Effect of grain size on Luders-type deformation and plastic deformation of V nanowires/NiTi composit
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Shi, Xiaobin↗
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Results for “plastic deformation”
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Plastic deformation mechanism of calcium-silicate hydrates determined by deviatoric-stress Raman spectroscopy
Highlights: • C-(A-)S-H samples under stress were characterized at the bond and grain level. • Small angle scattering showed that 720 MPa reduced grain thickness by 30%. • In-situ Raman showed that cross-linked C-A-S-H slips along its intralayer. • However, in-situ Raman showed that C-S-H slips along the interlayer. • In-situ Raman also showed a growth in CaCO{sub 3}, indicating fracture in both samples. Creep of the cement matrix affects the structural stability of concrete. In Portland cements, the creep is largely controlled by the binding phase calcium-(aluminum-)silicate-hydrate, or C-(A-)S-H. This phase has a lamellar structure and under deviatoric stress aligns its c-axis with the principal stress. However, the limiting resistance to this reorientation is unknown at the nanocrystalline level. Small-angle X-ray scattering shows that the lamellae thickness decreases under 100's MPa deviatoric stress. Deviatoric stress Raman spectroscopy shows that there are two ways that this break-up can occur. If the material's silicate chains are cross-linked, then strain in SiO bonds does not increase above certain stresses, indicating a relaxation adjacent to the SiO bond. If the chains are not cross-linked, then the silicate chains are broken up by rastering against each other, introducing defects. These results show that the plastic deformation of C-(A-)S-H is relevant for Portland cement creep.
36 MATERIALS SCIENCE↗
Practical solution of plastic deformation problems in elastic-plastic range
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.
COLUMNS, TUBULAR↗
Practical Solution of Plastic Deformation Problems in Elastic-Plastic Range
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.
Mendelson, A.↗
Study of the Micro-Nonuniformity of the Plastic Deformation of Steel
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.
Chechulin, B. B.↗
A plane strain analysis of the blunted crack tip using small strain deformation plasticity theory
A deformation plasticity analysis of the tip region of a blunted crack in plane strain is presented. The power hardening material is incompressible both elastically and plastically, in order to simulate behavior of a stress freezing material above critical temperature. Stress and displacement fields surrounding the crack tip are presented. The results indicate that the maximum stress seen at the crack tip is indeed limited and is determined by the tensile properties; however, the scale over which the stresses act is dependent on the loading. Comparisons are good between the forward crack tip displacement and micro-fractographic measurments of stretch zones observed in plane strain fracture toughness tests.
Mcgowan, J. J.↗
In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure
Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. Rough diamond anvils are introduced to reach maximum friction equal to yield strength in shear and the first in-situ study of the evolution of the pressure-dependent yield strength and radial distribution of nanostructural parameters are performed for severely pre-deformed Zr. ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent and reaches steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for a-Zr obtained with smooth and rough anvils are different, causing major challenge in plasticity theory. In-situ study of severe plastic deformation of α-Zr with rough diamond anvils revealed that pressure-dependent yield strength, crystallite size, and dislocation density are getting steady and plastic strain- and strain-path-independent.
36 MATERIALS SCIENCE↗
Data-driven analysis of neutron diffraction line profiles: application to plastically deformed Ta
Abstract Non-destructive evaluation of plastically deformed metals, particularly diffraction line profile analysis (DLPA), is valuable both to estimate dislocation densities and arrangements and to validate microstructure-aware constitutive models. To date, the interpretation of whole line diffraction profiles relies on the use of semi-analytical models such as the extended convolutional multiple whole profile (eCMWP) method. This study introduces and validates two data-driven DLPA models to extract dislocation densities from experimentally gathered whole line diffraction profiles. Using two distinct virtual diffraction models accounting for both strain and instrument induced broadening, a database of virtual diffraction whole line profiles of Ta single crystals is generated using discrete dislocation dynamics. The databases are mined to create Gaussian process regression-based surrogate models, allowing dislocation densities to be extracted from experimental profiles. The method is validated against 11 experimentally gathered whole line diffraction profiles from plastically deformed Ta polycrystals. The newly proposed model predicts dislocation densities consistent with estimates from eCMWP. Advantageously, this data driven LPA model can distinguish broadening originating from the instrument and from the dislocation content even at low dislocation densities. Finally, the data-driven model is used to explore the effect of heterogeneous dislocation densities in microstructures containing grains, which may lead to more accurate data-driven predictions of dislocation density in plastically deformed polycrystals.
