Browsing by Subject "Aluminum"
Now showing 1 - 20 of 29
Results Per Page
Sort Options
Item A quantitative analysis of the flame produced by a gas-fueled propellant simulating burner including: soot field characterization, temperature diagnostic techniques, spectral analysis, heat flux, and aluminum particle combustion(Texas Tech University, 2007-05) Jackson, Matthew N.; Pantoya, Michelle; Berg, Jordan M.; Seshaiyer, Padmanabhan; Parameswaran, Siva; Levitas, ValeryThis study details the characterization and implementation of a burner devised to simulate solid propellant fires. The burner is designed with the ability to introduce particles (particularly aluminum) to a gas reactant flame. This work encompasses four different studies that both evaluate the performance of the burner as well as display its ability as a versatile test platform. First, the burner is used to create a high temperature, heavily sooting flame as the basis of the development of a virtual thermocouple model in a fire code at Sandia National Laboratories (VULCAN). Secondly, similar conditions are created to evaluate the effectiveness of dual-pump coherent anti-Stokes Raman scattering (CARS) measurements in heavily sooting flames. These thermometry measurements indicate the temperature profiles that exist in fuel rich conditions. Laser induced incandescence (LII) measurements map soot volume fractions and give insight into the reactant gas mixing in the flame structure. The third project evaluates the aluminized flame conditions produced by this burner based on temperature, heat flux, spectral emission, product species, and particle velocity. Using these results, flame performance is quantified in comparison to other known flames including hydrocarbon and propellant fires. Lastly, an aluminized flame is used to measure the burning rate of the particles. This work indicates the capability of the burner as test platform for Sandia’s ongoing effort to develop a comprehensive particulate combustion model, particularly in propellant fires. These studies accomplish two primary objectives: (1) characterization of a flame produced by a new and unique burner; and, (2) verification that the burner fulfills its design purpose of recreating small scale propellant flame conditions.Item Characterizing energy transfer using an infrared camera from a reacting nano-composite thermite embedded in a steel target(2009-05) Crane, Charles A.; Pantoya, Michelle; James, Darryl; Rivero, Iris V.A method to study energy transfer from a reacted thermite placed on a steel target substrate was presented as a function of thermite composition. A high speed infrared camera captured a temporally evolving thermal distribution through the substrate, while the thermite, which was placed in a v-notch, self propagated. Two thermite compositions were studied: Boron with Iron (III) Oxide (B-Fe2O3) and Aluminum with Iron (III) Oxide (Al-Fe2O3). A numerical model was developed to predict temperatures near the v-notch in order to estimate the amount of energy transferred into the steel by using a control volume energy balance. Results quantified the percent of the overall energy available from the chemical reaction that was conducted through the substrate and was compared to energy lost. The B-Fe2O3 reaction was more efficient in transferring energy into the steel, 46% of its heat of reaction, than Al-Fe2O3, 10% of its heat of reaction, based largely on the lower contribution of losses by radiation and convection. The Al-Fe2O3 reaction produced more gas by chemistry, 10% by mass, which transported more energy away from the v-notch region as compared to the non gas producing B-Fe2O3. The reaction times for Al-Fe2O3 propagation rate were roughly two to three times faster than the B-Fe2O3 which lowered the heating rate of the substrate. Much work had been performed that examine the combustion behaviors from a reacting thermite, but there are very few studies that attempt to quantify the energy transfer from a reacting thermite to a target. This diagnostic approach and numerical analysis was the first step towards quantifying energy transferred from a thermite into a target, and lost to the environment.Item Combustion behavior of sol-gel synthesized aluminum and tungsten trioxide(Texas Tech University, 2006-05) Prentice, DanielCalcined (to remove impurities) and non-calcined tungsten trioxide (WO3) aerogels as well as micron-scale and nano-scale commercial WO3 powders were mixed with nano-scale aluminum (Al) and their combustion performance in the form of combustion wave speeds was compared in loose powder and pressed pellet configurations. Results show that both the calcined and non-calcined, aerogel based mixtures outperformed the commercial based mixtures in both configurations. Combustion wave speed was also found as a function of mixture bulk density. Results show that conduction is the dominant energy transfer mechanism in pressed pellets while convection is the dominant mechanism in loose powder form. This causes material purity to be the most important factor for pressed pellets and oxidizer particle size to be the most important factor for loose powders. A preliminary aging study was conducted which showed a 7% performance reduction after 4 days of laboratory air exposure and 91-98% performance reduction after 22 months of exposure.Item Combustion behaviors of