University Of Dayton Research Institute Research Articles

Meeting the challenges of hypervelocity impact testing at 10 km/s

The ability to evaluate the response of spacecraft hardware to the impacts of orbital debris at velocities of interest, e.g., 9 to 11 km/s, has been an elusive goal of the hypervelocity impact community. This velocity range is greater than the capability of two-stage, light-gas guns traditionally used to test spacecraft shields, structures, and thermal protection systems. To meet the need for test capabilities at these higher velocities, the University of Dayton Research Institute (UDRI) developed a three-stage, light-gas gun and used it to launch Nylon, aluminum, aluminum oxide, and stainless steel spheres to velocities up to 10 km/s. The development of the three-stage, light-gas gun, a reliable functioning sabot, and a method of discarding the sabot after its use posed significant design and operational challenges. This paper describes: (1) the three-stage, light-gas gun; (2) a unique, one-piece sabot design required to withstand the extreme accelerations and loads imposed on the spheres and sabots during their launch, and (3) a novel method of discarding the sabot after its use. It concludes with the presentation of the results of two tests performed on spacecraft hardware at impact velocities of 9.23 and 9.90 km/s.

Cityhawk VTOL to be Used as Air Ambulance

Steven Zabarnick, division head of fuels and combustion at the University of Dayton Research Institute describes his team's ongoing work developing standards for sustainable jet fuels

Clearing the Way for Alternative Fuels

Steven Zabarnick, division head of fuels and combustion at the University of Dayton Research Institute describes his team’s ongoing work developing standards for sustainable jet fuels

Molten Lithium Battery for Space Applications

Solid-state electrolytes (SEs) have gained much interest lately as a potential for mitigating the various issues inherent in a most energy dense lithium metal (anode) based batteries such as lithium ion, lithium sulfur (Li-S), and lithium oxygen. Notable high energy next generation cathodes such as sulfur have their own issues with a liquid electrolyte based system, where the polysulfides discharge product dissolve into the electrolyte causing both: a loss of cathode active material and an unwanted shuttling of the polysulfides over the polymer separator to the lithium anode limiting their practical use. Moreover, the formation of lithium dendrites in lithium batteries is yet another challenging issue that not only limits battery cycle-life but also poses safety risks. The use of SEs can potentially address most of the issues related to next generation lithium batteries such as Li-S batteries, but getting rid of dendrite issues may not be addressed completely. One way to eliminate the dendrite issue is to use molten lithium as an anode.The National Aeronautics and Space Administration (NASA) has an ambitious plan to explore one of the most challenging planets in our solar system: Venus. The surface temperature of Venus can reach as high as 465°C and at same time, the Venus atmosphere is filled with corrosive gases such as carbon dioxide, sulfur dioxide, carbon monoxide, etc. A battery for such a challenging space mission can be built only if battery components (especially the electrolyte) is stable beyond 500°C and must be stable with molten lithium and sulfur electrodes for at least hours or days if not months—longer is better. Last but not the least, yet another challenge is containment of gaseous sulfur inside the battery container at such a high temperature. The potential to replace sulfur with selenium may mitigate the issue but at cost of reduced energy density.Under a NASA funded project, the University of Dayton Research Institute (UDRI) is developing molten lithium sulfur (Li-S) or lithium-selenium (Li-Se) batteries with the help of a high temperature solid ceramic electrolyte (SCE) that can enable a operating temperature >465°C for several hours. UDRI has been working on a high temperature SCE such as phosphate-based Li1+ xAlxGe2- x(PO4)3 (LAGP) ceramic electrolyte material1 that is stable beyond 500°C and also shows broad electrochemical window (up to 5V) that is sufficient for a molten Li-S or Li-Se battery operation; provided LAGP is stable with Li and S or Se in such harsh conditions and temperature. Unfortunately, LAGP is not stable with Li (forms a highly resistive interface layer between LAGP and electrode) and its stability with sulfur or Se, needs to be determined.Under the NASA project, UDRI has been developing interface materials between LAGP and electrodes for Li-S and Li-Se cells that can be stable at wide temperature range (room temperature to 500°C). The presentation will include progress on high temperature (up to 465°C) i) SCE, ii) SCE/Li interface materials, iii) SCE/S interface material, iv) SCE/Se interface material, v) impedance and open circuit voltage of Li-S or Li-Se cells at 465°C, and vi) cycle-life of Li-S or Li-Se cells at 465°C. To the authors knowledge, there is no such report (molten Li-S or Li-Se cells that can function at 465°C) that exists in literature.B. Kumar, D. Thomas, J. Kumar, “Space-Charge-Mediated Superionic Transport in Lithium Ion Conducting Glass–Ceramics,” J. Electrochem. Soc. 156, A506 (2009)

