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1
Valkonen, Aki Ensio. "Plastic deformation and roughness of free metal surfaces /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487330761216718.
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Cai, Minghao. "Acousto-Plastic deformation of metals by nonlinear stress waves." The Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=osu1156445865.
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Siu, Kai-wing, and 蕭啟穎. "Effects on plastic deformation by high-frequency vibrations on metals." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50534087.
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The effect of softening due to vibrations induced on metals has been used in many industrial processes such as forming, machining and joining. These industrial applications utilize ultrasonic vibrations in addition to quasi-static stresses in order to deform metals more easily. The phenomenon of ultrasonic softening is also called the Blaha effect or acoustoplastic effect.
Besides the macro-scale softening due to ultrasonic vibrations imposed on quasi-static deformation stress, sub-micron level softening due to vibrations was also observed in nanoindentation experiments in recent years. These experiments made use of the oscillatory stresses of the vibrations provided by the continuous stiffness measurement (CSM) mode of nanoindentation. Lowering of loading and hardness data has been observed at shallow indent depths where the amplitude of vibration is relatively large.
Despite the common industrial usages of acoustoplastic effect and the observation of softening in CSM mode nanoindentation, the physical principle underlying is still not well understood. For acoustoplastic effect the existing understanding is usually one in which the ultrasonic irradiation either imposes additional stress waves to augment the quasi-static applied load, or causes heating of the metal. For the softening observed in CSM mode nanoindentation, the effect is either attributed to instrumental errors or enhancement of nucleation of dislocations which makes them move faster. Investigations on the link between microscopical changes and the softening have been rare.
In this thesis, indentation experiments in both macro and micro scales were performed on aluminium, copper and molybdenum samples with and without the simultaneously application of oscillatory stresses. Significant softening was observed, and the amount of softening from macro to micro scale indentation of similar displacement/amplitude ratios is similar. The deformation microstructures underneath the indents were investigated by a combination of cross-sectional microscopic techniques involving focused-ion-beam milling, transmission electron microscopy and crystal orientation mapping by electron backscattered diffraction. Electron microscopy analyses reveal subgrain formation under the vibrated indents, which implies intrinsic changes.
To further give physical insight into the phenomenon, dislocation dynamics simulations were carried out to investigate the interactions of dislocations under the combined influence of quasi-static and oscillatory stresses. Under a combined stress state, dislocation annihilation is found to be enhanced leading to larger strains at the same load history. The simulated strain evolution under different stress schemes also resembles closely certain experimental observations previously obtained. The discovery here goes far beyond the simple picture that the effect of vibration is merely an added-stress one, since here, the intrinsic strain-hardening potency of the material is found to be reduced by the oscillatory stress, through its effect on enhancing dislocation annihilation.
The experimental and simulation results collectively suggest that simultaneous application of oscillatory stress has the ability to enhance dipole annihilation and cause subgrain formation. The superimposed oscillatory stress causes dislocations to travel longer distances in a jerky manner, so that they can continuously explore until dipole annihilation. In addition, microscopic observations showed that subgrain formation and reduction in dislocation density generally occurred in different metals when stress oscillations were applied. These suggest that the intrinsic oscillation-induced effects of softening and dislocation annihilation are a rather general phenomenon occurring in metals with different stacking fault energies and crystal structures.published_or_final_version
Mechanical Engineering
Doctoral
Doctor of Philosophy
4
Zhang, Hao. "Energy Assisted-Surface Plastic Deformation of Hard-to-Deform Metals." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1574245713905713.
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Shen, Ninggang. "Microstructure prediction of severe plastic deformation manufacturing processes for metals." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6282.
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The objective of the research presented in this thesis has been to develop a physics-based dislocation density-based numerical framework to simulate microstructure evolution in severe plastic deformation (SPD) manufacturing processes for different materials. Different mechanisms of microstructure evolution in SPD manufacturing processes were investigated and summarized for different materials under dynamic or high strain rates over a wide temperature range. Thorough literature reviews were performed to clarify discrepancies of the mechanism responsible for the formation of nanocrystalline structure in the machined surface layer under both low-temperature and high-temperature conditions.
Under this framework, metallo-thermo-mechanically (MTM) coupled finite element (FE) models were developed to predict the microstructure evolution during different SPD manufacturing processes. Different material flow stress responses were modeled subject to responsible plastic deformation mechanisms. These MTM coupled FE models successfully captured the microstructure evolution process for various materials subjected to multiple mechanisms.
Cellular automaton models were developed for SPD manufacturing processes under intermediate to high strain rates for the first time to simulate the microstructure evolution subjected to discontinuous dynamic recrystallization and thermally driven grain growth. The cellular automaton simulations revealed that the recrystallization process usually cannot be completed by the end of the plastic deformation under intermediate to high strain rates. The completion of the recrystallization process during the cooling stage after the plastic deformation process was modeled for the first time for SPD manufacturing processes at elevated temperatures.
6
Thuramalla, Naveen. "Multiscale modeling and analysis of failure and stability during super plastic deformation -- under different loading conditions." Lexington, Ky. : [University of Kentucky Libraries], 2004. http://lib.uky.edu/ETD/ukymeen2004t00171/NAVEEN.pdf.
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Thesis (m.s.)--University of Kentucky, 2004.Title from document title page (viewed Jan. 5, 2005). Document formatted into pages; contains x, 112p. : ill. Includes abstract and vita. Includes bibliographical references.
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Bronkhorst, Curt Allan. "Plastic deformation and crystallographic texture evolution in face-centered cubic metals." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13457.
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Volk, Gregor. "Characterisation and modelling of non-proportional plastic deformation in sheet metals." Thesis, Ulster University, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685426.
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While sheet metal forming process analysis is well established, the complex material models often require experimental data that is difficult to obtain using single axis test equipment. This thesis outlines a new method in describing and determining yield and a methodology to measure multiaxial yield points. For the new yield point determination method, yielding in sheet metal aluminium alloys is critically reviewed. An intrinsic method of determining the yield point is then developed. This new method is compared with the accepted standard methods along with several alternative approaches to overcome the highlighted issues with the standard method. The new method also provides a means of determining a yield range, since all metals do not yield abruptly at a specific point. The Hill family of yield criteria are reviewed and calibration methods are compared and analysed. A new experimental method of reaching specific points on the yield surface is implemented. These different modes of deformation are achieved through the adaptation of an otherwise known test which is implemented in sheet metal aluminium alloy testing. A new test rig is developed to fit on a standard tensile test machine. The test rig controller and associated data acquisition analysis are developed with LabVIEW as a standalone system. The mathematical analysis of the data is developed and validated. A set of tests for an aluminium alloy was conducted to show the efficacy of this new form of material testing. The possibility of calibrating the Hill family of yield criteria with the new test results is investigated. Alternative data visualization methods are also implemented in order to illustrate the suitability of the new technique.
9
Hoover, Luke Daniel. "Large Strain Plastic Deformation of Traditionally Processed and Additively Manufactured Aerospace Metals." University of Dayton / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1627570139729633.
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Kuhr, Bryan Richard. "Modeling the Role of Surfaces and Grain Boundaries in Plastic Deformation." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78704.
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In this dissertation, simulation techniques are used to understand the role of surfaces and grain boundaries in the deformation response of metallic materials. This research utilizes atomistic scale modeling to study nanoscale deformation phenomena with time and spatial resolution not available in experimental testing. Molecular dynamics techniques are used to understand plastic deformation of grain boundaries and surfaces in metals under different configurations and loading procedures.
