Aerospace Engineering Commons^™

Studies Of Dynamic Crack Propagation And Crack Branching With Peridynamics, Youn Doh Ha, Florin Bobaru

Department of Engineering Mechanics: Faculty Publications

In this paper we discuss the peridynamic analysis of dynamic crack branching in brittle materials and show results of convergence studies under uniform grid refinement (m-convergence) and under decreasing the peridynamic horizon (δ-convergence). Comparisons with experimentally obtained values are made for the crack-tip propagation speed with three different peridynamic horizons.We also analyze the influence of the particular shape of themicro-modulus function and of different materials (Duran 50 glass and soda-lime glass) on the crack propagation behavior. We show that the peridynamic solution for this problem captures all the main features, observed experimentally, of dynamic crack propagation and branching, as well …

Multiscale Modeling Of Impact On Heterogeneous Viscoelastic Solids With Evolving Microcracks, Flavio V. Souza

Department of Engineering Mechanics: Dissertations, Theses, and Student Research

Multiscale computational techniques play a major role in solving problems related to viscoelastic composite materials due to the complexities inherent to these materials. In the present work, a numerical procedure for multiscale modeling of impact on heterogeneous viscoelastic solids containing evolving microcracks is proposed in which the (global scale) homogenized viscoelastic incremental constitutive equations have the same form as the local scale viscoelastic incremental constitutive equations, but the homogenized tangent constitutive tensor and the homogenized incremental history dependent stress tensor depend on the amount of damage accumulated at the local scale. Furthermore, the developed technique allows the computation of the …

United States Air Force Posture Statement 2009, U.S. Air Force

United States Air Force: Publications

Today, the United States faces a spectrum of challenges to our national security and global interests. As an integral member of the Joint team, America’s Air Force provides the critical capabilities of Global Vigilance, Global Reach, and Global Power. The United States Air Force is 'All In" today’s Joint fight. At the same time, our investments in new capabilities will ensure we are ready for tomorrow’s challenges. The mission of the United States Air Force is to "fly, fight, and win…in air, space and cyberspace"—as an integral member of the Joint …

Selecting And Conserving Lands For Biodiversity: The Role Of Remote Sensing, John Wiens, Robert Sutter, Mark Anderson, Jon Blanchard, Analie Barnett, Naikoa Aguilar-Amuchastegui, Chadwick Avery, Stephen Laine

United States Air Force: Publications

A major focus of conservation is on protecting areas to ensure the persistence of biological diversity. Because such areas may be large, not easily accessible, subject to change, and sensitive to the surrounding landscape, remote sensing can be a valuable tool in establishing and managing protected areas. We describe three case studies to illustrate how remote sensing can contribute to setting priorities for conservation actions, monitoring the status of conservation targets, and evaluating the effectiveness of conservation strategies. In the Connecticut River watershed, remote sensing has been used to assess flood regimes and identify key areas of floodplain forests and …

Perchlorate In Wet Deposition Across North America, Srinath Rajagopalan, Todd A. Anderson, Stephen Cox, Greg Harvey, Qiuqiong Cheng, W. Andrew Jackson

United States Air Force: Publications

Natural perchlorate is believed to be of atmospheric origin, yet no systematic study has been conducted to evaluate perchlorate deposition rate and possible seasonal or spatial variations. This study evaluated perchlorate concentrations in weekly composite wet deposition samples acquired through the National Atmospheric DepositionProgramfrom 26 sites across the continental United States, Alaska, and Puerto Rico for a 1-3 year period. Perchlorate concentrations varied from /L to a high of 102 ng/L with a mean of 14.1±13.5 ng/L for the 1578 total samples. The annual perchlorate flux by site ranged from a low of 12.5 (TX) to 157 mg/ha-year (NE) and …

A Location Analysis Approach For Military Maintenance Scheduling With Geographically Dispersed Service Areas, Dale L. Overholts Ii, John E. Bell, Marvin A. Arostegui