36 MATERIALS SCIENCE↗
Gas Bubble Evolution in Polycrystalline UMo Fuels Under Elastic-Plastic Deformation: A Phase-Field Model With Crystal-Plasticity
In monolithic UMo fuels, the interaction between the Al cladding and large gas bubble volumetric swelling causes both elastic-plastic and creep deformation. In this work, a phase-field model of gas bubble evolution in polycrystalline UMo under elastic-plastic deformation was developed for studying the dynamic interaction between evolving gas bubble/voids and deformation. A crystal plasticity model, which assumes that the plastic strain rate is proportional to resolved shear stresses of dislocation slip systems on their slip planes, was used to describe plastic deformation in polycrystalline UMo. Xe diffusion and gas bubble evolution are driven by the minimization of chemical and deformation energies in the phase-field model, while evolving gas bubble structure was used to update the mechanical properties in the crystal plasticity model. With the developed model, we simulated the effect of gas bubble structures (different volume fractions and internal gas pressures) on stress-strain curves and the effect of local stresses on gas bubble evolution. The results show that 1) the effective Young’s modulus and yield stress decrease with the increase of gas bubble volume fraction; 2) the hardening coefficient increases with the increase of gas bubble volume fraction, especially for gas bubbles with higher internal pressure; and 3) the pressure dependence of Xe thermodynamic and kinetic properties in addition to the local stress state determine gas bubble growth or shrinkage. The simulated results can serve as a guide to improve material property models for macroscale fuel performance modeling.
36 MATERIALS SCIENCE↗
Determination of near-surface plastic deformation in sliding contacts
It is pointed out that substantial plastic deformation occurs on and near the contact surfaces, when two solid bodies slide against each other without lubrication. It has been found that this deformation plays an important role in the tribological behavior of the sliding contact. The present investigation has the objective to develop an analytical model to predict the near-surface plastic deformation resulting from a single pass of one metallic surface over another. A finite element viscoplasticity program was written relating velocities to forces in a two-dimensional domain. The program was employed in the study of plastic deformation during a single pass of a hardened tool steel slider over a copper rub specimen. It was found that essentially the only material set in motion by the slider was directly under the contact zone. The agreement between values obtained in the analysis and experimental data is reasonably good.
Kennedy, F. E., Jr.↗
Ductile Glassy Polymer Networks Capable of Large Plastic Deformation and Heat-Induced Elastic Recovery
Many thermoplastic polymers are ductile by combining strength and large deformations. These deformations are irreversible - known as plastic deformation. Elastomers can deform reversibly but have low strength. To this end, we developed glassy and ductile polyamide networks capable of large plastic deformation (>200% strain) and high strength (~50 MPa tensile strength and ~1500 MPa Young’s modulus), similar to those of polyolefins and Nylon-66. We discovered that hydrogen bonding between meta-phthalamide groups was essential to the ductility. Since these polyamide networks are covalently bonded, we demonstrated their unique durability by repeatable elastic recovery at elevated temperatures, exhibiting indifferent tensile properties in each cycle. Furthermore, when we fixed the strain during the elastic recovery, these polyamide networks actuated stresses of 9–18 MPa, among the highest reported in shape-memory polymer actuators. Here, we envision these ductile, glassy polymer networks as promising alternatives to ductile thermoplastics, given the combined benefit of ductility and durability.
36 MATERIALS SCIENCE↗
Achieving high-ZT in Te/Se-based thermoelectric materials via volume-constrained shear-induced plastic deformation
This study investigated the correlation between severe plastic deformation and microstructural evolution, along with the corresponding response in the thermoelectric performance. Specifically, severe plastic deformation introduced into intrinsically brittle thermoelectric materials like Bi 2 Te 3 - x Se x leads to microstructural changes ranging from nano- to micro- scales, including phase transformation, phase segregation, and stacking faults. The resultant residual strain and lattice defects in the Bi 2 Te 3-x Se x materials led to engineering of electronic bands, which increases the effective mass of electrons while controlling their concentration, thereby enhancing the power factor.