Stress and strain localization phenomena are investigated at plastically deformed boundaries in axially strain thin film samples. Joint experimental and modelling work showed increased stress states at the intersections of slip planes and grain boundaries. This effect, as well as several other differences related to stress and strain localization are thoroughly examined in digital samples with two different grain boundary relaxation states. It is found that localized stress and strain is exacerbated by initial boundary disorder.
Dislocation content in the randomly generated boundaries of these samples was quantified via the dislocation extraction algorithm. Significant numbers of lattice dislocations were present in both deformed and undeformed samples. Trends in dislocation content during straining were identified for individual samples and boundaries but were not consistent across all examples. The various contributions to dislocation content and the implications on material behavior are discussed.
The effects of grain boundary hydrogen on the deformation response of a digital Ni polycrystalline thin film sample is reported. H content is found to change the structure of the boundaries and effect dislocation emission. The presence of dispersed hydrogen caused a slight increase in yield strength, followed by an increase in grain boundary dislocation emission and an increase in grain boundary crack formation and growth.
An atomistic nano indenter is employed to study the nanoscale contact behavior of the indenter-surface interface during nano-indentation. Several indentation simulations are executed with different interatomic potentials and different indenter orientations. A surface structure is identified that forms consistently regardless of these variables. This structure is found to affect several atomic layers of the sample. The implications of this effect on the onset of plasticity are discussed.
Finally, the implementation of an elastic/plastic continuum contact solution for use in mesoscale molecular dynamics simulations of solid spheres is discussed. The contact model improves on previous models for the forces response of colliding spheres by accounting for a plastic regime after the point of yield. The specifics of the model and its implementation are given in detail.
Overall, the dissertation presents insights into basic plastic deformation phenomena using a combination of experiment and theory. Despite the limitations of atomistic techniques, current computational power allows meaningful comparison with experiments.Ph. D.
11
Ng, Kwok-sing. "Plastic deformation of aluminium micro-specimens." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B4175802X.
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Ng, Kwok-sing, and 吳國勝. "Plastic deformation of aluminium micro-specimens." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B4175802X.
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Huang, Yi. "Mechanical property, microstructural development and constitutive analysis associated with the high temperature deformation of Inconel 718." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368453.
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Simm, Thomas. "The use of diffraction peak profile analysis in studying the plastic deformation of metals." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/the-use-of-diffraction-peak-profile-analysis-in-studying-the-plastic-deformation-of-metals(5e4f71e2-2ac7-4afe-b7c7-7a42a936c50c).html.
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Analysis of the shapes of diffraction peak profiles (DPPA) is a widely used method for characterising the microstructure of crystalline materials. The DPPA method can be used to determine details about a sample that include, the micro-strain, crystal size or dislocation cell size, dislocation density and arrangement, quantity of planar faults and dislocation slip system population.The main aim of this thesis is to evaluate the use of DPPA in studying the deformation of metals. The alloys studied are uni-axially deformed samples of nickel alloy, nickel-200, 304 and 316 stainless steel alloys and titanium alloys, Ti-6Al-4V and grade 2 CP-titanium.A number of DPPA methods were applied to these metals: a full-width method; a method that attributes size and strain broadening to the Lorentzian and Gaussian integral breadth of a Voigt; different forms of the variance method; the Williamson-Hall method; the alternative method; and variations of the Warren-Averbach method. It is found that in general the parameters calculated using the different methods qualitatively agree with the expectations and differences in the deformation of the different metals. For example, the dislocation density values found for all metals, are approximately the same as would be expected from TEM results on similar alloys. However, the meaning of the results are ambiguous, which makes it difficult to use them to characterise a metal. The most useful value that can be used to describe the state of a metal is the full-width. For a more detailed analysis the Warren-Averbach method in a particular form, the log format fitted to individual Fourier coefficients, is the most useful method.It was found that the shape of different diffraction peaks change in different texture components. These changes were found to be different for the different metals. A method to calculate the shape of diffraction peaks, in different texture components, using a polycrystal plasticity models was investigated. It was found that for FCC metals, the use of a Taylor model was able to qualitatively predict the changes in the shape of diffraction peaks, measured in different texture components. Whereas, for titanium alloys, a model which used the Schmid factor was able to qualitatively explain the changes. The differences in the FCC alloys was attributed to being due to differences in the stacking fault energy of the alloys. For nickel, which develops a heterogeneous cell structure, an additional term describing changes in the crystal size in different orientations is required. The differences between the titanium alloys were shown to be due the presence of twinning in CP-titanium and not in Ti-6Al-4V. This difference was thought to cause an additional broadening due to variations in intergranular strains in twinned and non-twinned regions. The use of polycrystal plasticity models, to explain the shape of diffraction peaks, raises questions as to the validity of some of the fundamental assumptions made in the use of most DPPA methods.
15
Ishizaki, Toshitaka. "Point defects and their clusters introduced in metals by irradiation damage and plastic deformation." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/148826.
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Chaloupka, Ondrej. "Modelling evolution of anisotropy in metals using crystal plasticity." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/8435.
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Many metals used in modern engineering exhibit anisotropy. A common
assumption when modelling anisotropic metals is that the level of anisotropy is
fixed throughout the calculation. As it is well understood that processes such as
cold rolling, forging or shock loading change the level of anisotropy, it is clear
that this assumption is not accurate when dealing with large deformations.
The aim of this project was to develop a tool capable to predict large
deformations of a single crystal or crystalline aggregate of a metal of interest
and able to trace an evolution of anisotropy within the material.
The outcome of this project is a verified computational tool capable of predicting
large deformations in metals. This computational tool is built on the Crystal
Plasticity Finite Element Method (CPFEM). The CPFEM in this project is an
implementation of an existing constitutive model, based on the crystal plasticity
theory (the single crystal strength model), into the framework of the FEA
software DYNA3D® .
Accuracy of the new tool was validated for a large deformation of a single
crystal of an annealed OFHC copper at room temperature. The implementation
was also tested for a large deformation of a polycrystalline aggregate comprised
of 512 crystals of an annealed anisotropic OFHC copper in a uniaxial
compression and tension test. Here sufficient agreement with the experimental
data was not achieved and further investigation was proposed in order to find
out the cause of the discrepancy. Moreover, the behaviour of anisotropic metals
during a large deformation was modelled and it was demonstrated that this tool
is able to trace the evolution of anisotropy.
The main benefit of having this computational tool lies in virtual material testing.
This testing has the advantage over experiments in time and cost expenses.
This tool and its future improvements, which were proposed, will allow studying
evolution of anisotropy in FCC and BCC materials during dynamic finite
deformations, which can lead to current material models improvement.
17
Fowler, Rebecca M. "Identification of deformation mechanisms during bi-axial straining of superplastic AA5083 material." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://handle.dtic.mil/100.2/ADA432796.
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Griffiths, Robert Joseph. "Dynamic and Post-Dynamic Microstructure Evolution in Additive Friction Stir Deposition." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104664.
