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1
May, Katelun. „Small Scale Tensile Testing of Titanium Alloys“. The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1282099780.
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2
Battocchi, Dante. „The Development, Characterization and Testing of Mg-rich Primers“. Diss., North Dakota State University, 2012. https://hdl.handle.net/10365/26453.
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Aluminum alloys are widely used in aircraft industry for their strength and light weight. Those alloys that are hardened by precipitation, especially the Copper-rich of the 2000 series, are prone to corrosion and are protected against it using chromate containing coatings. The primary component of these coating systems is Chromium 6+ (CrVI) that has been found to be very toxic in the environment and carcinogenic, toxic and mutagenic in humans.
The Mg-rich primer development is the result of a successful multi-year project funded by the US Air-force with its objective the replacement of coatings based on CrVI with a class of coatings less toxic and with comparable protective performances. The Mg rich primer fulfilled the USAF requirements and it is currently undergoing commercial and military qualifications testing.
The use of Mg as one of the active pigments in coatings allows the primer to protect the underlying Al sacrificially, not considered possible for this substrate until now. Mg is anodic to most of the other structural metals and when particulate Mg became available commercially, the concept of the primer was first developed by analogy to Zn-rich coatings for steel. When Mg and Al are in contact and immersed in a corrosive environment, magnesium corrodes preferentially and protects the aluminum.
3
Edgemon, Glenn Leon. „The time-temperature-sensitization behavior of alloy 800 as determined by the electrochemical potentiokinetic reactivation test and the modified strauss test“. Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20034.
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Speicher, Matthew S. „Cyclic testing and assessment of shape memory alloy recentering systems“. Diss., Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33834.
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In an effort to mitigate damage caused by earthquakes to the built environment, civil engineers have been commissioned to research, design, and build increasingly robust and resilient structural systems. Innovative means to accomplish this task have emerged, such as integrating Shape Memory Alloys (SMAs) into structural systems. SMAs are a unique class of materials that have the ability to spontaneously recover strain of up to 8%. With proper placement in a structural system, SMAs can act as superelastic "structural fuses", absorbing large deformations, dissipating energy, and recentering the structure after a loading event. Though few applications have made it into practice, the potential for widespread use has never been better due to improvements in material behavior and reductions in cost. In this research, three different SMA-based structural applications are developed and tested. The first is a tension/compression damper that utilizes nickel-titanium (NiTi) Belleville washers. The second is a partially restrained beam-column connection utilizing NiTi bars. The third is an articulated quadrilateral bracing system utilizing NiTi wire bundles in parallel with c-shape dampers. Each system was uniquely designed to allow a structure to undergo large drift demands and dissipate energy while retaining strength and recentering ability. This exploratory work highlights the potential for SMA-based structural applications to enhance seismic structural performance and community resilience.
5
Totty, Jennifer L. „Linear cellular copper in bending, compression and shear“. Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16913.
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6
Tibane, Meriam Malebo. „Phase stability study of Pt-Cr and Ru-Cr binary alloys“. Thesis, University of Limpopo (Turfloop Campus), 2011. http://hdl.handle.net/10386/737.
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Thesis (Ph.D. (Physics)) --University of Limpopo, 2011Planewave pseudopotential calculations were conducted to predict the energetics and phase stability of Pt-Cr and Ru-Cr binary alloys. Validation of appropriate number of k-points and planewave energy cut-off was carried out for all studied systems. At the composition of A3B and AB3 (where A = Cr and B = Pt or Ru) phases, the heats of formation determined for five different structures, L12, A15, tP16, DOC and DO′ C are almost of the same magnitude and the relaxed structures show no rotation. We observed that the cubic L12 Pt3Cr is the most stable structure in agreement with the experiments. The results for PtCr3 indicate the negative heat of formation for the A15 phase whereas all the remaining studied phases have positive heats of formation. It is clear that the PtCr3 (A15) is the most stable structure. PtCr (L10) was found to be more stable compared with PtCr (B2) phase. The L12 Pt3Cr, A15 PtCr3 and L10 PtCr phases could be considered as possible coatings to cover the engines which are exposed to aggresive environments. The heats of formation of all studied compositions and phases of Ru-Cr systems are positive, these results suggest that, generally, studied Ru-Cr phases are not stable. The effect of pressure and doping were investigated on A15 RuCr3 structure which was reported to exist at a higher temperature. Elastic constants and moduli were investigated to determine the strength of the PtCr systems. The strength of PtCr L10 is greater than that of B2 phase. The ratio of shear to bulk modulus (G/B) has been used to predict the ductility or the brittleness of the material. It was found that Pt3Cr L12 is the most ductile phase among those considered in this study. The density of states were calculated to further analyze the stability of systems. The magnetic properties of Cr were studied using VASP which predicted an anti-ferromagnetic and a non-magnetic ground state for pure Cr. We have investigated the thermal stability at 0 GPa for different phases of Pt3Cr, PtCr3, PtCr and RuCr3 A15 phase, where we detected the soft modes at X, G, M and R points of the Brillouin zone from the phonon spectra of Pt3Cr A15 phase. Pt3Cr L12 and PtCr3 A15 are predicted as dynamically stable structures. RuCr3 A15 phase was found to be dynamically stable but thermodynamically unstable. Phonon DOS were studied to observe the modes of vibration and atoms that contribute to soft modes. Lastly we investigated the thermal expansion of Pt3Cr L12 and A15 phases.
The National Research Foundation,and the South African Gas Turbine Research Program
7
Swalla, Dana Ray. „Microstructural characterization of titanium alloys with fretting damage“. Diss., Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-04082004-180428/unrestricted/swalla%5fdana%5fr%5f200312%5fphd.pdf.
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8
Phasha, Maje Jacob. „Fundamental study of immiscible Ti-Mg system : ball milling experiments and ab initio modelling“. Thesis, University of Limpopo, Turfloop Campus, 2013. http://hdl.handle.net/10386/1395.