bimodal aluminum size distributions in thermites(2005-05) Moore, Kevin M.; Pantoya, Michelle; Hope-Weeks, Louisa J.; Weeks, Brandon L.In recent years many studies that incorporated nano-scale or ultrafine aluminum (Al) as part of an energetic formulation demonstrated significant performance enhancement. Decreasing the fuel particle size from the micron to nanometer range alters the material¡¦s chemical and thermal-physical properties. The result is increased particle reactivity that translates to an increase in the combustion velocity and ignition sensitivity. Little is known, however, about the critical level of nano-sized fuel particles needed to enhance the performance of the energetic composite. Ignition sensitivity and combustion velocity experiments were performed using a thermite composite of Al and molybdenum trioxide (MoO3) at the theoretical maximum density (TMD) of a loose power (5% TMD) and a compressed pellet (50% TMD). A bimodal Al particle size distribution was prepared using 4 or 20 ƒÝm Al fuel particles that were replaced in 10% increments by 80 nm Al particles until the fuel was 100% 80 nm Al. These bimodal distributions allow the unique characteristics of nano-scale materials and their interactions with micron scale Al particles to be better understood.Item Combustion behaviors of bimodal aluminum sizedistributions in thermites(Texas Tech University, 2005-05) Moore, Kevin M.In recent years many studies that incorporated nano-scale or ultrafine aluminum (Al) as part of an energetic formulation demonstrated significant performance enhancement. Decreasing the fuel particle size from the micron to nanometer range alters the material¡¦s chemical and thermal-physical properties. The result is increased particle reactivity that translates to an increase in the combustion velocity and ignition sensitivity. Little is known, however, about the critical level of nano-sized fuel particles needed to enhance the performance of the energetic composite. Ignition sensitivity and combustion velocity experiments were performed using a thermite composite of Al and molybdenum trioxide (MoO3) at the theoretical maximum density (TMD) of a loose power (5% TMD) and a compressed pellet (50% TMD). A bimodal Al particle size distribution was prepared using 4 or 20 ƒÝm Al fuel particles that were replaced in 10% increments by 80 nm Al particles until the fuel was 100% 80 nm Al. These bimodal distributions allow the unique characteristics of nano-scale materials and their interactions with micron scale Al particles to be better understood.Item Consolidation of copper and aluminum micro and nanoparticles via equal channel angular extrusion(2009-05-15) Hutchins, Cathleen RuthUltrafine grained (UFG), and nanocrystalline (nc) materials are of interest because of the high strength, compared with coarse grained counterparts. Several current methods to fabricate UFG and nc materials result in samples too small for practical use. In addition, the fabrication of nc materials, in particular, is difficult, and defects in the material causes significant reduction in strength and ductility of these materials. The present study uses Equal Channel Angular Extrusion (ECAE) to produce relatively large consolidates of UFG and nc materials. ECAE has been used to consolidate micro and nanocrystalline powders. The behavior of consolidated pure Cu and aluminum alloys in the nano and micron size were explored. The effects of different routes, extrusion temperature, and post-ECAE processing on microstructure and mechanical behavior were studied. Processing parameters were explored to determine the influence of each parameter on the consolidation performance. The goals of experimenting with different processing parameters were to increase the ductility of the material, while maintaining relatively strong specimens. Comparisons were made with a recently developed powder compaction constitutive model and corresponding simulations. ECAE of microcrystalline powders produced relatively ductile materials, with high strength. Swaging of these consolidated powders produced samples which were softer and less ductile in tension, than the non-swaged samples. ECAE produced effective consolidation of Cu nanoparticles with average sizes of 100 nm, with an ultimate tensile strength of 680 MPa, with a fracture strain as much as 10%, which is higher than previously reported 7% [Haouaoui, 2005].Item 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.Item 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.Item Effect of oxide shell growth on nano-aluminum thermite propagation rates(2012-05) Gesner, Jeffrey; Pantoya, Michelle; Parameswaran, Siva; Christopher, GordonNanocomposite energetic materials show increased flame propagation rates over their micron scale counterparts. These energetic formulations consist of fuel and oxidizer powder mixtures, commonly referred to as thermites. A theory explaining the faster flame propagation speeds associated with nano-particles is called the melt dispersion mechanism and based on the mechanochemistry of the fuel particle’s core-shell structure. The theory supposes that if the ratio (M) of particle radius to shell thickness exceeds a critical threshold, the melt dispersion mechanism is activated, oxidation is accelerated and flame propagation will increase. This study expands on this theory by growing the