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Metal additive manufacturing stands poised to disrupt multiple industries with high material use efficiency and complex part production capabilities, however many technologies deposit material with sub-optimal properties, limiting their use. This decrease in performance largely stems from porosity laden parts, and asymmetric solidification-based microstructures. Solid-state additive manufacturing techniques bypass these flaws, using deformation and diffusion phenomena to bond material together layer by layer. Among these techniques, Additive Friction Stir Deposition (AFSD), stands out as unique for its freeform nature, and thermomechanical conditions during material processing. Leveraging its solid-state behavior, optimized microstructures produced by AFSD can reach performance levels near, at, or even above traditionally prepared metals. A strong understanding of the material conditions during AFSD and the phenomena responsible for microstructure evolution. Here we discuss two works aimed at improving the state of knowledge surrounding AFSD, promoting future microstructure optimization. First, a parametric study is performed, finding a wide array of producible microstructures across two material systems. In the second work, a stop-action type experiment is employed to observe the dynamic microstructure evolution across the AFSD material flow pathway, finding specific thermomechanical regimes that occur within. Finally, multiple conventional alloy systems are discussed as their microstructure evolution pertains to AFSD, as well as some more unique systems previously limited to small lab scale techniques, but now producible in bulk due to the additive nature of AFSD.Doctor of Philosophy
The microstructure of a material describes the atomic behavior at multiple length scales. In metals this microstructure generally revolves around the behavior of millions of individual crystals of metal combined to form the bulk material. The state and behavior of these crystals and the atoms that make them up influence the strength and usability of the material and can be observed using various high fidelity characterization techniques. In metal additive manufacturing (i.e. 3D printing) the microstructure experiences rapid and severe changes which can alter the final properties of the material, typical to a detrimental effect. Given the other benefits of additive manufacturing such as reduced costs and complex part creation, there is desire to predict and control the microstructure evolution to maximize the usability of printed material. Here, the microstructure evolution in a solid-state metal additive manufacturing, Additive Friction Stir Deposition (AFSD), is investigated for different metal material systems. The solid-state nature of AFSD means no melting of the metal occurs during processing, with deformation forcing material together layer by layer. The conditions experienced by the material during printing are in a thermomechanical regime, with both heating and deformation applied, akin to common blacksmithing. In this work specific microstructure evolution phenomena are discussed for multiple materials, highlighting how AFSD processing can be adjusted to change the resulting microstructure and properties. Additionally, specific AFSD process interactions are studied and described to provide better insight into cumulative microstructure evolution throughout the process. This work provides the groundwork for investigating microstructure evolution in AFSD, as well as evidence and results for a number of popular metal systems.
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Mathaudhu, Suveen Nigel. "Fabrication of amorphous metal matrix composites by severe plastic deformation." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4389.
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Bulk metallic glasses (BMGs) have displayed impressive mechanical properties, but
the use and dimensions of material have been limited due to critical cooling rate
requirements and low ductility. The application of severe plastic deformation by equal
channel angular extrusion (ECAE) for consolidation of bulk amorphous metals (BAM)
and amorphous metal matrix composites (AMMC) is investigated in this dissertation.
The objectives of this research are a) to better understand processing parameters which
promote bonding between particles and b) to determine by what mechanisms the
plasticity is enhanced in bulk amorphous metal matrix composites consolidated by
ECAE.
To accomplish the objectives BAM and AMMCs were produced via ECAE
consolidation of Vitreloy 106a (Zr58.5Nb2.8Cu15.6Ni12.8Al10.3-wt%), ARLloy #1
(Hf71.3Cu16.2Ni7.6Ti2.2Al2.6 -wt%), and both of these amorphous alloys blended with
crystalline phases of W, Cu and Ni. Novel instrumented extrusions and a host of postprocessing
material characterizations were used to evaluate processing conditions and
material properties. The results show that ECAE consolidation at temperatures within the supercooled liquid region gives near fully dense (>99%) and well bonded millimeter
scale BAM and AMMCs. The mechanical properties of the ECAE processed BMG are
comparable to cast material: ÃÂf = 1640 MPa, õf = 2.3%, E = 80 GPa for consolidated
Vitreloy 106a as compared to ÃÂf = 1800 MPa, õf = 2.5%, E = 85 GPa for cast Vitreloy
106, and ÃÂf = 1660 MPa, õf = 2.0%, E = 97 GPa for ARLloy #1 as compared to ÃÂf = 2150
MPa, õf < 2.5%, E = 102 GPa for Hf52Cu17.9Ni14.6Ti5Al10. The mechanical properties of
AMMCs are substandard compared to those obtained from melt-infiltrated composites
due to non-ideal particle bonding conditions such as surface oxides and crystalline phase
morphology and chemistry. It is demonstrated that the addition of a dispersed crystalline
phase to an amorphous matrix by ECAE powder consolidation increases the plasticity of
the amorphous matrix by providing locations for generation and/or arrest of adiabatic
shear bands. The ability of ECAE to consolidated BAM and AMMCs with improved
plasticity opens the possibility of overcoming the size and plasticity limitations of the
monolithic bulk metallic glasses.
20
Jang, Seonhee. "Molecular dynamics simulations of plastic deformation in nanocrystalline metal and alloy." NCSU, 2007. http://www.lib.ncsu.edu/theses/available/etd-10182007-151340/.
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Nanocrystalline metals have different mechanical properties from conventional grain sized metals. Hardness and yield strength have been found to increase with decreasing grain size in the nanocrystalline regime down to at least 15 nm on the basis of Hall-Petch mechanisms. Below grain sizes of ~10 nm, the strength decreases with further grain refinement, leading to the inverse Hall-Petch effect. Although the experimental evidence has found these deformation responses in nanocrystalline materials, the underlying mechanisms are not well identified. Molecular dynamics simulations were carried out for uniaxial tensile straining of two-dimensional columnar microstructures of aluminum (Al) and aluminum-lead (Al-Pb) alloys. Pure Al has a critical grain size at dc ≈ 15 to 20 nm, the crossover from ?normal? to ?inverse? Hall-Petch effect, accompanied with intra-grain mechanisms by partial dislocations and twins as grain sizes increases. With increasing grain size there exists a transition in plastic deformation mechanism from inter-grain processes to one that consists of both inter-grain and intra-grain processes. For Al-Pb alloys with a 10 nm grain size, Pb segregates completely to the grain boundaries and the grain boundaries become wider and more disorganized as the Pb content increases. A softening effect was observed in agreement with, but less than that found experimentally. As the Pb content increases, partial dislocation nucleation at grain boundaries is completely suppressed and the plastic strain is accommodated by mechanisms other than dislocation slip. As the grain sizes increase up to 15 or 20 nm, dislocation generation at grain boundaries is also suppressed. However, dislocation generation is not entirely suppressed at 3 equivalent at% Pb, compared to the 10 nm grain size showing complete suppression.
21
Di, Leo Claudio V. "A coupled theory for diffusion of hydrogen and large elastic-plastic deformations of metals." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74460.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 101-103).
A thermodynamically-consistent coupled-theory which accounts for diffusion of hydrogen, trapping of hydrogen, diffusion of heat, and large elastic-plastic deformations of metals is developed. Our theoretical framework places the widely-used notion of an "equilibrium" between hydrogen residing in normal interstitial lattice sites and hydrogen trapped at microstructural defects, within a thermodynamically-consistent framework. The theory has been numerically implemented in a finite element program. Using the numerical capability we study two important problems. First, we show the importance of using a prescribed chemical potential boundary condition in modeling the boundary between a metal system and a hydrogen atmosphere at a given partial pressure and temperature; specifically, we perform simulations using this boundary condition and compare our simulations to those in the published literature. Secondly, the effects of hydrogen on the plastic deformation of metals is studied through simulations of plane-strain tensile deformation and three-point bending of U-Notched specimens. Our simulations on the effects of hydrogen on three-point bending of U-notched specimens are shown to be in good qualitative agreement with published experiments.
by Claudio V. Di Leo.
S.M.
