Browsing by Subject "Aluminum"

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Construction and validation of a hot torsion testing instrument
(2014-05) Weldon, Andrew James; Taleff, Eric M.
The need to increase vehicle performance, particularly fuel efficiency, has led to an increased interest in using lightweight metals for vehicle structural components. Lightweight aluminum alloys offer the potential to significantly reduce vehicle mass when structural components that use steel are replaced. Mass reduction is a very efficient route to increase vehicle performance. In vehicles with traditional powertrains, mass reduction can increase fuel efficiency. In vehicles with electrical powertrains, mass reduction can increase driving range. Regardless of the specific structural application, the best performance of any aluminum alloy is only obtained by achieving a microstructure that produces the best material properties. For wrought aluminum alloys, hot and cold deformation steps are critical to obtaining a desirable microstructure prior to the forming of a final component. For sheet material, the first step in controlling the final microstructure is microstructure evolution during hot rolling the cast ingot material. Hot rolling precedes cold rolling of the sheet to final thickness in most commercial sheet manufacturing operations. Microstructure during hot rolling is difficult to study because it requires a combination of high temperatures, fast strain rates and large strains to do so. Furthermore, specimens for microstructural examination must be extracted from these conditions while retaining the characteristics of the specific conditions that are to be studied. Hot torsion testing is the traditional approach to meeting these experimental requirements. In this investigation, a new hot torsion testing instrument is designed, fabricated and validated to enable future experiments that will elucidate microstructure evolution under conditions pertinent to hot rolling. This new instrument is integrated with computerized control and data acquisition systems. Validation experiments were conducted to characterize its capabilities. It is concluded that the completed instrument meets the requirements necessary to study plastic deformation and microstructure evolution in aluminum alloys under conditions relevant to hot rolling.
Development of an experimental facility for biaxial compressive testing of fiber composite materials
(1991) Kotziapashis, Andreas Evangelou, 1962-; Kyriakides, S.
The purpose of this study was the development of a testing facility and test specimen for the characterization of laminated composites under biaxial compressive stress states. A biaxial testing facility capable of applying almost arbitrary stress paths in the in-plane compressive stress regime, to circular cylindrical test specimens, was designed, assembled and calibrated. The required biaxial load is achieved by applying combined axial compression and external pressure to the cylinder. The performance of the biaxial facility was verified by performing several exploratory experiments on Aluminum and Graphite/Epoxy specimens. Test specimens and testing procedures were designed such that material failure rather than structural failure would prevail under a prescribed loading path. A circular cylindrical shell was selected over the other possible biaxial test specimens, for its relatively simple manufacture, its potential in achieving a relatively homogeneous stress state within the test section and a boundary region that is relatively free of stress concentrations. An experiment was performed on a circular cylindrical Graphite/Epoxy specimen designed to fail by material failure. The test was conducted under hydrostatic loading. Failure of the specimen occurred at a pressure of 9035 psi. Post failure evaluation of the specimen confirmed that failure was the result of local buckling or “kinking” of the hoop fibers at the outer layers of the specimen
Drinking water treatment by alum coagulation : competition among fluoride, natural organic matter, and aluminum
(2012-12) Alfredo, Katherine Ann; Lawler, Desmond F.; Katz, Lynn Ellen; Liljestrand, Howard M.; Holcombe, James A.