Fatigue and crack-growth behavior in a titanium alloy under constant-amplitude and spectrum loading

A titanium alloy (Ti-6Al-4V STOA) plate material was provided by the University of Dayton Research Institute from a previous U.S. Air Force high-cycle fatigue study. Fatigue-crack-growth tests on compact, C(T), specimens have been previously performed at Mississippi State University on the same material over a wide range in rates from threshold to near fracture for several load ratios (R = Pmin/Pmax). These tests used the compression pre-cracking method to generate fatigue-crack-growth-rate data in the near-threshold regime. Current load-reduction procedures were found to give elevated thresholds compared to compression pre-cracking methods. A crack-closure model was then used to determine crack-front constraint and a plasticity-corrected effective stress-intensity-factor-range relation over a wide range in rates and load ratios. Some engineering estimates were made for extremely slow rates (small-crack behavior), below the commonly defined threshold rate. Newly-developed single-edge-notch-bend, SEN(B), fatigue specimens were machined from titanium alloy plates. These specimens were fatigue tested at two constant-amplitude load ratios (R = 0.1 and 0.5) and a modified Cold-Turbistan engine spectrum. All of the tests were conducted under laboratory air and room temperature conditions. Calculated fatigue lives from FASTRAN, a fatigue-life-prediction code, using small-crack theory with an equivalent-initial-flaw-size (semi-circular surface flaw) of 9-μm in radius at the center of the semi-circular edge notch fit the constant-amplitude test data fairly well, but under predicted the spectrum loading results by about a factor of 2–3. The reasons for the large under prediction were discussed. Life predictions made with linear-cumulative damage (LCD) calculations agreed fairly well with the spectrum tests.

Congratulations John Grant!

With this special issue, we are celebrating the outstanding career of John Grant, who is retiring from both his roles as SIA North‐American Editor and his affiliation with the University of Dayton Research Institute and the Air Force Materials Lab.We open this issue with a personal note from the Air Force Research Laboratory written by Neil Murphy. This note is followed by an essay by several of John's surface analysis colleagues, highlighting the professionalism that has been one of the hallmarks of John's career. We are all indebted to John for conveying the importance of true professionalism through his teaching, journal editorship and numerous other contributions to the surface analysis community. John's many professional activities and awards are summarized below.

Toughened Thermal Blanket for Micrometeoroid and Orbital Debris Protection

Toughened thermal blankets have been developed that greatly improve protection from hypervelocity micrometeoroid and orbital debris (MMOD) impacts. Three types of materials were added to the thermal blanket to enhance its MMOD performance: (1) disrupter layers, near the outside of the blanket to improve breakup of the projectile, (2) standoff layers, in the middle of the blanket to provide an area or gap that the broken-up projectile can expand, and (3) stopper layers, near the back of the blanket where the projectile debris is captured and stopped. Hypervelocity impact tests were performed on candidate toughened thermal blanket configurations at the NASA White Sands Test Facility and at the University of Dayton Research Institute. From these tests the best disrupter materials were found to be beta-cloth and fiberglass fabric. Polyimide open-cell foams provide a light-weight means to increase the blanket thickness and improve MMOD protection. The best stopper material is Spectra™ 1000-952 or Kevlar™ KM2-705. These blankets can be outfitted if so desired with a reliable means to determine the location, depth and extent of MMOD impact damage by incorporating an impact sensitive piezoelectric film.