22
Uribe, Restrepo Catalina. "Process-dependent microstructure and severe plastic deformation in SiCp?? reinforced aluminum metal matrix composites." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4712.
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Discontinuously reinforced MMCs with optimized microstructure are sought after for exceptional high strain rate behavior. The microstructure evolution of a stir-cast A359 aluminum composite reinforced with 30 vol.% SiCsubscript p] after isothermal anneal, successive hot-rolling, and high strain rate deformation has been investigated. Quantitative microstructural analysis was carried out for the as-cast, annealed (470??C, 538??C and 570??C) and successively hot rolled specimens (64, 75, 88, and 96% rolling reductions). Selected composites were also examined after high strain rate deformation. X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy were employed for microstructural characterization. The strength and ductility of the A359 Al alloys, and the composite, were greatly influenced by the brittle eutectic silicon phase and its morphology. Lamellar eutectic silicon spheroidized with isothermal anneal and successive hot rolling with a corresponding decrease in hardness. The hot rolling process also considerably decreased the SiC particle size (approximately 20% after 96% reduction) by breaking-up the hard SiC particles. However, this break-up of particles increased the homogeneity of SiCsubscript p] size distribution. Successive hot rolling also healed voids due to solidification shrinkage, incomplete infiltration of molten Al and defects originating from fractured particles. Four selected specimens of composites were examined after high strain rate deformation. Fractography and metallographic analysis for the craters, voids, and relevant regions affected by the high velocity impact were carried out. The deposition of impact residuals was frequently observed on the exposed fracture surfaces. These residuals were typically observed as "molten-and-solidified" as a consequence of excessive heat generated during and after the damage.; Particularly in regions of entry and exit of impact, intermixing of residuals and composite constituents were observed, demonstrating that the Al matrix of the composite also had melted. In all samples examined, cracks were observed to propagate through the eutectic Si network while a small number of broken reinforcement particles were observed. A slight variation in failure mechanisms was observed (e.g., radial, fragmentation, petalling) corresponding to the variation in ductility against high strain rate deformation. In selected specimens, parallel sub-cracks at the exit were observed at 45?? and 30??. These sub-cracks were again filled with intermixed constituents from projectile residuals and composites. This observation suggests that the melting of composite constituents that leads to intermixing occured after the crack propagation and other damage.ID: 030646232; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; On t.p. "p??" is subscript.; Thesis (M.S.M.S.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 86-88).
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Shamass, Rabee. "Numerical and analytical investigation into the plastic buckling paradox for metal cylinders." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/14235.
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It is widely accepted that, for many buckling problems of plates and shells in the plastic range, the flow theory of plasticity either fails to predict buckling or significantly overestimates buckling stresses and strains, while the deformation theory, which fails to capture important aspects of the underlying physics of plastic deformation, provides results that are more in line with experimental findings and is therefore generally recommended for use in practical applications. This thesis aims to contribute further understanding of the reasons behind the seeming differences between the predictions provided by these two theories, and therefore provide some explanation of this so-called ‘plastic buckling paradox’. The study focuses on circular cylindrical shells subjected to either axial compression or non-proportional loading, the latter consisting of combined axial tensile stress and increasing external pressure. In these two cases, geometrically nonlinear finite-element (FE) analyses for perfect and imperfect cylinders are conducted using both the flow and the deformation theories of plasticity, and the numerical results are compared with data from widely cited physical tests and with analytical results. The plastic buckling pressures for cylinders subjected to non-proportional loading, with various combinations of boundary conditions, tensile stresses, material properties and cylinder’s geometries, are also obtained with the help of the differential quadrature method (DQM). These results are compared with those obtained using the code BOSOR5 and with nonlinear FE results obtained using both the flow and deformation theories of plasticity. It is found that, contrary to common belief, by using a geometrically nonlinear FE formulation with carefully determined and validated constitutive laws, very good agreement between numerical and test results can be obtained in the case of the physically more sound flow theory of plasticity. The reason for the ‘plastic buckling paradox’ appears to be the over-constrained kinematics assumed in many analytical and numerical treatments, such as BOSOR5 and NAPAS, whereby a harmonic buckling shape in the circumferential direction is prescribed.
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Choudhury, Anshuman. "Statistics of dislocations at low temperature in pure metals with body centered cubic symmetry." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS569/document.
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Les observations de microscopie électronique in situ effectuées par Daniel Caillard (CEMES, Toulouse) au cours de la déformation de cristaux de symétrie cubique centrée ont montré que les dislocations vis effectuaient des sauts de plusieurs distances inter-atomiques alors que la théorie standard de Peierls prédit des sauts de une seul distance inter-atomique. Nous avons étudié par simulation atomique le glissement d'une dislocation vis dans un cristal de fer pure. Nous montrons que la propagation de décrochement le long de la dislocation induit un échauffement local qui favorise la nucléation de décrochements supplémentaires. L'accumulation de ces décrochements permet à la dislocation de parcourir plusieurs distances inter-atomiques. Ces simulations nous permettent de proposer une théorie pour l'explication des observations de D. CaillardIn situ straining tests in high purity α-Fe thin-foils at low temperatures have demonstrated that crystalline defects, called dislocations, have a jerky type of motion made of intermittent long jumps of several nanometers. Such an observation is in conflict with the standard Peierls mechanism for plastic deformation in bcc crystals, where the screw dislocation jumps are limited by inter-reticular distances, i.e. of a few Angstroms. Employing atomic-scale simulations, we show that although the short jumps are initially more favorable, their realization requires the propagation of a kinked profile along the dislocation line which yields coherent atomic vibrations acting as traveling thermal spikes. Such local heat bursts favor the thermally assisted nucleation of new kinks in the wake of primary ones. The accumulation of new kinks leads to long dislocation jumps like those observed experimentally. Our study constitutes an important step toward predictive atomic-scale theory for materials deformation
25
Fredriksson, Per. "Modelling and simulation of plastic deformation on small scales : interface conditions and size effects of thin films." Doctoral thesis, Stockholm : Hållfasthetslära, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4652.
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Subbarayan, Sapthagireesh. "Fabrication of a Novel Al/Mg Composite: : Processing and Characterization of Pure Aluminium, Al/AZ31 Alloy Bi-Metal and Aluminium based Sheet Composites by Severe Plastic Deformation." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23778.
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Хоменко, Олексій Віталійович, Алексей Витальевич Хоменко, Oleksii Vitaliiovych Khomenko, Дар`я Сергіївна Трощенко, Дарья Сергеевна Трощенко, Dar`ia Serhiivna Troshchenko, and И. О. Солонар. "Двухуровневая и двухмодовая кинетика фрагментации металлов при интенсивной пластической деформации." Thesis, Сумский государственный университет, 2017. http://essuir.sumdu.edu.ua/handle/123456789/65290.
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Обработка металлов методами интенсивной пластической деформации (ИПД) позволяет получить объемные образцы с практически
беспористой субмикрокристаллической (СМК) или нанокристаллической (НК) структурой, обладающей высокими физико-механическими
свойствами.
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Хоменко, Олексій Віталійович, Алексей Витальевич Хоменко, Oleksii Vitaliiovych Khomenko, Дар`я Сергіївна Трощенко, Дарья Сергеевна Трощенко, Dar`ia Serhiivna Troshchenko, and И. О. Солонар. "Двухуровневая и двухмодовая кинетика фрагментации металлов при интенсивной пластической деформации." Thesis, Сумский государственный университет, 2017. http://essuir.sumdu.edu.ua/handle/123456789/65669.
