Browsing by Subject "Impact"
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Item Design and evaluation of negative stiffness honeycombs for recoverable shock isolation(2015-05) Correa, Dixon Malcolm; Seepersad, Carolyn; Haberman, Michael RNegative stiffness elements are proven mechanisms for shock isolation. The work presented in this thesis investigates the behavior of negative stiffness beams when arranged in a honeycomb configuration. Regular honeycombs consisting of cells such as hexagonal, square, and triangular absorb energy by virtue of plastic deformation which is unrecoverable. The major goal of this research is to investigate the implementation of negative stiffness honeycombs as recoverable shock isolation so as to better the performance of regular honeycombs.To effectively model the honeycomb behavior, analytical expressions that define negative stiffness beam behavior are established and finite element analysis (FEA) is used to validate them. Further, the behavior of negative stiffness beams when arranged in rows and columns of a honeycomb is analyzed using FEA. Based on these findings, a procedure for the optimization of negative stiffness honeycombs for increased energy absorption at a desired force threshold is developed. The optimization procedure is used to predict trends in the behavior of negative stiffness beams when its design parameters are varied and these trends are compared to those observed in regular honeycombs. Additionally, experimental evaluations of negative stiffness honeycombs under quasi-static loading are carried out using prototypes built in nylon 11 material manufactured by selective laser sintering (SLS). Energy absorption calculations conclude that optimization of negative stiffness honeycombs can yield energy absorption levels comparable to regular honeycombs. A procedure for dynamic testing of negative stiffness honeycombs is discussed. Results from dynamic impact testing of negative stiffness honeycombs reveal excellent shock absorption characteristics. FE models are developed for static and dynamic loading and the results show strong correlation with experiments. Further, temperature dependency of nylon 11 is investigated using impact tests on honeycomb prototypes. Finally, example applications utilizing negative stiffness honeycombs are discussed and recommendations are made for their refinement.Item Dynamics of projectile impact in a granular material, and the dynamics of a single sedimenting sphere in fluid(2005) Lee, Andrew Thomas; Swinney, H. L., 1939-We have studied the dynamics of impact and sedimentation in two experimental systems. Tracking the incident object with high precision we examined the details of resulting trajectories through the ambient material in both cases. For each system direct numerical simulations have enabled us to gain insight into the forces leading to the resulting trajectories. A static bed of granular material in the absence of external forcing will remain in its steady state configuration. During impact, a projectile of sufficient energy causes a static bed of particles to become locally fluidized. The properties of the fluidized granular material allow for the projectile to penetrate into the bed. The granular drag force on the projectile as it penetrates is caused by dissipation and collisions between interacting particles. As the projectile velocity decreases the energy will become lower than the threshold for fluidization causing the granular bed to return to a static pile of material. The projectile rapidly slows to a stop. We have created a quasi-two-dimensional experiment to measure the granular drag force on a projectile as it penetrates a granular bed of particles. Our results show that the average drag force on the projectile is constant during penetration. Moreover, the magnitude of the drag force is proportional to the velocity of impact. We also report the surprising result that for a range of projectile impact velocities (50 < v < 400 cm/s) the projectile decelerates to v = 0 in t ≈ 0.15 s for all cases. Simulation results also show that the probability distribution of forces between individual particles in the bed remains unchanged during penetration. Based upon these simulation results we conclude that the granular drag force on the projectile is caused by the localized forces within the bed of particles that are within one diameter below the projectile. After a single sphere is released under the force of gravity within a Newtonian fluid medium, the sphere will reach terminal velocity. For large enough terminal velocities the sphere will begin to shed vortices. We have studied the case of a single sphere sedimenting between two closely spaced glass plates in a narrow aspect ratio cell (a Hele-Shaw cell). Using a very accurate tracking method we were able to track the position of a sphere during its fall for a range of Reynolds numbers (based on the terminal velocity and the diameter of a sphere), 20 < Re < 330. Simultaneous results of digital particle image velocimetry images provided a picture of the fluid wake behind the sphere. We found that the trajectory of the sphere is highly sensitive to the size of the gap, Γ = dgap/dsphere. For Γ ≤ 1.05 we observed nearly two dimensional vortices behind the sphere. These vortices caused very small oscillations in the motion