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Thesis (Ph. D. (Physics)) -- University of Limpopo, 2013.A combination of ball milling experiments and ab initio calculations in this study successfully yielded results that shed light into understanding the fundamental basis for immiscibility and the concept of mechanical alloying in Ti-Mg system. In addition, the conditions for achieving extended solid solubility in elements that usually do not dissolve in each other under thermodynamic equilibrium conditions have been predicted using ultrasoft (US) and norm-conserving (NC) pseudopotentials. Hydostatic pressures required to stabilize ordered phases were determined. Our new systematic representation of martensitic transformation (MT) paths as a result of dislocation necessary to induce α→FCC, α→BCC and α→ω phase transitions led to, for the first time, a direct determination of CRSS and tensile strength for Ti and Mg HCP metals. Furthermore, a new ω phase which is less stable than α phase at 0 GPa is proposed. Based on this phase, α→ω deformation path which yielded the onset of uniaxial transition pressure of 4.167 GPa is reported. Attempts of synthesizing Ti-Mg solid solutions by means of Simoloyer high energy ball mill were not successful; however, nanocrystalline Mg-TiH2-x composites were instead formed. These results were attributed to quick formation of metastable Ti hydrides or cold welding at early stages of BM prior to alloying, thus serving as possible obstacles to forming such solid solutions. The deformed Ti crystals adsorbed H+ from the stearic acid leading to formation of metastable orthorhombic TiH2-x phase which later transformed to a tetragonal TiH2-x or even cubic TiH2 when stoichiometric amount of H2 had been adsorbed. Although the yield was significantly lower, the product of milling a mixture of coarse Mg and fine Ti particles was comprised of Ti particles adhering around ductile Mg particles in a core shell manner. The adhesion of the fine hard titanium particles on the surface of the large ductile magnesium particles impeded the further plastic deformation of the titanium particles, thus suppressing the formation of the faults necessary for mechanical alloying. Nanocrystalline Ti powder of about 40 nm was produced by 30h ball milling. During BM of Ti powder, solid-state transformation from HCP to FCC occurred in the presence of PCA with lattice parameters of 4.242 and 4.240 Å after 24 and 30 h, respectively, v due to protonation. When Ti powder was milled in the absence of PCA, no phase transformation was observed for both uninterrupted and interrupted milling cycles. In addition, nanocrystalline Mg powder with crystallite size varying between 60 and below 40 nm was produced by ball milling. However, no solid-state transformation took place even if the powder was milled for 90 h. Therefore, we evidently report for the first time that the interstitial H+ is the driving force for α → FCC phase transformation in ball milled Ti powder. Our theoretical results predicted the ω phase to be the ground-state structure of Ti at 0K and P=0 GPa, in support of other previously reported calculations. We noticed that the stability of the α phase was surpassed by that of the FCC lattice at ~ 100 GPa, corresponding with sudden sharp rise in c/a ratio, hence attributed to α → FCC phase transition. Similar results were obtained for Mg at 50 GPa, although in this case the crossing of lattice energies coincided with minimum c/a. However, using our proposed HCP→BCC MT path mechanism for Mg, it is evident that the minimum c/a at 50 GPa corresponds to a change in the preferred deformation slip from basal (below 10 GPa) to prismatic rather than phase transition. Nonetheless, the proposed MT model predicts that both elemental Ti and Mg prefer to deform via prismatic slip as indicated by lower shear stress as well as CRSS values compared to those calculated for basal slip. Theoretical findings from ab initio calculations on hypothetical ordered Ti-Mg phases indicated absence of intermetallic phases at equilibrium conditions, in agreement with experimental data. However, the formation becomes possible at 80 GPa and above with respect to c/a ratio but requires at least 200 GPa with respect to stable lattices. Using calculated heats of formation, elasticity and DOS, it has been possible to show that L12 TiMg3 could not form even at high pressure as 250 GPa. Nonetheless, both approaches indicate that forming an intermetallic compound between Ti and Mg requires a crystal structure change, α→FCC for Ti and HCP→BCC for Mg. Proposed DFT-based solid solution model for predicting phase stability and elastic properties of binary random alloys, with Mg-Li system serving as a test case, successfully yielded reliable results comparable to experimental data. This method was successfully applied to study an immiscible Ti-Mg system and the solubility limit vi was for the first time theoretically established. Based on formation energy of Ti-Mg solid solutions, our calculations predicted for the first time that the solubility of up to 60 and 100 at.% Mg into Ti with the use of USP and NCP, respectively, to be thermodynamically favourable with necessary lattice kinetics being the main challenge. Nonetheless, NCP proved to be reliable in predicting structural and elastic properties of disordered alloys.
9
Whitelaw, Roberts S. III. „Experimental determination and constitutive modeling of the deformation behavior of lead-free solders“. Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/17224.
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10
Mukunthan, Kannappar. „Properties of ultra fine grain [beta]-CuAlNi strain memory alloys“. Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26724.
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A method has been developed to produce grain sizes as low as 5µm in β-CuAlNi alloys and the effect of grain size on mechanical and strain-memory properties was studied. The thermomechanical treatment procedure involved two. sequential warm working and recrystallization steps at 600° C and 800° C respectively on eutectoid alloys. Three different eutectoid alloys, two with Ms temperature of around 0°C and one with Ms = 220° C were used for the present studies. Even at fine grain sizes, the specimens produced were of single β- phase type without any second phases.
Two-stage characteristic stress-strain curves were obtained for most of the specimens in both the strain memory and pseudoelastic states. It was found that the ultimate tensile strength and strain to failure increased with decreasing grain size according to a Hall-Petch relationship down to a grain size of 5µm with the exception of one alloy. Fracture strengths of 1,200 MPa and fracture strains of 10% could be obtained.
It was found that the major recovery mode, whether pseudoelastic or strain memory, did not have any significant effect on the total recovery obtained. Recovery properties were not affected significantly by decreasing grain size. Approximately 86% recovery could be obtained for an initial applied strain of 5% at a grain size of around 10µm.
Grain refinement increased the fatigue life considerably, possibly due to high ultimate fracture strength and ductile fracture mode. Fatigue life of 275,000 cycles could be obtained for an applied stress of 330 MPa and a steady state strain of 0.6%.
Most of the fractures are due to intergranular-type brittle fracture. At fine grain sizes, transgranular-type brittle fracture and microvoid coalescence-type ductile fracture dominated the fracture mode. Oxygen segregation at grain boundaries is the possible explanation for the different mechanical properties shown by different alloys in the present work by being a major factor in causing intergranular-type fracture.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
11
George, Faith Olajumoke. „Chromium-free conversion coating of aluminium-copper alloys“. Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/chromiumfree-conversion-coating-of-aluminiumcopper-alloys(5176c8af-02af-44a8-a47f-44b5a0c2585c).html.
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Aluminium alloys are frequently pre-treated by a conversion coating before application of an organic coating in order to improve the corrosion resistance and adhesive properties of the surface and the corrosion resistance provided by the system. Chromate-containing conversion coatings are commonly used for this purpose. However, legislation limits future use of hexavalent chromium compounds due to their toxic and carcinogenic nature. Therefore, alternative, so-called chromium-free conversion coatings are being developed that are more environmentally-compliant.The purpose of the present work has therefore been to contribute to a better understanding of how the aluminium substrate affects the formation and properties of conversion coatings for adhesive bonding. In particular, a chrome-free zirconium-based conversion treatment process has been investigated as a possible replacement for conventional chromate conversion treatment. The influence of the conversion time on the thickness of the formed layer on pure aluminium was investigated using complementary surface analytical techniques. The conversion time was varied between 30 and 600 seconds.In this study, the structure and composition of zirconium-based chromium-free conversion coatings on magnetron sputtered superpure aluminium and a range of aluminium-copper alloys were characterised as a function of immersion time in the aqueous conversion bath to understand the mechanism of coating formation and protection. However, the presence of copper significantly influences the coating development and ultimately the performance of the conversion coatings formed on binary copper-containing aluminium alloys.The morphology and composition of the coatings have been probed using transmission electron microscopy, Rutherford backscattering spectroscopy and glow discharge optical emission spectroscopy, with loss of substrate through growth of the conversion coating also quantified. A comparison of the RBS spectra obtained for the superpure aluminium specimens after different immersion times revealed that zirconium (Zr) and oxygen (O) peaks were wider for longer immersion times, indicating thickening of the coating with increased immersion times. Thus, increasing the immersion time resulted in an increase in coating thickness but little change in coating composition occurred as determined by the RBS RUMP simulations. Alloying decreases the coating thickness, as well as metal consumption. Here, aspects of the corrosion behaviour of superpure aluminium and aluminium-copper alloys were also considered using electronoptical, electrochemical and surface analytical probing. The influence that short and prolonged treatment times exert on the performances of such conversion coating is discussed. The conversion coating formed after 60 s and 180 s of immersion in the zirconium-based conversion coating bath provide good corrosion resistance which can be attributed to the high stability of the compounds that constitute the surface oxide layer, and good adhesion properties.
