at room temperature. The phase-field method is used to generate realistic microstructures as the boundary conditions for DDD simulations in which a constant high uniaxial tensile load is applied along different crystallographic directions. In addition, the lattice mismatch between the γ and {γ\\prime} phases is taken into account as a source of internal stresses. Due to the high antiphase boundary energy and the rare formation of superdislocations, precipitate cutting is not observed in the present simulations. Therefore, the plastic deformation is mainly caused by dislocation motion in γ matrix channels. From a comparison of the macroscopic mechanical response and the dislocation evolution for different microstructures in each loading direction, we found that, for a given {γ\\prime} phase volume fraction, the optimal microstructure should possess narrow and homogeneous γ matrix channels.

Features of structure formation in the low modulus quasi-single crystal from Zr-25%Nb alloy at cold rolling

NASA Astrophysics Data System (ADS)

Isaenkova, M.; Perlovich, Yu.; Fesenko, V.; Babich, Y.; Zaripova, M.; Krapivka, N.

2018-05-01

The paper presents the results of investigation of the regularities of the structure and texture formation during rolling of single crystals of Zr-25%Nb alloy differing in their initial orientations relative to the external principal directions in the rolled plate: normal (ND) and rolling directions (RD). The features of rolled single crystals with initial orientations of planes {001}, {011} or {111} parallel to the rolling plane and different crystallographic directions along RD are considered. A comparison of the peculiarities of plastic deformation in a polycrystalline alloy of the same composition is made. For the samples studied, a decrease in the lattice parameter of the β-phase has been recorded, the minimum of the parameter being observed for different degrees of deformation, varying from 20 to 50%. Observed decrease in the unit cell parameter can be connected with the precipitation of the α(α')-Zr phase from the deformed nonequilibrium β-phase of the Zr-25%Nb alloy, i.e. change in the composition of the solid solution. Distributions of the increase in the dimensions of the deformed single crystal along RD and the transverse direction (TD) with its deformation up to 30% in thickness, which indicate the anisotropy of the plasticity of single crystals during their rolling, are constructed on stereographic projection. It is shown, that the deformation of single crystals occurs practically without increasing of their dimensions in the <110> direction with a total thickness deformation of up to 30%. Direction <110> is characterized by maximum hardening (microhardness) with indentation along it, which causes low plasticity of deformed and annealed foils from Zr-25%Nb alloy at the stretching along and across RD, that is connected with the features of their crystallographic texture.

Estimating Tunnel Strain in the Weak and Schistose Rock Mass Influenced by Stress Anisotropy: An Evaluation Based on Three Tunnel Cases from Nepal

NASA Astrophysics Data System (ADS)

Panthi, Krishna Kanta; Shrestha, Pawan Kumar

2018-06-01

Total plastic deformation in tunnels passing through weak and schistose rock mass consists of both time-independent and time-dependent deformations. The extent of this total deformation is heavily influenced by the rock mass deformability properties and in situ stress condition prevailing in the area. If in situ stress is not isotropic, the deformation magnitude is not only different along the longitudinal alignment but also along the periphery of the tunnel wall. This manuscript first evaluates the long-term plastic deformation records of three tunnel projects from the Nepal Himalaya and identifies interlink between the time-independent and time-dependent deformations using the convergence law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech 24(3):145-154, 1987a, Int J Rock Mech Min Sci Geomech 24(3):155-164, 1987b). Secondly, the manuscript attempts to establish a correlation between plastic deformations (tunnel strain) and rock mass deformable properties, support pressure and in situ stress conditions. Finally, patterns of time-independent and time-dependent plastic deformations are also evaluated and discussed. The long-term plastic deformation records of 24 tunnel sections representing four different rock types of three different headrace tunnel cases from Nepal Himalaya are extensively used in this endeavor. The authors believe that the proposed findings will be a step further in analysis of plastic deformations in tunnels passing through weak and schistose rock mass and along the anisotropic stress conditions.

Plastic Deformation and Failure Analysis of Phase Change Random Access Memory

NASA Astrophysics Data System (ADS)

Yang; Hongxin; Shi; Luping; Lee; Koon, Hock; Zhao; Rong; Li; Jianming; Lim; Guan, Kian; Chong; Chong, Tow

2009-04-01

Although lateral phase change random access memory (PCRAM) has attracted a lot of interest due to its simpler fabrication process and lower current compared to ovonic unified memory (OUM), it faces a problem of poor lifetime. This paper studied relation between plastic deformation and the failure of PCRAM through both experiment and simulation. OUM and lateral PCRAM incorporating Ge2Sb2Te5 were fabricated and tested. The overwriting test showed that lifetime of OUM exceeded 106 while that of lateral PCRAM was only about 100. Using atomic force microscopy (AFM), it was found that the plastic deformation after 106 overwriting reached several tens of nm for lateral PCRAM while it was negligible for OUM. The thermo-mechanical simulation results confirmed the similar results on larger plastic deformation of lateral PCRAM than that of OUM during overwriting. As plastic deformation involves of atomic bonds breaking and reforming in phase change material, the plastic deformation may be one main reason for the failure of lateral PCRAM.

Plastic deformation behaviors of Ni- and Zr-based bulk metallic glasses subjected to nanoindentation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weizhong, Liang, E-mail: wzliang1966@126.com; Zhiliang, Ning; Zhenqian, Dang

2013-12-15

Plastic deformation behaviors of Ni{sub 42}Ti{sub 20}Zr{sub 21.5}Al{sub 8}Cu{sub 5}Si{sub 3.5} and Zr{sub 51}Ti{sub 5}Ni{sub 10}Cu{sub 25}Al{sub 9} bulk metallic glasses at room temperature were studied by nanoindentation testing and atomic force microscopy under equivalent indentation experimental conditions. The different chemical composition of these two bulk metallic glasses produced variant tendencies for displacement serrated flow to occur during the loading process. The nanoindentation strain rate was calculated as a function of indentation displacement in order to verify the occurrence of displacement serrated flow at different loading rates. Atomic force microscopy revealed decreasing numbers of discrete shear bands around the indentationmore » sites as loading rates increased from 0.025 to 2.5 mNs{sup −1}. Variations in plastic deformation behaviors between Ni and Zr-based glasses materials can be explained by the different metastable microstructures and thermal stabilities of the two materials. The mechanism governing plastic deformation of these metallic glasses was analyzed in terms of an established model of the shear transformation zone. - Highlights: • Plastic deformation of Ni- and Zr-based BMG is studied under identical conditions • Zr-based BMG undergoes a greater extent of plastic deformation than Ni-based BMG • Nanoindentation strain rate is studied to clarify variation in plastic deformation • Metastable microstructure, thermal stability affect BMG plastic deformation.« less

Non-destructive and three-dimensional measurement of local strain development during tensile deformation in an aluminium alloy

NASA Astrophysics Data System (ADS)

Kobayashi, M.; Miura, H.; Toda, H.

2015-08-01

Anisotropy of mechanical responses depending on crystallographic orientation causes inhomogeneous deformation on the mesoscopic scale (grain size scale). Investigation of the local plastic strain development is important for discussing recrystallization mechanisms, because the sites with higher local plastic strain may act as potential nucleation sites for recrystallization. Recently, high-resolution X-ray tomography, which is non-destructive inspection method, has been utilized for observation of the materials structure. In synchrotron radiation X-ray tomography, more than 10,000 microstructural features, like precipitates, dispersions, compounds and hydrogen pores, can be observed in aluminium alloys. We have proposed employing these microstructural features as marker gauges to measure local strains, and then have developed a method to calculate the three-dimensional strain distribution by tracking the microstructural features. In this study, we report the development of local plastic strain as a function of the grain microstructure in an aluminium alloy by means of this three-dimensional strain measurement technique. Strongly heterogeneous strain development was observed during tensile loading to 30%. In other words, some parts of the sample deform little whereas another deforms a lot. However, strain in the whole specimen was keeping harmony. Comparing the microstructure with the strain concentration that is obtained by this method has a potential to reveal potential nucleation sites of recrystallization.

Mechanism for Angular Deformation of L-shaped Specimens —Influence of Filling Material and Shrinkage Factor—

NASA Astrophysics Data System (ADS)

Furuhashi, Hiroshi; Aoki, Takerou; Okabe, Sayaka; Arai, Tsuyoshi; Seto, Masahiro; Yamabe, Masashi

L-shape is the important and fundamental shape for injection molded parts. Therefore to reveal the corner angular deformation mechanism of this shape is also valuable for understanding the warpage mechanism of injection molded parts. In this study, we investigated the influence of the filling materials (fiber, talc and not filled) and two kinds of anisotropic shrinkage factors, solidification shrinkage and shrinkage caused by thermal expansion coefficient during cooling, to the angular deformation of L-shaped specimens and the following conclusions were obtained 1) The anisotropic solidification shrinkage of MD/TD and the anisotropic thermal expansion coefficient of MD/TD are considered to cause the angular deformation of L-shaped specimens. But the contribution ratios of these two anisotropies depend on the filling material for plastics. 2) The angular deformation of PP and PBT filled with glass fiber is mainly caused by the anisotropic thermal expansion coefficient and on the other hand, that of PP and PBT without filling material is caused by anisotropic solidification shrinkage. However both anisotropies cause the angular deformation of PP filled with talc. 3) The plate thickness dependence of the angular deformation of PP filled with talc is the singular peculiar phenomenon. The plate thickness dependence of anisotropic solidification shrinkage of this material (it is also singular) is considered to have an important influence on this phenomenon.

Deformation and recrystallization behavior of super high-purity niobium for SRF cavity

NASA Astrophysics Data System (ADS)

Yamaguchi, Y.; Doryo, H.; Yuasa, M.; Miyamoto, H.; Yamanaka, M.

2017-05-01

Deformation and recyrstallization behavior of pure niobium was investigated in order to clarify the origin of its low hydro-formability despite of its high ductility comparable with pure iron. It was found that pure niobium exhibits lower strain hardening in cold rolling compared with pure iron. Furthermore, in post-deformation annealing, the hardness of niobium decreased monotonously with an increase of temperature, and the typical sharp drop by recrystallization was not evident. This softening behavior was contrasted with the high-purity iron. It is suggested that niobium exhibit the so-called in-situ recrystallization possibly because of low elastic modulus and low accumulative plastic strain energy in spite of high melting temperature. The low hydro-formability of pure niobium sheets or tubes is caused by its low strain hardening and its unique plastic anisotropy which is associated with this recovered residual rolled texture.

High-rate deformation and spall fracture of hadfield steel under action of high-current nanosecond relativistic electron beam

NASA Astrophysics Data System (ADS)

Gnyusov, S. F.; Rotshtein, V. P.; Polevin, S. D.; Kitsanov, S. A.

2010-09-01

Features of the plastic deformation and dynamic spall fracture of Hadfield steel under conditions of shock wave loading at a straining rate of ˜106 s-1 have been studied. The shock load (˜30 GPa, ˜0.2 μs) was produced by pulses of a SINUS-7 electron accelerator, which generated relativistic electron bunches with an electron energy of up to 1.35 MeV, a duration of 45 ns, and a peak power on the target of 3.4 × 1010 W/cm2. It is established that the spalling proceeds via mixed viscous-brittle intergranular fracture, unlike the cases of quasi-static tensile and impact loading, where viscous transgranular fracture is typical. It is shown that the intergranular character of the spall fracture is caused by the localization of plastic deformation at grain boundaries containing precipitated carbide inclusions.

On the elastic–plastic decomposition of crystal deformation at the atomic scale

DOE PAGES

Stukowski, Alexander; Arsenlis, A.

2012-03-02

Given two snapshots of an atomistic system, taken at different stages of the deformation process, one can compute the incremental deformation gradient field, F, as defined by continuum mechanics theory, from the displacements of atoms. However, such a kinematic analysis of the total deformation does not reveal the respective contributions of elastic and plastic deformation. We develop a practical technique to perform the multiplicative decomposition of the deformation field, F = F eF p, into elastic and plastic parts for the case of crystalline materials. The described computational analysis method can be used to quantify plastic deformation in a materialmore » due to crystal slip-based mechanisms in molecular dynamics and molecular statics simulations. The knowledge of the plastic deformation field, F p, and its variation with time can provide insight into the number, motion and localization of relevant crystal defects such as dislocations. As a result, the computed elastic field, F e, provides information about inhomogeneous lattice strains and lattice rotations induced by the presence of defects.« less

Description of plastic deformation of structural materials in triaxial loading

NASA Astrophysics Data System (ADS)

Lagzdins, A.; Zilaucs, A.

2008-03-01

A model of nonassociated plasticity is put forward for initially isotropic materials deforming with residual changes in volume under the action of triaxial normal stresses. The model is based on novel plastic loading and plastic potential functions, which define closed, convex, every where smooth surfaces in the 6D space of symmetric second-rank stress tensors. By way of example, the plastic deformation of a cylindrical concrete specimen wrapped with a CFRP tape and loaded in axial compression is described.

Mechanical evolution of transpression zones affected by fault interactions: Insights from 3D elasto-plastic finite element models

NASA Astrophysics Data System (ADS)

Nabavi, Seyed Tohid; Alavi, Seyed Ahmad; Mohammadi, Soheil; Ghassemi, Mohammad Reza

2018-01-01

The mechanical evolution of transpression zones affected by fault interactions is investigated by a 3D elasto-plastic mechanical model solved with the finite-element method. Ductile transpression between non-rigid walls implies an upward and lateral extrusion. The model results demonstrate that a, transpression zone evolves in a 3D strain field along non-coaxial strain paths. Distributed plastic strain, slip transfer, and maximum plastic strain occur within the transpression zone. Outside the transpression zone, fault slip is reduced because deformation is accommodated by distributed plastic shear. With progressive deformation, the σ3 axis (the minimum compressive stress) rotates within the transpression zone to form an oblique angle to the regional transport direction (∼9°-10°). The magnitude of displacement increases faster within the transpression zone than outside it. Rotation of the displacement vectors of oblique convergence with time suggests that transpression zone evolves toward an overall non-plane strain deformation. The slip decreases along fault segments and with increasing depth. This can be attributed to the accommodation of bulk shortening over adjacent fault segments. The model result shows an almost symmetrical domal uplift due to off-fault deformation, generating a doubly plunging fold and a 'positive flower' structure. Outside the overlap zone, expanding asymmetric basins subside to 'negative flower' structures on both sides of the transpression zone and are called 'transpressional basins'. Deflection at fault segments causes the fault dip fall to less than 90° (∼86-89°) near the surface (∼1.5 km). This results in a pure-shear-dominated, triclinic, and discontinuous heterogeneous flow of the transpression zone.

Investigation of the effect of electric current on serrated deformation and acoustic emission in the aluminum-magnesium alloy 5056

NASA Astrophysics Data System (ADS)

Shibkov, A. A.; Denisov, A. A.; Zheltov, M. A.; Zolotov, A. E.; Gasanov, M. F.; Ivolgin, V. I.

2015-06-01

The effect of direct electric current on the serrated deformation of the aluminum-magnesium alloy 5056 has been studied using the acoustic emission method and high-speed video filming of propagating deformation bands. The phenomenon of the electric current-induced suppression of low-frequency acoustic emission signals has been revealed in the range of 1 Hz-2 kHz, which is connected with the development of Portevin-Le Chatelier deformation bands. The characteristic times of damping and growth of plastic instabilities and acoustic signals caused by them after current turn-on and turn-off, respectively, have been estimated.

Features of structural response of mechanically loaded crystallites to irradiation

NASA Astrophysics Data System (ADS)

Korchuganov, Aleksandr V.

2015-10-01

A molecular dynamics method is employed to investigate the origin and evolution of plastic deformation in elastically deformed iron and vanadium crystallites due to atomic displacement cascades. Elastic stress states of crystallites result from different degrees of specimen deformation. Crystallites are deformed under constant-volume conditions. Atomic displacement cascades with the primary knock-on atom energy up to 50 keV are generated in loaded specimens. It is shown that irradiation may cause not only the Frenkel pair formation but also large-scale structural rearrangements outside the irradiated area, which prove to be similar to rearrangements proceeding by the twinning mechanism in mechanically loaded specimens.

Comprehensive Deformation Analysis of a Newly Designed Ni-Free Duplex Stainless Steel with Enhanced Plasticity by Optimizing Austenite Stability

NASA Astrophysics Data System (ADS)

Moallemi, Mohammad; Zarei-Hanzaki, Abbas; Eskandari, Mostafa; Burrows, Andrew; Alimadadi, Hossein

2017-08-01

A new metastable Ni-free duplex stainless steel has been designed with superior plasticity by optimizing austenite stability using thermodynamic calculations of stacking fault energy and with reference to literature findings. Several characterization methods comprising optical microscopy, magnetic phase measurements, X-ray diffraction (XRD) and electron backscattered diffraction were employed to study the plastic deformation behavior and to identify the operating plasticity mechanisms. The results obtained show that the newly designed duplex alloy exhibits some extraordinary mechanical properties, including an ultimate tensile strength of 900 MPa and elongation to fracture of 94 pct due to the synergistic effects of transformation-induced plasticity and twinning-induced plasticity. The deformation mechanism of austenite is complex and includes deformation banding, strain-induced martensite formation, and deformation-induced twinning, while the ferrite phase mainly deforms by dislocation slip. Texture analysis indicates that the Copper and Rotated Brass textures in austenite (FCC phase) and {001}<110> texture in ferrite and martensite (BCC phases) are the main active components during tensile deformation. The predominance of these components is logically related to the strain-induced martensite and/or twin formation.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

NASA Astrophysics Data System (ADS)

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.; Higginbotham, A.; Lazicki, A.; Lee, H. J.; Nagler, B.; Park, H.-S.; Remington, B. A.; Rudd, R. E.; Sliwa, M.; Suggit, M.; Swift, D.; Tavella, F.; Zepeda-Ruiz, L.; Wark, J. S.

2017-10-01

Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.

We report that pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation ismore » challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. Lastly, the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.« less

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

DOE PAGES

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.; ...

2017-10-25

We report that pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation ismore » challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. Lastly, the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.« less

Non-Contact Acousto-Thermal Signatures of Plastic Deformation in TI-6AL-4V

NASA Astrophysics Data System (ADS)

Welter, J. T.; Malott, G.; Schehl, N.; Sathish, S.; Jata, K. V.; Blodgett, M. P.

2010-02-01

Plastic deformation introduces changes in a material which include increases in: dislocations, strains, residual stress, and yield stress. However, these changes have a very small impact on the material properties such as elastic modulus, conductivity and ultrasonic wave speed. This is due to the fact that interatomic forces govern these properties, and they are not affected by plastic deformation to any large degree. This is evident from the fact that the changes in electrical resistance and ultrasonic velocity in plastically deformed and virgin samples are very small and can only be determined by highly controlled experiments. Except for X-ray diffraction, there are no direct nondestructive methods for measuring strain and the residual stress. This paper presents an application of the non-contact acousto-thermal signature (NCATS) NDE methodology to detect plastic deformation in flat dog bone Ti-6Al-4V samples. Results of the NCATS measurements on samples subjected to incremental amounts of plastic deformation are presented. The maximum temperature attained by the sample due to acoustic excitation is found to be sensitive to the amount of plastic strain. It is observed that the temperature induced by acoustic excitation increases to a peak followed by a decrease to failure. The maximum temperature peak occurs at plastic strains of 12-14%. It is observed that there is a correlation between the peak in maximum temperature rise and the strain at the experimentally determined ultimate tensile strength. A microstructural based explanation for this will be presented. The results are discussed in reference to utilizing this technique for detection and evaluation of plastic deformation.

Early stage of plastic deformation in thin films undergoing electromigration

NASA Astrophysics Data System (ADS)

Valek, B. C.; Tamura, N.; Spolenak, R.; Caldwell, W. A.; MacDowell, A. A.; Celestre, R. S.; Padmore, H. A.; Bravman, J. C.; Batterman, B. W.; Nix, W. D.; Patel, J. R.

2003-09-01

Electromigration occurs when a high current density drives atomic motion from the cathode to the anode end of a conductor, such as a metal interconnect line in an integrated circuit. While electromigration eventually causes macroscopic damage, in the form of voids and hillocks, the earliest stage of the process when the stress in individual micron-sized grains is still building up is largely unexplored. Using synchrotron-based x-ray microdiffraction during an in-situ electromigration experiment, we have discovered an early prefailure mode of plastic deformation involving preferential dislocation generation and motion and the formation of a subgrain structure within individual grains of a passivated Al (Cu) interconnect. This behavior occurs long before macroscopic damage (hillocks and voids) is observed.

Elastic plastic self-consistent (EPSC) modeling of plastic deformation in fayalite olivine

DOE PAGES

Burnley, Pamela C

2015-07-01

Elastic plastic self-consistent (EPSC) simulations are used to model synchrotron X-ray diffraction observations from deformation experiments on fayalite olivine using the deformation DIA apparatus. Consistent with results from other in situ diffraction studies of monomineralic polycrystals, the results show substantial variations in stress levels among grain populations. Rather than averaging the lattice reflection stresses or choosing a single reflection to determine the macroscopic stress supported by the specimen, an EPSC simulation is used to forward model diffraction data and determine a macroscopic stress that is consistent with lattice strains of all measured diffraction lines. The EPSC simulation presented here includesmore » kink band formation among the plastic deformation mechanisms in the simulation. The inclusion of kink band formation is critical to the success of the models. This study demonstrates the importance of kink band formation as an accommodation mechanism during plastic deformation of olivine as well as the utility of using EPSC models to interpret diffraction from in situ deformation experiments.« less

Theory for plasticity of face-centered cubic metals.

PubMed

Jo, Minho; Koo, Yang Mo; Lee, Byeong-Joo; Johansson, Börje; Vitos, Levente; Kwon, Se Kyun

2014-05-06

The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control.

Theory for plasticity of face-centered cubic metals

PubMed Central

Jo, Minho; Koo, Yang Mo; Lee, Byeong-Joo; Johansson, Börje; Vitos, Levente; Kwon, Se Kyun

2014-01-01

The activation of plastic deformation mechanisms determines the mechanical behavior of crystalline materials. However, the complexity of plastic deformation and the lack of a unified theory of plasticity have seriously limited the exploration of the full capacity of metals. Current efforts to design high-strength structural materials in terms of stacking fault energy have not significantly reduced the laborious trial and error works on basic deformation properties. To remedy this situation, here we put forward a comprehensive and transparent theory for plastic deformation of face-centered cubic metals. This is based on a microscopic analysis that, without ambiguity, reveals the various deformation phenomena and elucidates the physical fundaments of the currently used phenomenological correlations. We identify an easily accessible single parameter derived from the intrinsic energy barriers, which fully specifies the potential diversity of metals. Based entirely on this parameter, a simple deformation mode diagram is shown to delineate a series of convenient design criteria, which clarifies a wide area of material functionality by texture control. PMID:24753563

Simulation of high-temperature superlocalization of plastic deformation in single-crystals of alloys with an L12 superstructure

NASA Astrophysics Data System (ADS)

Solov'eva, Yu. V.; Fakhrutdinova, Ya. D.; Starenchenko, V. A.

2015-01-01

The processes of the superlocalization of plastic deformation in L12 alloys have been studied numerically based on a combination of the model of the dislocation kinetics of the deformation-induced and heat-treatment-induced strengthening of an element of a deformable medium with the model of the mechanics of microplastic deformation described in terms of elastoplastic medium. It has been shown that the superlocalization of plastic deformation is determined by the presence of stress concentrators and by the nonmonotonic strengthening of the elements of the deformable medium. The multiple nonmonotonicity of the process of strengthening of the elementary volume of the medium can be responsible for the multiplicity of bands of microplastic localization of deformation.

Softening and Hardening of Alloys of the Al - Zn System Under Plastic Deformation

NASA Astrophysics Data System (ADS)

Skvortsov, A. I.; Polev, V. V.

2017-11-01

The proportion of hardening and softening under plastic deformation at room temperature in metals and alloys of the Al - Zn system has been studied as dependent on the regime of preliminary heat treatment. The influence of the strain rate on the dependence of alloy hardness on the degree of plastic deformation is estimated.

Nonlinear deformation of composites with consideration of the effect of couple-stresses

NASA Astrophysics Data System (ADS)

Lagzdiņš, A.; Teters, G.; Zilaucs, A.

1998-09-01

Nonlinear deformation of spatially reinforced composites under active loading (without unloading) is considered. All the theoretical constructions are based on the experimental data on unidirectional and ±π/4 cross-ply epoxy plastics reinforced with glass fibers. Based on the elastic properties of the fibers and EDT-10 epoxy binder, the linear elastic characteristics of a transversely isotropic unidirectionally reinforced fiberglass plastic are found, whereas the nonlinear characteristics are obtained from experiments. For calculating the deformation properties of the ±π/4 cross-ply plastic, a refined version of the Voigt method is applied taking into account also the couple-stresses arising in the composite due to relative rotation of the reinforcement fibers. In addition, a fourth-rank damage tensor is introduced in order to account for the impact of fracture caused by the couple-stresses. The unknown constants are found from the experimental uniaxial tension curve for the cross-ply composite. The comparison between the computed curves and experimental data for other loading paths shows that the description of the nonlinear behavior of composites can be improved by considering the effect of couple-stresses generated by rotations of the reinforcing fibers.

Structural defects in natural plastically deformed diamonds: Evidence from EPR spectroscopy

NASA Astrophysics Data System (ADS)

Mineeva, R. M.; Titkov, S. V.; Speransky, A. V.

2009-06-01

Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned lamellae. Numerous data on models of deformation centers in natural diamonds, including the M2 and M3 centers, which were observed in the studied collection for the first time, are discussed.

Inelastic deformation of metal matrix composites: Plasticity and damage mechanisms, part 2

NASA Technical Reports Server (NTRS)

Majumdar, B. S.; Newaz, G. M.

1992-01-01

The inelastic deformation mechanisms for the SiC (SCS-6)/Ti-15-3 system were studied at 538 C (1000 F) using a combination of mechanical measurements and detailed microstructural examinations. The objectives were to evaluate the contributions of plasticity and damage to the overall MMC response, and to compare the room temperature and elevated temperature deformation behaviors. Four different laminates were studied: (0)8, (90)8,(+ or -45)2s, and (0/90)2s, with the primary emphasis on the unidirectional (0)8, and (90)8 systems. The elevated temperature responses were similar to those at room temperature, involving a two-stage elastic-plastic type of response for the (0)8 system, and a characteristic three-stage deformation response for the (90)8 and (+ or -45)2s systems. The primary effects of elevated temperatures included: (1) reduction in the 'yield' and failure strengths; (2) plasticity through diffused slip rather than concentrated planar slip (which occurred at room temperature); and (3) time-dependent deformation. The inelastic deformation mechanism for the (0)8 MMC was dominated by plasticity at both temperatures. For the (90)8 and (+ or -45)2s MMCs, a combination of damage and plasticity contributed to the deformation at both temperatures.

Elastic-plastic finite element analyses of an unidirectional, 9 vol percent tungsten fiber reinforced copper matrix composite

NASA Technical Reports Server (NTRS)

Sanfeliz, Jose G.

1993-01-01

Micromechanical modeling via elastic-plastic finite element analyses were performed to investigate the effects that the residual stresses and the degree of matrix work hardening (i.e., cold-worked, annealed) have upon the behavior of a 9 vol percent, unidirectional W/Cu composite, undergoing tensile loading. The inclusion of the residual stress-containing state as well as the simulated matrix material conditions proved to be significant since the Cu matrix material exhibited plastic deformation, which affected the subsequent tensile response of the composite system. The stresses generated during cooldown to room temperature from the manufacturing temperature were more of a factor on the annealed-matrix composite, since they induced the softened matrix to plastically flow. This event limited the total load-carrying capacity of this matrix-dominated, ductile-ductile type material system. Plastic deformation of the hardened-matrix composite during the thermal cooldown stage was not considerable, therefore, the composite was able to sustain a higher stress before showing any appreciable matrix plasticity. The predicted room temperature, stress-strain response, and deformation stages under both material conditions represented upper and lower bounds characteristic of the composite's tensile behavior. The initial deformation stage for the hardened material condition showed negligible matrix plastic deformation while for the annealed state, its initial deformation stage showed extensive matrix plasticity. Both material conditions exhibited a final deformation stage where the fiber and matrix were straining plastically. The predicted stress-strain results were compared to the experimental, room temperature, tensile stress-strain curve generated from this particular composite system. The analyses indicated that the actual thermal-mechanical state of the composite's Cu matrix, represented by the experimental data, followed the annealed material condition.

Effect of Plastic Strain Range on Prediction of the Onset of Crack Growth for Low-Cycle Fatigue of SUS316NG Studied using Ultrasonic Back-Reflection

NASA Astrophysics Data System (ADS)

Nurul, Islam Md.; Arai, Yoshio; Araki, Wakako

Strain range controlled low-cycle fatigue tests were conducted using ultrasonic method in order to investigate the effect of plastic strain range on the remaining life of austenitic stainless steel SUS316NG before the onset of crack growth in its early stages of fatigue. It was found that the decrease in ultrasonic back-reflection intensity from the surface of the material, caused by the increase in average dislocation density with localized plastic deformation at persistent slip bands (PSBs), starts earlier with increase in the plastic strain range. The amount of decrease in ultrasonic back-reflection before the onset of crack growth increases for larger plastic strain range. The difference in the cumulative plastic strains at the onset of crack growth and at the onset of decrease in the ultrasonic back-reflection remained constant over the range of tested plastic strain. This result can be used to predict the remaining life before the onset of crack growth within the plastic strain range used in this study. In addition, we present and evaluate another method to predict damage evolution involving ultrasound attenuation caused by PSBs.

Semantic modeling of the structural and process entities during plastic deformation of crystals and rocks

NASA Astrophysics Data System (ADS)

Babaie, Hassan; Davarpanah, Armita

2016-04-01

We are semantically modeling the structural and dynamic process components of the plastic deformation of minerals and rocks in the Plastic Deformation Ontology (PDO). Applying the Ontology of Physics in Biology, the PDO classifies the spatial entities that participate in the diverse processes of plastic deformation into the Physical_Plastic_Deformation_Entity and Nonphysical_Plastic_Deformation_Entity classes. The Material_Physical_Plastic_Deformation_Entity class includes things such as microstructures, lattice defects, atoms, liquid, and grain boundaries, and the Immaterial_Physical_Plastic_Deformation_Entity class includes vacancies in crystals and voids along mineral grain boundaries. The objects under the many subclasses of these classes (e.g., crystal, lattice defect, layering) have spatial parts that are related to each other through taxonomic (e.g., Line_Defect isA Lattice_Defect), structural (mereological, e.g., Twin_Plane partOf Twin), spatial-topological (e.g., Vacancy adjacentTo Atom, Fluid locatedAlong Grain_Boundary), and domain specific (e.g., displaces, Fluid crystallizes Dissolved_Ion, Void existsAlong Grain_Boundary) relationships. The dynamic aspect of the plastic deformation is modeled under the dynamical Process_Entity class that subsumes classes such as Recrystallization and Pressure_Solution that define the flow of energy amongst the physical entities. The values of the dynamical state properties of the physical entities (e.g., Chemical_Potential, Temperature, Particle_Velocity) change while they take part in the deformational processes such as Diffusion and Dislocation_Glide. The process entities have temporal parts (phases) that are related to each other through temporal relations such as precedes, isSubprocessOf, and overlaps. The properties of the physical entities, defined under the Physical_Property class, change as they participate in the plastic deformational processes. The properties are categorized into dynamical, constitutive, spatial, temporal, statistical, and thermodynamical. The dynamical properties, categorized under the Dynamical_Rate_Property and Dynamical_State_Property classes, subsume different classes of properties (e.g., Fluid_Flow_Rate, Temperature, Chemical_Potential, Displacement, Electrical_Charge) based on the physical domain (e.g., fluid, heat, chemical, solid, electrical). The properties are related to the objects under the Physical_Entity class through diverse object type (e.g., physicalPropertyOf) and data type (e.g., Fluid_Pressure unit 'MPa') properties. The changes of the dynamical properties of the physical entities, described by the empirical laws (equations) modeled by experimental structural geologists, are modeled through the Physical_Property_Dependency class that subsumes the more specialized constitutive, kinetic, and thermodynamic expressions of the relationships among the dynamic properties. Annotation based on the PDO will make it possible to integrate and reuse experimental plastic deformation data, knowledge, and simulation models, and conduct semantic-based search of the source data originating from different rock testing laboratories.

Micrographic detection of plastic deformation in nickel base alloys

DOEpatents

Steeves, Arthur F.; Bibb, Albert E.

1984-01-01

A method for detecting low levels of plastic deformation in metal articles comprising electrolytically etching a flow free surface of the metal article with nital at a current density of less than about 0.1 amp/cm.sup.2 and microscopically examining the etched surface to determine the presence of alternating striations. The presence of striations indicates plastic deformation in the article.

Micrographic detection of plastic deformation in nickel-base alloys

DOEpatents

Steeves, A.F.; Bibb, A.E.

1980-09-20

A method for detecting low levels of plastic deformation in metal articles comprising electrolytically etching a flow free surface of the metal article with nital at a current density of less than about 0.1 amp/cm/sup 2/ and microscopically examining the etched surface to determine the presence of alternating striations. The presence of striations indicates plastic deformation in the article.

Thermodynamically consistent constitutive equations for nonisothermal large strain, elasto-plastic, creep behavior

NASA Technical Reports Server (NTRS)

Riff, R.; Carlson, R. L.; Simitses, G. J.

1985-01-01

The paper is concerned with the development of constitutive relations for large nonisothermal elastic-viscoplastic deformations for metals. The kinematics of elastic-plastic deformation, valid for finite strains and rotations, is presented. The resulting elastic-plastic uncoupled equations for the deformation rate combined with use of the incremental elasticity law permits a precise and purely deductive development of elastic-viscoplastic theory. It is shown that a phenomenological thermodynamic theory in which the elastic deformation and the temperature are state variables, including few internal variables, can be utilized to construct elastic-viscoplastic constitutive equations, which are appropriate for metals. The limiting case of inviscid plasticity is examined.

Size effect on the deformation mechanisms of nanocrystalline platinum thin films.

PubMed

Shu, Xinyu; Kong, Deli; Lu, Yan; Long, Haibo; Sun, Shiduo; Sha, Xuechao; Zhou, Hao; Chen, Yanhui; Mao, Shengcheng; Liu, Yinong

2017-10-16

This paper reports a study of time-resolved deformation process at the atomic scale of a nanocrystalline Pt thin film captured in situ under a transmission electron microscope. The main mechanism of plastic deformation was found to evolve from full dislocation activity-enabled plasticity in large grains (with grain size d > 10 nm), to partial dislocation plasticity in smaller grains (with grain size 10 nm < d < 6 nm), and grain boundary-mediated plasticity in the matrix with grain sizes d < 6 nm. The critical grain size for the transition from full dislocation activity to partial dislocation activity was estimated based on consideration of stacking fault energy. For grain boundary-mediated plasticity, the possible contributions to strain rate of grain creep, grain sliding and grain rotation to plastic deformation were estimated using established models. The contribution of grain creep is found to be negligible, the contribution of grain rotation is effective but limited in magnitude, and grain sliding is suggested to be the dominant deformation mechanism in nanocrystalline Pt thin films. This study provided the direct evidence of these deformation processes at the atomic scale.

Effects of Friction and Plastic Deformation in Shock-Comminuted Damaged Rocks on Impact Heating

NASA Astrophysics Data System (ADS)

Kurosawa, Kosuke; Genda, Hidenori

2018-01-01

Hypervelocity impacts cause significant heating of planetary bodies. Such events are recorded by a reset of 40Ar-36Ar ages and/or impact melts. Here we investigate the influence of friction and plastic deformation in shock-generated comminuted rocks on the degree of impact heating using the iSALE shock-physics code. We demonstrate that conversion from kinetic to internal energy in the targets with strength occurs during pressure release, and additional heating becomes significant for low-velocity impacts (<10 km s-1). This additional heat reduces the impact-velocity thresholds required to heat the targets with the 0.1 projectile mass to temperatures for the onset of Ar loss and melting from 8 and 10 km s-1, respectively, for strengthless rocks to 2 and 6 km s-1 for typical rocks. Our results suggest that the impact conditions required to produce the unique features caused by impact heating span a much wider range than previously thought.

The effect of postprocessing on tensile property and microstructure evolution of friction stir welding aluminum alloy joint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Z.L., E-mail: zhilihuhit@163.com; State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001; State Key Laboratory of Materials Processing and Die & Mould Technology, Huazhong University of Science and Technology

Friction stir welding is an efficient manufacturing method for joining aluminum alloy and can dramatically reduce grain size conferring excellent plastic deformation properties. Consequently, friction stir welding is used to manufacture tailor welded blanks to optimize weight or performance in the final component. In the study, the microstructural evolution and mechanical properties of friction stir welding joint during plastic forming and subsequent heat treatment were investigated. The microstructural characteristics of the friction stir welding joints were studied by Electron Backscattered Diffraction and Transmission Electron Microscopy. The mechanical properties were evaluated by tensile and microhardness tests. It is found that themore » tensile and yield strengths of friction stir welding joints are significantly improved after severe plastic deformation due to the grain refinement. Following heat treatment, the strength of the friction stir welding joints significantly decrease due to the obvious abnormal grain growth. Careful attention must be given to the processing route of any friction stir welding joint intended for plastic forming, especially the annealing between forming passes. Severe plastic deforming of the friction stir welding joint leads to a high level of stored energy/dislocation density, which causes the abnormal grain growth during subsequent heat treatment, and consequently reduce the mechanical properties of the friction stir welding joint. - Highlights: • Great changes are observed in the microstructure of FSW joint after postprocessing. • Postprocessing shows great effect on the microstructure stability of FSW joint. • The weld shows more significant decrease in strength than the BM due to the AGG. • Attention must be given to the processing route of FSW joint for plastic forming.« less

Patterns of residual stresses due to welding

NASA Technical Reports Server (NTRS)

Botros, B. M.

1983-01-01

Residual stresses caused by welding result from the nonuniform rate of cooling and the restrained thermal contraction or non-uniform plastic deformation. From the zone of extremely high temperature at the weld, heat flows into both the adjoining cool body and the surrounding atmosphere. The weld metal solidifies under very rapid cooling. The plasticity of the hot metal allows adjustment initially, but as the structure cools the rigidity of the surrounding cold metal inhibits further contraction. The zone is compressed and the weld is put under tensile stresses of high magnitude. The danger of cracking in these structural elements is great. Change in specific volume is caused by the change in temperature.

Deformation processes within wheel-rail adhesion in contact area

NASA Astrophysics Data System (ADS)

Albagachiev, A. Yu; Keropyan, A. M.

2018-03-01

The study of working surface deformation during interaction of open-pit locomotive tires allowed defining outstanding features of phenomena occurring in the contact area of interacting surfaces. It was found that processes typical for plastic saturated contact occur in the area of wheel-rail interaction of industrial railway transport. In case of plastic deformation exposed to heavy loads typical for open-pit locomotives, upon all rough surfaces of the contour contact area being fully deformed, the frame on which they are found is exposed to plastic deformation. Plastic deformation of roughness within the contact area of interacting surfaces leads to the increase in the actual area of their contact and, therefore, increases the towing capacity of mining machines. Finally, the available data on deformation characteristics with regard to processes occurring in the contact area of wheel-rail interaction will allow making theoretical forecasts on the expected design value of friction coefficient and, therefore, the towing capacity of open-pit locomotives.

Finite element simulation of the T-shaped ECAP processing of round samples

NASA Astrophysics Data System (ADS)

Shaban Ghazani, Mehdi; Fardi-Ilkhchy, Ali; Binesh, Behzad

2018-05-01

Grain refinement is the only mechanism that increases the yield strength and toughness of the materials simultaneously. Severe plastic deformation is one of the promising methods to refine the microstructure of materials. Among different severe plastic deformation processes, the T-shaped equal channel angular pressing (T-ECAP) is a relatively new technique. In the present study, finite element analysis was conducted to evaluate the deformation behavior of metals during T-ECAP process. The study was focused mainly on flow characteristics, plastic strain distribution and its homogeneity, damage development, and pressing force which are among the most important factors governing the sound and successful processing of nanostructured materials by severe plastic deformation techniques. The results showed that plastic strain is localized in the bottom side of sample and uniform deformation cannot be possible using T-ECAP processing. Friction coefficient between sample and die channel wall has a little effect on strain distributions in mirror plane and transverse plane of deformed sample. Also, damage analysis showed that superficial cracks may be initiated from bottom side of sample and their propagation will be limited due to the compressive state of stress. It was demonstrated that the V shaped deformation zone are existed in T-ECAP process and the pressing load needed for execution of deformation process is increased with friction.

Static strength of molybdenum to 92 GPa under radial X-ray diffraction

NASA Astrophysics Data System (ADS)

Xiong, L.; Tu, P.; Li, B.; Wu, S. Y.; Hao, J. B.; Bai, L. G.; Li, X. D.; Liu, J.

2018-06-01

The high-pressure strength of molybdenum (Mo) to 92 GPa has been studied by radial X-ray diffraction (RXRD) technique. The ratio of t/G is found to decrease above ˜24 GPa, showing the yield of Mo which is caused by plastic deformation at this pressure. Combined with high-pressure shear modulus, it was found that the differential stress corresponding to the yield of Mo at 24 GPa due to plastic deformation is 1.73 GPa. The second increase of t values occurs after ˜66 GPa, suggesting the strength of Mo with a differential stress of ˜1.93 GPa. In addition, the maximum difference stress of molybdenum at 87 GPa is 3.01 GPa.

Structure and microhardness of Al-Si-Cu-Ni alloy after severe plastic deformation and high-temperature annealing

NASA Astrophysics Data System (ADS)

Shvets, Karina; Khalikova, Gulnara; Korznikova, Elena; Trifonov, Vadim

2015-10-01

The effect of severe plastic deformation by high-pressure torsion (HPT) and subsequent annealing on the microstructure and microhardness of squeeze casting Al-22%Si-3%Cu-1.7%Ni alloy was investigated. HPT was performed at room temperature with 5 rotations under the pressure of 4 GPa. Annealing temperature range varied from 300 to 500°C for 5 min. HPT resulted in refinement and partial dissolution of the primary silicon and intermetallic particles in aluminum matrix and structure fragmentation that caused the microhardness increase. Subsequent annealing lead to the decomposition of the supersaturated solid solution that took place simultaneously with recovery and recrystallization of the fragmented structure. Increase of annealing temperature resulted in decrease of microhardness values.

Plastic deformation and failure mechanisms in nano-scale notched metallic glass specimens under tensile loading

NASA Astrophysics Data System (ADS)

Dutta, Tanmay; Chauniyal, Ashish; Singh, I.; Narasimhan, R.; Thamburaja, P.; Ramamurty, U.

2018-02-01

In this work, numerical simulations using molecular dynamics and non-local plasticity based finite element analysis are carried out on tensile loading of nano-scale double edge notched metallic glass specimens. The effect of acuteness of notches as well as the metallic glass chemical composition or internal material length scale on the plastic deformation response of the specimens are studied. Both MD and FE simulations, in spite of the fundamental differences in their nature, indicate near-identical deformation features. Results show two distinct transitions in the notch tip deformation behavior as the acuity is increased, first from single shear band dominant plastic flow localization to ligament necking, and then to double shear banding in notches that are very sharp. Specimens with moderately blunt notches and composition showing wider shear bands or higher material length scale characterizing the interaction stress associated with flow defects display profuse plastic deformation and failure by ligament necking. These results are rationalized from the role of the interaction stress and development of the notch root plastic zones.

The thermostimulated luminescence of radiation defects in KCl, KBr and KI crystals at elastic and plastic deformation

NASA Astrophysics Data System (ADS)

Shunkeyev, K.; Myasnikova, L.; Barmina, A.; Zhanturina, N.; Sagimbaeva, Sh; Aimaganbetova, Z.; Sergeyev, D.

2017-05-01

The efficiency of radiation defects formation in alkali halide crystals (AHC) was studied by the method of absorption spectroscopy. However, it is not possible to study the deformation-stimulated processes in detail by the absorption spectrum of radiation defects due to the limited sensitivity compared with luminescent spectroscopy. In this regard, thermally stimulated luminescence (TSL) of radiation defects at elastic and plastic deformation was applied in AHC. In the absence of deformation, the dominant peaks in TSL are ≤ft( {X_3^ - } \\right)aca^0-centers. After elastic deformation, low temperature peaks of TSL corresponding to F‧-, VK- and VF-centers became dominant. After plastic deformation, the peaks of TSL corresponding to ≤ft( {X_3^ - } \\right)aca^0-centers became dominant. The elastic deformation contributes to the increase in concentration of low-temperature F‧-, VK- and VF-centers, and the plastic one contributes to that of high temperature ≤ft( {X_3^ - } \\right)aca^0-centers (peaks of TSL in KCl at 360K, in KBr at 365K, in KI at 340K), composed by divacancies created by plastic deformation. At elastic deformation, unrelaxed interstitial halogen atoms are converted into VK- and VF-centers, and due to this fact the long-range interaction is absent, the result of which are the X_3^ - -centers.

Deformation Microstructures Near Vickers Indentations in SNO2/SI Coated Systems

NASA Astrophysics Data System (ADS)

Daria, G.; Evghenii, H.; Olga, S.; Zinaida, D.; Iana, M.; Victor, Z.

The micromechanical properties (hardness and brittleness) of the hard-on-hard SnO2 / Si-coated system (CS) and their modification depending the on load value has been studied. A nonmonotonic changing of microhardness with load growth was detected. The brittle/plastic behavior of the rigid/hard-on-hard SnO2 / Si CS and its response to concentrated load action explains it.A specific evolution of the indentation-deformed zone vs. load value attributed to the change in the internal stress redistribution between film and substrate was detected. It results in a brittleness indentation size effect (BISE) of the SnO2 / Si CS revealed in this experiment.It was shown that the greater portion of internal stresses under indentation is concentrated in the coating layer at small loads. This fact causes a strong elastic-plastic relaxation in the film and its delamination from substrate. The increase of brittle failure in the indentation-deformed zone with a decrease of indentation load was revealed.

Modeling plasticity by non-continuous deformation

NASA Astrophysics Data System (ADS)

Ben-Shmuel, Yaron; Altus, Eli

2017-10-01

Plasticity and failure theories are still subjects of intense research. Engineering constitutive models on the macroscale which are based on micro characteristics are very much in need. This study is motivated by the observation that continuum assumptions in plasticity in which neighbour material elements are inseparable at all-time are physically impossible, since local detachments, slips and neighbour switching must operate, i.e. non-continuous deformation. Material microstructure is modelled herein by a set of point elements (particles) interacting with their neighbours. Each particle can detach from and/or attach with its neighbours during deformation. Simulations on two- dimensional configurations subjected to uniaxial compression cycle are conducted. Stochastic heterogeneity is controlled by a single "disorder" parameter. It was found that (a) macro response resembles typical elasto-plastic behaviour; (b) plastic energy is proportional to the number of detachments; (c) residual plastic strain is proportional to the number of attachments, and (d) volume is preserved, which is consistent with macro plastic deformation. Rigid body displacements of local groups of elements are also observed. Higher disorder decreases the macro elastic moduli and increases plastic energy. Evolution of anisotropic effects is obtained with no additional parameters.

Deformation behavior of Nb nanowires in TiNiCu shape memory alloy matrix

DOE PAGES

Jiang, Daqiang; Liu, Yinong; Yu, Cun; ...

2015-08-18

An in-situ nanowire Nb/TiNiCu composite is fabricated based on the concept of strain under-matching between a phase transforming matrix and high strength nanomaterials. The deformation behavior of the Nb nanowire was investigated by means of in-situ synchrotron X-ray diffraction when the TiNiCu matrix underwent different deformation modes. The maximum lattice strain of the Nb nanowires was about 5% when the matrix deformed via martensitic transformation or 1% when deforming plastically by dislocation slip. As a result, the Nb nanowires showed a lattice strain of 3.5% when the matrix deformed in the mixed mode of plastic deformation and martensitic transformation, whichmore » means that the occurrence of plastic deformation does not impede load transfer from the matrix to the nanowires.« less

Plastic deformation in a metallic granular chain

NASA Astrophysics Data System (ADS)

Musson, Ryan W.; Carlson, William

2016-03-01

Solitary wave response was investigated in a metallic granular chain-piston system using LS-DYNA. A power law hardening material model was used to show that localized plastic deformation is present in a metallic granular chain for an impact velocity of 0.5 m/s. This loss due to plastic deformation was quantified via impulse, and it was shown that the loss scales nearly linearly with impact velocity. Therefore, metallic grains may not be suitable for devices that require high-amplitude solitary waves. There would be too much energy lost to plastic deformation. One can assume that ceramics will behave elastically; therefore, the response of an aluminum oxide granular chain was compared to that of a steel chain.

Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. I. Dislocation microstructures in as-received state and at different plastic strains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Long, Fei; Daymond, Mark R., E-mail: mark.daymond@queensu.ca; Yao, Zhongwen

Thin foil dog bone samples prepared from a hot rolled Zr-2.5Nb alloy have been deformed by tensile deformation to different plastic strains. The development of slip traces during loading was observed in situ through SEM, revealing that deformation starts preferentially in certain sets of grains during the elastic-plastic transition region. TEM characterization showed that sub-grain boundaries formed during hot rolling consisted of screw 〈a〉 dislocations or screw 〈c〉 and 〈a〉 dislocations. Prismatic 〈a〉 dislocations with large screw or edge components have been identified from the sample with 0.5% plastic strain. Basal 〈a〉 and pyramidal 〈c + a〉 dislocations were found in themore » sample that had been deformed with 1.5% plastic strain, implying that these dislocations require larger stresses to be activated.« less

Elasto-plastic impact of hemispherical shell impacting on hard rigid sphere

NASA Technical Reports Server (NTRS)

Raftopoulos, D. D.; Spicer, A. L.

1976-01-01

An analysis of plastic stress waves for cylindrical metallic projectile in impact is extended to an analysis of a hemispherical shell suffereing plastic deformation during the process of impact. It is assumed that the hemispherical shell with a prescribed launch velocity impinges a fixed rigid sphere of diameter equal to the internal diameter of the shell. The dynamic biaxial state of stress present in the shell during deformation is investigated. The analysis is valuable for studying the state of stress during large plastic deformation of a hemispherical shell.

Demonstration of finite element simulations in MOOSE using crystallographic models of irradiation hardening and plastic deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patra, Anirban; Wen, Wei; Martinez Saez, Enrique

This report describes the implementation of a crystal plasticity framework (VPSC) for irradiation hardening and plastic deformation in the finite element code, MOOSE. Constitutive models for irradiation hardening and the crystal plasticity framework are described in a previous report [1]. Here we describe these models briefly and then describe an algorithm for interfacing VPSC with finite elements. Example applications of tensile deformation of a dog bone specimen and a 3D pre-irradiated bar specimen performed using MOOSE are demonstrated.

Dependence of stress-induced omega transition and mechanical twinning on phase stability in metastable β Ti–V alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, X.L.; Li, L.; Mei, W.

2015-09-15

Tensile properties and deformation microstructures of a series of binary β Ti–16–22V alloys have been investigated. The results show that the plastic deformation mode changes from the plate-like stress-induced ω phase transformation with a special habit plane of (− 5052){sub ω}//(3 − 3 − 2){sub β} to (332)<113> type deformation twinning with increasing the content of vanadium in the β Ti–16–22 wt.% V alloys. The plate-like stress-induced ω phase has a special orientation relationship with the β phase matrix, i.e., [110]{sub β}//[− 12 − 10]{sub ω}, (3 − 3 − 2){sub β}//(− 5052){sub ω} and (− 55 − 4){sub β}//(30more » − 31){sub ω}. The alloys plastically deformed by stress-induced ω phase transformation exhibit relatively higher yield strength than those deformed via (332)<113> type deformation twinning. It can be concluded that the stability of β phase plays a significant role in plastic deformation mode, i.e., stress-induced ω phase transformation or (332)<113> type deformation twinning, which governs the mechanical property of the β Ti–16–22 wt.% V alloys. - Highlights: • Tensile properties and deformed microstructures of β Ti–16–22V alloys were studied. • Stress-induced ω phase transformation and (332)<113> twinning occur in the alloys. • Stability of β phase plays a significant role in plastic deformation mode. • Plastic deformation mode governs the mechanical property of the alloys.« less

Thermal Microstructural Stability of AZ31 Magnesium after Severe Plastic Deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, John P.; Askari, Hesam A.; Hovanski, Yuri

2015-03-01

Both equal channel angular pressing and friction stir processing have the ability to refine the grain size of twin roll cast AZ31 magnesium and potentially improve its superplastic properties. This work used isochronal and isothermal heat treatments to investigate the microstructural stability of twin roll cast, equal channel angular pressed and friction stir processed AZ31 magnesium. For both heat treatment conditions, it was found that the twin roll casted and equal channel angular pressed materials were more stable than the friction stir processed material. Calculations of the grain growth kinetics showed that severe plastic deformation processing decreased the activation energymore » for grain boundary motion with the equal channel angular pressed material having the greatest Q value of the severely plastically deformed materials and that increasing the tool travel speed of the friction stir processed material improved microstructural stability. The Hollomon-Jaffe parameter was found to be an accurate means of identifying the annealing conditions that will result in substantial grain growth and loss of potential superplastic properties in the severely plastically deformed materials. In addition, Humphreys’s model of cellular microstructural stability accurately predicted the relative microstructural stability of the severely plastically deformed materials and with some modification, closely predicted the maximum grain size ratio achieved by the severely plastically deformed materials.« less

Direct in situ observation of metallic glass deformation by real-time nano-scale indentation

NASA Astrophysics Data System (ADS)

Gu, Lin; Xu, Limei; Zhang, Qingsheng; Pan, Deng; Chen, Na; Louzguine-Luzgin, Dmitri V.; Yao, Ke-Fu; Wang, Weihua; Ikuhara, Yuichi

2015-03-01

A common understanding of plastic deformation of metallic glasses (MGs) at room temperature is that such deformation occurs via the formation of runaway shear bands that usually lead to catastrophic failure of MGs. Here we demonstrate that inhomogeneous plastic flow at nanoscale can evolve in a well-controlled manner without further developing of shear bands. It is suggested that the sample undergoes an elasto-plastic transition in terms of quasi steady-state localized shearing. During this transition, embryonic shear localization (ESL) propagates with a very slow velocity of order of ~1 nm/s without the formation of a hot matured shear band. This finding further advances our understanding of the microscopic deformation process associated with the elasto-plastic transition and may shed light on the theoretical development of shear deformation in MGs.

Method of determining elastic and plastic mechanical properties of ceramic materials using spherical indenters

DOEpatents

Adler, Thomas A.

1996-01-01

The invention pertains a method of determining elastic and plastic mechanical properties of ceramics, intermetallics, metals, plastics and other hard, brittle materials which fracture prior to plastically deforming when loads are applied. Elastic and plastic mechanical properties of ceramic materials are determined using spherical indenters. The method is most useful for measuring and calculating the plastic and elastic deformation of hard, brittle materials with low values of elastic modulus to hardness.

Development of pea protein-based bioplastics with antimicrobial properties.

PubMed

Perez-Puyana, Víctor; Felix, Manuel; Romero, Alberto; Guerrero, Antonio

2017-06-01

In the present work, bioplastics from renewable polymers were studied in order to reduce the huge generation of plastic wastes, causing an environmental problem that continues owing to the increasing demand for plastic products. Bioplastics with much better antimicrobial properties, in particular against Gram-positive bacteria, were obtained with the addition of nisin to the initial protein/plasticizer mixture. However, the addition of nisin produces more rigid but less deformable bioplastics (higher Young's modulus but lower strain at break). The results obtained are useful to demonstrate the antimicrobial properties of pea protein-based bioplastics by adding nisin and make them suitable as potential candidates to replace conventional plastics in food packaging. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

Correlating elastic and plastic deformation with magnetic permeability values

NASA Astrophysics Data System (ADS)

Papadopoulou, S.

2017-12-01

This paper investigates the utilization of magnetic permeability method in determining elastic and plastic deformation state of ferromagnetic steels. The results have shown a strong degradation of the magnetic values on plastically region due to the irreversible movements of the magnetic domain walls.

Nano-deformation behavior of silicon (100) film studied by depth sensing indentation and nanoscratch technique

NASA Astrophysics Data System (ADS)

Geetha, D.; Pratyank, R.; Kiran, P.

2018-04-01

Silicon being the most important material applied in microelectronic and photovoltaic technology, repeated investigation of the mechanical properties becomes essential. The nanoscale elastic-plastic deformation characteristics of Si (100) film were analyzed using nanoindentation and nanoscratch techniques. The hardness and elastic modulus values of the film obtained from nanoindentation tests were found to be consistent with the reported values. The load-displacement curves showed discontinuities and kinks which confirms the plastic behaviour of Si. The indentation induced plastic deformations were the consequences of the phase transformations. The critical shear stress, tensile strength and plastic zone size, of the Si film when subjected to nanoindentation were determined. The nanoscratch tests were performed to understand the tribological properties of the film. The SPM images of both the nanoindentation and nanoscratch profiles were useful in revealing the plastic character in terms of the piling up of matter in the vicinity of the dents. Conclusions were drawn in quantifying the plastic deformations and phase transformations.

[Plastic surgery to correct deformities of the ear].

PubMed

Naumann, A

2005-08-18

For the plastic-surgical correction of mild deformities of the ears, well-proven incisional and suturing techniques are available. Only in exceptional cases is skin grafting or the use of cartilage ersatz material required. In the plastic surgical treatment of moderate to severe ear deformities, in contrast, not only incisional and suturing techniques, but also free skin grafts and ersatz materials are needed. At the ENT Department of the Ludwig-Maximilian University in Munich, plastic reconstruction of moderate to severe deformities of the external ear using porous polyethylene implants instead of rib cartilage grafts has been practiced with success for the past two years or so. Porous polyethylene implants provide good results and may help to avoid pre- and postoperative morbidity at donor site defects.

