Tech Briefs

Monazite Deformation Twinning Research

AFRL scientists have significantly advanced the understanding of a phenomenon called deformation twinning, a major materials deformation mechanism that is particularly important at low temperatures and high strain rates. Working with industry, laboratory researchers successfully identified five deformation twin modes in monazite, a complex mineral with low symmetry. They were able to explain the existence of these modes using fundamental principles that should ultimately prove useful for the prediction of deformation twinning in more complex systems. These studies help scientists obtain the knowledge required to create better tools for analyzing the composition and application potential of minerals and other natural materials essential both to the development of national defense systems and to the research and development of dynamic new commercial products.

Posted in: Briefs, Materials

Dynamic Cavity Formation Imaging

When an Air Force bomber drops a penetrating munition, what happens as the warhead travels underground to the target? AFRL researchers at the Advanced Warhead Experimentation Facility (AWEF) recently captured X-ray images of laboratory-scale warheads as they penetrated sand targets at high speeds. These radiographs enhance the weapon design community's understanding of warhead/target interactions and aid in validating computer simulations as well.

To improve future warhead performance, AWEF researchers are striving to understand the physics behind a high-speed weapon's penetration of dry particulate media. The media under investigation undergoes very complex reactions during penetration because without the gluelike presence of moisture, the dry particles move freely with respect to each other. Consequently, the cavity formed around a high-speed projectile throughout its penetration collapses almost immediately after the projectile continues its progress. The diagnostic X-ray techniques that AFRL researchers are refining allow a glimpse of the temporary cavity, which provides a key indication of the penetration loading environment. Without knowledge of the physical interactions that occur during a weapon's penetration, weapon designers are limited to judging a new warhead's performance (e.g., penetration depth) through empirical trial-and-error methods. The incorporation of proven theoretical penetration models into advanced computer simulations will thus shorten the process of developing optimal warhead designs.

The current research effort is an expansion of a related study conducted in the 1970s. The previous study examined cylindrical rods traveling at conventional velocities through an unconfined sand trough. The recent experimental series, conducted in 2005, examined a variety of conventional warhead nose shapes in their highspeed penetration of confined sand targets. The investigated nose shapes included a sharply pointed ogive nose (see Figure 1), a blunted ogive nose (see

Figure 2), and a spherical nose.

Despite the past 30 years' progress in X-ray technology and the advent of digital processing, which enhances image contrast, obtaining useful images remains a challenge. For example, sand both absorbs and scatters X-rays. To maintain image quality, researchers therefore limited the target's diameter to 6 in., and to maximize the energy reaching the X-ray film, they kept the distance between the X-ray-generating power head and the film as small as possible. Due to the proximity of the equipment to the experiment's target location, however, flying fragments occasionally damaged both the film and the X-ray power head. As a result of this same proximity, the simultaneous triggering of the multiple X-ray heads produced shadows on the image. Throughout the experiments, researchers positioned the X-ray heads above and beside the projectile's expected flight path to show orthogonal views. This technique enabled the team to determine a projectile's pitch and yaw prior to its impact with the target and also provided a three-dimensional view of cavity formation during the penetration event. The researchers also found that by triggering a single X-ray pulse, they were able to mitigate the poor contrast and clutter caused by multiple shadow images. Despite the difficulties encountered, the series of experiments produced a dozen quality images.

The preliminary results surprised the research team. For example, the team discovered that the penetration cavity is much smaller than expected. Additionally, the area of the nose in physical contact with the target media is relatively small. In Figures 1 and 2, the light-colored objects are the projectiles and the dark region immediately surrounding each projectile is the cavity. In normal circumstances, the explosive payload would ride in the center of the projectile shaft. The thin white lines are the result of lead crosshairs placed on the film's exterior surface to align the X-ray head. Researchers are planning an additional series of experiments designed to increase the image database and refine the X-ray's diagnostic potential.

Understanding weapons penetration phenomena is essential to the efficient design of future weapons concepts. As a result of experimental efforts such as these, the intelligent warheads and other munitions of tomorrow may one day be capable of morphing their exterior shape to achieve the most efficient penetration of the media encountered.

Lt Christine E. Watkins, of the Air Force Research Laboratory's Munitions Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at Reference document MN-H-05-16.

Posted in: Briefs, Photonics

AFRL Teams With Indy Racing League® for Neck Protection

The bulletlike, open-wheel Indy racing cars hurtle around oval tracks at breakneck velocities, often approaching speeds of 220 mph or higher. While a crash at this speed is a violent, sometimes tragic event, it is nonetheless a key data source for AFRL researchers seeking ways to create a safer environment for Air Force (AF) fighter pilots during emergency ejection.