Solid Particle Erosion Testing of Helicopter Rotor Blade Materials

The Army Research Laboratory (ARL) was asked to participate in an OSD-funded erosion effort by the Coating Technology Integration Office at Wright Patterson Air Force Base. Solid particle (sand) erosion testing was conducted by the University of Dayton Research Institute to determine the erosion resistance of materials currently used on the leading edges of Army aviation rotor blades of aircraft in Southwest Asia (SWA). This testing and evaluation was important for two reasons; first, Iraq and Afghanistan are the primary locations of our current anti-terror operations, and second, the sands within these two countries are the worst in the world from an erosion standpoint (dry conditions + freshest grains of sand + predominantly angular quartz grains + blowing winds). The sand utilized herein is considered even more erosive than the sand from these two countries, since they contain a higher concentration of quartz than the SWA sand. In 2005, observations of actual SWA field failures of helicopter rotor blade protective tapes and coatings were compared to existing state-of-the-art, laboratory-based sand erosion data during a U.S. Army sponsored program. Laboratory-produced data did not match the severity of field-use damage, even under extremely high levels of particle loading. The need to test to erosive failure representative of this environment was determined to be paramount in establishing relative performance levels of erosion resistant protective systems being screened for potential field use. The goal of this effort was to provide two synthetic sand formulas capable of testing various polymer-based candidate rotor blade protective systems to failure. The test media was derived from characterization of sand and dust materials unique to SWA. The synthetic sand mixtures developed by this effort will be incorporated in a new test protocol for sand erosion to represent a truly “worst case” test, with extended application to other aerospace components susceptible to sand erosion damage applicable to Department of Defense activities in most dry—hot desert regions. Comprehensive post-test analysis performed by ARL included: visual examination, mass loss calculations, erosion rate determination, surface roughness testing, volume loss calculations, scanning electron microscopy characterization, and metallography. As a result of post-test analysis, many trends were observed, with the results documented herein. The results of this testing have been used as a baseline for future testing of alternative materials and coating systems, and to prepare a solid particle erosion test standard (MIL-STD-3033).

Characteristic strength, Weibull modulus, and failure probability of fused silica glass

The development of high-energy lasers has focused attention on the requirement to assess the mechanical strength of optical components made of fused silica or fused quartz (SiO2). The strength of this material is known to be highly dependent on the stressed area and the surface finish, but has not yet been properly characterized in the published literature. Recently, Detrio and collaborators at the University of Dayton Research Institute (UDRI) performed extensive ring-on-ring flexural strength measurements on fused SiO2 specimens ranging in size from 1 to 9 in. in diameter and of widely differing surface qualities. We report on a Weibull statistical analysis of the UDRI data-an analysis based on the procedure outlined in Proc. SPIE 4375, 241 (2001). We demonstrate that (1) a two-parameter Weibull model, including the area-scaling principle, applies; (2) the shape parameter (m10) is essentially independent of the stressed area as well as the surface finish; and (3) the characteristic strength (1-cm2 uniformly stressed area) obeys a linear law, C (in megapascals) 160−2.83× (in parts per million per steradian), where characterizes the surface/subsurface damage of an appropriate set of test specimens. In this light, we evaluate the cumulative failure probability and the failure probability density of polished and superpolished fused SiO2 windows as a function of the biaxial tensile stress, for stressed areas ranging from 0.3 to 100 cm2.

Preface

An elusive goal of the hypervelocity impact community has been the evaluation of the ballistic response of space hardware to impact velocities ranging from 8 to 11 km/s using projectiles with known properties. The design, development, and use, during the 1960s, of a three-stage, light-gas gun at McGill University is reviewed. The developers of this gun claim that they were able to launch cylindrical, 12.7-mm-diameter Lexan disks with masses of 1.5 and 1.1 g to velocities of 9.6 and 10.5 km/s, respectively. This paper presents the results of an internally funded program at the University of Dayton Research Institute (UDRI) to duplicate the published performance of the McGill University launcher. A support structure and various components of a third stage which used an 8.1-mm-diameter launch tube were added to the UDRI 75/30-mm, two-stage, light-gas gun, making the arrangement of the components similar to the one used by McGill University. Work on the development of the UDRI three-stage, light-gas gun is a continuing effort, with the goal of successfully launching small diameter (∼3 mm or less) aluminum spheres to velocities in excess of 9 km/s. To date, the highest projectile velocity achieved with the UDRI three-stage, light-gas gun has been 8.65 km/s.