oxide shell around aluminum fuel particles in a hot, oxygenated environment to achieve varying M ratios. Flame propagation was examined for untreated and treated aluminum particles in an Al-MoO3 thermite. Experimental setup consisted of a closed end tube shot and high speed photography. In all cases, alumina shell grew and was damaged due to treatment, and flames rates were reduced. Flame speed of several hundred meters per second, reduction in flame rate with damage to oxide shell, and weak dependence of the flame speed on the ratio M of particle radius to shell thickness in the range 6.1Item Essays in International Macroeconomics and Forecasting(2012-10-19) Bejarano Rojas, Jesus AntonioThis dissertation contains three essays in international macroeconomics and financial time series forecasting. In the first essay, I show, numerically, that a two-country New-Keynesian Sticky Prices model, driven by monetary and productivity shocks, is capable of explaining the highly positive correlation across the industrialized countries' inflation even though their cross-country correlation in money growth rate is negligible. The structure of this model generates cross-country correlations of inflation, output and consumption that appear to closely correspond to the data. Additionally, this model can explain the internal correlation between inflation and output observed in the data. The second essay presents two important results. First, gains from monetary policy cooperation are different from zero when the elasticity of substitution between domestic and imported goods consumption is different from one. Second, when monetary policy is endogenous in a two-country model, the only Nash equilibria supported by this model are those that are symmetrical. That is, all exporting firms in both countries choose to price in their own currency, or all exporting firms in both countries choose to price in the importer's currency. The last essay provides both conditional and unconditional predictive ability evaluations of the aluminum futures contracts prices, by using five different econometric models, in forecasting the aluminum spot price monthly return 3, 15, and 27-months ahead for the sample period 1989.01-2010.10. From these evaluations, the best model in forecasting the aluminum spot price monthly return 3 and 15 months ahead is followed by a (VAR) model whose variables are aluminum futures contracts price, aluminum spot price and risk free interest rate, whereas for the aluminum spot price monthly return 27 months ahead is a single equation model in which the aluminum spot price today is explained by the aluminum futures price 27 months earlier. Finally, it shows that iterated multiperiod-ahead time series forecasts have a better conditional out-of-sample forecasting performance of the aluminum spot price monthly return when an estimated (VAR) model is used as a forecasting tool.Item Experimental and Numerical Studies of Aluminum-Alumina Composites(2013-07-22) Gudlur, PradeepThe preliminary goal of this study is to determine the effects of processing conditions, compositions and microstructural morphologies of the constituents on the physical and thermo-mechanical properties of alumina (Al_2O_3) reinforced aluminum (Al) composites. Composites with 0, 5, 10, 20 and 25 vol% Al_2O_3 were manufactured using powder metallurgy method. The elastic properties (Young's and shear modulus) and the coefficient of thermal expansion (CTE) of the composites were determined using Resonant Ultrasound Spectroscopy (RUS) and Thermo Mechanical Analyzer (TMA) respectively at various temperatures. Increasing compacting pressure improved relative density (or lowered porosity) of the composites. Furthermore, increasing the Al_2O_3 vol% in the composite increased the elastic moduli and reduced the CTE of the composites. Increasing the testing temperature from 25 to 450 oC, significantly reduced the elastic moduli of the composites, while the CTE of the composites changed only slightly with temperatures. Secondly, the goal of this study is to determine the effect of microstructures on the effective thermo-mechanical properties of the manufactured Al-Al_2O_3 composites using finite element (FE) method. Software OOF was used to convert the SEM micrographs of the manufactured composites to FE meshed models, which were then used to determine the effective elastic modulus and CTE. It was observed that, effective modulus dropped by 19.7% when porosity increased by 2.3%; while the effective CTE was mildly affected by the porosity. Additionally, the effect of residual stress on the effective thermo-mechanical properties was studied, and the stress free temperature of the composites was determined. Another objective of this study is to examine the stress-strain response of Al-Al_2O_3 composites due to compressive loads at various temperatures. Elastic modulus, yield stress and strain hardening parameters were determined from the stress-strain curves and their dependency on temperature, porosity and volume fraction were studied. The experimental results were compared with the numerical results. It was observed that high-localized stresses were present near the pores and at the interfaces between Al and Al_2O_3 constituents. Finally, functionally graded materials (FGMs) with varying Al_2O_3 concentration (0, 5and 10 vol%) in Al were manufactured; and