Simulations of surface stress effects in nanoscale single crystals

NASA Astrophysics Data System (ADS)

Zadin, V.; Veske, M.; Vigonski, S.; Jansson, V.; Muszinsky, J.; Parviainen, S.; Aabloo, A.; Djurabekova, F.

2018-04-01

Onset of vacuum arcing near a metal surface is often associated with nanoscale asperities, which may dynamically appear due to different processes ongoing in the surface and subsurface layers in the presence of high electric fields. Thermally activated processes, as well as plastic deformation caused by tensile stress due to an applied electric field, are usually not accessible by atomistic simulations because of the long time needed for these processes to occur. On the other hand, finite element methods, able to describe the process of plastic deformations in materials at realistic stresses, do not include surface properties. The latter are particularly important for the problems where the surface plays crucial role in the studied process, as for instance, in the case of plastic deformations at a nanovoid. In the current study by means of molecular dynamics (MD) and finite element simulations we analyse the stress distribution in single crystal copper containing a nanovoid buried deep under the surface. We have developed a methodology to incorporate the surface effects into the solid mechanics framework by utilizing elastic properties of crystals, pre-calculated using MD simulations. The method leads to computationally efficient stress calculations and can be easily implemented in commercially available finite element software, making it an attractive analysis tool.

Characterization and Prediction of Flow Behavior in High-Manganese Twinning Induced Plasticity Steels: Part II. Jerky Flow and Instantaneous Strain Rate

NASA Astrophysics Data System (ADS)

Saeed-Akbari, A.; Mishra, A. K.; Mayer, J.; Bleck, W.

2012-05-01

The jerky and smooth flow curves in high-manganese twinning induced plasticity (TWIP) steels were investigated by comparing Fe-Mn-C and Fe-Mn-Al-C systems. The pronounced serrations on the flow curves of Fe-Mn-C TWIP steel, produced during tensile testing at 300 K (27 °C) and 373 K (100 °C), were shown to be the result of localized high-temperature Portevin Le-Chatelier (PLC) bands moving across the gage length throughout the deformation. The speed of the PLC bands and their temperature effects were found to be strongly dependent on the applied strain rate, which was controlled by adjusting the cross-head speed of the tensile testing machine. The localized temperature-dependent stacking fault energy (SFE) variations resulting from the PLC effect and adiabatic heating were analyzed and compared for both slow and fast deformation rates. The instabilities in the measured logarithmic strain values caused by jerky flow could cause the local strain rate to deviate systematically from the targeted (applied) strain rate. These instabilities are better observed by calculating the instantaneous strain rate (ISR) values for each instant of deformation along the entire gage length. Finally, a new type of diagram was developed by plotting the true stress against the ISR values. From the diagram, the onset of different mechanisms, such as deformation twinning, nonpronounced, and pronounced serrations, could be marked precisely.

Complexity and Anisotropy of Plastic Flow of α-Ti Probed by Acoustic Emission and Local Extensometry.

PubMed

Lebyodkin, Mikhail; Amouzou, Kékéli; Lebedkina, Tatiana; Richeton, Thiebaud; Roth, Amandine

2018-06-22

Current progress in the prediction of mechanical behavior of solids requires understanding of spatiotemporal complexity of plastic flow caused by self-organization of crystal defects. It may be particularly important in hexagonal materials because of their strong anisotropy and combination of different mechanisms of plasticity, such as dislocation glide and twinning. These materials often display complex behavior even on the macroscopic scale of deformation curves, e.g., a peculiar three-stage elastoplastic transition, the origin of which is a matter of debates. The present work is devoted to a multiscale study of plastic flow in α-Ti, based on simultaneous recording of deformation curves, 1D local strain field, and acoustic emission (AE). It is found that the average AE activity also reveals three-stage behavior, but in a qualitatively different way depending on the crystallographic orientation of the sample axis. On the finer scale, the statistical analysis of AE events and local strain rates testifies to an avalanche-like character of dislocation processes, reflected in power-law probability distribution functions. The results are discussed from the viewpoint of collective dislocation dynamics and are confronted to predictions of a recent micromechanical model of Ti strain hardening.

Plasticized Polymer Interlayer for Low-Temperature Fabrication of a High-Quality Silver Nanowire-Based Flexible Transparent and Conductive Film

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jo, Wonhee; Kang, Hong Suk; Choi, Jaeho

Silver nanowires (AgNWs) are one of the most promising materials to replace commercially available indium tin oxide in flexible transparent conductive films (TCFs); however, there are still numerous problems originating from poor AgNW junction formation and improper AgNW embedment into transparent substrates. To mitigate these problems, high-temperature processes have been adopted; however, unwanted substrate deformation prevents the use of these processes for the formation of flexible TCFs. In this work, we present a novel poly(methyl methacrylate) interlayer plasticized by dibutyl phthalate for low-temperature fabrication of AgNW-based TCFs, which does not cause any substrate deformation. By exploiting the viscoelastic properties ofmore » the plasticized interlayer near the lowered glass-transition temperature, a monolithic junction of AgNWs on the interlayer and embedment of the interconnected AgNWs into the interlayer are achieved in a single-step pressing. The resulting AgNW-TCFs are highly transparent (~92% at a wavelength of 550 nm), highly conductive (<90 Ω/sq), and environmentally and mechanically robust. Therefore, the plasticized interlayer provides a simple and effective route to fabricate high-quality AgNW-based TCFs.« less

Erosion of a grooved surface caused by impact of particle-laden flow

NASA Astrophysics Data System (ADS)

Jung, Sohyun; Yang, Eunjin; Kim, Ho-Young

2016-11-01

Solid erosion can be a life-limiting process for mechanical elements in erosive environments, thus it is of practical importance in many industries such as construction, mining, and coal conversion. Erosion caused by particle-laden flow occurs through diverse mechanisms, such as cutting, plastic deformation, brittle fracture, fatigue and melting, depending on particle velocity, total particle mass and impingement angle. Among a variety of attempts to lessen erosion, here we investigate the effectiveness of millimeter-sized grooves on the surface. By experimentally measuring the erosion rates of smooth and triangular-grooved surfaces under various impingement angles, we find that erosion can be significantly reduced within a finite range of impingement angles. We show that such erosion resistance is attributed to the swirls of air within grooves and the differences in erosive strength of normal and slanted impact. In particular, erosion is mitigated when we increase the effective area under normal impact causing plastic deformation and fracture while decreasing the area under slanted impact that cuts the surface to a large degree. Our quantitative model for the erosion rate of grooved surfaces considering the foregoing effects agrees with the measurement results.

Practical solution of plastic deformation problems in elastic-plastic range

NASA Technical Reports Server (NTRS)

Mendelson, A; Manson, S

1957-01-01

A practical method for solving plastic deformation problems in the elastic-plastic range is presented. The method is one of successive approximations and is illustrated by four examples which include a flat plate with temperature distribution across the width, a thin shell with axial temperature distribution, a solid cylinder with radial temperature distribution, and a rotating disk with radial temperature distribution.

Elastic-plastic analysis of AS4/PEEK composite laminate using a one-parameter plasticity model

NASA Technical Reports Server (NTRS)

Sun, C. T.; Yoon, K. J.

1992-01-01

A one-parameter plasticity model was shown to adequately describe the plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The elastic-plastic stress-strain relations of coupon specimens were measured and compared with those predicted by the finite element analysis using the one-parameter plasticity model. The results show that the one-parameter plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Formation of the structure and properties of an Mg-Al-Zn-Mn alloy during plastic deformation by rolling

NASA Astrophysics Data System (ADS)

Bozhko, S. A.; Betsofen, S. Ya.; Kolobov, Yu. R.; Vershinina, T. N.

2015-03-01

The laws of formation of an ultrafine structure in an Mg-Al-Zn-Mn alloy (MA5 alloy) under severe plastic deformation have been studied during lengthwise section rolling at a strain e = 1.59. The deformation behavior and the physical factors of anisotropy of yield strength during compression tests in various directions with respect to axis of rolling are analyzed. The role of crystallographic texture and twinning processes in the generation of strength processes and the development of plastic deformation of the alloy is analyzed.

Thermal cycling reliability of Cu/SnAg double-bump flip chip assemblies for 100 μm pitch applications

NASA Astrophysics Data System (ADS)

Son, Ho-Young; Kim, Ilho; Lee, Soon-Bok; Jung, Gi-Jo; Park, Byung-Jin; Paik, Kyung-Wook

2009-01-01

A thick Cu column based double-bump flip chip structure is one of the promising alternatives for fine pitch flip chip applications. In this study, the thermal cycling (T/C) reliability of Cu/SnAg double-bump flip chip assemblies was investigated, and the failure mechanism was analyzed through the correlation of T/C test and the finite element analysis (FEA) results. After 1000 thermal cycles, T/C failures occurred at some Cu/SnAg bumps located at the edge and corner of chips. Scanning acoustic microscope analysis and scanning electron microscope observations indicated that the failure site was the Cu column/Si chip interface. It was identified by a FEA where the maximum stress concentration was located during T/C. During T/C, the Al pad between the Si chip and a Cu column bump was displaced due to thermomechanical stress. Based on the low cycle fatigue model, the accumulation of equivalent plastic strain resulted in thermal fatigue deformation of the Cu column bumps and ultimately reduced the thermal cycling lifetime. The maximum equivalent plastic strains of some bumps at the chip edge increased with an increased number of thermal cycles. However, equivalent plastic strains of the inner bumps did not increase regardless of the number of thermal cycles. In addition, the z-directional normal plastic strain ɛ22 was determined to be compressive and was a dominant component causing the plastic deformation of Cu/SnAg double bumps. As the number of thermal cycles increased, normal plastic strains in the perpendicular direction to the Si chip and shear strains were accumulated on the Cu column bumps at the chip edge at low temperature region. Thus it was found that the Al pad at the Si chip/Cu column interface underwent thermal fatigue deformation by compressive normal strain and the contact loss by displacement failure of the Al pad, the main T/C failure mode of the Cu/SnAg flip chip assembly, then occurred at the Si chip/Cu column interface shear strain deformation during T/C.

The effect of hydrogen embrittlement on the localized plastic deformation of aluminum alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bochkareva, Anna, E-mail: avb@ispms.tsc.ru; Lunev, Aleksey, E-mail: agl@ispms.tsc.ru; National Research Tomsk Polytechnic University, Tomsk, 634050

2015-10-27

The effect of hydrogen embrittlement on the localized plastic deformation of aluminum alloy D1 was investigated. The studies were performed for the test samples of aluminum alloy subjected to electrolytic hydrogenation. It is found that the mechanical properties and localized plastic deformation parameters of aluminum alloy are affected adversely by hydrogen embrittlement. The hydrogenated counterpart of alloy has a lower degree of ductility relative to the original alloy; however, the plastic flow behavior of material remains virtually unaffected. Using scanning electron and atomic force microscopy methods, the changes in the fracture surface were investigated. The deformation diagrams were examined formore » the deformed samples of aluminum alloy. These are found to show all the plastic flow stages: the linear, parabolic and pre-failure stages would occur for the respective values of the exponent n from the Ludwik-Holomon equation. Using digital speckle image technique, the local strain patterns were being registered for the original alloy D1 and the counterpart subjected to electrolytic hydrogenation for 100 h.« less

Advanced Welding Tool

NASA Technical Reports Server (NTRS)

1982-01-01

Accutron Tool & Instrument Co.'s welder was originally developed as a tool specifically for joining parts made of plastic or composite materials in any atmosphere to include the airless environment of space. Developers decided on induction or magnetic heating to avoid causing deformation and it also can be used with almost any type of thermoplastic material. Induction coil transfers magnetic flux through the plastic to a metal screen that is sandwiched between the sheets of plastic to be joined. When welder is energized, alternating current produces inductive heating on the screen causing the adjacent plastic surfaces to melt and flow into the mesh, creating a bond on the total surface area. Dave Brown, owner of Great Falls Canoe and Kayak Repair, Vienna, VA, uses a special repair technique based on operation of the Induction Toroid Welder to fix canoes. Whitewater canoeing poses the problem of frequent gashes that are difficult to repair. The main reason is that many canoes are made of plastics. The commercial Induction model is a self-contained, portable welding gun with a switch on the handle to regulate the temperature of the plastic melting screen. Welder has a broad range of applications in the automobile, appliance, aerospace and construction industries.

Solution of elastic-plastic stress analysis problems by the p-version of the finite element method

NASA Technical Reports Server (NTRS)

Szabo, Barna A.; Actis, Ricardo L.; Holzer, Stefan M.

1993-01-01

The solution of small strain elastic-plastic stress analysis problems by the p-version of the finite element method is discussed. The formulation is based on the deformation theory of plasticity and the displacement method. Practical realization of controlling discretization errors for elastic-plastic problems is the main focus. Numerical examples which include comparisons between the deformation and incremental theories of plasticity under tight control of discretization errors are presented.

Extraordinary plasticity of an inorganic semiconductor in darkness.

PubMed

Oshima, Yu; Nakamura, Atsutomo; Matsunaga, Katsuyuki

2018-05-18

Inorganic semiconductors generally tend to fail in a brittle manner. Here, we report that extraordinary "plasticity" can take place in an inorganic semiconductor if the deformation is carried out "in complete darkness." Room-temperature deformation tests of zinc sulfide (ZnS) were performed under varying light conditions. ZnS crystals immediately fractured when they deformed under light irradiation. In contrast, it was found that ZnS crystals can be plastically deformed up to a deformation strain of ε t = 45% in complete darkness. In addition, the optical bandgap of the deformed ZnS crystals was distinctly decreased after deformation. These results suggest that dislocations in ZnS become mobile in complete darkness and that multiplied dislocations can affect the optical bandgap over the whole crystal. Inorganic semiconductors are not necessarily intrinsically brittle. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

SHAKING TABLE TESTS ON SEISMIC DEFORMATION OF PILE SUPPORTED PIER

NASA Astrophysics Data System (ADS)

Fujita, Daiki; Kohama, Eiji; Takenobu, Masahiro; Yoshida, Makoto; Kiku, Hiroyoshi

The seismic deformation characeteristics of a pile supported pier was examined with the shake table test, especially focusing on the pier after its deformation during earthquakes. The model based on the similitude of the fully-plastic moment in piles was prepared to confirm the deformation and stress characteristic after reaching the fully-plastic moment. Moreover, assuming transportation of emergency supplies and occurrence of after shock in the post-disaster period, the pile supported pier was loaded with weight after reaching fully-plastic moment and excited with the shaking table. As the result, it is identified that the displacement of the pile supported pier is comparatively small if bending strength of piles does not decrease after reaching fully-plastic moment due to nonoccourrence of local backling or strain hardening.

A Unified Constitutive Model for Subglacial Till, Part I: The Disturbed State Concept

NASA Astrophysics Data System (ADS)

Jenson, J. W.; Desai, C. S.; Clark, P. U.; Contractor, D. N.; Sane, S. M.; Carlson, A. E.

2006-12-01

Classical plasticity models such as Mohr-Coulomb may not adequately represent the full range of possible motion and failure in tills underlying ice sheets. Such models assume that deformations are initially elastic, and that when a peak or failure stress level is reached the system experiences sudden failure, after which the stress remains constant and the deformations can tend to infinite magnitudes. However, theory suggests that the actual behavior of deforming materials, including granular materials such as glacial till, can involve plastic or irreversible strains almost from the beginning, in which localized zones of microcracking and "failure" can be distributed over the material element. As the loading increases, and with associated plastic and creep deformations, the distributed failure zones coalesce. When the extent of such coalesced zones reaches critical values of stresses and strains, the critical condition (failure) can occur in the till, which would cause associated movements of the ice sheet. Failure or collapse then may occur at much larger strain levels. Classical models (e.g., Mohr-Coulomb) may therefore not be able to fully and realistically characterize deformation behavior and the gradual developments of localized failures tending to the global failure and movements. We present and propose the application of the Disturbed State Concept (DSC), a unified model that incorporates the actual pre- and post-failure behavior, for characterizing the behavior of subglacial tills. In this presentation (Part I), we describe the DSC and propose its application to subglacial till. Part II (Desai et al.) describes our application of the DSC with laboratory testing, model calibration, and validations to evaluate the mechanical properties of two regionally significant Pleistocene tills.

Sub-second carbon-nanotube-mediated microwave sintering for high-conductivity silver patterns on plastic substrates

NASA Astrophysics Data System (ADS)

Jung, Sunshin; Chun, Su Jin; Han, Joong Tark; Woo, Jong Seok; Shon, Cha-Hwa; Lee, Geon-Woong

2016-02-01

A method of microwave sintering that is mediated by carbon nanotubes (CNTs) has been developed to obtain high-conductivity Ag patterns on the top of heat-sensitive plastic substrates within a short time. The Ag patterns are printed on CNTs formed on plastic substrates and rapidly heated to a great extent by the heat transferred from the microwave-heated CNTs. The conductivity of the microwave-sintered Ag patterns reaches ~39% that of bulk Ag within 1 s without substrate deformation. Furthermore, microwave sintering enhances the adhesion of Ag patterns to the thermoplastic substrates because the sintering causes interfacial fusion between the Ag patterns and the substrates, and CNTs physically connect the patterns with the substrates.A method of microwave sintering that is mediated by carbon nanotubes (CNTs) has been developed to obtain high-conductivity Ag patterns on the top of heat-sensitive plastic substrates within a short time. The Ag patterns are printed on CNTs formed on plastic substrates and rapidly heated to a great extent by the heat transferred from the microwave-heated CNTs. The conductivity of the microwave-sintered Ag patterns reaches ~39% that of bulk Ag within 1 s without substrate deformation. Furthermore, microwave sintering enhances the adhesion of Ag patterns to the thermoplastic substrates because the sintering causes interfacial fusion between the Ag patterns and the substrates, and CNTs physically connect the patterns with the substrates. Electronic supplementary information (ESI) available: Temperature difference in Ag/CNT/PC samples; the carbon content and electrical performance after microwave sintering; microwave sintering of Ag/CNT patterns; physical connection between the substrate and sintered Ag lines; touch-piano (figure and movie). See DOI: 10.1039/c5nr08082g

The Mechanical Properties of Energetically Deposited Non-Crystalline Carbon Thin Films

DOE PAGES

Kracica, M.; Kocer, C.; Lau, D.; ...

2015-11-05

The mechanical behaviour of carbon films prepared with a variety of densities and microstructures was investigated using nanoindentation. Deposition energies between 25 and 600 eV and temperatures in the range 25-600 °C were used. Films prepared at low temperatures and moderate energy were amorphous with a high density. Finite element methods were used to model the stress fields, reproduce the indentation behaviour and evaluate elastic properties. Young s moduli up to 670 GPa and a low Poisson s ratio of ~ 0.17 were found, comparable to polycrystalline cubic boron nitride, one of the hardest materials known. Films with the samemore » density did not always show the same behaviour, emphasising the role of microstructure in determining mechanical response. Extended graphite- like regions within the films grown at high energy and high temperature observed in transmission electron microscopy caused plastic deformation and failure to recover after a complete indentation cycle. At low deposition energies, the graphite-like regions were smaller in size causing plastic deformation but with complete recovery after indentation.« less

Measurement of plastic and elastic deformation due to third-order torque in self-ligated orthodontic brackets.

PubMed

Major, Thomas W; Carey, Jason P; Nobes, David S; Heo, Giseon; Major, Paul W

2011-09-01

Control of root torque is often achieved by introducing a twist in a rectangular archwire. The purpose of this study was to investigate third-order torque on different types of self-ligated brackets by analyzing the bracket's elastic and plastic deformations in conjunction with the expressed torque at varying angles of twist. An orthodontic bracket was mounted to a load cell that measured forces and moments in all directions. The wire was twisted in the bracket via a stepper motor, controlled by custom software. Overhead images were taken by a camera through a microscope and processed by using optical correlation to measure deformation. At the maximum torquing angle of 63° with 0.019 × 0.025-in stainless steel wire, the total elastic and plastic deformation values were 0.063, 0.033, and 0.137 mm for Damon Q (Ormco, Orange, Calif), In-Ovation R (GAC, Bohemia, NY), and Speed (Strite Industries, Cambridge, Ontario, Canada), respectively. The total plastic deformation values were 0.015, 0.006, and 0.086 mm, respectively, measured at 0° of unloading. In-Ovation R had the least deformation due to torquing of the 3 investigated bracket types. Damon Q and Speed on average had approximately 2.5 and 14 times greater maximum plastic deformation, respectively, than did In-Ovation R. Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Microstructure Evolution and Mechanical Behavior of a Hot-Rolled High-Manganese Dual-Phase Transformation-Induced Plasticity/Twinning-Induced Plasticity Steel

NASA Astrophysics Data System (ADS)

Fu, Liming; Shan, Mokun; Zhang, Daoda; Wang, Huanrong; Wang, Wei; Shan, Aidang

2017-05-01

The microstructures and deformation behavior were studied in a high-temperature annealed high-manganese dual-phase (28 vol pct δ-ferrite and 72 vol pct γ-austenite) transformation-induced plasticity/twinning-induced plasticity (TRIP/TWIP) steel. The results showed that the steel exhibits a special Lüders-like yielding phenomenon at room temperature (RT) and 348 K (75 °C), while it shows continuous yielding at 423 K, 573 K and 673 K (150 °C, 300 °C and 400 °C) deformation. A significant TRIP effect takes place during Lüders-like deformation at RT and 348 K (75 °C) temperatures. Semiquantitative analysis of the TRIP effect on the Lüders-like yield phenomenon proves that a softening effect of the strain energy consumption of strain-induced transformation is mainly responsible for this Lüders-like phenomenon. The TWIP mechanism dominates the 423 K (150 °C) deformation process, while the dislocation glide controls the plasticity at 573 K (300 °C) deformation. The delta-ferrite, as a hard phase in annealed dual-phase steel, greatly affects the mechanical stability of austenite due to the heterogeneous strain distribution between the two phases during deformation. A delta-ferrite-aided TRIP effect, i.e., martensite transformation induced by localized strain concentration of the hard delta-ferrite, is proposed to explain this kind of Lüders-like phenomenon. Moreover, the tensile curve at RT exhibits an upward curved behavior in the middle deformation stage, which is principally attributed to the deformation twinning of austenite retained after Lüders-like deformation. The combination of the TRIP effect during Lüders-like deformation and the subsequent TWIP effect greatly enhances the ductility in this annealed high-manganese dual-phase TRIP/TWIP steel.

Investigation of plastic deformation heterogeneities in duplex steel by EBSD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wronski, S., E-mail: wronski@ftj.agh.edu.pl; Tarasiuk, J., E-mail: tarasiuk@ftj.agh.edu.pl; Bacroix, B., E-mail: brigitte.bacroix@univ-paris13.fr

2012-11-15

An EBSD analysis of a duplex steel (austeno-ferritic) deformed in tension up to fracture is presented. The main purpose of the paper is to describe, qualitatively and quantitatively, the differences in the behavior of the two phases during plastic deformation. In order to do so, several topological maps are measured on the deformed state using the electron backscatter diffraction technique. Distributions of grain size, misorientation, image quality factor and texture are then analyzed in detail. - Highlights: Black-Right-Pointing-Pointer Heterogeneities in duplex steel is studied. Black-Right-Pointing-Pointer The behavior of the two phases during plastic deformation is studied. Black-Right-Pointing-Pointer IQ factor distributionmore » and misorientation characteristics are examined using EBSD.« less

Modelling of the plastic deformation and primary creep of metals coupled with DC in terms of the synthetic theory of irrecoverable deformation

NASA Astrophysics Data System (ADS)

Rusinko, Andrew; Varga, Peter

2018-04-01

The paper deals with modelling of the plastic and creep deformation of metals coupled with current. The passage of DC manifests itself in the increase in creep deformation and leads to primary creep time shortening. With plastic deformation, a short electric impulse results in the step-wise decrease of stress (stress-drop) on the stress-strain diagram. To catch these phenomena, we utilize the synthetic theory of recoverable deformation. The constitutive equation of this theory is supplemented by a term taking into account the intensity of DC. Further, we introduce DC intensity into the function governing transient creep. As a result, we predict the parameters of transient creep and calculate the stress-drop as a function of current intensity. The model results show good agreement with experimental data.

Inelastic Deformation of Metal Matrix Composites. Part 1; Plasticity and Damage Mechanisms

NASA Technical Reports Server (NTRS)

Majumdar, B. S.; Newaz, G. M.

1992-01-01

The deformation mechanisms of a Ti 15-3/SCS6 (SiC fiber) metal matrix composite (MMC) were investigated using a combination of mechanical measurements and microstructural analysis. The objectives were to evaluate the contributions of plasticity and damage to the overall inelastic response, and to confirm the mechanisms by rigorous microstructural evaluations. The results of room temperature experiments performed on 0 degree and 90 degree systems primarily are reported in this report. Results of experiments performed on other laminate systems and at high temperatures will be provided in a forthcoming report. Inelastic deformation of the 0 degree MMC (fibers parallel to load direction) was dominated by the plasticity of the matrix. In contrast, inelastic deformations of the 90 degree composite (fibers perpendicular to loading direction) occurred by both damage and plasticity. The predictions of a continuum elastic plastic model were compared with experimental data. The model was adequate for predicting the 0 degree response; however, it was inadequate for predicting the 90 degree response largely because it neglected damage. The importance of validating constitutive models using a combination of mechanical measurements and microstructural analysis is pointed out. The deformation mechanisms, and the likely sequence of events associated with the inelastic deformation of MMCs, are indicated in this paper.

Characterization of plastic deformation in a disk bend test

NASA Astrophysics Data System (ADS)

Byun, T. S.; Lee, E. H.; Hunn, J. D.; Farrell, K.; Mansur, L. K.

2001-04-01

A disk bend test technique has been developed to study deformation mechanisms as well as mechanical properties. In the disk bend test, a transmission electron microscopy (TEM) disk size specimen of 3 mm diameter ×0.25 mm thick is clamped around its rim in a circular holder and indented with a tungsten carbide ball of 1 mm diameter on its back face. AISI 316LN austenitic stainless steel and 9Cr-2WVTa ferritic/martensitic steel were selected as test materials. A model was developed to determine the average plastic strain and surface plastic strain in the disk bend test. The deformation regimes of the plastic strain versus deflection curves corresponded to those of the load versus deflection curves. The stress state of the disk bend deformation was analyzed for the two test materials and compared with those of other mechanical tests such as uniaxial tensile, compact tension, and ball indentation tests. Slip line features at the deformed surface and the corresponding TEM microstructures were examined for both tensile and disk bend specimens. Differences and similarities in deformation between the disk bend and the tensile tests are described.

Grain size constraints on twin expansion in hexagonal close packed crystals

DOE PAGES

Kumar, Mariyappan Arul; Beyerlein, Irene Jane; Tome, Carlos N.

2016-10-20

Deformation twins are stress-induced transformed domains of lamellar shape that form when polycrystalline hexagonal close packed metals, like Mg, are strained. Several studies have reported that the propensity of deformation twinning reduces as grain size decreases. Here, we use a 3D crystal plasticity based micromechanics model to calculate the effect of grain size on the driving forces responsible for expanding twin lamellae. The calculations reveal that constraints from the neighboring grain where the grain boundary and twin lamella meet induce a stress reversal in the twin lamella. A pronounced grain size effect arises as reductions in grain size cause thesemore » stress-reversal fields from twin/grain boundary junctions to affect twin growth. We further show that the severity of this neighboring grain constraint depends on the crystallographic orientation and plastic response of the neighboring grain. We show that these stress-reversal fields from twin/grain boundary junctions will affect twin growth, below a critical parent grain size. Finally, these results reveal an unconventional yet influential role that grain size and grain neighbors can play on deformation twinning.« less

Allotropic forms of carbon in the Invar Fe-Ni-C alloy before and after plastic deformation by upsetting

NASA Astrophysics Data System (ADS)

Nadutov, V. M.; Vashchuk, D. L.; Karbivskii, V. L.; Volosevich, P. Yu.; Davydenko, O. A.

2018-04-01

The effect of cold plastic deformation by upsetting (e = 1.13) on structure and hybridised bonds of carbon in the fcc Invar Fe-30.9%Ni-1.23% C alloy was studied by means of X-ray phase analysis and X-ray photoelectron spectroscopy. Carbon precipitates along grain boundaries and inside of grains in the alloy after annealing and plastic deformation were revealed. The presence of mainly sp2- and sp3-hybridised C-C bonds attributing to graphite and amorphous carbon as well as the carbon bonds with impurity atoms and metallic Fe and Ni atoms in austenitic phase were revealed in the annealed and deformed alloy. It was shown for the first time that plastic deformation of the alloy results in partial destruction of the graphite crystal structure, increasing the relative part of amorphous carbon, and redistribution of carbon between structural elements as well as in a solid solution of austenitic phase.

Influence of thermally activated processes on the deformation behavior during low temperature ECAP

NASA Astrophysics Data System (ADS)

Fritsch, S.; Scholze, M.; F-X Wagner, M.

2016-03-01

High strength aluminum alloys are generally hard to deform. Therefore, the application of conventional severe plastic deformation methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low temperature deformation in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically deform a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially deformed from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low temperatures, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic deformation at low temperatures. We then discuss how the deformation temperature and velocity influence the occurrence of PLC effects and the homogeneity of the deformed ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low temperature deformed materials as a function of deformation temperature.

Tectonic and hydrological controls on multiscale deformations in the Levant: numerical modeling and theoretical analysis

NASA Astrophysics Data System (ADS)

Belferman, Mariana; Katsman, Regina; Agnon, Amotz; Ben Avraham, Zvi

2016-04-01

Understanding the role of the dynamics of water bodies in triggering deformations in the upper crust and subsequently leading to earthquakes has been attracting considerable attention. We suggest that dynamic changes in the levels of the water bodies occupying tectonic depressions along the Dead Sea Transform (DST) cause significant variations in the shallow crustal stress field and affect local fault systems in a way that eventually leads to earthquakes. This mechanism and its spatial and temporal scales differ from those in tectonically-driven deformations. In this study we present a new thermo-mechanical model, constructed using the finite element method, and extended by including a fluid flow component in the upper crust. The latter is modeled on a basis of two-way poroelastic coupling with the momentum equation. This coupling is essential for capturing fluid flow evolution induced by dynamic water loading in the DST depressions and to resolve porosity changes. All the components of the model, namely elasticity, creep, plasticity, heat transfer, and fluid flow, have been extensively verified and presented in the study. The two-way coupling between localized plastic volumetric deformations and enhanced fluid flow is addressed, as well as the role of variability of the rheological and the hydrological parameters in inducing deformations in specific faulting environments. Correlations with historical and contemporary earthquakes in the region are discussed.

The effects of CuO particle size on microstructure evolution of AgCuO compo-sites in plastic deformation process: finite element simulation and experimental study

NASA Astrophysics Data System (ADS)

Li, Zhiguo; Cao, Hanxing; Zhou, Xiaolong; Zhou, Zhaobo; Cao, Jianchun

2018-04-01

The effects of CuO with different particle sizes on the microstructure evolution of AgCuO composite material during plastic deformation process were investigated by finite element (FE) analysis and experiment. The results are as follows: with the decrease of CuO particle size, the degree of radial compression and axial elongation of CuO particle cluster increase gradually, as well as the dispersion of CuO also increase. Meanwhile, the shape of CuO particles is constantly transformed from polygonal to fibrous, which makes the number of linear fibrous CuO increase continuously while bent fibrous CuO reduce gradually. By comparing the simulation and experiment results we find that there are four different typical microstructure regions, which caused by the interaction between monoclinic and cubic CuO during the extrusion process.

Intergranular stress study of TC11 titanium alloy after laser shock peening by synchrotron-based high-energy X-ray diffraction

NASA Astrophysics Data System (ADS)

Su, R.; Li, L.; Wang, Y. D.; Nie, Z. H.; Ren, Y.; Zhou, X.; Wang, J.

2018-05-01

The distribution of residual lattice strain as a function of depth were carefully investigated by synchrotron-based high energy X-ray diffraction (HEXRD) in TC11 titanium alloy after laser shock peening (LSP). The results presented big compressive residual lattice strains at surface and subsurface, then tensile residual lattice strains in deeper region, and finally close to zero lattice strains in further deep interior with no plastic deformation thereafter. These evolutions in residual lattice strains were attributed to the balance of direct load effect from laser shock wave and the derivative restriction force effect from surrounding material. Significant intergranular stress was evidenced in the processed sample. The intergranular stress exhibited the largest value at surface, and rapidly decreased with depth increase. The magnitude of intergranular stress was proportional to the severity of the plastic deformation caused by LSP. Two shocks generated larger intergranular stress than one shock.

MD simulation of plastic deformation nucleation in stressed crystallites under irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korchuganov, A. V., E-mail: avkor@ispms.tsc.ru; Zolnikov, K. P., E-mail: kost@ispms.tsc.ru; Kryzhevich, D. S., E-mail: kryzhev@ispms.tsc.ru

2016-12-15

The investigation of plastic deformation nucleation in metals and alloys under irradiation and mechanical loading is one of the topical issues of materials science. Specific features of nucleation and evolution of the defect system in stressed and irradiated iron, vanadium, and copper crystallites were studied by molecular dynamics simulation. Mechanical loading was performed in such a way that the modeled crystallite volume remained unchanged. The energy of the primary knock-on atom initiating a cascade of atomic displacements in a stressed crystallite was varied from 0.05 to 50 keV. It was found that atomic displacement cascades might cause global structural transformationsmore » in a region far larger than the radiation-damaged area. These changes are similar to the ones occurring in the process of mechanical loading of samples. They are implemented by twinning (in iron and vanadium) or through the formation of partial dislocation loops (in copper).« less

Tensile Fracture of Ductile Materials. M.S. Thesis

NASA Technical Reports Server (NTRS)

Pai, D. M.

1984-01-01

For brittle materials, circular voids play an important role relative to fracture, intensifing both tensile and compressive stresses. A maximum intensified tensile stress failure criterion applies quite well to brittle materials. An attempt was made to explore the possibility of extending the approach to the tensile fracture of ductile materials. The three dimensional voids that exist in reality are modelled by circular holes in sheet metal. Mathematical relationships are sought between the shape and size of the hole, after the material is plastically deformed, and the amount of deformation induced. Then, the effect of hole shape, size and orientation on the mechanical properties is considered experimentally. The presence of the voids does not affect the ultimate tensile strength of the ductile materials because plastic flow wipes out the stress intensification caused by them. However, the shape and orientation of the defect is found to play an important role in affecting the strain at fracture.

A defect density-based constitutive crystal plasticity framework for modeling the plastic deformation of Fe-Cr-Al cladding alloys subsequent to irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patra, Anirban; Wen, Wei; Martinez Saez, Enrique

2016-02-05

It is essential to understand the deformation behavior of these Fe-Cr-Al alloys, in order to be able to develop models for predicting their mechanical response under varied loading conditions. Interaction of dislocations with the radiation-induced defects governs the crystallographic deformation mechanisms. A crystal plasticity framework is employed to model these mechanisms in Fe-Cr-Al alloys. This work builds on a previously developed defect density-based crystal plasticity model for bcc metals and alloys, with necessary modifications made to account for the defect substructure observed in Fe-Cr-Al alloys. The model is implemented in a Visco-Plastic Self Consistent (VPSC) framework, to predict the mechanicalmore » behavior under quasi-static loading.« less

Plastic Deformation of Magnesium Alloy Subjected to Compression-First Cyclic Loading

NASA Astrophysics Data System (ADS)

Lee, Soo Yeol; Gharghouri, Michael A.; Root, John H.

In-situ neutron diffraction has been employed to study the deformation mechanisms in a precipitation-hardened and extruded Mg-8.5wt.% Al alloy subjected to compression followed by reverse tension. The starting texture is such that the basal poles of most grains are oriented normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis. Diffraction peak intensities for several grain orientations monitored in-situ during deformation show that deformation twinning plays an important role in the elastic-plastic transition and subsequent plastic deformation behavior. Significant non-linear behavior is observed during unloading after compression and appears to be due to detwinning. This effect is much stronger after compressive loading than after tensile loading.

Calculation of recovery plasticity in multistage hot forging under isothermal conditions.

PubMed

Zhbankov, Iaroslav G; Perig, Alexander V; Aliieva, Leila I

2016-01-01

A widely used method for hot forming steels and alloys, especially heavy forging, is the process of multistage forging with pauses between stages. The well-known effect which accompanies multistage hot forging is metal plasticity recovery in comparison with monotonic deformation. A method which takes into consideration the recovery of plasticity in pauses between hot deformations of a billet under isothermal conditions is proposed. This method allows the prediction of billet forming limits as a function of deformation during the forging stage and the duration of the pause between the stages. This method takes into account the duration of pauses between deformations and the magnitude of subdivided deformations. A hot isothermal upsetting process with pauses was calculated by the proposed method. Results of the calculations have been confirmed with experimental data.

A method of increasing the depth of the plastically deformed layer in the roller burnishing process

NASA Astrophysics Data System (ADS)

Kowalik, Marek; Trzepiecinski, Tomasz

2018-05-01

The subject of this paper is an analysis of the determination of the depth of the plastically deformed layer in the process of roller burnishing a shaft using a newly developed method in which a braking moment is applied to the roller. It is possible to increase the depth of the plastically deformed layer by applying the braking moment to the roller during the burnishing process. The theoretical considerations presented are based on the Hertz-Bielayev and Huber-Mises theories and permit the calculation of the depth of plastic deformation of the top layer of the burnished shaft. The theoretical analysis has been verified experimentally and using numerical calculations based on the finite element method using the Msc.MARC program. Experimental tests were carried out on ring-shaped samples made of C45 carbon steel. The samples were burnished at different values of roller force and different values of braking moment. A significant increase was found in the depth of the plastically deformed surface layer of roller burnished shafts. Usage of the phenomenon of strain hardening of steel allows the technology presented here to increase the fatigue life of the shafts.

Influence of Near-Surface Severe Plastic Deformation of Mild Steel on the Inhibition Performance of Sodium Molybdate and 1H-Benzotriazole in Artificial Sea Water

NASA Astrophysics Data System (ADS)

Sabet Bokati, Kazem; Dehghanian, Changiz; Babaei, Mahdi

2018-02-01

The effects of near-surface severe plastic deformation (NS-SPD) on the inhibition performance of sodium molybdate (SM) and 1H-benzotriazole (BTA) for mild steel were investigated using weight loss, polarization and electrochemical impedance spectroscopy measurements. The crystal grain size of NS-SPD-processed surface was analyzed by x-ray diffractometry and field emission scanning electron microscopy. A deformed layer with thickness of 20 ± 5 µm was produced on mild steel surface after NS-SPD process due to accumulated strains. The NS-SPD process caused more effective adsorption of corrosion inhibitors due to the fabrication of a surface with a high density of preferential adsorption sites. However, the stability of protective layer was predominantly influenced by the effect of NS-SPD process on inhibition efficiency. The fairly good persistence of protective layer formed on the surface by SM-containing solution and also positive effect of NS-SPD process on adsorption of molybdate ions caused higher inhibition performance for sodium molybdate. However, NS-SPD process encouraged deterioration of protective layer formed on steel surface in the presence of BTA inhibitor. It was ascribed to partial coverage of surface, low stability of adsorbed layer and thus more adsorption of aggressive ions on unprotected area which was uncovered during immersion time.

Nonlinear analysis of AS4/PEEK thermoplastic composite laminate using a one parameter plasticity model

NASA Technical Reports Server (NTRS)

Sun, C. T.; Yoon, K. J.

1990-01-01

A one-parameter plasticity model was shown to adequately describe the orthotropic plastic deformation of AS4/PEEK (APC-2) unidirectional thermoplastic composite. This model was verified further for unidirectional and laminated composite panels with and without a hole. The nonlinear stress-strain relations were measured and compared with those predicted by the finite element analysis using the one-parameter elastic-plastic constitutive model. The results show that the one-parameter orthotropic plasticity model is suitable for the analysis of elastic-plastic deformation of AS4/PEEK composite laminates.

Development of mathematical models for automation of strength calculation during plastic deformation processing

NASA Astrophysics Data System (ADS)

Steposhina, S. V.; Fedonin, O. N.

2018-03-01

Dependencies that make it possible to automate the force calculation during surface plastic deformation (SPD) processing and, thus, to shorten the time for technological preparation of production have been developed.

Understanding the Effect of Plastic Deformation on Elastic Modulus of Metals Based on a Percolation Model with Electron Work Function

NASA Astrophysics Data System (ADS)

Li, Qingda; Hua, Guomin; Lu, Hao; Yu, Bin; Li, D. Y.

2018-05-01

The elastic modulus of materials is usually treated as a constant in engineering applications. However, plastic deformation may result in changes in the elastic modulus of metallic materials. Using brass, aluminum, and low-carbon steel as sample materials, it is demonstrated that plastic deformation decreased the elastic modulus of the materials by 10% to 20%. A percolation model incorporating the electron work function is proposed to correlate such plastic-strain-induced variations in the elastic modulus to corresponding changes in the electron work function. Efforts are made to understand the observed phenomenon on an electronic basis. The obtained experimental results are consistent with the theoretical analysis.

In situ nanoindentation study of plastic Co-deformation in Al-TiN nanocomposites

DOE PAGES

Li, N.; Wang, H.; Misra, A.; ...

2014-10-16

We performed in situ indentation in a transmission electron microscope on Al-TiN multilayers with individual layer thicknesses of 50 nm, 5 nm and 2.7 nm to explore the effect of length scales on the plastic co-deformability of a metal and a ceramic. At 50 nm, plasticity was confined to the Al layers with easy initiation of cracks in the TiN layers. At 5 nm and below, cracking in TiN was suppressed and post mortem measurements indicated a reduction in layer thickness in both layers. Our results demonstrate the profound size effect in enhancing plastic co-deformability in nanoscale metal-ceramic multilayers.

Phase transformation and deformation behavior of NiTi-Nb eutectic joined NiTi wires

PubMed Central

Wang, Liqiang; Wang, Cong; Zhang, Lai-Chang; Chen, Liangyu; Lu, Weijie; Zhang, Di

2016-01-01

NiTi wires were brazed together via eutectic reaction between NiTi and Nb powder deposited at the wire contact region. Phase transformation and deformation behavior of the NiTi-Nb eutectic microstructure were investigated using transmission electron microscopy (TEM) and cyclic loading-unloading tests. Results show that R phase and B19′ martensite transformation are induced by plastic deformation. R phase transformation, which significantly contributes to superelasticity, preferentially occurs at the interfaces between NiTi and eutectic region. Round-shaped Nb-rich phase with rod-like and lamellar-type eutectics are observed in eutectic regions. These phases appear to affect the deformation behavior of the brazed NiTi-Nb region via five distinct stages in stress-strain curves: (I) R phase reorientation, (II) R phase transformation from parent phase, (III) elastic deformation of reoriented martensite accompanied by the plastic deformation of Nb-rich phase and lamellar NiTi-Nb eutectic, (IV) B19′ martensitic transformation, and (V) plastic deformation of the specimen. PMID:27049025

Terminal ballistics of the 9mm with Action Safety bullet or Blitz-Action-Trauma (BAT) ammunition.

PubMed

Lantz, P E; Stone, R S; Broudy, D; Morgan, T M

1994-05-01

Specialty ammunition creating atypical gunshot wounds of entrance can create confusion and may be misinterpreted by pathologists unfamiliar with the terminal ballistics of these projectiles. The previously unreported wound ballistics caused by the 9mm with Action Safety bullet described in a homicide highlights the atypical entrance wound(s) and wounding capacity of this novel ammunition. Manufactured by Geco division of Dynamit Nobel, the bullet consists of a nonjacketed solid copper alloy bullet body without a conventional lead core. The large deformation well and part of the smaller central channel is filled with a hard plastic core and post that creates a round nose bullet. The internal ballistics and unique design allow the plastic nose cap and post to separate from the copper alloy base while still in the barrel. The radiolucent nose cap leaves the bullet's path but can still penetrate tissue giving the appearance of a separate but smaller entrance wound. The sharp leading edge of the deformation well and relative high velocity of the bullet body creates a punched out entrance wound with minimal marginal abrasion. When the plastic nose cap or fragments of the plastic post impact the subject, test firings may allow an inference to the muzzle-target distance even in the absence of soot deposition or stippling.

Deformation behavior of human dentin in liquid nitrogen: a diametral compression test.

PubMed

Zaytsev, Dmitry; Panfilov, Peter

2014-09-01

Contribution of the collagen fibers into the plasticity of human dentin is considered. Mechanical testing of dentin at low temperature allows excluding the plastic response of its organic matrix. Therefore, deformation and fracture behavior of the dentin samples under diametral compression at room temperature and liquid nitrogen temperature are compared. At 77K dentin behaves like almost brittle material: it is deformed exclusively in the elastic regime and it fails due to growth of the sole crack. On the contrary, dentin demonstrates the ductile response at 300K. There are both elastic and plastic contributions in the deformation of dentin samples. Multiple cracking and crack tip blunting precede the failure of samples. Organic phase plays an important role in fracture of dentin: plasticity of the collagen fibers could inhibit the crack growth. Copyright © 2014 Elsevier B.V. All rights reserved.

Thermally induced processes in mixtures of aluminum with organic acids after plastic deformations under high pressure

NASA Astrophysics Data System (ADS)

Zhorin, V. A.; Kiselev, M. R.; Roldugin, V. I.

2017-11-01

DSC is used to measure the thermal effects of processes in mixtures of solid organic dibasic acids with powdered aluminum, subjected to plastic deformation under pressures in the range of 0.5-4.0 GPa using an anvil-type high-pressure setup. Analysis of thermograms obtained for the samples after plastic deformation suggests a correlation between the exothermal peaks observed around the temperatures of degradation of the acids and the thermally induced chemical reactions between products of acid degradation and freshly formed surfaces of aluminum particles. The release of heat in the mixtures begins at 30-40°C. The thermal effects in the mixtures of different acids change according to the order of acid reactivity in solutions. The extreme baric dependences of enthalpies of thermal effects are associated with the rearrangement of the electron subsystem of aluminum upon plastic deformation at high pressures.

Predicting Hot Deformation of AA5182 Sheet

NASA Astrophysics Data System (ADS)

Lee, John T.; Carpenter, Alexander J.; Jodlowski, Jakub P.; Taleff, Eric M.

Aluminum 5000-series alloy sheet materials exhibit substantial ductilities at hot and warm temperatures, even when grain size is not particularly fine. The relatively high strain-rate sensitivity exhibited by these non-superplastic materials, when deforming under solute-drag creep, is a primary contributor to large tensile ductilities. This active deformation mechanism influences both plastic flow and microstructure evolution across conditions of interest for hot- and warm-forming. Data are presented from uniaxial tensile and biaxial bulge tests of AA5182 sheet material at elevated temperatures. These data are used to construct a material constitutive model for plastic flow, which is applied in finite-element-method (FEM) simulations of plastic deformation under multiaxial stress states. Simulation results are directly compared against experimental data to explore the usefulness of this constitutive model. The effects of temperature and stress state on plastic response and microstructure evolution are discussed.

Microstructural Analysis of Severe Plastic Deformed Twin Roll Cast AZ31 for the Optimization of Superplastic Properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Young, John P.; Askari, Hesam A.; Heiden, Michael J.

2013-07-08

In recent years magnesium alloys have attracted significant attention as potential candidates to replace many of the heavier metals used in some automotive applications. However, the limited formability of magnesium and its alloys at room temperature has driven interest in the superplastic forming magnesium as an alternative shaping method. Severe plastic deformation techniques have become a well studied method of refining the grain size and modifying the microstructural characteristics of many magnesium alloys to achieve greater superplastic properties. In this study twin roll cast (TRC) AZ31 magnesium alloy was subjected to equal channel angular pressing (ECAP) and friction stir weldingmore » (FSW). The influence of these severe plastic deformation processes on the grain size, texture and grain boundary character distribution was investigated to identify the optimum severe plastic deformation process for the superplastic forming of AZ31.« less

Changes in the physical and mechanical properties of Al-Mg alloy processed by severe plastic deformation

NASA Astrophysics Data System (ADS)

Krasnoveikin, V. A.; Kozulin, A. A.; Skripnyak, V. A.; Moskvichev, E. N.; Borodulin, D. A.

2017-12-01

This paper presents the results of studies into the effect of severe plastic deformation on the microstructure, physical and mechanical properties of coarse-grained Al-Mg alloy 1560 in the as-received state with an average grain size of 50 µm. Severe plastic deformation is performed by four-pass equal channel angular pressing (ECAP), which results in the formation of an ultrafine-grained structure with an average grain size of 3 µm in the alloy. Analysis of experimental data revealed that the physical and mechanical properties change significantly after severe plastic deformation. The microhardness of the ECAPed alloy increases by 50%, tensile yield strength by 80%, and ultimate strength by 44% in comparison with these parameters in the as-received state. The constants of approximating functions have been determined for the experimental stress-strain curves of the alloy specimens in the as-received and ECAPed states.

Model of Nanostructuring Burnishing by a Spherical Indenter Taking into Consideration Plastic Deformations

NASA Astrophysics Data System (ADS)

Lyashenko, Ya. A.; Popov, V. L.

2018-01-01

A dynamic model of the nanostructuring burnishing of a surface of metallic details taking into consideration plastic deformations has been suggested. To describe the plasticity, the ideology of dimension reduction method supplemented with the plasticity criterion is used. The model considers the action of the normal burnishing force and the tangential friction force. The effect of the coefficient of friction and the periodical oscillation of the burnishing force on the burnishing kinetics are investigated.

Investigation of features of plastic deformation and fracture of fine-crystalline V-4Ti-4Cr alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grinyaev, Konstantin V., E-mail: kvgrinyaev@inbox.ru; Tyumentsev, Alexander N., E-mail: tyuments@phys.tsu.ru; Siberian Physical-Technical Institute, Tomsk, 634050

2014-11-14

With the use of transmission electron microscopy the investigation of defect substructure was carried out in the V-4Ti-4Cr-(C, N, O) alloy with disperse strengthening (by nanoparticles of oxy-carbo-nitride phase) after deformation by active tension at temperatures of 20 and 800 °C. It has been shown that an important feature of plastic deformation is deformation localization with crystal lattice reorientation.

A Reformulation of Nonlinear Anisotropic Elasticity for Impact Physics

DTIC Science & Technology

2014-02-01

aluminum, copper, and magnesium . 15. SUBJECT TERMS impact physics, shock compression, elasticity, plasticity 16. SECURITY CLASSIFICATION OF: 17... deformation wave propagation code accounting for dissipative inelastic mechanisms. • Accuracy of the new nonlinear elastic- plastic model(s) will be...gradient and its transpose. A new general thermomechanical theory accounting for both elastic and plastic deformations has been briefly outlined in

Stress relaxation study of fillers for directly compressed tablets

PubMed Central

Rehula, M.; Adamek, R.; Spacek, V.

2012-01-01

It is possible to assess viscoelastic properties of materials by means of the stress relaxation test. This method records the decrease in pressing power in a tablet at its constant height. The cited method was used to evaluate the time-dependent deformation for six various materials: microcrystalline cellulose, cellulose powder, hydroxypropyl methylcellulose, mannitol, lactose monohydrate, and hydrogen phosphate monohydrate. The decrease in pressing powering of a tablet during a 180 s period was described mathematically by the parameters of three exponential equations, where the whole course of the stress relaxation is divided into three individual processes (instant elastic deformation, retarded elastic deformation and permanent plastic deformation). Three values of the moduli of plasticity and elasticity were calculated for each compound. The values of elastic parameters ATi have a strong relationship with bulk density. The plastic parameters PTi represent particle tendency to form bonds. The values of plasticity in the third process PT3 ranged from 400 to 600 MPas. Mannitol had higher plasticity and lactose monohydrate on the contrary reduced plasticity. A linear relation exists between AT3 and PT3 for the third process. No similar interpretation of moduli calculated on the basis of three exponential equations has been realized yet. PMID:24850972

Deformation field heterogeneity in punch indentation

PubMed Central

Murthy, Tejas G.; Saldana, Christopher; Hudspeth, Matthew; M'Saoubi, Rachid

2014-01-01

Plastic heterogeneity in indentation is fundamental for understanding mechanics of hardness testing and impression-based deformation processing methods. The heterogeneous deformation underlying plane-strain indentation was investigated in plastic loading of copper by a flat punch. Deformation parameters were measured, in situ, by tracking the motion of asperities in high-speed optical imaging. These measurements were coupled with multi-scale analyses of strength, microstructure and crystallographic texture in the vicinity of the indentation. Self-consistency is demonstrated in description of the deformation field using the in situ mechanics-based measurements and post-mortem materials characterization. Salient features of the punch indentation process elucidated include, among others, the presence of a dead-metal zone underneath the indenter, regions of intense strain rate (e.g. slip lines) and extent of the plastic flow field. Perhaps more intriguing are the transitions between shear-type and compression-type deformation modes over the indentation region that were quantified by the high-resolution crystallographic texture measurements. The evolution of the field concomitant to the progress of indentation is discussed and primary differences between the mechanics of indentation for a rigid perfectly plastic material and a strain-hardening material are described. PMID:24910521

Numerical Study of the Plasticity-Induced Stabilization Effect on Martensitic Transformations in Shape Memory Alloys

NASA Astrophysics Data System (ADS)

Junker, Philipp; Hempel, Philipp

2017-12-01

It is well known that plastic deformations in shape memory alloys stabilize the martensitic phase. Furthermore, the knowledge concerning the plastic state is crucial for a reliable sustainability analysis of construction parts. Numerical simulations serve as a tool for the realistic investigation of the complex interactions between phase transformations and plastic deformations. To account also for irreversible deformations, we expand an energy-based material model by including a non-linear isotropic hardening plasticity model. An implementation of this material model into commercial finite element programs, e.g., Abaqus, offers the opportunity to analyze entire structural components at low costs and fast computation times. Along with the theoretical derivation and expansion of the model, several simulation results for various boundary value problems are presented and interpreted for improved construction designing.

Finite element analysis of large transient elastic-plastic deformations of simple structures, with application to the engine rotor fragment containment/deflection problem

NASA Technical Reports Server (NTRS)

Wu, R. W.; Witmer, E. A.

1972-01-01

Assumed-displacement versions of the finite-element method are developed to predict large-deformation elastic-plastic transient deformations of structures. Both the conventional and a new improved finite-element variational formulation are derived. These formulations are then developed in detail for straight-beam and curved-beam elements undergoing (1) Bernoulli-Euler-Kirchhoff or (2) Timoshenko deformation behavior, in one plane. For each of these categories, several types of assumed-displacement finite elements are developed, and transient response predictions are compared with available exact solutions for small-deflection, linear-elastic transient responses. The present finite-element predictions for large-deflection elastic-plastic transient responses are evaluated via several beam and ring examples for which experimental measurements of transient strains and large transient deformations and independent finite-difference predictions are available.

Analysis and Modeling of Process of Residual Deformations Accumulation in Soils and Granular Materials

NASA Astrophysics Data System (ADS)

Aleksandrov, A. S.; Dolgih, G. V.; Kalinin, A. L.

2017-11-01

It is established that under the influence of repeated loads the process of plastic deformation in soils and discrete materials is hereditary. To perform the mathematical modeling of plastic deformation, the authors applied the integral equation by solution of which they manage to obtain the power and logarithmic dependencies connecting plastic deformation with the number of repeated loads, the parameters of the material and components of the stress tensor in the principal axes. It is shown that these dependences generalize a number of models proposed earlier in Russia and abroad. Based on the analysis of the experimental data obtained during material testing in the dynamic devices of triaxial compression at different values of the stress deviator, the coefficients in the proposed models of deformation are determined. The authors determined the application domain for logarithmic and degree dependences.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Binder, I.

TiC/Ni compositions with 10, 20, and 40 percent nickel were tested for transverse rupture strengths up to 1600 deg C. Transverse bend, cantilever beam, hot deformation, and hot extrusion experiments were performed in order to study the onset of plastic deformation. These materials were plastically deformed, and their microstructures were studied to learn about the mode of deiormation, plastic flow of the nickel binder, and alignment of the carbide grains. Other refractory hardmetal compositions, both single phase and cemented, were tested in transverse rupture up to 1600 deg C and were also subjected to various forms of hot deformation. Transversemore » strength peaks, versus temperature, were found for each material in the range 800 to 1500 deg C. Reasons for this behavior are developed. Microstructures of these materials were examined in connection with the strength tests and deformation studies. (auth)« less

Mechanical Behaviour of Light Metal Alloys at High Strain Rates. Computer Simulation on Mesoscale Levels

NASA Astrophysics Data System (ADS)

Skripnyak, Vladimir; Skripnyak, Evgeniya; Meyer, Lothar W.; Herzig, Norman; Skripnyak, Nataliya

2012-02-01

Researches of the last years have allowed to establish that the laws of deformation and fracture of bulk ultrafine-grained and coarse-grained materials are various both in static and in dynamic loading conditions. Development of adequate constitutive equations for the description of mechanical behavior of bulk ultrafine-grained materials at intensive dynamic influences is complicated in consequence of insufficient knowledge about general rules of inelastic deformation and nucleation and growth of cracks. Multi-scale computational model was used for the investigation of deformation and fracture of bulk structured aluminum and magnesium alloys under stress pulse loadings on mesoscale level. The increment of plastic deformation is defined by the sum of the increments caused by a nucleation and gliding of dislocations, the twinning, meso-blocks movement, and grain boundary sliding. The model takes into account the influence on mechanical properties of alloys an average grains size, grain sizes distribution of and concentration of precipitates. It was obtained the nucleation and gliding of dislocations caused the high attenuation rate of the elastic precursor of ultrafine-grained alloys than in coarse grained counterparts.