United States Air Force: Publications

This research uses a two-stage maximal covering location problem (MCLP) model to develop Intercontinental ballistic missile (ICBM) maintenance schedules for the US Air Force. Solutions are compared to actual missile maintenance activities accomplished at F. E. Warren Air Force Base (AFB), Wyoming in May 2005. Sensitivity analysis is performed to determine the impact of altering security response times and the number of security patrol are as on the quality of daily maintenance schedules and personnel usage. Results indicate marked improvement over traditional Air Force scheduling methods. In addition, sensitivity analysis identifies the levels at which the quality and quantity of …

The 2008 Strategy For United States Air Force Intelligence, Surveillance And Reconnaissance, United States Air Force

United States Air Force: Publications

Since the inception of the Air Force, our Nation has asked us to create aerospace forces that no adversary could "out gun" under any circumstances. For over six decades we have answered that call. Now the Nation demands that we also create a set of capabilities that no adversary can "out smart" in the future. This strategy outlines our response in the realm of Intelligence, Surveillance and Reconnaissance (ISR).
This is a new document that specifies why and how our Air Force will provide the capacity and capability for full spectrum ISR. It provides the foundation for enabling our air …

An Integer Programming Approach To Support The Us Air Force’S Air Mobility Network, Corbin G. Koepke, Andrew P. Armacost, Cynthia Barnhart, Stephan E. Kolitz

United States Air Force: Publications

The United States Air Force’s air mobility command is responsible for creating a schedule and executing that schedule for a large-scale air mobility network that encompasses aircraft with prioritized missions. Aerial ports (airports) can process or park a maximum number of aircraft, called the maximum on ground (MOG). As the schedule changes due to disruptions, such as equipment failure or weather, the MOG constraint can cause the new schedule to be infeasible. Traditionally, re-planning the channel route schedule to adhere to MOG constraints has been a manual process that usually stops after the first feasible set of changes is found, …

United States Air Force Posture Statement 2008, U.S. Air Force

United States Air Force: Publications

The United States Air Force provides the Nation with a powerful deterrent force in times of peace, and it sets the conditions for Joint and Coalition victory in times of war. For over seventeen years, since Operation DESERT SHIELD, the United States Air Force has been engaged in continuous combat operations. Our Airmen have maintained constant watch, deployed continuously, engaged America’s adversaries directly, responded to human crises around the world, and provided the Global Vigilance, Global Reach, and Global Power to secure our Nation.

Electrical Control Of The Thermodiffusive Instability In Premixed Propane–Air Flames, D. L. Wisman, S. D. Marcum, B. N. Ganguly

United States Air Force: Publications

This work focuses upon the effects of DC electric fields on the stability of downward propagating atmospheric pressure premixed propane–air flames under experimental conditions that provide close coupling of the electric field to the flame. With the appropriate electrode geometry, modest applied voltages are shown to drive a stable conical flame first into a wrinkled-laminar flamelet geometry, and then further toward either a highly unstable distributed flamelet regime or a collective oscillation of the flame front. Applied potentials up through +5 kV over a 40-mm gap encompassing the flame front have been used to force the above transition sequence in …

United States Air Force Posture Statement 2007, U.S. Air Force

United States Air Force: Publications

Our 2007 Posture Statement articulates the major elements required to fulfill our mission. It reaffirms our commitment to focus our energies on the Global War on Terror; to develop and care for our Airmen and their families; and to recapitalize and modernize our aging aircraft, spacecraft and equipment.

The Complete Management Of Extremity Vascular Injury In A Local Population: A Wartime Report From The 332nd Expeditionary Medical Group/Air Force Theater Hospital, Balad Air Base, Iraq, Michael A. Peck, W. Darrin Clouse, Mitchell W. Cox, Andrew N. Bowser, Jonathan L. Eliason, Donald H. Jenkins, David L. Smith, Todd E. Rasmussen

United States Air Force: Publications

Background: Although the management of vascular injury in coalition forces during Operation Iraqi Freedom has been described, there are no reports on the in-theater treatment of wartime vascular injury in the local population. This study reports the complete management of extremity vascular injury in a local wartime population and illustrates the unique aspects of this cohort and management strategy.

Methods: From September 1, 2004, to August 31, 2006, all vascular injuries treated at the Air Force Theater Hospital (AFTH) in Balad, Iraq, were registered. Those in non-coalition troops were identified and retrospectively reviewed.