Impact of thin aluminum sheets with aluminum spheres up to 9 km/s

The results of further development of the University of Dayton Research Institute (UDRI), three-stage, light-gas gun and impact test data are presented. We have successfully launched 2.38-mm-diameter aluminum spheres to velocities in excess of 9 km/s with no damage to the launcher components. The results of several tests in which 2.38-mm-diameter aluminum spheres impacted thin aluminum sheets at velocities up to 9.10 km/s are presented. Quantitative data obtained from these tests were used to extend previously established relationships to velocities which are typical of the collisions of orbital debris with spacecraft. These test results include: bumper-sheet hole diameter as a function of impact velocity; determination of the fragmentation-initiation-threshold velocity for spheres impacting very thin sheets; and continued demonstration of the “scalability” of the test results using the bumper-thickness-to-projectile-diameter ratio ( t / D ) as the scaling factor.

New Thinking on Flame Retardants

No one wants their bed, couch, chair, computer, or TV to catch on fire. “If an ordinary upholstered chair in your home gets ignited, it can essentially take your whole house down,” says Richard Gann, a senior research scientist at the U.S. National Institute of Standards and Technology’s (NIST) Building and Fire Research Laboratory. The most flammable part of a mattress or couch is its plastic polyurethane foam cushioning, he explains. Once a fire gets through a chair or mattress’s fabric covering and into this cushioning, it can start a catastrophic reaction that quickly leads to “flashover,” in which nearly everything combustible inside a room ignites simultaneously. Until very recently, brominated flame retardants, especially polybrominated diphenyl ethers (PBDEs), were one of the main materials used to reduce the speed with which the plastic components of consumer goods including beds, couches, chairs, and electronics could be consumed by fire. However, growing evidence shows that PBDE compounds are escaping from the products they protect and making their way into the products’ users. Moreover, the chemicals may disrupt human thyroid hormone functioning and cause other health effects, prompting many nations to ban or suspend their use in new consumer goods. [For more information on the health effects of PBDEs, see “Unwelcome Guest: PBDEs in Indoor Dust, p. A202 this issue.] Although bromine- and chlorine-containing flame retardants are still used in some products, the need for new alternatives is being driven by a confluence of policy, standards, and pressure from environmental groups. Europe banned the use of two formulations, PBDE pentaBDE and octaBDE, in 2004, the same year they were withdrawn from the North American market. A third compound, decaBDE, was banned 1 April 2008 by the European Court of Justice. Stateside, Maine has banned the use of decaBDE, the only PBDE still on the market in North America, in mattresses and residential upholstered furniture produced and sold in that state, and will extend the ban to electronics in 2010. Washington prohibits the use of decaBDE in mattresses and sets a process for a future ban in furniture and electronics if the state can identify a safer and feasible alternative that meets fire safety standards. Asian countries and other U.S. states have similar legislation in the works. “Instead of adding new fire retardant chemicals that ultimately may be shown to cause health problems, we should be asking whether we need to use these chemicals or if there are other ways to achieve equivalent fire safety,” contends Arlene Blum, a biophysical chemist and visiting scholar at the University of California, Berkeley. “So many of the chemicals we have banned in the past were flame retardants—think about asbestos, polychlorinated biphenyls, polybrominated biphenyls, tris(2,3-dibromopropyl) phosphate, PBDEs—[and] they all ended up in the environment and in people,” she points out. “We need to think carefully about adding these sorts of chemicals to consumer products before there is adequate health information.”