Full textAbstract:
Обработка металлов методами интенсивной пластической деформации (ИПД) позволяет получить объемные образцы с практически
беспористой субмикрокристаллической (СМК) или нанокристаллической (НК) структурой, обладающей высокими физико-механическими
свойствами.
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Pavier, M. J. "The numerical prediction of large plastic deformations in metal forming." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332753.
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Man, Ondřej. "Aplikace metody difrakce zpětně odražených elektronů v materiálovém inženýrství." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-233915.
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The thesis deals with principles and common applications of the electron backscatter diffraction (EBSD) method. Some practical experience in application of the method to a study of highly deformed structure of copper and its thermal stability is described on one hand, and, on the other hand, to a study of phase composition of TRIP steel on various levels of imposed strain. The limitations of EBSD method are discussed along with its resolution in comparison with other complimentary techniques.
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Хоменко, Олексій Віталійович, Алексей Витальевич Хоменко, Oleksii Vitaliiovych Khomenko, Дар`я Сергіївна Трощенко, Дарья Сергеевна Трощенко, Dar`ia Serhiivna Troshchenko, М. О. Хоменко, М. А. Хоменко, and М. А. Khomenko. "Моделювання зовнішнього періодичного впливу на фазову діаграму та кінетику фрагментації металів при інтенсивній пластичній деформації." Thesis, Львівський національний університет ім. І. Франка, 2015. http://essuir.sumdu.edu.ua/handle/123456789/41622.
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Нюкало, Д. О. "Дослідження фрагментації матеріалів з урахуванням щільності дислокацій та меж зерен." Master's thesis, Сумський державний університет, 2019. http://essuir.sumdu.edu.ua/handle/123456789/75457.
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Метою роботи є дослідження фрагментації матеріалів під час інтенсивної пластичної деформації. В магістерській роботі була розвинена феноменологічна модель, що дозволяє описати процес фрагментації металів та сплавів, отриманих під час дії інтенсивної пластичної деформації; були досліджені стійкі стани з урахуванням впливу основних параметрів системи, проаналізована кінетика процесу фрагментації та стійкість отриманих станів в процесі еволюції структурних дефектів.
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Weaver, J. M. R. "The ultrasonic imaging of plastic deformation." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375316.
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Thompson, Robert Peter. "Plastic deformation in complex crystal structures." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/286335.
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Many materials with complex crystal structures have attractive properties, including high specific strength, good creep resistance, oxidation resistance, often through high silicon or aluminium content. This makes them of interest for high temperature structural applications, but the use of many such phases is limited by low toughness. Even outside structural applications, brittle failure is a primary cause of failure in coatings and device materials and, therefore, improved toughness is desirable. In complex crystals plasticity, and hence toughness, is limited by the energy increases that occur as linear defects, dislocations, move. This is known as the lattice resistance. By understanding the factors controlling the lattice resistance in complex crystal structures, it is hoped that a general method for tailoring the flow stress of a material might be found. Present ductile-brittle criteria are based on simple ratios of polycrystalline elastic constants and are too limited to accurately capture flow behaviour. There are complex materials which, despite such criteria predicting brittle behaviour, exhibit low flow stresses, though on a limited number of slip systems: MAX phases, Mo$_2$BC, Nb$_2$Co$_7$ and Ta$_4$C$_{3-x}$ are examples of this. Where plastic flow is limited by the lattice resistance we must consider the effect of crystal structure on dislocation motion more directly. Aspects which are lost by considering bulk polycrystalline properties are elastic heterogeneity, elastic anisotropy and contributions to the energy changes by other interactions, such as electrostatic interactions. In this work examples of each of these are presented and modelled using an adapted version of the Peierls model. A Peierls model generalised to use the entire stiffness tensor has been implemented in Python; this allows the investigation of the effect of varying anisotropy on the yield stress of materials that would not be picked up by the use of polycrystalline elastic constants. Calculations using the changing elastic tensor during hydrogen loading of cementite suggest that hydrogen loading causes a dramatic reduction in the flow stress, consistent with experiments and associated with hydrogen embrittlement of steel. Materials for which empirical potentials can provide more insight than linear elasticity are explored with the example of ionic materials. This is done with a Peierls dislocation configuration and a molecular statics energy calculation. A simple model built electrostatic and Lennard-Jones interactions was used for the rocksalt structure, this model was found to describe the hard slip system well, but was insufficient to describe the softer slip system. Local heterogeneity in elastic properties is explored in the MAX phases where local variation in chemical environment, characterised by electronegativity, produces pronounced variation in the local stiffness within the unit cell. These local variations have been modelled with density functional theory and have been shown to be consistent with the macroscopic elastic properties while also explaining the apparent scatter in the elastic properties. These non-uniform strains are shown to have a dramatic effect on the flow stress of the MAX phases. The face-centred cubic Ti$_2$Ni structure has been used to experimentally demonstrate this effect of heterogeneity softening. The slip system was characterised by micropillar compression and the slip planes were found to be the {1 1 1} planes. The hardness of a range of alloys with the Ti$_2$Ni structure was characterised by nanoindentation of the {1 1 1} faces of single crystals. The hardness was found to decrease as the chemical, and thus elastic, heterogeneity of the unit cell increased, as expected. This effect of heterogeneity softening presents a potential route to tailoring the yield stress of crystals.
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Kajbaji, Mohamed El. "Etude du joint de grain [SIGMA] = 9 dans le silicium parfait, déformé et recuit par microscopie électronique à haute résolution." Grenoble 1, 1986. http://www.theses.fr/1986GRE10102.
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Etude des mecanismes d'interaction joint de grain dislocations lors de la deformation du bicristal, mettant en evidence la dissociation des dislocations entrant dans le joint, leur perte d'identite et l'interaction entre eux des residus. Determination des structures des dislocations residuelles. Apparition de precipites lors du recuit du bicristal deforme
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Spirig, John Vincent. "A new generation of high temperature oxygen sensors." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1188570727.
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Mentha, S. N. "High strain rate deformation of metals." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235014.
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The evolution of the physical sciences and engineering has involved a detailed and quantified understanding of the properties of metals. In particular, it is necessary to know how metals deform and the stresses that are involved which, in turn, are affected by the rate at which strain is applied. The nature and layout of this work is outlined. The history of the pressure bar transducer is summarised. The original concept of Hopkinson in 1914 was to use a long metal bar to study the propagation of wave pulses. During the Second World War, Davies refined the instrumentation and studied the shape of such pulses as modified by dispersion. Kolsky in 1949 adapted the technique to investigate the dynamic plasticity of specimens wedged between two instrumented pressure bars. Subsequent workers have used variants of this apparatus to make measurements at strain rates up to 105 s-1, whilst others have considered the effects of friction and inertia on the specimen. After an explanation of the particular design requirements, a description is given of the high strain rate apparatus that forms the basis for the research reported in this dissertation. The components that make up the system are described separately and the experimental procedures are outlined. The accuracy of components critical to the experimental technique is investigated. The effects of friction at the specimen interfaces, inertia during deformation and wave dispersion in the pressure bar are discussed. Bar calibration is described. Experiments have been carried out on copper in five different microstructural states at average strain rates of 6 x 104 s-1 and 5 x 10-2 s-1 and their behaviour compared. The metal has been specially worked to induce anisotropy in the form of texture. Special techniques have been developed to prepare specimens of known orientation from the bulk of the raw material. The results show correlations between the texture severity and the anisotropy of stress-strain properties. A dynamic work hardening effect is observed. There is evidence that the Petch relationship holds at high strain rates. The high strain rate deformation of uranium alloyed with titanium or molybdenum is investigated. Specimens often display evidence of macroscopic localised shear bands whose adiabatic formation is accompanied by a sharp fall in the materials' dynamic strength. Metallographic sections reveal the morphology of these bands and the relative motion of microstructural features during deformation. Results are presented on a eutectoid zinc-22% aluminium alloy in a lamellar and superplastic microstructural state and a gun steel. The high strain rate deformation of titanium-6% aluminium-4% vanadium alloy is compared with uranium-0.75% titanium alloy regarding their tendency to form macroscopic shear bands. The dynamic behaviour of copper is contrasted with that of uranium alloy. In conclusion, the current work is viewed in the context of the historical development of the miniaturised Hopkinson pressure bar. Some comments are made about the application of the technique, and the scope for further research.