Some community water systems using sources containing elevated levels of fluoride, in the United States and worldwide, struggle to treat their drinking water to healthy fluoride concentrations. Many treatment plants in the U.S. currently use aluminum based salts, such as aluminum sulfate and polyaluminium chloride, as coagulants during conventional treatment for removal of particles from drinking water sources. Moreover, enhanced aluminum sulfate, or alum, coagulation requires higher concentrations of aluminum added to the process and has been shown to be effective for removal of disinfectant byproduct precursors, i.e., natural organic matter (NOM). The presence of fluoride may interfere with the formation of aluminum hydroxide precipitates, and interrelationships among NOM, aluminum precipitation and fluoride removal are not well understood. A fundamental understanding of how fluoride alters the properties of aluminum precipitates and how fluoride and NOM molecules compete as ligands interacting with soluble aluminum species is lacking. As a result, the development of guidelines for implementation and optimization of a treatment scheme that uses aluminum in the presence of fluoride requires a multi-faceted approach in which the development of a mechanistic understanding of these interactions is conducted in concert with macroscopic experiments to identify optimum conditions for simultaneous removal of fluoride and NOM. To date, little research has looked at the efficiency of removing both fluoride and organics from the perspective of the precipitation process. To provide a foundation for revising treatment techniques, this research evaluated the effect of co-precipitating aluminum in the presence of fluoride, organics, and in multi-ligand systems to characterize the solid precipitate and removal competition. This research verified the formation of a co-precipitate in the presence of fluoride and certain low molecular weight organics. Co-precipitation from organics and fluoride competes for removal, especially at low alum coagulant doses, complicating treatment for resource limited areas.
Fast rate fracture of aluminum using high intensity lasers
(2009-08) Dalton, Douglas Allen; Ditmire, Todd R.
Laser induced shock experiments were performed to study the dynamics of various solid state material processes, including shock-induced melt, fast rate fracture, and elastic to plastic response. Fast rate fracture and dynamic yielding are greatly influenced by microstructural features such as grain boundaries, impurity particles and alloying atoms. Fast fracture experiments using lasers are aimed at studying how material microstructure affects the tensile fracture characteristics at strain rates above 106 s-1. We used the Z-Beamlet Laser at Sandia National Laboratories to drive shocks via ablation and we measured the maximum tensile stress of aluminum targets with various microstructures. Using a velocity interferometer and sample recovery, we are able to measure the maximum tensile stress and determine the source of fracture initiation in these targets. We have explored the role that grain size, impurity particles and alloying in aluminum play in dynamic yielding and spall fracture at tensile strain rates of ~3x106 s-1. Preliminary results and analysis indicated that material grain size plays a vital role in the fracture morphology and spall strength results. In a study with single crystal aluminum specimens, velocity measurements and fracture analysis revealed that a smaller amplitude tensile stress was initiated by impurity particles; however, these particles served no purpose in dynamic yielding. An aluminum-magnesium alloy with various grain sizes presented the lowest spall strength, but the greatest dynamic yield strength. Fracture mode in this alloy was initiated by both grain boundaries and impurity particles. With respect to dynamic yielding, alloying elements such as magnesium serve to decrease the onset of plastic response. The fracture stress and yield stress showed no evidence of grain size dependence. Hydrodynamic simulations with material strength models are used to compare with our experiments. In order to study the strain rate dependence of spall in aluminum we used a shorter pulsed laser and thinner targets. From these experiments we do not observe an increase in spall strength for aluminum up to strain rates of ~2x107 s-1.
