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Microescultura por laser de superfícies metálicas para manufatura de laminados híbridos metal/fibra / Laser microesculpture of metallic surfaces to hybrid fiber-metal laminatesDias, Rita de Cássia Costa 22 February 2013 (has links)
Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas. / This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.
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Microescultura por laser de superfícies metálicas para manufatura de laminados híbridos metal/fibra / Laser microesculpture of metallic surfaces to hybrid fiber-metal laminatesRita de Cássia Costa Dias 22 February 2013 (has links)
Este trabalho objetivou a manufatura de laminados híbridos metal-fibra (LMF) empregando-se chapas com 0,5 mm de espessura de liga-\'TI\'6\'AL\'4\'V\' com superfícies modificadas por laser de fibra de modo a otimizar a sua adesão com polímero termoplástico poli-sulfeto de fenileno (PPS). Observou-se que a microtextura superficial da liga metálica dependeu fortemente da potência do feixe laser, quando potências mais baixas levaram à verdadeira texturização da superfície metálica, enquanto que potências mais elevadas conduziram à ablação da mesma. A texturização superficial metálica sob laser de baixa potência aparentou ser a condição mais apropriada para a adesão metal-polímero por ancoragem mecânica de macromoléculas, o que foi contrabalanceado por elevados níveis de tensão residual das chapas metálicas, gerando grande distorção das mesmas e inviabilizando sua utilização. O emprego de uma potência intermediária (160 W) mostrou-se propício à otimização entre a adesão física entre metal-polímero e o nível de tensões residuais criado nas chapas metálicas. Concluiu-se que os espécimes extraídos do centro dos laminados metal-fibra exibem uma tensão limite média para falha por cisalhamento interlaminar consideravelmente superior à dos espécimes usinados a partir da borda dos LMF. O LMF manufaturado sob maiores pressão e temperatura exibiu uma maior compactação e melhor consolidação, culminando num máximo desempenho médio sob carga de cisalhamento interlaminar. Evidências de uma correlação entre o mecanismo de falha por cisalhamento interlaminar do corpo de prova e o seu nível de resistência a este tipo de carregamento mecânico foram documentadas e discutidas. / This work aimed at manufacturing hybrid fiber-metal laminates (FML) by employing 0,5 mm-thick \'TI\'6\'AL\'4\'V\'-alloy plaques with fiber laser modified surface in order to optimize metal adhesion with poli-phenylene sulfide (PPS) thermoplastic polymer. The surface microtexture of metallic alloy strongly depended upon the laser power, inasmuch as low-power laser led to true texturization of metal surface, whereas high-power laser light drove to its ablation. Surface metal texturization under low-power laser apparently was the most appropriate condition to metal-polymer adhesion via mechanical entanglement of macromolecules, which was offset by high levels of residual stresses on metallic plaques, bringing them quite warped and useless. The use of an intermediate laser power (160 W) has been shown benign to the optimization between metal-polymer physical adhesion and the residual stress level created in the metal plates. It has been concluded that testpieces machined from the FML central position exhibited average ultimate interlaminar shear strenght considerably higher than those extracted from the FML borders. The FML manufactured under higher pressure and temperature was more compacted and better consolidated, so that it displayed the greatest average performance under interlaminar shear loading. Evidences of a correlation between the failure mechanism by interlaminar shearing of test coupon and its allowance to this type of mechanical loading were documented and discussed.
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NUMERICAL MODELING AND EXPERIMENTAL ANALYSIS OF RESIDUAL STRESSES AND MICROSTRUCTURAL DEVELOPMENT DURING LASER-BASED MANUFACTURING PROCESSESNeil S. Bailey (5929484) 16 June 2020 (has links)
<p>This study is
focused on the prediction of residual stresses and microstructure development of
steel and aluminum alloys during laser-based manufacturing processes by means
of multi-physics numerical modeling.</p>
<p>A finite
element model is developed to predict solid-state phase transformation,
material hardness, and residual stresses produced during laser-based
manufacturing processes such as laser hardening and laser additive
manufacturing processes based on the predicted temperature and geometry from a
free-surface tracking laser deposition model. The solid-state phase
transformational model considers heating, cooling, and multiple laser track heating
and cooling as well as multiple layer tempering effects. The residual stress
model is applied to the laser hardening of 4140 steel and to laser direct deposition
of H13 tool steel and includes the effects of thermal strain and solid-state
phase transformational strain based on the resultant phase distributions.
Predicted results, including material hardness and residual stresses, are
validated with measured values.</p>
<p>Two dendrite
growth predictive models are also developed to simulate microsegregation and
dendrite growth during laser-based manufacturing processes that involve melting
and solidification of multicomponent alloys such as laser welding and laser-based
additive manufacturing processes. The first model uses the Phase Field method
to predict dendrite growth and microsegregation in 2D and 3D. It is validated
against simple 2D and 3D cases of single dendrite growth as well as 2D and 3D
cases of multiple dendrite growth. It is then applied to laser welding of
aluminum alloy Al 6061 and used to predict microstructure within a small domain.