Effect of an aggressive medium on discontinuous deformation of aluminum-magnesium alloy AlMg6

NASA Astrophysics Data System (ADS)

Shibkov, A. A.; Denisov, A. A.; Zolotov, A. E.; Kochegarov, S. S.

2017-01-01

It is experimentally shown that the molecular (chemical) process of surface etching of deformed aluminum-magnesium alloy AlMg6 causes the development of a macroscopic plastic strain step with an amplitude of a few percent. Using numerical simulation of the polycrystalline solid etching process, it is shown that the corrosion front morphology varies during etching from Euclid (flat) to fractal (rough). The results obtained show the key role of the surface state on the development of macroscopic mechanical instability of a material exhibiting the Portevin-Le Chatelier effect.

Recovery of strain-hardening rate in Ni-Si alloys.

PubMed

Yang, C L; Zhang, Z J; Cai, T; Zhang, P; Zhang, Z F

2015-10-21

In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major reason for this RSHR. By taking into account other metals that also exhibit RSHR during tension, a more general mechanism for the RSHR was proposed, i.e. the occurrence of a sharp decrease of dislocation mean free path (Λ) during plastic deformation, caused by either planar defects or linear defects.

Recovery of strain-hardening rate in Ni-Si alloys

PubMed Central

Yang, C. L.; Zhang, Z. J.; Cai, T.; Zhang, P.; Zhang, Z. F.

2015-01-01

In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major reason for this RSHR. By taking into account other metals that also exhibit RSHR during tension, a more general mechanism for the RSHR was proposed, i.e. the occurrence of a sharp decrease of dislocation mean free path (Λ) during plastic deformation, caused by either planar defects or linear defects. PMID:26487419

Recovery of strain-hardening rate in Ni-Si alloys

NASA Astrophysics Data System (ADS)

Yang, C. L.; Zhang, Z. J.; Cai, T.; Zhang, P.; Zhang, Z. F.

2015-10-01

In this study, the recovery of strain-hardening rate (RSHR) was discovered for the first time in polycrystalline materials (Ni-Si alloys) that have only dislocation activities during tensile test. Detailed microstructure characterizations show that the activation of dislocations in the secondary slip systems during tensile deformation is the major reason for this RSHR. By taking into account other metals that also exhibit RSHR during tension, a more general mechanism for the RSHR was proposed, i.e. the occurrence of a sharp decrease of dislocation mean free path (Λ) during plastic deformation, caused by either planar defects or linear defects.

Atomistic simulations of deformation mechanisms in ultralight weight Mg-Li alloys

NASA Astrophysics Data System (ADS)

Karewar, Shivraj

Mg alloys have spurred a renewed academic and industrial interest because of their ultra-light-weight and high specific strength properties. Hexagonal close packed Mg has low deformability and a high plastic anisotropy between basal and non-basal slip systems at room temperature. Alloying with Li and other elements is believed to counter this deficiency by activating non-basal slip by reducing their nucleation stress. In this work I study how Li addition affects deformation mechanisms in Mg using atomistic simulations. In the first part, I create a reliable and transferable concentration dependent embedded atom method (CD-EAM) potential for my molecular dynamics study of deformation. This potential describes the Mg-Li phase diagram, which accurately describes the phase stability as a function of Li concentration and temperature. Also, it reproduces the heat of mixing, lattice parameters, and bulk moduli of the alloy as a function of Li concentration. Most importantly, our CD-EAM potential reproduces the variation of stacking fault energy for basal, prismatic, and pyramidal slip systems that in uences the deformation mechanisms as a function of Li concentration. This success of CD-EAM Mg-Li potential in reproducing different properties, as compared to literature data, shows its reliability and transferability. Next, I use this newly created potential to study the effect of Li addition on deformation mechanisms in Mg-Li nanocrystalline (NC) alloys. Mg-Li NC alloys show basal slip, pyramidal type-I slip, tension twinning, and two-compression twinning deformation modes. Li addition reduces the plastic anisotropy between basal and non-basal slip systems by modifying the energetics of Mg-Li alloys. This causes the solid solution softening. The inverse relationship between strength and ductility therefore suggests a concomitant increase in alloy ductility. A comparison of the NC results with single crystal deformation results helps to understand the qualitative and quantitative effect of Li addition in Mg on nucleation stress and fault energies of each deformation mode. The nucleation stress and fault energies of basal dislocations and compression twins in single crystal Mg-Li alloy increase while those for pyramidal dislocations and tension twinning decrease. This variation in respective values explains the reduction in plastic anisotropy and increase in ductility for Mg-Li alloys.

Deformation mechanisms to ameliorate the mechanical properties of novel TRIP/TWIP Co-Cr-Mo-(Cu) ultrafine eutectic alloys

PubMed Central

Kim, J. T.; Hong, S. H.; Park, H. J.; Kim, Y. S.; Suh, J. Y.; Lee, J. K.; Park, J. M.; Maity, T.; Eckert, J.; Kim, K. B.

2017-01-01

In the present study, the microstructural evolution and the modulation of the mechanical properties have been investigated for a Co-Cr-Mo (CCM) ternary eutectic alloy by addition of a small amount of copper (0.5 and 1 at.%). The microstructural observations reveal a distinct dissimilarity in the eutectic structure such as a broken lamellar structure and a well-aligned lamellar structure and an increasing volume fraction of Co lamellae as increasing amount of copper addition. This microstructural evolution leads to improved plasticity from 1% to 10% without the typical tradeoff between the overall strength and compressive plasticity. Moreover, investigation of the fractured samples indicates that the CCMCu alloy exhibits higher plastic deformability and combinatorial mechanisms for improved plastic behavior. The improved plasticity of CCMCu alloys originates from several deformation mechanisms; i) slip, ii) deformation twinning, iii) strain-induced transformation and iv) shear banding. These results reveal that the mechanical properties of eutectic alloys in the Co-Cr-Mo system can be ameliorated by micro-alloying such as Cu addition. PMID:28067248

Simulating Thermal Cycling and Isothermal Deformation Response of Polycrystalline NiTi

NASA Technical Reports Server (NTRS)

Manchiraju, Sivom; Gaydosh, Darrell J.; Noebe, Ronald D.; Anderson, Peter M.

2011-01-01

A microstructure-based FEM model that couples crystal plasticity, crystallographic descriptions of the B2-B19' martensitic phase transformation, and anisotropic elasticity is used to simulate thermal cycling and isothermal deformation in polycrystalline NiTi (49.9at% Ni). The model inputs include anisotropic elastic properties, polycrystalline texture, DSC data, and a subset of isothermal deformation and load-biased thermal cycling data. A key experimental trend is captured.namely, the transformation strain during thermal cycling is predicted to reach a peak with increasing bias stress, due to the onset of plasticity at larger bias stress. Plasticity induces internal stress that affects both thermal cycling and isothermal deformation responses. Affected thermal cycling features include hysteretic width, two-way shape memory effect, and evolution of texture with increasing bias stress. Affected isothermal deformation features include increased hardening during loading and retained martensite after unloading. These trends are not captured by microstructural models that lack plasticity, nor are they all captured in a robust manner by phenomenological approaches. Despite this advance in microstructural modeling, quantitative differences exist, such as underprediction of open loop strain during thermal cycling.

Effect of small perturbations on the evolution of polycrystalline structure during plastic deformation

NASA Astrophysics Data System (ADS)

Korznikova, E. A.; Baimova, Yu. A.; Kistanov, A. A.; Dmitriev, S. V.; Korznikov, A. V.

2014-09-01

The method of molecular dynamics has been used to study the influence of initial perturbations on the evolution of grain boundaries during the shear plastic deformation of a two-dimensional polycrystalline material with nanoscale grains. It has been shown that short-term thermalization-induced small perturbations result in noticeable differences in grain boundaries configurations at the deformation of 0.05 and the polycrystal completely loses its initial grain boundary structure at the deformation of 0.4.

Modeling the Hot Ductility of AA6061 Aluminum Alloy After Severe Plastic Deformation

NASA Astrophysics Data System (ADS)

Khamei, A. A.; Dehghani, K.; Mahmudi, R.

2015-05-01

Solutionized AA6061 aluminum alloy was processed by equal-channel angular pressing followed by cold rolling. The hot ductility of the material was studied after severe plastic deformation. The hot tensile tests were carried out in the temperature range of 300-500°C and at the strain rates of 0.0005-0.01 s-1. Depending on the temperature and strain rate, the applied strain level exhibited significant effects on the hot ductility, strain-rate sensitivity, and activation energy. It can be suggested that the possible mechanism dominated the hot deformation during tensile testing is dynamic recovery and dislocation creep. Constitutive equations were developed to model the hot ductility of the severe plastic deformed AA6061 alloy.

Method for measuring residual stresses in materials by plastically deforming the material and interference pattern comparison

DOEpatents

Pechersky, Martin J.

1995-01-01

A method for measuring residual stress in a material comprising the steps of establishing a speckle pattern on the surface with a first laser then heating a portion of that pattern with an infrared laser until the surface plastically deforms. Comparing the speckle patterns before and after deformation by subtracting one pattern from the other will produce a fringe pattern that serves as a visual and quantitative indication of the degree to which the plasticized surface responded to the stress dung heating and enables calculation of the stress.

Atomic simulations of deformation mechanisms of crystalline Mg/amorphous Mg-Al nanocomposites

NASA Astrophysics Data System (ADS)

Song, H. Y.; Li, Y. L.

2015-09-01

The effects of amorphous boundary (AB) spacing on the deformation behavior of crystalline/amorphous (C/A) Mg/Mgsbnd Al nanocomposites under tensile load are investigated using molecular dynamics method. The results show that the plasticity of nano-polycrystal Mg can be enhanced with the introduction of C/A interfaces. For samples 5.2 nm in AB spacing and larger, the superior tensile ductility and nearly perfect plastic flow behavior occur during plastic deformation. The studies indicate that the cooperative interactions between crystalline and amorphous are the main reason for excellent ductility enhancements in C/A Mg/Mgsbnd Al nanocomposites.

Detection of structural changes and mechanical properties of light alloys after severe plastic deformation

NASA Astrophysics Data System (ADS)

Krasnoveikin, V. A.; Kozulin, A. A.; Skripnyak, V. A.

2017-11-01

Severe plastic deformation by equal channel angular pressing has been performed to produce light aluminum and magnesium alloy billets with ultrafine-grained structure. The physical and mechanical properties of the processed alloys are examined by studying their microstructure, measuring microhardness, yield strength, and uniaxial tensile strength. A nondestructive testing technique using three-dimensional X-ray tomography is proposed for detecting internal structural defects and monitoring damage formation in the structure of alloys subjected to severe plastic deformation. The investigation results prove the efficiency of the chosen method and selected mode of producing ultrafine-grained light alloys.

The hidden life of pyrite: how low can it go?

NASA Astrophysics Data System (ADS)

Boyle, Alan; Barrie, Craig; Salter, Michael

2010-05-01

Pyrite is the most abundant sulphide mineral in the Earth's crust, being present in most rock units but only volumetrically important in sulphide ore deposits. Thus, rheological behaviour of pyrite does not have significant implications for crustal deformation as a whole, but it does for deformation of ore deposits. Therefore, understanding pyrite behaviour in ore deposits may help understanding of deformation in rocks where it is of low abundance. Pyrite is a difficult mineral to study because it is both opaque and cubic, two properties that hide most of its microstructure when studied using optical microscopy as well as standard SEM back-scattered electron imaging. Etching can reveal some of the internal secrets of pyrite, but the technique is not universally applicable. The generally accepted view from such studies, coupled with experimental deformation and some TEM studies, is that pyrite is a robust mineral, which, under typical geological strain-rates, deforms by plastic deformation mechanisms above ~425 °C and by brittle or pressure-solution diffusive mechanisms below. Over the last decade or so, the advent of reliable and fast SEM-based electron backscattered diffraction (EBSD) systems, coupled with orientation contrast (OC) imaging techniques, has revolutionised study of microstructure in cubic minerals. Plastic deformation can now be readily identified in pyrite; it is no longer hidden. Freitag et al (2004) documented relatively low temperature (~350 °C) plastic deformation of pyrite from Green's Creek, Alaska, raising the possibility that pyrite deforms plastically at lower temperatures than is generally accepted. In this presentation we describe pyrite microstructures from a series of pyrite-rich polymetallic ore deposits (Parys Mountain, Anglesey; Løkken, Norway; Baia Borsa, Romania), deformed at low temperature metamorphic conditions (~200-420 °C). Our results (Barrie et al. 2009) indicate that pyrite grains in all of the ore deposits studied preserve internal lattice ‘distortion' or ‘bending' indicating plastic deformation mechanisms operated. Many pyrite grains in the ore deposits also contain low-angle (~2°) sub-grain boundaries or ‘dislocation walls', indicating that both dislocation glide and creep deformation mechanisms have operated within the pyrite grains. These results indicate that plastic deformation of pyrite, under geological strain-rates, can go down to as low as ~200 °C suggesting the brittle-ductile transition in pyrite occurs at temperatures potentially as low as ~200 °C; much lower than the generally accepted temperature of ~425 °C. Many pyrite grains in sulphide ore deposits preserve internal chemical zonation of trace elements (e.g. Large et al. 2009). The potential relationship between plastic deformation and trace element distribution in pyrite will be discussed. Barrie, C. D., Boyle, A. P. & Salter, M., 2009. How low can you go? - Extending downwards the limits of plastic deformation in pyrite. Mineralogical Magazine, 73(6), 895-913. Freitag, K., Boyle, A. P., Nelson, E., Hitzman, M., Churchill, J. & Lopez-Pedrosa, M., 2004. The use of electron backscatter diffraction and orientation contrast imaging as tools for sulphide textural studies: example from the Greens Creek deposit (Alaska). Mineralium Deposita, 39, 103-113. Large, R. R., Danyushevsky, L., Hollit, C., Maslennikov, V., Meffre, S., Gilbert, S., Bull, S., Scott, R., Emsbo, P., Thomas, H., Singh, B. & Foster, J., 2009. Gold and Trace Element Zonation in Pyrite Using a Laser Imaging Technique: Implications for the Timing of Gold in Orogenic and Carlin-Style Sediment-Hosted Deposits. Economic Geology, 104(5), 635-668.

Crystal plasticity in Cu damascene interconnect lines undergoing electromigration as revealed by synchrotron x-ray microdiffraction

NASA Astrophysics Data System (ADS)

Budiman, A. S.; Nix, W. D.; Tamura, N.; Valek, B. C.; Gadre, K.; Maiz, J.; Spolenak, R.; Patel, J. R.

2006-06-01

Plastic deformation was observed in damascene Cu interconnect test structures during an in situ electromigration experiment and before the onset of visible microstructural damage (voiding, hillock formation). We show here, using a synchrotron technique of white beam x-ray microdiffraction, that the extent of this electromigration-induced plasticity is dependent on the linewidth. In wide lines, plastic deformation manifests itself as grain bending and the formation of subgrain structures, while only grain rotation is observed in the narrower lines. The deformation geometry leads us to conclude that dislocations introduced by plastic flow lie predominantly in the direction of electron flow and may provide additional easy paths for the transport of point defects. Since these findings occur long before any observable voids or hillocks are formed, they may have direct bearing on the final failure stages of electromigration.

[Material found on the cleaned diamond turbine drilling heads after injury cases].

PubMed

Dielert, E

1979-06-01

Grinding of the hard tissues of the teeth with diamond points and airotor led to bullet-like flying off of part of the instrument. The causes were investigated: Unsatisfactory fixation in the turbine head, deficient material in the rotating instrument, unnecessary notches in the shaft resulting in reduction of diameter, and finally the so far uncorrected radial vibration of the rotating instrument. All of these causes may result in plastic deformation or breakage of the points.

Reasons for service failure of an ÉKG-20 power shovel bogie wheel

NASA Astrophysics Data System (ADS)

Yakovleva, S. P.; Milokhin, S. E.

1985-10-01

Early failure of a bogie wheel is caused by the occurrence after heat treatment of a working surface structure with insufficient resistance to plastic deformation, which under the specific conditions of contact loading causes flattening of it with the formation of accumulations of material on the side surfaces. This leads to the occurrence of significant stresses on the faces of the wheel which intensify the nonuniformity of the structure obtained after machining of the side surface.

Equilibrium stability of a cylindrical body subject to the internal structure of the material and inelastic behaviour of the completely compressed matrix

NASA Astrophysics Data System (ADS)

Gotsev, D. V.; Perunov, N. S.; Sviridova, E. N.

2018-03-01

The mathematical model describing the stress-strain state of a cylindrical body under the uniform radial compression effect is constructed. The model of the material is the porous medium model. The compressed skeleton of the porous medium possesses hardening elastic-plastic properties. Deforming of the porous medium under the specified compressive loads is divided into two stages: elastic deforming of the porous medium and further elastic-plastic deforming of the material with completely compressed matrix. The analytical relations that define the fields of stress and displacement at each stage of the deforming are obtained. The influence of the porosity and other physical, mechanical and geometric parameters of the construction on the size of the plastic zone is evaluated. The question of the ground state equilibrium instability is investigated within the framework of the three-dimensional linearized relationships of the stability theory of deformed bodies.

Behavior of lateral-deformation coefficients during elastoplastic deformation of metals

NASA Astrophysics Data System (ADS)

Zimin, B. A.; Smirnov, I. V.; Sudenkov, Yu. V.

2017-06-01

The results of investigations into variation of the coefficients of lateral deformation (the Poisson ratio) during single-axis tension of samples of steel 12Kh18N10T and St3, titanium VT1, the aluminum alloy D16AM, copper M1, and a magnesium alloy are considered. The technique developed on the basis of the optoacoustic effect and simultaneous measurements of the longitudinal and surface speeds of sound in metallic samples during the tension makes it possible to measure the rates at various stages of the deformation process. The data obtained make it possible to construct the dependences of variation of the lateral-deformation coefficients at all stages of the plastic flow. The correlation of these variations both with known processes of structural reconstructions at various stages of plastic flow and with the process of localization of plastic-shear bands in the aluminum alloy is noted.

Structure and mechanical properties of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation by high-pressure torsion

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-04-01

The structural and phase transformations have been studied in aging commercial aluminum-lithium alloy Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg in the as-delivered state and after severe plastic deformation by torsion for 1, 5 and 10 revolutions under a high pressure of 4 GPa. Deformation-induced nanofragmentation and dynamic recrystallization have been found to occur in the alloy. The degree of recrystallization increases with deformation. Nanofragmentation and recrystallization processes are accompanied by the deformation-induced decomposition of solid solution and changes in both the nucleation mechanism of precipitation and the phase composition of the alloy. The influence of a nanostructured nanophase state of the alloy on its mechanical properties (microhardness, plasticity, elastic modulus, and stiffness) is discussed.

Effect of initial grain size on inhomogeneous plastic deformation and twinning behavior in high manganese austenitic steel with a polycrystalline microstructure

NASA Astrophysics Data System (ADS)

Ueji, R.; Tsuchida, N.; Harada, K.; Takaki, K.; Fujii, H.

2015-08-01

The grain size effect on the deformation twinning in a high manganese austenitic steel which is so-called TWIP (twining induced plastic deformation) steel was studied in order to understand how to control deformation twinning. The 31wt%Mn-3%Al-3% Si steel was cold rolled and annealed at various temperatures to obtain fully recrystallized structures with different mean grain sizes. These annealed sheets were examined by room temperature tensile tests at a strain rate of 10-4/s. The coarse grained sample (grain size: 49.6μm) showed many deformation twins and the deformation twinning was preferentially found in the grains in which the tensile axis is parallel near to [111]. On the other hand, the sample with finer grains (1.8 μm) had few grains with twinning even after the tensile deformation. The electron back scattering diffraction (EB SD) measurements clarified the relationship between the anisotropy of deformation twinning and that of inhomogeneous plastic deformation. Based on the EBSD analysis, the mechanism of the suppression of deformation twinning by grain refinement was discussed with the concept of the slip pattern competition between the slip system governed by a grain boundary and that activated by the macroscopic load.

Dynamic strength properties of the surface of an ultra-fine-grained aluminum alloy under conditions of high-speed erosion

NASA Astrophysics Data System (ADS)

Kazarinov, N. A.; Evstifeev, A. D.; Petrov, Yu. V.; Lashkov, V. A.

2016-05-01

The influence of severe plastic deformation on the material surface is investigated under highspeed erosion conditions. The AD1 aluminum alloy was tested with the structure changed by severe plastic torsional deformation.

Numerical study of impact erosion of multiple solid particle

NASA Astrophysics Data System (ADS)

Zheng, Chao; Liu, Yonghong; Chen, Cheng; Qin, Jie; Ji, Renjie; Cai, Baoping

2017-11-01

Material erosion caused by continuous particle impingement during hydraulic fracturing results in significant economic loss and increased production risks. The erosion process is complex and has not been clearly explained through physical experiments. To address this problem, a multiple particle model in a 3D configuration was proposed to investigate the dynamic erosion process. This approach can significantly reduce experiment costs. The numerical model considered material damping and elastic-plastic material behavior of target material. The effects of impact parameters on erosion characteristics, such as plastic deformation, contact time, and energy loss rate, were investigated. Based on comprehensive studies, the dynamic erosion mechanism and geometry evolution of eroded crater was obtained. These findings can provide a detailed erosion process of target material and insights into the material erosion caused by multiple particle impingement.

An experimental investigation of energy absorption in TRIP steel under impact three-point bending deformation

NASA Astrophysics Data System (ADS)

Pham, Hang; Iwamoto, Takeshi

2015-09-01

TRIP (Transformation-induced Plasticity) steel is nowadays in widespread use in the automobile industry because of their favorable mechanical properties such as high strength, excellent formability and toughness because of strain-induced martensitic transformation. Moreover, when TRIP steel is applied to the components of the vehicles, it is expected that huge amount of kinetic energy will be absorbed into both plastic deformation and martensitic transformation during the collision. Basically, bending deformation due to buckling is one of the major crash deformation modes of automobile structures. Thus, an investigation of energy absorption during bending deformation at high impact velocity for TRIP steel is indispensable. Although TRIP steel have particularly attracted the recent interest of the scientific community, just few studies can be found on the energy absorption characteristic of TRIP steel, especially at impact loading condition. In present study, experimental investigations of bending deformation behaviors of TRIP steel are conducted in the three-point bending tests for both smooth and pre-cracked specimen. Then, energy absorption characteristic during plastic deformation and fracture process at high impact velocity in TRIP steel will be discussed.

DEFORMATION PROCESSES IN MATERIALS. Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Washburn, J.; Parker, E.R.; Tinder, R.F.

1962-08-01

It was found that irreversible plastic deformation occurs in polycrystaliine specimens of zinc, copper and its dilute alloys, and aluminum at room temperature, beginning at stresses indetectably above zero applied stress. Neither Frank-Read source generation nor simple bowing of dislocations between fixed nodes can explain the irreversible plastic behavior observed at small stresses in the metals studied. More extensive rearrangements of the dislocation substructure that probably involve glide of nodes and formation of new nodes seem to be required. Prestrained specimens of copper and its dilute alloys often exhibited bursts of plastic deformation which could possibly be due to cooperativemore » rearrangement of the dislocation substructure in one or a few grains. The introduction, by particle bombardment, of new lengths of dislocations into the gage section surface of specimens of copper and its dilute alloys produced extensive irreversible plastic flow beginning at stresses indetectably above zero applied stress. The effect of prestraln on the shape of the loading and unloading curves for zinc shows that dislocation rearrangements that cause forward and reverse strain can occur simultaneously. The net strain rate can be the algebraic sum of the strain recovery rate and the forward creep rate. The present quantitative theories of the Peierls-Nabarro stress are insufficient to permit an estimate of its magnitude from the results of this investigation. In dilute copper alloys containing up to 0.1 at.% impurity, there were many dislocations in the grown-in networks that were not locked by segregation of the foreign atoms. The study of creep behavior over a range of temperatures and at the same strain sensitivity used in these experiments combined with dislocation etch pit observations of dislocation substructure appears to be a particularly fruitful field for further investigation. (auth)« less

Room temperature deformation mechanisms of alumina particles observed from in situ micro-compression and atomistic simulations.

DOE PAGES

Sarobol, Pylin; Chandross, Michael E.; Carroll, Jay D.; ...

2015-09-22

Aerosol deposition (AD) is a solid-state deposition technology that has been developed to fabricate ceramic coatings nominally at room temperature. Sub-micron ceramic particles accelerated by pressurized gas impact, deform, and consolidate on substrates under vacuum. Ceramic particle consolidation in AD coatings is highly dependent on particle deformation and bonding; these behaviors are not well understood. In this work, atomistic simulations and in situ micro-compressions in the scanning electron microscope, and the transmission electron microscope (TEM) were utilized to investigate fundamental mechanisms responsible for plastic deformation/fracture of particles under applied compression. Results showed that highly defective micron-sized alumina particles, initially containingmore » numerous dislocations or a grain boundary, exhibited no observable shape change before fracture/fragmentation. Simulations and experimental results indicated that particles containing a grain boundary only accommodate low strain energy per unit volume before crack nucleation and propagation. In contrast, nearly defect-free, sub-micron, single crystal alumina particles exhibited plastic deformation and fracture without fragmentation. Dislocation nucleation/motion, significant plastic deformation, and shape change were observed. Simulation and TEM in situ micro-compression results indicated that nearly defect-free particles accommodate high strain energy per unit volume associated with dislocation plasticity before fracture. As a result, the identified deformation mechanisms provide insight into feedstock design for AD.« less

Effects of solutes on dislocation nucleation from grain boundaries

DOE PAGES

Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.

2016-12-27

When grain sizes are reduced to the nanoscale, grain boundaries (GB) become the dominant sources of the dislocations that enable plastic deformation. Here, we present the first molecular dynamics (MD) study of the effect of substitutional solutes on the dislocation nucleation process from GBs during uniaxial tensile deformation. A simple bi-crystal geometry is utilized in which the nucleation and propagation of dislocations away from a GB is the only active mechanism of plastic deformation. Solutes with atomic radii both larger and smaller than the solvent atomic radius were considered. Although the segregation sites are different for the two cases, bothmore » produce increases in the stress required to nucleate a dislocation. MD simulations at room temperature revealed that this increase in the nucleation stress is associated with changes of the GB structure at the emission site caused by dislocation emission, leading to increases in the heats of segregation of the solute atoms, which cannot diffuse to lower-energy sites on the timescale of the nucleation event. These results contribute directly to understanding the strength of nanocrystalline materials, and suggest suitable directions for nanocrystalline alloy design leading toward structural applications.« less

Field Performance of Recycled Plastic Foundation for Pipeline

PubMed Central

Kim, Seongkyum; Lee, Kwanho

2015-01-01

The incidence of failure of embedded pipelines has increased in Korea due to the increasing applied load and the improper compaction of bedding and backfill materials. To overcome these problems, a prefabricated lightweight plastic foundation using recycled plastic was developed for sewer pipelines. A small scale laboratory chamber test and two field tests were conducted to verify its construction workability and performance. From the small scale laboratory chamber test, the applied loads at 2.5% and 5.0% of deformation were 3.45 kgf/cm2 and 5.85 kgf/cm2 for Case S1, and 4.42 kgf/cm2 and 6.43 kgf/cm2 for Case S2, respectively. From the first field test, the vertical deformation of the recycled plastic foundation (Case A2) was very small. According to the analysis based on the PE pipe deformation at the connection (CN) and at the center (CT), the pipe deformation at each part for Case A1 was larger than that for Case A2, which adopted the recycled lightweight plastic foundation. From the second field test, the measured maximum settlements of Case B1 and Case B2 were 1.05 cm and 0.54 cm, respectively. The use of a plastic foundation can reduce the settlement of an embedded pipeline and be an alternative construction method.

Study on sand particles creep model and open pit mine landslide mechanism caused by sand fatigue liquefaction

NASA Astrophysics Data System (ADS)

Du, Dong-Ning; Wang, Lai-Gui; Zhang, Xiang-Dong; Zhang, Shu-Kun

2017-06-01

The sand particles in the sand - rock composite slope of the open pit mine occurs creep deformation and fatigue liquefaction under the action of vehicle load vibration and hydraulic gradient, which causes landslide geological disasters and it destroys the surface environment. To reveal the mechanism, a mechanics model based on the model considering the soil structural change with a new “plastic hinge” element is developed, to improve its constitutive and creep curve equations. Data from sand creep experiments are used to identify the parameters in the model and to validate the model. The results show that the mechanical model can describe the rotation progress between the sand particles, disclose the negative acceleration creep deformation stage during the third phase, and require fewer parameters while maintaining accuracy. It provides a new creep model considering rotation to analyze sand creep mechanism, which provides a theoretical basis for revealing the open pit mine landslide mechanism induced by creep deformation and fatigue liquefaction of sandy soil.

Atomistic simulation on the plastic deformation and fracture of bio-inspired graphene/Ni nanocomposites

NASA Astrophysics Data System (ADS)

Yang, Zhenyu; Wang, Dandan; Lu, Zixing; Hu, Wenjun

2016-11-01

Molecular dynamics simulations were performed to investigate the plastic deformation and fracture behaviors of bio-inspired graphene/metal nanocomposites, which have a "brick-and-mortar" nanostructure, consisting of hard graphene single-layers embedded in a soft Ni matrix. The plastic deformation mechanisms of the nanocomposites were analyzed as well as their effects on the mechanical properties with various geometrical variations. It was found that the strength and ductility of the metal matrix can be highly enhanced with the addition of the staggered graphene layers, and the plastic deformation can be attributed to the interfacial sliding, dislocation nucleation, and cracks' combination. The strength of the nanocomposites strongly depends on the length scale of the nanostructure and the interlayer distance as well. In addition, slip at the interface releases the stress in graphene layers, leading to the stress distribution on the graphene more uniform. The present results are expected to contribute to the design of the nanolayered graphene/metal composites with high performance.

Ultrasound Velocity Measurements in High-Chromium Steel Under Plastic Deformation

NASA Astrophysics Data System (ADS)

Lunev, Aleksey; Bochkareva, Anna; Barannikova, Svetlana; Zuev, Lev

2016-04-01

In the present study, the variation of the propagation velocity of ultrasound in the plastic deformation of corrosion-resistant high-chromium steel 40X13 with ferrite-carbide (delivery status), martensitic (quenched) and sorbitol (after high-temperature tempering) structures have beem studied/ It is found that each state shows its view of the loading curve. In the delivery state diagram loading is substantially parabolic throughout, while in the martensitic state contains only linear strain hardening step and in the sorbitol state the plastic flow curve is three-step. The velocity of ultrasonic surface waves (Rayleigh waves) was measured simultaneously with the registration of the loading curve in the investigated steel in tension. It is shown that the dependence of the velocity of ultrasound in active loading is determined by the law of plastic flow, that is, the staging of the corresponding diagram of loading. Structural state of the investigated steel is not only changing the type of the deformation curve under uniaxial tension, but also changes the nature of ultrasound speed of deformation.

High-Oriented Thermoelectric Nano-Bulk Fabricated from Thermoelectric Ink

NASA Astrophysics Data System (ADS)

Koyano, M.; Mizutani, S.; Hayashi, Y.; Nishino, S.; Miyata, M.; Tanaka, T.; Fukuda, K.

2017-05-01

Printing technology is expected to provide innovative and environmentally friendly processes for thermoelectric (TE) module fabrication. As described in this paper, we propose an orientation control process using plastic deformation at high temperatures and present high-oriented TE nano-bulks fabricated from bismuth telluride (Bi-Te) TE inks using this process. In the case of n-type Bi-Te, surface x-ray diffraction reveals that crystalline grains in the plastic-deformed nano-bulk demonstrate a c-plane orientation parallel to the pressed face. According to the high orientation, electrical resistivity ρ, thermal conductivity κ, and figure of merit ZT show anisotropic behavior. It is noteworthy that ( ZT)// almost reaches unity ( ZT)// ˜1 at 340 K, even at low temperatures of the plastic deformation process. In contrast, the ZT of plastic-deformed p-type nano-bulk indicates isotropic behavior. The difference in the process temperature dependence of ZT suggests that n-type and p-type nano-bulk orientation mechanisms mutually differ.

Structural Transformations in Metallic Materials During Plastic Deformation

NASA Astrophysics Data System (ADS)

Zasimchuk, E.; Turchak, T.; Baskova, A.; Chausov, N.; Hutsaylyuk, V.

2017-03-01

In this paper, the structure formation during the plastic deformation of polycrystalline nickel and aluminum based alloy 2024-T3 is investigated. The possibility of the relaxation and synergetic structure formation is examined. It is shown the deformation softening to be due to the crystallization of the amorphous structure of hydrodynamics flow channels (synergetic structure) HC as micrograins and their subsequent growth. The possible mechanism of micrograins' growth is proposed. The deformation processes change the phase composition of the multiphase alloy 2024-T3. It is shown by the quantitative analysis of the structures which were deformed in different regimes of the alloy samples. A method for increasing of the fatigue life through a dynamic pre-deformation is suggested.

Gradient Plasticity Model and its Implementation into MARMOT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barker, Erin I.; Li, Dongsheng; Zbib, Hussein M.

2013-08-01

The influence of strain gradient on deformation behavior of nuclear structural materials, such as boby centered cubic (bcc) iron alloys has been investigated. We have developed and implemented a dislocation based strain gradient crystal plasticity material model. A mesoscale crystal plasticity model for inelastic deformation of metallic material, bcc steel, has been developed and implemented numerically. Continuum Dislocation Dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals, as well as polycrystalline materials by coupling CDD and crystal plasticity (CP). The dislocation density evolution law in thismore » model is mechanism-based, with parameters measured from experiments or simulated with lower-length scale models, not an empirical law with parameters back-fitted from the flow curves.« less

The evolution of rifting process in the tectonic history of the Earth

NASA Technical Reports Server (NTRS)

Milanovsky, E. E.; Nikishin, A. M.

1985-01-01

The continental rifting is the response of the lithosphere to the oriented tension. The distribution of viscosity in the lithosphere plays an essential role during all stages of the rifting. The viscosity is a function of the temperature, the lithostatic pressure, the rock composition, the deformation rate and other factors. The temperature is the most important factor. The vertical section of continental lithosphere of the rift zone may be divided into the following layers: the upper crust, in which brittle deformation prevails; the medialcrust, in which the role of plastic deformation increases; the lower crust, in which plastic deformation prevails; and the uppermost plastic part of the mantle overlapping asthenosphere. The depth of the boundaries in the crust layers are mainly controlled by the temperature.

Deformation bands, the LEDS theory, and their importance in texture development: Part II. Theoretical conclusions

NASA Astrophysics Data System (ADS)

Kuhlmann-Wilsdorf, D.

1999-09-01

The facts regarding “regular” deformation bands (DBs) outlined in Part I of this series of articles are related to the low-energy dislocation structure (LEDS) theory of dislocation-based plasticity. They prompt an expansion of the theory by including the stresses due to strain gradients on account of changing selections of slip systems to the previously known dislocation driving forces. This last and until now neglected driving force is much smaller than the components considered hitherto, principally due to the applied stress and to mutual stress-screening among neighbor dislocations. As a result, it permits a near-proof of the LEDS hypothesis, to wit that among all structures which, in principle, are accessible to the dislocations, that one is realized which has the lowest free energy. Specifically, the temperature rises that would result from annihilating the largest DBs amount to only several millidegrees Centigrade, meaning that they, and by implication the entire dislocation structures, are close to thermodynamical equilibrium. This is in stark contrast to the assumption of the presently widespread self-organizing dislocation structures (SODS) modeling that plastic deformation occurs far from equilibrium and is subject to Prigogine’s thermodynamics of energy-flow-through systems. It also holds out promise for future rapid advances in the construction of constitutive equations, since the LEDS hypothesis is the principal basis of the LEDS theory of plastic deformation and follows directly from the second law of thermodynamics in conjunction with Newton’s third law. By contrast, all other known models of metal plasticity are in conflict with the LEDS hypothesis. In regard to texture modeling, the present analysis shows that Taylor’s criterion of minimum plastic work is incorrect and should be replaced by the criterion of minimum free energy in the stressed state. Last, the LEDS hypothesis is but a special case of the more general low-energy structure (LES) hypothesis, applying to plastic deformation independent of the deformation mechanism. It is thus seen that plastic deformation is one of nature’s means to generate order, as a byproduct of the entropy generation when mechanical work is largely converted into heat.

Plasticity of ductile metallic glasses: a self-organized critical state.

PubMed

Sun, B A; Yu, H B; Jiao, W; Bai, H Y; Zhao, D Q; Wang, W H

2010-07-16

We report a close correlation between the dynamic behavior of serrated flow and the plasticity in metallic glasses (MGs) and show that the plastic deformation of ductile MGs can evolve into a self-organized critical state characterized by the power-law distribution of shear avalanches. A stick-slip model considering the interaction of multiple shear bands is presented to reveal complex scale-free intermittent shear-band motions in ductile MGs and quantitatively reproduce the experimental observations. Our studies have implications for understanding the precise plastic deformation mechanism of MGs.

An investigation of the inelastic behaviour of trabecular bone during the press-fit implantation of a tibial component in total knee arthroplasty.

PubMed

Kelly, N; Cawley, D T; Shannon, F J; McGarry, J P

2013-11-01

The stress distribution and plastic deformation of peri-prosthetic trabecular bone during press-fit tibial component implantation in total knee arthroplasty is investigated using experimental and finite element techniques. It is revealed that the computed stress distribution, implantation force and plastic deformation in the trabecular bone is highly dependent on the plasticity formulation implemented. By incorporating pressure dependent yielding using a crushable foam plasticity formulation to simulate the trabecular bone during implantation, highly localised stress concentrations and plastic deformation are computed at the bone-implant interface. If the pressure dependent yield is neglected using a traditional von Mises plasticity formulation, a significantly different stress distribution and implantation force is computed in the peri-prosthetic trabecular bone. The results of the study highlight the importance of: (i) simulating the insertion process of press-fit stem implantation; (ii) implementing a pressure dependent plasticity formulation, such as the crushable foam plasticity formulation, for the trabecular bone; (iii) incorporating friction at the implant-bone interface during stem insertion. Simulation of the press-fit implantation process with an appropriate pressure dependent plasticity formulation should be implemented in the design and assessment of arthroplasty prostheses. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

Size effects in olivine control strength in low-temperature plasticity regime

NASA Astrophysics Data System (ADS)

Kumamoto, K. M.; Thom, C.; Wallis, D.; Hansen, L. N.; Armstrong, D. E. J.; Goldsby, D. L.; Warren, J. M.; Wilkinson, A. J.

2017-12-01

The strength of the lithospheric mantle during deformation by low-temperature plasticity controls a range of geological phenomena, including lithospheric-scale strain localization, the evolution of friction on deep seismogenic faults, and the flexure of tectonic plates. However, constraints on the strength of olivine in this deformation regime are difficult to obtain from conventional rock-deformation experiments, and previous results vary considerably. We demonstrate via nanoindentation that the strength of olivine in the low-temperature plasticity regime is dependent on the length-scale of the test, with experiments on smaller volumes of material exhibiting larger yield stresses. This "size effect" has previously been explained in engineering materials as a result of the role of strain gradients and associated geometrically necessary dislocations in modifying plastic behavior. The Hall-Petch effect, in which a material with a small grain size exhibits a higher strength than one with a large grain size, is thought to arise from the same mechanism. The presence of a size effect resolves discrepancies among previous experimental measurements of olivine, which were either conducted using indentation methods or were conducted on polycrystalline samples with small grain sizes. An analysis of different low-temperature plasticity flow laws extrapolated to room temperature reveals a power-law relationship between length-scale (grain size for polycrystalline deformation and contact radius for indentation tests) and yield strength. This suggests that data from samples with large inherent length scales best represent the plastic strength of the coarse-grained lithospheric mantle. Additionally, the plastic deformation of nanometer- to micrometer-sized asperities on fault surfaces may control the evolution of fault roughness due to their size-dependent strength.

Tensile elastic properties of 18:8 chromium-nickel steel as affected by plastic deformation

NASA Technical Reports Server (NTRS)

Mcadam, D J; Mebs, R W

1939-01-01

The relationship between stress and strain, and between stress and permanent set, for 18:8 alloy as affected by prior plastic deformation is discussed. Hysteresis and creep and their effects on the stress-strain and stress-set curves are also considered, as well as the influence of duration of the rest interval after cold work and the influence of plastic deformation on proof stresses, on the modulus of elasticity at zero stress, and on the curvature of the stress-strain line. A constant (c sub 1) is suggested to represent the variation of the modulus of elasticity with stress.

Strand Plasticity Governs Fatigue in Colloidal Gels

NASA Astrophysics Data System (ADS)

van Doorn, Jan Maarten; Verweij, Joanne E.; Sprakel, Joris; van der Gucht, Jasper

2018-05-01

The repeated loading of a solid leads to microstructural damage that ultimately results in catastrophic material failure. While posing a major threat to the stability of virtually all materials, the microscopic origins of fatigue, especially for soft solids, remain elusive. Here we explore fatigue in colloidal gels as prototypical inhomogeneous soft solids by combining experiments and computer simulations. Our results reveal how mechanical loading leads to irreversible strand stretching, which builds slack into the network that softens the solid at small strains and causes strain hardening at larger deformations. We thus find that microscopic plasticity governs fatigue at much larger scales. This gives rise to a new picture of fatigue in soft thermal solids and calls for new theoretical descriptions of soft gel mechanics in which local plasticity is taken into account.

Structural and mechanical modifications induced on Zr-based bulk metallic glass by laser shock peening

NASA Astrophysics Data System (ADS)

Zhu, Yunhu; Fu, Jie; Zheng, Chao; Ji, Zhong

2016-12-01

In this study, surface modification of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 (vit1) bulk metallic glass (BMG) has been studied in an effort to improve the mechanical properties by laser shock peening (LSP) treatment. The phase structure, mechanical properties, and microstructural evolution of the as-cast and LSP treated specimens were systematically investigated. It was found that the vit1 BMG still consisted of fully amorphous structure after LSP treatment. Measurements of the heat relaxation indicate that a large amount of free volume is introduced into vit1 BMG during LSP process. LSP treatment causes a decrease of hardness attributable to generation of free volume. The plastic deformation ability of vit1 BMG was investigated under three-point bending conditions. The results demonstrate that the plastic strain of LSP treated specimen is 1.83 times as large as that of the as-cast specimen. The effect of LSP technology on the hardness and plastic deformation ability of vit1 BMG is discussed on the basis of free volume theory. The high dense shear bands on the side surface, the increase of striations and critical shear displacement on the tensile fracture region, and more uniform dimples structure on the compressive fracture region also demonstrate that the plasticity of vit1 BMG can be enhanced by LSP.

Effect of tensile twins on the subsequent plastic deformation in rolled Mg-3Al-1Zn alloy

NASA Astrophysics Data System (ADS)

Yoon, Jonghun; Kim, Se-Jong; Lee, Youngseon

2013-12-01

The {101¯2} tensile twins influence plastic flow of magnesium alloys for the subsequent plastic deformation since it contributes to grain refinement and texture hardening between the twinned and untwined regions. This paper investigates the variation of plastic flow of the rolled Mg-3Al-1Zn alloy which is compressed with a small plastic strain at the room temperature to induce the twins in the initial specimen. Subsequent tension and compression along the rolling and transverse direction are conducted with the twin induced specimens in order to examine the effect of the initial tensile twins.

Ductilisation of tungsten (W): Tungsten laminated composites

DOE PAGES

Reiser, Jens; Garrison, Lauren M.; Greuner, Henri; ...

2017-08-02

Here we elucidate the mechanisms of plastic deformation and fracture of tungsten laminated composites. Furthermore our results suggest that the mechanical response of the laminates is governed by the plastic deformation of the tungsten plies. In most cases, the impact of the interlayer is of secondary importance.

Strength, corrosion resistance, and biocompatibility of ultrafine-grained Mg alloys after different modes of severe plastic deformation

NASA Astrophysics Data System (ADS)

Dobatkin, S. V.; Lukyanova, E. A.; Martynenko, N. S.; Anisimova, N. Yu; Kiselevskiy, M. V.; Gorshenkov, M. V.; Yurchenko, N. Yu; Raab, G. I.; Yusupov, V. S.; Birbilis, N.; Salishchev, G. A.; Estrin, Y. Z.

2017-05-01

The effect of severe plastic deformation on the structure, mechanical properties, corrosion resistance, and biocompatibility of the WE43 (Mg-Y-Nd-Zr) alloy earmarked for applications as bioresorbable material has been studied. The alloy was deformed by rotary swaging (RS), equal channel angular pressing (ECAP), and multiaxial deformation (MAD). The microstructure examination by transmission electron microscopy showed that all SPD modes lead to the formation of ultrafine-grained structure with a structural element size of 0.5-1 µm and the Mg12Nd phase particles 0.3 µm in size. The microstructure refinement by all three treatments resulted in strengthening of the alloy. ECAP and MAD also raised ductility to up to 12-17%, while RS increased the ultimate tensile strength to up to 415 MPa. The study of the corrosion properties showed that SPD does not affect the electrochemical corrosion of the alloy. Its biocompatibility in vitro was estimated after incubation of the samples with red blood cells (hemolysis study), white blood cells (cell viability assay), and mesenchymal stromal cells (cell proliferation analysis). The biodegradation rate in fetal bovine serum was also evaluated. ECAP and MAD were found to cause some deceleration of biodegradation by slowing down the gas formation in the biological fluid and, compared to MSC, to improve the biocompatibility of the WE43 alloy.

Correlating Single Crystal Structure, Nanomechanical, and Bulk Compaction Behavior of Febuxostat Polymorphs.

PubMed

Yadav, Jayprakash A; Khomane, Kailas S; Modi, Sameer R; Ugale, Bharat; Yadav, Ram Naresh; Nagaraja, C M; Kumar, Navin; Bansal, Arvind K

2017-03-06

Febuxostat exhibits unprecedented solid forms with a total of 40 polymorphs and pseudopolymorphs reported. Polymorphs differ in molecular arrangement and conformation, intermolecular interactions, and various physicochemical properties, including mechanical properties. Febuxostat Form Q (FXT Q) and Form H1 (FXT H1) were investigated for crystal structure, nanomechanical parameters, and bulk deformation behavior. FXT Q showed greater compressibility, densification, and plastic deformation as compared to FXT H1 at a given compaction pressure. Lower mechanical hardness of FXT Q (0.214 GPa) as compared to FXT H1 (0.310 GPa) was found to be consistent with greater compressibility and lower mean yield pressure (38 MPa) of FXT Q. Superior compaction behavior of FXT Q was attributed to the presence of active slip systems in crystals which offered greater plastic deformation. By virtue of greater compressibility and densification, FXT Q showed higher tabletability over FXT H1. Significant correlation was found with anticipation that the preferred orientation of molecular planes into a crystal lattice translated nanomechanical parameters to a bulk compaction process. Moreover, prediction of compactibility of materials based on true density or molecular packing should be carefully evaluated, as slip-planes may cause deviation in the structure-property relationship. This study supported how molecular level crystal structure confers a bridge between particle level nanomechanical parameters and bulk level deformation behavior.

Reprint of: Effects of cold deformation, electron irradiation and extrusion on deuterium desorption behavior in Zr-1%Nb alloy

NASA Astrophysics Data System (ADS)

Morozov, O.; Mats, O.; Mats, V.; Zhurba, V.; Khaimovich, P.

2018-01-01

The present article introduces the data of analysis of ranges of ion-implanted deuterium desorption from Zr-1% Nb alloy. The samples studied underwent plastic deformation, low temperature extrusion and electron irradiation. Plastic rolling of the samples at temperature ∼300 K resulted in plastic deformation with the degree of ε = 3.9 and the formation of nanostructural state with the average grain size of d = 61 nm. The high degree of defectiveness is shown in thermodesorption spectrum as an additional area of the deuterium desorption in the temperature ranges 650-850 K. The further processing of the sample (that had undergone plastic deformation by plastic rolling) with electron irradiation resulted in the reduction of the average grain size (58 nm) and an increase in borders concentration. As a result the amount of deuterium desorpted increased in the temperature ranges 650-900 K. In case of Zr-1% Nb samples deformed by extrusion the extension of desorption area is observed towards the temperature reduction down to 420 K. The formation of the phase state of deuterium solid solution in zirconium was not observed. The structural state behavior is a control factor in the process of deuterium thermodesorption spectrum structure formation with a fixed implanted deuterium dose (hydrogen diagnostics). It appears as additional temperature ranges of deuterium desorption depending on the type, character and defect content.

A Computational Study of Plastic Deformation in AISI 304 Induced by Surface Mechanical Attrition Treatment

NASA Astrophysics Data System (ADS)

Zhang, X. C.; Lu, J.; Shi, S. Q.

2010-05-01

As a technique of grain refinement process by plastic deformation, surface mechanical attrition treatment (SMAT) has been developed to be one of the most effective ways to optimize the mechanical properties of various materials including pure metals and alloys. SMAT can significantly reduce grain size into nanometer regime in the surface layer of bulk materials, providing tremendous opportunities for improving physical, chemical and mechanical properties of the materials. In this work, a computational modeling of the surface mechanical attrition treatment (SMAT) process is presented, in which Johnson-Cook plasticity model and the finite element method were employed to study the high strain rate, elastic-plastic dynamic process of ball impact on a metallic target. AISI 304 steel with low stacking fault energy was chosen as the target material. First, a random impact model was used to analyze the statistic characteristics of ball impact, and then the plastic deformation behavior and residual stress distribution in AISI 304 stainless steel during SMAT were studied. The simulation results show that the compressive residual stress and vertical deformation of the surface structures were directly affected by ball impact frequency, incident impact angle and ball diameter used in SMAT process.

Osteoporosis affects both post-yield microdamage accumulation and plasticity degradation in vertebra of ovariectomized rats

NASA Astrophysics Data System (ADS)

Li, Siwei; Niu, Guodong; Dong, Neil X.; Wang, Xiaodu; Liu, Zhongjun; Song, Chunli; Leng, Huijie

2017-04-01

Estrogen withdrawal in postmenopausal women increases bone loss and bone fragility in the vertebra. Bone loss with osteoporosis not only reduces bone mineral density (BMD), but actually alters bone quality, which can be comprehensively represented by bone post-yield behaviors. This study aimed to provide some information as to how osteoporosis induced by estrogen depletion could influence the evolution of post-yield microdamage accumulation and plastic deformation in vertebral bodies. This study also tried to reveal the part of the mechanisms of how estrogen deficiency-induced osteoporosis would increase the bone fracture risk. A rat bilateral ovariectomy (OVX) model was used to induce osteoporosis. Progressive cyclic compression loading was developed for vertebra testing to elucidate the post-yield behaviors. BMD, bone volume fraction, stiffness degradation, and plastic deformation evolution were compared among rats raised for 5 weeks (ovx5w and sham5w groups) and 35 weeks (ovx35w and sham35w groups) after sham surgery and OVX. The results showed that a higher bone loss in vertebral bodies corresponded to lower stiffness and higher plastic deformation. Thus, osteoporosis could increase the vertebral fracture risk probably through microdamage accumulation and plastic deforming degradation.

A study of microindentation hardness tests by mechanism-based strain gradient plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Y.; Xue, Z.; Gao, H.

2000-08-01

We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicron-length scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model.more » In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework. (c) 2000 Materials Research Society.« less

Static Buckling Model Tests and Elasto-plastic Finite Element Analysis of a Pile in Layers with Various Thicknesses

NASA Astrophysics Data System (ADS)

Okajima, Kenji; Imai, Junichi; Tanaka, Tadatsugu; Iida, Toshiaki

Damage to piles in the liquefied ground is frequently reported. Buckling by the excess vertical load could be one of the causes of the pile damage, as well as the lateral flow of the ground and the lateral load at the pile head. The buckling mechanism is described as a complicated interaction between the pile deformation by the vertical load and the earth pressure change cased by the pile deformation. In this study, series of static buckling model tests of a pile were carried out in dried sand ground with various thickness of the layer. Finite element analysis was applied to the test results to verify the effectiveness of the elasto-plastic finite element analysis combining the implicit-explicit mixed type dynamic relaxation method with the return mapping method to the pile buckling problems. The test results and the analysis indicated the possibility that the buckling load of a pile decreases greatly where the thickness of the layer increases.

Effect of high-temperature water and hydrogen on the fracture behavior of a low-alloy reactor pressure vessel steel

NASA Astrophysics Data System (ADS)

Roychowdhury, S.; Seifert, H.-P.; Spätig, P.; Que, Z.

2016-09-01

Structural integrity of reactor pressure vessels (RPV) is critical for safety and lifetime. Possible degradation of fracture resistance of RPV steel due to exposure to coolant and hydrogen is a concern. In this study tensile and elastic-plastic fracture mechanics (EPFM) tests in air (hydrogen pre-charged) and EFPM tests in hydrogenated/oxygenated high-temperature water (HTW) was done, using a low-alloy RPV steel. 2-5 wppm hydrogen caused embrittlement in air tensile tests at room temperature (25 °C) and at 288 °C, effects being more significant at 25 °C and in simulated weld coarse grain heat affected zone material. Embrittlement at 288 °C is strain rate dependent and is due to localized plastic deformation. Hydrogen pre-charging/HTW exposure did not deteriorate the fracture resistance at 288 °C in base metal, for investigated loading rate range. Clear change in fracture morphology and deformation structures was observed, similar to that after air tests with hydrogen.

Estimation of constitutive parameters for the Belridge Diatomite, South Belridge Diatomite Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fossum, A.F.; Fredrich, J.T.

1998-06-01

A cooperative national laboratory/industry research program was initiated in 1994 that improved understanding of the geomechanical processes causing well casing damage during oil production from weak, compactible formations. The program focused on the shallow diatomaceous oil reservoirs located in California`s San Joaquin Valley, and combined analyses of historical field data, experimental determination of rock mechanical behavior, and geomechanical simulation of the reservoir and overburden response to production and injection. Sandia National Laboratories` quasi-static, large-deformation structural mechanics finite element code JAS3D was used to perform the three-dimensional geomechanical simulations. One of the material models implemented in JAS3D to simulate the time-independentmore » inelastic (non-linear) deformation of geomaterials is a generalized version of the Sandler and Rubin cap plasticity model (Sandler and Rubin, 1979). This report documents the experimental rock mechanics data and material cap plasticity models that were derived to describe the Belridge Diatomite reservoir rock at the South Belridge Diatomite Field, Section 33.« less

Effect of severe plastic deformation on the structure and crystal-lattice distortions in the Ni3(Al, X) ( X = Ti, Nb) intermetallic compound

NASA Astrophysics Data System (ADS)

Kazantseva, N. V.; Pilyugin, V. P.; Danilov, S. E.; Kolosov, V. Yu.

2015-05-01

A systematic combined study of crystal lattice distortions caused by doping and by severe plastic deformation (SPD) of Ti- and Nb-doped Ni3Al intermetallic compound has been carried out using methods of X-ray diffraction, electron microscopy, and electrical-resistance measurements. The degree of imperfection of the alloys has been estimated based on the results obtained by all three methods. The degree of structural perfection of niobium-doped crystals was found to be higher than in the case of Ti doping. The character of stresses (tensile stresses after doping; and compressive stresses after SPD) in the crystal lattice has been established and their values have been calculated. A significant increase in the density of dislocations, point defects, and lattice curvature has been found after SPD. A nanocrystalline structure is formed in these alloys, but no complete disordering of the intermetallic phase is observed.

Mechanistic Models of Friction Stir Welding

NASA Technical Reports Server (NTRS)

Stewart, Michael B.

1998-01-01

Friction stir welding is a welding process developed at The Welding Institute (TWI) in England. The method uses very large strain plastic deformation of the material to join two pieces of metal together. The material is deformed using a tool which is forced between the two pieces which rotates causing a bond. Beyond this, very little is actually known although many people working in the field are willing to speculate on the detailed mechanisms involved. Some measurements made using sacrificial thermocouples at the weld joint indicate that the maximum temperature during the weld process is on the order of 370C - well below the melting temperature of the material. However, at this temperature, the material properties are highly temperature dependent, and the yield stress is approximately an order of magnitude less at this temperature than it is at room temperature. As expected, there are many interpretations of the physical mechanisms occurring during the weld process. Although there is very little published concerned with FSW, some of the anecdotal theories will be described. One describes the primary mechanism as frictional heating at the front of the tool caused by slip between the tool and the material. At elevated temperatures, the weld material becomes soft and deforms around the tool but not essentially altered by the tool rotation, similar to an extrusion. As the material meets again at the rear of the tool, the temperatures and pressures are sufficient to cause the material to bond. All other structures seen are secondary and unimportant. Another theory examined last summer at NASA's Marshall Space Flight Center (MSFC) was that there was no slip between the tool and the material resulting in a rotating mass of plastic weld material traveling at a variety of angular velocities - the greatest at the tool surface diminishing to zero at the outer edge of the plastic mass surrounding the tool. This conceptual model was followed by simplified calculations which showed that the balance of moments through the weld plug was not possible under steady state conditions and realistic temperature profiles. This led to some consideration of a quasi-steady oscillating process. Later when force measurements became available some models were modified and new ones were proposed.