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Dahlen, Anfrid. "Plastic deformation and fracture of polymer materials." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15968.
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Polymer materials are known to dilate during plastic deformation. This thesis is a study on some of the mechanisms behind the volume change and how it is affected by triaxiality in stress. The goal was to assess how the current hyperelastic-viscoplastic constitutive material model for thermoplastics made at Structural Impact Laboratory (SIMLab) could be developed further. The volume change was studied by conducting tension tests on axisymmetric smooth and notched specimens made of high-density polyethylene (HDPE) and polyvinyl chloride (PVC). In order to change the stress triaxiality, the notched specimens had four different notch radii. All tests were monitored by a digital charge-coupled device (CCD) camera. To map the deformations of the specimens, the images were postprocessed in a custom-made digital image correlation (DIC) algorithm that was created in the numerical computing environment and programming language MATLAB. Further, simulations of the tests were run in the finite element software LS-DYNA, using the implemented material model for thermoplastics developed at SIMLab. SIMLab's material model is currently based on the Raghava yield surface and plastic potential. Amodification of the model, employing the Gurson - Tvergaard - Needleman (GTN) yield surface and plasticpotential incorporating the evolution of voids during deformation of the material, was also evaluated. A relationship between the stress triaxiality and the volume strain during plastic deformations was found from the tests. The stress triaxiality was also found to affect the yield stress, the local strain rate, the radial strain,the equivalent plastic fracture strain and the fracture surface. The tests also suggest that nucleation of voids should be described as strain controlled. Comparing the tests to the simulations it was evident that thevolume change in the materials was not captured properly with the model employing the Raghava potential.The simulations using the GTN potential however, showed far better estimations of the volume strain.Adjustments of the model employing the GTN yield surface and plastic potential are still required to simulatethe strain softening properly.
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Wu, Xijia. "Constitutive laws of plastic deformation and fracture." Thesis, University of Ottawa (Canada), 1992. http://hdl.handle.net/10393/7821.
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Environment assisted fatigue involves plastic deformation and degrading chemical reactions, which occur in a localized region ahead of the crack tip. Basically, transgranular crack growth proceeds by alternating slip processes. In this study, a transgranular fatigue crack growth rate model is developed on the basis of restricted slip reversibility (RSR), where transgranular fatigue crack growth rate is related to plastic deformation accommodation ahead of the crack tip (the product of the cyclic plastic strain range and the plastic zone size). The model is shown to take the form of the Paris equation with a power law exponent of 3 at positive R values. Fatigue crack growth behavior of a 8090 aluminum-lithium alloy has been examined by a series of tests using compact tension (C(T)) specimens with the load axis (a) parallel to the rolling direction (LT specimen), (b) inclined at 15$\sp\circ$ (L + 15$\sp\circ$), (c) inclined at 30$\sp\circ$ (L + 30$\sp\circ$), (d) inclined at 45$\sp\circ$ (L + 45$\sp\circ$) to the rolling direction. It has been found that in the LT, L + 15$\sp\circ$ and L + 30$\sp\circ$ specimens macroscopic cracks propagate along the plane normal to the rolling direction regardless of the deviation of loading directions and the fatigue crack in the L + 45$\sp\circ$ specimen propagates along the plane of specimen symmetry. Fatigue crack growth rate has been found to vary with the specimen orientation with the LT direction exhibiting the best fatigue crack growth resistance. These phenomena are discussed in terms of the crystallographic texture and the highly planar slip behavior of this ally. A revised RSR model is developed for the description of transgranular fatigue crack growth in aluminum-lithium alloys, where the effect of texture is related to a geometric factor for the favorable slip planes. Extension of the RSR model to environment assisted fatigue is also discussed. It is recognized that environmental effects contribute to crack propagation by the formation and rupture of an embrittlement zone in front of the crack tip. By incorporating a corrosion damage zone into the RSR model, fatigue crack growth rate in a deleterious environment is shown to be consists of two components: (i) mechanical fatigue which occurs by partially reversible slip and (ii) environmental enhancement of crack growth that results from the rupture of the embrittlement zone and is directly related to the characteristic dimension of this corrosion damage zone. In addition, fracture kinetics analysis is extended to crack growth behavior which exhibits the positive-negative temperature dependence. A constitutive law is derived from the general rate equation for a two-barrier consecutive system which represents stress corrosion cracking. The transition condition of the positive-negative temperature dependence is discussed and defined in terms of microstructural characteristic quantities (activation energy and work factor) and loading constraints (stress intensity factor and temperature). For the description of plastic deformation, a set of evolutionary rate equations is developed from deformation kinetics theory. Corresponding constitutive equations are derived for the dislocation glide mechanism, glide-plus-climb mechanism and diffusional flow. The operational equations are solved from the governing differential rate equation to determine deformation responses under different loading constraints.
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Ющенко, Ольга Володимирівна, Ольга Владимировна Ющенко, Olha Volodymyrivna Yushchenko, and D. S. Yurko. "Investigation of Plastic Deformation Considering Nanoscale Effects." Thesis, Sumy State University, 2015. http://essuir.sumdu.edu.ua/handle/123456789/42640.
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The self-consistent theory of plastic deformation in solid was considered within the framework of the presence of the nanoscale defects ensemble. The synergetic equations describing the self-organization of nanoscale defects were analyzed. An effective potential that distinguish plastic and solid states was obtained. For the plastic deformation waves the dispersion law depending on the diffusion coefficient of the defects was considered.
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Borodachenkova, Marina. "Severe plastic deformation of Al–Zn alloys." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/15492.
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Doutoramento em Engenharia MecânicaIn this work, the R&D work mainly focused on the mechanical and microstructural analysis of severe plastic deformation (SPD) of Al–Zn alloys and the development of microstructure–based models to explain the observed behaviors is presented. Evolution of the microstructure and mechanical properties of Al–30wt% Zn alloy after the SPD by the high–pressure torsion (HPT) has been investigated in detail regarding the increasing amount of deformation. SPD leads to the gradual grain refinement and decomposition of the Al–based supersaturated solid solution. The initial microstructure of the Al–30wt% Zn alloy contains Al and Zn phases with grains sizes respectively of 15 and 1 micron. The SPD in compression leads to a gradual decrease of the Al and Zn phase grain sizes down to 4 microns and 252 nm, respectively, until a plastic strain of 0.25 is reached. At the same time, the average size of the Zn particles in the bulk of the Al grains increases from 20 to 60 nm and that of the Zn precipitates near or at the grain boundaries increases as well. This microstructure transformation is accompanied at the macroscopic scale by a marked softening of the alloy. The SPD produced by HPT is conducted up to a shear strain of 314. The final Al and Zn grains refine down to the nanoscale with sizes of 370 nm and 170 nm, respectively. As a result of HPT, the Zn–rich (Al) supersaturated solid solution decomposes completely and reaches the equilibrium state corresponding to room temperature and its leads to the material softening. A new microstructure–based model is proposed to describe the softening process occurring during the compression of the supersaturated Al–30wt% Zn alloy. The model successfully describes the above–mentioned phenomena based on a new evolution law expressing the dislocation mean free path as a function of the plastic strain. The softening of the material behavior during HPT process is captured very well by the proposed model that takes into consideration the effects of solid solution hardening and its decomposition, Orowan looping and dislocation density evolution. In particular, it is demonstrated that the softening process that occurs during HPT can be attributed mainly to the decomposition of the supersaturated solid solution and, in a lesser extent, to the evolution of the dislocation mean free path with plastic strain.