Fluoride, natural organic matter, and particles : the effect of ligand competition on the size distribution of aluminum precipitates in flocculation
(2016-05) Herrboldt, Jonathan Philip; Lawler, Desmond F.; Katz, Lynn Ellen
Fluoride occurs at elevated concentrations naturally in surface and ground waters around the world. If consumed at low concentrations in drinking water (< 1.5 mg/L), fluoride is shown to reduce the occurrence of dental caries and the Centers for Disease Control and Prevention named fluoridation of public water systems one of the 10 Great Public Health Achievements of the 20th Century (CDC, 1999). However, prolonged exposure to high concentrations of fluoride (> 2.0 mg/L) causes adverse health effects to teeth and bones. For this reason the United State Environmental Protection Agency (USEPA) enacted a maximum contaminant level (MCL) for fluoride at 4.0 mg/L. This rule is currently under review following a recent risk assessment and may be lowered. If the MCL were lowered, water systems previously meeting treatment standards would suddenly find themselves out of compliance and will need to implement additional treatment to meet the new standard. Defluoridation by alum coagulation is a proposed defluoridation method. However, the interaction between fluoride and natural organic matter (NOM) and their effects on the particle size distribution of aluminum precipitates is not well understood. Because the particle size distribution of aluminum precipitates is an important parameter in the efficiency of sedimentation and filtration systems, a thorough understanding of these interactions and their potential effect on sedimentation and filtration is needed to inform the implementation of defluoridation by alum coagulation. This work utilized a series of jar tests on synthetic surface water to determine the effect of fluoride and NOM on the particle size distribution of aluminum precipitates. It was found that fluoride caused the volume distribution of aluminum precipitates to shift toward smaller particle sizes. However, NOM caused the formation of a larger number of aluminum precipitates, which resulted in a dramatic increase in the total volume of precipitates. When both fluoride and NOM were in the system, a combination of the two effects was observed: the volume distribution shifted toward smaller particle sizes but the peak of the distribution shifted toward a greater volume, indicating both smaller particles were being formed and a greater overall volume of particles precipitated.
On the axial crushing and failure of aluminum alloy tubes : experiments and numerical simulations
(2020-05-01) Haley, Jake Andrew; Kyriakides, S.
The use of aluminum alloys for light-weighting purposes in energy absorbing components of automobiles is hindered by the relatively low ductility and more complicated constitutive behavior of these alloys. This study presents results from series of quasi-static and dynamic axial crushing experiments on extruded Al-6061-T6 circular tubes of varying D/t ratios. A custom drop-weight testing facility was used to perform the dynamic experiments. Crushing led to axisymmetric, mode-2, and mode-3 concertina folding. In the quasi-static experiments, the folding was monitored using time-lapse photography; dynamic crushing was monitored using high-speed photography. The crushing responses and energy absorption capacities are evaluated and failures were recorded. Failure was observed in most of the experiments with the severity depending on the D/t and mode of folding. The experiments are simulated with three-dimensional, nonlinear finite element analysis using the von Mises, the non-quadratic Hosford, and the calibrated anisotropic Yld04-3D models. The Yld04-3D model was found to most accurately reproduce the structural response under both quasi-static and dynamic loadings. This model was used to the monitor the strains induced in two example cases: axisymmetric folding under quasi-static loading, and mode-2 folding under dynamic loading. The analysis predicted maximum strains to develop at locations on the model tube where failure is observed on the specimen in the experiments. It is concluded that the Yld04-3D constitutive model is most suitable for the prediction of the structural response and failure in tube crushing of this aluminum alloy.
On the crushing of honeycomb under axial compression
(2010-12) Wilbert, Adrien; Kyriakides, S.; Ravi-Chandar, Krishnaswamy
This thesis presents a comprehensive study of the compressive response of hexagonal honeycomb panels from the initial elastic regime to a fully crushed state. Expanded aluminum alloy honeycomb panels with a cell size of 0.375 in (9.53 mm), a relative density of 0.026, and a height of 0.625 in (15.9 mm) are laterally compressed quasi statically between rigid platens under displacement control. The cells buckle elastically and collapse at a higher stress due to inelastic action. Deformation then first localizes at mid-height and the cells crush by progressive formation of folds; associated with each fold family is a stress undulation. The response densifies when the whole panel height is consumed by folds. The buckling, collapse, and crushing events are simulated numerically using finite element models involving periodic domains of a single or several characteristic cells. The models idealize the microstructure as hexagonal, with double walls in one direction. The nonlinear behavior is initiated by elastic buckling while inelastic collapse that leads to the localization observed in the experiments occurs at a significantly higher load. The collapse stress is found to be mildly sensitive to various problem imperfections. For the particular honeycomb studied, the collapse stress is 67% higher than the buckling stress. It was also shown that all aspects of the compressive behavior can be reproduced numerically using periodic domains with a fine mesh capable of capturing the complexity of the folds. The calculated buckling stress is reduced when considering periodic square domains as the compatibility of the buckles between neighboring cells tends to make the structure more compliant. The mode consisting of three half waves is observed in every simulation but its amplitude is seen to be accented at the center of the domains. The calculated crushing response is shown to better resemble measured ones when a 4x4 cell domain is used, which is smoother and reproduces decays in the amplitude of load peaks. However, the average crushing stress can be captured with engineering accuracy even from a single cell domain.