Grain refinement and texture development of cast bismuth-antimony alloy via severe plastic deformation

NASA Astrophysics Data System (ADS)

Im, Jae-Taek

The purpose of this work was to study learn about grain refinement mechanisms and texture development in cast n-type Bi90Sb10 alloy caused by severe plastic deformation. The practical objective is to produce a fine grained and textured microstructure in Bi90Sb10 alloy with enhanced thermoelectric performance and mechanical strength. In the study, twelve millimeter diameter cast bars of Bi90Sb 10 alloy were encapsulated in square cross section aluminum 6061 alloy containers. The composite bars were equal channel angular (ECAE) extruded through a 90 degree angle die at high homologous temperature. Various extrusion conditions were studied including punch speed (0.1, 0.3 and 0.6 in/min), extrusion temperature (220, 235 and 250°C), number of extrusion passes (1, 2 and 4), route (A, BC and C), and exit channel area reduction ratio (half and quarter area of inlet channel). The affect of an intermediate long term heat treatment (for 100 hours at 250°C under 10-3 torr vacuum) was explored. Processed materials were characterized by optical microscopy, x-ray diffraction, energy dispersive spectroscopy, wavelength dispersive spectroscopy and scanning electron microscopy. Texture was analyzed using the {006} reflection plane to identify the orientation of the basal poles in processed materials. The cast grains were irregularly shaped, had a grain size of hundreds-of-microns to millimeters, and showed inhomogeneous chemical composition. Severe plastic deformation refines the cast grains through dynamic recrystallization and causes the development of a bimodal microstructure consisting of fine grains (5-30 micron) and coarse grains (50-300 micron). ECAE processing of homogenizied Bi-Sb alloy causes grain refinement and produces a more uniform microstructure. Texture results show that ECAE route C processing gives a similar or slightly stronger texture than ECAE route A processing. In both cases, the basal-plane poles become aligned with the shear direction. Reduction area exit channel extrusion is more effective for both grain refinement and texture enhancement than simple ECAE processing.

Developments in Processing by Severe Plastic Deformation at the 3rd Pan American Materials Congress

NASA Astrophysics Data System (ADS)

Figueiredo, Roberto B.; Kawasaki, Megumi; Langdon, Terence G.

2017-10-01

The 3rd Pan American Materials Congress in San Diego, California, February 26-March 2, 2017, provided an opportunity to bring together many participants working in the field of severe plastic deformation. This article provides a brief review of these activities.

Atomic-level deformation of CuxZr100-x metallic glasses under shock loading

NASA Astrophysics Data System (ADS)

Demaske, Brian J.; Wen, Peng; Phillpot, Simon R.; Spearot, Douglas E.

2018-06-01

Plastic deformation mechanisms in CuxZr100-x bulk metallic glasses (MGs) subjected to shock are investigated using molecular dynamics simulations. MGs with Cu compositions between 30 and 70 at. % subjected to shock waves generated via piston velocities that range from 0.125 to 2.0 km/s are considered. In agreement with prior studies, plastic deformation is initiated via formation of localized regions of high von Mises shear strain, known as shear transformation zones (STZs). At low impact velocities, but above the Hugoniot elastic limit, STZ nucleation is dispersed behind the shock front. As impact velocity is increased, STZ nucleation becomes more homogeneous, eventually leading to shock-induced melting, which is identified in this work via high atomic diffusivity. The shear stress necessary to initiate plastic deformation within the shock front is independent of composition at shock intensities near the elastic limit but increases with increasing Cu content at high shock intensities. By contrast, both the flow stress in the plastically deformed MG and the critical shock pressure associated with melting behind the shock front are found to increase with increasing Cu content over the entire range of impact velocities. The evolution of the short-range order in the MG samples during shock wave propagation is analyzed using a polydisperse Voronoi tessellation method. Cu-centered polyhedra with full icosahedral symmetry are found to be most resistant to change under shock loading independent of the MG composition. A saturation is observed in the involvement of select Cu-centered polyhedra in the plastic deformation processes at a piston velocity around 0.75 km/s.

Twinning-mediated work hardening and texture evolution in CrCoFeMnNi high entropy alloys at cryogenic temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, T. K.; Wu, Z.; Stoica, A. D.

The cryogenic plastic deformation of CrCoFeMnNi high entropy alloy is characterized by three distinct stages based on the change of the work hardening rate. Microstructure and bulk texture at different strain levels were studied by electron backscatter diffraction (EBSD) and neutron diffraction. Our findings indicate that the deformation twins led to the constant work hardening rate at Stage II and resulted in the appearance of <115 >//TA texture component, while the dislocation slip was involved all though the entire plastic deformation. As a result, the twinning-mediated tensile plastic deformation at cryogenic temperature finally induced the strong {111}- < 112 >more » texture component and minor {001} < 110 > texture component accompanied with twinning-induced {115}< 552 > texture component.« less

Twinning-mediated work hardening and texture evolution in CrCoFeMnNi high entropy alloys at cryogenic temperature

DOE PAGES

Liu, T. K.; Wu, Z.; Stoica, A. D.; ...

2017-06-17

The cryogenic plastic deformation of CrCoFeMnNi high entropy alloy is characterized by three distinct stages based on the change of the work hardening rate. Microstructure and bulk texture at different strain levels were studied by electron backscatter diffraction (EBSD) and neutron diffraction. Our findings indicate that the deformation twins led to the constant work hardening rate at Stage II and resulted in the appearance of <115 >//TA texture component, while the dislocation slip was involved all though the entire plastic deformation. As a result, the twinning-mediated tensile plastic deformation at cryogenic temperature finally induced the strong {111}- < 112 >more » texture component and minor {001} < 110 > texture component accompanied with twinning-induced {115}< 552 > texture component.« less

Phyllotactic transformations as plastic deformations of tubular crystals with defects

NASA Astrophysics Data System (ADS)

Beller, Daniel; Nelson, David

Tubular crystals are 2D lattices in cylindrical topologies, which could be realized as assemblies of colloidal particles, and occur naturally in biological microtubules and in single-walled carbon nanotubes. Their geometry can be understood in the language of phyllotaxis borrowed from botany. We study the mechanics of plastic deformations in tubular crystals in response to tensile stress, as mediated by the formation and separation of dislocation pairs in a triangular lattice. Dislocation motion allows the growth of one phyllotactic arrangement at the expense of another, offering a low-energy, stepwise mode of plastic deformation in response to external stresses. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, dislocation glide. The crystal's bending modulus is found to produce simple but important corrections to the tube's deformation mechanics.

Deformation Behavior and Structure of i-Al-Cu-Fe Quasicrystalline Alloy in Vicinity of Nanoindenter Indentation

NASA Astrophysics Data System (ADS)

Shalaeva, E. V.; Selyanin, I. O.; Smirnova, E. O.; Smirnov, S. V.; Novachek, D. D.

2018-02-01

The nanoindentation tests have been carried out for the quasicrystalline polygrain Al62.4Cu25.3Fe12.3 alloy with the icosahedral structure i; the load P-displacement h diagrams have been used to estimate the contributions of plastic deformation (monotonic and intermittent), and the structures of the transverse microscopic sections have been studied in the vicinity of indentations by electron microscopy. It is shown that several systems of deformation bands are formed in the elasto-plastic zone in the vicinity of the indentations along the close-packed planes of the i lattice with the five-fold and two-fold symmetry axes; the bands often begin from cracks and manifest the signs of the dislocation structure. The traces of the phase transformation with the formation of the β-phase areas are observed only in a thin layer under an indenter. The effects of intermittent deformation are up to 50% of the total inelastic deformation and are related to the plastic behavior of the quasicrystal-activation and passage of deformation bands and also the formation of undersurface micro- and nanosized cracks.

Using the two-way shape memory effect of NiTi to control surface texture for cellular mechanotransduction

NASA Astrophysics Data System (ADS)

Liang, Yuan; Qin, Haifeng; Hou, Xiaoning; Doll, Gary L.; Ye, Chang; Dong, Yalin

2018-07-01

Mechanical force can crucially affect form and function of cells, and play critical roles in many diseases. While techniques to conveniently apply mechanical force to cells are limited, we fabricate a surface actuator prototype for cellular mechanotransduction by imparting severe plastic deformation into the surface of shape memory alloy (SMA). Using ultrasonic nanocrystal surface modification (UNSM), a deformation-based surface engineering technique with high controllability, micro surface patterns can be generated on the surface of SMA so that the micro-size cell can conform to the pattern; meanwhile, phase transformation can be induced in the subsurface by severe plastic deformation. By controlling plastic deformation and phase transformation, it is possible to establish a quantitative relation between deformation and temperature. When cells are cultured on the UNSM-treated surface, such surface can dynamically deform in response to external temperature change, and therefore apply controllable mechanical force to cells. Through this study, we demonstrate a novel way to fabricate a low-cost surface actuator that has the potential to be used for high-throughput cellular mechanotransduction.

Coupled THM processes in EDZ of crystalline rocks using an elasto-plastic cellular automaton

NASA Astrophysics Data System (ADS)

Pan, Peng-Zhi; Feng, Xia-Ting; Huang, Xiao-Hua; Cui, Qiang; Zhou, Hui

2009-05-01

This paper aims at a numerical study of coupled thermal, hydrological and mechanical processes in the excavation disturbed zones (EDZ) around nuclear waste emplacement drifts in fractured crystalline rocks. The study was conducted for two model domains close to an emplacement tunnel; (1) a near-field domain and (2) a smaller wall-block domain. Goodman element and weak element were used to represent the fractures in the rock mass and the rock matrix was represented as elasto-visco-plastic material. Mohr-Coulomb criterion and a non-associated plastic flow rule were adopted to consider the viscoplastic deformation in the EDZ. A relation between volumetric strain and permeability was established. Using a self-developed EPCA2D code, the elastic, elasto-plastic and creep analyses to study the evolution of stress and deformations, as well as failure and permeability evolution in the EDZ were conducted. Results indicate a strong impact of fractures, plastic deformation and time effects on the behavior of EDZ especially the evolution of permeability around the drift.

Constitutive Law and Flow Mechanism in Diamond Deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong

2012-11-19

Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significantmore » ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.« less

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Superior room-temperature ductility of typically brittle quasicrystals at small sizes

PubMed Central

Zou, Yu; Kuczera, Pawel; Sologubenko, Alla; Sumigawa, Takashi; Kitamura, Takayuki; Steurer, Walter; Spolenak, Ralph

2016-01-01

The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformation has been found to only be possible at high temperatures or under hydrostatic pressures, and their deformation mechanism at low temperatures is still unclear. Here, we report that typically brittle quasicrystals can exhibit remarkable ductility of over 50% strains and high strengths of ∼4.5 GPa at room temperature and sub-micrometer scales. In contrast to the generally accepted dominant deformation mechanism in quasicrystals—dislocation climb, our observation suggests that dislocation glide may govern plasticity under high-stress and low-temperature conditions. The ability to plastically deform quasicrystals at room temperature should lead to an improved understanding of their deformation mechanism and application in small-scale devices. PMID:27515779

Bright x-rays reveal shifting deformation states and effects of the microstructure on the plastic deformation of crystalline materials

DOE PAGES

Beaudoin, A. J.; Shade, P. A.; Schuren, J. C.; ...

2017-11-30

The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the prism of the microstructure in polycrystalline materials disperses and redistributes the load on a grain-by-grain basis, additional length and time scales are involved. Thus, the question is open as to how deformation intermittency manifests for the nonuniform grain-scale internal driving forces interacting with the finer-scale dislocation ensemble behavior. In this work we track the evolution of elastic strain withinmore » individual grains of a creep-loaded titanium alloy, revealing widely varying internal strains that fluctuate over time. Here, the findings provide direct evidence of how flow intermittency proceeds for an aggregate of ~700 grains while showing the influences of multiscale ensemble interactions and opening new avenues for advancing plasticity modeling.« less

Plastic Deformation as a Means to Achieve Stretchable Polymer Semiconductors

NASA Astrophysics Data System (ADS)

O'Connor, Brendan

Developing intrinsically stretchable semiconductors will seamlessly transition traditional devices into a stretchable platform. Polymer semiconductors are inherently soft materials due to the weak van der Waal intermolecular bonding allowing for flexible devices. However, these materials are not typically stretchable and when large strains are applied they either crack or plastically deform. Here, we study the use of repeated plastic deformation as a means of achieving stretchable films. In this talk, critical aspects of polymer semiconductor material selection, morphology and interface properties will be discussed that enable this approach of achieving stretchable films. We show that one can employ high performance donor-acceptor polymer semiconductors that are typically brittle through proper polymer blending to significantly increase ductility to achieve stretchable films. We demonstrate a polymer blend film that can be repeatedly deformed over 65%, while maintaining charge mobility consistently above 0.15 cm2/Vs. During the stretching process we show that the films follow a well-controlled repeated deformation pattern for over 100 stretching cycles.

Tensile fracture of coarse-Grained cast austenitic manganese steels

NASA Astrophysics Data System (ADS)

Rittel, D.; Roman, I.

1988-09-01

Tensile fracture of coarse-grained (0.25 to 1 mm) cast austenitic manganese (Hadfield) steels has been investigated. Numerous surface discontinuities nucleate in coarse slip bands, on the heavily deformed surface of tensile specimens. These discontinuities do not propagate radially and final fracture results from central specimen cracking at higher strains. On the microscopic scale, bulk voids nucleate during the entire plastic deformation and they do not coalesce by shear localization (e.g., void-sheet) mechanism. Close voids coalesce by internal necking, whereas distant voids are bridged by means of small voids which nucleate at later stages of the plastic deformation. The high toughness of Hadfield steels is due to their high strain-hardening capacity which stabilizes the plastic deformation, and avoids shear localization and loss of load-bearing capacity. The observed dependence of measured mechanical properties on the specimen’s geometry results from the development of a surface layer which charac-terizes the deformation of this coarse-grained material.

The effect of hydrogenation on strain hardening and deformation mechanisms in <113> single crystals of Hadfield steel

NASA Astrophysics Data System (ADS)

Astafurova, Elena; Maier, Galina; Melnikov, Eugene; Koshovkina, Vera; Moskvina, Valentina; Smirnov, Alexander; Bataev, Vladimir

2015-10-01

The effect of hydrogenation on the strain-hardening behavior and the deformation mechanisms of <113>-oriented single crystals of Hadfield steel was investigated under tension at room temperature. The stages of plastic flow and deformation mechanisms for hydrogen-charged specimens are similar to one in hydrogen-free state: slip → slip + single twinning → slip + multiple twinning. Hydrogen alloying favors to mechanical twinning, micro- and macrolocalization of plastic flow.

Deformation of compound shells under action of internal shock wave loading

NASA Astrophysics Data System (ADS)

Chernobryvko, Marina; Kruszka, Leopold; Avramov, Konstantin

2015-09-01

The compound shells under the action of internal shock wave loading are considered. The compound shell consists of a thin cylindrical shell and two thin parabolic shells at the edges. The boundary conditions in the shells joints satisfy the equality of displacements. The internal shock wave loading is modelled as the surplus pressure surface. This pressure is a function of the shell coordinates and time. The strain rate deformation of compound shell takes place in both the elastic and in plastic stages. In the elastic stage the equations of the structure motions are obtained by the assumed-modes method, which uses the kinetic and potential energies of the cylindrical and two parabolic shells. The dynamic behaviour of compound shells is treated. In local plastic zones the 3-D thermo-elastic-plastic model is used. The deformations are described by nonlinear model. The stress tensor elements are determined using dynamic deformation theory. The deformation properties of materials are influenced by the strain rate behaviour, the influence of temperature parameters, and the elastic-plastic properties of materials. The dynamic yield point of materials and Pisarenko-Lebedev's criterion of destruction are used. The modified adaptive finite differences method of numerical analysis is suggested for those simulations. The accuracy of the numerical simulation is verified on each temporal step of calculation and in the case of large deformation gradients.

Multiscale deformation behavior for multilayered steel by in-situ FE-SEM

NASA Astrophysics Data System (ADS)

Tanaka, Y.; Kishimoto, S.; Yin, F.; Kobayashi, M.; Tomimatsu, T.; Kagawa, K.

2010-03-01

The multi-scale deformation behavior of multi-layered steel during tensile loading was investigated by in-situ FE-SEM observation coupled with multi-scale pattern. The material used was multi-layered steel sheet consisting of martensitic and austenitic stainless steel layers. Prior to in-situ tensile testing, the multi-scale pattern combined with a grid and random dots were fabricated by electron beam lithography on the polished surface in the area of 1 mm2 to facilitate direct observation of multi-scale deformation. Both of the grids with pitches of 10 μm and a random speckle pattern ranging from 200 nm to a few μm sizes were drawn onto the specimen surface at same location. The electron moiré method was applied to measure the strain distribution in the deformed specimens at a millimeter scale and digital images correlation method was applied to measure the in-plane deformation and strain distribution at a micron meter scale acquired before and after at various increments of straining. The results showed that the plastic deformation in the austenitic stainless steel layer was larger than the martensitic steel layer at millimeter scale. However, heterogeneous intrinsic grain-scale plastic deformation was clearly observed and it increased with increasing the plastic deformation.

Effect of Severe Plastic Deformation on Structure and Properties of Al-Sc-Ta and Al-Sc-Ti Alloys

NASA Astrophysics Data System (ADS)

Berezina, Alla; Monastyrska, Tetiana; Davydenko, Olexandr; Molebny, Oleh; Polishchuk, Sergey

2017-03-01

The comparative analysis of the effect of monotonous and non-monotonous severe plastic deformations (SPD) on the structure and properties of aluminum alloys has been carried out. Conventional hydrostatic extrusion (HE) with a constant deformation direction and equal-channel angular hydroextrusion (ECAH) with an abrupt change in the deformation direction were chosen for the cases of monotonous and non-monotonous SPD, respectively. Model cast hypoeutectic Al-0.3%Sc alloys and hypereutectic Al-0.6%Sc alloys with Ta and Ti additives were chosen for studying. It was demonstrated that SPD of the alloys resulted in the segregation of the material into active and inactive zones which formed a banded structure. The active zones were shown to be bands of localized plastic deformation. The distance between zones was found to be independent of the accumulated strain degree and was in the range of 0.6-1 μm. Dynamic recrystallization in the active zones was observed using TEM. The dynamic recrystallization was accompanied by the formation of disclinations, deformation bands, low-angle, and high-angle boundaries, i.e., rotational deformation modes developed. The dynamic recrystallization was more intense during the non-monotonous deformation as compared with the monotonous one, which was confirmed by the reduction of texture degree in the materials after ECAH.

Study on Plastic Deformation Characteristics of Shot Peening of Ni-Based Superalloy GH4079

NASA Astrophysics Data System (ADS)

Zhong, L. Q.; Liang, Y. L.; Hu, H.

2017-09-01

In this paper, the X-ray stress diffractometer, surface roughness tester, field emission scanning electron microscope(SEM), dynamic ultra-small microhardness tester were used to measure the surface residual stress and roughness, topography and surface hardness changes of GH4079 superalloy, which was processed by metallographic grinding, turning, metallographic grinding +shot peening and turning + shot peening. Analysized the effects of shot peening parameters on shot peening plastic deformation features; and the effects of the surface state before shot peening on shot peening plastic deformation characteristics. Results show that: the surface residual compressive stress, surface roughness and surface hardness of GH4079 superalloy were increased by shot peening, in addition, the increment of the surface residual compressive stress, surface roughness and surface hardness induced by shot peening increased with increasing shot peening intensity, shot peening time, shot peening pressure and shot hardness, but harden layer depth was not affected considerably. The more plastic deformation degree of before shot peening surface state, the less increment of the surface residual compressive stress, surface roughness and surface hardness induced by shot peening.

Microstructural record of pressure solution and crystal plastic deformation in carbonate fault rocks from a shallow crustal strike-slip fault, Northern Calcareous Alps (Austria)

NASA Astrophysics Data System (ADS)

Bauer, Helene; Rogowitz, Anna; Grasemann, Benhard; Decker, Kurt

2017-04-01

This study presents microstructural investigations of natural carbonate fault rocks that formed by a suite of different deformation processes, involving hydro-fracturing, dissolution-precipitation creep and cataclasis. Some fault rocks show also clear indications of crystal plastic deformation, which is quite unexpected, as the fault rocks were formed in an upper crustal setting, raising the question of possible strongly localised, low temperature ductile deformation in carbonate rocks. The investigated carbonate fault rocks are from an exhumed, sinistral strike-slip fault at the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps (Austria). The SEMP fault system formed during eastward lateral extrusion of the Eastern Alps in the Oligocene to Lower Miocene. Based on vitrinite reflectance data form intramontane Teritary basins within the Northern Calcareous Alps, a maximum burial depth of 4 km for the investigated fault segment is estimated. The investigated fault accommodated sinistral slip of several hundreds of meters. Microstructural analysis of fault rocks includes scanning electron microscopy, optical microscopy and electron backscattered diffraction mapping. The data show that fault rocks underwent various stages of evolution including early intense veining (hydro-fracturing) and stylolite formation reworked by localised shear zones. Cross cutting relationship reveals that veins never cross cut clay seams accumulated along stylolites. We conclude that pressure solution processes occured after hydro-fracturing. Clay enriched zones localized further deformation, producing a network of small-scale clay-rich shear zones of up to 1 mm thickness anastomosing around carbonate microlithons, varying from several mm down to some µm in size. Clay seams consist of kaolinit, chlorite and illite matrix and form (sub) parallel zones in which calcite was dissolved. Beside pressure solution, calcite microlithons show also ductile deformation microstructures, including deformation twinning, undulose extinction, subgrain rotation recrystallization and even grain boundary migration. Especially coarse grained calcites from veins localized ductile deformation and record dislocation glide. The investigated fault rocks are excellent examples of frictional, pressure solution and crystal plastic deformation processes. We speculated that crystal plastic deformation typical for higher metamorphic shear zones in marbles, can be either produced under much lower temperature conditions or the temperature necessary for crystal plastic deformation was generated by frictional slip or strain heating within the fault zone.

Metal nanoplates: Smaller is weaker due to failure by elastic instability

NASA Astrophysics Data System (ADS)

Ho, Duc Tam; Kwon, Soon-Yong; Park, Harold S.; Kim, Sung Youb

2017-11-01

Under mechanical loading, crystalline solids deform elastically, and subsequently yield and fail via plastic deformation. Thus crystalline materials experience two mechanical regimes: elasticity and plasticity. Here, we provide numerical and theoretical evidence to show that metal nanoplates exhibit an intermediate mechanical regime that occurs between elasticity and plasticity, which we call the elastic instability regime. The elastic instability regime begins with a decrease in stress, during which the nanoplates fail via global, and not local, deformation mechanisms that are distinctly different from traditional dislocation-mediated plasticity. Because the nanoplates fail via elastic instability, the governing strength criterion is the ideal strength, rather than the yield strength, and as a result, we observe a unique "smaller is weaker" trend. We develop a simple surface-stress-based analytic model to predict the ideal strength of the metal nanoplates, which accurately reproduces the smaller is weaker behavior observed in the atomistic simulations.

Stability of a horizontal well and hydraulic fracture initiation in rocks of the bazhenov formation

NASA Astrophysics Data System (ADS)

Stefanov, Yu. P.; Bakeev, R. A.; Myasnikov, A. V.; Akhtyamova, A. I.; Romanov, A. S.

2017-12-01

Three-dimensional numerical modeling of the formation of the stress-strain state in the vicinity of a horizontal well in weakened rocks of the Bazhenov formation is carried out. The influence of the well orientation and plastic deformation on the stress-strain state and the possibility of hydraulic fracturing are considered. It is shown that the deviation of the well from the direction of maximum compression leads to an increase in plastic deformation and a discrepancy between tangential stresses around the well bore and principle stresses in the surrounding medium. In an elastoplastic medium, an increase in the pressure in the well can lead to a large-scale development of plastic deformation, at which no tensile stresses necessary for hydraulic fracturing according to the classical scheme arise. In this case, there occur plastic expansion and fracture of the well.

Evolution of microstructure and mechanical properties of steel in the course of pressing-drawing

NASA Astrophysics Data System (ADS)

Lezhnev, S. N.; Volokitina, I. E.; Volokitin, A. V.

2017-11-01

The combined continuous pressing-drawing process is proposed after a comprehensive analysis of available plastic structure-forming techniques taking into account the promising trends in their development. This combination of severe plastic deformation in equal-channel step die and drawing allows one to obtain a wire of desired size and shape in the cross section with an ultrafine-grained structure after a few deformation cycles. It also enables initial workpieces of any length to be processed and, therefore, allows one to obtain finished products up to several tens of meters in length. The aim of this study is to investigate the effect of new combined pressing-drawing technique of plastic deformation on the structure and mechanical properties of the steel. These studies have shown that the proposed deformation technique has a significant advantage of the techniques currently used to manufacture a steel wire.

Effect of plastic deformation on the magnetic properties and dislocation luminescence of isotopically enriched silicon {sup 29}Si:B

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koplak, O. V.; Shteynman, E. A.; Tereschenko, A. N.

2015-09-15

A correlation between the temperature dependences of the D1-line intensity of dislocation luminescence and the magnetic moment of plastically deformed isotopically enriched crystals {sup 29}Si:B is found. It is established that the magnetic susceptibility of the deformed crystals obtained by integration of the spectra of electron spin resonance and the D1-line intensity undergo similar nonmonotonic variations with temperature varying in the range of 20–32 K.

Numerical simulation of elasto-plastic deformation of composites: evolution of stress microfields and implications for homogenization models

NASA Astrophysics Data System (ADS)

González, C.; Segurado, J.; LLorca, J.

2004-07-01

The deformation of a composite made up of a random and homogeneous dispersion of elastic spheres in an elasto-plastic matrix was simulated by the finite element analysis of three-dimensional multiparticle cubic cells with periodic boundary conditions. "Exact" results (to a few percent) in tension and shear were determined by averaging 12 stress-strain curves obtained from cells containing 30 spheres, and they were compared with the predictions of secant homogenization models. In addition, the numerical simulations supplied detailed information of the stress microfields, which was used to ascertain the accuracy and the limitations of the homogenization models to include the nonlinear deformation of the matrix. It was found that secant approximations based on the volume-averaged second-order moment of the matrix stress tensor, combined with a highly accurate linear homogenization model, provided excellent predictions of the composite response when the matrix strain hardening rate was high. This was not the case, however, in composites which exhibited marked plastic strain localization in the matrix. The analysis of the evolution of the matrix stresses revealed that better predictions of the composite behavior can be obtained with new homogenization models which capture the essential differences in the stress carried by the elastic and plastic regions in the matrix at the onset of plastic deformation.

Understanding deformation mechanisms during powder compaction using principal component analysis of compression data.

PubMed

Roopwani, Rahul; Buckner, Ira S

2011-10-14

Principal component analysis (PCA) was applied to pharmaceutical powder compaction. A solid fraction parameter (SF(c/d)) and a mechanical work parameter (W(c/d)) representing irreversible compression behavior were determined as functions of applied load. Multivariate analysis of the compression data was carried out using PCA. The first principal component (PC1) showed loadings for the solid fraction and work values that agreed with changes in the relative significance of plastic deformation to consolidation at different pressures. The PC1 scores showed the same rank order as the relative plasticity ranking derived from the literature for common pharmaceutical materials. The utility of PC1 in understanding deformation was extended to binary mixtures using a subset of the original materials. Combinations of brittle and plastic materials were characterized using the PCA method. The relationships between PC1 scores and the weight fractions of the mixtures were typically linear showing ideal mixing in their deformation behaviors. The mixture consisting of two plastic materials was the only combination to show a consistent positive deviation from ideality. The application of PCA to solid fraction and mechanical work data appears to be an effective means of predicting deformation behavior during compaction of simple powder mixtures. Copyright © 2011 Elsevier B.V. All rights reserved.

Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones

NASA Astrophysics Data System (ADS)

Yao, D. J.; Zhou, D. R.; Xu, P. Q.; Lu, F. G.

2017-05-01

The as-welded Invar fusion zones were fabricated between cemented carbides and carbon steel using a Fe-Ni Invar interlayer and laser welding method. Three regions in the as-welded Invar fusion zones were defined to compare microstructures, and these were characterized and confirmed by scanning electron microscopy and X-ray diffractometry. The structure and plastic deformation mechanism for initial Invar Fe-Ni alloys and the as-welded Invar fusion zones are discussed. (1) After undergoing high-temperature thermal cycles, the microstructure of the as-welded Invar fusion zones contains γ-(Fe, Ni) solid solution (nickel dissolving in γ-Fe) with a face-centered cubic (fcc) crystal structure and mixed carbides (eutectic colonies, mixed carbides between two adjacent grains). The mixed carbides exhibited larger, coarser eutectic microstructures with a decrease in welding speed and an increase in heat input. (2) The structure of the initial Invar and the as-welded Invar is face-centered cubic γ-(Fe, Ni). (3) The as-welded Invar has a larger plastic deformation than initial Invar with an increase in local strain field and dislocation density. Slip deformation is propagated along the (111) plane. This finding helps us to understand microstructure and the formation of dislocation and plastic deformation when the Invar Fe-Ni alloy undergoes a high-temperature process.

Spring back of infinite honeycomb sheets beyond plastic deformation

NASA Astrophysics Data System (ADS)

Bonfanti, A.; Bhaskar, A.

2015-02-01

Cellular structures are promising for applications where high stiffness and strength are required with the minimal use of material. They are often used in applications where the plastic deformation plays an important role, such as those involving crashworthiness, energy absorption, and stents. The elastic analysis of a honeycomb sheet has been carried out in the past [1]. The present analysis extends this classical work in the elasto-plastic regime. Recoil analysis due to elastic recovery is absent from the published literature. This work aims to develop an analytical model to calculate the spring back for a simplified case, that of an infinite honeycomb sheet. An elastic-perfectly plastic material model is assumed. The recoil for a clamped beam with a load and moment applied at the free edge is analytically calculated first. This is carried out by relating the stress distribution of the cross section to the final deformed shape. The part corresponding to the elastic contribution is subsequently subtracted in order to obtain the final configuration after the external load is removed. This simple elasto-plastic analysis is then incorporated into the analysis of an infinite sheet made of uniform hexagonal cells. The translational symmetry of the lattice is exploited along with the analysis of a beam under tip loading through to plastic stage and recoil. The final shape of the struts upon the removal of the remote stress is completely determined by the plastic deformation which cannot be recovered. The expression for the beam thus obtained is then used to build an analytical model for an infinite honeycomb sheet loaded in both directions.

High Pressure Elastic Constants of High-Pressure Iron Analog Osmium

NASA Astrophysics Data System (ADS)

Godwal, B. K.; Geballe, Z.; Jeanloz, R.

2011-12-01

Understanding the elasticity of hcp iron is important both for ascertaining the stable phase and for explaining the observed seismic anomalies of Earth's inner core. A systematic experimental study of analog materials is warranted because experiments at inner-core conditions remain exceptionally challenging and theory has yielded conflicting results for iron. The deformation of hexagonal close-packed (hcp) Os, an analog for the high-pressure hcp form of Fe, has been characterized under non-hydrostatic stresses using synchrotron-based angular-dispersive radial x-ray diffraction to pressures of 60 GPa at room temperature. Starting with published ultrasonic values of elastic constants and previous measurements of linear and volume compressibilities, we estimate the single-crystal elasticity tensor of osmium to 60 GPa and find that the crystal orientation with the largest shear modulus, (002), accommodates the largest shear stress (10 GPa) and a differential strain surpassing the Voigt iso-strain limit. We find the conventional elastic model, bounded by Reuss (iso-stress) and Voigt limits, inadequate for explaining our measurements. Instead, we infer that plastic deformation limits the amount of shear stress supported by the crystal planes near the a-axis, causing the more elastically strong c-axis to support the majority of the differential strain. This conclusion is consistent with the elasto-plastic self-consistent approach used to model the effect of plasticity on the high-pressure deformation of hcp-Co (Merkel et al, PRB 79, 064110 (2009)). Importantly, we document a strength anisotropy so large that the Voigt (elastic) limit is clearly surpassed.

Multiaxial mechanical properties and constitutive modeling of human adipose tissue: a basis for preoperative simulations in plastic and reconstructive surgery.

PubMed

Sommer, Gerhard; Eder, Maximilian; Kovacs, Laszlo; Pathak, Heramb; Bonitz, Lars; Mueller, Christoph; Regitnig, Peter; Holzapfel, Gerhard A

2013-11-01

A preoperative simulation of soft tissue deformations during plastic and reconstructive surgery is desirable to support the surgeon's planning and to improve surgical outcomes. The current development of constitutive adipose tissue models, for the implementation in multilayer computational frameworks for the simulation of human soft tissue deformations, has proved difficult because knowledge of the required mechanical parameters of fat tissue is limited. Therefore, for the first time, human abdominal adipose tissues were mechanically investigated by biaxial tensile and triaxial shear tests. The results of this study suggest that human abdominal adipose tissues under quasi-static and dynamic multiaxial loadings can be characterized as a nonlinear, anisotropic and viscoelastic soft biological material. The nonlinear and anisotropic features are consequences of the material's collagenous microstructure. The aligned collagenous septa observed in histological investigations causes the anisotropy of the tissue. A hyperelastic model used in this study was appropriate to represent the quasi-static multiaxial mechanical behavior of fat tissue. The constitutive parameters are intended to serve as a basis for soft tissue simulations using the finite element method, which is an apparent method for obtaining promising results in the field of plastic and reconstructive surgery. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

High temperature monotonic and cyclic deformation in a directionally solidified nickel-base superalloy

NASA Technical Reports Server (NTRS)

Huron, Eric S.

1986-01-01

Directionally solidified (DS) MAR-M246+Hf was tested in tension and fatigue, at temperatures from 20 C to 1093 C. Tests were performed on (001) oriented specimens at strain rates of 50 % and 0.5 % per minute. In tension, the yield strength was constant up to 704 C, above which the strength dropped off rapidly. A strong dependence of strength on strain rate was seen at the higher temperatures. The deformation mode was observed to change from heterogeneous to homogeneous with increasing temperature. Low Cycle Fatigue tests were done using a fully reversed waveform and total strain control. For a given plastic strain range, lives increased with increasing temperature. For a given temperature strain rate had a strong effect on life. At 704 C, decreasing strain rates decreased life, while at the higher temperatures, decreasing strain rates increased life, for a given plastic strain range. These results could be explained through considerations of the deformation modes and stress levels. At the higher temperatures, marked coarsening caused beneficial stress reductions, but oxidation limited the life. The longitudinal grain boundaries were found to influence slip behavior. The degree of secondary slip adjacent to the boundaries was found to be related to the degree of misorientation between the grains.

Investigation of Interface Bonding Mechanism of an Explosively Welded Tri-Metal Titanium/Aluminum/Magnesium Plate by Nanoindentation

NASA Astrophysics Data System (ADS)

Zhang, T. T.; Wang, W. X.; Zhou, J.; Cao, X. Q.; Yan, Z. F.; Wei, Y.; Zhang, W.

2018-04-01

A tri-metal titanium/aluminum/magnesium (Ti/Al/Mg) cladding plate, with an aluminum alloy interlayer plate, was fabricated for the first time by explosive welding. Nanoindentation tests and associated microstructure analysis were conducted to investigate the interface bonding mechanisms of the Ti/Al/Mg cladding plate. A periodic wavy bonding interface (with an amplitude of approximately 30 μm and a wavelength of approximately 160 μm) without a molten zone was formed between the Ti and Al plates. The bonding interface between the Al and the Mg demonstrated a similar wavy shape, but the wave at this location was much larger with an amplitude of approximately 390 μm and a wavelength of approximately 1580 μm, and some localized melted zones also existed at this location. The formation of the wavy interface was found to result from a severe deformation at the interface, which was caused by the strong impact or collision. The nanoindentation tests showed that the material hardness decreased with increasing distance from the bonding interface. Material hardness at a location was found to be correlated with the degree of plastic deformation at that site. A larger plastic deformation was correlated with an increase in hardness.

Application of activated barrier hopping theory to viscoplastic modeling of glassy polymers

NASA Astrophysics Data System (ADS)

Sweeney, J.; Spencer, P. E.; Vgenopoulos, D.; Babenko, M.; Boutenel, F.; Caton-Rose, P.; Coates, P. D.

2018-05-01

An established statistical mechanical theory of amorphous polymer deformation has been incorporated as a plastic mechanism into a constitutive model and applied to a range of polymer mechanical deformations. The temperature and rate dependence of the tensile yield of PVC, as reported in early studies, has been modeled to high levels of accuracy. Tensile experiments on PET reported here are analyzed similarly and good accuracy is also achieved. The frequently observed increase in the gradient of the plot of yield stress against logarithm of strain rate is an inherent feature of the constitutive model. The form of temperature dependence of the yield that is predicted by the model is found to give an accurate representation. The constitutive model is developed in two-dimensional form and implemented as a user-defined subroutine in the finite element package ABAQUS. This analysis is applied to the tensile experiments on PET, in some of which strain is localized in the form of shear bands and necks. These deformations are modeled with partial success, though adiabatic heating of the instability causes inaccuracies for this isothermal implementation of the model. The plastic mechanism has advantages over the Eyring process, is equally tractable, and presents no particular difficulties in implementation with finite elements.

Application of activated barrier hopping theory to viscoplastic modeling of glassy polymers

NASA Astrophysics Data System (ADS)

Sweeney, J.; Spencer, P. E.; Vgenopoulos, D.; Babenko, M.; Boutenel, F.; Caton-Rose, P.; Coates, P. D.

2017-10-01

An established statistical mechanical theory of amorphous polymer deformation has been incorporated as a plastic mechanism into a constitutive model and applied to a range of polymer mechanical deformations. The temperature and rate dependence of the tensile yield of PVC, as reported in early studies, has been modeled to high levels of accuracy. Tensile experiments on PET reported here are analyzed similarly and good accuracy is also achieved. The frequently observed increase in the gradient of the plot of yield stress against logarithm of strain rate is an inherent feature of the constitutive model. The form of temperature dependence of the yield that is predicted by the model is found to give an accurate representation. The constitutive model is developed in two-dimensional form and implemented as a user-defined subroutine in the finite element package ABAQUS. This analysis is applied to the tensile experiments on PET, in some of which strain is localized in the form of shear bands and necks. These deformations are modeled with partial success, though adiabatic heating of the instability causes inaccuracies for this isothermal implementation of the model. The plastic mechanism has advantages over the Eyring process, is equally tractable, and presents no particular difficulties in implementation with finite elements.

Occurrence of cohesion of metals during combined plastic deformation

NASA Technical Reports Server (NTRS)

Aynbinder, S. G.; Klokova, E. F.

1980-01-01

Experiments were conducted to study the cohesion of metals with surface films of varying thickness and hardness. It was established that the deformation necessary for the occurrence of cohesion is determined by the correlation of mechanical properties of the films and the base metal. The greater the relative hardness of the film the lower the deformation necessary for the occurrence of cohesion. The films are as plastic as the base metal prevent cohesion, since in this case it is impossible for sections of metal to appear that are free of contaminants. The physical perculiarities of metals that determine their capability for coalescence under conditions of dry friction are the relative hardness and plasticity of the oxide films formed on their surface under atmospheric conditions.

The noncontinuum crack tip deformation behavior of surface microcracks

NASA Astrophysics Data System (ADS)

Morris, W. L.

1980-07-01

The crack tip opening displacement (CTOD) of small surface fatigue cracks (lengths of the grain size) in Al 2219-T851 depends upon the location of a crack relative to the grain boundaries. Both CTOD and crack tip closure stress are greatest when the crack tip is a large distance from the next grain boundary in the direction of crack propagation. Contrary to behavioral trends predicted by continuum fracture mechanics, crack length has no detectable effect on the contribution of plastic deformation to CTOD. It is apparent from these observations that the region of significant plastic deformation is confined by the grain boundaries, resulting in a plastic zone size that is insensitive to crack length and to external load.

Electromigration-induced Plasticity and Texture in Cu Interconnects

NASA Astrophysics Data System (ADS)

Budiman, A. S.; Hau-Riege, C. S.; Besser, P. R.; Marathe, A.; Joo, Y.-C.; Tamura, N.; Patel, J. R.; Nix, W. D.

2007-10-01

Plastic deformation has been observed in damascene Cu interconnect test structures during an in-situ electromigration experiment and before the onset of visible microstructural damage (ie. voiding) using a synchrotron technique of white beam X-ray microdiffraction. We show here that the extent of this electromigration-induced plasticity is dependent on the texture of the Cu grains in the line. In lines with strong <111> textures, the extent of plastic deformation is found to be relatively large compared to our plasticity results in the previous study[1] using another set of Cu lines with weaker textures. This is consistent with our earlier observation that the occurrence of plastic deformation in a given grain can be strongly correlated with the availability of a <112> direction of the crystal in the proximity of the direction of the electron flow in the line (within an angle of 10°). In <111> out-of-plane oriented grains in a damascene interconnect scheme, the crystal plane facing the sidewall tends to be a {110} plane,[2-4] so as to minimize interfacial energy. Therefore, it is deterministic rather than probabilistic that the <111> grains will have a <112> direction nearly parallel to the direction of electron flow. Thus, strong <111> textures lead to more plasticity, as we observe.

Characterization of plastic deformation and chemical reaction in titanium-polytetrafluoroethylene mixture

NASA Astrophysics Data System (ADS)

Davis, Jeffery Jon

1998-09-01

The subject of this dissertation is the deformation process of a single metal - polymer system (titanium - polytetrafluoroethylene) and how this process leads to initiation of chemical reaction. Several different kinds of experiments were performed to characterize the behavior of this material to shock and impact. These mechanical conditions induce a rapid plastic deformation of the sample. All of the samples tested had an initial porosity which increased the plastic flow condition. It is currently believed that during the deformation process two important conditions occur: removal of the oxide layer from the metal and decomposition of the polymer. These conditions allow for rapid chemical reaction. The research from this dissertation has provided insight into the complex behavior of plastic deformation and chemical reactions in titanium - polytetrafluoroethylene (PTFE, Teflon). A hydrodynamic computational code was used to model the plastic flow for correlation with the results from the experiments. The results from this work are being used to develop an ignition and growth model for metal/polymer systems. Three sets of experiments were used to examine deformation of the 80% Ti and 20% Teflon materials: drop- weight, gas gun, and split-Hopkinson pressure bar. Recovery studies included post shot analysis of the samples using x-ray diffraction. Lagrangian hydrocode DYNA2D modeling of the drop-weight tests was performed for comparison with experiments. One of the reactions know to occur is Ti + C → TiC (s) which results in an exothermic release. However, the believed initial reactions occur between Ti and fluorine which produces TixFy gases. The thermochemical code CHEETAH was used to investigate the detonation products and concentrations possible during Ti - Teflon reaction. CHEETAH shows that the Ti - fluorine reactions are thermodynamically favorable. This research represents the most comprehensive to date study of deformation induced chemical reaction in metal/polymers.

Simultaneous increase in the strength, plasticity, and corrosion resistance of an ultrafine-grained Ti-4Al-2V pseudo-alpha-titanium alloy

NASA Astrophysics Data System (ADS)

Chuvil'deev, V. N.; Kopylov, V. I.; Nokhrin, A. V.; Bakhmet'ev, A. M.; Sandler, N. G.; Kozlova, N. A.; Tryaev, P. V.; Tabachkova, N. Yu.; Mikhailov, A. S.; Ershova, A. V.; Gryaznov, M. Yu.; Chegurov, M. K.; Sysoev, A. N.; Smirnova, E. S.

2017-05-01

The influence of severe plastic deformation on the structural-phase state of grain boundaries in a Ti-4Al-2V (commercial PT3V grade) pseudo-alpha-titanium alloy has been studied. It is established that increase in the strength, plasticity, and corrosion resistance of this alloy is related to the formation of an ultrafine- grained structure. In particular, it is shown that an increase in the resistance to hot-salt intergranular corrosion is due to diffusion-controlled redistribution of aluminum and vanadium atoms at the grain boundaries of titanium formed during thermal severe plastic deformation.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie; Zheng, Jie

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie; Zheng, Jie

2016-11-01

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Study of an athermal quasi static plastic deformation in a 2D granular material

NASA Astrophysics Data System (ADS)

Zhang, Jie

2017-11-01

In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bi-disperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands.

Deformation-driven diffusion and plastic flow in amorphous granular pillars.

PubMed

Li, Wenbin; Rieser, Jennifer M; Liu, Andrea J; Durian, Douglas J; Li, Ju

2015-06-01

We report a combined experimental and simulation study of deformation-induced diffusion in compacted quasi-two-dimensional amorphous granular pillars, in which thermal fluctuations play a negligible role. The pillars, consisting of bidisperse cylindrical acetal plastic particles standing upright on a substrate, are deformed uniaxially and quasistatically by a rigid bar moving at a constant speed. The plastic flow and particle rearrangements in the pillars are characterized by computing the best-fit affine transformation strain and nonaffine displacement associated with each particle between two stages of deformation. The nonaffine displacement exhibits exponential crossover from ballistic to diffusive behavior with respect to the cumulative deviatoric strain, indicating that in athermal granular packings, the cumulative deviatoric strain plays the role of time in thermal systems and drives effective particle diffusion. We further study the size-dependent deformation of the granular pillars by simulation, and find that different-sized pillars follow self-similar shape evolution during deformation. In addition, the yield stress of the pillars increases linearly with pillar size. Formation of transient shear lines in the pillars during deformation becomes more evident as pillar size increases. The width of these elementary shear bands is about twice the diameter of a particle, and does not vary with pillar size.

Influence of Localized Plasticity on IASCC Sensitivity of Austenitic Stainless Steels under PWR Primary Water

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Tanguy, Benoit; Laffont, Lydia; Lafont, Marie-Christine; Guerre, Catherine; Andrieu, Eric

The sensibility of precipitation-strengthened A286 austenitic stainless steel to Stress Corrosion Cracking (SCC) is studied by means of Slow Strain Rate Tests (SSRT). First, alloy cold working by Low Cycle Fatigue (LCF) is investigated. Fatigue tests under plastic strain control are performed at different strain levels (Δ ɛp/2=0.2%, 0.5% and 0.8%) in order to establish correlation between stress softening and deformation microstructure resulting from LCF tests. Deformed microstructures have been identified through TEM investigations. Three states of cyclic behaviour for precipitation-strengthened A286 have been identified: hardening, cyclic softening and finally saturation of softening. It is shown that the A286 alloy cyclic softening is due to microstructural features such as defects — free deformation bands resulting from dislocations motion along family plans <111>, that swept defects or γ' precipitates and lead to deformation localization. In order to quantify effects of plastic localized deformation on intergranular stress corrosion cracking (IGSCC) of the A286 alloy in PWR primary water, slow strain rate tests are conducted. For each cycling conditions, two specimens at a similar stress level are tested: the first containing free precipitate deformation bands, the other not significant of a localized deformation state. SSRT tests are still in progress.

Measurement of installation deformation of the acetabulum during prosthetic replacement of a hip joint using digital image correlation

NASA Astrophysics Data System (ADS)

Lei, Dong; Bai, Pengxiang; Zhu, Feipeng

2018-01-01

Nowadays, acetabulum prosthesis replacement is widely used in clinical medicine. However, there is no efficient way to evaluate the implantation effect of the prosthesis. Based on a modern photomechanics technique called digital image correlation (DIC), the evaluation method of the installation effect of the acetabulum was established during a prosthetic replacement of a hip joint. The DIC method determines strain field by comparing the speckle images between the undeformed sample and the deformed counterpart. Three groups of experiments were carried out to verify the feasibility of the DIC method on the acetabulum installation deformation test. Experimental results indicate that the installation deformation of acetabulum generally includes elastic deformation (corresponding to the principal strain of about 1.2%) and plastic deformation. When the installation angle is ideal, the plastic deformation can be effectively reduced, which could prolong the service life of acetabulum prostheses.

Modeling multiscale evolution of numerous voids in shocked brittle material.

PubMed

Yu, Yin; Wang, Wenqiang; He, Hongliang; Lu, Tiecheng

2014-04-01

The influence of the evolution of numerous voids on macroscopic properties of materials is a multiscale problem that challenges computational research. A shock-wave compression model for brittle material, which can obtain both microscopic evolution and macroscopic shock properties, was developed using discrete element methods (lattice model). Using a model interaction-parameter-mapping procedure, qualitative features, as well as trends in the calculated shock-wave profiles, are shown to agree with experimental results. The shock wave splits into an elastic wave and a deformation wave in porous brittle materials, indicating significant shock plasticity. Void collapses in the deformation wave were the natural reason for volume shrinkage and deformation. However, media slippage and rotation deformations indicated by complex vortex patterns composed of relative velocity vectors were also confirmed as an important source of shock plasticity. With increasing pressure, the contribution from slippage deformation to the final plastic strain increased. Porosity was found to determine the amplitude of the elastic wave; porosity and shock stress together determine propagation speed of the deformation wave, as well as stress and strain on the final equilibrium state. Thus, shock behaviors of porous brittle material can be systematically designed for specific applications.

Deformation behavior of human enamel and dentin-enamel junction under compression.

PubMed

Zaytsev, Dmitry; Panfilov, Peter

2014-01-01

Deformation behavior under uniaxial compression of human enamel and dentin-enamel junction (DEJ) is considered in comparison with human dentin. This deformation scheme allows estimating the total response from all levels of the hierarchical composite material in contrast with the indentation, which are limited by the mesoscopic and microscopic scales. It was shown for the first time that dental enamel is the strength (up to 1850MPa) hard tissue, which is able to consider some elastic (up to 8%) and plastic (up to 5%) deformation under compression. In so doing, it is almost undeformable substance under the creep condition. Mechanical properties of human enamel depend on the geometry of sample. Human dentin exhibits the similar deformation behavior under compression, but the values of its elasticity (up to 40%) and plasticity (up to 18%) are much more, while its strength (up to 800MPa) is less in two times. Despite the difference in mechanical properties, human enamel is able to suppress the cracking alike dentin. Deformation behavior under the compression of the samples contained DEJ as the same to dentin. This feature allows a tooth to be elastic-plastic (as dentin) and wear resistible (as enamel), simultaneously. © 2013 Elsevier B.V. All rights reserved.

Coupled thermal stress simulations of ductile tearing

DOE PAGES

Neilsen, Michael K.; Dion, Kristin

2016-03-01

Predictions for ductile tearing of a geometrically complex Ti-6Al-4V plate were generated using a Unified Creep Plasticity Damage model in fully coupled thermal stress simulations. Uniaxial tension and butterfly shear tests performed at displacement rates of 0.0254 and 25.4 mm/s were also simulated. Results from these simulations revealed that the material temperature increase due to plastic work can have a dramatic effect on material ductility predictions in materials that exhibit little strain hardening. Furthermore, this occurs because the temperature increase causes the apparent hardening of the material to decrease which leads to the initiation of deformation localization and subsequent ductilemore » tearing earlier in the loading process.« less

Semantic modeling of plastic deformation of polycrystalline rock

NASA Astrophysics Data System (ADS)

Babaie, Hassan A.; Davarpanah, Armita

2018-02-01

We have developed the first iteration of the Plastic Rock Deformation (PRD) ontology by modeling the semantics of a selected set of deformational processes and mechanisms that produce, reconfigure, displace, and/or consume the material components of inhomogeneous polycrystalline rocks. The PRD knowledge model also classifies and formalizes the properties (relations) that hold between instances of the dynamic physical and chemical processes and the rock components, the complex physio-chemical, mathematical, and informational concepts of the plastic rock deformation system, the measured or calculated laboratory testing conditions, experimental procedures and protocols, the state and system variables, and the empirical flow laws that define the inter-relationships among the variables. The ontology reuses classes and properties from several existing ontologies that are built for physics, chemistry, biology, and mathematics. With its flexible design, the PRD ontology is well positioned to incrementally develop into a model that more fully represents the knowledge of plastic deformation of polycrystalline rocks in the future. The domain ontology will be used to consistently annotate varied data and information related to the microstructures and the physical and chemical processes that produce them at different spatial and temporal scales in the laboratory and in the solid Earth. The PRDKB knowledge base, when built based on the ontology, will help the community of experimental structural geologists and metamorphic petrologists to coherently and uniformly distribute, discover, access, share, and use their data through automated reasoning and integration and query of heterogeneous experimental deformation data that originate from autonomous rock testing laboratories.

Effect of Severe Plastic Deformation on Structure and Properties of Al-Sc-Ta and Al-Sc-Ti Alloys.

PubMed

Berezina, Alla; Monastyrska, Tetiana; Davydenko, Olexandr; Molebny, Oleh; Polishchuk, Sergey

2017-12-01

The comparative analysis of the effect of monotonous and non-monotonous severe plastic deformations (SPD) on the structure and properties of aluminum alloys has been carried out. Conventional hydrostatic extrusion (HE) with a constant deformation direction and equal-channel angular hydroextrusion (ECAH) with an abrupt change in the deformation direction were chosen for the cases of monotonous and non-monotonous SPD, respectively. Model cast hypoeutectic Al-0.3%Sc alloys and hypereutectic Al-0.6%Sc alloys with Ta and Ti additives were chosen for studying. It was demonstrated that SPD of the alloys resulted in the segregation of the material into active and inactive zones which formed a banded structure. The active zones were shown to be bands of localized plastic deformation. The distance between zones was found to be independent of the accumulated strain degree and was in the range of 0.6-1 μm. Dynamic recrystallization in the active zones was observed using TEM. The dynamic recrystallization was accompanied by the formation of disclinations, deformation bands, low-angle, and high-angle boundaries, i.e., rotational deformation modes developed. The dynamic recrystallization was more intense during the non-monotonous deformation as compared with the monotonous one, which was confirmed by the reduction of texture degree in the materials after ECAH.

Influence of severe plastic deformation on intermetallic particles in Mg-12 wt.%Zn alloy investigated using transmission electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Němec, M., E-mail: nemecm@fzu.cz

The in-depth microstructural characterization of intermetallic particles in an Mg-12 wt.%Zn binary alloy subjected to a severe plastic deformation is presented. The alloy was processed by four passes via equal channel angular pressing with an applied back pressure at a gradually decreasing temperature and analyzed using transmission electron microscopy techniques to observe the influence of processing on intermetallic particles. The results are compared with the initial state of the material prior to severe plastic deformation. The microstructural evolution of the α-Mg matrix and the Mg{sub 21}Zn{sub 25}, Mg{sub 51}Zn{sub 20} and MgZn{sub 2} was analyzed using bright field imaging, selectedmore » area electron diffraction, high-resolution transmission electron microscopy and high-angle annular dark field imaging in scanning mode. The plastic deformation process influenced the α-Mg matrix and each type of intermetallic particle. The α-Mg matrix consisted of two types of areas. The first type of area had a highly deformed structure, and the second type of area had a partially recrystallized structure with an average grain size of approximately 250 nm. The Mg{sub 21}Zn{sub 25} microparticles exhibited distinct forms in the α-Mg matrix that were characterized as a single-crystalline form, a nano-crystalline form and a broken up form. No evidence of Mg{sub 51}Zn{sub 20} nanoparticles within the α-Mg matrix was found in the microstructure, which indicates their dissolution or phase transformation during the deformation process. MgZn{sub 2} nanoparticles exhibited different behavior in both types of α-Mg matrix. Two orientation relationships toward the highly deformed α-Mg matrix were observed; however, there was no relationship toward the partially recrystallized α-Mg matrix. Additionally, the growth of the MgZn{sub 2} nanoparticles was different in the two types of α-Mg matrix. The Mg{sub 51}Zn{sub 20} nanoparticles inside Mg{sub 21}Zn{sub 25} microparticles exhibited a distinct behavior within the single-crystalline or nano-crystalline form of the parent Mg{sub 21}Zn{sub 25} microparticles. The Mg{sub 21}Zn{sub 25} + Mg{sub 51}Zn{sub 20} eutectic compound was confirmed for both forms of the parent Mg{sub 21}Zn{sub 25} microparticles, and the growth of Mg{sub 51}Zn{sub 20} nanoparticles is discussed. - Highlights: •Comprehensive microstructure characterization of Mg-12 wt.%Zn alloy after ECAP-BP •TEM analysis of changes of intermetallic phases caused by SPD •Mg{sub 21}Zn{sub 25} particles exhibit nano-crystalline regions with grain size below 100 nm. •MgZn{sub 2} preserved its orientation relationship toward highly deformed α-Mg after SPD. •Existence of Mg{sub 21}Zn{sub 25} + Mg{sub 51}Zn{sub 20} eutectic remained for each Mg{sub 21}Zn{sub 25} particle form.« less

The relationship between strain geometry and geometrically necessary dislocations

NASA Astrophysics Data System (ADS)

Hansen, Lars; Wallis, David

2016-04-01

The kinematics of past deformations are often a primary goal in structural analyses of strained rocks. Details of the strain geometry, in particular, can help distinguish hypotheses about large-scale tectonic phenomena. Microstructural indicators of strain geometry have been heavily utilized to investigate large-scale kinematics. However, many of the existing techniques require structures for which the initial morphology is known, and those structures must undergo the same deformation as imposed macroscopically. Many deformed rocks do not exhibit such convenient features, and therefore the strain geometry is often difficult (if not impossible) to ascertain. Alternatively, crystallographic textures contain information about the strain geometry, but the influence of strain geometry can be difficult to separate from other environmental factors that might affect slip system activity and therefore the textural evolution. Here we explore the ability for geometrically necessary dislocations to record information about the deformation geometry. It is well known that crystallographic slip due to the motion of dislocations yields macroscopic plastic strain, and the mathematics are established to relate dislocation glide on multiple slip systems to the strain tensor of a crystal. This theoretical description generally assumes that dislocations propagate across the entire crystal. However, at any point during the deformation, dislocations are present that have not fully transected the crystal, existing either as free dislocations or as dislocations organized into substructures like subgrain boundaries. These dislocations can remain in the lattice after deformation if the crystal is quenched sufficiently fast, and we hypothesize that this residual dislocation population can be linked to the plastic strain geometry in a quantitative manner. To test this hypothesis, we use high-resolution electron backscatter diffraction to measure lattice curvatures in experimentally deformed single crystals and aggregates of olivine for which the strain geometry is known. Tested geometries include constrictional strain, flattening strain, and plane strain. We use measured lattice curvatures to calculate the densities and spatial distributions of geometrically necessary dislocations. Dislocation densities are calculated for each of the major dislocation types in olivine. These densities are then used to estimate the plastic strain geometry under the assumption that the population of geometrically necessary dislocations accurately represents the relative activity of different dislocations during deformation. Our initial results demonstrate compelling relationships between the imposed strain geometry and the calculated plastic strain geometry. In addition, the calculated plastic strain geometry is linked to the distribution of crystallographic orientations, giving insight into the nature of plastic anisotropy in textured olivine aggregates. We present this technique as a new microstructural tool for assessing the kinematic history of deformed rocks.