of the sphere in the transverse direction . For larger gap sizes (1.10 ≤ Γ ≤ 1.40), the trajectory of the sphere was very different due to a change in the wake structure from nearly two-dimensional to fully three-dimensional. For these cases we observed oscillatory behavior in both the transverse and streamwise directions. Simulations confirmed spiral trajectories and indicated that vortices are formed in parallel tubes which are shed for large Re. Our detailed transition map shows that for small gap cases there are similarities to results for fixed cylinders while the transitions for the large gap cases are similar to those for flow past a fixed sphere without the presence of confining walls.Item The economic development impacts of investing in an Interstate 10 expansion project in Texas(2012-08) Evans, Stephen Daniel; Walton, C. Michael; Prozzi, JolandaTransportation planners, engineers, and administrators face the difficult tasks of prioritizing and justifying proposed investments in transportation infrastructure, particularly as government budgets tighten and alternative investments compete for public funding. One means by which professionals can prioritize and justify large transportation investments is by describing how a proposed project will impact an area’s economy in terms of creating new jobs, raising aggregate income, and increasing business revenues. The report begins by examining the general impact of transportation investments on economic development. Then it surveys various methods and tools that have been proposed for estimating economic impacts. Among these, the TREDIS economic impact model is selected and used to estimate the economic impacts of a current interstate highway project in Texas.Item Formulation and simulation of impact dynamics for multilayer fabrics with various weaves(2011-12) Shimek, Moss Evan; Fahrenthold, Eric P.; Longoria, Raul G.; Crawford, Richard H.; Traver, Alfred E.; Sepehrnoori, KamyThe high strength, light weight, and flexibility of fabric protection systems makes them the preferred solution for a number of ballistic applications. Examples include body armor, fan blade containment for jet engines, and orbital debris shielding. In general, these protection systems employ plain woven fabric, most suitable for flat or gently curved geometries. Highly curved surfaces, such as personnel extremities, may be more effectively protected using fabrics of different weaves. This dissertation presents the first numerical model developed to simulate ballistic impacts into plain, harness satin, twill, and basket weave fabrics. It extends previous work on hybrid particle-finite element methods developed for fabric modeling. The extended formulation closely replicates the tensile load response and contact-impact dynamics of highly flexible yarns, by generalizing the kinematic model and density interpolation used in previous work. The formulation has been validated in three dimensional simulations of impact experiments conducted to investigate the effects of weave type on fabric ballistic performance.Item Numerical simulations of the flow produced by a comet impact on the Moon and its effects on ice deposition in cold traps(2010-05) Stewart, Bénédicte; Goldstein, David Benjamin, doctor of aeronautics; Varghese, Philip; Trafton, Laurence; Raman, Venkatramanan; Hurley, DanaThe primary purpose of this study is to model the water vapor flow produced by a comet impact on the Moon using the Direct Simulation Monte Carlo (DSMC) method. Toward that end, our DSMC solver was modified in order to model the cometary water from the time of impact until it is either destroyed due to escape or photodestruction processes or captured inside one of the lunar polar cold traps. In order to model the complex flow induced by a comet impact, a 3D spherical parallel version of the DSMC method was implemented. The DSMC solver was also modified to take as input the solution from the SOVA hydrocode for the impact event at a fixed interface. An unsteady multi-domain approach and a collision limiting scheme were also added to the previous implementation in order to follow the water from the continuum regions near the point of impact to the much later rarefied atmospheric flow around the Moon. The present implementation was tested on a simple unsteady hemispherical expansion flow into a vacuum. For these simulations, the data at the interface were provided by a 1D analytical model instead of the SOVA solution. Good results were obtained downstream of the interface for density, temperature and radial velocity. Freezing of the vibrational modes was also observed in the transitional regime as the flow became collisionless. The 45° oblique impact of a 1 km radius ice sphere at 30 km/s was simulated up to several months after impact. Most of the water crosses the interface under 5 s moving mostly directly downstream of the interface. Most of the water escapes the gravity well of the Moon within the first few hours after impact. For such a comet impact, only ~3% of the comet mass remains on the Moon after impact. As the Moon rotates, the molecules begin to migrate until they are destroyed or captured in a cold trap. Of the 3% of the water remaining on the Moon after impact, only a small fraction, ~0.14% of the comet mass, actually reaches the cold traps; nearly all of the rest