On the hydraulic bulge testing of thin sheets
(2013-12) Mersch, John Philip; Kyriakides, S.
The bulge test is a commonly used experiment to establish the material stress-strain response at the highest possible strain levels. It consists of a metal sheet placed in a die with a circular opening. It is clamped in place and inflated with hydraulic pressure. In this thesis, a bulge testing apparatus was designed, fabricated, calibrated and used to measure the stress-strain response of an aluminum sheet metal and establish its onset of failure. The custom design incorporates a draw-bead for clamping the plate. A closed loop controlled servohydraulic pressurization system consisting of a pressure booster is used to pressurize the specimens. Deformations of the bulge are monitored with a 3D digital image correlation (DIC) system. Bulging experiments on 0.040 in thick Al-2024-T3 sheets were successfully performed. The 3D nature of the DIC enables simultaneous estimates of local strains as well as the local radius of curvature. The successful performance of the tests required careful design of the draw-bead clamping arrangement. Experiments on four plates are presented, three of which burst in the test section as expected. Finite deformation isotropic plasticity was used to extract the true equivalent stress-strain responses from each specimen. The bulge test results correlated well with the uniaxial results as they tended to fall between tensile test results in the rolling and transverse directions. The bulge tests results extended the stress-strain response to strain levels of the order of 40%, as opposed to failure strains of the order of 10% for the tensile tests. Three-dimensional shell and solid models were used to investigate the onset of localization that precedes failure. In both models, the calculated pressure-deformation responses were found to be in reasonable agreement with the measured ones. The solid element model was shown to better capture the localization and its evolution. The corresponding pressure maximum was shown to be imperfection sensitive.
Retrogression forming and reaging of two high strength aluminum alloys
(2021-05-07) Rader, Katherine Elizabeth; Taleff, Eric M.; Kovar, Desiderio; Mangolini, Filippo; Engelhardt, Michael D
Retrogression forming and reaging is a new scientific approach to warm forming high strength aluminum alloys designed to produce automotive components with tensile strengths equivalent or superior to those of the T6 temper. Retrogression forming and reaging is investigated for two high strength aluminum alloys, AA7075-T6 and AA6013-T6. A retrogression and reaging response is identified in AA6013-T6. Retrogression and reaging behaviors are characterized in AA7075-T6 and AA6013-T6. The activation energies for retrogression are measured as 97 kJ/mol for AA7075-T6 and 160 kJ/mol for AA6013-T6. These data are used to develop a method for predicting appropriate times and temperatures for retrogression. The tensile behaviors of AA7075 and AA6013 are fully characterized across conditions appropriate for retrogression forming. Plastic flow of both materials at the warm temperatures examined is determined to be thermally activated. The activation energies of plastic flow are measured as 221 kJ/mol for AA7075 and 253 kJ/mol for AA6013. Ductility improves at elevated temperatures because fracture is delayed until after necking. Retrogression forming conditions are recommended that provide enhanced ductility and allow a single reaging heat treatment to restore strength to that of the T6 condition after forming. Forming experiments implement retrogression forming to produce parts with a geometry representative of automotive structural components. In-plane major strains of up to 22 % are measured in these parts. Accumulated reduced retrogression time is used to successfully design retrogression forming processes and enable a single reaging heat treatment to restore T6 strength. Retrogression forming followed by a single reaging heat treatment produced strengths equivalent or superior to those of the original T6 condition. Simultaneous plastic deformation during a retrogression heat treatment does not impede the ability of the recommended reaging heat treatment or the automotive paint-bake to restore T6 strength in AA7075. Reaging with the automotive paint-bake, a heat treatment process applied to the vehicle body-in-white, might be effective for restoring T6 strength in retrogression formed automotive components.