Plastic Deformation of Micromachined Silicon Diaphragms with a Sealed Cavity at High Temperatures

PubMed Central

Ren, Juan; Ward, Michael; Kinnell, Peter; Craddock, Russell; Wei, Xueyong

2016-01-01

Single crystal silicon (SCS) diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. However, for harsh environments applications, pure silicon diaphragms are hardly used because of the deterioration of SCS in both electrical and mechanical properties. To survive at the elevated temperature, the silicon structures must work in combination with other advanced materials, such as silicon carbide (SiC) or silicon on insulator (SOI), for improved performance and reduced cost. Hence, in order to extend the operating temperatures of existing SCS microstructures, this work investigates the mechanical behavior of pressurized SCS diaphragms at high temperatures. A model was developed to predict the plastic deformation of SCS diaphragms and was verified by the experiments. The evolution of the deformation was obtained by studying the surface profiles at different anneal stages. The slow continuous deformation was considered as creep for the diaphragms with a radius of 2.5 mm at 600 °C. The occurrence of plastic deformation was successfully predicted by the model and was observed at the operating temperature of 800 °C and 900 °C, respectively. PMID:26861332

Design of an Orthodontic Torque Simulator for Measurement of Bracket Deformation

NASA Astrophysics Data System (ADS)

Melenka, G. W.; Nobes, D. S.; Major, P. W.; Carey, J. P.

2013-12-01

The design and testing of an orthodontic torque simulator that reproduces the effect of archwire rotation on orthodontic brackets is described. This unique device is capable of simultaneously measuring the deformation and loads applied to an orthodontic bracket due to archwire rotation. Archwire rotation is used by orthodontists to correct the inclination of teeth within the mouth. This orthodontic torque simulator will provide knowledge of the deformation and loads applied to orthodontic bracket that will aide clinicians by describing the effect of archwire rotation on brackets. This will also impact that design on new archwirebracket systems by providing an assessment of performance. Deformation of the orthodontic bracket tie wings is measured using a digital image correlation process to measure elastic and plastic deformation. The magnitude of force and moments applied to the bracket though the archwire is also measured using a six-axis load cell. Initial tests have been performed on two orthodontic brackets of varying geometry to demonstrate the measurement capability of the orthodontic torque simulator. The demonstration experiment shows that a Damon Q bracket had a final plastic deformation after a single loading of 0.022 mm while the Speed bracket deformed 0.071 mm. This indicates that the Speed bracket plastically deforms 3.2 times more than the Damon Q bracket for similar magnitude of applied moment. The demonstration experiment demonstrates that bracket geometry affect the deformation of orthodontic brackets and this difference can be detected using the orthodontic torque simulator.

Inelastic deformation and phenomenological modeling of aluminum including transient effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cho, C.W.

A review was made of several phenomenological theories which have recently been proposed to describe the inelastic deformation of crystalline solids. Hart's deformation theory has many advantages, but there are disagreements with experimental deformation at stress levels below yield. A new inelastic deformation theory was proposed, introducing the concept of microplasticity. The new model consists of five deformation elements: a friction element representing a deformation element controlled by dislocation glide, a nonrecoverable plastic element representing the dislocation leakage rate over the strong dislocation barriers, a microplastic element representing the dislocation leakage rate over the weak barriers, a short range anelasticmore » spring element representing the recoverable anelastic strain stored by piled-up dislocations against the weak barriers, and a long range anelastic spring element representing the recoverable strain stored by piled-up dislocations against the strong barriers. Load relaxation and tensile testing in the plastic range were used to determine the material parameters for the plastic friction elements. The short range and long range anelastic moduli and the material parameters for the kinetics of microplasticity were determined by the measurement of anelastic loops and by performing load relaxation tests in the microplastic region. Experimental results were compared with a computer simulation of the transient deformation behavior of commercial purity aluminum. An attempt was made to correlate the material parameters and the microstructure from TEM. Stability of material parameters during inelastic deformation was discussed and effect of metallurgical variables was examined experimentally. 71 figures, 5 tables.« less

Dynamic room temperature precipitation during cyclic deformation of an Al-Zn-Mg-Cu alloy

NASA Astrophysics Data System (ADS)

Hutchinson, C. R.; de Geuser, F.; Deschamps, A.

The effect of pre-straining on a precipitation heat treatment is a well-chartered area and is relevant to a number of Al alloy manufacturing processes. When straining and precipitation occur concurrently, the situation is less clear. This may arise during creep, fatigue or elevated temperature forming operations. Straining introduces dislocations and strain-induced vacancies that may enhance nucleation and growth processes but the dislocations may also shear and/or cause precipitate dissolution. This study reports a systematic characterization of precipitation during room temperature cyclic deformation of the AA7050 (Al-Zn-Mg-Cu) alloy. The mechanical response is monitored using plastic strain controlled cyclic deformation tests and the precipitation state is characterized using small angle x-ray scattering. It is shown that the precipitate volume fraction increases with the number of deformation cycles and is well correlated with the hardening increment observed but the mean precipitate radii remains relatively constant during cycling at 4-5A.

Modelling highly deformable metal extrusion using SPH

NASA Astrophysics Data System (ADS)

Prakash, Mahesh; Cleary, Paul W.

2015-05-01

Computational modelling is often used to reduce trial extrusions through accurate defect prediction. Traditionally, metal extrusion is modelled using mesh based finite element methods. However, large plastic deformations can lead to heavy re-meshing and numerical diffusion. Here we use the mesh-less smoothed particle hydrodynamics method since it allows simulation of large deformations without re-meshing and the tracking of history dependent properties such as plastic strain making it suitable for defect prediction. The variation in plastic strain and deformation for aluminium alloy in a cylindrical 3D geometry with extrusion ratio and die angle is evaluated. The extrusion process is found to have three distinct phases consisting of an initial sharp rise in extrusion force, a steady phase requiring constant force and terminating in a sharp decline in force as metal is completely extruded. Deformation and plastic strain increased significantly with extrusion ratio but only moderately with die angle. Extrusion force increased by 150 % as the extrusion ratio increased from 2:1 to 4:1 but had only a marginal change with die angle. A low strain zone in the centre of the extruded product was found to be a function of extrusion ratio but was persistent and did not vary with die angle. Simulation of a complex 3D building industry component showed large variations in plastic strain along the length of the product at two scales. These were due to change in metal behaviour as extrusion progressed from phase 1 to phase 2. A stagnation zone at the back of the die was predicted that could lead to the "funnel" or "pipe" defect.

The mechanics of solids in the plastically-deformable state

NASA Technical Reports Server (NTRS)

Mises, R. V.

1986-01-01

The mechanics of continua, which is based on the general stress model of Cauchy, up to the present has almost exclusively been applied to liquid and solid elastic bodies. Saint-Venant has developed a theory for the plastic or remaining form changes of solids, but it does not give the required number of equations for determining motion. A complete set of equations of motion for plastic deformable bodies is derived. This is done within the framework of Cauch mechanics. And it is supported by certain experimental facts which characterize the range of applications.

Modeling of surface effects in crystalline materials within the framework of gradient crystal plasticity

NASA Astrophysics Data System (ADS)

Peng, Xiang-Long; Husser, Edgar; Huang, Gan-Yun; Bargmann, Swantje

2018-03-01

A finite-deformation gradient crystal plasticity theory is developed, which takes into account the interaction between dislocations and surfaces. The model captures both energetic and dissipative effects for surfaces penetrable by dislocations. By taking advantage of the principle of virtual power, the surface microscopic boundary equations are obtained naturally. Surface equations govern surface yielding and hardening. A thin film under shear deformation serves as a benchmark problem for validation of the proposed model. It is found that both energetic and dissipative surface effects significantly affect the plastic behavior.

Size-dependent plastic deformation of twinned nanopillars in body-centered cubic tungsten

NASA Astrophysics Data System (ADS)

Xu, Shuozhi; Startt, Jacob K.; Payne, Thomas G.; Deo, Chaitanya S.; McDowell, David L.

2017-05-01

Compared with face-centered cubic metals, twinned nanopillars in body-centered cubic (BCC) systems are much less explored partly due to the more complicated plastic deformation behavior and a lack of reliable interatomic potentials for the latter. In this paper, the fault energies predicted by two semi-empirical interatomic potentials in BCC tungsten (W) are first benchmarked against density functional theory calculations. Then, the more accurate potential is employed in large scale molecular dynamics simulations of tensile and compressive loading of twinned nanopillars in BCC W with different cross sectional shapes and sizes. A single crystal, a twinned crystal, and single crystalline nanopillars are also studied as references. Analyses of the stress-strain response and defect nucleation reveal a strong tension-compression asymmetry and a weak pillar size dependence in the yield strength. Under both tensile and compressive loading, plastic deformation in the twinned nanopillars is dominated by dislocation slip on {110} planes that are nucleated from the intersections between the twin boundary and the pillar surface. It is also found that the cross sectional shape of nanopillars affects the strength and the initial site of defect nucleation but not the overall stress-strain response and plastic deformation behavior.

Quantitative Analyses of the Modes of Deformation in Engineering Thermoplastics

NASA Astrophysics Data System (ADS)

Landes, B. G.; Bubeck, R. A.; Scott, R. L.; Heaney, M. D.

1998-03-01

Synchrotron-based real-time small-angle X-ray scattering (RTSAXS) studies have been performed on rubber-toughened engineering thermoplastics with amorphous and semi-crystalline matrices. Scattering patterns are measured at successive time intervals of 3 ms were analyzed to determine the plastic strain due to crazing. Simultaneous measurements of the absorption of the primary beam by the sample permits the total plastic strain to be concurrently computed. The plastic strain due to other deformation mechanisms (e.g., particle cavitation and macroscopic shear yield can be determined from the difference between the total and craze-derived plastic strains. The contribution from macroscopic shear deformation can be determined from video-based optical data measured simultaneously with the X-ray data. These types of time-resolved experiments result in the generation of prodigious quantities of data, the analysis of which can considerably delay the determination of key results. A newly developed software package that runs in WINDOWSa 95 permits the rapid analysis of the relative contributions of the deformation modes from these time-resolved experiments. Examples of using these techniques on ABS-type and QUESTRAa syndiotactic polystyrene type engineering resins will be given.

Cell response to nanocrystallized metallic substrates obtained through severe plastic deformation.

PubMed

Bagherifard, Sara; Ghelichi, Ramin; Khademhosseini, Ali; Guagliano, Mario

2014-06-11

Cell-substrate interface is known to control the cell response and subsequent cell functions. Among the various biophysical signals, grain structure, which indicates the repeating arrangement of atoms in the material, has also proved to play a role of significant importance in mediating the cell activities. Moreover, refining the grain size through severe plastic deformation is known to provide the processed material with novel mechanical properties. The potential application of such advanced materials as biomedical implants has recently been evaluated by investigating the effect of different substrate grain sizes on a wide variety of cell activities. In this review, recent advances in biomedical applications of severe plastic deformation techniques are highlighted with special attention to the effect of the obtained nano/ultra-fine-grain size on cell-substrate interactions. Various severe plastic deformation techniques used for this purpose are discussed presenting a brief description of the mechanism for each process. The results obtained for each treatment on cell morphology, adhesion, proliferation, and differentiation, as well as the in vivo studies, are discussed. Finally, the advantages and challenges regarding the application of these techniques to produce multifunctional bio-implant materials are addressed.

Sessile dislocations by reactions in NiAl severely deformed at room temperature

DOE PAGES

Geist, D.; Gammer, C.; Rentenberger, C.; ...

2015-02-05

B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocationmore » reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.« less

The Surface Layer Mechanical Condition and Residual Stress Forming Model in Surface Plastic Deformation Process with the Hardened Body Effect Consideration

NASA Astrophysics Data System (ADS)

Mahalov, M. S.; Blumenstein, V. Yu

2017-10-01

The mechanical condition and residual stresses (RS) research and computational algorithms creation in complex types of loading on the product lifecycle stages relevance is shown. The mechanical state and RS forming finite element model at surface plastic deformation strengthening machining, including technological inheritance effect, is presented. A model feature is the production previous stages obtained transformation properties consideration, as well as these properties evolution during metal particles displacement through the deformation space in the present loading step.

The Special Features of the Deformation Behavior of an Ultrafine-Grained Aluminum Alloy of the Al-Mg-Li System at Room Temperature

NASA Astrophysics Data System (ADS)

Naydenkin, E. V.; Mishin, I. P.; Ivanov, K. V.

2015-04-01

The special features of the deformation behavior of an ultrafine-grained aluminum alloy produced by severe plastic deformation are investigated. Unlike ultrafine-grained pure aluminum, the second-phase particles precipitated in the bulk and at the grain boundaries of the alloy are shown to hinder the development of grain boundary sliding and plastic strain localization. This increases the length of the strain hardening stage and uniformity of elongation of a heterogeneous aluminum alloy specimen as compared to pure aluminum.

A Versatile Method for Nanostructuring Metals, Alloys and Metal Based Composites

NASA Astrophysics Data System (ADS)

Gurau, G.; Gurau, C.; Bujoreanu, L. G.; Sampath, V.

2017-06-01

A new severe plastic deformation method based on High Pressure Torsion is described. The method patented as High Speed High Pressure Torsion (HSHPT) shows a wide scope and excellent adaptability assuring large plastic deformation degree on metals, alloys even on hard to deform or brittle alloys. The paper present results obtained on aluminium, magnesium, titan, iron and coper alloys. In addition capability of HSHPT to process metallic composites is described. OM SEM, TEM, DSC, RDX and HV investigation methods were employed to confirm fine and ultrafine structure.

AFM study of the plastic deformation behavior of poly-synthetically-twinned (PST) titanium aluminide crystals

NASA Astrophysics Data System (ADS)

Chen, Yali

The plastic deformation behavior of PST TiAl crystals was investigated using AFM techniques to reveal the effects of lamellar structure on the deform mechanisms of two-phase TiAl materials. PST crystals with a nominal composition of Ti52Al48 (atomic percent) were grown by the floating zone method and at various orientations deformed in compression at room temperature. Atomic Force Microscopy (AFM) was employed to investigate the deformation structure on the free surfaces. The deformation of the PST crystals is highly anisotropic and the deformation mechanism changes dramatically with sample orientation. When the angle between the loading axis and the lamellar interfaces is below 20°, the gamma lamellae deform by dislocation slip and twinning on planes oblique to the lamellar interfaces, but the Burgers vectors or the resultant shear vectors are parallel to the lamellar interfaces inside each lamella. When the angle is between 20° and 80° the gamma phase deforms by shear on planes parallel to the lamellar interfaces. Some domains deform by a combination of ordinary dislocation slip and twinning. In the domains where twinning cannot be activated, slip occurs by ordinary dislocations or superdislocations. When the loading axis is nearly perpendicular to the lamellar interfaces ordinary dislocation slip and twinning on slip planes inclined with the lamellar interfaces are dominant and the shear is trans-lamellar. The three deformation modes are termed as A, B and N type deformation modes respectively. In the A type mode the alpha2 lamellae concomitantly deform by prismatic slip. In the other two modes, the alpha2 phase does not deform and acts as strong obstacles to the transfer of deformation. Abundant misfit dislocations are emitted from the lamellar interfaces which is beneficial for the plastic deformation. On the other hand, the lamellar interfaces strongly impede trans-lamellar deformation and channel the deformation inside each lamella. The inhomogeneous coherency stresses at the lamellar interfaces also lead to heterogeneous deformation of PST crystals. The deformation behavior of the lamellar grains produces remarkable strain incompatibility in lamellar polycrystals and deteriorates the deformability.

Comparison of dislocation density tensor fields derived from discrete dislocation dynamics and crystal plasticity simulations of torsion

DOE PAGES

Jones, Reese E.; Zimmerman, Jonathan A.; Po, Giacomo; ...

2016-02-01

Accurate simulation of the plastic deformation of ductile metals is important to the design of structures and components to performance and failure criteria. Many techniques exist that address the length scales relevant to deformation processes, including dislocation dynamics (DD), which models the interaction and evolution of discrete dislocation line segments, and crystal plasticity (CP), which incorporates the crystalline nature and restricted motion of dislocations into a higher scale continuous field framework. While these two methods are conceptually related, there have been only nominal efforts focused at the global material response that use DD-generated information to enhance the fidelity of CPmore » models. To ascertain to what degree the predictions of CP are consistent with those of DD, we compare their global and microstructural response in a number of deformation modes. After using nominally homogeneous compression and shear deformation dislocation dynamics simulations to calibrate crystal plasticity ow rule parameters, we compare not only the system-level stress-strain response of prismatic wires in torsion but also the resulting geometrically necessary dislocation density fields. To establish a connection between explicit description of dislocations and the continuum assumed with crystal plasticity simulations we ascertain the minimum length-scale at which meaningful dislocation density fields appear. Furthermore, our results show that, for the case of torsion, that the two material models can produce comparable spatial dislocation density distributions.« less

The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

NASA Astrophysics Data System (ADS)

Ji, L. K.; Xu, T.; Zhang, J. M.; Wang, H. T.; Tong, M. X.; Zhu, R. H.; Zhou, G. S.

2017-07-01

Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10-5, 1.25 × 10-4, 2.5 × 10-3, and 1.25 × 10-2 s-1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10-3 s-1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10-5 s-1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10-3 s-1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.

Analysis of Plastic Flow Instability During Superplastic Deformation of the Zn-Al Eutectoid Alloy Modified with 2 wt.% Cu

NASA Astrophysics Data System (ADS)

Ramos-Azpeitia, Mitsuo; Elizabeth Martínez-Flores, E.; Hernandez-Rivera, Jose Luis; Torres-Villaseñor, Gabriel

2017-11-01

The aim of this work is to analyze the plastic flow instability in Zn-21Al-2Cu alloy deformed under 10-3 s-1 and 513 K, which are optimum conditions for inducing superplastic behavior in this alloy. An evaluation using the Hart and Wilkinson-Caceres criteria showed that the limited stability of plastic flow observed in this alloy is related to low values of the strain-rate sensitivity index ( m) and the strain-hardening coefficient ( γ), combined with the tendency of these parameters to decrease depending on true strain ( ɛ). The reduction in m and γ values could be associated with the early onset of plastic instability and with microstructural changes observed as function of the strain. Grain growth induced by deformation seems to be important during the first stage of deformation of this alloy. However, when ɛ > 0.4 this growth is accompanied by other microstructural rearrangements. These results suggest that in this alloy, a grain boundary sliding mechanism acts to allow a steady superplastic flow only for ɛ < 0.4. For ɛ values between 0.4 and 0.7, observed occurrences of microstructural changes and severe neck formation lead to the supposition that there is a transition in the deformation mechanism. These changes are more evident when ɛ > 0.7 as another mechanism is thought to take over.

Studies of Point Defects and Defect Interactions in Metals Using Perturbed Gamma Gamma Angular Correlations

NASA Astrophysics Data System (ADS)

Shropshire, Steven Leslie

Point defects in plastically deformed Au, Pt, and Ni were studied with atomic-scale sensitivity using the perturbed gamma-gamma angular correlations (PAC) technique by monitoring formation and transformation of complexes of vacancy defects with very dilute ^{111}In/ ^{111}Cd solute probes. Three topics were investigated: (1) Production of vacancy defects during plastic deformation of Au was investigated to differentiate models of defect production. Concentrations of mono-, di-, and tri-vacancy species were measured in Au, and the ratio of mono- to di-vacancies was found to be independent of the amount of deformation. Results indicate that point defects are produced in correlated lattice locations, such as in "strings", as a consequence of dislocation interactions and not at random locations. (2) Hydrogen interactions with vacancy-solute complexes were studied in Pt. From thermal detrapping experiments, binding of hydrogen in complexes with mono-, di- and tri-vacancies was determined using a model for hydrogen diffusing in a medium with traps, with enthalpies all measured in the narrow range 0.23-0.28 eV, proving that the binding is insensitive to the precise structure of small vacancy clusters. Nuclear relaxation of the probe in a trivacancy complex in Pt was studied as a function of temperature, from which an activation energy of 0.34 eV was measured. This value is inconsistent with relaxation caused by diffusion or trapping of hydrogen, but explainable by dynamical hopping of the PAC probe atom in a cage of vacancies. (3) By observing transformations between vacancy-solute complexes induced by annihilation reactions, it was demonstrated that interstitials are produced during plastic deformation. The evolution of concentrations of the different vacancy complexes under an interstitial flux was measured and analyzed using a kinetic-rate model, from which interstitial capture cross-sections for the different vacancy complexes and the relative quantities of interstitial species in the flux were determined. Deformation of Au was found to produce only mono- and di-interstitial fluxes in a 1:2 ratio. Cross-sections increased rapidly with the number of vacancies, which is attributed to the amount of relaxation of lattice strains around solute-vacancy complexes.

On the indentation failure of carbon-epoxy cross-ply laminates, and its suppression by elasto-plastic interleaves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joergensen, O.; Horsewell, A.

1997-08-01

Elastic and elasto-plastic modelling of indentation in CFRP cross-ply laminates has been performed. Detailed knowledge of the field solutions in the volume below the indentor forms the basis for the reported micromechanical interpretation of the observed damage in test specimens. The analysis shows that matrix cracks originate at sites of maximum tensile stress perpendicular to fibers. The predicted stress fields due to indentation show that stress concentrations occur in the interface between alternating plies. It is found that microcracking in this zone is a precursor to the observed failure. This analysis is supported by in-situ scanning electron microscopy during loadingmore » by a cylindrical indentor onto the laminate supported on a rigid substrate. The microscopy reveals microdamage in the region of interfacial tensile stress concentrations. The onset of indentation failure in these layered composites suggests that plastic interleaves would delay failure. It is shown numerically that plastic deformation of the interleaves redistributes stresses and thereby weakens the tensile stress concentrations which arise during indentation. Experimentally it is shown that aluminium interleaves affect the formation of indentation failure. In a cross-ply laminate, where alternating ply groups are separated by aluminium sheets, matrix cracking and delamination failures are suppressed by the occurrence of plastic deformation. Since the aluminium is likely to be weakly bonded to the plies, it is seen that weak interlaminar fracture toughness does not necessarily cause delaminations, nor lead to a lower indentation strength. High indentation strength and delamination resistance are complex qualities which, among others, seem to be achieved in laminate geometries which have a minimum of stress concentration at interfaces between ply groups of different orientation.« less

Nature of the ``yield tooth'' under torsion in plastic-deformed whiskers

NASA Astrophysics Data System (ADS)

Bataronov, I. L.; Belikov, A. M.; Drozhzhin, A. I.; Roshchupkin, A. M.

1987-07-01

The plastic torsion of whiskers with high Peierls barriers has been studied. As the samples for the studies we chose p-type germanium whiskers with <111> growth axis. The diameter of the whisker was (5 60)·10-6 m and the gauge length was (1 4)·10-3 m. The whiskers were dislocation-free in the initial state. Within the framework of the continuum model developed by us for the plastic deformation of whiskers under torsion, we analyze the anomalies of the torsional stress-strain diagram under different testing conditions and with preliminary deformation. The “flow tooth” during the torsion of a whisker is attributable to the nonuniform distribution of dislocations over the cross section of the whisker and high barriers to the dislocation motion.

Segregation-Assisted Plasticity in Ni-Based Superalloys

NASA Astrophysics Data System (ADS)

Barba, D.; Smith, T. M.; Miao, J.; Mills, M. J.; Reed, R. C.

2018-03-01

Correlative high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy are used to study deformation-induced planar faults in the single-crystal superalloy MD2 crept at 800 °C and 650 MPa. Segregation of Cr and Co at microtwins, anti-phase boundaries (APB), and complex/superlattice extrinsic and intrinsic stacking faults (CESF/SESF and CISF/SISF) is confirmed and quantified. The extent of this is found to depend upon the fault type, being most pronounced for the APB. The CESF/SESF is studied in detail due to its role as a precursor of the microtwins causing the majority of plasticity under these conditions. Quantitative modeling is carried out to rationalize the findings; the experimental results are consistent with a greater predicted velocity for the lengthening of the CESF/SESF—compared with the other types of fault—and hence confirm its role in the diffusion-assisted plasticity needed for the microtwinning mechanism to be operative.

Atomic scale characterization of white etching area and its adjacent matrix in a martensitic 100Cr6 bearing steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y.J., E-mail: y.li@mpie.de

Atom probe tomography was employed to characterize the microstructure and C distribution in the white etching area (WEA) of a martensitic 100Cr6 bearing steel subjected to rolling contact fatigue. Different from its surrounding matrix where a plate-like martensitic structure prevails, the WEA exhibits equiaxed grains with a uniform grain size of about 10 nm. Significant C grain boundary enrichment (>7.5at.%) and an overall higher C concentration than the nominal value are observed in the WEA. These results suggest that the formation of WEA results from severe local plastic deformation that causes dissolution of carbides and the redistribution of C. -more » Highlights: •APT has been applied to characterize the microstructure of white etching area (WEA). •Quantitative analyses of C distribution indicate that carbides are dissolved on the WEA. •WEA contains equiaxed grains with a uniform grain size of 10 nm. •C segregation at grain boundaries stabilizes the nanosized grain structure. •Formation of WEA is explained by severe local plastic deformation introduced by cyclic contact loading.« less

The Correlation Between Dislocations and Vacancy Defects Using Positron Annihilation Spectroscopy

NASA Astrophysics Data System (ADS)

Pang, Jinbiao; Li, Hui; Zhou, Kai; Wang, Zhu

2012-07-01

An analysis program for positron annihilation lifetime spectra is only applicable to isolated defects, but is of no use in the presence of defective correlations. Such limitations have long caused problems for positron researchers in their studies of complicated defective systems. In order to solve this problem, we aim to take a semiconductor material, for example, to achieve a credible average lifetime of single crystal silicon under plastic deformation at different temperatures using positron life time spectroscopy. By establishing reasonable positron trapping models with defective correlations and sorting out four lifetime components with multiple parameters, as well as their respective intensities, information is obtained on the positron trapping centers, such as the positron trapping rates of defects, the density of the dislocation lines and correlation between the dislocation lines, and the vacancy defects, by fitting with the average lifetime with the aid of Matlab software. These results give strong grounds for the existence of dislocation-vacancy correlation in plastically deformed silicon, and lay a theoretical foundation for the analysis of positron lifetime spectra when the positron trapping model involves dislocation-related defects.

Influence of voids distribution on the deformation behavior of nanocrystalline palladium

NASA Astrophysics Data System (ADS)

Bachurin, D. V.

2018-07-01

Uniaxial deformation of three-dimensional nanocrystalline palladium containing porosity in the form of voids was investigated by means of molecular dynamics method. Simulations were performed at temperature of 300 K and at a constant strain rate of 108s-1. Two cases of voids distribution were considered: random and at triple or quadrupole junctions. It has been revealed that both the voids distribution and subsequent annealing at elevated temperature influence the deformation behavior of nanocrystalline palladium. In particular, the presence of voids at grain junctions results in a reduction of the Young's modulus and more pronounced softening effect during plastic deformation. The subsequent annealing evokes shrinkage of voids and strengthening effect. Contribution of grain boundary accommodation processes into both elastic and plastic deformation of nanocrystalline materials is discussed.

MAGNETIC MEASUREMENT OF THE PLASTIC STRESS-STRAIN CURVE OF MULTICRYSTALLINE NICKEL (in German)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwink, Ch.; Zankl, G.

1962-01-01

Ballistic measurements of the coercive force H/sub c/ and the initial permeability mu /sub alpha / were made on nlckel wires, and their dependence on plastic tensile deformation was followed. The results are shown graphically. H/ sub c/ and 1/ mu /sub alpha / start to increase at a given tensile stress with the introduction of plastic expansion and increases almost linearly with the tensile stress applied. At a tensile stress of 7.2 plus or minus 0.5 kp/mm/sup 2/ both curves have noticable bends. The bend point is related by a special process to the plastic deformation of the multicrystallinemore » material. (J.S.R.)« less

Some aspects of the stability of the plane deformation mode of filaments of finite stiffness beyond the elasticity limits

NASA Astrophysics Data System (ADS)

Shimanovskii, A. V.

A method for calculating the plane bending of elastic-plastic filaments of finite stiffness is proposed on the basis of plastic flow theory. The problem considered is shown to reduce to relations similar to Kirchhoff equations for elastic work. Expressions are obtained for determining the normalized stiffness characteristics for the cross section of a filament with plastic regions containing beam theory equations as a particular case. A study is made of the effect of the plastic region size on the position of the elastic deformation-unloading interface and on the normalized stiffness of the filament cross section. Calculation results are presented in graphic form.

Finite element solutions for crack-tip behavior in small-scale yielding

NASA Technical Reports Server (NTRS)

Tracey, D. M.

1976-01-01

The subject considered is the stress and deformation fields in a cracked elastic-plastic power law hardening material under plane strain tensile loading. An incremental plasticity finite element formulation is developed for accurate analysis of the complete field problem including the extensively deformed near tip region, the elastic-plastic region, and the remote elastic region. The formulation has general applicability and was used to solve the small scale yielding problem for a set of material hardening exponents. Distributions of stress, strain, and crack opening displacement at the crack tip and through the elastic-plastic zone are presented as a function of the elastic stress intensity factor and material properties.

Treatment of plastic deformation of the forearm in young adults with double-level osteotomies: case reports.

PubMed

Moon, Edward S; Howlett, John; Wiater, Brett P; Trumble, Thomas E

2011-04-01

Plastic deformation of the forearm is a rare injury in young adults that occurs when a slow bending or rotational force is applied to the arm, most commonly in the setting of an industrial workplace accident. There are currently no guidelines for treatment of the residual forearm deformity that often results in limitations of forearm supination and pronation. We present 2 cases demonstrating that deformity correction with single cortex, double-level osteotomies combined with rigid plate fixation and early range of motion exercise that results in good functional outcomes. Copyright © 2011 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Insights from the Lattice-Strain Evolution on Deformation Mechanisms in Metallic-Glass-Matrix Composites

DOE PAGES

Jia, Haoling; Zheng, Lili; Li, Weidong; ...

2015-02-18

In this paper, in situ high-energy synchrotron X-ray diffraction experiments and micromechanics-based finite element simulations have been conducted to examine the lattice-strain evolution in metallic-glass-matrix composites (MGMCs) with dendritic crystalline phases dispersed in the metallic-glass matrix. Significant plastic deformation can be observed prior to failure from the macroscopic stress–strain curves in these MGMCs. The entire lattice-strain evolution curves can be divided into elastic–elastic (denoting deformation behavior of matrix and inclusion, respectively), elastic–plastic, and plastic–plastic stages. Characteristics of these three stages are governed by the constitutive laws of the two phases (modeled by free-volume theory and crystal plasticity) and geometric informationmore » (crystalline phase morphology and distribution). The load-partitioning mechanisms have been revealed among various crystalline orientations and between the two phases, as determined by slip strain fields in crystalline phase and by strain localizations in matrix. Finally, implications on ductility enhancement of MGMCs are also discussed.« less

Evolution of plastic deformation and its effect on mechanical properties of laser additive repaired Ti64ELI titanium alloy

NASA Astrophysics Data System (ADS)

Zhao, Zhuang; Chen, Jing; Tan, Hua; Lin, Xin; Huang, Weidong

2017-07-01

In this paper, laser additive manufacturing (LAM) technology with powder feeding has been employed to fabricate 50%LAMed specimens (i.e. the volume fraction of the laser deposited zone was set to 50%). With aid of the 3D-DIC technique, the tensile deformation behavior of 50%LAMed Ti64ELI titanium alloy was investigated. The 50%LAMed specimen exhibits a significant characteristic of strength mismatch due to the heterogeneous microstructure. The tensile fracture of 50%LAMed specimen occurs in WSZ (wrought substrate zone), but the tensile strength is slightly higher and the plastic elongation is significantly lower than that of the wrought specimen. The 3D-DIC results shows that the 50%LAMed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and the maximal strain is invariably concentrated in WSZ. The ABAQUS simulation indicates that, the LDZ (laser deposited zone) can constrain the plastic deformation of the WSZ and biaxial stresses develop at the interface after yielding.

Microstructural evolution of bainitic steel severely deformed by equal channel angular pressing.

PubMed

Nili-Ahmadabadi, M; Haji Akbari, F; Rad, F; Karimi, Z; Iranpour, M; Poorganji, B; Furuhara, T

2010-09-01

High Si bainitic steel has been received much of interest because of combined ultra high strength, good ductility along with high wear resistance. In this study a high Si bainitic steel (Fe-0.22C-2.0Si-3.0Mn) was used with a proper microstructure which could endure severe plastic deformation. In order to study the effect of severe plastic deformation on the microstructure and properties of bainitic steel, Equal Channel Angular Pressing was performed in two passes at room temperature. Optical, SEM and TEM microscopies were used to examine the microstructure of specimens before and after Equal Channel Angular Pressing processing. X-ray diffraction was used to measure retained austenite after austempering and Equal Channel Angular Pressing processing. It can be seen that retained austenite picks had removed after Equal Channel Angular Pressing which could attributed to the transformation of austenite to martensite during severe plastic deformation. Enhancement of hardness values by number of Equal Channel Angular Pressing confirms this idea.

Parameter determination of hereditary models of deformation of composite materials based on identification method

NASA Astrophysics Data System (ADS)

Kayumov, R. A.; Muhamedova, I. Z.; Tazyukov, B. F.; Shakirzjanov, F. R.

2018-03-01

In this paper, based on the analysis of some experimental data, a study and selection of hereditary models of deformation of reinforced polymeric composite materials, such as organic plastic, carbon plastic and a matrix of film-fabric composite, was pursued. On the basis of an analysis of a series of experiments it has been established that organo-plastic samples behave like viscoelastic bodies. It is shown that for sufficiently large load levels, the behavior of the material in question should be described by the relations of the nonlinear theory of heredity. An attempt to describe the process of deformation by means of linear relations of the theory of heredity leads to large discrepancies between the experimental and calculated deformation values. The use of the theory of accumulation of micro-damages leads to much better description of the experimental results. With the help of the hierarchical approach, a good approximation of the experimental values was successful only in the first three sections of loading.

A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal–metal composites

DOE PAGES

Tian, Liang; Russell, Alan; Anderson, Iver

2014-01-03

Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts themore » strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.« less

Multiple deformation mechanisms operating at seismogenic depths: Tectonic pseudotachylyte and associated deformation from the central Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Prante, M. R.; Evans, J. P.

2012-12-01

Description and identification of fault-related deformation products that are diagnostic of seismic slip have implications for the energy budget of earthquakes, fault strength, and fault-rock assemblages. We describe tectonic pseduotachylyte, cataclastic rocks, crystal-plastic deformation, and hydrothermal alteration form faults exhumed from seismogenic depths in the Volcanic Lakes area, in northern Sequoia and Kings Canyon National Park, CA, USA. Fault rock protoliths include Mesozoic granite and granodiorite plutonic and limited metasedimentary and metavolcanic rocks. These plutonic and metamorphic rocks are cross-cut by the E-W striking, steeply dipping, left-lateral strike-slip Granite Pass (GPF) and Glacier Lakes faults (GLF). Cross-cutting relationships and microstructural data suggest that the GPF is the oldest fault in the area and preserves evidence for coeval brittle and plastic crystal deformation, and hydrothermal fluid-flow. Tectonic pseudotachylyte from the area has been dated using the 40Ar/39Ar method at 76.6 ± 0.3 Ma; when placed into a thermochronologic framework for the plutonic host rock it can be inferred that the pseudotachylyte formed at depths between 2.4-6.0 km with ambient temperatures between 110-160°C. Exceptionally well preserved tectonic pseudotachylyte from the GLF and GPF contain evidence for a frictional melt origin including: 1) plagioclase spherulites and microlites, 2) injection vein morphology, 3) amygdules, 4) viscous flow banding and folds, and 5) embayed and corroded clasts. Pseudotachylyte from the GPF and GLF is associated with brittle and plastic deformation in the damage zone of the faults. Evidence for plastic deformation includes undulose extinction, deformation lamellae, subgrain development, and grain boundary bulging in quartz; and limited undulose extinction in feldspar. Additionally, abundant hydrothermal alteration and mineralization has been documented in the GPF and GLF fault zones, including, chlorite pseudomorphs after biotite and alteration of mafic phases to epidote, sericite and calcite alteration of albite, and calcite and chlorite filled veins. Cross-cutting calcite veins contain fine-grained calcite with abundant twins up to 20 μm-thick. Multiple pseudotachylyte injection veins and reworked pseudotachylyte in cataclastic rock suggest multiple earthquakes along the GPF and GLF at depths favorable to pseudotachylyte formation. Abundant hydrothermal alteration and cross-cutting calcite veins with thick (> 1 μm) twins is consistent with ambient temperatures between 170 and 200°C. These temperatures are generally consistent with the reported ambient temperature conditions during pseudotachylyte formation. Crystal-plastic deformation of quartz and feldspar in the GPF and GLF zones is consistent with deformation at temperatures between 200-400°C. Frictional melt and associated brittle and plastic deformation, and fluid alteration are presumed to have occurred at similar temperature conditions and may be coeval. These results have important implication for understanding energy sinks associated with seismic slip and the conditions of tectonic pseudotachylyte formation.

Simulation study of the effect of strain rate on the mechanical properties and tensile deformation of gold nanowire

NASA Astrophysics Data System (ADS)

Shi, Guo-Jie; Wang, Jin-Guo; Hou, Zhao-Yang; Wang, Zhen; Liu, Rang-Su

2017-09-01

The mechanical properties and deformation mechanisms of Au nanowire during the tensile processes at different strain rates are revealed by the molecular dynamics method. It is found that the Au nanowire displays three distinct types of mechanical behaviors when tensioning at low, medium and high strain rates, respectively. At the low strain rate, the stress-strain curve displays a periodic zigzag increase-decrease feature, and the plastic deformation is resulted from the slide of dislocation. The dislocations nucleate, propagate, and finally annihilate in every decreasing stages of stress, and the nanowire always can recover to FCC-ordered structure. At the medium strain rate, the stress-strain curve gently decreases during the plastic process, and the deformation is contributed from sliding and twinning. The dislocations formed in the yield stage do not fully propagate and further escape from the nanowire. At the high strain rate, the stress-strain curve wave-like oscillates during the plastic process, and the deformation is resulted from amorphization. The FCC atoms quickly transform into disordered amorphous structure in the yield stage. The relative magnitude between the loading velocity of strain and the propagation velocity of phonons determines the different deformation mechanisms. The mechanical behavior of Au nanowire is similar to Ni, Cu and Pt nanowires, but their deformation mechanisms are not completely identical with each other.

Modeling elasto-viscoplasticity in a consistent phase field framework

DOE PAGES

Cheng, Tian -Le; Wen, You -Hai; Hawk, Jeffrey A.

2017-05-19

Existing continuum level phase field plasticity theories seek to solve plastic strain by minimizing the shear strain energy. However, rigorously speaking, for thermodynamic consistency it is required to minimize the total strain energy unless there is proof that hydrostatic strain energy is independent of plastic strain which is unfortunately absent. In this work, we extend the phase-field microelasticity theory of Khachaturyan et al. by minimizing the total elastic energy with constraint of incompressibility of plastic strain. We show that the flow rules derived from the Ginzburg-Landau type kinetic equation can be in line with Odqvist's law for viscoplasticity and Prandtl-Reussmore » theory. Free surfaces (external surfaces or internal cracks/voids) are treated in the model. Deformation caused by a misfitting spherical precipitate in an elasto-plastic matrix is studied by large-scale three-dimensional simulations in four different regimes in terms of the matrix: (a) elasto-perfectly-plastic, (b) elastoplastic with linear hardening, (c) elastoplastic with power-law hardening, and (d) elasto-perfectly-plastic with a free surface. The results are compared with analytical/numerical solutions of Lee et al. for (a-c) and analytical solution derived in this work for (d). Additionally, the J integral of a fixed crack is calculated in the phase-field model and discussed in the context of fracture mechanics.« less

Modeling elasto-viscoplasticity in a consistent phase field framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Tian -Le; Wen, You -Hai; Hawk, Jeffrey A.

Existing continuum level phase field plasticity theories seek to solve plastic strain by minimizing the shear strain energy. However, rigorously speaking, for thermodynamic consistency it is required to minimize the total strain energy unless there is proof that hydrostatic strain energy is independent of plastic strain which is unfortunately absent. In this work, we extend the phase-field microelasticity theory of Khachaturyan et al. by minimizing the total elastic energy with constraint of incompressibility of plastic strain. We show that the flow rules derived from the Ginzburg-Landau type kinetic equation can be in line with Odqvist's law for viscoplasticity and Prandtl-Reussmore » theory. Free surfaces (external surfaces or internal cracks/voids) are treated in the model. Deformation caused by a misfitting spherical precipitate in an elasto-plastic matrix is studied by large-scale three-dimensional simulations in four different regimes in terms of the matrix: (a) elasto-perfectly-plastic, (b) elastoplastic with linear hardening, (c) elastoplastic with power-law hardening, and (d) elasto-perfectly-plastic with a free surface. The results are compared with analytical/numerical solutions of Lee et al. for (a-c) and analytical solution derived in this work for (d). Additionally, the J integral of a fixed crack is calculated in the phase-field model and discussed in the context of fracture mechanics.« less

Mechanical and time-dependent behavior of wood-plastic composites subjected to tension and compression

Treesearch

Scott E. Hamel; John C. Hermanson; Steven M. Cramer

2012-01-01

The thermoplastics within wood—plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the...

Effect of hot plastic deformation on the structural state of a Al-10%SiC composite

NASA Astrophysics Data System (ADS)

Pugacheva, N. B.; Vichuzhanin, D. I.; Michurov, N. S.; Smirnov, A. S.

2017-12-01

The paper studies the microstructure of honeycomb aluminum matrix composites with a granulated Al-Zn-Cu-Mg alloy matrix filled SiC particles amounting to 10 vol % after hot plastic deformation at near-solidus temperatures. It demonstrates the possibility of the collapse of the SiC filler network and the formation of filler clusters separated from each other.

Estimation Model for Magnetic Properties of Stamped Electrical Steel Sheet

NASA Astrophysics Data System (ADS)

Kashiwara, Yoshiyuki; Fujimura, Hiroshi; Okamura, Kazuo; Imanishi, Kenji; Yashiki, Hiroyoshi

Less deterioration in magnetic properties of electrical steel sheets in the process of stamping out iron-core are necessary in order to maintain its performance. First, the influence of plastic strain and stress on magnetic properties was studied by test pieces, in which plastic strain was added uniformly and residual stress was not induced. Because the influence of plastic strain was expressed by equivalent plastic strain, at each equivalent plastic strain state the influence of load stress was investigated. Secondly, elastic limit was determined about 60% of macroscopic yield point (MYP), and it was found to agree with stress limit inducing irreversible deterioration in magnetic properties. Therefore simulation models, where beyond elastic limit plastic deformation begins and magnetic properties are deteriorated steeply, are proposed. Besides considered points in the deformation analysis are strain-rate sensitivity of flow stress, anisotropy under deformation, and influence of stress triaxiality on fracture. Finally, proposed models have been shown to be valid, because magnetic properties of 5mm width rectangular sheets stamped out from non-oriented electrical steel sheet (35A250 JIS grade) can be estimated with good accuracy. It is concluded that the elastic limit must be taken into account in both stamping process simulation and magnetic field calculation.

Influence of deformation on structural-phase state of weld material in St3 steel

NASA Astrophysics Data System (ADS)

Smirnov, Alexander; Kozlov, Eduard; Ababkov, Nicolay; Popova, Natalya; Nikonenko, Elena; Ozhiganov, Yevgeniy; Zboykova, Nadezhda; Koneva, Nina

2016-01-01

The structural-phase condition of the weld material subjected to the plastic deformation was investigated using the translucent diffraction electron microscopy method. The investigations were carried out near the joint of the weld and the base metal. The seam was done by the method of manual arc welding without artificial defects. The St3 steel was taken as the welded material. Influence of the plastic deformation on morphology, phase composition, defect structure and its parameters of weld metal was revealed. All investigations were done at the distance of 0.5 mm from the joint of the weld and the base metal at the deformation degrees from 0 to 5% and after destruction of a sample. It was established that deformation of the sample did not lead to qualitative changes in the structure (the structure is still presented by ferrite-pearlite mixture) but changed the quantitative parameters of the structure, namely, with the increase of plastic deformation a part of the pearlite component becomes more and more imperfect. In the beginning it turns into the destroyed pearlite then into ferrite, the volume fraction of pearlite is decreased. The polarization of dislocation structure takes place but it doesn't lead to the internal stresses that can destroy the sample.

Rheology of the lithosphere and the folding caused by horizontal compression

NASA Astrophysics Data System (ADS)

Birger, B. I.

2015-05-01

The laboratory tests of rock specimens show that transient creep, at which deformations increase with time whereas strain rate decreases occurs when creep strains are sufficiently small. Since plate tectonics only permits small deformations in the lithospheric plates, the creep of the lithosphere is transient (non-steady-state). In this work, we study how the rheology of the lithosphere that possesses elasticity, brittleness (pseudo-plasticity), and creep affects the folding in the Earth's crust. Folding is caused by horizontal compression that results from the collision between the lithospheric plates. The effective viscosity characterizing the transient creep is lower than in the case of a steady-state creep and depends on the characteristic time of the considered process. The allowance for transient creep gives the distribution of the rheological properties of the horizontally compressed lithosphere in which the upper crust is brittle, whereas the lower crust and mantle lithosphere are dominated by transient creep. It is shown that the flows that arise in the lithosphere due to the instability under horizontal compression and cause folding are small-scale. These flows are concentrated in the upper brittle crust, they determine the short-wave Earth's surface topography, penetrate into the lower, creep-dominated crust to a shallow depth, and do not penetrate into the mantle. Therefore, these flows do not deform the Moho.

Rock Failure Analysis Based on a Coupled Elastoplastic-Logarithmic Damage Model

NASA Astrophysics Data System (ADS)

Abdia, M.; Molladavoodi, H.; Salarirad, H.

2017-12-01

The rock materials surrounding the underground excavations typically demonstrate nonlinear mechanical response and irreversible behavior in particular under high in-situ stress states. The dominant causes of irreversible behavior are plastic flow and damage process. The plastic flow is controlled by the presence of local shear stresses which cause the frictional sliding. During this process, the net number of bonds remains unchanged practically. The overall macroscopic consequence of plastic flow is that the elastic properties (e.g. the stiffness of the material) are insensitive to this type of irreversible change. The main cause of irreversible changes in quasi-brittle materials such as rock is the damage process occurring within the material. From a microscopic viewpoint, damage initiates with the nucleation and growth of microcracks. When the microcracks length reaches a critical value, the coalescence of them occurs and finally, the localized meso-cracks appear. The macroscopic and phenomenological consequence of damage process is stiffness degradation, dilatation and softening response. In this paper, a coupled elastoplastic-logarithmic damage model was used to simulate the irreversible deformations and stiffness degradation of rock materials under loading. In this model, damage evolution & plastic flow rules were formulated in the framework of irreversible thermodynamics principles. To take into account the stiffness degradation and softening on post-peak region, logarithmic damage variable was implemented. Also, a plastic model with Drucker-Prager yield function was used to model plastic strains. Then, an algorithm was proposed to calculate the numerical steps based on the proposed coupled plastic and damage constitutive model. The developed model has been programmed in VC++ environment. Then, it was used as a separate and new constitutive model in DEM code (UDEC). Finally, the experimental Oolitic limestone rock behavior was simulated based on the developed model. The irreversible strains, softening and stiffness degradation were reproduced in the numerical results. Furthermore, the confinement pressure dependency of rock behavior was simulated in according to experimental observations.

Macroscopic tensile plasticity by scalarizating stress distribution in bulk metallic glass

PubMed Central

Gao, Meng; Dong, Jie; Huan, Yong; Wang, Yong Tian; Wang, Wei-Hua

2016-01-01

The macroscopic tensile plasticity of bulk metallic glasses (BMGs) is highly desirable for various engineering applications. However, upon yielding, plastic deformation of BMGs is highly localized into narrow shear bands and then leads to the “work softening” behaviors and subsequently catastrophic fracture, which is the major obstacle for their structural applications. Here we report that macroscopic tensile plasticity in BMG can be obtained by designing surface pore distribution using laser surface texturing. The surface pore array by design creates a complex stress field compared to the uniaxial tensile stress field of conventional glassy specimens, and the stress field scalarization induces the unusual tensile plasticity. By systematically analyzing fracture behaviors and finite element simulation, we show that the stress field scalarization can resist the main shear band propagation and promote the formation of larger plastic zones near the pores, which undertake the homogeneous tensile plasticity. These results might give enlightenment for understanding the deformation mechanism and for further improvement of the mechanical performance of metallic glasses. PMID:26902264

Strain rate dependent calcite microfabric evolution - An experiment carried out by nature

NASA Astrophysics Data System (ADS)

Rogowitz, Anna; Grasemann, Bernhard; Huet, Benjamin; Habler, Gerlinde

2014-12-01

A flanking structure developed along a secondary shear zone in calcite marbles, on Syros (Cyclades, Greece), provides a natural laboratory for directly studying the effects of strain rate variations on calcite deformation at identical pressure and temperature conditions. The presence and rotation of a fracture during progressive deformation caused extreme variations in finite strain and strain rate, forming a localized ductile shear zone that shows different microstructures and textures. Textures and the degree of intracrystalline deformation were measured by electron backscattered diffraction. Marbles from the host rocks and the shear zone, which deformed at various strain rates, display crystal-preferred orientation, suggesting that the calcite preferentially deformed by intracrystalline-plastic deformation. Increasing strain rate results in a switch from subgrain rotation to bulging recrystallization in the dislocation-creep regime. With increasing strain rate, we observe in fine-grained (3 μm) ultramylonitic zones a change in deformation regime from grain-size insensitive to grain-size sensitive. Paleowattmeter and the paleopiezometer suggest strain rates for the localized shear zone around 10-10 s-1 and for the marble host rock around 10-12 s-1. We conclude that varying natural strain rates can have a first-order effect on the microstructures and textures that developed under the same metamorphic conditions.

EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nanstad, Randy K; Sokolov, Mikhail A; Merkle, John Graham

2007-01-01

To enable determination of the fracture toughness reference temperature, T0, with reactor pressure vessel surveillance specimens, the precracked Charpy (PCVN) three-point bend, SE(B), specimen is of interest. Compared with the 25-mm (1 in.) thick compact, 1TC(T), specimen, tests with the PCVN specimen (10x10x55 mm) have resulted in T0 temperatures as much as 40 XC lower (a so-called specimen bias effect). The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory developed a two-part project to evaluate the C(T) versus PCVN differences, (1) calibration experiments concentrating on test practices, and (2) a matrix of transition range tests with various specimenmore » geometries and sizes, including 1T SE(B) and 1TC(T). The test material selected was a plate of A533 grade B class 1 steel. The calibration experiments included assessment of the computational validity of J-integral determinations, while the constraint characteristics of various specimen types and sizes were evaluated using key curves and notch strength determinations. The results indicate that J-integral solutions for the small PCVN specimen are comparable in terms of J-integral validity with 1T bend specimens. Regarding constraint evaluations, Phase I deformation is defined where plastic deformation is confined to crack tip plastic zone development, whereas Phase II deformation is defined where plastic hinging deformation develops. In Phase II deformation, the 0.5T SE(B) B B specimen (slightly larger than the PCVN specimen) consistently showed the highest constraint of all SE(B) specimens evaluated for constraint comparisons. The PCVN specimen begins the Phase II type of deformation at relatively low KR levels, with the result that KJc values above about 70 MPa m from precracked Charpy specimens are under extensive plastic hinging deformation.« less

Effect of material inhomogeneity on the cyclic plastic deformation behavior at the microstructural level: micromechanics-based modeling of dual-phase steel

NASA Astrophysics Data System (ADS)

Paul, Surajit Kumar

2013-07-01

The microstructure of dual-phase (DP) steels typically consists of a soft ferrite matrix with dispersed islands of hard martensite phase. Due to the composite effect of ferrite and martensite, DP steels exhibit a unique combination of strain hardening, strength and ductility. A microstructure-based micromechanical modeling approach is adopted in this work to capture the tensile and cyclic plastic deformation behavior of DP steel. During tensile straining, strain incompatibility between the softer ferrite matrix and the harder martensite phase arises due to a difference in the flow characteristics of these two phases. Microstructural-level inhomogeneity serves as the initial imperfection, triggering strain incompatibility, strain partitioning and finally shear band localization during tensile straining. The local deformation in the ferrite phase is constrained by adjacent martensite islands, which locally results in stress triaxiality development in the ferrite phase. As the martensite distribution varies within the microstructure, the stress triaxiality also varies in a band within the microstructure. Inhomogeneous stress and strain distribution within the softer ferrite phase arises even during small tensile straining because of material inhomogeneity. The magnitude of cyclic plastic deformation within the softer ferrite phase also varies according to the stress distribution in the first-quarter cycle tensile loading. Accumulation of tensile/compressive plastic strain with number of cycles is noted in different locations within the ferrite phase during both symmetric stress and strain controlled cycling. The basic mode of cyclic plastic deformation in an inhomogeneous material is cyclic strain accumulation, i.e. ratcheting. Microstructural inhomogeneity results in cyclic strain accumulation in the aggregate DP material even in symmetric stress cycling.

The effect of hydrogen on the parameters of plastic deformation localization in low carbon steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lunev, Aleksey G., E-mail: agl@ispms.tsc.ru, E-mail: nadjozhkin@ispms.tsc.ru; Nadezhkin, Mikhail V., E-mail: agl@ispms.tsc.ru, E-mail: nadjozhkin@ispms.tsc.ru; Shlyakhova, Galina V., E-mail: shgv@ispms.tsc.ru

2014-11-14

In the present study, the effect of interstitial hydrogen atoms on the mechanical properties and plastic strain localization patterns in tensile tested polycrystals of low-carbon steel Fe-0.07%C has been studied using double exposure speckle photography technique. The main parameters of plastic flow localization at various stages of deformation hardening have been determined in polycrystals of steel electrolytically saturated with hydrogen in a three-electrode electrochemical cell at a controlled constant cathode potential. Also, the effect of hydrogen on changing of microstructure by using optical microscopy has been demonstrated.

Nanosized carbon modifier used to control plastic deformations of asphalt concrete

NASA Astrophysics Data System (ADS)

Vysotskaya, M. A.; Shekhovtsova, S. Yu; Barkovsky, D. V.

2018-03-01

Aspects related to plastic track, the formation of which directly depends on the properties of the binder in the composition of asphalt concrete, are considered in this article. The effect of primary carbon nanomaterials on the quality of polymer and bitumen binder in comparison with the traditional binder including cross-linking agent is evaluated. The influence of binders on the resistance to the track formation of type B asphalt concrete is studied. To quantify the service life of surfacing, a calculation method based on the criteria for the resistance of surfacing material to plastic deformations is used.

Correlation between elastic and plastic deformations of partially cured epoxy networks

NASA Astrophysics Data System (ADS)

Müller, Michael; Böhm, Robert; Geller, Sirko; Kupfer, Robert; Jäger, Hubert; Gude, Maik

2018-05-01

The thermo-mechanical behavior of polymer matrix materials is strongly dependent on the curing reaction as well as temperature and time. To date, investigations of epoxy resins and their composites mainly focused on the elastic domain because plastic deformation of cross-linked polymer networks was considered as irrelevant or not feasible. This paper presents a novel approach which combines both elastic and plastic domain. Based on an analytical framework describing the storage modulus, analogous parameter combinations are defined in order to reduce complexity when variations in temperature, strain rate and degree of cure are encountered.

Detection of plasticity mechanisms in an energetic molecular crystal through shock-like 3D unidirectional compressions: A Molecular Dynamics study

NASA Astrophysics Data System (ADS)

Lafourcade, Paul; Denoual, Christophe; Maillet, Jean-Bernard

2017-06-01

TATB crystal structure consists in graphitic-like sheets arranged in the a-b plane where a, b and c define the edge vectors of the unit cell. This type of stacking provides the TATB monocrystal very anisotropic physical, chemical and mechanical properties. In order to explore which mechanisms are involved in TATB plasticity, we use a Molecular Dynamics code in which the overall deformation is prescribed as a function of time, for any deformation path. Furthermore, a computation of the Green-Lagrange strain tensor is proposed, which helps reveal various defects and plasticity mechanisms. Through prescribed large strain of shock-like deformations, a three-dimensional characterization of TATB monocrystal yield stress has been obtained, confirming the very anisotropic behavior of this energetic material. Various plasticity mechanisms are triggered during these simulations, including counter intuitive defects onset such as gliding along transveral planes containing perfect dislocations and twinning. Gliding in the a-b plane occurs systematically and does not lead to significant plastic behavior, in accordance with a previous study on dislocation core structures for this plane, based on a coupling between the Peierls-Nabarro-Galerkin method and Molecular Dynamics simulations.

Crystal plasticity assisted prediction on the yield locus evolution and forming limit curves

NASA Astrophysics Data System (ADS)

Lian, Junhe; Liu, Wenqi; Shen, Fuhui; Münstermann, Sebastian

2017-10-01

The aim of this study is to predict the plastic anisotropy evolution and its associated forming limit curves of bcc steels purely based on their microstructural features by establishing an integrated multiscale modelling approach. Crystal plasticity models are employed to describe the micro deformation mechanism and correlate the microstructure with mechanical behaviour on micro and mesoscale. Virtual laboratory is performed considering the statistical information of the microstructure, which serves as the input for the phenomenological plasticity model on the macroscale. For both scales, the microstructure evolution induced evolving features, such as the anisotropic hardening, r-value and yield locus evolution are seamlessly integrated. The predicted plasticity behaviour by the numerical simulations are compared with experiments. These evolutionary features of the material deformation behaviour are eventually considered for the prediction of formability.