is photo-destroyed. Based on the surface area of the cold traps used in the present simulations, ~1 mm of ice would have accumulated in the polar cold traps after such an impact. Estimates for the total mass of water accumulated in the polar cold traps over one billion years are consistent with recent observations.Item 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.Item Parametric study of LCROSS impact plume(2013-12) Lamb, Justin Meredith; Goldstein, David Benjamin, doctor of aeronauticsIn 2009, NASA's LCROSS mission impacted Cabeus Crater near the Lunar South Pole with the spent Centaur upper stage rocket. The impact was observed by the trailing sheperding spacecraft (S-S/C) that impacted the moon 250 seconds after the Centaur impact. The main objective of the LCROSS mission was to verify the existence of water ice in the lunar regolith---the subsequent analysis of the data confirmed water ice present in the crater. The analysis of the S-S/C instrument data suggested that the plume consisted of two components: a central "spike" component and a thin, outward "cone" component. A model has been developed at The University of Texas at Austin improve the analysis of the data obtained by the S-S/C. This model is created with a free-molecular ballistic grain code that involves simulating individual regolith grains in the debris plume through grain-heating and grain-movement models and then modeling the spectral radiance properties of the grains as observed by the S-S/C. Mie scattering theory is used to model scattering and absorption of incoming solar radiation by the particles in the plume assuming they are perfect spheres. The UT LCROSS code was utilized in a parametric study that evaluated the effect of variations in assumed model plume parameters on the modeling of S-S/C UV-VIS instrument observations. The plume parameters were chosen based on the assumption that the dust plume was split into two components: a central spike and a surrounding high angle cone. The following parameters were varied: the spike and cone angles, the spike and cone grain radius distributions, and the spike mass fraction. The following parameters could be varied but were given fixed values: ice fraction between plume components, ice grain purity, albedo, and ice fraction in plume. The impact of these plume parameters upon plume brightness and blue/red color ratio was determined. Two grain models were used. In the initial grain species model all grains have a soil core surrounded by a thin ice shell. In the second, two species model two grain types were utilized: a pure ice grain component and a pure soil grain component.Item Predicting deformation mechanisms during high speed impact of Ag nanoparticles(2020-03-27) Chitrakar, Tushar Vijay; Kovar, Desiderio; Becker, Michael F.; Keto, John W; Taleff, Eric MA number of aerosol deposition methods are currently used to produce thick films by impacting particles onto a substrate at high velocities. Though these processes operate at a similar range of velocities, there are significant differences in the sizes of the particles used in the aerosol. Conventional aerosol deposition methods deposit 0.1–40 μm sized-particles, whereas the laser ablation of microparticle aerosol process uses very fine 2–40 nm nanoparticles (NPs) to produce thick films. For particles smaller than 0.1 μm, deformation mechanisms that occur upon impact have not been studied previously in a systematic manner. In this dissertation, molecular dynamic simulations are used to study the time-evolution of deformation mechanisms that occur at very small timescales and high strain rates during high speed impact of Ag NPs. The defect evolution and the underlying mechanisms for deformation are systematically studied and documented by varying the NP size, the NP impact velocity, and the NP crystallographic orientation relative to the substrate. A wide range of microstructures ranging from polycrystalline to epitaxial morphologies are observed for these simulations. Because epitaxial deposition by particle impact has not been experimentally obtained, considerable attention is given to understanding the factors that are predicted to lead to epitaxy. Disordering is an important mechanism because it can play a role in epitaxial growth at high deposition velocities. A critical parameter is proposed to predict disordering that occurs upon impact. An alternative method to obtain epitaxial deposition at lower deposition velocities is also explored. The goal of this dissertation is to develop a thorough understanding of the available processing parameters for controlling the microstructure for a single NP deposition event. The impact studies in this dissertation provide fundamental guidelines needed to ultimately understand the formation of thick films where thousands of particles are impacted to produce a film.Item Real vs. imaginary users: measuring the impact of home movie collections on historical scholarship(2014-08) Treat, Laura Jean; Galloway, Patricia Kay; Frick, CarolineIn the past thirty years, a growing community has emerged to advocate for the preservation and recognition of home movie collections based on their historical significance. Despite the significant cost of preserving and providing access to these collections and the myriad challenges they pose to archivists and researchers, no