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Tan, Kian Sing. „Dynamic loading characteristics in metals and composites“. Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FTan_Kian_Sing.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Kwon, Young. Second Reader: Didoszak, Jarema. "December 2009." Description based on title screen as viewed on January 26, 2010. Author(s) subject terms: Tensile tests, Strain rate effects, Dynamic loading, Failure criterion. Includes bibliographical references (p. 37-38). Also available in print.
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Zellner, Samantha R. „Charpy Impact Testing of Twinning Induced Plasticity and Transformation Induced Plasticity High Entropy Alloys“. Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1538702/.
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High entropy alloys (HEAs) are a new class of solid solution alloys that contain multiple principal elements and possess excellent mechanical properties, from corrosion resistance to fatigue and wear resistance. Even more recently, twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) non-equiatomic high entropy alloys have been engineered, promising increased strength and ductility as compared to their equiatomic counterparts. However, impact and fracture resistance of these HEAs has not been studied as much as their other mechanical properties. In this thesis, the hardness, tensile properties, and Charpy impact energy of Al0.3CoCrFeNi, a TWIP HEA, and 50Fe-30Mn-10Co-10Cr (at.%), a TRIP HEA, was explored. First, three processing conditions, (1) as-received, (2) recrystallized, and (3) peak hardness, were chosen for each alloy and verified with Vickers microhardness measurements. Next, the tensile properties of each alloy and condition were investigated. Charpy impact specimen size was then selected based on the final plate thickness, and the machined samples were tested. Plastic zone size and change in sample thickness in the deformed region of each condition after testing was measured. Post-impact test inspection of the samples in all conditions showed that the samples were in tension near the V-notch root and in compression at the impact surface. Plastic zone size is seen to change as a function of distance from the V-notch root moving towards the impact surface in conditions that exhibited higher ductility. Overall, the TWIP alloy displayed high fracture resistance, and further microstructural optimization will likely increase the fracture resistance of these alloys.
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Nourani, Mohamadreza. „Integrated multiphysics modeling, testing and optimization of friction stir welding of aluminum alloys“. Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45659.
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The main objective of this work is the development of a novel integrated multiphysics modeling, testing, and optimization of friction stir welding (FSW) for aluminum alloys, and thereby facilitating a better understating of processing-microstructure-properties relationships in this relatively new welding technique. To this end, in this paper-based dissertation, first we review various models and optimization methods used in the field of FSW. Next, based on the current state-of-the-art and a validated 3D thermal model for aluminum 6061 along with a Taguchi design of experiments approach, we make a proposition that hot welds (with maximum temperature during FSW) have the lowest mechanical properties as opposed to cold welds. Using further experimental studies we also propose that another determining parameter in the resulting mechanical properties of FSW welds is the material flow around the tool which in very cold weld conditions may cause low mechanical properties due to low mechanical bonding.
Next, we develop and validate a novel two-dimensional Eulerian steady-state “integrated multiphysics” model of FSW of aluminum 6061 which did not exist earlier in the literature and can simultaneously predict temperature, shear strain rate, shear stress and strain fields over the entire workpiece. The model can additionally predict microstructural changes during and after FSW as well as residual stresses. In order to investigate the effect of different material constitutive equations on this integrated multiphysics model, we implement and compare most commonly used CFD (Computational Fluid Dynamics) and CSM (Computational Solid Mechanics) constitutive equations and show their similarities and differences. Using the same integrated multiphysics model, for the first time we also present a new semi-experimental approach to measure strain during FSW using visioplasticity.
Finally, we perform a comprehensive experimental study (tensile testing, Electron Back Scatter Diffraction, Scanning Electron Microscopy, and micro-hardness testing) on FSW of aluminum 6061 samples in order to further validate the developed numerical model and optimize the welding process parameters (tool rotation speed, weld speed and axial force). The experimental study also prove the above mentioned preposition on a correlation among the processing-microstructure-mechanical properties during FSW, especially when comparing the UTS of samples from cold and hot weld conditions.
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Ehret, Steven J. „Instrumentation for anodization and in-situ testing of titanium alloys for capacitor anodes“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1311612394.
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Palmer, Benjamin. „Environmentally-Assisted Cracking Response in Field-Retrieved 5XXX Alloys“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1585061712231734.
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17
Mwita, Wambura Mwiryenyi. „Development and testing an intelligent hybrid polymeric composite beam with healing ability embedded with Ni-Ti shape memory alloy“. Thesis, Cape Peninsula University of Technology, 2010. http://hdl.handle.net/20.500.11838/1251.
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Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2010.Hybrid polymeric composites (HPC) are widely used for the design of aerospace, automobile and civil engineering structures. One of the major challenges posed by these materials and structures is their brittle nature. When subjected to impact and dynamic loads, the polymeric composite structures undergo micro cracking. The cracks coalesce, propagate and can lead to catastrophic failure of the material and structures. In this thesis, an intelligent hybrid polymeric composite (IHPC) beam with healing ability was developed and tested. The IHPC beam developed consisted of a 3% prestrained 1mm diameter Ni-Ti shape memory alloy (SMA) wire actuator embedded in the polymeric host matrix. The function of the embedded Ni-Ti shape memory alloy was to enhance intelligence and healing ability to the IHPC beam. Upon electric current resistance heating, the Ni-Ti SMA actuator responds by contracting as a result of detwinned martensite → austenite phase transformation. Contraction of the SMA in the IHPC beam was utilized to stiffen and enhance healing by retarding crack growth and recovery of the strain induced in the loaded IHPC beam. This can result to increase of the flexural stiffness EI (defined as the product of the Young’s Modulus E of the material and the moment of inertia I of the geometry of the beam) and mode I fracture stress intensity factor KIC of the IHPC beam. One (1) mm diameter Ni-Ti SMA wire was used in the experimental work in this thesis. The wire was cut into 35 pieces, 200 mm long each. Ni-Ti SMA wires were heated in the furnace to a temperature of 250ºC for ten (10) hours then were left to cool in the ambient air. The heat treatment was aimed to release any residual stress and to stabilize the austenite start (AS) and austenite finish (Af) transformation temperatures of the Ni-Ti SMA. After heat treatment, the Ni-Ti SMA wires were prestrained by 3% (based on a gauge length of 150mm) on a tensile testing machine. Prestraining of the Ni-Ti SMA wires was aimed to induce detwinned martensite volume fraction in them hence increasing the transformation strain and recovery force of the Ni-Ti SMA actuator. Intelligent hybrid polymeric composite (IHPC) beams and polymeric virgin (PV) beams, all of dimensions 150mmx25mmx10mm were manufactured by casting 60D polyurethane thermosetting epoxy resin in a silicon mould. transformation strain and recovery force of the Ni-Ti SMA actuator.
18
Wallace, Jon Michael. „Fretting fatigue crack nucleation in Ti-6A1-4V“. Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17266.