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Moore, John A.; Barton, Nathan R.; Florando, Jeff; Mulay, Rupalee; Kumar, Mukul

2017-10-01

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material’s structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V’s mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments or lower fidelity models. The results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.

The influence of severe plastic deformation by high pressure torsion on structure and mechanical properties of Hadfield steel single crystals

NASA Astrophysics Data System (ADS)

Zakharova, G. G.; Astafurova, E. G.

2010-07-01

Hadfield steel single crystals have been deformed by high pressure torsion at room temperature (P=5GPa) for 1, 2, 3 revolutions. The resulting microstructure has been studied by means of transmission electron microscopy (TEM) and X-ray analysis. The size of fragments decreases with increasing number of revolutions due to interaction of slip dislocations, microbands and thin twins. As a result of severe plastic deformation, the microhardness of the Hadfield steel has been increased, and a portion of epsilon, α' martensite has been found.

Electromigration-induced plastic deformation in passivated metal lines

NASA Astrophysics Data System (ADS)

Valek, B. C.; Bravman, J. C.; Tamura, N.; MacDowell, A. A.; Celestre, R. S.; Padmore, H. A.; Spolenak, R.; Brown, W. L.; Batterman, B. W.; Patel, J. R.

2002-11-01

We have used scanning white beam x-ray microdiffraction to study microstructural evolution during an in situ electromigration experiment on a passivated Al(Cu) test line. The data show plastic deformation and grain rotations occurring under the influence of electromigration, seen as broadening, movement, and splitting of reflections diffracted from individual metal grains. We believe this deformation is due to localized shear stresses that arise due to the inhomogeneous transfer of metal along the line. Deviatoric stress measurements show changes in the components of stress within the line, including relaxation of stress when current is removed.

Strain Hardening of Hadfield Manganese Steel

NASA Astrophysics Data System (ADS)

Adler, P. H.; Olson, G. B.; Owen, W. S.

1986-10-01

The plastic flow behavior of Hadfield manganese steel in uniaxial tension and compression is shown to be greatly influenced by transformation plasticity phenomena. Changes in the stress-strain (σ-ɛ) curves with temperature correlate with the observed extent of deformation twinning, consistent with a softening effect of twinning as a deformation mechanism and a hardening effect of the twinned microstructure. The combined effects give upward curvature to the σ-ɛ curve over extensive ranges of plastic strain. A higher strain hardening in compression compared with tension appears to be consistent with the observed texture development. The composition dependence of stacking fault energy computed using a thermodynamic model suggests that the Hadfield composition is optimum for a maximum rate of deformation twinning. Comparisons of the Hadfield steel with a Co-33Ni alloy exhibiting similar twinning kinetics, and an Fe-21Ni-lC alloy deforming by slip indicate no unusual strain hardening at low strains where deformation is controlled by slip, but an unusual amount of structural hardening associated with the twin formation in the Hadfield steel. A possible mechanism of anomalous twin hardening is discussed in terms of modified twinning behavior (pseudotwinning) in nonrandom solid solutions.

Sectional Finite Element Analysis on Viscous Pressure Forming of Sheet Metal

NASA Astrophysics Data System (ADS)

Liu, Jianguang; Wang, Zhongjin; Liu, Yan

2007-05-01

Viscous pressure forming (VPF) is a recently developed sheet flexible-die forming process, which uses a kind of semi-solid, flowable and viscous material as pressure-carrying medium that typically applied on one side of the sheet metal or on both sides of sheet metal. Different from traditional sheet metal forming processes in which sheet metal is the unique deformation-body, VPF is a coupling process of visco-elastoplastic bulk deformation of viscous medium and elasto-plastic deformation of sheet metal. A sectional finite element model for the coupled deformation between visco-elastoplastic body and elasto-plastic sheet metal was proposed to analyze VPF. The resolution of the Updated Lagrangian formulation is based on a static approach. By using static-explicit time integration strategy, the deformation of elasto-plastic sheet metal and visco-elastoplastic body can keep stable. The frictional contact between sheet metal and visco-elastoplastic body is treated by penalty function method. Using the proposed algorithm, sheet metal viscous pressure bulging (VPB) process is analyzed and compared with experiments. A good agreement between numerical simulation results and experimental ones proved the efficiency and stability of this algorithm.

Modeling of stresses at grain boundaries with respect to occurrence of stress corrosion cracking

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozaczek, K.J.; Sinharoy, A.; Ruud, C.O.

The distributions of elastic stresses/strains in the grain boundary regions were studied by the analytical and the finite element models. The grain boundaries represent the sites where stress concentration occurs as a result of discontinuity of elastic properties across the grain boundary and the presence of second phase particles elastically different from the surrounding matrix grains. A quantitative analysis of those stresses for steels and nickel based alloys showed that the stress concentrations in the grain boundary regions are high enough to cause a local microplastic deformation even when the material is in the macroscopic elastic regime. The stress redistributionmore » as a result of such a plastic deformation was discussed.« less

Analyses of Fatigue Crack Growth and Closure Near Threshold Conditions for Large-Crack Behavior

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1999-01-01

A plasticity-induced crack-closure model was used to study fatigue crack growth and closure in thin 2024-T3 aluminum alloy under constant-R and constant-K(sub max) threshold testing procedures. Two methods of calculating crack-opening stresses were compared. One method was based on a contact-K analyses and the other on crack-opening-displacement (COD) analyses. These methods gave nearly identical results under constant-amplitude loading, but under threshold simulations the contact-K analyses gave lower opening stresses than the contact COD method. Crack-growth predictions tend to support the use of contact-K analyses. Crack-growth simulations showed that remote closure can cause a rapid rise in opening stresses in the near threshold regime for low-constraint and high applied stress levels. Under low applied stress levels and high constraint, a rise in opening stresses was not observed near threshold conditions. But crack-tip-opening displacement (CTOD) were of the order of measured oxide thicknesses in the 2024 alloy under constant-R simulations. In contrast, under constant-K(sub max) testing the CTOD near threshold conditions were an order-of-magnitude larger than measured oxide thicknesses. Residual-plastic deformations under both constant-R and constant-K(sub max) threshold simulations were several times larger than the expected oxide thicknesses. Thus, residual-plastic deformations, in addition to oxide and roughness, play an integral part in threshold development.

Development of Intergranular Residual Stress and Its Implication to Mechanical Behaviors at Elevated Temperatures in AL6XN Austenitic Stainless Steel

NASA Astrophysics Data System (ADS)

Hong, Yanyan; Li, Shilei; Li, Hongjia; Li, Jian; Sun, Guangai; Wang, Yan-Dong

2018-05-01

Neutron diffraction was used to investigate the residual lattice strains in AL6XN austenitic stainless steel subjected to tensile loading at different temperatures, revealing the development of large intergranular stresses after plastic deformation. Elastic-plastic self-consistent modeling was employed to simulate the micromechanical behavior at room temperature. The overall variations of the modeled lattice strains as a function of the sample direction with respect to the loading axis agree in general with the experimental values, indicating that dislocation slip is the main plastic deformation mode. At 300 °C, the serrated flow in the stress-strain curve and the great amount of slip bands indicate the appearance of dynamic strain aging. Except for promoting the local strain concentration, the long-range stress field caused by the planar slip bands near the grain boundaries is also attributed to the decrease in the experimental intergranular strains. An increase in the lattice strains localized at some specific specimen orientations for reflections at 600 °C may be explained by the segregation of solute atoms (Cr and Mo) at dislocation slip bands. The evolution of full-width at half-maximum demonstrates that the dynamic recovery indeed plays an important role in alleviating the local strain concentrations during tensile loading at 600 °C.

Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qian, Dan; Xue, Jiawei; Zhang, Anfeng

Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 μm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane.more » Based on Schmid's law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.« less

Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy

DOE PAGES

Qian, Dan; Xue, Jiawei; Zhang, Anfeng; ...

2017-06-06

Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 μm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane.more » Based on Schmid's law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.« less

The effect of plastic strain on the evolution of crystallographic texture in Zircaloy-2

NASA Astrophysics Data System (ADS)

Ballinger, R. G.; Lucas, G. E.; Pelloux, R. M.

1984-09-01

The evolution of crystallographic texture during plastic deformation was investigated in Zircaloy-2 using X-ray and metallographic techniques. Inverse pole figures, the resolved fraction of basal poles, and the volume fraction of twinned material, were determined as a function of plastic strain for several strain paths and initial textures at 298 K and 623 K. Incremental transverse platic strain ratios ( R) were mesured as a function of plastic strain. Texture rotation occurs early in the deformation process, after as little as 1.5% plastic strain. For compressive plastic strains, the resolved fraction of basal poles increases in the direction parallel to the strain axis. For tensile plastic strains, the resolved fraction of basal poles decreases in the direction parallel to the strain axis. The rate of change of the resolved fraction of basal poles with plastic strain is a function of the initial resolved fraction of basal poles. The texture rotation can be explained by considering the operation of the principal tensile twinning systems, {101¯2}<1¯011>.

Texture and structure contribution to low-temperature plasticity enhancement of Mg-Al-Zn-Mn Alloy MA2-1hp after ECAP and annealing

NASA Astrophysics Data System (ADS)

Serebryany, V. N.; D'yakonov, G. S.; Kopylov, V. I.; Salishchev, G. A.; Dobatkin, S. V.

2013-05-01

Equal channel angular pressing (ECAP) in magnesium alloys due to severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40°-50° to the pressing direction. These changes in microstructure and texture contribute to the improvement of low-temperature plasticity of the alloys. Quantitative texture X-ray diffraction analysis and diffraction of backscattered electrons are used to study the main textural and structural factors responsible for enhanced low-temperature plasticity based on the example of magnesium alloy MA2-1hp of the Mg-Al-Zn-Mn system. The possible mechanisms of deformation that lead to this positive effect are discussed.

Size-Tuned Plastic Flow Localization in Irradiated Materials at the Submicron Scale

NASA Astrophysics Data System (ADS)

Cui, Yinan; Po, Giacomo; Ghoniem, Nasr

2018-05-01

Three-dimensional discrete dislocation dynamics (3D-DDD) simulations reveal that, with reduction of sample size in the submicron regime, the mechanism of plastic flow localization in irradiated materials transitions from irradiation-controlled to an intrinsic dislocation source controlled. Furthermore, the spatial correlation of plastic deformation decreases due to weaker dislocation interactions and less frequent cross slip as the system size decreases, thus manifesting itself in thinner dislocation channels. A simple model of discrete dislocation source activation coupled with cross slip channel widening is developed to reproduce and physically explain this transition. In order to quantify the phenomenon of plastic flow localization, we introduce a "deformation localization index," with implications to the design of radiation-resistant materials.

Interaction of heat production, strain rate and stress power in a plastically deforming body under tensile test

NASA Technical Reports Server (NTRS)

Paglietti, A.

1982-01-01

At high strain rates the heat produced by plastic deformation can give rise to a rate dependent response even if the material has rate independent constitutive equations. This effect has to be evaluated when interpreting a material test, or else it could erroneously be ascribed to viscosity. A general thermodynamic theory of tensile testing of elastic-plastic materials is given in this paper; it is valid for large strain at finite strain rates. It enables discovery of the parameters governing the thermodynamic strain rate effect, provides a method for proper interpretation of the results of the tests of dynamic plasticity, and suggests a way of planning experiments in order to detect the real contribution of viscosity.

Amplified effect of mild plastic anisotropy on residual stress and strain anisotropy

DOE PAGES

Prime, Michael B.

2017-07-01

Axisymmetric indentation of a geometrically axisymmetric disk produced residual stresses by non-uniform plastic deformation. The 2024 aluminum plate used to make the disk exhibited mild plastic anisotropy with about 10% lower strength in the transverse direction compared to the rolling and through-thickness directions. Residual stresses and strains in the disk were measured with neutron diffraction, slitting, the contour method, x-ray diffraction and hole drilling. Surprisingly, the residual-stress anisotropy measured in the disk was about 40%, the residual-strain anisotropy was an impressive 100%, and the residual stresses were higher in the weaker direction. The high residual stress anisotropy relative to themore » mild plastic anisotropy and the direction of the highest stress are explained by considering the mechanics of indentation: constraint on deformation provided by the material surrounding the indentation and preferential deformation in the most compliant direction for incremental deformation. By contrast, the much larger anisotropy in residual strain compared to that in residual stress is independent of the fabrication process and is instead explained by considering Hookean elasticity. For Poisson's ratio of 1/3, the relationship simplifies to the residual strain anisotropy equaling the square of the residual stress anisotropy, which matches the observed results (2 ≈ 1.4^2). Furthermore, a lesson from this study is that to accurately predict residual stresses and strains, one must be wary of seemingly reasonable simplifying assumptions such as neglecting mild plastic anisotropy.« less

Amplified effect of mild plastic anisotropy on residual stress and strain anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prime, Michael B.

Axisymmetric indentation of a geometrically axisymmetric disk produced residual stresses by non-uniform plastic deformation. The 2024 aluminum plate used to make the disk exhibited mild plastic anisotropy with about 10% lower strength in the transverse direction compared to the rolling and through-thickness directions. Residual stresses and strains in the disk were measured with neutron diffraction, slitting, the contour method, x-ray diffraction and hole drilling. Surprisingly, the residual-stress anisotropy measured in the disk was about 40%, the residual-strain anisotropy was an impressive 100%, and the residual stresses were higher in the weaker direction. The high residual stress anisotropy relative to themore » mild plastic anisotropy and the direction of the highest stress are explained by considering the mechanics of indentation: constraint on deformation provided by the material surrounding the indentation and preferential deformation in the most compliant direction for incremental deformation. By contrast, the much larger anisotropy in residual strain compared to that in residual stress is independent of the fabrication process and is instead explained by considering Hookean elasticity. For Poisson's ratio of 1/3, the relationship simplifies to the residual strain anisotropy equaling the square of the residual stress anisotropy, which matches the observed results (2 ≈ 1.4^2). Furthermore, a lesson from this study is that to accurately predict residual stresses and strains, one must be wary of seemingly reasonable simplifying assumptions such as neglecting mild plastic anisotropy.« less

Features of plastic deformation and fracture of dispersion-strengthened V–Cr–Zr–W alloy depending on temperature of tension

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ditenberg, Ivan A.; Grinyaev, Konstantin V.; Tyumentsev, Alexander N.

2015-10-27

Influence of tension temperature on features of plastic deformation and fracture of V–4.23Cr–1.69Zr–7.56W alloy was investigated by scanning and transmission electron microscopy. It is shown that temperature increase leads to activation of the recovery processes, which manifests in the coarsening of microstructure elements, reducing the dislocation density, relaxation of continuous misorientations.

Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laplanche, Guillaume; Bonneville, J.; Varvenne, C.

To reveal the operating mechanisms of plastic deformation in an FCC high-entropy alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, σ y, the activation volume varies from ~60 b3 at 77 K to ~360 b 3 at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with σ - σ y (Haasenmore » plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-strengthened alloy. Lastly, these results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.« less

Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy

DOE PAGES

Laplanche, Guillaume; Bonneville, J.; Varvenne, C.; ...

2017-10-06

To reveal the operating mechanisms of plastic deformation in an FCC high-entropy alloy, the activation volumes in CrMnFeCoNi have been measured as a function of plastic strain and temperature between 77 K and 423 K using repeated load relaxation experiments. At the yield stress, σ y, the activation volume varies from ~60 b3 at 77 K to ~360 b 3 at 293 K and scales inversely with yield stress. With increasing plastic strain, the activation volume decreases and the trends follow the Cottrell-Stokes law, according to which the inverse activation volume should increase linearly with σ - σ y (Haasenmore » plot). This is consistent with the notion that hardening due to an increase in the density of forest dislocations is naturally associated with a decrease in the activation volume because the spacing between dislocations decreases. The values and trends in activation volume agree with theoretical predictions that treat the HEA as a high-concentration solid-solution-strengthened alloy. Lastly, these results demonstrate that this HEA deforms by the mechanisms typical of solute strengthening in FCC alloys, and thus indicate that the high compositional/structural complexity does not introduce any new intrinsic deformation mechanisms.« less

The effects of perturbations on the strain distribution in numerical simulations - elasto-viscoplastic modeling of boudinage as a case study

NASA Astrophysics Data System (ADS)

Peters, Max; Karrech, Ali; Poulet, Thomas; Herwegh, Marco; Regenauer-Lieb, Klaus

2014-05-01

During necking of a mechanically stiffer layer embedded in a weaker matrix, relatively large amounts of strain localize in small areas. As this deformation style appears under distinct geological conditions, necking phenomena, e.g. boudinaged veins, are associated with a variety of deformation modes. So far, there exists rather limited knowledge about the origin of instabilities and their role as precursory structures, i.e. strong localization of elastic energy affecting further plastic deformation (e.g. Regenauer-Lieb & Yuen, 1998; 2004; Karrech et al., 2011a). We applied the finite element solver ABAQUS in order to investigate the 2-D strain distribution in layers including different mechanical material properties during plane strain co-axial deformation. First, linear perturbation analyses were performed in order to evaluate the imperfection sensitivity in the elastic and viscous regimes. We perform a classical modal analysis to determine the natural mode shapes and frequencies of our geological structure during arbitrary vibrations. This analysis aims at detecting the eigenmodes of the geological structure, which are sinusoidal vibrations with geometry specific natural modal shapes and frequencies. The eigenvalues represent the nodal points where the onset of (visco)-elasto-plastic localization can initiate in the structure (Rice, 1977). The eigenmodes, eigenvalues and eigenvectors are highly sensitive to the layer-box' aspect ratio and differences in Young's moduli, or effective viscosity, respectively. Boundary effect-free strain propagation occurs for layer-box aspect ratios smaller than 1:10. Second, these preloading structures were used as seeds for imperfections in elasto-viscoplastic numerical modeling of continuous necking of a coarse-grained mineral layer embedded in a finer-grained matrix (pinch-and-swell type of boudinage), following the thermo-mechanical coupling of grain size evolutions by Herwegh et al. (in press). The evolution of symmetric necks seems to coincide with the transition from dislocation to diffusion creep dominated viscous flow with dramatic grain size reduction and grain growth from swell to neck, respectively, at relatively high extensional strains. Strain propagates from initial stress concentrations in the layer (necks) at an angle of 45° into the matrix, in form of conjugate shear band sets. Preliminary results show that pre-calculated eigenmodes (and corresponding imperfection sizes) amplify these concentrations and lead to a significant reduction of computational time for individual simulations. Moreover, the strain imperfections seeded around the pre-calculated distribution severely change the geometry of necking structures and amount of accommodated plastic strain. We reveal that elastic stress concentrations control localized visco-plastic deformation, which is expressed in the plastic strain energy increase in necking structures. These findings underline the importance of the transient (elasticity and strain hardening) deformation regimes as triggers for plastic deformation and the need for thermodynamics-based (total) energy considerations. REFERENCES Herwegh, M., Poulet, T., Karrech, A. and Regenauer-Lieb, K. (in press). From transient to steady state deformation and grain size: A thermodynamic approach using elasto-visco-plastic numerical modeling. Journal of Geophysical Research. Karrech, A., Regenauer-Lieb, K. and Poulet, T. (2011a). A Damaged visco-plasticity model for pressure and temperature sensitive geomaterials. Journal of Engineering Science 49. Regenauer-Lieb, K., Yuen, D., 1998: Rapid conversion of elastic energy into plastic shear heating during incipient necking of the lithosphere. Geophysical Research Letters, 25. Regenauer-Lieb, K., Yuen, D., 2004. Positive feedback of interacting ductile faults from coupling of equation of state, rheology and thermal-mechanics. Physics of the Earth and Planetary Interiors, 142. Rice, J. R. (1977). The localization of plastic deformation. Theoretical and Applied Mechanics. W. T. Koiter. Amsterdam, North-Holland: 207-220.

Discontinuous precipitation at the deformation band in copper alloy

NASA Astrophysics Data System (ADS)

Han, Seung Zeon; Ahn, Jee Hyuk; You, Young Soo; Lee, Jehyun; Goto, Masahiro; Kim, Kwangho; Kim, Sangshik

2018-01-01

The Cu-Ni-Si alloy is known as a precipitation hardening alloy, where the Ni2Si intermetallic compound is precipitated in the matrix during aging. There are two types of precipitation of Ni2Si: continuous and discontinuous cellular. The discontinuous cellular precipitation is generally initiated at interfaces especially grain boundaries in the matrix. To observe the grain boundary effect on the discontinuous precipitation, a large-grained Cu-Ni-Si-Ti alloy was intentionally fabricated by unidirectional solidification and plastically deformed by groove rolling. While discontinuous cellular precipitation has been generally known to occur only at the high angled grain boundaries in the alloys, we found that it was also generated inside the grains, at the deformation bands formed by plastic deformation.

Soft sediment deformation structures in the Maastrichtian Ajali Formation Western Flank of Anambra Basin, Southern Nigeria

NASA Astrophysics Data System (ADS)

Olabode, Solomon Ojo

2014-01-01

Soft sediment deformation structures were recognized in the Maastrichtian shallow marine wave to tide influenced regressive sediments of Ajali Formation in the western flank of Anambra basin, southern Nigerian. The soft sediment deformation structures were in association with cross bedded sands, clay and silt and show different morphological types. Two main types recognised are plastic deformations represented by different types of recumbent folds and injection structure represented by clastic dykes. Other structures in association with the plastic deformation structures include distorted convolute lamination, subsidence lobes, pillars, cusps and sand balls. These structures are interpreted to have been formed by liquefaction and fluidization mechanisms. The driving forces inferred include gravitational instabilities and hydraulic processes. Facies analysis, detailed morphologic study of the soft sediment deformation structures and previous tectonic history of the basin indicate that the main trigger agent for deformation is earthquake shock. The soft sediment deformation structures recognised in the western part of Anambra basin provide a continuous record of the tectonic processes that acted on the regressive Ajali Formation during the Maastrichtian.

Modeling Near-Crack-Tip Plasticity from Nano- to Micro-Scales

NASA Technical Reports Server (NTRS)

Glaessgen, Edward H.; Saether, Erik; Hochhalter, Jake D.; Yamakov, Vesselin I.

2010-01-01

Several efforts that are aimed at understanding the plastic deformation mechanisms related to crack propagation at the nano-, meso- and micro-length scales including atomistic simulation, discrete dislocation plasticity, strain gradient plasticity and crystal plasticity are discussed. The paper focuses on discussion of newly developed methodologies and their application to understanding damage processes in aluminum and its alloys. Examination of plastic mechanisms as a function of increasing length scale illustrates increasingly complex phenomena governing plasticity

Understanding thermally activated plastic deformation behavior of Zircaloy-4

NASA Astrophysics Data System (ADS)

Kumar, N.; Alomari, A.; Murty, K. L.

2018-06-01

Understanding micromechanics of plastic deformation of existing materials is essential for improving their properties further and/or developing advanced materials for much more severe load bearing applications. The objective of the present work was to understand micromechanics of plastic deformation of Zircaloy-4, a zirconium-based alloy used as fuel cladding and channel (in BWRs) material in nuclear reactors. The Zircaloy-4 in recrystallized (at 973 K for 4 h) condition was subjected to uniaxial tensile testing at a constant cross-head velocity at temperatures in the range 293 K-1073 K and repeated stress relaxation tests at 293 K, 573 K, and 773 K. The minimum in the total elongation was indicative of dynamic strain aging phenomenon in this alloy in the intermediate temperature regime. The yield stress of the alloy was separated into effective and athermal components and the transition from thermally activated dislocation glide to athermal regime took place at around 673 K with the athermal stress estimated to be 115 MPa. The activation volume was found to be in the range of 40 b3 to 160 b3. The activation volume values and the data analyses using the solid-solution models in literature indicated dislocation-solute interaction to be a potential deformation mechanism in thermally activated regime. The activation energy calculated at 573 K was very close to that found for diffusivity of oxygen in α-Zr that was suggestive of dislocations-oxygen interaction during plastic deformation. This type of information may be helpful in alloy design in selecting different elements to control the deformation behavior of the material and impart desired mechanical properties in those materials for specific applications.

Effect of upsetting deformation temperature on the formation of the fine-grained cast alloy structure of the Ni-Mn-Ga system

NASA Astrophysics Data System (ADS)

Musabirov, I. I.; Safarov, I. M.; Sharipov, I. Z.; Nagimov, M. I.; Koledov, V. V.; Khovailo, V. V.; Mulyukov, R. R.

2017-08-01

The plastic behavior during deformation by upsetting and its effect on the microstructure in the polycrystalline Ni2.19Fe0.04Mn0.77Ga alloy are studied. The temperatures of martensitic and magnetic phase transformations were determined by the method for analyzing the temperature dependence of the specific magnetization as M F = 320 K, A S = 360 K, and T C = 380 K. Using differential scanning calorimetry, it is shown that the phase transition from the ordered phase L21 to the disordered phase B2 is observed in the alloy during sample heating in the temperature range of 930-1070 K. The melting temperature is 1426 K. An analysis of the load curves constructed for sample deposition at temperatures of 773, 873, and 973 K shows that the behavior of the stress-strain curve at a temperature of 773 K is inherent to cold deformation. The behavior of the dependences for 873 and 973 K is typical of hot deformation. After deforming the alloy, its microstructure is studied using backscattered scanning electron microscopy. Plastic deformation of the alloy at study temperatures results in grain structure fragmentation in the localized deformation region. At all temperatures, a recrystallized grain structure is observed. It is found that the structure is heterogeneously recrystallized after upsetting at 973 K due to the process intensity at such a high temperature. The alloy microstructure after plastic deformation at a temperature of 873 K is most homogeneous in terms of the average grain size.

Use of first derivative of displacement vs. force profiles to determine deformation behavior of compressed powders.

PubMed

Gharaibeh, Shadi F; Aburub, Aktham

2013-03-01

Displacement (D) vs. force (F) profiles obtained during compaction of powders have been reported by several researchers. These profiles are usually used to obtain mechanical energies associated with the compaction of powders. In this work, we obtained displacement-force data associated with the compression of six powders; Avicel PH101, Avicel PH301, pregelatinized corn starch, anhydrous lactose, dicalcium phosphate, and mannitol. The first three powders are known to deform predominantly by plastic behavior while the later ones are known to deform predominantly by brittle fracture. Displacement-force data was utilized to perform in-die Heckel analysis and to calculate the first derivative (dD/dF) of displacement-force plots. First derivative results were then plotted against mean force (F') at each point and against 1/F' at compression forces between 1 and 20 kN. Results of the in-die Heckle analysis are in very good agreement with the known deformation behavior of the compressed materials. First derivative plots show that materials that deform predominantly by plastic behavior have first derivative values (0.0006-0.0016 mm/ N) larger than those of brittle materials (0.0004 mm/N). Moreover, when dD/dF is plotted against 1/F' for each powder, a linear correlation can be obtained (R2=>0.98). The slopes of the dD/dF vs. 1/F' plots for plastically deforming materials are relatively larger than those for materials that deform by brittle behavior. It is concluded that first derivative plots of displacement-force profiles can be used to determine deformation behavior of powders.

Structural Crashworthiness and Failure

DTIC Science & Technology

1993-04-16

body motion occurs. This rigid -plastic idealization for dynamically loaded structures is based upon the fact that the plastic deformation of a...in general, for any tensor variable x, i represents the convective derivative. It should be noted that the rigid body rotation is included in the...clamped, impulsively loaded, rigid - plastic beam.’ (a) First phase of motion with stationary transverse plastic hinges at A and E and stationary plastic

Capability evaluation of ultrasonic cavitation peening at different standoff distances.

PubMed

Bai, Fushi; Saalbach, Kai-Alexander; Long, Yangyang; Twiefel, Jens; Wallaschek, Jörg

2018-03-01

Ultrasonic cavitation peening is a novel surface treatment technology which utilizes the effect of cavitation bubble collapses to improve the properties of metal surfaces. In order to obtain high impact during ultrasonic cavitation peening, a small standoff distance between a sound radiator and a rigid reflector (the surface of treated specimen) is necessary. However, the effects of different standoff distances on the capability of ultrasonic cavitation peening are not yet clear. In this paper, a simplified model was developed to evaluate the cavitation capability at different standoff distances. Meanwhile, to validate the theoretical model, the plastic deformation or erosion on the peening surface before and after treatment were compared. It was found that at a very small standoff distance the impact pressure generated by cavitation bubbles did not cause much deformation or erosion, as the dynamics of cavitation bubbles was limited. At a large standoff distance, due to much attenuation of sound propagation in the bubbly liquid, little impact pressure was generated by the collapse of cavitation bubbles and reached the treated surface. A fixed vibration amplitude, however, corresponded to a standoff distance which caused the largest deformation or erosion on the treated surface. Copyright © 2017 Elsevier B.V. All rights reserved.

In situ strain profiling of elastoplastic bending in Ti-6Al-4V alloy by synchrotron energy dispersive x-ray diffraction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croft, M.; National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York 11973; Shukla, V.

Elastic and plastic strain evolution under four-point bending has been studied by synchrotron energy dispersive x-ray diffraction. Measured strain profiles across the specimen thickness showed an increasing linear elastic strain gradient under increasing four-point bending load up to approx2 kN. The bulk elastic modulus of Ti-6Al-4V was determined as 118 GPa. The onset of plastic deformation was found to set in at a total in-plane strain of approx0.008, both under tension and compression. Plastic deformation under bending is initiated in the vicinity of the surface and at a stress of 1100 MPa, and propagates inward, while a finite core regionmore » remains elastically deformed up to 3.67 kN loading. The onset of the plastic regime and the plastic regime itself has been verified by monitoring the line broadening of the (100) peak of alpha-Ti. The effective compression/tension stress-strain curve has been obtained from the scaling collapse of strain profile data taken at seven external load levels. A similar multiple load scaling collapse of the plastic strain variation has also been obtained. The level of precision in strain measurement reported herein was evaluated and found to be 1.5x10{sup -5} or better.« less

Molecular dynamics simulation of the plastic behavior anisotropy of shock-compressed monocrystal nickel

NASA Astrophysics Data System (ADS)

Chen, Ya-Zhou; Zhou, Liu-Cheng; He, Wei-Feng; Sun, Yu; Li, Ying-Hong; Jiao, Yang; Luo, Si-Hai

2017-01-01

Molecular dynamics simulations were used to study the plastic behavior of monocrystalline nickel under shock compression along the [100] and [110] orientations. The shock Hugoniot relation, local stress curve, and process of microstructure development were determined. Results showed the apparent anisotropic behavior of monocrystalline nickel under shock compression. The separation of elastic and plastic waves was also obvious. Plastic deformation was more severely altered along the [110] direction than the [100] direction. The main microstructure phase transformed from face-centered cubic to body-centered cubic and generated a large-scale and low-density stacking fault along the family of { 111 } crystal planes under shock compression along the [100] direction. By contrast, the main mechanism of plastic deformation in the [110] direction was the nucleation of the hexagonal, close-packed phase, which generated a high density of stacking faults along the [110] and [1̅10] directions.

Viscoelasticity and plasticity mechanisms of human dentin

NASA Astrophysics Data System (ADS)

Borodin, E. N.; Seyedkavoosi, S.; Zaitsev, D.; Drach, B.; Mikaelyan, K. N.; Panfilov, P. E.; Gutkin, M. Yu.; Sevostianov, I.

2018-01-01

Theoretical models of viscoelastic behavior and plastic deformation mechanisms of human dentin are considered. Using the linear viscoelasticity theory in which creep and relaxation kernels have the form of fraction-exponential functions, numerical values of instantaneous and long-time Young's moduli and other characteristics of dentin viscoelasticity under uniaxial compression are found. As dentin plastic deformation mechanisms, mutual collagen fiber sliding in the region of contact of their side surfaces, separation of these fibers from each other, and irreversible tension of some collagen fibers, are proposed. It is shown that the second mechanism activation requires a smaller stress than that for activating others. The models of plastic zones at the mode I crack tip, which correspond to these mechanisms, are studied. It is shown that the plastic zone size can increase from a few hundreds of nanometers to hundreds of micrometers with increasing applied stress.

A study on the plasticity of soda-lime silica glass via molecular dynamics simulations.

PubMed

Urata, Shingo; Sato, Yosuke

2017-11-07

Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses. Furthermore, the effect of ion-exchange on the SLSG plasticity was examined by using MD simulations. As a result, it was demonstrated that the effects of the initial compressive stress on the yield and maximum stresses are anisotropic contrary to our expectations.

A study on the plasticity of soda-lime silica glass via molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Urata, Shingo; Sato, Yosuke

2017-11-01

Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses. Furthermore, the effect of ion-exchange on the SLSG plasticity was examined by using MD simulations. As a result, it was demonstrated that the effects of the initial compressive stress on the yield and maximum stresses are anisotropic contrary to our expectations.

Evolution of Deformation Studies on Active Hawaiian Volcanoes

USGS Publications Warehouse

Decker, Robert W.; Okamura, Arnold; Miklius, Asta; Poland, Michael

2008-01-01

Everything responds to pressure, even rocks. Deformation studies involve measuring and interpreting the changes in elevations and horizontal positions of the land surface or sea floor. These studies are variously referred to as geodetic changes or ground-surface deformations and are sometimes indexed under the general heading of geodesy. Deformation studies have been particularly useful on active volcanoes and in active tectonic areas. A great amount of time and energy has been spent on measuring geodetic changes on Kilauea and Mauna Loa Volcanoes in Hawai`i. These changes include the build-up of the surface by the piling up and ponding of lava flows, the changes in the surface caused by erosion, and the uplift, subsidence, and horizontal displacements of the surface caused by internal processes acting beneath the surface. It is these latter changes that are the principal concern of this review. A complete and objective review of deformation studies on active Hawaiian volcanoes would take many volumes. Instead, we attempt to follow the evolution of the most significant observations and interpretations in a roughly chronological way. It is correct to say that this is a subjective review. We have spent years measuring and recording deformation changes on these great volcanoes and more years trying to understand what makes these changes occur. We attempt to make this a balanced as well as a subjective review; the references are also selective rather than exhaustive. Geodetic changes caused by internal geologic processes vary in magnitude from the nearly infinitesimal - one micron or less, to the very large - hundreds of meters. Their apparent causes also are varied and include changes in material properties and composition, atmospheric pressure, tidal stress, thermal stress, subsurface-fluid pressure (including magma pressure, magma intrusion, or magma removal), gravity, and tectonic stress. Deformation is measured in units of strain or displacement. For example, tilt of the ground surface on the rim of Kilauea Caldera is measured in microradians, a strain unit that gives the change in angle from some reference. The direction in which the tilt is measured must be defined - north or south, or some direction normal to the maximum changes. For displacements related to surface faulting, the changes are normally given in linear measures of offset. Changes in the diameter of a caldera can be given in either displacements or strain units. In the later case, the displacement divided by the 'original' diameter gives the strain ratio. Strains are dimensionless numbers; displacements have the dimensions of length. Vectors commonly are used to show the direction and amount of displacements in plan view. Strain results from stress. It can be elastic strain, when the strain is linearly related to stress and is recoverable; it can be viscous strain, where the rate of strain is proportional to the stress and is not recoverable; or it can be plastic strain that is often some complex stress-strain relationship, for example, elastic up to some yield strength and viscous beyond. Volcanic rocks are brittle when cold and under near-surface pressures but plastic to viscous under higher temperature and pressure regimes. It is important in deformation studies to try to define the nature of the strain and the rheology of the rocks being deformed. A good text on rheology is 'The Structure and Rheology of Complex Fluids' by R.G. Larson, 1999. Under changing tensional or compressional stresses, tiny cracks in brittle rocks may open or close, causing a quasielastic strain response. If the stresses exceed the breaking strength of the rock, brittle failure occurs, and the stress-strain relationship breaks down. This is generally the situation with near-field deformation related to earthquakes. Stresses change in complex patterns in both the near- and far-fields of the fracture, and the near-fiel

Room- and Low-Temperature Deformation of Multilayered Fiberglass Plastics Reinforced with a Fabric of Sateen Weave

NASA Astrophysics Data System (ADS)

Kucher, N. K.; Dveyrin, A. Z.; Zarazovskii, M. N.; Zemtsov, M. P.

2004-05-01

The regularities of elastic deformation of multilayered fiberglass plastics reinforced with a fabric of sateen weave are studied. The effect of cooling to 77 K on the averaged elastic characteristics of the orthotropic material is analyzed. The efficiency of mathematical modeling in calculating the stiffness and compliance parameters of the woven composites based on the geometry and mechanical properties of their constituents is investigated.

USSR and Eastern Europe Scientific Abstracts. Engineering and Equipment. Number 26

DTIC Science & Technology

1976-11-10

harbor in- volves a sea sector and a river sector. The author indicates the hypotheses taken into consideration, including the number of berths in the...river and sea sectors, the arrivals of sea - and river-going ships, and ship operation time. Also indicated is the system of equations describing...diffusion for plastic deformation by torsion is greater than plastic deformation by tension. The main energy diffusion mechanism is microplastic

LWH and ACH Helmet Hardware Study

DTIC Science & Technology

2015-11-30

stiffer and stronger than Kevlar panels, does not plastically deform (and therefore Figure 11. Typical ductile fracture surface resulting from a...striker from deflecting. The substrate is ¼ inch thick fiberglass plate supported on a base plate of 5083 aluminum alloy . Figure 13. Close ups of...project. We note that the impact damage to the top of the screw heads, is entirely plastic deformation of the slot and top of the head, and is clearly

LWH & ACH Helmet Hardware Study

DTIC Science & Technology

2015-11-30

stiffer and stronger than Kevlar panels, does not plastically deform (and therefore Figure 11. Typical ductile fracture surface resulting from a...striker from deflecting. The substrate is ¼ inch thick fiberglass plate supported on a base plate of 5083 aluminum alloy . Figure 13. Close ups of...project. We note that the impact damage to the top of the screw heads, is entirely plastic deformation of the slot and top of the head, and is clearly

Structure of Al-Fe alloys prepared by different methods after severe plastic deformation under pressure

NASA Astrophysics Data System (ADS)

Dobromyslov, A. V.; Taluts, N. I.

2017-06-01

Al-Fe alloys prepared by casting, rapid quenching from the melt, and mechanical alloying from elemental powders have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and microhardness measurements in the initial state and after severe plastic deformation by high-pressure torsion using Bridgman anvils. The relationship between the phase composition, microstructure, and the microhardness of the investigated alloys has been established.

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montgomery, Robert; Tomé, Carlos; Liu, Wenfeng

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. CASL has endeavored to improve upon this approach by incorporating a microstructurally-based, atomistically-informed, zirconium alloy mechanical deformation analysis capability into the BISON-CASL engineering scale fuel performance code. Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed bymore » Lebensohn and Tome´ [2], has been coupled with BISON-CASL to represent the mechanistic material processes controlling the deformation behavior of the cladding. A critical component of VPSC is the representation of the crystallographic orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON-CASL and provides initial results utilizing the coupled functionality.« less

Deposition behavior of mixed binary metallic powders in cold spraying process

NASA Astrophysics Data System (ADS)

Zhou, X. L.; Mou, S. J.; Wu, X. K.; Zhang, J. S.

2011-10-01

In the present study, Zn/Al composite coating was selected for the typical case to study the deposition behavior and the deformation of binary mixing particles in cold spraying process by means of an experiment and numerical simulation. The experimental results demonstrated that the coating had a dense microstructure, and that Zn and Al were uniformly distributed in the coating. Al particles deformed more severely than Zn particles, and extensively deformed Al particles had a local jet-metallic mixing area. The steel substrate underwent a small amount of deformation when impacted by Zn particles, whereas the substrate did not deform when impacted by Al particles. XRD results show that the Zn/Al composite coating did not form a new phase, and only resulted in the mechanical mixing of Zn and Al, producing a pseudo-alloy coating. In addition, a binary Zn/Al multiparticle impact was first simulated using the finite element analysis software ANSYS/LS-DYNA. The effective plastic strain contour, which enabled the description of the particle deposit procedure, was demonstrated. The plastic deformation evolution of Zn and Al particles in the composite coating was analyzed individually, and the curves of effective plastic strain versus time of typical monitored elements at the edge of the Zn and Al particles were plotted. The simulations showed good concordance with the experimental results.

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawrence, Samantha K.; Somerday, Brian P.; Ingraham, Mathew Duffy

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yieldingmore » in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.« less

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, John A.; Barton, Nathan R.; Florando, Jeff

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

DOE PAGES

Lawrence, Samantha K.; Somerday, Brian P.; Ingraham, Mathew Duffy; ...

2018-04-11

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yieldingmore » in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.« less

Crystal plasticity modeling of β phase deformation in Ti-6Al-4V

DOE PAGES

Moore, John A.; Barton, Nathan R.; Florando, Jeff; ...

2017-08-24

Ti-6Al-4V is an alloy of titanium that dominates titanium usage in applications ranging from mass-produced consumer goods to high-end aerospace parts. The material's structure on a microscale is known to affect its mechanical properties but these effects are not fully understood. Specifically, this work will address the effects of low volume fraction intergranular β phase on Ti-6Al-4V's mechanical response during the transition from elastic to plastic deformation. A crystal plasticity-based finite element model is used to fully resolve the deformation of the β phase for the first time. This high fidelity model captures mechanisms difficult to access via experiments ormore » lower fidelity models. Lastly, the results are used to assess lower fidelity modeling assumptions and identify phenomena that have ramifications for failure of the material.« less

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

NASA Technical Reports Server (NTRS)

Johnson, R D; Young, A P; Schwope, A D

1956-01-01

This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

Atomistic basis for the plastic yield criterion of metallic glass.

PubMed

Schuh, Christopher A; Lund, Alan C

2003-07-01

Because of their disordered atomic structure, amorphous metals (termed metallic glasses) have fundamentally different deformation mechanisms compared with polycrystalline metals. These different mechanisms give metallic glasses high strength, but the extent to which they affect other macroscopic deformation properties is uncertain. For example, the nature of the plastic-yield criterion is a point of contention, with some studies reporting yield behaviour roughly in line with that of polycrystalline metals, and others indicating strong fundamental differences. In particular, it is unclear whether pressure- or normal stress-dependence needs to be included in the plastic-yield criterion of metallic glasses, and how such a dependence could arise from their disordered structure. In this work we provide an atomic-level explanation for pressure-dependent yield in amorphous metals, based on an elementary unit of deformation. This simple model compares favourably with new atomistic simulations of metallic glasses, as well as existing experimental data.

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

NASA Astrophysics Data System (ADS)

Lawrence, S. K.; Somerday, B. P.; Ingraham, M. D.; Bahr, D. F.

2018-04-01

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases 22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases 20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yielding in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal a direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.

Molecular dynamics modeling and simulation of void growth in two dimensions

NASA Astrophysics Data System (ADS)

Chang, H.-J.; Segurado, J.; Rodríguez de la Fuente, O.; Pabón, B. M.; LLorca, J.

2013-10-01

The mechanisms of growth of a circular void by plastic deformation were studied by means of molecular dynamics in two dimensions (2D). While previous molecular dynamics (MD) simulations in three dimensions (3D) have been limited to small voids (up to ≈10 nm in radius), this strategy allows us to study the behavior of voids of up to 100 nm in radius. MD simulations showed that plastic deformation was triggered by the nucleation of dislocations at the atomic steps of the void surface in the whole range of void sizes studied. The yield stress, defined as stress necessary to nucleate stable dislocations, decreased with temperature, but the void growth rate was not very sensitive to this parameter. Simulations under uniaxial tension, uniaxial deformation and biaxial deformation showed that the void growth rate increased very rapidly with multiaxiality but it did not depend on the initial void radius. These results were compared with previous 3D MD and 2D dislocation dynamics simulations to establish a map of mechanisms and size effects for plastic void growth in crystalline solids.

North America-Pacific plate boundary, an elastic-plastic megashear - Evidence from very long baseline interferometry

NASA Technical Reports Server (NTRS)

Ward, Steven N.

1988-01-01

Data obtained by Mark III VLBI measurements of radio signals from permanent and mobile VLBI sites for 5.5 years of observations, starting in October 1982, were used to derive a picture of the earth crust deformation near the North America-Pacific plate boundary. The data, which included the vector positions of the VLBI sites and their rate of change, were used for comparison with a number of lithospheric deformation models based upon the concept that the motions of points near the North America-Pacific plate boundary are a linear combination of North America and Pacific velocities. The best of these models were found to fit 95 percent of the variance in 139 VLBI length and transverse velocity observations. Instantaneous shear deformation associated with plate tectonics is apparently developing in a zone 450 km wide paralleling the San Andreas Fault; some of this deformation will be recovered through elastic rebound, while the rest will be permanently set through plastic processes. Because the VLBI data have not been collected for a significant fraction of the earthquake cycle, they cannot discriminate between elastic and plastic behaviors.

Preparation, deformation, and failure of functional Al-Sn and Al-Sn-Pb nanocrystalline alloys

NASA Astrophysics Data System (ADS)

Noskova, N. I.; Vil'Danova, N. F.; Filippov, Yu. I.; Churbaev, R. V.; Pereturina, I. A.; Korshunov, L. G.; Korznikov, A. V.

2006-12-01

Changes in the structure, hardness, mechanical properties, and friction coefficient of Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb (wt %) alloys subjected to severe plastic deformation by equal-channel angular pressing (with a force of 40 tonne) and by shear at a pressure of 5 GPa have been studied. The transition into the nanocrystalline state was shown to occur at different degrees of plastic deformation. The hardness exhibits nonmonotonic variations, namely, first it increases and subsequently decreases. The friction coefficient of the Al-30% Sn, Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys quenched from the melt was found to be 0.33; the friction coefficients of these alloys in the submicrocrystalline state (after equal-channel angular pressing) equal 0.24, 0.32, and 0.35, respectively. The effect of disintegration into nano-sized powders was found to occur in the Al-15% Sn-25% Pb, and Al-5% Sn-35% Pb alloys after severe plastic deformation to ɛ = 6.4 and subsequent short-time holding.

Thermodynamically consistent relations involving plasticity, internal energy and thermal effects.

PubMed

Schreyer, H L; Maudlin, P J

2005-11-15

Experimental data associated with plastic deformations indicate that the temperature is less than that predicted from dissipation based on plastic work. To obtain reasonable correlation between theoretical and experimental results, the plastic work is often multiplied by a constant beta. This paper provides an alternative thermodynamic framework in which it is proposed that there is an additional internal energy associated with dislocation pile-up or increase in dislocation density. The form of this internal energy follows from experimental data that relates flow stress to dislocation density and to equivalent plastic strain. The result is that beta is not a constant but a derived function. Representative results for beta and temperature as functions of effective plastic strain are provided for both an uncoupled and a coupled thermoplastic theory. In addition to providing features that are believed to be representative of many metals, the formulation can be used as a basis for more advanced theories such as those needed for large deformations and general forms of internal energy.

Nature and mechanisms of elastic deformations for a rock mass with several workings. [Deviations from superposition of individual effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagunov, A.S.; Seryakov, V.M.

1985-07-01

This paper presents results of a study which indicates that as a result of the solution for a nonuniform rock mass by the FEM it is established that, first, from the direction of the hanging wall of workings and at the surface, the nature of elastic deformation of the rock is equivalent to that observed under natural conditions, and from the direction of the lying wall of workings and close to their ends there is short-lived rotational creation of elastic displacements, extinguished as plastic deformation develops. Second, the superposition principle, taken as the basis for algebraic summation of displacements andmore » deformations due to individual workings, is not entirely observed in their joint effect on the rock mass in the elastic stage, and with plastic and shear deformation of rocks (partial or complete), depending on their bedding conditions.« less

Evaluating the damage of steel 09G2S under static and cyclic loading with regard for the level of residual stresses in the metal

NASA Astrophysics Data System (ADS)

Kuznetsov, A. V.; Kamantsev, I. S.; Zadvorkin, S. M.; Drukarenko, N. A.; Goruleva, L. S.; Veselova, V. E.

2017-12-01

An approach to the estimation of the residual durability of structural elements in view of their initial stress-strain state is proposed. The adequacy of the developed approach is confirmed by experiments on cyclic loading of specimens without pronounced stress concentrators simulating the work of real structural elements under conditions of overshooting the total stresses causing local plastic deformation of the material, with regard for residual stresses.

Fatigue-Crack-Growth Structural Analysis

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.

1986-01-01

Elastic and plastic deformations calculated under variety of loading conditions. Prediction of fatigue-crack-growth lives made with FatigueCrack-Growth Structural Analysis (FASTRAN) computer program. As cyclic loads are applied to initial crack configuration, FASTRAN predicts crack length and other parameters until complete break occurs. Loads are tensile or compressive and of variable or constant amplitude. FASTRAN incorporates linear-elastic fracture mechanics with modifications of load-interaction effects caused by crack closure. FASTRAN considered research tool, because of lengthy calculation times. FASTRAN written in FORTRAN IV for batch execution.

Interfacial diffusion aided deformation during nanoindentation

DOE PAGES

Samanta, Amit; E., Weinan

2015-07-06

Nanoindentation is commonly used to quantify the mechanical response of material surfaces. Despite its widespread use, a detailed understanding of the deformation mechanisms responsible for plasticity during these experiments has remained elusive. Nanoindentation measurements often show stress values close to a material’s ideal strength which suggests that dislocation nucleation and subsequent dislocation activity dominates the deformation. However, low strain-rate exponents and small activation volumes have also been reported which indicates high temperature sensitivity of the deformation processes. Using an order parameter aided temperature accelerated sampling technique called adiabatic free energy dynamics [J. B. Abrams and M. E. Tuckerman, J. Phys.more » Chem. B, 112, 15742 (2008)], and molecular dynamics we have probed the diffusive mode of deformation during nanoindentation. Localized processes such as surface vacancy and ad-atom pair formation, vacancy diffusion are found to play an important role during indentation. Furthermore, our analysis suggests a change in the dominant deformation mode from dislocation mediated plasticity to diffusional flow at high temperatures, slow indentation rates and small indenter tip radii.« less

Elasticity and anelasticity of microcrystalline aluminum samples having various deformation and thermal histories

NASA Astrophysics Data System (ADS)

Betekhtin, V. I.; Kadomtsev, A. G.; Kardashev, B. K.

2006-08-01

The effect of the amplitude of vibrational deformation on the elastic modulus and internal friction of microcrystalline aluminum samples produced by equal-channel angular pressing was studied. The samples have various deformation and thermal histories. The elastic and inelastic (microplastic) properties of the samples are investigated. As the degree of plastic deformation increases, the Young’s modulus E, the amplitude-independent decrement δi, and the microplastic flow stress σ increase. As the annealing temperature increases, the quantities δi and σ decrease noticeably and the modulus E exhibits a more complex behavior. The experimental data are discussed under the assumption that the dislocation mobility depends on both the spectrum of point defects and the internal stresses, whose level is determined by the degree of plastic deformation and the temperature of subsequent annealing. The concept of internal stresses is also used to analyze the data on the effect of the degree of deformation and annealing on the rupture strength of the samples.

Experimental and numerical investigation on laser-assisted bending of pre-loaded metal plate

NASA Astrophysics Data System (ADS)

Nowak, Zdzisław; Nowak, Marcin; Widłaszewski, Jacek; Kurp, Piotr

2018-01-01

The laser forming technique has an important disadvantage, which is the limitation of plastic deformation generated by a single laser beam pass. To increase the plastic deformation it is possible to apply external forces in the laser forming process. In this paper, we investigate the influence of external pre-loads on the laser bending of steel plate. The pre-loads investigated generate bending towards the laser beam. The thermal, elastic-plastic analysis is performed using the commercial nonlinear finite element analysis package ABAQUS. The focus of the paper is to identify how this pattern of the pre-load influence the final bend angle of the plate.

Ultra fine grained Ti prepared by severe plastic deformation

NASA Astrophysics Data System (ADS)

Lukáč, F.; Čížek, J.; Knapp, J.; Procházka, I.; Zháňal, P.; Islamgaliev, R. K.

2016-01-01

The positron annihilation spectroscopy was employed for characterisation of defects in pure Ti with ultra fine grained (UFG) structure. UFG Ti samples were prepared by two techniques based on severe plastic deformation (SPD): (i) high pressure torsion (HPT) and (ii) equal channel angular pressing (ECAP). Although HPT is the most efficient technique for grain refinement, the size of HPT-deformed specimens is limited. On the other hand, ECAP is less efficient in grain refinement but enables to produce larger samples more suitable for industrial applications. Characterisation of defects by positron annihilation spectroscopy was accompanied by hardness testing in order to monitor the development of mechanical properties of UFG Ti.

High-strength laser welding of aluminum-lithium scandium-doped alloys

NASA Astrophysics Data System (ADS)

Malikov, A. G.; Ivanova, M. Yu.

2016-11-01

The work presents the experimental investigation of laser welding of an aluminum alloy (system Al-Mg-Li) and aluminum alloy (system Al-Cu-Li) doped with Sc. The influence of nano-structuring of the surface layer welded joint by cold plastic deformation on the strength properties of the welded joint is determined. It is founded that, regarding the deformation degree over the thickness, the varying value of the welded joint strength is different for these aluminum alloys. The strength of the plastically deformed welded joint, aluminum alloys of the Al-Mg-Li and Al-Cu-Li systems reached 0.95 and 0.6 of the base alloy strength, respectively.

Structure of aging Al-Li-Cu-Zr-Sc-Ag alloy after severe plastic deformation and long-term storage

NASA Astrophysics Data System (ADS)

Kaigorodova, L. I.; Rasposienko, D. Yu.; Pushin, V. G.; Pilyugin, V. P.; Smirnov, S. V.

2015-11-01

Structural and phase transformations in commercial aging aluminum-lithium Al-1.2 Li-3.2 Cu-0.09 Zr-0.11 Sc-0.4 Ag-0.3 Mg alloy have been studied after severe plastic deformation by high-pressure torsion (at a pressure of 4 GPa with 1, 5, and 10 revolutions of the anvil) and natural aging (roomtemperature storage) for 1 week and 2 years. It has been found that, in this case, the process of static recrystallization is achieved in the alloy, the degree of which increases with an increasing degree of deformation and time of storage.

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE PAGES

Gao, Yanfei

2015-11-30

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Deformation fields near a steady fatigue crack with anisotropic plasticity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Yanfei

In this work, from finite element simulations based on an irreversible, hysteretic cohesive interface model, a steady fatigue crack can be realized if the crack extension exceeds about twice the plastic zone size, and both the crack increment per loading cycle and the crack bridging zone size are smaller than the plastic zone size. The corresponding deformation fields develop a plastic wake behind the crack tip and a compressive residual stress field ahead of the crack tip. In addition, the Hill’s plasticity model is used to study the role of plastic anisotropy on the retardation of fatigue crack growth andmore » the elastic strain fields. It is found that for Mode-I cyclic loading, an enhanced yield stress in directions that are inclined from the crack plane will lead to slower crack growth rate, but this retardation is insignificant for typical degrees of plastic anisotropy. Furthermore, these results provide key inputs for future comparisons to neutron and synchrotron diffraction measurements that provide full-field lattice strain mapping near fracture and fatigue crack tips, especially in textured materials such as wrought or rolled Mg alloys.« less

Grain refinement and Lattice Imperfections in Commercial Aluminum Alloy Processed by Severe Plastic Deformation

NASA Astrophysics Data System (ADS)

Charfeddine, Saifeddine; Zehani, Karim; Besais, Lotfi; Korchef, Atef

2014-08-01

In the present work, investigations on the microstructure of an aluminum alloy that had been subjected to severe plastic deformation (SPD) by equal channel angular pressing (ECAP), filing and ball milling, were carried out using X-ray diffraction and scanning electron microscopy. SPD leads to lattice distortions, increased dislocation density and an intensive refinement of the microstructure. The refinement and lattice imperfections of the material are greatly affected by the deformation modes and loading performance occurring during SPD. During the milling, the dislocation annihilation increases at higher strains thereby resulting in a smaller crystallite size. After ECAP, the material manifests a strong shear texture and anisotropy of the deformation behavior. Strain anisotropy is less pronounced in filed and ball milled powder particles.

Deformation Twins in Nanocrystalline Body-Centered Cubic Mo as Predicted by Molecular Dynamics Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michael Tonks; Bulent biner; Yongfeng Zhang

2012-10-01

This work studies deformation twins in nanocrystalline body-centered cubic Mo, including the nucleation and growth mechanisms as well as their effects on ductility, through molecular dynamics simulations. The deformation processes of nanocrystalline Mo are simulated using a columnar grain model with three different orientations. The deformation mechanisms identified, including dislocation slip, grain-boundary-mediated plasticity, deformation twins and martensitic transformation, are in agreement with previous studies. In (1 1 0) columnar grains, the deformation is dominated by twinning, which nucleates primarily from the grain boundaries by successive emission of twinning partials and thickens by jog nucleation in the grain interiors. Upon arrestmore » by a grain boundary, the twin may either produce continuous plastic strain across the grain boundary by activating compatible twinning/slip systems or result in intergranular failure in the absence of compatible twinning/slip systems in the neighboring grain. Multiple twinning systems can be activated in the same grain, and the competition between them favors those capable of producing continuous deformation across the grain boundary.« less

Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

NASA Astrophysics Data System (ADS)

Satheesh Kumar, S. S.; Raghu, T.

2015-02-01

Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

Microstructural Changes During Plastic Deformation and Corrosion Properties of Biomedical Co-20Cr-15W-10Ni Alloy Heat-Treated at 873 K

NASA Astrophysics Data System (ADS)

Ueki, Kosuke; Ueda, Kyosuke; Nakai, Masaaki; Nakano, Takayoshi; Narushima, Takayuki

2018-04-01

Microstructural changes were observed during the plastic deformation of ASTM F90 Co-20Cr-15W-10Ni (mass pct) alloy heat-treated at 873 K (600 °C) for 14.4 ks, and analyzed by electron backscatter diffraction and in situ X-ray diffraction techniques. The obtained results revealed that the area fraction of the ɛ-phase (f ɛ ) in the as-received alloy was higher than that in the heat-treated alloy in the low-to-middle strain region (≤ 50 pct), whereas the f ɛ of the heat-treated alloy was higher than that of the as-received alloy at the fracture point. During plastic deformation, the ɛ-phase was preferentially formed at the twin boundaries of the heat-treated alloy rather than at the grain boundaries. According to the transmission electron microscopy observations, the thin ɛ-phase layer formed due to the alloy heat treatment acted as the origin of deformation twinning, which decreased the stress concentration at the grain boundaries. The results of anodic polarization testing showed that neither the heat treatment at 873 K (600 °C) nor plastic deformation affected the alloy corrosion properties. To the best of our knowledge, this is the first study proving that the formation of a thin ɛ-phase layer during the low-temperature heat treatment of the studied alloy represents an effective method for the enhancement of the alloy ductility without sacrificing its strength and corrosion properties.