Retrogression-reaging and hot forming of AA7075
(2014-05) Ivanoff, Thomas Alexander; Taleff, Eric M.
The retrogression-reaging (RRA) and hot forming behavior of AA7075 were studied. AA7075 is a high-strength alloy used in applications where weight is of particular importance, such as in automobiles. Like many of the high-strength aluminum alloys, AA7075 requires elevated temperature forming to achieve ductility comparable to steels at room temperature. Since AA7075 is a precipitation hardening alloy, heat treatments during forming and production need to be closely controlled to limit any loss of strength due to changes in the microstructure. Two new forming concepts are introduced to explore the feasibility of forming AA7075 in manners compatible with current automotive manufacturing processes. They are RRA forming and solution forming. These concepts seek to improve upon the room-temperature formability of AA7075-T6 and incorporate the paint-bake cycle (PBC) into the heat treatment process. The PBC is a mandatory heat treatment used to cure the paint applied to automobiles during production. Currently, the PBC is conducted at 180 °C for 30 minutes. RRA behavior was studied with molten salt bath treatments between 200 and 350 °C. The PBC was used in lieu of the standard 24 hour reaging treatment conducted at 121 °C. It was determined that retrogression treating below 250 °C was acceptable for RRA forming, with retrogressing at 200 °C producing the hardest material after reaging by the PBC. The formability of AA7075-T6 during RRA forming was evaluated by tensile testing at 200 and 225 °C. Ductility of AA7075-T6 at RRA forming temperatures was double compared to those produced at room temperature. RRA forming was demonstrated to achieve this improved ductility and a final material hardness after the PBC of only slightly less than the peak-aged condition. In addition, solution forming behavior was studied at 480 °C. Solution forming can increase ductility compared to RRA forming, but it requires aging at 121 °C prior to the PBC to produce peak-aged hardness.
Selective laser melting of elemental aluminum silicon mixtures
(2016-12) Roberts, Christopher Eli; Bourell, David Lee
Additive manufacturing technologies have generated increasing interest by public, government, and academic institutions alike. While past research has increased part quality, build speed, and process reliability, there remains few materials which can be processed through selective laser melting (SLM). Historically, metal feedstock for powder bed fusion processes have been pre-alloyed, near-eutectic grades similar to traditional casting alloys. This thesis discusses an alternative processing route utilizing elemental mixtures for off-eutectic, difficult-to-processes alloys which exhibit a large freezing range and solidification shrinkage such as that found in many wrought aluminum alloys. One such alloy is aluminum 6061. This material is of great commercial interest due to its widespread use within the traditional manufacturing industry, successful prior certification in aerospace industries, and good mechanical properties. Since AA6061 consists of multiple elements, a representative system of aluminum and silicon was utilized for consideration in this thesis. A powder feedstock of commercially pure aluminum and silicon was prepared and processed through SLM. Samples were then heat treated to homogenize the silicon aluminum matrix. Metallographic analysis was performed throughout the experiment to determine the underlying materials processes. Dense parts without solidification cracking were produced and silicon dissolution into the aluminum matrix was verified using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). The combined-powder process that is outlined could be expanded to other material systems which are not compatible with current additive manufacturing technologies. An overview of the theory behind the use of elemental mixtures as well as the results from the aluminum silicon (Al-Si) mixture are presented. Future work needed to be accomplished and potential challenges associated with this processing route are also discussed.