substantive research exists that evaluates their actual scholarly use or impact. Through a publication analysis and a survey of the Association of Moving Image Archivists, I sought to determine if there is a difference between whom archivists think should be using home movie collections and who is actually them. Though my findings suggest that home movies have yet to impact the scholarly work of historians, I offer recommendations for future research and professional development that may encourage increased scholarly use as well as increased collaboration between archivists and historians.Item Resisting slactorvism : toward theatrical activism in service of organizing beyond the stage(2021-05-03) Joaquin, Anna Michaela Rogelio; Bonin-Rodriguez, PaulWhile theatre practitioners often intend to create art in service of social change, academic theatre and performance studies programs do not adequately prepare artists to do so. Despite their interdisciplinary nature and bridging of theory and practice, these programs often neglect the opportunity to ground theatrical training in theories of social change (Dolan 53). As a result, many professional artists are poised to make work with activist aims detached from the political analysis necessary to responsibly and effectively work toward concrete goals. This thesis puts social change studies and performance studies in conversation with each other, drawing on theories of organizing, artistic activism, and privileged spectatorship. I first frame organizing as the most effective theory of social change—a tactic I believe to have strong potential for collaboration with theatrical events. Then, I examine strengths and limitations of theatre as artistic activism, naming The Center for Artistic Activism’s concept of AEffect as a framework for analyzing impact (Duncombe and Lambert 5). I also introduce applied theatre scholar Dani Snyder-Young’s concept of privileged spectatorship as what theatre is up against (100). These theories inform my methodology for assessing impact of two case studies: Steppenwolf Theatre Company’s 2018-2019 production of La Ruta by Isaac Gómez and Gathering Ground Theatre and Tenants Speak Up! Theatre’s 2020 production of A Tale of Two Citizens: A People’s Struggle with Housing in the Capital City. Through a critical discourse analysis of production materials and audience impact surveys, this thesis presents a generative call for a more active assessment of insularity, intentions, and impacts of contemporary theatre pursuing social change, as well as the necessity of resisting slactorvism by ensuring theatrical activism serves organizing beyond the stage.Item Tailored functional colloids and interfaces for nanoparticle impact electroanalysis(2016-05) Robinson III, Donald Arlington; Crooks, Richard M. (Richard McConnell); Stevenson, Keith J.; Johnston, Keith P; Mullins, Charles B; Shear, Jason B; Yeh, Hsin-ChihNanoparticle impact electroanalysis (NIE) is a new electrochemical method under development for fundamental physicochemical studies of single nanoparticles (NPs) and potential applications in biosensing of single molecules with ultralow limits of detection. This dissertation introduces the tailored design, synthesis, characterization, and optimization of functional materials that comprise the foundation for the NIE detection strategy of interest, which is based on the principle of electrocatatlytic amplication (ECA). The investigations presented herein focus on two materials that function as the foundation in the ECA-NIE detection strategy: 1) the ultramicroelectrode (UME) used to contact these NPs individually from solution and 2) the NPs themselves, which are the primary focus of this dissertation. The specially designed materials described have helped to overcome major fundamental limitations associated with the ECA detection strategy and thus improve critical figures of merit for NIE. In Chapter 1, the incorporation of Hg as the UME material is shown to significantly improve signal-to-noise, reproducibility, and time resolution for the NIE platform. In Chapter 2, the fundamental problem of colloidal instability is addressed and rectified by experimentally guided systematic optimization of the ECA solution conditions, in turn providing the means to properly calibrate and theoretically model NP impact events in terms of NP size and rate of impact at the UME surface. Chapters 3 and 4 highlight the synthesis, characterization, and analytical application of bifunctional catalytic/magnetic Pt-decorated iron oxide NPs for NIE. The bifunctional NPs serve as essential tools to overcome fundamental limitations of mass transport, which is achieved by physical manipulation using an externally applied magnetic field focused at the UME detection surface. The incorporation of magnetophoretically focused and accelerated NP transport results in a significantly improved limit of detection in comparison to diffusion-limited NIE strategies. In Chapter 5 we return to the study of NP aggregation kinetics with NIE and discuss mechanistic insights into the physicochemical processes that most likely influence Pt NP colloidal stability. The methodologies described in this dissertation provide an experimental blueprint to help establish a solid physical/analytical foundation of this rapidly evolving field of research.