Microstructural Changes During Plastic Deformation and Corrosion Properties of Biomedical Co-20Cr-15W-10Ni Alloy Heat-Treated at 873 K

NASA Astrophysics Data System (ADS)

Ueki, Kosuke; Ueda, Kyosuke; Nakai, Masaaki; Nakano, Takayoshi; Narushima, Takayuki

2018-06-01

Microstructural changes were observed during the plastic deformation of ASTM F90 Co-20Cr-15W-10Ni (mass pct) alloy heat-treated at 873 K (600 °C) for 14.4 ks, and analyzed by electron backscatter diffraction and in situ X-ray diffraction techniques. The obtained results revealed that the area fraction of the ɛ-phase ( f ɛ ) in the as-received alloy was higher than that in the heat-treated alloy in the low-to-middle strain region (≤ 50 pct), whereas the f ɛ of the heat-treated alloy was higher than that of the as-received alloy at the fracture point. During plastic deformation, the ɛ-phase was preferentially formed at the twin boundaries of the heat-treated alloy rather than at the grain boundaries. According to the transmission electron microscopy observations, the thin ɛ-phase layer formed due to the alloy heat treatment acted as the origin of deformation twinning, which decreased the stress concentration at the grain boundaries. The results of anodic polarization testing showed that neither the heat treatment at 873 K (600 °C) nor plastic deformation affected the alloy corrosion properties. To the best of our knowledge, this is the first study proving that the formation of a thin ɛ-phase layer during the low-temperature heat treatment of the studied alloy represents an effective method for the enhancement of the alloy ductility without sacrificing its strength and corrosion properties.

Ultrafine-Grained Pure Ti Processed by New SPD Scheme Combining Drawing with Shear

NASA Astrophysics Data System (ADS)

Raab, A. G.; Bobruk, E. V.; Raab, G. I.

2018-05-01

The paper displays the results of the studies and analysis of a promising severe plastic deformation scheme that implements the conditions of a non-monotonous impact during shear drawing of long-length bulk metal materials. The paper describes the efficiency of the proposed severe plastic deformation technique to form a gradient ultrafine-grained state in rod-shaped billets on the example of commercially pure Ti and its further development for future industrial applications.

A unified dislocation density-dependent physical-based constitutive model for cold metal forming

NASA Astrophysics Data System (ADS)

Schacht, K.; Motaman, A. H.; Prahl, U.; Bleck, W.

2017-10-01

Dislocation-density-dependent physical-based constitutive models of metal plasticity while are computationally efficient and history-dependent, can accurately account for varying process parameters such as strain, strain rate and temperature; different loading modes such as continuous deformation, creep and relaxation; microscopic metallurgical processes; and varying chemical composition within an alloy family. Since these models are founded on essential phenomena dominating the deformation, they have a larger range of usability and validity. Also, they are suitable for manufacturing chain simulations since they can efficiently compute the cumulative effect of the various manufacturing processes by following the material state through the entire manufacturing chain and also interpass periods and give a realistic prediction of the material behavior and final product properties. In the physical-based constitutive model of cold metal plasticity introduced in this study, physical processes influencing cold and warm plastic deformation in polycrystalline metals are described using physical/metallurgical internal variables such as dislocation density and effective grain size. The evolution of these internal variables are calculated using adequate equations that describe the physical processes dominating the material behavior during cold plastic deformation. For validation, the model is numerically implemented in general implicit isotropic elasto-viscoplasticity algorithm as a user-defined material subroutine (UMAT) in ABAQUS/Standard and used for finite element simulation of upsetting tests and a complete cold forging cycle of case hardenable MnCr steel family.

Dislocation-mediated trapping of deuterium in tungsten under high-flux high-temperature exposures

NASA Astrophysics Data System (ADS)

Bakaeva, A.; Terentyev, D.; De Temmerman, G.; Lambrinou, K.; Morgan, T. W.; Dubinko, A.; Grigorev, P.; Verbeken, K.; Noterdaeme, J. M.

2016-10-01

The effect of severe plastic deformation on the deuterium retention in tungsten exposed to high-flux low-energy plasma (flux ∼1024 m-2 s-1, energy ∼50 eV and fluence up to 5 × 1025 D/m2) was studied experimentally in a wide temperature range (460-1000 K) relevant for application in ITER. The desorption spectra in both reference and plastically-deformed samples were deconvoluted into three contributions associated with the detrapping from dislocations, deuterium-vacancy clusters and pores. As the exposure temperature increases, the positions of the release peaks in the plastically-deformed material remain in the same temperature range but the peak amplitudes are altered as compared to the reference material. The desorption peak attributed to the release from pores (i.e. cavities and bubbles) was suppressed in the plastically deformed samples for the low-temperature exposures, but became dominant for exposures above 700 K. The observed strong modulation of the deuterium storage in "shallow" and "deep" traps, as well as the reduction of the integral retention above 700 K, suggest that the dislocation network changes its role from "trapping sites" to "diffusion channels" above a certain temperature. The major experimental observations of the present work are in line with recent computational assessment based on atomistic and mean field theory calculations available in literature.

Temperature-compensated strain measurement using fiber Bragg grating sensors embedded in composite laminates

NASA Astrophysics Data System (ADS)

Tanaka, Nobuhira; Okabe, Yoji; Takeda, Nobuo

2003-12-01

For accurate strain measurement by fiber Bragg grating (FBG) sensors, it is necessary to compensate the influence of temperature change. In this study two devices using FBG sensors have been developed for temperature-compensated strain measurement. They are named 'hybrid sensor' and 'laminate sensor', respectively. The former consists of two different materials connected in series: carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic. Each material contains an FBG sensor with a different Bragg wavelength, and both ends of the device are glued to a structure. Using the difference of their Young's moduli and coefficients of thermal expansion, both strain and temperature can be measured. The latter sensor is a laminate of two 90° plies of CFRP and an epoxy plate, and an FBG sensor is embedded in the epoxy plate. When the temperature changes, the cross section of the optical fiber is deformed by the thermal residual stress. The deformation of the fiber causes the birefringence and widens the reflection spectrum. Since the temperature can be calculated from the spectrum width, which changes in proportion to the temperature, the accuracy of the strain measurement is improved. The usefulness of these sensors was experimentally confirmed.

Temperature-compensated strain measurement using FBG sensors embedded in composite laminates

NASA Astrophysics Data System (ADS)

Tanaka, Nobuhira; Okabe, Yoji; Takeda, Nobuo

2002-07-01

For accurate strain measurement by fiber Bragg grating (FBG) sensors, it is necessary to compensate the influence of temperature change. In this study two devices using FBG sensors have been developed for temperature-compensated strain measurement. They are named hybrid sensor and laminate sensor, respectively. The former consists of two different materials connected in series: carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP). Each material contains an FBG sensor with a different Bragg wavelength, and both ends of the device are glue to a structure. Using the difference of their Young's moduli and coefficients of thermal expansion (CTEs), both strain and temperature can be measured. The latter sensor is a laminate of two 90 degree(s) plies of CFRP and an epoxy plate, and an FBG sensor is embedded in the epoxy plate. When the temperature changes, the cross section of the optical fiber is deformed by the thermal residual stress. The deformation of the fiber causes the birefringence and widens the reflection spectrum. Since the temperature can be calculated from the spectrum width, which changes in proportion to the temperature, the accuracy of the strain measurement is improved. The usefulness of these sensors were experimentally confirmed.

Effect of thermomechanical treatment on the microstructure, phase composition, and mechanical properties of Al-Cu-Mn-Mg-Zr alloy

NASA Astrophysics Data System (ADS)

Zuiko, I. S.; Gazizov, M. R.; Kaibyshev, R. O.

2016-09-01

The effect of the thermomechanical treatment on the microstructure, phase composition, and mechanical properties of heat-treatable AA2519 aluminum alloy (according to the classification of the Aluminum Association) has been considered. After solid-solution treatment, quenching, and artificial aging (T6 treatment) at 180°C for the peak strength, the yield stress, ultimate tensile strength, and elongation to failure are ~300 MPa, 435 MPa, and 21.7%, respectively. It has been shown that treatments that include intermediate plastic deformations with degrees of 7 and 15% (T87 and T815 treatments, respectively) have a significant effect on the phase composition and morphology of strengthening particles precipitated during peak aging T8X type, where X is pre-strain percent, treatments initiate the precipitation of significant amounts of particles of the θ'- and Ω-phases. After T6 treatment, predominantly homogeneously distributed particles of θ″-phase have been observed. Changes in the microstructure and phase composition of the AA2519 alloy, which are caused by intermediate deformation, lead to a significant increase in the yield stress and ultimate tensile strength (by ~40 and ~8%, respectively), whereas the plasticity decreases by 40-50%.

Investigations of lunar materials

NASA Technical Reports Server (NTRS)

Comstock, G. M.; Fvwaraye, A. O.; Fleischer, R. L.; Hart, H. R., Jr.

1972-01-01

The investigations were directed at determining the radiation history and surface chronology of lunar materials using the etched particle track technique. The major lunar materials studied are the igneous rocks and double core from Apollo 12, the breccia and soil samples from Apollo 14, and the core samples from Luna 16. In the course of this work two new and potentially important observations were made: (1) Cosmic ray-induced spallation-recoil tracks were identified. The density of such tracks, when compared with the density of tracks induced by a known flux of accelerator protons, yields the time of exposure of a sample within the top meter or two of moon's surface. (2) Natural, fine scale plastic deformation was found to have fragmented pre-existing charged particle tracks, allowing the dating of the mechanical event causing the deformation.

Analysis of Surface and Subsurface Damage Morphology in Rotary Ultrasonic Machining of BK7 Glass

NASA Astrophysics Data System (ADS)

Hong-xiang, Wang; Chu, Wang; Jun-liang, Liu; Shi, Gao; Wen-Jie, Zhai

2017-11-01

This paper investigates the formation process of surface/subsurface damage in the rotary ultrasonic machining of BK7 glass. The results show that during the milling using the end face of the tool, the cutting depth and the residual height between the abrasive grains constantly change with the high-frequency vibration, generating lots of cracks on both sides of the scratches. The high-frequency vibration accelerates the chips falling from the surface, so that the chips and thermal damage are reduced, causing the grinding surface quality better. A plastic deformation area is formed during the grinding, due to the non-uniform cutting force on the material surface, and the residual stress is produced in the deformation area, inducing the median/lateral cracks.

Evading the strength–ductility trade-off dilemma in steel through gradient hierarchical nanotwins

PubMed Central

Wei, Yujie; Li, Yongqiang; Zhu, Lianchun; Liu, Yao; Lei, Xianqi; Wang, Gang; Wu, Yanxin; Mi, Zhenli; Liu, Jiabin; Wang, Hongtao; Gao, Huajian

2014-01-01

The strength–ductility trade-off has been a long-standing dilemma in materials science. This has limited the potential of many structural materials, steels in particular. Here we report a way of enhancing the strength of twinning-induced plasticity steel at no ductility trade-off. After applying torsion to cylindrical twinning-induced plasticity steel samples to generate a gradient nanotwinned structure along the radial direction, we find that the yielding strength of the material can be doubled at no reduction in ductility. It is shown that this evasion of strength–ductility trade-off is due to the formation of a gradient hierarchical nanotwinned structure during pre-torsion and subsequent tensile deformation. A series of finite element simulations based on crystal plasticity are performed to understand why the gradient twin structure can cause strengthening and ductility retention, and how sequential torsion and tension lead to the observed hierarchical nanotwinned structure through activation of different twinning systems. PMID:24686581

The effect of matrix microstructure on cyclic response and fatigue behavior of particle-reinforced 2219 aluminum: Part II. Behavior at 150 °C

NASA Astrophysics Data System (ADS)

Vyletel, G. M.; van Aken, D. C.; Allison, J. E.

1995-12-01

The 150 °C cyclic response of peak-aged and overaged 2219/TiC/15p and 2219 Al was examined using fully reversed plastic strain-controlled testing. The cyclic response of peak-aged and overaged particle-reinforced materials showed extensive cyclic softening. This softening began at the commencement of cycling and continued until failure. At a plastic strain below 5 × 103, the unreinforced materials did not show evidence of cyclic softening until approximately 30 pct of the life was consumed. In addition, the degree of cyclic softening (†σ) was significantly lower in the unreinforced microstructures. The cyclic softening in both reinforced and unreinforced materials was attributed to the decomposition of the θ' strengthening precipitates. The extent of the precipitate decomposition was much greater in the composite materials due to the increased levels of local plastic strain in the matrix caused by constrained deformation near the TiC particles.

Rapid Grain Size Reduction in the Upper Mantle at a Plate Boundary

NASA Astrophysics Data System (ADS)

Kidder, S. B.; Scott, J.; Prior, D. J.; Lubicich, E. J.

2017-12-01

A few spinel peridotite xenoliths found near the Alpine Fault, New Zealand, exhibit a mylonitic texture and, locally, an extremely fine 30 micron grain size. The harzburgite xenoliths were emplaced in a 200 km-long elongate dike zone interpreted as a gigantic tension fracture or Reidel shear associated with Alpine Fault initiation 25 Ma. The presence of thin ( 1 mm) ultramylonite zones with px-ol phase mixing and fine grain sizes, minimal crustal-scale strain associated with the dike swarm, and the absence of mylonites at four of the five xenolith localities associated with the dike swarm indicate that upper mantle deformation was highly localized. Strings of small, recrystallized grains (planes in 3D) are found in the interiors of olivine porphyroclasts. In some cases, bands 1-2 grains thick are traced from the edges of olivine grains and terminate in their interiors. Thicker zones of recrystallized grains are also observed crossing olivine porphyroclasts without apparent offset of the unrecrystallized remnants of the porphyroclasts. We suggest a brittle-plastic origin for these features since the traditional recrystallization mechanisms associated with dislocation creep require much more strain than occurred within these porphyroclasts. Analogous microstructures in quartz and feldspar in mid-crust deformation zones are attributed to brittle-plastic processes. We hypothesize that such fine-grained zones were the precursors of the observed, higher-strain ultramylonite zones. Given the size of the new grains preserved in the porphyroclasts ( 100 micron) and a moho temperature > 650°C, grain growth calculations indicate that the observed brittle-plastic deformation occurred <10,000 yrs. prior to eruption. It is likely then that either brittle-plastic deformation was coeval with the ductile shearing occurring in the ultramylonite bands, or possibly, if deformation can be separated into brittle-plastic (early) and ductile (later) phases, that the entire localization process was very rapid (<10,000 yrs). In either case we interpret that semi-brittle deformation was a key process responsible for rapid localization in this initiating plate-scale mantle shear zone.

Evaluation of cutting ability and plastic deformation of reciprocating files.

PubMed

Kowalczuck, Alexandre; Sydney, Gilson Blitzkow; Martinez, Elizabeth Ferreira; Cardoso, Rielson José Alves

2016-01-01

This in vitro study evaluated the cutting ability of reciprocating files and the deformations caused by their multiple use. Five Reciproc® R25 files were divided into five groups for 10 simulated root canal preparations each. The resin blocks were weighed and photographed (12.5X and 20X) before and after preparation. The canals were prepared according to the manufacturer's instructions. Enlargement of the root canals was evaluated by comparison of pre- and post-preparation images using a computer software. The preoperative and postoperative weight differences determined the cutting ability of repeatedly used instruments. The data were analyzed using Lilliefors and Friedman statistical tests. The cutting ability and enlargement of the canals gradually decreased after each use, with significant differences observed at the 8th and 9th repetitions, respectively. There was no evidence of file deformation. The cutting ability and enlargement of the simulated canals gradually decreased when a reciprocating file was used up to 10 times.

The Work Softening by Deformation-Induced Disordering and Cold Rolling of 6.5 wt pct Si Steel Thin Sheets

NASA Astrophysics Data System (ADS)

Wang, Xianglong; Li, Haoze; Zhang, Weina; Liu, Zhenyu; Wang, Guodong; Luo, Zhonghan; Zhang, Fengquan

2016-09-01

As-cast strip of 6.5 wt pct Si steel was fabricated by twin-roll strip casting. After hot rolling at 1323 K (1050 °C), thin sheets with the thickness of 0.35 mm were produced by warm rolling at 373 K (100 °C) with rolling reductions of 15, 25, 35, 45, 55, and 65 pct. Influence of warm rolling reduction on ductility was investigated by room temperature bending test. The measurement of macro-hardness showed that "work softening" could begin when the warm rolling reduction exceeded 35 pct. The room temperature ductility of the thin sheets gradually increased with the increase of warm rolling reductions, and the plastic deformation during bending began to form when the warm rolling reduction was greater than 45 pct, the 65 pct rolled thin sheet exhibited the maximum plastic deformation of about 0.6 pct during bending at room temperature, with a few small dimples having been observed on the fracture surfaces. B2-ordered domains were formed in the 15, 25, 35, 45, and 55 pct rolled specimens, and their average size decreased with the increase of warm rolling reductions. By contrast, no B2-ordered domain could be found in the 65 pct rolled specimen. It had been observed that large-ordered domains could be split into several small parts by the slip of partial super-dislocations during warm rolling, which led to significant decrease of the order degree to cause the phenomenon of deformation-induced disordering. On the basis of these results, cold rolling schedule was developed to successfully fabricate 0.25-mm-thick sheets with good surface qualities and magnetic properties from warm rolled sheets.

Distortion-free foamed-plastic parts

NASA Technical Reports Server (NTRS)

Hogenson, P. A.; Jackson, R. G.

1979-01-01

In process for molding foamed-plastic products, gases that are formed as byproducts of foaming reaction escape through perforated die. Thus, volatiles are not trapped in pockets that can deform and weaken the molded part.

Elasto-limited plastic analysis of structures for probabilistic conditions

NASA Astrophysics Data System (ADS)

Movahedi Rad, M.

2018-06-01

With applying plastic analysis and design methods, significant saving in material can be obtained. However, as a result of this benefit excessive plastic deformations and large residual displacements might develop, which in turn might lead to unserviceability and collapse of the structure. In this study, for deterministic problem the residual deformation of structures is limited by considering a constraint on the complementary strain energy of the residual forces. For probabilistic problem the constraint for the complementary strain energy of the residual forces is given randomly and critical stresses updated during the iteration. Limit curves are presented for the plastic limit load factors. The results show that these constraints have significant effects on the load factors. The formulations of the deterministic and probabilistic problems lead to mathematical programming which are solved by the use of nonlinear algorithm.

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

DOE PAGES

Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; ...

2015-10-19

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. We demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. Furthermore, this “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising frommore » increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. Our results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen.« less

Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

PubMed Central

Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; Liu, Zhan-Li; Ma, Evan; Li, Ju; Sun, Jun; Zhuang, Zhuo; Dao, Ming; Shan, Zhi-Wei; Suresh, Subra

2015-01-01

When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen. PMID:26483463

Investigation of Thermal Hardening of the FCC Material Containing Strengthening Particles with an L12 Superstructure

NASA Astrophysics Data System (ADS)

Daneyko, O. I.; Kulaeva, N. A.; Kovalevskaya, C. A.; Kolupaeva, S. N.

2015-07-01

A mathematical model of plastic deformation of dispersion-hardened materials with an fcc matrix containing strengthening particles with an L12 superstructure having a coherent relationship with the matrix is presented. The model is based on the balance equations of deformation defects of different types with taking into account their transformation during plastic deformation. The influence of scale characteristics of the hardening phase, temperature, and deformation rate on the evolution of the dislocation subsystem and strain hardening of an alloy with an fcc matrix hardened by particles with an L12 super structure is studied. A temperature anomaly of mechanical properties is found for the materials with different fcc matrices (Al,Cu, Ni). It is shown that the temperature anomaly is more pronounced for the material with larger volume fraction of the hardening phase.

Calculation of cracking under pulsed heat loads in tungsten manufactured according to ITER specifications

NASA Astrophysics Data System (ADS)

Arakcheev, A. S.; Skovorodin, D. I.; Burdakov, A. V.; Shoshin, A. A.; Polosatkin, S. V.; Vasilyev, A. A.; Postupaev, V. V.; Vyacheslavov, L. N.; Kasatov, A. A.; Huber, A.; Mertens, Ph; Wirtz, M.; Linsmeier, Ch; Kreter, A.; Löwenhoff, Th; Begrambekov, L.; Grunin, A.; Sadovskiy, Ya

2015-12-01

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle-ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating-cooling cycle for a material without initial plastic deformation. The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths.

Procedures for experimental measurement and theoretical analysis of large plastic deformations

NASA Technical Reports Server (NTRS)

Morris, R. E.

1974-01-01

Theoretical equations are derived and analytical procedures are presented for the interpretation of experimental measurements of large plastic strains in the surface of a plate. Orthogonal gage lengths established on the metal surface are measured before and after deformation. The change in orthogonality after deformation is also measured. Equations yield the principal strains, deviatoric stresses in the absence of surface friction forces, true stresses if the stress normal to the surface is known, and the orientation angle between the deformed gage line and the principal stress-strain axes. Errors in the measurement of nominal strains greater than 3 percent are within engineering accuracy. Applications suggested for this strain measurement system include the large-strain-stress analysis of impact test models, burst tests of spherical or cylindrical pressure vessels, and to augment small-strain instrumentation tests where large strains are anticipated.

Influence of localized plasticity on oxidation behaviour of austenitic stainless steels under primary water reactor

NASA Astrophysics Data System (ADS)

Cissé, Sarata; Laffont, Lydia; Lafont, Marie-Christine; Tanguy, Benoit; Andrieu, Eric

2013-02-01

The sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δɛp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown.

Phase transformation dependence on initial plastic deformation mode in Si via nanoindentation

DOE PAGES

Wong, Sherman; Haberl, Bianca; Williams, James S.; ...

2016-09-30

Silicon in its diamond-cubic phase is known to phase transform to a technologically interesting mixture of the body-centred cubic and rhombohedral phases under nanoindentation pressure. In this study, we demonstrate that during plastic deformation the sample can traverse two distinct pathways, one that initially nucleates a phase transformation while the other initially nucleates crystalline defects. These two pathways remain distinct even after sufficient pressure is applied such that both deformation mechanisms are present within the sample. Here, it is further shown that the indents that initially nucleate a phase transformation generate larger, more uniform volumes of the phase transformed materialmore » than indents that initially nucleate crystalline defects.« less

Mechanisms of grain refinement in aluminum alloys in the process of severe plastic deformation

NASA Astrophysics Data System (ADS)

Kaibyshev, R. O.; Mazurina, I. A.; Gromov, D. A.

2006-01-01

A study of the mechanisms of grain refinement in the process of severe plastic deformation of two aluminum alloys, i.e., 2219 bearing nanometric particles of Al3Zr and low-alloy Al-3% Cu, is described. The alloys are deformed by the method of equal channel angular pressing at 250°C to a maximum strain degree of about 12. The angles of (sub)grain boundaries in alloy 2219 are determined with the help of transmission electron microscopy by the method of Kikuchi lines. The evolution of the microstructure in alloy Al-3% Cu is studied with the help of grain-boundary maps obtained by the method of electron back-scattered diffraction.

Plastic deformation at surface during unlubricated sliding

NASA Technical Reports Server (NTRS)

Yamamoto, T.; Buckley, D. H.

1982-01-01

The plastic deformation and wear of 304 stainless-steel surface slid against an aluminum oxide rider were observed by using a scanning electron microscope and an optical microscope. Experiments were conducted in a vacuum of 0.000001 Pa and in an environment of 0.0005 Pa chlorine gas at 25 C. The load was 500 grams and the sliding velocity was 0.5 centimeter per second. The deformed surface layer which accumulates and develops successively is left behind the rider, and step-shaped protuberances are developed even after single pass sliding under both environmental conditions. A fully developed surface layer is gradually torn off leaving a characteristic pattern. These observations result from both adhesion and an adhesive wear mechanism.

Finite Deformations and Internal Forces in Elastic-Plastic Crystals: Interpretations From Nonlinear Elasticity and Anharmonic Lattice Statics

DTIC Science & Technology

2009-09-01

Sec. 2, while the latter ase—which implicitly includes the effects of image forces of efects in neighboring volume elements—may be more practical rom...versetzungen und eigenspannungen,” Arch . Ration. Mech. Anal., 4, pp. 273–334. 25 Lee, E. H., 1969, “Elastic-Plastic Deformation at Finite Strains,” ASME J...Rev., 73, pp. 373–382. 27 Kroner, E., and Seeger, A., 1959, “Nicht-Lineare Elastizitatstheorie der Verset- zungen und Eigenspannungen,” Arch . Ration

Hydrogen Induced Intergranular Cracking of Nickel-Base Alloys.

DTIC Science & Technology

1982-02-01

alloys are discussed. Experimental The steel used in the present investigation is a fully bainitic 2 1/4 Cr-lMo pressure vessel steel , ASTM A542 Class 3...Appendix A describes recent experiments performed in order to study the influence of plastic deformation on hydrogen transport in a 214 Cr-lMo steel (8...PLASTIC DEFORMATION ON HYDROGEN TRANSPORT IN 2 1/4 Cr-lMo STEEL M. Kurkela, G.S. Frankel, and R.M. Latanision Department of Materials Science and

European Conference on Molecular Beam Epitaxy and Related Growth Methods (6th) Held in Tampere, Finland on 21-14 April 1991

DTIC Science & Technology

1991-04-24

2X2) structure caracteristic of a cation rich surface. During the growth we observe intense RHEED oscillations, which show that the growth of Hg...layer which then suffers plastic deformation when the energy stored in the epilayer (proportional to its thickness) is sufficient to create dislocations...table I we present the variation of the in plane lattice mismatch vs. layerthickness. Plastic deformation of the layer starts around 4 to 5 ML, which can

Local microstructure evolution at shear bands in metallic glasses with nanoscale phase separation

PubMed Central

He, Jie; Kaban, Ivan; Mattern, Norbert; Song, Kaikai; Sun, Baoan; Zhao, Jiuzhou; Kim, Do Hyang; Eckert, Jürgen; Greer, A. Lindsay

2016-01-01

At room temperature, plastic flow of metallic glasses (MGs) is sharply localized in shear bands, which are a key feature of the plastic deformation in MGs. Despite their clear importance and decades of study, the conditions for formation of shear bands, their structural evolution and multiplication mechanism are still under debate. In this work, we investigate the local conditions at shear bands in new phase-separated bulk MGs containing glassy nanospheres and exhibiting exceptional plasticity under compression. It is found that the glassy nanospheres within the shear band dissolve through mechanical mixing driven by the sharp strain localization there, while those nearby in the matrix coarsen by Ostwald ripening due to the increased atomic mobility. The experimental evidence demonstrates that there exists an affected zone around the shear band. This zone may arise from low-strain plastic deformation in the matrix between the bands. These results suggest that measured property changes originate not only from the shear bands themselves, but also from the affected zones in the adjacent matrix. This work sheds light on direct visualization of deformation-related effects, in particular increased atomic mobility, in the region around shear bands. PMID:27181922

DYCAST: A finite element program for the crash analysis of structures

NASA Technical Reports Server (NTRS)

Pifko, A. B.; Winter, R.; Ogilvie, P.

1987-01-01

DYCAST is a nonlinear structural dynamic finite element computer code developed for crash simulation. The element library contains stringers, beams, membrane skin triangles, plate bending triangles and spring elements. Changing stiffnesses in the structure are accounted for by plasticity and very large deflections. Material nonlinearities are accommodated by one of three options: elastic-perfectly plastic, elastic-linear hardening plastic, or elastic-nonlinear hardening plastic of the Ramberg-Osgood type. Geometric nonlinearities are handled in an updated Lagrangian formulation by reforming the structure into its deformed shape after small time increments while accumulating deformations, strains, and forces. The nonlinearities due to combined loadings are maintained, and stiffness variation due to structural failures are computed. Numerical time integrators available are fixed-step central difference, modified Adams, Newmark-beta, and Wilson-theta. The last three have a variable time step capability, which is controlled internally by a solution convergence error measure. Other features include: multiple time-load history tables to subject the structure to time dependent loading; gravity loading; initial pitch, roll, yaw, and translation of the structural model with respect to the global system; a bandwidth optimizer as a pre-processor; and deformed plots and graphics as post-processors.

Stability of surface plastic flow in large strain deformation of metals

NASA Astrophysics Data System (ADS)

Viswanathan, Koushik; Udapa, Anirduh; Sagapuram, Dinakar; Mann, James; Chandrasekar, Srinivasan

We examine large-strain unconstrained simple shear deformation in metals using a model two-dimensional cutting system and high-speed in situ imaging. The nature of the deformation mode is shown to be a function of the initial microstructure state of the metal and the deformation geometry. For annealed metals, which exhibit large ductility and strain hardening capacity, the commonly assumed laminar flow mode is inherently unstable. Instead, the imposed shear is accommodated by a highly rotational flow-sinuous flow-with vortex-like components and large-amplitude folding on the mesoscale. Sinuous flow is triggered by a plastic instability on the material surface ahead of the primary region of shear. On the other hand, when the material is extensively strain-hardened prior to shear, laminar flow again becomes unstable giving way to shear banding. The existence of these flow modes is established by stability analysis of laminar flow. The role of the initial microstructure state in determining the change in stability from laminar to sinuous / shear-banded flows in metals is elucidated. The implications for cutting, forming and wear processes for metals, and to surface plasticity phenomena such as mechanochemical Rehbinder effects are discussed.

New design strategy for reversible plasticity shape memory polymers with deformable glassy aggregates.

PubMed

Lin, Tengfei; Tang, Zhenghai; Guo, Baochun

2014-12-10

Reversible plasticity shape memory (RPSM) is a new concept in the study of shape memory performance behavior and describes a phenomenon in which shape memory polymers (SMPs) can undergo a large plastic deformation at room temperature and subsequently recover their original shape upon heating. To date, RPSM behavior has been demonstrated in only a few polymers. In the present study, we implement a new design strategy, in which deformable glassy hindered phenol (AO-80) aggregates are incorporated into an amorphous network of epoxidized natural rubber (ENR) cured with zinc diacrylate (ZDA), in order to achieve RPSM properties. We propose that AO-80 continuously tunes the glass transition temperature (Tg) and improves the chain mobility of the SMP, providing traction and anchoring the ENR chains by intermolecular hydrogen bonding interactions. The RPSM behavior of the amorphous SMPs is characterized, and the results demonstrate good fixity at large deformations (up to 300%) and excellent recovery upon heating. Large energy storage capacities at Td in these RPSM materials are demonstrated compared with those achieved at elevated temperature in traditional SMPs. Interestingly, the further revealed self-healing properties of these materials are closely related to their RPSM behavior.

Shock wave absorber having a deformable liner

DOEpatents

Youngdahl, C.K.; Wiedermann, A.H.; Shin, Y.W.; Kot, C.A.; Ockert, C.E.

1983-08-26

This invention discloses a shock wave absorber for a piping system carrying liquid. The absorber has a plastically deformable liner defining the normal flow boundary for an axial segment of the piping system, and a nondeformable housing is spaced outwardly from the liner so as to define a gas-tight space therebetween. The flow capacity of the liner generally corresponds to the flow capacity of the piping system line, but the liner has a noncircular cross section and extends axially of the piping system line a distance between one and twenty times the diameter thereof. Gas pressurizes the gas-tight space equal to the normal liquid pressure in the piping system. The liner has sufficient structural capacity to withstand between one and one-half and two times this normal liquid pressures; but at greater pressures it begins to plastically deform initially with respect to shape to a more circular cross section, and then with respect to material extension by circumferentially stretching the wall of the liner. A high energy shock wave passing through the liner thus plastically deforms the liner radially into the gas space and progressively also as needed in the axial direction of the shock wave to minimize transmission of the shock wave beyond the absorber.

Forecasting Low-Cycle Fatigue Performance of Twinning-Induced Plasticity Steels: Difficulty and Attempt

NASA Astrophysics Data System (ADS)

Shao, C. W.; Zhang, P.; Zhang, Z. J.; Liu, R.; Zhang, Z. F.

2017-12-01

We find the existing empirical relations based on monotonic tensile properties and/or hardness cannot satisfactorily predict the low-cycle fatigue (LCF) performance of materials, especially for twinning-induced plasticity (TWIP) steels. Given this, we first identified the different deformation mechanisms under monotonic and cyclic deformation after a comprehensive study of stress-strain behaviors and microstructure evolutions for Fe-Mn-C alloys during tension and LCF, respectively. It is found that the good tensile properties of TWIP steel mainly originate from the large activation of multiple twinning systems, which may be attributed to the grain rotation during tensile deformation; while its LCF performance depends more on the dislocation slip mode, in addition to its strength and plasticity. Based on this, we further investigate the essential relations between microscopic damage mechanism (dislocation-dislocation interaction) and cyclic stress response, and propose a hysteresis loop model based on dislocation annihilation theory, trying to quickly assess the LCF resistance of Fe-Mn-C steels as well as other engineering materials. It is suggested that the hysteresis loop and its evolution can provide significant information on cyclic deformation behavior, e.g., (point) defect multiplication and vacancy aggregation, which may help estimate the LCF properties.

Critical Deposition Condition of CoNiCrAlY Cold Spray Based on Particle Deformation Behavior

NASA Astrophysics Data System (ADS)

Ichikawa, Yuji; Ogawa, Kazuhiro

2017-02-01

Previous research has demonstrated deposition of MCrAlY coating via the cold spray process; however, the deposition mechanism of cold spraying has not been clearly explained—only empirically described by impact velocity. The purpose of this study was to elucidate the critical deposit condition. Microscale experimental measurements of individual particle deposit dimensions were incorporated with numerical simulation to investigate particle deformation behavior. Dimensional parameters were determined from scanning electron microscopy analysis of focused ion beam-fabricated cross sections of deposited particles to describe the deposition threshold. From Johnson-Cook finite element method simulation results, there is a direct correlation between the dimensional parameters and the impact velocity. Therefore, the critical velocity can describe the deposition threshold. Moreover, the maximum equivalent plastic strain is also strongly dependent on the impact velocity. Thus, the threshold condition required for particle deposition can instead be represented by the equivalent plastic strain of the particle and substrate. For particle-substrate combinations of similar materials, the substrate is more difficult to deform. Thus, this study establishes that the dominant factor of particle deposition in the cold spray process is the maximum equivalent plastic strain of the substrate, which occurs during impact and deformation.

Stochastic dislocation kinetics and fractal structures in deforming metals probed by acoustic emission and surface topography measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vinogradov, A.; Laboratory of Hybrid Nanostructured Materials, NITU MISiS, Moscow 119490; Yasnikov, I. S.

2014-06-21

We demonstrate that the fractal dimension (FD) of the dislocation population in a deforming material is an important quantitative characteristic of the evolution of the dislocation structure. Thus, we show that peaking of FD signifies a nearing loss of uniformity of plastic flow and the onset of strain localization. Two techniques were employed to determine FD: (i) inspection of surface morphology of the deforming crystal by white light interferometry and (ii) monitoring of acoustic emission (AE) during uniaxial tensile deformation. A connection between the AE characteristics and the fractal dimension determined from surface topography measurements was established. As a commonmore » platform for the two methods, the dislocation density evolution in the bulk was used. The relations found made it possible to identify the occurrence of a peak in the median frequency of AE as a harbinger of plastic instability leading to necking. It is suggested that access to the fractal dimension provided by AE measurements and by surface topography analysis makes these techniques important tools for monitoring the evolution of the dislocation structure during plastic deformation—both as stand-alone methods and especially when used in tandem.« less

Small-scale plasticity critically needs a new mechanics description

NASA Astrophysics Data System (ADS)

Ngan, Alfonso H. W.

2013-06-01

Continuum constitutive laws describe the plastic deformation of materials as a smooth, continuously differentiable process. However, provided that the measurement is done with a fine enough resolution, the plastic deformation of real materials is often found to comprise discrete events usually nanometric in size. For bulk-sized specimens, such nanoscale events are minute compared with the specimen size, and so their associated strain changes are negligibly small, and this is why the continuum laws work well. However, when the specimen size is in the micrometer scale or smaller, the strain changes due to the discrete events could be significant, and the continuum description would be highly unsatisfactory. Yet, because of the advent of microtechnology and nanotechnolgy, small-sized materials will be increasingly used, and so there is a strong need to develop suitable replacement descriptions for plasticity of small materials. As the occurrence of the discrete plastic events is also strongly stochastic, their satisfactory description should also be one of a probabilistic, rather than deterministic, nature.

Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation

PubMed Central

Gayle, Andrew J.; Cook, Robert F.

2016-01-01

An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes. PMID:27563168

Study on the Strain Hardening Behaviors of TWIP/TRIP Steels

NASA Astrophysics Data System (ADS)

Huang, T. T.; Dan, W. J.; Zhang, W. G.

2017-10-01

Due to the complex coupling of twinning-induced plasticity (TWIP), transformation-induced plasticity (TRIP), and dislocation glide in TWIP/TRIP steels, it is difficult as well as essential to build a comprehensive strain hardening model to describe the interactions between different deformation mechanisms ( i.e., deformation twinning, martensitic transformation, and dislocation glide) and the resulted strain hardening behaviors. To address this issue, a micromechanical model is established in this paper to predict the deformation process of TWIP/TRIP steels considering both TWIP and TRIP effects. In the proposed model, the generation of deformation twinning and martensitic transformation is controlled by the stacking fault energy (SFE) of the material. In the thermodynamic calculation of SFE, deformation temperature, chemical compositions, microstrain, and temperature rise during deformation are taken into account. Varied by experimental results, the developed model can predict the stress-strain response and strain hardening behaviors of TWIP/TRIP steels precisely. In addition, the improved strength and enhanced strain hardening in Fe-Mn-C TWIP/TRIP steels due to the increased carbon content is also analyzed, which consists with literature.

High Strain Rate and Shock-Induced Deformation in Metals

NASA Astrophysics Data System (ADS)

Ravelo, Ramon

2012-02-01

Large-scale non-equilibrium molecular Dynamics (MD) simulations are now commonly used to study material deformation at high strain rates (10^9-10^12 s-1). They can provide detailed information-- such as defect morphology, dislocation densities, and temperature and stress profiles, unavailable or hard to measure experimentally. Computational studies of shock-induced plasticity and melting in fcc and bcc single, mono-crystal metals, exhibit generic characteristics: high elastic limits, large directional anisotropies in the yield stress and pre-melting much below the equilibrium melt temperature for shock wave propagation along specific crystallographic directions. These generic features in the response of single crystals subjected to high strain rates of deformation can be explained from the changes in the energy landscape of the uniaxially compressed crystal lattice. For time scales relevant to dynamic shock loading, the directional-dependence of the yield strength in single crystals is shown to be due to the onset of instabilities in elastic-wave propagation velocities. The elastic-plastic transition threshold can accurately be predicted by a wave-propagation stability analysis. These strain-induced instabilities create incipient defect structures, which can be quite different from the ones, which characterize the long-time, asymptotic state of the compressed solid. With increase compression and strain rate, plastic deformation via extended defects gives way to amorphization associated with the loss in shear rigidity along specific deformation paths. The hot amorphous or (super-cooled liquid) metal re-crystallizes at rates, which depend on the temperature difference between the amorphous solid and the equilibrium melt line. This plastic-amorphous transition threshold can be computed from shear-waves stability analyses. Examples from selected fcc and bcc metals will be presented employing semi-empirical potentials of the embedded atom method (EAM) type as well as results from density functional theory calculations.

Modeling dislocation generation in high pressure Czochralski growth of indium phosphide single crystals

NASA Astrophysics Data System (ADS)

Pendurti, Srinivas

InP is an important material for opto-electronic and high speed electronics applications. Its main use today is as the substrate material for epitaxy to produce GaInAsP lasers. The present technology for growing bulk InP is the high pressure Czochralski process. Bulk InP grown through this technique suffers from presence of a high density of line defects or dislocations, which are produced by thermal stresses the material goes through during its growth in the high temperature furnace. Modeling of these thermal stresses and the resulting plastic deformation, giving rise to dislocation densities, entails simulation of the entire thermal history of the crystal during its growth in the furnace, and studying the deformation of the crystal through suitable visco-plastic constitutive equations. Accordingly, a suitable visco-plastic model for deformation of InP was constructed, integrated with the ABAQUS finite element code, and verified through experimental data for uniaxial constant strain rate deformation tests available in literature. This was then coupled with a computation fluid dynamics model, predicting the entire temperature history in the furnace during crystal growth, to study the plastic deformation and dislocation density evolution in the crystal during growth. Growth in a variety of conditions was simulated and those conditions that generate minimum dislocation density identified. Macroscopic controllable parameters that affect the dislocation densities the most, have also been delineated. It was found that the strength of gas convection in the Czochralski furnace has the strongest effect on the dislocation densities in the fully grown crystal. Comparison of the simulated dislocation densities on wafers, with experimentally recorded etch pit profiles on as-grown crystals was reasonable. Finally some limitations in the work are discussed and avenues for future work identified.

Weld residual stresses and plastic deformation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybicki, E.; Shiratori, M.

1989-01-01

Residual stresses due to welding can play a primary role in the performance of piping systems and pressure vessels. The stresses are high, in the range of the yield stress of the material, and can influence the fatigue and fracture behavior as well as component service life. Thus, it is important to have an understanding of weld residual stresses. The papers in this section address the important topic of residual stresses and failure analysis. The paper by Boyles reviews computer simulation in the prediction and analysis of fatigue, fracture, and creep of welded structures. The growing use of expert systemsmore » for these purposes is also covered. Karisson, et al, determine the deformations and stresses during the butt-welding of a pipe. The determination of residual deformations and stresses is also presented. Oddy, Goldak, and McDill propose a method to incorporate transformation plasticity in a finite element program. A three-dimensional analysis of a short longitudinal pipe weld in a typical pressure vessel steel is presented. Chaaban, Morin, Ma, and Bazergui study the influence of ligament thickness, strain hardening, expansion sequence, and level of applied expansion pressure on the interference fit in a model of a tube-to-tubesheet joint in a heat exchanger. This section contains papers dealing with models for plastic deformation. Imatani, Teraura, and Inoue formulate a viscoplastic constitutive model based on an anisotropic yield criterion. Comparisons with experimental results obtained using thin walled tubular specimens made from SUS 304 stainless steel show that the present yield criterion adequately accounts for prior deformation history. Niitsu, Horiguchi, and Ikegami investigate the plastic behavior of S25C mild steel tubular specimens subjected to combined axial and torsional loading at both constant and variable temperatures.« less

Simulation of finite-strain inelastic phenomena governed by creep and plasticity

NASA Astrophysics Data System (ADS)

Li, Zhen; Bloomfield, Max O.; Oberai, Assad A.

2017-11-01

Inelastic mechanical behavior plays an important role in many applications in science and engineering. Phenomenologically, this behavior is often modeled as plasticity or creep. Plasticity is used to represent the rate-independent component of inelastic deformation and creep is used to represent the rate-dependent component. In several applications, especially those at elevated temperatures and stresses, these processes occur simultaneously. In order to model these process, we develop a rate-objective, finite-deformation constitutive model for plasticity and creep. The plastic component of this model is based on rate-independent J_2 plasticity, and the creep component is based on a thermally activated Norton model. We describe the implementation of this model within a finite element formulation, and present a radial return mapping algorithm for it. This approach reduces the additional complexity of modeling plasticity and creep, over thermoelasticity, to just solving one nonlinear scalar equation at each quadrature point. We implement this algorithm within a multiphysics finite element code and evaluate the consistent tangent through automatic differentiation. We verify and validate the implementation, apply it to modeling the evolution of stresses in the flip chip manufacturing process, and test its parallel strong-scaling performance.

Gradient-type modeling of the effects of plastic recovery and surface passivation in thin films

NASA Astrophysics Data System (ADS)

Liu, Jinxing; Kah Soh, Ai

2016-08-01

The elasto-plastic responses of thin films subjected to cyclic tension-compression loading and bending are studied, with a focus on Bauschinger and size effects. For this purpose, a model is established by incorporating plastic recovery into the strain gradient plasticity theory we proposed recently. Elastic and plastic parts of strain and strain gradient, which are determined by the elasto-plastic decomposition according to the associative rule, are assumed to have a degree of material-dependent reversibility. Based on the above assumption, a dislocation reversibility-dependent rule is built to describe evolutions of different deformation components under cyclic loadings. Furthermore, a simple strategy is provided to implement the passivated boundary effects by introducing a gradual change to relevant material parameters in the yield function. Based on this theory, both bulge and bending tests under cyclic loading conditions are investigated. By comparing the present predictions with the existing experimental data, it is found that the yield function is able to exhibit the size effect, the Bauschinger effect, the influence of surface passivation and the hysteresis-loop phenomenon. Thus, the proposed model is deemed helpful in studying plastic deformations of micron-scale films.

Auxetic hexachiral structures with wavy ligaments for large elasto-plastic deformation

NASA Astrophysics Data System (ADS)

Zhu, Yilin; Wang, Zhen-Pei; Hien Poh, Leong

2018-05-01

The hexachiral structure is in-plane isotropic in small deformation. When subjected to large elasto-plastic deformation, however, the hexachiral structure tends to lose its auxeticity and/or isotropy—properties which are desirable in many potential applications. The objective of this study is to improve these two mechanical properties, without significantly compromising the effective yield stress, in the regime with significant material and geometrical nonlinearity effects. It is found that the deformation mechanisms underlying the auxeticity and isotropy properties of a hexachiral structure are largely influenced by the extent of rotation of the central ring in a unit cell. To facilitate the development of this deformation mechanism, an improved design with wavy ligaments is proposed. The improved performance of the proposed hexachiral structure is demonstrated. An initial study on possible applications as a protective material is next carried out, where the improved hexachiral design is shown to exhibit higher specific energy absorption capacity compared to the original design, as well as standard honeycomb structures.

Transition of temporal scaling behavior in percolation assisted shear-branching structure during plastic deformation

DOE PAGES

Ren, Jingli; Chen, Cun; Wang, Gang; ...

2017-03-22

This study explores the temporal scaling behavior induced shear-branching structure in response to variant temperatures and strain rates during plastic deformation of Zr-based bulk metallic glass (BMG). The data analysis based on the compression tests suggests that there are two states of shear-branching structures: the fractal structure with a long-range order at an intermediate temperature of 223 K and a larger strain rate of 2.5 × 10 –2 s –1; the disordered structure dominated at other temperature and strain rate. It can be deduced from the percolation theory that the compressive ductility, ec, can reach the maximum value at themore » intermediate temperature. Furthermore, a dynamical model involving temperature is given for depicting the shear-sliding process, reflecting the plastic deformation has fractal structure at the temperature of 223 K and strain rate of 2.5 × 10 –2 s –1.« less

Plastic deformation of B2-NiTi - is it slip or twinning?

NASA Astrophysics Data System (ADS)

Sehitoglu, H.; Wu, Y.; Alkan, S.; Ertekin, E.

2017-06-01

The work addresses two main questions that have baffled the shape memory research community. Firstly, the superb ductility of B2-NiTi cannot be solely attributed to slip on {0 1 1} planes, because there are not a sufficient number of independent slip systems under arbitrary deformations. We show unequivocally, upon diffraction measurements and local strain field traces, that deformation twinning on {1 1 4} planes that can provide additional systems to accommodate plastic flow is activated. Secondly, the slip direction on the {0 1 1} planes has not been established in NiTi with certainty. It is proved precisely to be in ?0 0 1? direction based on crystallographic shear analysis producing the specific strain tensor components (measured at mesoscale with digital image correlation, DIC). Based on the single-crystal experiments, the CRSSs (critical resolved shear stress) are established as 250 and 330 MPa for slip and twinning, respectively. The results have implications in devising correct crystal plasticity formulations for shape memory alloys.

Elementary model of severe plastic deformation by KoBo process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gusak, A.; Storozhuk, N.; Danielewski, M., E-mail: daniel@agh.edu.pl

2014-01-21

Self-consistent model of generation, interaction, and annihilation of point defects in the gradient of oscillating stresses is presented. This model describes the recently suggested method of severe plastic deformation by combination of pressure and oscillating rotations of the die along the billet axis (KoBo process). Model provides the existence of distinct zone of reduced viscosity with sharply increased concentration of point defects. This zone provides the high extrusion velocity. Presented model confirms that the Severe Plastic Deformation (SPD) in KoBo may be treated as non-equilibrium phase transition of abrupt drop of viscosity in rather well defined spatial zone. In thismore » very zone, an intensive lateral rotational movement proceeds together with generation of point defects which in self-organized manner make rotation possible by the decrease of viscosity. The special properties of material under KoBo version of SPD can be described without using the concepts of nonequilibrium grain boundaries, ballistic jumps and amorphization. The model can be extended to include different SPD processes.« less

Embrittlement and Flow Localization in Reactor Structural Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xianglin Wu; Xiao Pan; James Stubbins

2006-10-06

Many reactor components and structural members are made from metal alloys due, in large part, to their strength and ability to resist brittle fracture by plastic deformation. However, brittle fracture can occur when structural material cannot undergo extensive, or even limited, plastic deformation due to irradiation exposure. Certain irradiation conditions lead to the development of a damage microstructure where plastic flow is limited to very small volumes or regions of material, as opposed to the general plastic flow in unexposed materials. This process is referred to as flow localization or plastic instability. The true stress at the onset of neckingmore » is a constant regardless of the irradiation level. It is called 'critical stress' and this critical stress has strong temperature dependence. Interrupted tensile testes of 316L SS have been performed to investigate the microstructure evolution and competing mechanism between mechanic twinning and planar slip which are believed to be the controlling mechanism for flow localization. Deformation twinning is the major contribution of strain hardening and good ductility for low temperatures, and the activation of twinning system is determined by the critical twinning stress. Phases transform and texture analyses are also discussed in this study. Finite element analysis is carried out to complement the microstructural analysis and for the prediction of materaials performance with and without stress concentration and irradiation.« less

Unusual plastic deformation and damage features in titanium: Experimental tests and constitutive modeling

NASA Astrophysics Data System (ADS)

Revil-Baudard, Benoit; Cazacu, Oana; Flater, Philip; Chandola, Nitin; Alves, J. L.

2016-03-01

In this paper, we present an experimental study on plastic deformation and damage of polycrystalline pure HCP Ti, as well as modeling of the observed behavior. Mechanical characterization data were conducted, which indicate that the material is orthotropic and displays tension-compression asymmetry. The ex-situ and in-situ X-ray tomography measurements conducted reveal that damage distribution and evolution in this HCP Ti material is markedly different than in a typical FCC material such as copper. Stewart and Cazacu (2011) anisotropic elastic/plastic damage model is used to describe the behavior. All the parameters involved in this model have a clear physical significance, being related to plastic properties, and are determined from very few simple mechanical tests. It is shown that this model predicts correctly the anisotropy in plastic deformation, and its strong influence on damage distribution and damage accumulation. Specifically, for a smooth axisymmetric specimen subject to uniaxial tension, damage initiates at the center of the specimen, and is diffuse; the level of damage close to failure being very low. On the other hand, for a notched specimen subject to the same loading the model predicts that damage initiates at the outer surface of the specimen, and further grows from the outer surface to the center of the specimen, which corroborates with the in-situ tomography data.

Microstructural change in electroformed copper liners of shaped charges upon plastic deformation at ultra-high strain rate

NASA Astrophysics Data System (ADS)

Tian, W. H.; Hu, S. L.; Fan, A. L.; Wang, Z.

2002-01-01

Transmission electron microscopy (TEM) observations were carried out for examining the as-formed and post-deformed microstructures in a variety of electroformed copper liners of shaped charges. The deformation was carried out at an ultra-high strain rate. Specifically, the electron backscattering Kikuchi pattern (EBSP) technique was utilized to examine the micro-texture of these materials. TEM observations revealed that these electroformed copper liners of shaped charges have a grain size of about 1-3 mum, EBSP analysis demonstrated that the as-grown copper liners of shaped charges exhibit a l 10) fiber micro-texture which is parallel to the normal direction of the surface of the liners of shaped charges. Having undergone plastic deformation at ultra-high strain rate (10(7) s(-1)), the specimens which were recovered from the copper slugs were found to have grain size of the same order as that before deformation. EBSP analysis revealed that the (110) fiber texture existed in the as-formed copper liners disappears in the course of deformation. TEM examination results indicate that dynamic recovery and recrystallization play a significant role in this deformation process.

Generalized continuum modeling of scale-dependent crystalline plasticity

NASA Astrophysics Data System (ADS)

Mayeur, Jason R.

The use of metallic material systems (e.g. pure metals, alloys, metal matrix composites) in a wide range of engineering applications from medical devices to electronic components to automobiles continues to motivate the development of improved constitutive models to meet increased performance demands while minimizing cost. Emerging technologies often incorporate materials in which the dominant microstructural features have characteristic dimensions reaching into the submicron and nanometer regime. Metals comprised of such fine microstructures often exhibit unique and size-dependent mechanical response, and classical approaches to constitutive model development at engineering (continuum) scales, being local in nature, are inadequate for describing such behavior. Therefore, traditional modeling frameworks must be augmented and/or reformulated to account for such phenomena. Crystal plasticity constitutive models have proven quite capable of capturing first-order microstructural effects such as grain orientation (elastic/plastic anisotropy), grain morphology, phase distribution, etc. on the deformation behavior of both single and polycrystals, yet suffer from the same limitations as other local continuum theories with regard to capturing scale-dependent mechanical response. This research is focused on the development, numerical implementation, and application of a generalized (nonlocal) theory of single crystal plasticity capable of describing the scale-dependent mechanical response of both single and polycrystalline metals that arises as a result of heterogeneous deformation. This research developed a dislocation-based theory of micropolar single crystal plasticity. The majority of nonlocal crystal plasticity theories are predicated on the connection between gradients of slip and geometrically necessary dislocations. Due to the diversity of existing nonlocal crystal plasticity theories, a review, summary, and comparison of representative model classes is presented in Chapter 2 from a unified dislocation-based perspective. The discussion of the continuum crystal plasticity theories is prefaced by a brief review of discrete dislocation plasticity, which facilitates the comparison of certain model aspects and also serves as a reference for latter segments of the research which make connection to this constitutive description. Chapter 2 has utility not only as a literature review, but also as a synthesis and analysis of competing and alternative nonlocal crystal plasticity modeling strategies from a common viewpoint. The micropolar theory of single crystal plasticity is presented in Chapter 3. Two different types of flow criteria are considered - the so-called single and multicriterion theories, and several variations of the dislocation-based strength models appropriate for each theory are presented and discussed. The numerical implementation of the two-dimensional version of the constitutive theory is given in Chapter 4. A user element subroutine for the implicit commercial finite element code Abaqus/Standard is developed and validated through the solution of initial-boundary value problems with closed-form solutions. Convergent behavior of the subroutine is also demonstrated for an initial-boundary value problem exhibiting strain localization. In Chapter 5, the models are employed to solve several standard initial-boundary value problems for heterogeneously deforming single crystals including simple shearing of a semi-infinite constrained thin film, pure bending of thin films, and simple shearing of a metal matrix composite with elastic inclusions. The simulation results are compared to those obtained from the solution of equivalent boundary value problems using discrete dislocation dynamics and alternative generalized crystal plasticity theories. Comparison and calibration with respect to the former provides guidance in the specification of non-traditional material parameters that arise in the model formulation and demonstrates its effectiveness at capturing the heterogeneous deformation fields and size-dependent mechanical behavior predicted by a finer scale constitutive description. Finally, in Chapter 6, the models are applied to simulate the deformation behavior of small polycrystalline ensembles. Several grain boundary constitutive descriptions are explored and the response characteristics are analyzed with respect to experimental observations as well as results obtained from discrete dislocation dynamics and alternative nonlocal crystal plasticity theories. Particular attention is focused on how the various grain boundary descriptions serve to either locally concentrate or diffuse deformation heterogeneity as a function of grain size.

Comparison studies on the percolation thresholds of binary mixture tablets containing excipients of plastic/brittle and plastic/plastic deformation properties.

PubMed

Amin, Mohd C I; Fell, John T

2004-01-01

Percolation theory has been used with great interest in understanding the design and characterization of dosage forms. In this study, work has been carried out to investigate the behavior of binary mixture tablets containing excipients of similar and different deformation properties. The binary mixture tablets were prepared by direct compression using lactose, polyvinyl chloride (PVC), Eudragit RS 100, and microcrystalline cellulose (MCC). The application of percolation theory on the relationships between compactibility, Pmax, or compression susceptibility (compressibility), gamma, and mixture compositions reveals the presence of percolation thresholds even for mixtures of similar deformation properties. The results showed that all mixture compositions exhibited at least one discreet change in the slope, which was referred to as the percolation threshold. The PVC/Eudragit RS100 mixture compositions showed significant percolation threshold at 80% (w/w) PVC loading. Two percolation thresholds were observed from a series of binary mixtures containing similar plastic deformation materials (PVC/MCC). The percolation thresholds were determined at 20% (w/w) and 80% (w/w) PVC loading. These are areas where one of the components percolates throughout the system and the properties of the tablets are expected to experience a sudden change. Experimental results, however, showed that total disruption of the tablet physical properties at the specified percolation thresholds can be observed for PVC/lactose mixtures at 20-30% (w/w) loading while only minor changes in the tablets' strength for PVC/MCC or PVC/Eudragit RS 100 mixtures were observed.