their stress-strain response and CTE were determined at various temperatures.Item Experimental measurement of residual stresses in cold-drawn aluminum tubes(Texas Tech University, 1990-08) Farahaninia, KamalOne of the most common sources of residual stresses is the non-uniform plastic deformation encountered in metal-forming operations. Determination of residual stresses is of major importance in many processes as well as precision equipment components. All destructive techniques, such as hole-drilling and boring-out techniques, are based on the principle of removing part of the stressed material and measuring the resulting strains as the material adjusts its shape to maintain equilibrium. The purpose of this study was to measure the residual stress distributions in cold-drawn aluminum tubes via a modified Sachs boring-out technique utilizing electrochemical machining (ECM) as the means of material removal. Electrochemical machining (electropolishing) was performed on the inner surface of the tubes while measuring the developed strains at the outer surface. Material removal by electropolishing technique was found suitable enough to produce a homogeneous and damage-free surface for measurement of required strains.Item 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.Item 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 EllenFluoride 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.Item Hybrid Rocket Burning Rate Enhancement by Nano-Scale Additives in HTPB Fuel Grains(2014-12-10) Thomas, James CLow regression rates in hybrid rockets limit their use and capability, but additive aluminum nano-particles represent a possible solution to this problem. In this thesis, aluminum nano-particles were characterized and added to hybrid motor grains to assess their effects on the combustion behavior of hybrid rocket fuel grains. Procedures for the fabrication of 6-inch-long motors with combustion port diameters of 1 cm and 2.54 cm (1 inch) were developed for formulations with and without additive particles. The implementation of commercial aluminum particles at a mass loading of 5% as a burning rate enhancer was assessed on a lab-scale burner. Traditional temporally and spatially averaged techniques were applied to determine the regression rates of plain and aluminized HTPB motors burning in gaseous oxygen. Resistance-based regression sensors were embedded in motor grains and used to determine instantaneous and averaged burning rates. The resistive-based sensors exhibited good accuracy and unique capabilities not achievable with other regression measurement techniques, but still have limitations. The addition of commercial nano-aluminum, with a diameter of 100 nm, to hybrid motors increased the motor surface regression rate for oxidizer mass fluxes in the range of 0-15 g/cm2-s. Future testing will focus on the evaluation of motors containing novel aluminum particles manufactured in situ with the HTPB at a mass loading of 5%, which are expected to perform better than similar commercially aluminized motors.Item Influence of alumina shell on nano aluminum melting temperature depression(2007-12) Chauhan, Garima; Pantoya, Michelle; Levitas, Valery; Bhattacharya, SukalyanAs particle size reduces from the micron- to the nano-scale, physical properties of the material can be affected and impact thermal and reaction dynamics of the particles. In the case of nano-aluminum particles encased in an alumina passivation shell, as particle size decreases the shell strength approaches theoretical. Also, nano particles can exhibit a melting temperature depression following the Gibbs-Thomson relationship based on surface tension effects. Understanding how shell strength and surface tension influence each other is an objective of this study. Specifically, the effect of the alumina shell on the nano aluminum melting temperature depression is examined using thermal analysis techniques. Nano aluminum particles of various particle sizes ranging from 17 to 108 nm having virtually undamaged alumina shells were selected for this study. Melting temperatures for each of these powders were measured using differential scanning calorimetry. These measured values were compared with theoretical melting temperatures calculated using the Gibbs-Thomson equation. It was observed that the melting temperatures of alumina encapsulated nano-aluminum particles matched qualitatively with the theoretical trend but not quantitatively. For example, melting temperatures of nano-aluminum particles with undamaged shells exhibited melting temperatures on average 5 K greater than theoretical predictions. The alumina shells of these particles were then damaged mechanically by grinding them between two cylindrical dies in Hydraulic-press. Melting temperatures of the mechanically damaged particles were measured using differential scanning calorimetry and found to have reduced melting temperatures when compared to undamaged particles. The melting temperatures of nano-aluminum particles with damaged shells were in better agreement with theoretical values. Using the difference in melting temperatures of damaged and undamaged powders pressure build-up within the aluminum core was calculated and compared with the pressures calculated using elasticity theory. The comparison showed that the pressure build-up in most of the particles was due to the