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Smith, Brian J. „A critical assessment of the potential of shape memory alloys for seismic resistant designs and retrofits“. Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19599.
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20
Vu, Chinh Q. L. „Fatigue Characteristics of New ECO Series Aluminum 7175 Alloy“. PDXScholar, 2019. https://pdxscholar.library.pdx.edu/open_access_etds/4985.
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In this dissertation, the fatigue characteristics of three newly developed experimental compositions for aluminum 7175, with improved mechanical strength, that uses magnesium-calcium alloy instead of pure magnesium are studied.
Specimens of each variant were fabricated and subjected to fatigue life testing, fatigue life data analysis, and observation of their fracture characteristics through optical microscopy and scanning electron microscopy (SEM), and metallography to study their grains and surface characteristics.
Fatigue life testing shows all three variants have a fatigue strength that is approaching approximately 200 MPa. ECO7175v3 is shown to have the highest fatigue strength of approximately 220 MPa at 5x107 cycles, approximately 40% of its tensile strength of 550 MPa. This is shown by its considerably higher fatigue strength coefficient determined by Basquin's equation compared to the other two variants. ECO7175v1 is shown to generally have large scatter in its fatigue life at higher stress levels (65% or higher of their tensile strength) with coefficient of variations typically twice or more to those of ECO7175v2 and ECO7175v3.
The results of the SEM analysis shows that irrespective of the stress levels, ECO7175v1 and ECO7175v3 all have crack initiation points at the surface with no inclusions to act as stress concentrators. The lack of inclusions are supported by the reliability analysis which shows the hazard rates for all variants remains relatively constant the majority of the time before increasing towards the end. These trends for all variants indicates failures are due to wear-outs instead of defects, which were not seen. Reliability analysis also shows that at any given fatigue life cycle and stress level, ECO7175v3 has a lower probability of failure when compared to ECO7175v1 and ECO7175v2. On the other hand, at any given fatigue life cycle and stress level, ECO7175v1 is shown to have a higher probability of failure when compared to ECO7175v2 and ECO7175v3.
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Ghasemi, Hamid-Reza M. R. „Computer simulation of carburization corrosion of nickel-base superalloys“. Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/76035.
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A computer model for diffusion-controlled internal precipitation was used to simulate the corrosion behavior of Ni-based superalloys in carburizing atmospheres. The model is based on Crank-Nicholson finite difference solution of the diffusion equation. The code also includes the ternary cross diffusion effect due to substitutional alloying elements that are preferentially oxidized. The model can treat two sets of boundary conditions corresponding to the presence or absence of a protective oxide scale. It accounts for internal precipitation of corrosion products whenever thermodynamic solubility limits are exceeded. Up to four different carbides can be treated simultaneously. The solubility product is computed for each reaction and the amount of carbon that reacts is removed from the diffusion process. Under non-protective conditions, the predictions of model were compared to carburization profiles obtained experimentally in H₂-CH₄ environment tests. Results are presented for the formation of Cr, Mo, Ti, W, and Nb carbides in Ni-based superalloys. The predicted corrosion profiles are in qualitative agreement with experimental data.Master of Science
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Rockett, Chris H. „Flexural Testing of Molybdenum-Silicon-Boron Alloys Reacted from Molybdenum, Silicon Nitride, and Boron Nitride“. Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16293.
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MoSiB alloys show promise as the next-generation turbine blade material due to their high-temperature strength and oxidation resistance afforded by a protective borosilicate surface layer. Powder processing and reactive synthesis of these alloys has proven to be a viable method and offers several advantages over conventional melt processing routes. Microstructures obtained have well-dispersed intermetallics in a continuous matrix of molybdenum solid-solution (Mo-ss). However, bend testing of pure Mo and Mo-ss samples has shown that, while the powder processing route can produce ductile Mo metal, the hardening effect of Si and B in solid-solution renders the matrix brittle. Testing at elevated temperatures (200°C) was performed in order to determine the ductile-to-brittle transition temperature of the metal as an indication of ductility. Methods of ductilizing the Mo-ss matrix such as annealing and alloying additions have been investigated.
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Slagsvold, Marius. „Effect of Fe and Si content in Aluminium Alloys as a result of increased recycling : Testing of high purity Aluminium Alloys in uniaxial tension“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16320.
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The recycling of aluminium from used aluminium scrap leads to an unavoidable presence of pollutions in the form of elements of various amounts. Two such elements are iron and silicon. These will always be present to some extent in an aluminium alloy as they are introduced to the alloy during processing. Iron and silicon are accumulative elements, meaning that they can never be completely eliminated once introduced into the aluminium. Some alloys have very narrow compositional windows, they have strict regulations concerning amount of alloying elements allowed. This is of grave importance for the recycling process; to be able to produce specific alloys with limitations regarding content and mechanical properties. A project to uncover the effects of common elements in aluminium such as Mg, Si and Fe has been initiated by the industry. This work is closely related to the project and was carried out as a report during fall 2010 and continued as a master thesis during spring 2011. The aim of this work was to study the effects of variation of small amounts of iron and silicon in 4 different alloys of high and ultra high purity (>99.7 and >99.999 wt% Al, respectively). The main focus was to uncover the effect of the elements on mechanical properties. Tensile test experiments with specimens in uniaxial tension were conducted to uncover the mechanical properties of the alloys. In addition to the tensile tests other parameters like texture, particles, recrystallisation and micro structure development were investigated. DC-cast, extruded flat profiles and rolled and recrystallised versions of the 4 alloys were used during the work.The results from tensile tests performed on the rolled and recrystallised aluminium showed that an initial introduction of 0.066 wt % Fe and Si 0.068 wt % to an alloy containing no pollutions lead to a dramatic increase in strength properties (up to 100% for the tensile strength) and a mild decrease in elongation. The increased strength properties and reduced formability was traced to iron and silicon in solid solution. From the same tensile tests it was concluded that a further increase of iron and an introduction of a small amount of pollutions had close to no effect on the mechanical properties.
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Ded, Gurdish S. „CHARACTERIZATION OF Ni-RICH NiTiHf BASED HIGH TEMPERATURE SHAPE MEMORY ALLOYS“. UKnowledge, 2010. http://uknowledge.uky.edu/gradschool_theses/55.
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Among the potential high temperature shape memory alloys, due to its low cost, medium ductility and high work output NiTiHf seems to be the most promising HTSMA for a wide range of applications in the 100-250ºC. A detailed investigation into the shape memory properties and transformation behavior for the Ni-rich HTSMA with the compositions of Ni45.3Cu5Ti29.7Hf20, Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 was carried out. It is possible to form Ni-rich precipitates in Ni-rich NiTiHf alloys and tailor the TTs by heat treatments that results in increased strength and stable response at high temperatures. The coherent Ni-rich precipitates deplete the Ni content from the matrix increasing the transformation temperatures and strengthen the material by hindering the dislocation motion. The effect of aging on the microstructure, shape memory and mechanical properties are revealed. Optimum aging conditions have been found determined to get the most favorable combination of high transformation temperatures with stable and good shape memory properties. The Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 aged at 500ºC-600 ºC were found to be formidable candidates for high temperature applications.
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Clark, David A. „Durability of the residual stresses surrounding cold expanded fastener holes in 7050-T7451 aluminum“. Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17828.