Results: During the study …

Impact Of Phlebotomine Sand Flies On U.S. Military Operations At Tallil Air Base, Iraq: 3. Evaluation Of Surveillance Devices For The Collection Of Adult Sand Flies, Douglas A. Burkett, Ronald Knight, James A. Dennett, Van Sherwood, Edgar Rowton, Russell E. Coleman

United States Air Force: Publications

We evaluated the effectiveness of commercially available light traps and sticky traps baited with chemical light sticks for the collection of phlebotomine sand flies. Evaluations were conducted at Tallil Air Base, Iraq, in 2003. In an initial study, a Centers for Disease Control and Prevention (CDC)-style trap with UV bulb collected significantly more sand flies than did an up-draft CDC trap, a standard down-draft CDC trap (STD-CDC), or a sticky strap with a green chemical light stick. In a subsequent study, we found that the addition of chemical light sticks to sticky traps resulted in a significant increase in the …

Basic Materials Research Programs At The U.S. Air Force Office Of Scientific Research, Herbert C. Carlson, K. C. Goretta

United States Air Force: Publications

The Air Force Office of Scientific Research (AFOSR) annually sponsors approximately 5000 research scientists at 1000 universities and laboratories, generating about 10,000 Ph.D. graduates per decade, all expected to publish their basic research findings in peer-reviewed journals. After a brief introduction of the nature of AFOSR’s support to basic research in the U.S. and international scientific communities, work it supports at the frontiers of materials science is highlighted. One focused research theme that drives our investment is the MEANS program. It begins with the end in mind; materials are designed with practicable manufacture as an explicit initial goal. AFOSR’s broad …

Atomic Force Microscope Tip Spontaneous Retraction From Dielectric Surfaces Under Applied Electrostatic Potential, S. F. Lyuksyutov, P. B. Paramonov, O. V. Mayevska, M. A. Reagan, E. Sancaktar, R. A. Vaia, S. Juhl

United States Air Force: Publications

A time-resolved method for tip’ retraction at µs-scale away from dielectric surfaces has been developed. Analysis of the forces in the system comprising AFM tip, water meniscus, and polymer film suggests that an electrostatic repulsion of the tip from the surface in the double-layered (water and polymer) system, and water condensation in the tip–surface junction are the dominant factors enabling the mechanical work for tip retraction. Nanostructures of 5–80nm height are formed in polymeric surfaces as a result. This interesting physical phenomenon could be used for nanostructures patterning in polymeric materials at enhanced aspect ratio.

Perchlorate Toxicity And Risk Assessment, David R. Mattie, Joan Strawson, Jay Zhao

United States Air Force: Publications

Ammonium perchlorate is the oxidizer ingredient in solid propellant mixtures for rockets, missiles and munitions such as Titan, Minuteman, Peacekeeper, Hawk, Polaris and the Space Shuttle. Perchlorate salts may also be used in medicine, matches, munitions and pyrotechnics (illuminating and signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, photo-flash compounds and fireworks). Perchlorate is also found in lubricating oils, finished leather, fabric fixer, dyes, electroplating, aluminum refining, manufacture of rubber, paint and enamel production, as an additive in cattle feed, in magnesium batteries and as a component of automobile air bag inflators.'

Atomic Force Microscopy Of Bacillus Spore Surface Morphology, Ruth A. Zolock, Guangming Li, Charles Bleckmann, Larry Burggraf, Douglas C. Fuller

United States Air Force: Publications

Bacillus spore surface morphology was imaged with atomic force microscopy (AFM) to determine if characteristic surface features could be used to distinguish between four closely related species; Bacillus anthracis Sterne strain, Bacillus thuringiensis var. kurstaki, Bacillus cereus strain 569, and Bacillus globigii var. niger. AFM surface height images showed an irregular topography across the curved upper surface of the spores. Phase images showed a superficial grain structure with different levels of phase contrast and significant differences in average surface morphologies among the four species. Although spores of the same species showed similarities, there was significant variability within each …

Towards Monitoring Galileo: The European Gnss Supervisory Authority In Statu Nascendi = Zur Künftigen Überwachungsagentur Des Galileo Systems, Vers Une Autorité De Surveillance Du Système Galileo, Frans G. Von Der Dunk

Space, Cyber, and Telecommunications Law Program: Faculty Publications

There is little doubt that one of the most interesting and revolutionary, but also complicated and challenging space projects of today is Galileo, Europe’s own full-fledged second-generation navigation satellite system. Developed jointly by the European Union through the Commission and the European Space Agency, Galileo should by the end of the decade have thirty operational satellites in middle-earth-orbits providing timing, positioning and navigation signals across the globe.