Este trabalho foi dedicado à análise mecânica e microestrutural de uma liga Al–Zn submetida a um processo de deformação plástica severa (SPD) e ao desenvolvimento de modelos microestruturais para descrever os comportamentos observados. Foi investigada detalhadamente a evolução das propriedades mecânicas e da microestrutura da liga Al–30wt% Zn, após ensaios de torção a alta pressão (HPT), em função do grau de deformação. A SPD promoveu o refinamento gradual do grão e a decomposição da solução sólida de base Al sobressaturada. A microestrutura inicial da liga Al–30wt% Zn continha fases de Al e Zn com grãos de tamanhos 15 e 1 m, respetivamente. A deformação plástica até 0.25, em compressão, promoveu a diminuição gradual do tamanho dos grãos de Al e Zn até 4 m e 252 nm, respetivamente. Simultaneamente, o tamanho médio das partículas de Zn na rede cristalina de grãos de Al aumentou de 20 para 60 nm e, de forma idêntica, também aumentaram os precipitados de Zn na proximidade ou nos contornos de grão. Esta transformação microestrutural foi acompanhada, à escala macroscópica, por um forte amaciamento da liga. Os ensaios HPT foram conduzidos até uma deformação de corte de 314. Com esta SPD, as dimensões dos grãos de Al e Zn diminuiram até à nanoescala; para 370 nm e 170 nm, respetivamente. Como resultado do ensaio HPT, a solução sólida sobressaturada de Al rica em Zn decompôs–se completamente e atingiu o estado de equilíbrio à temperatura ambiente, com o consequente amaciamento do material. Foi criado um novo modelo, baseado na microestrutura do material, que permite descrever o processo de amaciamento que ocorre durante a forte compressão da liga Al–30wt% Zn. O fenómeno foi definido por uma nova lei que relaciona o caminho livre médio das deslocações com a deformação plástica. O modelo proposto permite prever muito bem o amaciamento do material durante o processo HPT, tendo em consideração os efeitos do endurecimento por solução sólida e sua decomposição, o mecanismo de Orowan e a evolução da densidade de deslocações. Em particular, ficou demonstrado que o processo de amaciamento que ocorre durante o ensaio HPT pode ser atribuído principalmente à decomposição da solução sólida sobressaturada e, em menor medida, à evolução do caminho livre médio das deslocações com a deformação plástica.
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MAGRO, TOMMASO. "Severe plastic deformation by backward tube flowforming." Doctoral thesis, Università degli studi di Padova, 2022. http://hdl.handle.net/11577/3459215.
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Tailored components are increasingly used in modern industry, as they allow the exploitation of key properties, such as strength, thickness, corrosion protection, type of material, in specific areas of interest of the workpiece, removing the weight where not necessary for performance purposes. It is possible to use a class of processes called “Severe Plastic Deformation” to modify some of these properties. Through the considerable refinement of the crystalline grain resulting from the high plastic deformation to which the component is subjected, not only does the resistance of the material increase, but also decreases the presence of internal defects, and consequently increases the fatigue resistance. The smaller dimensions of the crystalline grain are finally linked to a higher resistance to corrosion.
These processes, developed by the most common massive deformation processes such as extrusion, torsion, bending, rolling, are subject to various critical issues, including the laboratory-scale dimensions of the components that can be produced, resulting in poor industrial applicability, the problematic design and implementation of the process, and finally the high costs. From a review of the literature, it was possible to identify some critical points of scientific interest, first of all, the need to develop a process that at the same time guarantees a double objective: to obtain a component with high mechanical characteristics, typical of SPD processes, but with of suitable dimensions for possible use on an industrial scale. To implement a similar approach, attention was focused on the tube flowforming process, also known as tube spinning, which is generally not included among the SPD processes. However, since there are many elements in common (high refinement of the crystalline grain, absence of internal defects, high plastic strain), it was decided to use this technique to obtain two different types of products. The first is a tubular element, very difficult to make at present given the buckling and sticking problems, while the second type of product that can be obtained is a flat element, characterized by the same properties of the tubular component, obtained after cutting and straightening conducted on the tube.
The purpose of this PhD thesis is to evaluate the feasibility of using the backward tube flowforming process to obtain tailored SPD components, thus assessing the influence of various process parameters both numerically and experimentally in some of the properties of the final component. To this end, two different equipment have been developed to perform the experimental tests, a traditional one, designed starting from the peculiar characteristics of the process available in the literature and simulated numerically, and an innovative equipment that uses a constraint placed radially to the tube, helpful in increasing the strain imposed during the process and improving the surface quality of the final component.