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Zbären, Christoph Oliver. „The effect of thermal cycling on metal-ceramic bond strength /“. [S.l.] : [s.n.], 2009. http://opac.nebis.ch/cgi-bin/showAbstract.pl?sys=000288150.
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Imrich, Kenneth J. „The SCC behavior of austenitic alloys in an oxygen-free CO₂ environment containing chloride ions“. Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/77903.
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Stress-corrosion cracking of austenitic alloys in an oxygen-free carbon dioxide environment containing chloride ions was studied under static conditions. Stiffness and X-ray measurements supported results obtained from SEM photomicrographs indicating that the CT specimens loaded to a stress intensity of 22 ksi-in.5 were not susceptible to SCC in this environment. These alloys were also evaluated for their SCC resistance in boiling MgCl₂ and NaCl solutions. Results of this study indicated that alloys containing higher nickel contents were more resistant to chloride SCC.Master of Science
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Mireles, Omar R. (Omar Roberto). „Non-Nuclear Materials Compatibility Testing of Niobium - 1% Zirconium and 316 Stainless Steel for Space Fission Reactor Applications“. Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5267.
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A new generation of compact and highly efficient power production and propulsion technologies are critically needed in enabling NASAs long-term goals. Nuclear fission power technologies as part of project Prometheus are in development to meet this need. Proposed reactor concepts utilize a combination of refractory metals and stainless steels. One such refractory alloy, Niobium 1% Zirconium (Nb-1Zr), will be used because of its strength at high temperatures, neutron absorption properties, and resistance to corrosion by liquid alkali metals. One potential problem in using Nb-1Zr is that it undergoes rapid high temperature oxidation, even in low oxygen concentrations. Long-term oxidation of the niobium matrix can significantly deteriorate the mechanical properties of the alloy. This thesis reports on experimental studies of the high temperature interaction of 316 stainless steel (316 SS) and Nb-1Zr under prototypic space fission reactor operating conditions. Specifically, how the high temperature oxidation rate of Nb-1Zr changes when in contact with 316 SS at low external oxygen concentrations.
The objective of the project is to determine if transport of gaseous contaminants, such as oxygen, will occur when Nb-1Zr is in contact with 316 SS, thereby increasing the oxidation rate and degrading material properties. Experiments were preformed in a realistic non-nuclear environment at the appropriate operating conditions. Thermal Gravimetric Analysis techniques were used to quantify results. Coupons of Nb-1Zr and Nb-1Zr in contact with 316 SS foil are subjected to flowing argon with oxygen concentrations between 4-15ppm and heated to a temperature of 500, 750, and 1000oC for 2 to 10 hours. Experiments were conducted at the Early Flight Fission Test Facility at NASA Marshall Space Flight Center.
The experimental results indicate that a complex oxidation process, which depends greatly on temperature and oxygen concentration, occurs at the expected operating conditions. Non-linear regression techniques were applied to experimental data in order to derive correlations for the approximate oxidation rate of Nb-1Zr and Nb-1Zr in contact with 316 SS as a function of time, temperature, and oxygen concentration.
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Krishnan, Vinu Bala. „DESIGN, FABRICATION AND TESTING OF A SHAPE MEMORY ALLOY BASED CRYOGENIC THERMAL CONDUCTION SWITCH“. Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4404.
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Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Mechanical, Materials and Aerospace Engineering
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Abu-Farha, Fadi K. „INTEGRATED APPROACH TO THE SUPERPLASTIC FORMING OF MAGNESIUM ALLOYS“. UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_diss/493.
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The economical and environmental issues associated with fossil fuels have been urging the automotive industry to cut the fuel consumption and exhaust emission levels, mainly by reducing the weight of vehicles. However, customers increasing demands for safer, more powerful and luxurious vehicles have been adding more weight to the various categories of vehicles, even the smallest ones. Leading car manufacturers have shown that significant weight reduction, yet satisfying the growing demands of customers, would not be feasible without the extensive use of lightweight materials. Magnesium is the lightest constructional metal on earth, offering a great potential for weight-savings. However, magnesium and its alloys exhibit inferior ductility at low temperatures, limiting their practical sheet metal applications. Interestingly, some magnesium alloys exhibit superplastic behaviour at elevated temperatures; mirrored by the extraordinarily large ductility, surpassing that of conventional steels and aluminium alloys. Superplastic forming technique is the process used to form materials of such nature, having the ability to deliver highly-profiled, yet very uniform sheet-metal products, in one single stage. Despite the several attractions, the technique is not widely-used because of a number of issues and obstacles. This study aims at advancing the superplastic forming technique, and offering it as an efficient process for broader utilisation of magnesium alloys for sheet metal applications. The focus is primarily directed to the AZ31 magnesium alloy, since it is commercially available in sheet form, possesses good mechanical properties and high strength/weight ratio. A general multi-axial anisotropic microstructure-based constitutive model that describes the deformation behaviour during superplastic forming is first developed. To calibrate the model for the AZ31 magnesium alloy, systematic uniaxial and biaxial stretching tests are carried out over wide-ranging conditions, using 3 specially-designed fixtures. In a collaborative effort thereafter, the calibrated constitutive model is fed into a FE code in conjunction with a stability criterion, in order to accurately simulate, control and ultimately optimise the superplastic forming process. Special pneumatic bulge forming setup is used to validate some proposed optimisation schemes, by forming sheets into dies of various geometries. Finally, the materials post-superplastic-forming properties are investigated systematically, based on geometrical, mechanical and microstructural measures.
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Dohr, Judith. „Micromechanical testing of oxidized grain boundaries“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:fb8a08ef-87d8-47ab-9ac8-89bf300203ea.
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Primary water stress corrosion cracking (SCC) of metals in pressurized water reactors (PWRs) is known to be one of the most challenging and cost intensive modes of failure in the nuclear industry. Even though it is known that cracking in Ni-base alloys proceeds mainly intergranular (IG), the initiation and propagation of cracks in ductile metals are not yet understood and a much-desired accurate prediction of SCC related failure seems unobtainable. In this thesis, a combination of microcantilever fracture experiments, scanning electron- (SEM) and transmission electron microscopy (TEM) techniques was employed to study and compare the failure of oxidized grain boundaries of Ni-base Alloy 600 with high and low intergranular carbide coverage and different sample history. A new technique for lifting-out whole cantilevers after testing and for performing 3D focussed ion beam sequencing (3D FIB-SEM) while preserving a thin central region of the cantilever for further TEM sample preparation was developed and is presented. In lieu with recent efforts of the main project sponsor Électricité de France (EDF) to build a predictive model for IGSCC based on localized/microscopic information, one of the main objectives was the extraction of the stress at failure of individual oxidized GBs. Supported by finite element simulations, microcantilever fracture tests revealed that surface oxides on top of individual GBs have the capability to alter the mechanical response by delaying/suppressing the onset of failure. An overestimation of the failure stress (> 230 MPa) was observed, proving that the presence of the surface oxide on top of the test structures cannot be neglected. The failure stress on both samples, tested without influence of the surface oxide, was found to cover a range of 300 - 600 MPa, which agreed well with finite element simulations of the tests and further demonstrates the reliability of the obtained data. The second objective was to gain a better understanding of the observed fracture behaviour and the role of local microstructure. Using the gathered microscopy data, it was found that the crack clearly favours a progression along the IG oxide-metal interface in the presence of carbide precipitates. Electron energy loss spectroscopy (EELS) revealed that the observed crack path can be linked to compositional and density variations of the IG oxide. In the presence of carbides the oxide was layered. An oxide close to the stoichiometry of chromia was located at the original GB and next to the carbides. Next to this Cr-rich oxide, Fe-rich mixed spinel oxides of varying composition and density were found. An explanation for density variations based on the possible formation of defective spinel oxides of the type A2+B3+2O4, due to an unavailability of certain cation species is presented. No clear interface preference was observed in the absence of precipitation, where the IG oxide was found to be thin and often incomplete with Cr-richer oxides preferentially located at the original GB. While these observations were consistent on both samples (high and low carbide coverage), bigger void-like defects were located at the Fe-richer oxide-metal interface of the cold worked sample with high IG carbide precipitation only. These weak spots seemed to be the preferred path for crack propagation on this sample. The sample with low intergranular carbide coverage showed no obvious porosities at this interface but a Cr- depleted region was seen. Introducing a multi-faceted investigation strategy, supported by finite element simulations, the presented thesis provides the most accurate determination of the failure stress of oxidized GBs on Alloy 600 to date and and adds new valuable insights to our understanding of IGSCC and the future prediction of SCC related failures.