Development of a three-stage, light-gas gun at the University of Dayton Research Institute

An elusive goal of the hypervelocity impact community has been the evaluation of the ballistic response of space hardware to impact velocities ranging from 8 to 11 km/s using projectiles with known properties. The design, development, and use, during the 1960s, of a three-stage, light-gas gun at McGill University is reviewed. The developers of this gun claim that they were able to launch cylindrical, 12.7-mm-diameter Lexan disks with masses of 1.5 and 1.1 g to velocities of 9.6 and 10.5 km/s, respectively. This paper presents the results of an internally funded program at the University of Dayton Research Institute (UDRI) to duplicate the published performance of the McGill University launcher. A support structure and various components of a third stage which used an 8.1-mm-diameter launch tube were added to the UDRI 75/30-mm, two-stage, light-gas gun, making the arrangement of the components similar to the one used by McGill University. Work on the development of the UDRI three-stage, light-gas gun is a continuing effort, with the goal of successfully launching small diameter (∼3 mm or less) aluminum spheres to velocities in excess of 9 km/s. To date, the highest projectile velocity achieved with the UDRI three-stage, light-gas gun has been 8.65 km/s.

Application of Cognitive Task Analysis in User Requirements Definition and Prototype Design

The Aircraft Maintenance Intuitive Troubleshooting (AMIT) project is a three-year Air Force Research Laboratory (AFRL) effort headed by the Logistics Readiness Branch, Warfighter Readiness Research Division, Human Effectiveness Directorate (HEAL) through NCI Information Systems, Inc, with the support of the University of Dayton Research Institute (UDRI). AMIT's goal is to support aircraft maintenance technicians by providing the right information, appropriate to their experience level, so they will more efficiently and effectively complete their task. Multiple data collection strategies were adopted, including an extensive literature review, a series of process interviews, and a progression of CTA interviews. The CTA effort was designed to capture where the process is inadequate or breaks down. Areas of the maintenance process identified as most challenging includes debrief, problem duplication, and troubleshooting. Resulting design recommendations include Graphical System Representations, electronic technical orders, electronic wiring diagrams, access to other information sources, and application of case based reasoning.

An automated ultrasonic system for inspection of aircraft turbine engine components

The University of Dayton Research Institute (UDRI), under contract by the U.S. Air Force, has designed and constructed a fully automated ultrasonic inspection system for the detection of embedded defects inside in-service gas turbine engine disks. This system uses many new approaches that conduct automated ultrasonic inspections to produce highly reliable engine disk inspections without human involvement. The ultrasonic inspection system incorporates off-the-shelf, industry standard components typically not found in NDI systems, that have been integrated using a modular-architecture approach to produce a system capable of sustained operation in an Air Force depot environment. Designed to he rugged and easily maintained, the system consists of a six-axis articulated robotic arm, rotating water tank, phased-array ultrasonic instrument, automated probe changing of 'smart' probes, collision avoidance hardware, PC-based industrial computer, Windows-based operating system, digital vision system, and a specialised water management system that eliminates air bubbles in the water. The robotic manipulation of the probes allows ultrasound to be directed at almost all features of the engine component. Use of the phased-array ultrasonic instrument and probes allows for optimisation of both the sensitivity and resolution for each inspection through electronic beamforming, scanning, and focusing processes. The system requires an operator to load the part, and then conducts all parts of the inspection automatically. including part recognition, part dimensioning, probe changing, probe calibration, inspection, and accept/reject decisions. This paper discusses the components and specifications of the system and technology improvements over conventional systems that have been incorporated.

Cellular Automation Approach to Model Aircraft Corrosion Pit Damage Growth

The pitting corrosion damage growth in aircraft aluminum is investigated. The main objective is to develop a corrosion pit damage growth process model using the local rules governing the electrochemical reactions and simulate them as a discrete dynamic system using cellular automata approach. The results of corrosion damage growth obtained from simulation are compared qualitatively as well as quantitatively to the experimental data obtained from Center for Materials Diagnostics at the University of Dayton Research Institute, Dayton, Ohio. The effect of various electrochemical parameters on the damage growth are obtained from the simulation are presented and discussed. The results presented illustrate the new approach using cellular automata to model pit damage growth in aircraft aluminum materials. The simulation program is developed in JAVA environment for ease of portability and usability.