From the very beginning Galileo was envisaged in particular by the Commission as a public-private-partnership (PPP). On the one hand, a private concessionaire should operate the system as of full operational capability (originally …

Field-Scale Demonstration Of Induced Biogeochemical Reductive Dechlorination At Dover Air Force Base, Dover, Delaware, Lonnie G. Kennedy, Jess W. Everett, Erica Becvar, Donald Defeo

United States Air Force: Publications

Biogeochemical reductive dechlorination (BiRD) is a new remediation approach for chlorinated aliphatic hydrocarbons (CAHs). The approach stimulates common sulfate-reducing soil bacteria, facilitating the geochemical conversion of native iron minerals into iron sulfides. Iron sulfides have the ability to chemically reduce many common CAH compounds including PCE, TCE, DCE, similar to zero valent iron (Fe⁰). Results of a field test at Dover Air Force Base, Dover, Delaware, are given in this paper. BiRD was stimulated by direct injection of Epson salt (MgSO₄·7H₂O) and sodium (L) lactate (NaC₃H₅O₃) in five …

Force Protection Using Composite Sandwich Structures, R. L. Sierakowski, M. L. Hughes

United States Air Force: Publications

In the recent past, advances have been made in the attempt to utilize composite materials as components in protective structures such as those employed by the Air Force to secure critical military assets. In such applications, where lightweight materials that exhibit large levels of energy absorption and high strength/stiffness characteristics are desirable, composite sandwich constructions offer an attractive solution.

In an attempt to evaluate the suitability of certain sandwich structures for use in force protection applications, several sandwich constructions with somewhat novel core materials were identified. A group of thermoplastic core materials have been developed that possess features of both …

United States Air Force Posture Statement 2006, U.S. Air Force

United States Air Force: Publications

Over a century ago, America crossed the threshold of powered flight and gave wings to the world. Soon military leaders realized the implications of this development, and warfare was changed forever. America was fortunate to have "Great Captains" with the vision to imagine the possibilities of air and space power - Airmen like Billy Mitchell, Frank Andrews, Hap Arnold, Ira Eaker, Jimmy Doolittle, Bennie Schriever. They have given us a proud heritage of courage, excellence and innovation. In so doing, they also give us a sense of perspective and a way to understand the Air Force's future.

Laboratory Evaluation Of Colored Light As An Attractant For Female Aedes Aegypti, Aedes Albopictus, Anopheles Quadrimaculatus, And Culex Nigripalpus, Douglas A. Burkett, Jerry F. Butler

United States Air Force: Publications

Mosquito feeding activity was monitored in an electronic apparatus (visualometer), having ten ports, illuminated from below with narrow bandwidths of light (700, 650, 600, 550, 500, 450, 400, or 350 nm). Responses of adult female Aedes albopictus Skuse, Ae. aegypti (L.), Anopheles quadrimaculatus, Say and Culex nigripalpus Theobald to feeding stations (blood containers) over each light port. No-light and broad spectrum white light were used as controls. Color preferences were based on electronic detection of feeding times. Aedes aegypti showed no significant feeding preferences over any of the colors. Conversely, Ae. albopictus, An. quadrimaculatus, and Cx. nigripalpus showed …

United States Air Force Posture Statement 2005, U.S. Air Force

United States Air Force: Publications

Today's security environment is characterized by change and ambiguity. The future will include a variety of challenges, including the risk of catastrophic attacks on the homeland and possibly of disruptive technological breakthroughs by our adversaries.

Sample Preparation And Characterization Of Artificially Aged Aircraft Coatings For Microstructural Analysis, Lisa M. Farrier, Stephen A. Szaruga

United States Air Force: Publications

The paper describes a method for metallographic preparation of artificially aged aircraft coatings. In order to better understand the in-service performance and identify degradation mechanisms of an aircraft coating, complete characterization of the microstructure is essential. This paper discusses metallographic sample preparation and subsequent microscopy techniques (light optical microscopy, scanning electron microscopy) for characterization of a standard polyurethane aircraft coating system. The preparation method has proven to produce good, consistent results on a wide range of laboratory-produced simulated environmental exposures.