Selective laser melting of metals using elemental mixtures
(2018-06-14) Roberts, Christopher Eli; Bourell, David Lee; Taleff, Eric M; Kovar, Desiderio; Juenger, Maria
Processes to additively manufacture (AM) metal parts have greatly improved in recent years, garnering increasing interest from the public and industry. However, while improvements in part quality, reliability, build speed, and build volume have been made, the variety of commercially available materials remains quite limited. In particular, only one aluminum alloy, AlSi10Mg, is in current widespread production despite the abundance of wrought and cast aluminum alloy grades in use by traditional manufacturing processes. Attempts to process off-eutectic alloys have resulted in poor part quality and density primarily due to the presence of hot tearing throughout the microstructure. The limited materials space greatly inhibits the further penetration of AM processes into industry as the materials are both unfamiliar to designers and are performance limited. In the present study, a processing approach to process traditionally AM incompatible materials utilizing elemental mixtures was investigated. To determine the constraints unique to this approach, metallographic samples were fabricated from mixtures of elemental aluminum, silicon, and magnesium approximating the composition of AA6061. Additional samples using aluminum-Mg₂Si and aluminum-copper mixtures were produced to analyze varying aspects of the proposed processing approach. After production, samples were homogenized and aged in post-processing to achieve the desired alloy and mechanical performance. Optical microscopy, electron microscopy, and energy dispersive x-ray spectroscopy (EDS) were utilized to map the processing window while hardness testing and EDS were utilized to indirectly indicate proper homogenization and aging. It was shown that the elemental mixture approach shows great promise in minimizing hot tearing in certain metal systems when processed through selective laser melting; however, several factors must be considered when utilizing this approach. Several avenues to addressing challenges associated with processing such mixtures were presented along with design rules to guide further exploration of this processing route.
Simulation and experimental investigation of hot forming of aluminum alloy AA5182 with application towards warm forming
(2012-05) Lee, John Thomas; Taleff, Eric M.; Bourell, David L.
This study focuses on hot and warm forming properties of aluminum alloy AA5182 sheet, with attention toward warm forming, by using gas pressure to form sheet material. A temperature range of 300°C to 450°C and a pressure range of 690 kPa (100 psi) to 2410 kPa (350 psi) were used in a test matrix of twenty one different test conditions for gas-pressure forming of a sheet into hemispherical dome in a gas-pressure bulge test. Multiple sets of tensile data were used to develop a material model that predicts the dome height and shape of an axisymmetric bulge specimen at any given time during forming. In simulations of the forming process, 17 simulations of the total 21 experimental conditions showed good agreement with the experimentally measured dome heights throughout forming tests. The four cases that did not show good agreement between simulation and experiment are a result of strain-hardening in the material during forming. Strain hardening was not significant in tension testing of specimens and was not accounted for in the material model, which considered only strain rates slower than for these experimental bulge testing. This demonstrates an effect which must be considered in future simulations to predict forming approaching warm conditions. Two experimental bulge specimens were cross-sectioned post forming and grain sizes were measured to determine if grain growth occurred during the forming process. Experimental bulge specimens show no grain growth during the forming process. The tensile specimens from which the material model data were taken were measured to determine if plastic anisotropy was a possible issue. All specimens measured were proved to have deformed nearly isotropically. The results of this study show that predicting warm and hot forming of aluminum alloy AA5182 using gas pressure is possible, but that a more complex material model will be required for accurate predictions of warm forming. This is a very important step toward making hot and warm forming commercially viable mass production techniques.
Solid-state production of single-crystal aluminum and aluminum-magnesium alloys
(2010-08) Pedrazas, Nicholas Alan; Taleff, Eric M.; Bourell, David L.