AVS Hosts Meetings in San Francisco

AVS Hosts Meetings in San Francisco

A discussion of rain erosion testing at the United States Air Force rain erosion test facility

For the past twenty-five years the University of Dayton Research Institute has operated the Rain Erosion Test Facility for the United States Air Force Wright Laboratory Materials Directorate at Wright-Patterson Air Force Base, Ohio. This is a commercially available, whirling-arm facility that produces a 25.4 mm per h rain field and is capable of providing specimen velocities up to 290 m s −1 (650 mile h −1, 0.87 Mach). Various attack angles of specimen-to-rainfall are also possible ranging from 15° to normal. The average rainfall drop size is 2 mm (0.079 in). The facility is in use on a daily basis and serves the aerospace community on virtually a world-wide basis. Almost 40 000 test specimens have been evaluated as of January 1994. This paper will describe the facility in some detail. The method of testing and operation will be described and discussion will include the many types of specimens and materials that can be tested—ranging from metals, composites, plastics, honeycomb constructions, glass/optical, ceramics—and their allowable size and configurations. The mode of operation and the evaluation procedures used will be detailed. Failure mechanisms as erosion and adhesion loss will be discussed and related to materials performance and applications. Work in this facility has become the cornerstone for testing to many Military Specification coatings' requirements. It has been referred to as a ‘national resource’ by USAF personnel.

Using dense, low melting point projectiles to simulate hypervelocity impacts on typical spacecraft shields

In this paper the authors investigate the use of a dense, low melting point projectile, i.e., cadmium, launched at light-gas gun velocities, to simulate higher velocity, lower density projectiles such as aluminum. This technique was first suggested by Morrison [l], for craters in semi-infinite targets. Hypervelocity tests performed at the University of Dayton Research Institute, using cadmium projectiles to impact aluminum Whipple and multiple, NextelTM ceramic-bumper shields are described, and the results are compared with similar Whipple shields tested at the NASA Ames Research Center, using aluminum projectiles at maximum light-gas gun speeds. The cadmium and aluminum projectiles had the same masses, and the initial impact momenta were maintained as close as possible, i.e., 92 to 96%. Computer simulations of two of the cadmium projectile-aluminum Whipple shield tests are presented, together with the physical states in the debris-bubble and the impact momentum on the rear-wall. These results are compared with sequential X-radiographs of the impact debris and the damage sustained by the rear walls. Photographic evidence of the damage is included in the report. The calculations of the aluminum projectile mass and velocity that match the cadmium results and give the equivalent impulsive loading on the rear-wall are discussed, and scaling analysis is used to determine the appropriate size and speed of the projectile. The enhanced all-aluminum verification test capability resulting from the technique described in this paper is shown to be at least 8.3 km/s, a 30% increase over the normal light-gas gun velocity for the mass in question.

Analysis of the UDRI tests on Nextel multi-shock shields

This paper analyzes the results of further development of the Nextel ceramic cloth, multiple-bumper or multi-shock shield, first presented at the 1989 HVIS and published as Cour-Palais and Crews (1990). The supporting hypervelocity impact testing was done by the University of Dayton Research Institute, Dayton, Ohio, in their Impact Physics Laboratory, using 0.953cm aluminum spheres and equal-mass (l/d=0.16) aluminum discs. The projectiles were launched at 6.6 to 6.9km/s by a 50 20 mm , two-stage light gas gun, normal to the targets. The objective of this development project was to investigate light-weight, flexible, multiple-bumper shields for possible use as protection for some elements of Space Station Freedom. The analysis discusses the performance of shields consisting of different combinations of Nextel ceramic cloth bumpers and aluminum rear sheets. Several Nextel fiber strengths and weaves were investigated as bumpers and a baseline, light-weight shield that met the failure criteria was established using the spherical aluminum projectiles. This same target was then tested against the aluminum discs to investigate the effect of projectile shape. The multi-shock phenomena was also investigated during this project using the UDRI multiple, orthogonal x-ray system to observe the first three or four sequential impacts of the projectile fragments. Some of these are reproduced in the paper, together with views of the associated rear sheet damage. Similarities between the shock effects of the Nextel and thin aluminum bumpers are shown, and the aluminum multiple-bumper shield results are used to further understand the multi-shock process. Finally, the paper modifies the equation constants given by Cour-Palais and Crews (1990), adds constants for the l/d=0.16 disc, and provides evidence that they scale with momentum to 10km/s.