</p>
The second model uses a novel technique by
combining the Cellular Automata method and the Phase Field method to accurately
predict solidification on a larger scale with the intent of modeling dendrite
growth. The greater computational efficiency of the this model allows for the
simulation of entire weld pools in 2D. The model is validated against an
analytical model and results in the literature.
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Engineering of Temperature Profiles for Location-Specific Control of Material Micro-Structure in Laser Powder Bed Fusion Additive ManufacturingLewandowski, George 15 June 2020 (has links)
No description available.
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Improving Fatigue Life of LENS Deposited Ti-6Al-4V through Microstructure and Process ControlPrabhu, Avinash W. 02 June 2014 (has links)
No description available.
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Microstructural Characterization of LENS<sup>TM</sup> Ti-6Al-4V: Investigating the Effects of Process Variables Across Multiple Deposit GeometriesDavidson, Laura Christine January 2018 (has links)
No description available.
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Laser Additive Manufacturing of Magnetic MaterialsMikler, Calvin V. 08 1900 (has links)
A matrix of variably processed Fe-30at%Ni was deposited with variations in laser travel speeds as well and laser powers. A complete shift in phase stability occurred as a function of varying laser travel speed. At slow travel speeds, the microstructure was dominated by a columnar fcc phase. Intermediate travel speeds yielded a mixed microstructure comprised of both the columnar fcc and a martensite-like bcc phase. At the fastest travel speed, the microstructure was dominated by the bcc phase. This shift in phase stability subsequently affected the magnetic properties, specifically saturation magnetization. Ni-Fe-Mo and Ni-Fe-V permalloys were deposited from an elemental blend of powders as well. Both systems exhibited featureless microstructures dominated by an fcc phase. Magnetic measurements yielded saturation magnetizations on par with conventionally processed permalloys, however coercivities were significantly larger; this difference is attributed to microstructural defects that occur during the additive manufacturing process.
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Simulation of Laser Additive Manufacturing and its ApplicationsLee, Yousub January 2015 (has links)
No description available.
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Development of Simultaneous Transformation Kinetics Microstructure Model with Application to Laser Metal Deposited Ti-6Al-4V and Alloy 718Makiewicz, Kurt Timothy 09 August 2013 (has links)
No description available.
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Experimental study of double-pulse laser micro sintering, ultrasound-assisted water-confined laser micromachining and laser-induced plasmaWeidong Liu (15360391) 29 April 2023 (has links)
<p>This dissertation presents research work related to laser micro sintering, laser micro machining and laser-induced plasma. Firstly, we present extensive experimental studies of double-pulse laser micro sintering (DP-LMS), which typically utilizes the high pressure generated by laser-induced plasma over the powder bed surface to promote molten flow and enhance densification. Chapter 2 shows a single-track experimental study of the DP-LMS process using cobalt powder. The related fundamental mechanisms and effects of different laser parameters on the sintering results are analyzed with the help of <em>in-situ</em> time-resolved temperature measurements. Chapter 3 shows a multi-track experimental study of the DP-LMS process using iron powder. The sintered materials are characterized via the top surface porosity, elemental composition, grain microstructure, nanohardness and metal phase. Three strategic guidelines for laser parameter selection are summarized in the end. Chapter 4 shows time-resolved imaging and OES measurements for plasma induced during DP-LMS. The plasma temperature and free electron number density are deduced by its optical emission spectra (OES). These three chapters have clearly demonstrated DP-LMS can produce much more continuous and densified materials than LMS only using the sintering or pressing laser pulses.</p>
<p><br></p>
<p>Then, we present laser micro grooving of silicon carbide (SiC) in Chapter 5 by ultrasound-assisted water-confined laser micromachining (UWLM), in comparison with laser machining in water without ultrasound and laser machining in air. UWLM applies <em>in-situ</em> ultrasound to the water-immersed workpiece surface to improve the machining quality and/or productivity. Time-resolved water pressure measurements are carried out to help analyze relevant mechanisms. It has been demonstrated UWLM can be a competitive approach to produce high-quality micro grooves on SiC. The crack problem appears to be effectively solved using a high pulse repetition rate.</p>
<p><br></p>
<p>Finally, we report a double-front phenomenon for plasma induced by high-intensity nanosecond laser ablation of aluminum in Chapter 6. An additional plasma front is observed via an intensified CCD (ICCD) camera, which propagates very fast at the beginning but stops propagating soon after the laser pulse mostly ends. Its formation could be caused by the inverse bremsstrahlung absorption of laser energy by the ionized ambient gas. Three possible mechanisms on how the ambient gas breakdown is initiated are proposed. </p>
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