Three sheet materials, including high purity aluminum, commercial purity aluminum, and an aluminum-magnesium alloy with 3 wt% magnesium, were produced into single-crystals in the solid-state. The method, developed in 1939 by T. Fujiwara at Hiroshima University, involves straining a fully recrystallized material then passing it into a furnace with a high temperature gradient at a specific rate. This method preserves composition and particulate distributions that melt-solidification methods do not. Large single crystals were measured for their orientation preferences and growth rates. The single-crystals were found to preferably orient their growth direction to the <120> to <110> directions, and <100> to <111> directions normal to the specimen surface. The grain boundary mobility of each material was found to be a function of impurity content. The mobility constants observed were similar to those reported in the literature, indicating that this method of crystal growth provides an estimate of grain boundary mobility. This is the first study the effect of impurities and alloying to this single-crystal production process, and to show this method’s applicability in determining grain boundary mobility information.
Synthesis, characterization, and applications of mono([mu]-alkoxo)bis(alkylaluminum) catalysts for epoxide polymerization
(2021-05-10) Imbrogno, Jennifer Francesca; Lynd, Nathaniel A.; Keitz, Benjamin K; Rosales, Adrianne; Rose, Michael
Recent advances in medicine, membranes for gas separations, and batteries have been made possible through associated advances in polyether materials. Further advances will be enabled by continued materials innovation enabled by advances in polymerization catalysis. Polyethers, derived from epoxides, represent a versatile class of functional polymeric materials with the potential for true compositional control of structure-property relationships in a macromolecular platform due to the high thermodynamic ring-strain driving force for polymerization. Despite this promise, there is currently no consensus polymerization technique available for epoxides that provides access to polyether materials with consistently controlled molecular weights, chain-end functionality, tolerance to monomer functionality, and is available to the non-specialist. The Vandenberg catalyst is a well-established, empirically developed, industrial catalyst solution for polyether-based elastomers derived from epoxides. Investigation of compositionally related complexes led to the discovery of well-defined mono(µ-alkoxo)bis(alkylaluminum) (MOB) complexes which function as effective catalyst/initiator for epoxide polymerizations, capable of producing > 10 kg/mol polyethers in minutes depending on MOB composition and epoxide monomer. Variation of alkylaluminum used in the MOB synthesis led to a four-fold variation in polymerization rate, whereas variation of N,N′-alkylamino-ethanol structure led to a 400-fold variation in polymerization rate of epichlorohydrin. The MOB structure appeared to rearrange and dimerize upon addition of polar compounds, E.g., epoxide monomers, revealing an aluminum alkoxide as the site of monomer addition and a N–Al Lewis pair functioning as catalyst. With new epoxide polymerization catalyst in hand, a series of investigations into new polymer structure and compositions was possible. Chain-extension polymerizations were conducted from poly(ethylene oxide) macroinitiators to create block polymer materials, whose architecture and solution self-assembly were investigated. Atactic polyethers exhibiting semi-crystallinity mediated by long alkyl side chains were synthesized and studied as phase-change materials. Finally, our synthetic advances enabled a fundamental study of polymer electrolyte structure-property relationships by varying dielectric constants among a series of homologous polymer structures revealing the important role of polarity in dictating ion transport properties. These studies highlight the enabling role of new polymerization catalysis in materials science and engineering.
T
(2013-05) Vu, Bich N.; Mickey, Susan E.; Isackes, Richard; Stoney, John
T is a thesis installation that explores the semiotics of public dress through the fundamentals of sculpture: mass and form, material and process, site and context. This exhibition consists of four T-shirt shaped objects made out of steel, aluminum, talcum, and sugar . A T-shirt is arguably a universally recognizable article of clothing, but its familiarity when juxtaposed with everyday material challenges the social identity of dress. As a theatrical designer experimenting with sculpture, Bich Vu investigates the ways clothing and space facilitates a narrative. The different arrangements of the objects within the installation are performances created in collaboration with guest directors and choreographers from the Department of Theatre & Dance.
Tear resistance and stress relaxation behavior of high-strength AA7075-T6 aluminum alloy sheet at warm temperatures near 200 °C
(2020-12-09) Nikolai, Daniel Edward; Taleff, Eric M.