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Stang, Eric Thomas. „Constitutive Modeling of Creep in Leaded and Lead-Free Solder Alloys Using Constant Strain Rate Tensile Testing“. Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1548338008633472.
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Tzamtzis, Spyridon. „Solidification behaviour and mechanical properties of cast Mg-alloys and Al-based particulate metal matrix composites under intensive shearing“. Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/5079.
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Magnesium alloys, as the lightest of all structural metallic materials, and aluminium-based particulate metal matrix composites (PMMCs), offering unified combination of metallic and ceramic properties, have attracted increased interest from the automotive, aerospace, electronic and recreation industries. Current processing technologies for PMMCs do not achieve a uniform distribution of fine-sized reinforcements and produce agglomerated particles in the ductile matrix, which are detrimental to the ductility. At the same time, molten magnesium alloys contain impurities and oxides and when cast conventionally, the final components usually exhibit a coarse and non-uniform microstructure with various casting defects. The key idea in this thesis has been to adopt a novel intensive melt conditioning process, allowing the application of sufficient shear stress that would disperse solid particles present in the melt and offer unique solidification behaviour, improved fluidity and die-filling during casting. The Melt Conditioned High Pressure Die Casting (MC-HPDC) process, where intensive shearing is directly imposed on the alloy melt, which is then cast by the conventional HPDC process, has been used to produce PMMC and magnesium alloy castings. The MC-HPDC process for PMMCs leads to a uniform dispersion of the reinforcement in the matrix, confirmed by quantitative statistical analysis, and increased mechanical performance as indicated by an increase in the hardness and the tensile properties of the composites. We describe a solidification path for aluminium containing magnesium alloys, where intensive shearing prior to casting leads to effective dispersion of solid oxide particles, which then effectively act as nucleation sites for magnesium grains, resulting in significant grain refinement. The MC-HPDC processed magnesium castings have a significantly refined microstructure, with reduced porosity levels and casting defects. Evaluation of the mechanical properties of the castings reveals the beneficial effect of intensive shearing. After careful optimization, the MC-HPDC process shows promising potential for the direct recycling of high purity magnesium die casting scrap, producing casting with mechanical properties comparable to those of primary magnesium alloys.
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Cortés, Puentes Wilmar Leonardo. „Seismic Retrofit of Squat Reinforced Concrete Shear Walls Using Shape Memory Alloys“. Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36167.
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Squat reinforced concrete shear walls are stiff structural elements incorporated in buildings and other structures and are capable of resisting large seismic demands. However, when not properly designed, they are prone to shear-related brittle failure. To improve the seismic behaviour of these structural elements, a retrofitting bracing system incorporating superelastic Shape Memory Alloys (SMAs) was developed. Superelastic Shape Memory Alloys (SMAs) are smart materials with the ability to sustain and recover large pseudo-plastic deformations while dissipating energy. The SMA bracing system consists of tension-only SMA links coupled with rigid steel elements. The SMA links were designed to sustain and recover the elongation experienced by the bracing system, while the steel elements were designed to sustain negligible elastic elongations.
The SMA bracing system was installed on third-scale, 2000 mm × 2000 mm, shear walls, which were tested to failure under incremental reverse cyclic loading. The experimental results demonstrated that the tension-only SMA braces improve the seismic response of squat reinforced concrete walls. The retrofitted walls experienced higher strength, greater energy dissipation, and less permanent deformation. The re-centering properties of the SMA contributed to the reduction of pinching in the hysteretic response due mainly to the clamping action of the SMA bracings while recovering their original length. The walls were numerically simulated with the nonlinear finite element program VecTor2. The numerical simulations accurately captured the hysteretic response of both the original and the retrofitted walls. A parametric study was conducted to assess the effect of axial loading and size of the SMA braces.
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Seifi, Mohsen. „Sensitization Effects on Environmentally Assisted Cracking of Al-Mg Naval Alloys“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1450805183.
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Iversen, Jørgen Tandberg. „Implementation and Testing of Numerical Models for Evolution of Microchemistry and Microstructure During Back-Annealing of Aluminium Alloys“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26682.
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Precipal and Alsoft are two separate models for simulating the effects of back-annealing on microchemistry and microstructure, respectively, in AA3xxx-type aluminium alloys (i.e Mn containing alloys). The precipitation model simulates the precipitation and growth of dispersoids, growth of constituents, and the resulting change in the solid solution concentration. Alsoft is a physical softening model which combines the effects of recovery and recrystallization.Precipal was originally implemented in Fortran 77, while the softening model, Alsoft, is implemented in Python. It would be beneficial for both the precipitation and softening model to be coupled with each other, as both models provide parameters and state variables that are given as input parameters in the other model (e.g information about the precipitates from Precipal can be used to calculate the Zener-drag, currently given as an external input parameter in Alsoft).In order to facilitate this coupling the precipitation model is reimplemented in Python. This model is then validated against the old implementation, and a parameter sensitivity study is performed to identify the most critical input parameters. The new implementation of the precipitation model is then coupled with the softening model and simulations has been performed and compared with experimental data.Precipal consists of two different precipitation models: a physical model based on physical equations, and one phenomenological model which introduces a number of fitting parameters which are determined experimentally. The physical model was shown to have too fast and abrupt precipitation behavior compared with experimental results. The phenomenological model on the other hand was able to reproduce the experimental precipitation behavior at a given temperature, but failed to successfully predict the effect of different annealing temperatures.The effects on the simulated recrystallization kinetics due to the coupling was found to be minimal, except when the precipitation halted recrystallization completely due to a large Zener-drag. The reason for this lacking effect it believed to be the assumption of site-saturation nucleation in Alsoft, which implies that the Zener-drag effect from concurrent precipitation on recrystallization nucleation is not modeled.
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Carrick, David. „Investigation of microstructure and corrosion in Al-Cu and Al-Mg alloys with and without Li additions“. Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/21302.