The experimental tests, carried out using the AA6082-T4 alloy as reference material, allowed us to evaluate the variations in the mechanical characteristics of the starting material, reporting a high increase in microhardness and mechanical properties intended as yield strength and UTS. At the same time, following the theoretical result that associates an increase in mechanical performance with a decrease in the size of the crystalline grain, there was a high reduction in the size of the crystalline grain, with a portion of the tube characterized by a structure with microstructure highly refined, typical of SPD processes. The high deformation impressed on the tubular elements led to a reduction in ductility, which in any case did not affect the execution of the flattening process performed downstream of the flowforming process, allowing to obtain plates characterized by the same microstructure and mechanical characteristics of the initial flowformed tube.L’utilizzo di componenti “su misura” trova sempre più spazio nell'industria moderna, poiché il loro impiego permette di sfruttare delle proprietà chiave, quali resistenza, spessore, protezione dalla corrosione, tipologia del materiale, in specifiche aree di interesse del pezzo, rimuovendo il peso dove non necessario ai fini prestazionali. Per modificare alcune di queste proprietà è possibile utilizzare una tipologia di processi denominata “Severe Plastic Deformation”. Tramite il notevole raffinamento della grana cristallina conseguente all’elevata deformazione plastica a cui il componente è soggetto, si ottiene un aumento della resistenza del materiale, ma si diminuisce la presenza di difetti interni, e conseguentemente si aumenta la resistenza a fatica. Le dimensioni inferiori della grana cristallina sono infine collegate ad una più elevata resistenza alla corrosione. Questi processi, sviluppati partendo dai più comuni processi di deformazione massiva quali estrusione, torsione, piegatura, laminazione, sono soggetti a diverse criticità, tra cui: le dimensioni su scala di laboratorio dei componenti che possono essere prodotti, con conseguente scarsa applicabilità industriale, la difficile progettazione e realizzazione del processo, e infine i costi elevati. Da una revisione della letteratura è stato possibile individuare alcuni punti critici di interesse scientifico, primo tra tutti l’esigenza di sviluppare un processo che allo stesso tempo garantisce un obiettivo duplice: ottenere un componente con caratteristiche meccaniche elevate, tipico dei processi SPD, ma con delle dimensioni idonee ad un eventuale utilizzo su scala industriale. Per attuare un simile approccio l’attenzione è stata focalizzata sul processo di tube flowforming, che generalmente non si annovera tra i processi SPD. Essendo molteplici gli elementi in comune (elevato raffinamento della grana cristallina, assenza di difetti interni, elevata deformazione plastica) si è deciso di utilizzare questa tecnica per ottenere due diverse tipologie di prodotto. Il primo è un elemento tubolare, molto difficile da realizzare allo stato attuale visti i problemi di buckling e sticking, mentre il secondo è un elemento piatto, caratterizzato dalle stesse proprietà dell’elemento tubolare, ricavato dopo le operazioni di taglio e spianatura condotte sul tubo. Lo scopo di questa tesi di dottorato è quello di valutare la fattibilità nell’utilizzo del processo di backward tube flowforming per ottenere componenti con microstruttura raffinata creati “su misura”, valutando quindi sia a livello numerico sia a livello sperimentale l’influenza di vari parametri di processo su alcune delle proprietà del componente finale. A tal fine per eseguire le prove sperimentali sono state sviluppate due diverse attrezzature, una tradizionale, progettata partendo dalle caratteristiche peculiari del processo reperibili in letteratura e simulate numericamente, ed un’attrezzatura innovativa che utilizza un vincolo radiale, utile per aumentare la deformazione impressa durante il processo e per aumentare la qualità superficiale del componente finale. Le prove sperimentali, condotte utilizzando come materiale di riferimento la lega di alluminio 6082-T4, hanno permesso di valutare le variazioni delle caratteristiche meccaniche del materiale di partenza, riportando un elevato incremento di durezza e delle proprietà meccaniche intese come limite di snervamento e UTS. Allo stesso tempo si è avuta un’elevata riduzione della dimensione del grano cristallino, con una porzione di tubo caratterizzata da una microstruttura altamente raffinata. L’elevata deformazione ha comportato una riduzione della duttilità, che comunque non ha influito sull'esecuzione del processo di spianatura e di ottenere piatti con caratteristiche uguali al tubo flowformato di partenza.
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Plunkett, Brian W. "Plastic anisotropy of hexagonal closed packed metals." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0012500.
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Beaude, Nicolas. "Etude théorique et expérimentale du comportement élasto-plastique et de la localisation de la déformation dans les monocristaux." Paris 13, 1988. http://www.theses.fr/1988PA132005.
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Etude experimentale sur des monocristaux en superalliage à base de nickel soumis à des essais à chaud d'écrouissage cyclique à basse fréquence. Observation d'un phénomene d'instabilité plastique accompagné de la formation de lignes de glissement cristallographiques sur le fut de l'éprouvette. Modélisation du comportement élasto-plastique par une généralisation de la loi de schmid. L'extension de la loi de normalite permet de déterminer la direction de l'écoulement plastique et les systèmes actifs du glissement octaédrique. C'est la bifurcation locale de cette loi de comportement qui rend compte de l'instabilite observée
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Yapici, Guney Guven. "Severe plastic deformation of difficult-to-work alloys." Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/531.
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The present work aims to reveal the microstructural evolution and post-processing mechanical behavior of difficult-to-work alloys upon severe plastic deformation. Severe plastic deformation is applied using equal channel angular extrusion (ECAE) where billets are pressed through a 90o corner die achieving simple shear deformation. Three different materials are studied in this research, namely Ti-6Al-4V, Ti-6Al-4V reinforced with 10% TiC and AISI 316L stainless steel. Microstructure and mechanical properties of successfully extruded billets were reported using light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), tension and compression experiments and microhardness measurements. The effects of extrusion conditions (temperature and processing route) on the microstructure and mechanical properties are investigated. The underlying mechanisms responsible for observed mechanical behaviors are explored. It is seen that ECAE shear deformation leads to refinement in α plates and elimination of prior β boundaries in Ti-6Al-4V. Decreasing extrusion temperature and increasing number of passes decreases α plate size and grain size. Refined α grain size leads to a significant increase in tensile and compressive flow stresses at room temperature. Texture produced by ECAE has a pronounced effect on mechanical properties. Specifically it leads to tension/compression asymmetry in flow strengths and strain hardening coefficients may be described by the activation of differing slip systems under tension and compression loading. ECAE of Ti-6Al-4V+10%TiC samples also improved mechanical properties due to α plate size refinement. Nevertheless, further extrusion passes should be carried out for tailoring reinforcement size and distribution providing optimum strength and ductility. ECAE deformation of AISI 316L stainless steel at high homologous temperatures (0.55 to 0.60 Tm) results in deformation twinning as an effective deformation mechanism which is attributed to the effect of the high stress levels on the partial dislocation separation. Deformation twinning gives rise to high stress levels during post-processing room temperature tension and compression experiments by providing additional barriers to dislocation motion and decreasing the mean free path of dislocations. The highest tensile flow stress observed in the sample processed at 700 oC following one pass route A was on the order of 1200 MPa which is very high for 316L stainless steel. The ultimate goal of this study is to produce stabilized end microstructures with improved mechanical properties and demonstrate the applicability of ECAE on difficult-to-work alloys.
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Tan, Evren. "Severe Plastic Deformation Of Age Hardenable Aluminum Alloys." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614968/index.pdf.
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Industrial products of high-strength Al-alloys are currently manufactured by thermo-mechanical processes, which are only applicable in the integrated plants requiring high investment cost. Moreover, reduction of the average grain size not less than 10 &mum and re-adjustment of process parameters for each alloy type is evaluated as disadvantage. Therefore, recently there have been many research studies for development of alternative manufacturing techniques for aluminum alloys. Research activities have shown that it is possible to improve the strength of Al-alloys remarkably by severe plastic deformation which results in ultra-fine grain size. This study aims to design and manufacture the laboratory scale set-ups for severe plastic deformation of aluminum alloys, and to characterize the severely deformed samples. The stages of the study are summarized below: First, for optimization of die design and investigation of parameters affecting the deformation finite element modeling simulations were performed. The effects of process parameters (die geometry, friction coefficient) and material properties (strain hardening, strain-rate sensitivity) were investigated. Next, Equal Channel Angular Pressing (ECAP) system that can severely deform the rod shaped samples were designed and manufactured. The variations in the microstructure and mechanical properties of 2024 Al-alloy rods deformed by ECAP were investigated. Finally, based on the experience gained, a Dissimilar Channel Angular Pressing (DCAP) system for severe plastic deformation of flat products was designed and manufactured
then, 6061 Al-alloy strips were deformed. By performing hardness and tension tests on the strips that were deformed by various passes, the capability of the DCAP set-up for production of ultra-fine grain sized high-strength aluminum flat samples were investigated.
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Whitten, Philip Gregory. "Friction induced plastic deformation of high polymer surfaces." Access electronically, 2004. http://www.library.uow.edu.au/adt-NWU/public/adt-NWU20050118.113517/index.html.
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Chen, Zhiming [Verfasser]. "Modelling the plastic deformation of iron / Zhiming Chen." Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.
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Ebeling, Timo [Verfasser]. "Plastic Deformation Modeling of Magnesium Alloys / Timo Ebeling." Aachen : Shaker, 2010. http://d-nb.info/1122546262/34.
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Kamyab, Morad. "Deformation of soft plastic solids by rigid walls." Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241826.
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