The use of lightweight metals is of great interest to the automotive industry for improving vehicle efficiency. The automotive industry is particularly interested in lightweight metals with high strength-to-density ratios that can perform well in crash scenarios. To this end, high-strength aluminum alloys are investigated for body-in-white applications. Currently, 6xxx series aluminum alloys are the most commonly used aluminum materials for the body-in-white. AA7075-T6 offers comparable density to and significantly higher strength than the 6xxx series aluminum alloys. However, AA7075-T6 demonstrates low ductility and formability at room temperature, which are barriers to producing and mechanically fastening components for the body-in-white. Prior investigations by Rader et. al. demonstrated that the ductility of AA7075-T6 sheet is approximately doubled at warm temperatures near 200 °C, allowing it to be stamped to complex geometries. However, joining of AA7075-T6 sheet remains a significant challenge. The present study investigates the material behaviors necessary to determine the potential for joining of AA7075-T6 sheet at warm temperatures by self-piercing riveting. Self-piercing riveting is commonly used with the lower strength 6xxx series aluminum alloys in the automotive industry. Tear-resistance and stress-relaxation experiments are conducted to evaluate the potential for successfully implementing of self-pierce riveting in AA7075-T6 sheet at warm temperatures. Tear energy measurements at warm temperatures appropriate for retrogression heat treatments in AA7075-T6 are compared to measurements at room temperature. A four-fold increase in the tear energy of AA7075-T6 at warm temperatures suggests a high possibility for success with self-piercing riveting at these temperatures. Rapid stress relaxation of up to 45% of the flow stress produced during deformation at warm temperatures indicates a potentially significant reduction in residual stresses after deformation, which should reduce spring-back after forming and reduce the chance of delayed cracking in AA7075-T6 sheet after the application of a self-piercing rivet. These experimental results support the potential to successfully apply a self-piercing rivet to AA7075-T6 sheet at a warm temperature while simultaneously retrogressing the material. Because a subsequent reaging heat treatment is known to restore full strength following a retrogression heat treatment, the retrogression riveting and reaging process is proposed as a method to successfully join AA7075-T6 sheet material while retaining the full strength of the T6 condition.
The tensile behavior of AA6013 at room temperature and 240 °C
(2021-12-07) Fascitelli, Dominic Gianni; Taleff, Eric M.
Automotive manufacturers are pursuing technologies, such as lightweighting, that improve vehicle fuel-efficiency and reduce emissions. High-strength aluminum alloys might provide performance equal to the current ultra-high-strength steels while decreasing vehicle weight. High-strength 6xxx-series aluminum alloys, such as AA6013, are candidates for lightweighting structural components of vehicles because of their high strength-to-weight ratios compared to steel. In the peak-aged condition, these alloys often lack the ductility necessary to form complex part geometries at room temperature. Forming at elevated temperatures increases the ductility but can reduce strength. Retrogression forming and reaging (RFRA) is a relatively new technology for warm forming parts in high-strength aluminum alloys and then recovering strength to equal the peak-aged condition. Previous studies on aluminum alloy AA6013 performed by Rader et al. demonstrated a significant response to retrogression and reaging. New data for AA6013 are presented from tension tests at room temperature and 240 °C, an appropriate temperature for retrogression of this alloy. The effects of different heat treatments on room temperature properties are investigated. The effects of temperature and time at temperature on plastic deformation are investigated using experiments at 240 °C. Retrogression from the T6 temper reduced room-temperature strength by 3.5%, but subsequent reaging restored strength to within 2% of the original T6 temper. At 240 °C, the yield stress was 25 to 30% lower and elongations after rupture were 42% higher than at room temperature for the T6 temper. Stress relaxation at 240 °C decreased stress by 32 to 43% at a fixed elongation within approximately three minutes. These results suggest that RFRA could be viable for forming complex components in AA6013-T6