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The corrosion performance of Al-Cu and Al-Mg alloys with and without Li additions have been investigated. These include; AA2024-T3, AA2099-T8E77 (coarse and fine grain structure), AA5083-T351, spray formed Al-Mg-Li and spray formed Al-Mg-Li-Cu-Zn alloy. Atmospheric corrosion was investigated for up to 12 months of exposure in a rural-urban environment, prolonged immersion testing in 3.5 wt.% NaCl for up to 96 hr s and potentiodynamic polarisation in 3.5 wt.% NaCl were examined. This was to answer whether Li additions, spray forming and grain size impacted on the corrosion resistance. Atmospheric exposure showed Al2(CO3)3, NOx, SOx and NaCl compounds being deposited. Cathodic intermetallic compounds (Fe, Si, Mn and Cu rich) were shown to be associated with pitting corrosion, whereas anodic intermetallic compounds (Mg rich) offered sacrificial protection to the matrix. The Al-Cu alloys showed more corrosion compared to the Al-Mg alloys in all three corrosion investigations. The Al-Cu alloys showed pitting corrosion and intergranular corrosion, compared to primarily pitting corrosion on the Al-Mg alloys. AA2024-T3 developed a weakened, friable layer on the surface, consisting of a network of intergranular corrosion and numerous shallow pits. The Al-Cu-Li alloys also showed intergranular corrosion and pitting corrosion, but also developed selective grain dissolution, leading to extensive sub-surface cavities. This showed that Li additions in the Al-Cu alloys was detrimental and was primarily associated with the T type phases likely to be; T1 phase (Al2CuLi). Li additions in the Al-Mg alloys did not show any measurable improvement or reduction in corrosion resistance. Spray forming also did not appear to improve the corrosion resistance. Grain size in turn was shown to impact on corrosion resistance, with the general consensus being that finer grains offer increased corrosion resistances. Al-Cu alloys showed fine grain structures developed easy path propagation for intergranular corrosion, whereas fine grain structures on Al-Mg alloys promoted increased corrosion resistance.
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Amruthaluri, Sushma. „An Investigation on Biocompatibility of Bio-Absorbable Polymer Coated Magnesium Alloys“. FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1742.
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Advances in biomaterials have enabled medical practitioners to replace diseased body parts or to assist in the healing process. In situations where a permanent biomaterial implant is used for a temporary application, additional surgeries are required to remove these implants once the healing process is complete, which increases medical costs and patient morbidity. Bio-absorbable materials dissolve and are metabolized by the body after the healing process is complete thereby negating additional surgeries for removal of implants.
Magnesium alloys as novel bio-absorbable biomaterials, have attracted great attention recently because of their good mechanical properties, biocompatibility and corrosion rate in physiological environments. However, usage of Mg as biodegradable implant has been limited by its poor corrosion resistance in the physiological solutions. An optimal biodegradable implant must initially have slow degradation to ensure total mechanical integrity then degrade over time as the tissue heals.
The current research focuses on surface modification of Mg alloy (MZC) by surface treatment and polymer coating in an effort to enhance the corrosion rate and biocompatibility. It is envisaged that the results obtained from this investigation would provide the academic community with insights for the utilization of bio-absorbable implants particularly for patients suffering from atherosclerosis.
The alloying elements used in this study are zinc and calcium both of which are essential minerals in the human metabolic and healing processes. A hydrophobic biodegradable co-polymer, polyglycolic-co-caprolactone (PGCL), was used to coat the surface treated MZC to retard the initial degradation rate. Two surface treatments were selected: (a) acid etching and (b) anodization to produce different surface morphologies, roughness, surface energy, chemistry and hydrophobicity that are pivotal for PGCL adhesion onto the MZC. Additionally, analyses of biodegradation, biocompatibility, and mechanical integrity were performed in order to investigate the optimum surface modification process, suitable for biomaterial implants.
The study concluded that anodization created better adhesion between the MZC and PGCL coating. Furthermore, PGCL coated anodized MZC exhibited lower corrosion rate, good mechanical integrity, and better biocompatibility as compared with acid etched.
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Luan, LiKang [Verfasser], und M. [Akademischer Betreuer] Heilmaier. „Micro-tensile creep testing for polycrystalline and single crystalline nickel-based high temperature alloys / LiKang Luan ; Betreuer: M. Heilmaier“. Karlsruhe : KIT-Bibliothek, 2020. http://d-nb.info/1205001905/34.
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Whelchel, Ricky Lee. „Characterization of a nickel-base superalloy through electrical resistivity-microstructure relationships facilitated by small angle scattering“. Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41130.
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Nickel-base superalloys obtain high temperature mechanical properties through formation of precipitate phases formed via heat treatment. The precipitate microstructure evolves with heat treatment or thermal exposure, which can lead to degrading mechanical properties. This project focuses on the use of electrical resistivity as a non-destructive testing method to monitor the precipitate phase in Waspaloy (a polycrystalline nickel-base superalloy). The evolution of the precipitate microstructure is characterized throughout the volume of the specimens using both small angle neutron scattering (SANS) and ultra small angle X-ray scattering (USAXS) measurements. These measurements are also aided by microscopy and X-ray diffraction measurements.
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Msomi, Velaphi. „Modelling and testing smart aileron servo tabs : developing simulation tools for smart materials“. Thesis, Cape Peninsula University of Technology, 2015. http://hdl.handle.net/20.500.11838/2150.
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Thesis (DTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2015.This dissertation addresses the development and the testing of a simulation tool to be used to predict the behaviour of smart material/structures. Along with the development of the simulation tool, a new form of the model describing the behaviour of shape-memory alloy was developed and implemented. The proposed model was developed based on the existing cosine model, conventionally used in literature, but it uses hyperbolic tangent functions. The hyperbolic tangent function was chosen so as to allow the simulation of any range of temperatures. Experiments were performed to obtain the parameters to be used in the simulation and to validate the numerical results. Two different simulations were performed: a one dimensional FEA analysis with a two dimensional orientation (NiTi SMA wire simulation) and a three dimensional FEA analysis (NiTi SMA plate) [Msomi and Oliver, 2015]. Alongside the FEA analysis, two experiments were performed with the purpose of obtaining the material parameters to be used in FEA analysis and to compare the FEA results to the experimental results.
Airbus Company
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Hess, W. Gregory (Willard). „Cyclic behavior of shape memory alloy tendons and steel bolted t-stubs in beam-column connections“. Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/20740.
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Martin, Alexander Charles. „Initial Weldability of High Entropy Alloys for High Temperature Applications“. The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555496040477991.
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Lalgudi, Srinivas Bhadrinarayanan. „Experimental evalution of oxide growth in binary zirconium alloys along with pure zirconium and Zircaloy-2 by steam corrosion testing“. Thesis, KTH, Fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95310.
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Norton, Seth J. „Development of a gleeble based test for post weld heat treatment cracking in nickel alloys“. The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1057177289.
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Zaidi, Mohammed. „Experimental Testing and Reliability Analysis of Repaired SMA and Steel Reinforced Shear Walls“. Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35357.