Wireless measurement of elastic and plastic deformation by a metamaterial-based sensor.

PubMed

Ozbey, Burak; Demir, Hilmi Volkan; Kurc, Ozgur; Erturk, Vakur B; Altintas, Ayhan

2014-10-20

We report remote strain and displacement measurement during elastic and plastic deformation using a metamaterial-based wireless and passive sensor. The sensor is made of a comb-like nested split ring resonator (NSRR) probe operating in the near-field of an antenna, which functions as both the transmitter and the receiver. The NSRR probe is fixed on a standard steel reinforcing bar (rebar), and its frequency response is monitored telemetrically by a network analyzer connected to the antenna across the whole stress-strain curve. This wireless measurement includes both the elastic and plastic region deformation together for the first time, where wired technologies, like strain gauges, typically fail to capture. The experiments are further repeated in the presence of a concrete block between the antenna and the probe, and it is shown that the sensing system is capable of functioning through the concrete. The comparison of the wireless sensor measurement with those undertaken using strain gauges and extensometers reveals that the sensor is able to measure both the average strain and the relative displacement on the rebar as a result of the applied force in a considerably accurate way. The performance of the sensor is tested for different types of misalignments that can possibly occur due to the acting force. These results indicate that the metamaterial-based sensor holds great promise for its accurate, robust and wireless measurement of the elastic and plastic deformation of a rebar, providing beneficial information for remote structural health monitoring and post-earthquake damage assessment.

Investigation of coatings of austenitic steels produced by supersonic laser deposition

NASA Astrophysics Data System (ADS)

Gorunov, A. I.; Gilmutdinov, A. Kh.

2017-02-01

The structure and properties of stainless austenitic steel coatings obtained by the supersonic laser deposition are studied in the paper. Implantation of the powder particles into the substrate surface and simultaneous plastic deformation at partial melting improved the mechanical properties of the coatings - tensile strength limit was 650 MPa and adhesion strength was 105 MPa. It was shown that insufficient laser power leads to disruption of the deposition process stability and coating cracking. Surface temperature increase caused by laser heating above 1300 °C resulted in coating melting. The X-ray analysis showed that radiation intensifies the cold spray process and does not cause changes in the austenitic base structure.

Thermomechanical coupling and dynamic strain ageing in ductile fracture

NASA Astrophysics Data System (ADS)

Delafosse, David

1995-01-01

This work is concerned with plastic deformation at the tip of a ductile tearing crack during propagation. Two kinds of effects are investigated: the thermomechanical coupling at the tip of a mobile ductile crack, and the influence of Dynamic Strain Aging (DSA) on ductile fracture. Three alloys are studied: a nickel based superalloy (N18), a soft carbon steel, and an Al-Li light alloy (2091). The experimental study of the thermo mechanical coupling effects by means of infrared thermography stresses the importance of plastic dissipation in the energy balance of ductile fracture. Numerical simulations involving plastic deformation as the only dissipation mechanism account for the main part of the measured heating. The effects of DSA on ductile tearing are investigated in the 2091 Al-Li alloy. Based on the strain rate/temperature dependence predicted by the standard model of DSA, an experimental procedure is set up for this purpose. Three main effects are evidenced. A maximum in tearing resistance is shown to be associated with the minimum of strain rate sensitivity. Through a simple model, this peak in tearing resistance is attributed to an increase in plastic dissipation as the strain rate sensitivity is decreased. Heterogenous plastic deformation is observed in the crack tip plastic zone. Comparison with uniaxial testing allows us to identify the observed strain heterogeneities as Portevin-Le Chatelier instabilities in the crack tip plastic zone. We perform a simplified numerical analysis of the effect of strain localization on crack tip screening. Finally, small crack propagation instabilities appear at temperatures slightly above that of the tearing resistance peak. These are interpreted as resulting from a positive feed-back between the local heating at the tip of a moving crack and the decrease in tearing resistance with increasing temperature.

Three-dimensional printing and deformation behavior of low-density target structures by two-photon polymerization

NASA Astrophysics Data System (ADS)

Liu, Ying; Stein, Ori; Campbell, John H.; Jiang, Lijia; Petta, Nicole; Lu, Yongfeng

2017-08-01

Two-photon polymerization (2PP), a 3D nano to microscale additive manufacturing process, is being used for the first time to fabricate small custom experimental packages ("targets") to support laser-driven high-energy-density (HED) physics research. Of particular interest is the use of 2PP to deterministically print low-density, low atomic-number (CHO) polymer matrices ("foams") at millimeter scale with sub-micrometer resolution. Deformation during development and drying of the foam structures remains a challenge when using certain commercial photo-resins; here we compare use of acrylic resins IP-S and IP-Dip. The mechanical strength of polymeric beam and foam structures is examined particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage in the two resins in quantified by printing sample structures and by use of FEA to simulate the deformation. Capillary drying forces are shown to be small and likely below the elastic limit of the core foam structure. In contrast the substantial shrinkage in IP-Dip ( 5-10%) cause large shear stresses and associated plastic deformation particularly near constrained boundaries such as the substrate and locations with sharp density variation. The inherent weakness of stitching boundaries is also evident and in certain cases can lead to delamination. Use of IP-S shows marked reduction in deformation with a minor loss of print resolution

Elastic And Plastic Deformations In Butt Welds

NASA Technical Reports Server (NTRS)

Verderaime, V.

1992-01-01

Report presents study of mathematical modeling of stresses and strains, reaching beyond limits of elasticity, in bars and plates. Study oriented toward development of capability to predict stresses and resulting elastic and plastic strains in butt welds.

On the Variation of Hardness Due to Uniaxial and Equi-Biaxial Residual Surface Stresses at Elastic-Plastic Indentation

NASA Astrophysics Data System (ADS)

Larsson, Per-Lennart

2018-05-01

It is established long since that the material hardness is independent of residual stresses at predominantly plastic deformation close to the contact region at indentation. Recently though, it has been shown that when elastic and plastic deformations are of equal magnitude this invariance is lost. For materials such as ceramics and polymers, this will complicate residual stress determination but can also, if properly understood, provide additional important information for performing such a task. Indeed, when the residual stresses are equi-biaxial, the situation is quite well understood, but additional efforts have to be made to understand the mechanical behavior in other loading states. Presently therefore, the variation of hardness, due to residual stresses, is examined at a uniaxial stress state. Correlation with global indentation quantities is analyzed, discussed and compared to corresponding equi-biaxial results. Cone indentation of elastic-perfectly plastic materials is considered.

The use of COD and plastic instability in crack propagation and arrest in shells

NASA Technical Reports Server (NTRS)

Erdogan, F.; Ratwani, M.

1974-01-01

The initiation, growth, and possible arrest of fracture in cylindrical shells containing initial defects are dealt with. For those defects which may be approximated by a part-through semi-elliptic surface crack which is sufficiently shallow so that part of the net ligament in the plane of the crack is still elastic, the existing flat plate solution is modified to take into account the shell curvature effect as well as the effect of the thickness and the small scale plastic deformations. The problem of large defects is then considered under the assumptions that the defect may be approximated by a relatively deep meridional part-through surface crack and the net ligament through the shell wall is fully yielded. The results given are based on an 8th order bending theory of shallow shells using a conventional plastic strip model to account for the plastic deformations around the crack border.

Significance of grain bondary sliding for localization of ductile deformation in rocks

NASA Astrophysics Data System (ADS)

Dimanov, A.; Bourcier, M.; Gaye, A.; Héripré, E.; Bornert, M.; Raphanel, J. L.; Gharbi, H.; Ludwig, W.

2016-12-01

Ductile strain localizes in mylonites, with microstructural signatures of several concomitant deformation mechanisms. Crystal plasticity dominates in volume, but grain boundary sliding and diffusive/solution mass transport act along interfaces. Because the chronology and the interactions between these mechanisms are unclear, inference of the overall rheology seems illusory. In order to clarify these aspects we underwent a multi-scale investigation of the ductile deformation of synthetic rock salt. The mechanical tests were combined with in-situ optical microscopy, scanning electron microscopy and X ray tomography (MCT). Digital image correlation (DIC) techniques allowed for measurements and characterization of the multiscale organization of 2D and 3D full strain fields. Macroscopic and mesoscopic shear bands appear at the sample and microstructure scales, respectively. Discrete slip bands within individual grains allowed for identification of dominant crystal plasticity and of the activated slip systems. Conversely, we clearly evidenced grain boundary sliding (GBS). DIC allowed the precise quantification of the relative contribution of each mechanism. GBS is continuously operational along with crystal slip plasticity, which indicates that in spite of being a secondary mechanism (< 5% contribution) it is a necessary one. Both the localized activity of secondary slip systems in the vicinity of interfaces and GBS are inferred to be necessary in order to accommodate for plastic strain incompatibilities between neighboring grains. More specifically, GBS accommodation mechanisms allow for relaxation of local stress enhancement and reduction of strain hardening. GBS appears to be directly involved in the formation of localized shear bands at the microstructural scale, but also to allow for the transmission of ductile strain throughout the whole specimen. Finite element (FE) modeling of the viscoplastic behavior of rock salt based on crystal plasticity alone is inadequate. If GBS is not considered the computed strain fields do not sufficiently match the experimentally measured ones. Our major conclusion about ductile deformation of rocks is that crystal plasticity and GBS are not really dissociable. They appear as co-operative mechanisms due to the pronounced plastic anisotropy of minerals.

Numerical Modeling of the Deformation Behavior of Fault Bounded Lens Shaped Bodies in 2D

NASA Astrophysics Data System (ADS)

van der Zee, W.; Urai, J. L.

2001-12-01

Fault zones cause dramatic discontinuous changes in mechanical properties. The early stages of evolution of fault zones are important for its long-term behavior. We consider faults which develop from deformation bands or pre-existing joints which are the initially unconnected discontinuities. With further deformation, these coalesce into a connected network, and develop into a 'mature' fault gouge. When segments are not coplanar, soft linkage or bends in the fault plane (releasing and restraining bends, fault bounded lens-shaped bodies etc) necessarily occurs. Further movement causes additional deformation, and the fault zone has a strongly variable thickness. Here, we present the results of detailed fieldwork combined with numerical modeling on the deformation of fault bounded lens-shaped bodies in the fault zone. Detailed study of a number of lenses in the field shows that the lens is invariably more deformed than the surrounding material. This observation can be explained in several ways. In one end member most of the deformation in the future lens occurs before full coalescence of the slip planes and the formation of the lens. The other end member is that the slip planes coalesce before plastic deformation of the lens is occurring. The internal deformation of the lens occurs after the lens is formed, due to the redistributed stresses in the structure. If this is the case, then lens shaped bodies can be always expected to deform preferentially. Finite element models were used to investigate the shear behavior of a planar fault with a lens shaped body or a sinus-shaped asperity. In a sensitivity analysis, we consider different lens shapes and fault friction coefficients. Results show that 1) during slip, the asperity shears off to form a lens shaped body 2) lens interior deforms more than the surroundings, due to the redistribution of stresses 3) important parameters in this system are the length-thickness ratio of the lens and the fault friction coefficient 4) lens structures can evolve in different ways, but in the final stage the result is a lens with deformed interior In the later stages after further displacement, these zones of preferential deformation evolve into sections containing thick gouge, and the initial lens width controls long term fault gouge thickness.

Stress and deformation characteristics of sea ice in a high resolution numerical sea ice model.

NASA Astrophysics Data System (ADS)

Heorton, Harry; Feltham, Daniel; Tsamados, Michel

2017-04-01

The drift and deformation of sea ice floating on the polar oceans is due to the applied wind and ocean currents. The deformations of sea ice over ocean basin length scales have observable patterns; cracks and leads in satellite images and within the velocity fields generated from floe tracking. In a climate sea ice model the deformation of sea ice over ocean basin length scales is modelled using a rheology that represents the relationship between stresses and deformation within the sea ice cover. Here we investigate the link between observable deformation characteristics and the underlying internal sea ice stresses and force balance using the Los Alamos numerical sea ice climate model. In order to mimic laboratory experiments on the deformation of small cubes of sea ice we have developed an idealised square domain that tests the model response at spatial resolutions of up to 500m. We use the Elastic Anisotropic Plastic and Elastic Viscous Plastic rheologies, comparing their stability over varying resolutions and time scales. Sea ice within the domain is forced by idealised winds in order to compare the confinement of wind stresses and internal sea ice stresses. We document the characteristic deformation patterns of convergent, divergent and rotating stress states.

Instrumented Taylor anvil-on-rod impact tests for validating applicability of standard strength models to transient deformation states

NASA Astrophysics Data System (ADS)

Eakins, D. E.; Thadhani, N. N.

2006-10-01

Instrumented Taylor anvil-on-rod impact tests have been conducted on oxygen-free electronic copper to validate the accuracy of current strength models for predicting transient states during dynamic deformation events. The experiments coupled the use of high-speed digital photography to record the transient deformation states and laser interferometry to monitor the sample back (free surface) velocity as a measure of the elastic/plastic wave propagation through the sample length. Numerical continuum dynamics simulations of the impact and plastic wave propagation employing the Johnson-Cook [Proceedings of the Seventh International Symposium on Ballistics, 1983, The Netherlands (Am. Def. Prep. Assoc. (ADPA)), pp. 541-547], Zerilli-Armstrong [J. Appl. Phys. C1, 1816 (1987)], and Steinberg-Guinan [J. Appl. Phys. 51, 1498 (1980)] constitutive equations were used to generate transient deformation profiles and the free surface velocity traces. While these simulations showed good correlation with the measured free surface velocity traces and the final deformed sample shape, varying degrees of deviations were observed between the photographed and calculated specimen profiles at intermediate deformation states. The results illustrate the usefulness of the instrumented Taylor anvil-on-rod impact technique for validating constitutive equations that can describe the path-dependent deformation response and can therefore predict the transient and final deformation states.

Observational Constraints on Lithospheric Rheology and Their Implications for Lithospheric Dynamics and Plate Tectonics

NASA Astrophysics Data System (ADS)

Zhong, S.; Watts, A. B.

2014-12-01

Lithospheric rheology and strength are important for understanding crust and lithosphere dynamics, and the conditions for plate tectonics. Laboratory studies suggest that lithospheric rheology is controlled by frictional sliding, semi-brittle, low-temperature plasticity, and high-temperature creep deformation mechanisms as pressure and temperature increase from shallow to large depths. Although rheological equations for these deformation mechanisms have been determined in laboratory settings, it is necessary to validate them using field observations. Here we present an overview of lithospheric rheology constrained by observations of seismic structure and load-induced flexure. Together with mantle dynamic modeling, rheological equations for high-temperature creep derived from laboratory studies (Hirth and Kohlstedt, 2003; Karato and Jung, 2003) satisfactorily explain the seismic structure of the Pacific upper mantle (Hunen et al., 2005) and Hawaiian swell topography (Asaadi et al., 2011). In a recent study that compared modeled surface flexure and stress induced by volcano loads in the Hawaiian Islands region with the observed flexure and seismicity, Zhong and Watts (2013) showed that the coefficient of friction is between 0.25 and 0.7, and is consistent with laboratory studies and also in-situ borehole measurements. However, this study indicated that the rheological equation for the low-temperature plasticity from laboratory studies (e.g., Mei et al., 2010) significantly over-predicts lithospheric strength and viscosity. Zhong and Watts (2013) also showed that the maximum lithospheric stress beneath Hawaiian volcano loads is about 100-200 MPa, which may be viewed as the largest lithospheric stress in the Earth's lithosphere. We show that the relatively weak lithospheric strength in the low-temperature plasticity regime is consistent with seismic observation of reactivated mantle lithosphere in the western US and the eastern North China. We discuss here the causes of this weakening in the context of the potential effects on laboratory studies of reduced grain size and Peierls stress on the low-temperature deformation regime.

Vertical forearc tectonic displacements offer insights into underlying interplate thrust zone processes: 104-105 yr uplift/subsidence cycles in Southwest Pacific arcs may represent recoverable plastic deformation that is often falsely attributed to other causes

NASA Astrophysics Data System (ADS)

Taylor, F. W.; Lavier, L. L.; Frohlich, C.; Thirumalai, K.; Papabatu, A. K.

2015-12-01

In the forearcs of subduction zones, the characteristics of both short-term (temporary earthquake cycle) and longer-term permanent vertical deformation offer insights into processes by which plates subduct. But permanent vertical deformation may be a product of several simultaneous processes, including tectonic erosion/underplating, changing dip of the slab, upward displacement due to buoyancy or bathymetric features, and plastic shortening/extension of the forearc wedge. Here we note the rarely recognized, but possibly common, phenomenon of intermediate time scale transient vertical movements (TVM's). Both the central New Hebrides and Western Solomon forearcs have uplifted ≥500 m over time scales of 105 yr. Uplift started abruptly (over ≤10 ky) and proceeded at localized rates up to 7-8 mm/yr. Both initial uplifts terminated preceding rapid subsidence of similar dimensions and rates that, in turn, had followed yet older uplift. However, these uplifts and subsidences are superimposed on a yet longer-term trend of uplift on time scales >105 yr. The most recent uplifts extended 100-200 km along-arc and 60-90 km cross-arc while plate convergence was <10 km. These 105 yr vertical oscillations are most likely due to plastic shortening/extension driven by strong horizontal forces related to rugged seafloor bathymetry impinging on the outer forearc. Subsidence follows uplift when horizontal force abates temporarily and uplift is no longer supported by enhanced interplate coupling. Over the 105 yr time frame when interplate slip is <10 km, it is difficult to account for the timing, geography, and amounts of up and down motion by processes such as buoyancy or volumetric displacement of downgoing bathymetric features or by tectonic underplating/erosion. Instead, ~1% of shortening within the upper plate is sufficient to account for up to several hundred m of uplift across a large area of the forearc.

Numerical studies of cavitation erosion on an elastic-plastic material caused by shock-induced bubble collapse

NASA Astrophysics Data System (ADS)

Turangan, C. K.; Ball, G. J.; Jamaluddin, A. R.; Leighton, T. G.

2017-09-01

We present a study of shock-induced collapse of single bubbles near/attached to an elastic-plastic solid using the free-Lagrange method, which forms the latest part of our shock-induced collapse studies. We simulated the collapse of 40 μm radius single bubbles near/attached to rigid and aluminium walls by a 60 MPa lithotripter shock for various scenarios based on bubble-wall separations, and the collapse of a 255 μm radius bubble attached to aluminium foil with a 65 MPa lithotripter shock. The coupling of the multi-phases, compressibility, axisymmetric geometry and elastic-plastic material model within a single solver has enabled us to examine the impingement of high-speed liquid jets from the shock-induced collapsing bubbles, which imposes an extreme compression in the aluminium that leads to pitting and plastic deformation. For certain scenarios, instead of the high-speed jet, a radially inwards flow along the aluminium surface contracts the bubble to produce a `mushroom shape'. This work provides methods for quantifying which parameters (e.g. bubble sizes and separations from the solid) might promote or inhibit erosion on solid surfaces.

Microstructure heterogeneity after the ECAP process and its influence on recrystallization in aluminium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wronski, S., E-mail: wronski@fis.agh.edu.pl; Tarasiuk, J., E-mail: tarasiuk@ftj.agh.edu.pl; Bacroix, B., E-mail: brigitte.bacroix@univ-paris13.fr

The main purpose of the present work is to describe the qualitative and quantitative behaviours of aluminium during high strain plastic deformation and the effect of deformation on the subsequent recrystallization process. An Electron Backscatter Diffraction analysis of aluminium after the Equal channel angular pressing (ECAP) and recrystallization process is presented. In order to do this, several topological maps are measured for samples processed by 4 and 8 passes and recrystallized. The processing was conducted with route C. For all samples, distributions of grain size, misorientation, image quality factor (IQ) and texture were preceded and then analysed in some detail.more » - Highlights: ► Describe the microstructure fragmentation in aluminum. ► High strain plastic deformation and effect of deformation on recrystallization. ► The microstructure fragmentation and its influence on recrystallization. ► Image quality factor and misorientation characteristics are examined using EBSD.« less

Texture developed during deformation of Transformation Induced Plasticity (TRIP) steels

NASA Astrophysics Data System (ADS)

Bhargava, M.; Shanta, C.; Asim, T.; Sushil, M.

2015-04-01

Automotive industry is currently focusing on using advanced high strength steels (AHSS) due to its high strength and formability for closure applications. Transformation Induced Plasticity (TRIP) steel is promising material for this application among other AHSS. The present work is focused on the microstructure development during deformation of TRIP steel sheets. To mimic complex strain path condition during forming of automotive body, Limit Dome Height (LDH) tests were conducted and samples were deformed in servo hydraulic press to find the different strain path. FEM Simulations were done to predict different strain path diagrams and compared with experimental results. There is a significant difference between experimental and simulation results as the existing material models are not applicable for TRIP steels. Micro texture studies were performed on the samples using EBSD and X-RD techniques. It was observed that austenite is transformed to martensite and texture developed during deformation had strong impact on limit strain and strain path.

Modelling of deformation process for the layer of elastoviscoplastic media under surface action of periodic force of arbitrary type

NASA Astrophysics Data System (ADS)

Mikheyev, V. V.; Saveliev, S. V.

2018-01-01

Description of deflected mode for different types of materials under action of external force plays special role for wide variety of applications - from construction mechanics to circuits engineering. This article con-siders the problem of plastic deformation of the layer of elastoviscolastic soil under surface periodic force. The problem was solved with use of the modified lumped parameters approach which takes into account close to real distribution of normal stress in the depth of the layer along with changes in local mechanical properties of the material taking place during plastic deformation. Special numeric algorithm was worked out for computer modeling of the process. As an example of application suggested algorithm was realized for the deformation of the layer of elasoviscoplastic material by the source of external lateral force with the parameters of real technological process of soil compaction.

Progressive deformation of ultramafic rocks accompanied with deflection of layered structure and mylonitization culminating into a pseudotachylyte-bearing seismogenic fault - a field evidence of plastic instability

NASA Astrophysics Data System (ADS)

Ueda, T.; Obata, M.

2011-12-01

Plastic instability leading to rupture nucleation and propagetion (e.g. Hobbs et al.1986, Kelemen and Hirth, 2007) is an attractive hypothesis for deep earthquakes but lacked clear field evidences. 1D across-fault shear localization observed in some places (e.g. Jin et al.1998) is not clear if the deformation is directly related with seismicity. We present a clear field evidence of plastic instability as guided by pyroxenite/peridotite layering deflection structure (hereafter called LD structure, see figure) accompanied with mylonitization in spinel(Sp)-peridotite facies (P>~1GPa) in Balmuccia peridotite, Ivrea-Verbano Zone, Italy. The studied area contains abundant PST-bearing faults and N-S trending primary pyroxenite layers. Many faults in the area cut pyroxenite layers, but LD structure is found only in one place presented here. Many PSTs in the area have been (re)crystallized in Sp-peridotite facies, and have typically ultramylonitic texture (Ueda et al., 2008) with some injection veins. The fault with LD structure is situated in a fault system, which has two dominant attitudes with regional N-S extension. The shear strain of LD structure measured on outcrop surface is ~2.0. Near the fault, elongated Opx porphyroclasts (ellipses in figure) oblique to local layering are visible in peridotite. The dominant deformation textures are dynamic recrystallization in peridotite and kinking or undulatory extinction in pyroxenite. The mineral assemblages of the mylonite neoblast in the peridotite and the pyroxenite are Ol+Opx+Cpx+Sp+hornblende(Hbl), Cpx+Opx+Sp, respectively. Hbl typically occur only in neoblast. In the vicinity (several hundreds of micron) of the fault, dolomite(Dol) also occur in equilibrium with the assemblage above. The recrystallized grain sizes are 20-50 microns in peridotite and 10-30 microns in pyroxenite. The rarity of LD structure is consistent with general conception that deformation processes which lead to dynamic rupture initiation ought to be recorded in limited area on a resultant fault surface. The N-S extensional arrangement of the fault system including the fault of LD structure, the depth of PST (re)crystallization and mylonitization, all indicate that the rupture nucleation occurred in extensional tectonics (Souquiere and Fabbri , 2010). The occurrence of Dol in the vicinity of the PST fault suggests that this is the very place where plastic instability accompanied with fluid chemistry evolution (from H2O-rich to CO2-rich, caused by mylonitization and hydration) of Ueda et al. (2008.) had taken place.

The effects of plastic waves on the numerical convergence of the viscous-plastic and elastic-viscous-plastic sea-ice models

NASA Astrophysics Data System (ADS)

Williams, James; Tremblay, L. Bruno; Lemieux, Jean-François

2017-07-01

The plastic wave speed is derived from the linearized 1-D version of the widely used viscous-plastic (VP) and elastic-viscous-plastic (EVP) sea-ice models. Courant-Friedrichs-Lewy (CFL) conditions are derived using the propagation speed of the wave. 1-D numerical experiments of the VP, EVP and EVP* models successfully recreate a reference solution when the CFL conditions are satisfied, in agreement with the theory presented. The IMplicit-EXplicit (IMEX) method is shown to effectively alleviate the plastic wave CFL constraint on the timestep in the implicitly solved VP model in both 1-D and 2-D. In 2-D, the EVP and EVP* models show first order error in the simulated velocity field when the plastic wave is not resolved. EVP simulations are performed with various advective timestep, number of subcycles, and elastic-wave damping timescales. It is found that increasing the number of subcycles beyond that needed to resolve the elastic wave does not improve the quality of the solution. It is found that reducing the elastic wave damping timescale reduces the spatial extent of first order errors cause by the unresolved plastic wave. Reducing the advective timestep so that the plastic wave is resolved also reduces the velocity error in terms of magnitude and spatial extent. However, the parameter set required for convergence to within the error bars of satellite (RGPS) deformation fields is impractical for use in climate model simulations. The behavior of the EVP* method is analogous to that of the EVP method except that it is not possible to reduce the damping timescale with α = β.

A coupled creep plasticity model for residual stress relaxation of a shot-peened nickel-based superalloy

NASA Astrophysics Data System (ADS)

Buchanan, Dennis J.; John, Reji; Brockman, Robert A.; Rosenberger, Andrew H.

2010-01-01

Shot peening is a commonly used surface treatment process that imparts compressive residual stresses into the surface of metal components. Compressive residual stresses retard initiation and growth of fatigue cracks. During component loading history, shot-peened residual stresses may change due to thermal exposure, creep, and cyclic loading. In these instances, taking full credit for compressive residual stresses would result in a nonconservative life prediction. This article describes a methodical approach for characterizing and modeling residual stress relaxation under elevated temperature loading, near and above the monotonic yield strength of INI 00. The model incorporates the dominant creep deformation mechanism, coupling between the creep and plasticity models, and effects of prior plastic strain to simulate surface treatment deformation.

Simulations of X-ray diffraction of shock-compressed single-crystal tantalum with synchrotron undulator sources.

PubMed

Tang, M X; Zhang, Y Y; E, J C; Luo, S N

2018-05-01

Polychromatic synchrotron undulator X-ray sources are useful for ultrafast single-crystal diffraction under shock compression. Here, simulations of X-ray diffraction of shock-compressed single-crystal tantalum with realistic undulator sources are reported, based on large-scale molecular dynamics simulations. Purely elastic deformation, elastic-plastic two-wave structure, and severe plastic deformation under different impact velocities are explored, as well as an edge release case. Transmission-mode diffraction simulations consider crystallographic orientation, loading direction, incident beam direction, X-ray spectrum bandwidth and realistic detector size. Diffraction patterns and reciprocal space nodes are obtained from atomic configurations for different loading (elastic and plastic) and detection conditions, and interpretation of the diffraction patterns is discussed.

Simulations of X-ray diffraction of shock-compressed single-crystal tantalum with synchrotron undulator sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, M. X.; Zhang, Y. Y.; E, J. C.

Polychromatic synchrotron undulator X-ray sources are useful for ultrafast single-crystal diffraction under shock compression. Here, simulations of X-ray diffraction of shock-compressed single-crystal tantalum with realistic undulator sources are reported, based on large-scale molecular dynamics simulations. Purely elastic deformation, elastic–plastic two-wave structure, and severe plastic deformation under different impact velocities are explored, as well as an edge release case. Transmission-mode diffraction simulations consider crystallographic orientation, loading direction, incident beam direction, X-ray spectrum bandwidth and realistic detector size. Diffraction patterns and reciprocal space nodes are obtained from atomic configurations for different loading (elastic and plastic) and detection conditions, and interpretation of themore » diffraction patterns is discussed.« less

Optimization of an asymmetric thin-walled tube in rotary draw bending process

NASA Astrophysics Data System (ADS)

Xue, Xin; Liao, Juan; Vincze, Gabriela; Gracio, Jose J.

2013-12-01

The rotary draw bending is one of the advanced thin-walled tube forming processes with high efficiency, low consumption and good flexibility in several industries such as automotive, aerospace and shipping. However it may cause undesirable deformations such as over-thinning and ovalization, which bring the weakening of the strength and difficulties in the assembly process respectively. Accurate modeling and effective optimization design to eliminate or reduce undesirable deformations in tube bending process have been a challenging topic. In this paper, in order to study the deformation behaviors of an asymmetric thin-walled tube in rotary draw bending process, a 3D elastic-plastic finite element model has been built under the ABAQUS environment, and the reliability of the model is validated by comparison with experiment. Then, the deformation mechanism of thin-walled tube in bending process was briefly analysis and the effects of wall thickness ratio, section height width ratio and mandrel extension on wall thinning and ovalization in bending process were investigated by using Response Surface Methodology. Finally, multi-objective optimization method was used to obtain an optimum solution of design variables based on simulation results.

Revealing flow behaviors of metallic glass based on activation of flow units

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, T. P.; Wang, W. H.; Bai, H. Y., E-mail: hybai@iphy.ac.cn

2016-05-28

Atomic level flow plays a critical role in the mechanical behavior of metallic glass (MG) while the connection between the flow and the heterogeneous microstructure of the glass remains unclear. We describe the heterogeneity of MGs as the elastic matrix with “inclusions” of nano-scale liquid-like flow units, and the plastic flow behavior of MGs is considered to be accommodated by the flow units. We show that the model can explain the various deformation behaviors, the transformation from inhomogeneous deformation to homogeneous flow upon strain rate or temperature, and the deformation map in MGs, which might provide insights into the flowmore » mechanisms in glasses and inspiration for improving the plasticity of MGs.« less

Definition of criteria for estimating alternative technologies of increasing quality of rotor shaft neck by electroerosive alloying and surface plastic deformation methods

NASA Astrophysics Data System (ADS)

Martsynkovskyy, V.; Kirik, G.; Tarelnyk, V.; Zharkov, P.; Konoplianchenko, Ie; Dovzhyk, M.

2017-08-01

There are represented the results of influence of the surface plastic deformation (SPD) methods, namely, diamond smoothing (DS) and ball-rolling surface roughness generation (BSRG) ones on the qualitative parameters (residual stresses, fatigue strength and wear resistance values) of the steel substrate surface layers formed by the electroerosive alloying (EEA) method. There are proposed the most rational methods of deformation and also the composition for electroerosive coatings providing the presence of the favorable residual compressive stresses in the surface layer, increasing fatigue strength and wear resistance values. There are stated the criteria for estimating the alternative variants of the combined technologies and choosing the most rational ones thereof.

Stress wave riveting. [of aircraft metal skin

NASA Technical Reports Server (NTRS)

Leftheris, B. P.

1972-01-01

The stress wave riveter deforms the rivet material by a high amplitude stress wave. Thus, the entire rivet is set in motion radially. The rivet expands rapidly and impacts the hole surface before the rivet tail begins to form. Unlike the oversqueezed rivets, therefore, it sets up uniform interference without distortion in the skins. Furthermore, the radial velocity is so high (over 200 in./sec) that upon impact with the hole surface it deforms the surface plastically. This is especially effective in aluminum skins. Thus the SWR combines the advantages of plastically deforming the hole and the economic advantage of a relatively nonprecision hole and inexpensive rivets like those used in oversqueezing. The additional advantage SWR offers is that it is a portable tool.

Dynamic fracture of the surface of an aluminum alloy under conditions of high-speed erosion

NASA Astrophysics Data System (ADS)

Petrov, Yu. V.; Atroshenko, S. A.; Kazarinov, N. A.; Evstifeev, A. D.; Solov'ev, V. Yu.

2017-04-01

The kinetics of fracture and deformation of the standard aluminum alloy AD1 and a similar alloy subjected to severe plastic deformation by high-pressure torsion under conditions of high-speed erosion has been investigated. It has been shown that, with an increase in the loading rate, the fraction of the brittle component on the fracture surface of the standard material, as well as the thickness of the damaged layer, increases more significantly than that for the material after the severe plastic deformation by high-pressure torsion. A relationship of the surface roughness of the material after the erosion with the loading rate and the thickness of the erosion-damaged layer has been established.

High-Aspect-Ratio Ridge Structures Induced by Plastic Deformation as a Novel Microfabrication Technique.

PubMed

Takei, Atsushi; Jin, Lihua; Fujita, Hiroyuki; Takei, A; Fujita, H; Jin, Lihua

2016-09-14

Wrinkles on thin film/elastomer bilayer systems provide functional surfaces. The aspect ratio of these wrinkles is critical to their functionality. Much effort has been dedicated to creating high-aspect-ratio structures on the surface of bilayer systems. A highly prestretched elastomer attached to a thin film has recently been shown to form a high-aspect-ratio structure, called a ridge structure, due to a large strain induced in the elastomer. However, the prestretch requirements of the elastomer during thin film attachment are not compatible with conventional thin film deposition methods, such as spin coating, dip coating, and chemical vapor deposition (CVD). Thus, the fabrication method is complex, and ridge structure formation is limited to planar surfaces. This paper presents a new and simple method for constructing ridge structures on a nonplanar surface using a plastic thin film/elastomer bilayer system. A plastic thin film is attached to a stress-free elastomer, and the resulting bilayer system is highly stretched one- or two-dimensionally. Upon the release of the stretch load, the deformation of the elastomer is reversible, while the plastically deformed thin film stays elongated. The combination of the length mismatch and the large strain induced in the elastomer generates ridge structures. The morphology of the plastic thin film/elastomer bilayer system is experimentally studied by varying the physical parameters, and the functionality and the applicability to a nonplanar surface are demonstrated. Finally, we simulate the effect of plasticity on morphology. This study presents a new technique for generating microscale high-aspect-ratio structures and its potential for functional surfaces.

Finite Element Studies of Solitary Waves in Granular Chains

NASA Astrophysics Data System (ADS)

Musson, Ryan W.

Solitary wave propagation in a monodisperse metallic granular chain was simulated using the finite element method. The model was built to address a discrepancy between numerical and experimental results from Lazaridi and Nesterenko (J. Appl. Mech. Tech. Phys., 26 [3] 405-408 1985). In their work, solitary waves were generated in a chain of particles through impact of a piston, and results were quantified by comparing the chains' reactions to a rigid wall. Their numerical calculations resulted in a solitary wave with a force amplitude of 83 N, while it was measured experimentally to be 71 N. In the present work, the configuration of the granular chain and piston was duplicated from Lazaridi and Nesterenko (J. Appl. Mech. Tech. Phys., 26 [3] 405-408 1985). Qualitatively similar solitary waves were produced, and von Mises stress values indicated that localized plastic deformation is possible, even at low piston impact velocities. These results show that localized plastic deformation was a likely source of dissipation in experiments performed by Lazaridi and Nesterenko. Solitary wave response was investigated in the same metallic granular chain-piston system using LS-DYNA. A power-law hardening material model was used to show that localized plastic deformation is present in the metallic granular chain, even for an impact velocity of 0.5 m/s. This loss due to plastic deformation was quantified via impulse, and it was shown that the loss scales nearly linearly with impact velocity. Therefore, metallic grains may not be suitable for devices that require high amplitude solitary waves. There would be too much energy lost to plastic deformation. The response of an aluminum oxide granular chain was subsequently compared to that of a steel chain because ceramics are inherently elastic. It was shown that solitary waves travel faster and the initial peak is slightly lower when compared to a steel chain. The response of granular chains to impulse loading was investigated as a function of material properties. COMSOL Multiphysics was used to study the effect of density and elastic modulus on a granular chain with fixed Poisson's ratio. Solitary wave velocity and amplitude increased with elastic modulus. Increasing density caused a decrease in wave velocity and an increase in amplitude. In addition, higher density granular chains exhibited a decrease in the number of solitary waves in their respective solitary wave trains. LS-DYNA was then used to explore the response of a variety of ceramic and metallic granular chains. Density, elastic modulus, and Poisson's ratio were all set to representative values for the respective material. It was shown that solitary wave development and decay occur at different rates for different materials. In addition, the kinetic energy decay of the impactor was slower for glass compared with tungsten. Finally, it was shown that a single solitary wave with no train could be produced by impacting a high density, high modulus chain such as tungsten with a glass piston, which has relatively low density and elastic modulus. Increasing impact velocity for this case resulted in a single high-amplitude solitary wave with no train.

Use of multiscale zirconium alloy deformation models in nuclear fuel behavior analysis

NASA Astrophysics Data System (ADS)

Montgomery, Robert; Tomé, Carlos; Liu, Wenfeng; Alankar, Alankar; Subramanian, Gopinath; Stanek, Christopher

2017-01-01

Accurate prediction of cladding mechanical behavior is a key aspect of modeling nuclear fuel behavior, especially for conditions of pellet-cladding interaction (PCI), reactivity-initiated accidents (RIA), and loss of coolant accidents (LOCA). Current approaches to fuel performance modeling rely on empirical constitutive models for cladding creep, growth and plastic deformation, which are limited to the materials and conditions for which the models were developed. To improve upon this approach, a microstructurally-based zirconium alloy mechanical deformation analysis capability is being developed within the United States Department of Energy Consortium for Advanced Simulation of Light Water Reactors (CASL). Specifically, the viscoplastic self-consistent (VPSC) polycrystal plasticity modeling approach, developed by Lebensohn and Tomé [1], has been coupled with the BISON engineering scale fuel performance code to represent the mechanistic material processes controlling the deformation behavior of light water reactor (LWR) cladding. A critical component of VPSC is the representation of the crystallographic nature (defect and dislocation movement) and orientation of the grains within the matrix material and the ability to account for the role of texture on deformation. A future goal is for VPSC to obtain information on reaction rate kinetics from atomistic calculations to inform the defect and dislocation behavior models described in VPSC. The multiscale modeling of cladding deformation mechanisms allowed by VPSC far exceed the functionality of typical semi-empirical constitutive models employed in nuclear fuel behavior codes to model irradiation growth and creep, thermal creep, or plasticity. This paper describes the implementation of an interface between VPSC and BISON and provides initial results utilizing the coupled functionality.

Production of ultrafine grained aluminum by cyclic severe plastic deformation at ambient temperature

NASA Astrophysics Data System (ADS)

Bereczki, P.; Szombathelyi, V.; Krallics, G.

2014-08-01

In the present study the possibilities of grain refinement was investigated by applying large-scale of cyclic plastic deformation to aluminum at ambient temperature. The specimens are processed by multiaxial forging, which is one of the severe plastic deformation techniques. The aim of the experiments with the aluminum alloy 6082M was the determination of the equivalent stress and strain by multiaxial forging and the investigation of evolution of mechanical properties in relation with the accumulated deformation in the specimen. The mechanical properties of raw material was determined by plane strain compression test as well as by hardness measurements. The forming experiments were carried out on Gleeble 3800 physical simulator with MaxStrain System. The mechanical properties of the forged specimens were investigated by micro hardness measurements and tensile tests. A mechanical model, based on the principle of virtual velocities was developed to calculate the flow curves using the measured dimensional changes of the specimen and the measured force. With respect to the evolution of these curves, the cyclic growth of the flow stress can be observed at every characteristic points of the calculated flow curves. In accordance with this tendency, the evolution of the hardness along the middle cross section of the deformed volume has also a nonmonotonous characteristic and the magnitudes of these values are much smaller than by the specimen after plane strain compression test. This difference between the flow stresses respect to the monotonic and non-monotonic deformation can be also observed. The formed microstructure, after a 10-passes multiaxial forging process, consists of mainly equiaxial grains in the submicron grain scale.

Anisotropy of the Hot Plastic Deformation of Ti-6Al-4V Single-Colony Samples (Preprint)

DTIC Science & Technology

2009-04-01

April 2009 Journal Article Preprint 01 April 2009- 01 April 2009 4 . TITLE AND SUBTITLE ANISOTROPY OF THE HOT PLASTIC DEFORMATION OF Ti-6Al-4V SINGLE...COLONY SAMPLES (PREPRINT) 5a. CONTRACT NUMBER In-house 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 62102F 6 . AUTHOR(S) A.A. Salem and S.L...resistance, and low density, Ti-6Al-4V is the most commonly used alpha/beta titanium alloy. It accounts for approximately 80% of the total titanium used in

Texture-induced anisotropy and high-strain rate deformation in metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schiferl, S.K.; Maudlin, P.J.

1990-01-01

We have used crystallographic texture calculations to model anisotropic yielding behavior for polycrystalline materials with strong preferred orientations and strong plastic anisotropy. Fitted yield surfaces were incorporated into an explicit Lagrangian finite-element code. We consider different anisotropic orientations, as well as different yield-surface forms, for Taylor cylinder impacts of hcp metals such as titanium and zirconium. Some deformed shapes are intrinsic to anisotropic response. Also, yield surface curvature, as distinct from strength anisotropy, has a strong influence on plastic flow. 13 refs., 5 figs.

Influence of Rare-Earth Additions on Properties of Titanium Alloys - Effects of Yttrium and Erbium Additions on Ti-8Al and Ti-10Al Alloy.

DTIC Science & Technology

1980-08-31

loop generated during the alternate tension-compression fatigue testing of Ti-8A1 alloy at 6000C at a plastic strain amplitude of * 0.5Z...Dependence of peak stress on the number of cycles in the longitudinal orientation of Ti-lOAl-RE alloys deformed in alternate tension-compression at...of cycles in the transverse orientation of Ti-OAl-RE alloys deformed in alternate tension- A compression fatigue at 500 0C at a plastic strain

Flow units perspective on elastic recovery under sharp contact loading in metallic glasses

NASA Astrophysics Data System (ADS)

Shahzad, K.; Gulzar, A.; Wang, W. H.

2016-12-01

The obscure nature of glass physics has led to develop various correlations between different parameters and properties of metallic glasses. Despite these correlations, the clear picture of plastic deformation is still lacking. We have measured elastic recovery in metallic glasses by indentation, and found the elastic recovery correlate with different properties and parameters of metallic glasses. All these observations can be quite well explained with flow unit model which could provide clearer picture on the plastic deformations and nature of the metallic glasses.

FEM modeling of postseismic deformation of poroelastic material

NASA Astrophysics Data System (ADS)

Kawamoto, S.; Ito, T.; Hirahara, K.

2004-12-01

Following a large earthquake, postseismic deformation in the focal region has been observed by GPS, leveling measurements and the other geodetic measurements. To explain the postseismic deformation, researchers have proposed and well investigated two physical mechanisms of afterslip and viscoelastic relaxation. In some cases, however, there have been observed postseismic deformation which can not be explained by these mechanisms. Therefore, another mechanism has been proposed, where the crust is treated as "poroelastic material". This concept is called "poroelasticity". In this concept, postseismic deformation is caused by pore fluid flow due to the coseismic stress redistribution. We explored, therefore, the postseismic deformation due to pore fluid flow in a poroelastic material using finite element method (FEM), which can easily handle lateral variations of hydraulic diffusivity and elastic or plastic property. We used the FEM program 'CAMBIOT3D' originally developed by Geotech. Lab. Gunma University, Japan (2003). Because this program was developed for soil mechanics, we must have modified so as to calculate deformation due to earthquake faulting. We implemented the 'split node technique' (Melosh and Refsky, 1981) to calculate the coseismic deformation. In addition to this, we modified the program to calculate the deformation taking into account the Skempton's B. This coefficient B determines what fraction of the coseismic stress due to an earthquake is allotted to pore pressure. Without Skempton's B, coseismic pore pressure becomes too large and hence postseismic deformation is calculated too large. We evaluated the postseismic deformation in a poroelastic material to show that the poroelastic deformation is quite different from that of afterslip and viscoelastic relaxation models. In this presentation, we show the postseismic deformation due to pore fluids flow in a poroelastic material and the effect of Skempton's B. Especially, we discuss what different pattern of postseismic deformation is produced depending on the lateral variation of hydraulic diffusivity structures in and around the fault zone, which structures have been differently inferred from fault zone core sampling researches and so on.

Stress evolution in elastic-plastic electrodes during electrochemical processes: A numerical method and its applications

NASA Astrophysics Data System (ADS)

Wen, Jici; Wei, Yujie; Cheng, Yang-Tse

2018-07-01

Monitoring in real time the stress state in high capacity electrodes during charge-discharge processes is pivotal to the performance assessment and structural optimization of advanced batteries. The wafer curvature measurement technique broadly employed in thin-film industry, together with stress analysis using the Stoney equation, has been successfully adopted to measure in situ the stress in thin film electrodes. How large plastic deformation or interfacial delamination during electrochemical cycles in such electrodes affects the applicability of Stoney equation remains unclear. Here we develop a robust electrochemical-mechanical coupled numerical procedure to investigate the influence of large plastic deformation and interfacial failure on the measured stress in thin film electrodes. We identify how the constitutive behavior of electrode materials and film-substrate interfacial properties affect the measured stress-capacity curves of electrodes, and hence establish the relationship of electrode material parameters with the characteristics of stress-capacity curves. Using Li-ions batteries as examples, we show that plastic deformation and interfacial delamination account for the asymmetric stress-capacity loops seen in in situ stress measurements. The methods used here, along with the finite-element code in the supplementary material, may be used to model the electrode behavior as a function of the state of charge.

Examination of the collision force method for analyzing the responses of simple containment/deflection structures to impact by one engine rotor blade fragment

NASA Technical Reports Server (NTRS)

Zirin, R. M.; Witmer, E. A.

1972-01-01

An approximate collision analysis, termed the collision-force method, was developed for studying impact-interaction of an engine rotor blade fragment with an initially circular containment ring. This collision analysis utilizes basic mass, material property, geometry, and pre-impact velocity information for the fragment, together with any one of three postulated patterns of blade deformation behavior: (1) the elastic straight blade model, (2) the elastic-plastic straight shortening blade model, and (3) the elastic-plastic curling blade model. The collision-induced forces are used to predict the resulting motions of both the blade fragment and the containment ring. Containment ring transient responses are predicted by a finite element computer code which accommodates the large deformation, elastic-plastic planar deformation behavior of simple structures such as beams and/or rings. The effects of varying the values of certain parameters in each blade-behavior model were studied. Comparisons of predictions with experimental data indicate that of the three postulated blade-behavior models, the elastic-plastic curling blade model appears to be the most plausible and satisfactory for predicting the impact-induced motions of a ductile engine rotor blade and a containment ring against which the blade impacts.

A cell-centered Lagrangian finite volume approach for computing elasto-plastic response of solids in cylindrical axisymmetric geometries

NASA Astrophysics Data System (ADS)

Sambasivan, Shiv Kumar; Shashkov, Mikhail J.; Burton, Donald E.

2013-03-01

A finite volume cell-centered Lagrangian formulation is presented for solving large deformation problems in cylindrical axisymmetric geometries. Since solid materials can sustain significant shear deformation, evolution equations for stress and strain fields are solved in addition to mass, momentum and energy conservation laws. The total strain-rate realized in the material is split into an elastic and plastic response. The elastic and plastic components in turn are modeled using hypo-elastic theory. In accordance with the hypo-elastic model, a predictor-corrector algorithm is employed for evolving the deviatoric component of the stress tensor. A trial elastic deviatoric stress state is obtained by integrating a rate equation, cast in the form of an objective (Jaumann) derivative, based on Hooke's law. The dilatational response of the material is modeled using an equation of state of the Mie-Grüneisen form. The plastic deformation is accounted for via an iterative radial return algorithm constructed from the J2 von Mises yield condition. Several benchmark example problems with non-linear strain hardening and thermal softening yield models are presented. Extensive comparisons with representative Eulerian and Lagrangian hydrocodes in addition to analytical and experimental results are made to validate the current approach.

Reproducing Kernel Particle Method in Plasticity of Pressure-Sensitive Material with Reference to Powder Forming Process

NASA Astrophysics Data System (ADS)

Khoei, A. R.; Samimi, M.; Azami, A. R.

2007-02-01

In this paper, an application of the reproducing kernel particle method (RKPM) is presented in plasticity behavior of pressure-sensitive material. The RKPM technique is implemented in large deformation analysis of powder compaction process. The RKPM shape function and its derivatives are constructed by imposing the consistency conditions. The essential boundary conditions are enforced by the use of the penalty approach. The support of the RKPM shape function covers the same set of particles during powder compaction, hence no instability is encountered in the large deformation computation. A double-surface plasticity model is developed in numerical simulation of pressure-sensitive material. The plasticity model includes a failure surface and an elliptical cap, which closes the open space between the failure surface and hydrostatic axis. The moving cap expands in the stress space according to a specified hardening rule. The cap model is presented within the framework of large deformation RKPM analysis in order to predict the non-uniform relative density distribution during powder die pressing. Numerical computations are performed to demonstrate the applicability of the algorithm in modeling of powder forming processes and the results are compared to those obtained from finite element simulation to demonstrate the accuracy of the proposed model.

Scratching technique for the study and analysis of soil surface abrasion mechanism

NASA Astrophysics Data System (ADS)

Ta, Wanquan

2007-11-01

Aeolian abrasion is the most fundamental and active surface process that takes place in arid and semi-arid environments. Its nature is a wear process for wind blown grains impinging on a soil or sediment surface, which causes particles and aggregates to fracture from the soil surface through a series of plastic and brittle cracking deformation such as cutting, ploughing and brittle fracturing. Using a Universal Micro-Tribometer (UMT), a scratching test was carried out on six soil surfaces (sandy soil, sand loam, silt loam, loam, silt clay loam, and silt clay). The results indicate that traces of normal and tangential force vs. time show a jagged curve, which can reflect the plastic deformation and brittle fracturing of aggregates and particles of various sizes fractured from the soil surfaces. The jagged curve peaks, and the area enclosed underneath, may represent the bonding forces and bonding energies of some aggregates and grains on the soil surface, respectively. Connecting the scratching test with an impact abrasion experiment furthermore demonstrates that soil surface abrasion rates are proportional to the square of speeds of impacting particles and to the 2.6 power of mean soil grain size, and inversely proportional to the 1.5 power of specific surface abrasive energy or to the 1.7 power of specific surface hardness.

Cerium Addition Improved the Dry Sliding Wear Resistance of Surface Welding AZ91 Alloy

PubMed Central

Zhao, Zhihao; Zhu, Qingfeng; Wang, Gaosong; Tao, Kai

2018-01-01

In this study, the effects of cerium (Ce) addition on the friction and wear properties of surface welding AZ91 magnesium alloys were evaluated by pin-on-disk dry sliding friction and wear tests at normal temperature. The results show that both the friction coefficient and wear rate of surfacing magnesium alloys decreased with the decrease in load and increase in sliding speed. The surfacing AZ91 alloy with 1.5% Ce had the lowest friction coefficient and wear rate. The alloy without Ce had the worst wear resistance, mainly because it contained a lot of irregularly shaped and coarse β-Mg17Al12 phases. During friction, the β phase readily caused stress concentration and thus formed cracks at the interface between β phase and α-Mg matrix. The addition of Ce reduced the size and amount of Mg17Al12, while generating Al4Ce phase with a higher thermal stability. The Al-Ce phase could hinder the grain-boundary sliding and migration and reduced the degree of plastic deformation of subsurface metal. Scanning electron microscopy observation showed that the surfacing AZ91 alloy with 1.5% Ce had a total of four types of wear mechanism: abrasion, oxidation, and severe plastic deformation were the primary mechanisms; delamination was the secondary mechanism. PMID:29415492

Effect of Electropulsing-Assisted Ultrasonic Nanocrystalline Surface Modification on the Surface Mechanical Properties and Microstructure of Ti-6Al-4V Alloy

NASA Astrophysics Data System (ADS)

Ye, Yongda; Wang, Haibo; Tang, Guoyi; Song, Guolin

2018-05-01

The effect of electropulsing-assisted ultrasonic nanocrystalline surface modification (EP-UNSM) on surface mechanical properties and microstructure of Ti-6Al-4V alloy is investigated. Compared to conventional ultrasonic nanocrystalline surface modification (UNSM), EP-UNSM can effectively facilitate surface roughness and morphology, leading to excellent surface roughness (reduced from Ra 0.918 to Ra 0.028 μm by UNSM and Ra 0.019 μm by EP-UNSM) and smoother morphology with less cracks and defects. Surface friction coefficients are enhanced, resulting in lower and smoother friction coefficients. In addition, the surface-strengthened layer and ultra-refined grains are significantly enhanced with more severe plastic deformation and a greater surface hardness (a maximum hardness value of 407 HV and an effective depth of 550 μm, in comparison with the maximum hardness value of 364 HV and effective depth of 300 μm obtained by conventional UNSM). Remarkable enhancement of surface mechanical properties can be attributed to the refined gradient microstructure and the enhanced severe plastic deformation layer induced by coupling the effects of UNSM and electropulsing. The accelerated dislocation mobility and atom diffusion caused by the thermal and athermal effects of electropulsing treatment may be the primary intrinsic reasons for these improvements.

Micromechanics of Ultrafine Particle Adhesion—Contact Models

NASA Astrophysics Data System (ADS)

Tomas, Jürgen

2009-06-01

Ultrafine, dry, cohesive and compressible powders (particle diameter d<10 μm) show a wide variety of flow problems that cause insufficient apparatus and system reliability of processing plants. Thus, the understanding of the micromechanics of particle adhesion is essential to assess the product quality and to improve the process performance in particle technology. Comprehensive models are shown that describe the elastic-plastic force-displacement and frictional moment-angle behavior of adhesive contacts of isotropic smooth spheres. By the model stiff particles with soft contacts, a sphere-sphere interaction of van der Waals forces without any contact deformation describes the stiff attractive term. But, the soft micro-contact response generates a flattened contact, i.e. plate-plate interaction, and increasing adhesion. These increasing adhesion forces between particles directly depend on this frozen irreversible deformation. Thus, the adhesion force is found to be load dependent. It contributes to the tangential forces in an elastic-plastic frictional contact with partially sticking and micro-slip within the contact plane. The load dependent rolling resistance and torque of mobilized frictional contact rotation (spin around its principal axis) are also shown. This reasonable combination of particle contact micromechanics and powder continuum mechanics is used to model analytically the macroscopic friction limits of incipient powder consolidation, yield and cohesive steady-state shear flow on physical basis.

3D numerical simulations of multiphase continental rifting

NASA Astrophysics Data System (ADS)

Naliboff, J.; Glerum, A.; Brune, S.

2017-12-01

Observations of rifted margin architecture suggest continental breakup occurs through multiple phases of extension with distinct styles of deformation. The initial rifting stages are often characterized by slow extension rates and distributed normal faulting in the upper crust decoupled from deformation in the lower crust and mantle lithosphere. Further rifting marks a transition to higher extension rates and coupling between the crust and mantle lithosphere, with deformation typically focused along large-scale detachment faults. Significantly, recent detailed reconstructions and high-resolution 2D numerical simulations suggest that rather than remaining focused on a single long-lived detachment fault, deformation in this phase may progress toward lithospheric breakup through a complex process of fault interaction and development. The numerical simulations also suggest that an initial phase of distributed normal faulting can play a key role in the development of these complex fault networks and the resulting finite deformation patterns. Motivated by these findings, we will present 3D numerical simulations of continental rifting that examine the role of temporal increases in extension velocity on rifted margin structure. The numerical simulations are developed with the massively parallel finite-element code ASPECT. While originally designed to model mantle convection using advanced solvers and adaptive mesh refinement techniques, ASPECT has been extended to model visco-plastic deformation that combines a Drucker Prager yield criterion with non-linear dislocation and diffusion creep. To promote deformation localization, the internal friction angle and cohesion weaken as a function of accumulated plastic strain. Rather than prescribing a single zone of weakness to initiate deformation, an initial random perturbation of the plastic strain field combined with rapid strain weakening produces distributed normal faulting at relatively slow rates of extension in both 2D and 3D simulations. Our presentation will focus on both the numerical assumptions required to produce these results and variations in 3D rifted margin architecture arising from a transition from slow to rapid rates of extension.

Dual self-organised shear banding behaviours and enhanced ductility in phase separating Zr-based bulk metallic glasses

NASA Astrophysics Data System (ADS)

Zhang, Z. Q.; Song, K. K.; Sun, B. A.; Wang, L.; Cui, W. C.; Qin, Y. S.; Han, X. L.; Xue, Q. S.; Peng, C. X.; Sarac, B.; Spieckermann, F.; Kaban, I.; Eckert, J.

2018-07-01

The multiplication and interaction of self-organised shear bands often transform to a stick-slip behaviour of a major shear band along the primary shear plane, and ultimately the major shear band becomes runaway and terminates the plasticity of bulk metallic glasses (BMGs). Here, we examined the deformation behaviours of the nanoscale phase-separating Zr65-xCu25Al10Fex (x = 5 and 7.5 at.%) BMGs. The formation of multi-step phase separation, being mainly governed by nucleation and growth, results in the microstructural inhomogeneity on a wide range of length-scales and leads to obviously macroscopic and repeatable ductility. The good deformability can be attributed to two mechanisms for stabilizing shear banding process, i.e. the mutual interaction of multiple shear bands away from the major shear band and the delaying slip-to-failure of dense fine shear bands around the major shear band, both of which show a self-organised criticality yet with different power-law exponents. The two mechanisms could come into effect in the intermediate (stable) and later plastic deformation regime, respectively. Our findings provide a possibility to enhance the shear banding stability over the whole plastic deformation through a proper design of microstructure heterogeneities.