interfacial surface energies between alumina-aluminum, alumin-air and solid-liquid aluminum.Item On the crushing of honeycomb under axial compression(2010-12) Wilbert, Adrien; Kyriakides, S.; Ravi-Chandar, KrishnaswamyThis 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.Item 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.Item Quantification of heat flux from a reacting thermite spray(2009-08) Nixon, Eric; Pantoya, Michelle; Berg, Jordan M.; Oler, James W.Characterizing the combustion behaviors of energetic materials requires diagnostic tools that are often not readily or commercially available. For example, a jet of thermite spray provides a high temperature and pressure reaction that can also be highly corrosive and promote undesirable conditions for the survivability of any sensor. Developing a diagnostic to quantify heat flux from a thermite spray is the objective of this study. Quick response sensors such as thin film heat flux sensors can not survive the harsh conditions of the spray, but more rugged sensors lack the response time for the resolution desired. A sensor that will allow for adequate response time while surviving the entire test duration was constructed. The sensor outputs interior temperatures of the probes at known locations and utilizes an inverse heat conduction code to calculate heat flux values. The details of this device are discussed and illustrated. Temperature and heat flux measurements of various thermite spray conditions are reported. Results indicate that this newly developed energetic material heat flux sensor provides quantitative data with good repeatability.Item Reactions of aluminum with halogen containing oxides(2013-05) Farley, Cory; Pantoya, Michelle; Long, Kevin; Christopher, Gordon; Berg, Jordan M.; Bhattacharya, SukalyanDue to increasing threats of biological attacks, new methods for the neutralization of spore forming bacteria are currently being examined. Thermites may be an effective method to produce high temperature reactions, and some compositions such as aluminum (Al) and iodine pentoxide (I2O5) also have biocidal properties. This study examines the thermal degradation behavior of I2O5 mixed with micron and nanometer scale aluminum (Al) particles. Differential scanning calorimetry (DSC) and thermo-gravimetric (TG) analyses were performed in an argon environment on both particle scales revealing a non-reaction for micron Al and a complex multistep reaction for the nanometer scale Al. Results show that upon I2O5 decomposition, iodine ion adsorption into the alumina shell passivating Al particles is the rate controlling step of the Al-I2O5 reaction. This pre-ignition reaction is unique to nano-Al mixtures and attributed to the significantly higher specific surface area of the nanometric Al particles which provide increased sites for I- sorption. A similar pre-ignition reaction had previously been observed with fluoride ions and the alumina shell passivating Al particles. Composite energetic materials comprised of nanoparticle fuel and oxidizer can exhibit high flame propagation speeds on the order of 1000m/s when burning in an unconfined environment. In particular, halogen based formulations such as aluminum and iodine pentoxide have received significant attention due to both high flame speeds and biocidal properties. Studies have attributed high flame speeds to convective influences within a reaction driving the heat forward in a pressure wave accelerating ignition of unburned powders. This study examines factors contributing to convective flows such as gas and heat generation and their relationship to the measured flame speed as well as fundamental chemical kinetics influencing the observed flame speeds. The goal is to understand parameters directly related to high flame speeds in halogen containing composites. Results show a direct correlation between apparent activation energy and flame speed indicating that flame speed is directly influenced by chemical kinetics. For this reason, the intermediate chemistry associated with Al and iodine species was examined to identify chemical influences accelerating flame speeds. Ab initio quantum chemical calculations of gas-phase reactions resolve key exothermic intermediate reactions contributing toward the kinetics of the fastest burning mixtures. Condensed phase density functional theory calculations of Al2O3/I2O5 interfaces resolved adsorption/desorption properties. This study examines the effect of atmospheric oxygen concentration (4 or 93% oxygen) on energy propagation of nanometric aluminum with copper oxide (Al+CuO), iron oxide (Al+Fe2O3), calcium iodate (Al+Ca(IO3)2), and iodine pentoxide (I2O5). In all cases energy propagation was examined in terms of flame speed and higher in the high oxygen environments. However, the convectively driven mixtures showed a smaller percent increase in flame speeds. This behavior is attributed to the increased availability of oxygen as a result of solid oxidizer thermal decomposition at lower temperatures. The slower Al+Fe2O3 reaction showed greater increases in flame speed attributed to early stage reactions involving atmospheric oxygen that promote oxide decomposition and faster flame speeds. A predictor based on solid oxidizer thermal decomposition and flame speed was developed to evaluate the sensitivity of a reaction to atmospheric oxygen concentration.