36 MATERIALS SCIENCE↗
A high-order, localized-artificial-diffusivity method for Eulerian simulation of multi-material elastic-plastic deformation with strain hardening
A high-order method for Eulerian simulation of material undergoing large elastic–plastic deformation is developed. Thermodynamically consistent hyperelastic constitutive relations are assumed, facilitating the treatment of solids, liquids, and gases in a unified manner. Here, the method enables the simulation of multi-material interactions using a diffuse interface approach. Numerical capturing of material interfaces, shock waves, contact surfaces, and elastic-plastic strain discontinuities using high-order compact-difference schemes is assisted by Localized Artificial Diffusivity (LAD). In the new setting involving elastic–plastic deformation, the previously established terms for the artificial properties are verified to effectively regularize normal shocks. Additional LAD terms are introduced to the elastic and plastic kinematic equations to regularize shear shocks and other strain discontinuities, improving solution stability. Other important features of the method that improve robustness include the numerical treatment of compatibility terms in the kinematic equations, and the treatment of rotation. Particular emphasis is focused toward new advancements of the methods for plastic-deformation integration and the associated strain hardening of the material, including rate-dependent plasticity. The method is demonstrated on a variety of test problems, including 1-D impacts, a variant of the Shu-Osher problem, a Taylor impact, and a Richtmyer-Meshkov instability between two elastic–plastic solids with strain hardening.
42 ENGINEERING↗
Role of interfaces on phase formation during severe plastic deformation
The role of interfaces on phase formation during severe plastic deformation (SPD) was investigated using molecular dynamics simulations. It is found that dilute solute additions that segregate to interphase boundaries, and strengthen them, can greatly extend the solubility limits of the bounding phases at steady state, providing a novel approach to processing nanocomposite alloys by SPD. Here, the results are rationalized in terms of a modified effective temperature model, whereby increasing the interface strength leads to higher effective temperatures and correspondingly to higher solubilities. Comparison of the segregation coefficient at the interphase boundary with solubilities in the bounding phases illustrates the effective temperature model is self-consistent and comprehensive. Past experimental studies on severe plastic deformation are found consistent with these observations.
36 MATERIALS SCIENCE↗
Water ice phases II, III, and V - Plastic deformation and phase relationships
The ordinary water phase I was transformed to the ice phases that are known to exist in the interiors of large ice moons, such as Ganymede and Callisto for the purpose of investigating plastic deformation behavior of these ices. Ices II, III, and V were prepared using an apparatus and techniques similar to those described by Durham et al. (1983) and subsequently deformed in a gas deformation apparatus, and their deformation data were obtained. It was found that ice II was the strongest of the high-pressure phases, with a strength that was comparable to that of ice I; ice III was very weak, with the flow rate 100 to 1000 times higher than that of ice II at the same levels of stress. It was also found that ices III and V can exist metastably within the ice II field and that they may be deformed plastically within much of the metastable region without reverting to ice II. It is suggested that the weakness of the ice III phase may have profoundly influenced the evolution and the present-day behavior of the icy moons.
Durham, W. B.↗
Structural properties of plastically deformed SrTiO 3 and KTaO 3
Dislocation engineering has the potential to open new avenues toward the exploration and modification of the properties of quantum materials. Strontium titanate (SrTiO 3 , STO) and potassium tantalate (KTaO 3 , KTO) are incipient ferroelectrics that show metallization and superconductivity at extremely low charge-carrier concentrations and have been the subject of resurgent interest. These materials also exhibit remarkable ambient-temperature ductility, and thus represent exceptional platforms for studies of the effects of deformation-induced dislocation structures on electronic properties. Recent work on plastically deformed STO revealed an enhancement of the superconducting transition temperature and the emergence of local ferroelectricity and magnetism near self-organized dislocation walls. Here, in this work, we present a comprehensive structural analysis of plastically deformed STO and KTO, employing specially designed strain cells, diffuse neutron and x-ray scattering, Raman scattering, and nuclear magnetic resonance (NMR). Diffuse scattering and NMR provide insight into the dislocation configurations and densities and their dependence on strain. As in the prior work on STO, Raman scattering reveals evidence for local ferroelectric order near dislocation walls in plastically deformed KTO. Our findings provide valuable information about the self-organized defect structures in both materials, and they position KTO as a second model system in which to explore the associated emergent physics.
36 MATERIALS SCIENCE↗
Copper-Tantalum Metal Matrix Composites Consolidated from Powder Blends by Severe Plastic Deformation
We investigated the effectiveness of severe plastic deformation by equal channel angular extrusion (ECAE) for consolidation of metal powders into metal matrix composites. Equal volumes of copper (Cu) and tantalum (Ta) powders were consolidated at ambient temperature via different ECAE routes. Composites processed by ECAE routes 4E and 4Bc were also processed at 300 °C. The resulting materials were characterized by scanning electron microscopy (SEM) and compression testing. Processing by route 4Bc at 300 °C resulted in the highest compressive strength, lowest anisotropy, and least strain rate sensitivity. We conclude that the superior properties achieved by this route arise from mechanical bonding due to interlocking Cu and Ta phases as well as enhanced metallurgical bonds from contact of pristine metal surfaces when the material is sheared along orthogonal planes.
36 MATERIALS SCIENCE↗