The military specification coating system under study (MIL-PRF-85285C and MIL-PRF-23377G) degrades severely after accelerated weathering. Typical degradation includes deterioration of …

Improving Pilot Mental Workload Classification Through Feature Exploitation And Combination: A Feasibility Study, Jeremy B. Noel, Kenneth W. Bauer, Jr., Jeffrey W. Lanning

United States Air Force: Publications

Predicting high pilot mental workload is important to the United States Air Force because lives and aircraft have been lost due to errors made during periods of flight associated with mental overload and task saturation. Current research efforts use psychophysiological measures such as electroencephalography (EEG), cardiac, ocular, and respiration measures in an attempt to identify and predict mental workload levels. Existing classification methods successfully classify pilot mental workload using flight data for a single pilot on a given day, but are unsuccessful across different pilots and/or days. We demonstrate a small subset of combined and calibrated psychophysiological features collected from …

The U.S. Air Force Remotely Piloted Aircraft And Unmanned Aerial Vehicle Strategic Vision, U.S. Air Force

United States Air Force: Publications

The U.S. Air Force Remotely Piloted Aircraft and Unmanned Aerial Vehicle Strategic Vision (hereafter referred to as The Strategic Vision) examines the future role of Air Force remotely piloted aircraft (RPAs) and unmanned aerial vehicles (UAVs) and their integration with other Air Force and joint systems. The Strategic Vision is presented in five sections.

Decision Support For The Career Field Selection Process At The Us Air Force Academy, Andrew P. Armacost, James K. Lowe

United States Air Force: Publications

Each year, the US Air Force Academy graduates nearly 1000 young men and women. To support the decision of which cadets will be classified into which career fields, we describe a linear programming formulation with appealing computational properties that enable it as the core of a decision support tool. We explore methods for measuring and balancing cadets' class standing, Air Force career field requirements, and cadets' career field preferences in the context of this model. Our computational experiments demonstrate the improvement of this method over previous classification approaches, yielding more than 10% increase in the number of cadets assigned to …

United States Air Force Posture Statement 2004, U.S. Air Force

United States Air Force: Publications

In 2003, U.S. and coalition military operations produced unprecedented mission successes - across the spectrum of conflict and around the globe. The joint warfighting team demonstated combat capability never previously witnessed in the history of conflict.

Biomimetic Model Of Skeletal Muscle Isometric Contraction: I. An Energetic–Viscoelastic Model For The Skeletal Muscle Isometric Force Twitch, C. A. Phillips, D. W. Repperger, A. T. Neidhard-Doll, D. B. Reynolds

United States Air Force: Publications

This paper describes a revision of the Hill-type muscle model so that it will describe the chemo-mechanical energy conversion process (energetic) and the internal-element sti2ness variation (viscoelastic) during a skeletal muscle isometric force twitch contraction. The derivation of this energetic–viscoelastic model is described by a 3rst-order linear ordinary di2erential equation with constant energetic and viscoelastic coe5cients. The model has been implemented as part of a biomimetic model, which describes the excitation–contraction coupling necessary to drive the energetic–viscoelastic model. Finally, the energetic–viscoelastic model is validated by comparing its isometric force–time pro3le with that of various muscles reported in the literature.

The Houston Conference Revisited, Ralph M. Reitan, Jim Hom, Janet Van De Voorde, Daniel E. Stanczak, Deborah Wolfson

United States Air Force: Publications

This paper presents a review and critique of the Houston Conference on Specialty Education and Training in Clinical Neuropsychology, together with an informal summary of opinions of a number of neuropsychologists. Issues regarding the role of the Clinical Neuropsychology Synarchy (CNS) and the applicability of the conference policies are offered. Several deficiencies and limitations of the policy statement are discussed. An informal survey of neuropsychologists interested in the Houston Conference indicates rather different opinions concerning the training and education of neuropsychologists. It is our contention that the results of the Houston Conference can only be considered controversial at best and …