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Superelastic Shape Memory Alloys (SMAs) are being explored as alternative reinforcing materials to traditional deformed steel reinforcement for seismic applications. The main advantage is the ability of the SMA to recover large nonlinear strains, which promotes the self-centering phenomenon. The primary objective of this research is to present the performance, before and after repair, of slender reinforced concrete shear walls, one reinforced internally with SMAs in the boundary zones within the plastic hinge region and other control wall reinforced with conventional steel only. The repair procedure included removal of damaged concrete within the plastic hinge region, replacing fractured and buckled reinforcement, followed by shortening of the SMA reinforcement in the boundary zones of SMA wall. The removed concrete was replaced with self-consolidating concrete, while the concrete above the plastic hinge region remained intact.
The SMA reinforced concrete shear wall (before and after repair) exhibited stable hysteretic response with significant strength, and displacement and energy dissipation capacities. In addition, the walls exhibited pinching in the hysteretic response as a result of minimizing the residual displacements due to the restoring capacity of the SMA reinforcement. The results demonstrate that SMA reinforced components are self-centering, permitting repairing of damaged areas. Furthermore, the SMA reinforcement is re-usable given its capacity to reset to its original state. The length of the SMA bars in the original and repaired wall, in addition to the presence of starter bars in the original wall, were significant factors in the location of failure of the walls.
The conventional steel wall prior to repair was unstable due to large residual displacements experienced during the original test. After repair the wall exhibited ratcheting in hysteretic response but with significant strength. The conventional wall, before and after repair, dissipated more energy than the SMA wall. This was the result of the wider hysteretic loops with reduced punching, but at the cost of large residual displacements. The starter bars in the conventional wall before repair controlled the location of failure, while the presence of couplers in the plastic hinge region was the main factor in determining the failure location in the repaired conventional wall.
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Cherif, Chokri, Rico Hickmann, Andreas Nocke, Matthias Schäfer, Klaus Röbenack, Sven Wießner und Gerald Gerlach. „Development and testing of controlled adaptive fiber-reinforced elastomer composites“. Sage, 2018. https://tud.qucosa.de/id/qucosa%3A35534.
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The integration of shape memory alloys (SMAs) into textile-reinforced composites produces a class of smart materials whose shape can be actively influenced. In this paper, Ni-Ti SMA wires are inserted during the weaving of a glass fiber reinforcement textile. This ‘‘active’’ reinforcement is then combined with an elastomeric matrix to produce a highly flexible composite sheet, which maintains high rigidity in the longitudinal direction. By activating the SMAs, high deflection ratios of up to 35% (relative to the component’s length) are achieved. To adjust the composite’s deflection to defined values, a closed-loop control is set up to adjust the current flow through the SMA wires. A control algorithm is designed and evaluated for several test cases. The high deformability and the controllable behavior show the high potential of these materials for applications such as aerodynamic flow control, automation and architecture.
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Aceves, Maureen. „Subsurface deformation micromechanisms induced during machining of titanium alloys at low temperatures, and a novel testing methodology to examine their machining behaviour“. Thesis, University of Sheffield, 2019. http://etheses.whiterose.ac.uk/23100/.
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The aerospace industry's drive towards higher productivity has led manufacturers to strive for higher surface speeds in metal cutting. Machining of titanium alloys leads to high temperatures attributed to their low thermal properties, resulting in high tool wear rates. To counter this, large amounts of coolants are used. These contain toxic chemicals, which are harmful to both people and the environment. To reduce these hazards, near-dry strategies such as cryogenic cooling and minimum quantity lubrication (MQL) are investigated in this thesis. A fundamental knowledge gap in the literature was identified, which is the characterisation of the subsurface microstructural evolution during plastic deformation in the machining of titanium alloys. Besides, its impact on surface integrity needs to be investigated in detail. The aims of this PhD research were (1) To determine the "machinability" of titanium alloys by designing a novel and straightforward cutting test. (2) To determine the effect of low temperatures (LTs) on the underlying deformation mechanisms during plastic deformation in the machining of aero-structural Ti-6Al-4V. In particular, during the application of a cryogen media such as LN2 and CO2. (3) To build a constitutive model to predict the experimental flow behaviour. (4) To analyse the imparted subsurface deformation and relate to its subsurface integrity. A material's inherent mechanical, physical and thermal properties strongly influence its machining behaviour. In the uniaxial compression test, it was determined that β annealed Ti-6Al-4V ELI: undergoes shear localisation even at quasi-static strain rates, has a high sensitivity to temperature and a lower sensitivity to strain rate. The higher the temperature, the higher the strain rate sensitivity. Plastic deformation at LTs exhibited higher flow stresses vs ambient temperature. The true strain at the onset of thermal instability (softening) and at fracture was identified, it was c30% smaller at LTs vs room temperature, leading to a reduction in c20% energy for cutting at LTs. The strain-hardening rate during plastic deformation decreases linearly with further imparted strain and decreases faster at LTs. Machining generates a graded subsurface microstructure. Four different regions were identified in this investigation. (1) Severe plastic deformation region (SPD), where a nanocrystalline grain structure was observed through electron microscopy from cryogenic machining under CO2, resulting in a significant increase in strength. (2) Gross plastic deformation region. (3) Twinned region. (4) Undeformed bulk. In conclusion, machining of titanium alloys at cryogenic temperatures is easier as a lower strain is required for shearing, leading to lower energy spent for chip generation. Nevertheless, a larger microstructural damage depth is introduced into the subsurface, leading to more potential sites for crack nucleation. The main challenges that lie ahead are: (1) to determine the extent of the effect the microstructural damage has on the fatigue life during dynamic loading, and (2) to determine whether easy diffusion is allowed to occur under thermal exposure, which would negatively affect their mechanical properties.
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ANTUNES, RENATO A. „Correlacao entre ensaios acelerados e ensaios de campo em corpos-de-provas de aco carbono e aco patinavel, sem e com revestimento“. reponame:Repositório Institucional do IPEN, 2002. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11036.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Tkacz, Jakub. „Reaktivita a úprava vlastností kovových materiálů“. Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2010. http://www.nusl.cz/ntk/nusl-216602.
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This thesis is focused on corrosion protection of magnesium alloys AZ 91. Very important is material corrosion in some environments and last but not least surface treatment as grinding, polishing and etching. Theoretical part of this thesis is about magnesium and magnesium alloy. It focuses on properties, in order to determine the best procedure for corrosion protection. It characterize material corrosion- for example corrosion in special environment (atmosphere, water, etc.) or elektrolyte corrosion. Big part of theoretical part is focused on electrochemistry, in particular kinetic aspects (Tafel diagrams, corrosion current, etc.) and potentiostatic testing, where are observed properties of material in relation to potential: corrosion potential Ecorr, brakedown potential Ebd and repassivation potential Erp. This work present preparing, utilization and positive or negative aspects of corrosion protection. Metallography is important too since metallographical preparation is crucial for the research on the material. Described metallography procedures are mounting, grinding, polishing, etching and interpretation. Experimental part of this thesis is in particular about corrosion properties of magnesium alloy AZ 91. It focuses on calculation of corrosion rate in defferent environments. Principle is mass defekt of the alloy. The environments are: destilled water, hot service water and 3% NaCl solution (like sea water). Last but not least are important. procedure manipulation with materials. Very important are choice and composition of solutions, etching time, choice of polishing cloth, lubricant solution and good pressure. Beacuse of this aspects can be show corrosion action of environments on magnesium alloy AZ 91 by photographies.