Instituting a practical alliance of human peril and scientific research, AFRL engineers are teaming with the Indy Racing League (IRL) to share crash impact and injury data. Indy car drivers wear a miniature earplug accelerometer (see figure) that records vertical, lateral, and longitudinal accelerations of the driver's head during a crash. "This data will provide valuable information for criteria and model validation," states Ms. Erica Doczy, biomedical engineer in AFRL's Biomechanics Branch. "We need reallive human injury data to validate our models and criteria. In the lab, you can't re-create that [trauma], so this is just one way to collect that data, because accidents do occur in the motor sports industry."

The data helps researchers learn more about the dynamics of a highspeed impact and the effects of acceleration and impact on a human's head and neck. Researchers typically create models based on manikin and cadaver testing, but data from living humans is essential for validating the models. With the availability of detailed information about the car's speed and movement, and how the driver's head reacts at each stage of a crash sequence, researchers no longer have to theorize about the exact nature and cause of head and neck injuries. "We'll know what the car did, we'll know what the driver's head did, and we'll have medical data (the end result), so it's a way of validating the entire [series of] criteria," explains Dr. Joseph Pellettiere, technical advisor for the Biomechanics Branch.

The agreement with the IRL builds upon AFRL's long-standing program for improving neck protection for AF aircrew members during all phases of flight, and especially during high-risk, emergency ejection. "We develop the injury criteria and guidelines for how a flight helmet should be developed in terms of its mass properties—such as weight, center of gravity, and location of night vision goggles or other systems— such that it's safe for crew members to wear," elaborates Dr. Pellettiere.

AFRL researchers routinely feed updated data to flight helmet designers and manufacturers, who use the data to create safer next-generation equipment. The researchers also recommend the development and availability of preejection instructions that tell pilots how to physically prepare for ejection, including directions for assuming correct body position and bracing. "New helmet programs are using our criteria now," Dr. Pellettiere points out. "They are making their designs [according] to the guidelines we provide." Both the F-35 Joint Strike Fighter and the Panoramic Night Vision Goggle programs are developing helmets based on AFRL-supplied impact and injury data.

Indy car drivers benefit from the crash data through revised safety and equipment requirements which, in turn, improve racing safety levels. The research team also shares results with the commercial automotive industry through conferences and universities, a practice that can prompt safety-related policy changes for auto manufacturers.

As both technology and policy continue to evolve, the AF must persist in its efforts to evaluate pilot safety. This ongoing need is reflected in the following example, which illustrates how today's heavier helmet, coupled with a revised physical profile for pilots, has increased the risk of serious neck injuries during ejection. To accommodate a broader physical range of females (who currently constitute about 18% of AF pilots), the AF reduced the minimum body-weight limit for pilots to 103 lbs, with an associated decrease in neck muscle size and strength. Helmet weight, however, increases as peripheral systems are added to pilot headgear. A typical (3 lb) flight helmet's weight can increase to nearly 5 lbs after extra items, such as night vision goggles, are installed. According to Ms. Doczy, "Two additional pounds may not seem like much, but during an ejection, it adds a significant amount of force on the pilot's neck."

In addition to realizing safety improvements, the AF expects to achieve significant financial savings as a result of AFRL's neck protection advancements. "The potential for cost savings is tremendous, since the AF invests several million dollars to train each pilot," Ms. Doczy affirms. In addition to lost training dollars, the federal government bears the burden of an injured pilot through hospital and rehabilitation expenses. Preventing injuries and fatalities during ejection would minimize such costs. Cost-related advantages aside, the key goal for AFRL's neck protection program engineers— adeptly expressed in their motto, "Always Come Home Safely"—is to develop technology and use it to keep aircrew safe, not only during ejection, but ultimately in all phases of operational flight situations.

Mr. John Schutte (Ball Aerospace and Technologies Corporation), of the Air Force Research Laboratory's Human Effectiveness Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at Reference document HE-H-05-04.

Posted in: Briefs, Medical

Scientists Create Optically Equivalent Synthetic Human Tissue

Lasers are an integral part of the modern battlefield, used for applications as diverse as point-to-point communications and ballistic missile defense. Their widespread use increases the warfighter's likelihood of being exposed to laser hazards, and damage to an individual's eyes and skin can be serious. AFRL has served as a leading authority on laser-induced damage thresholds for many years.

Posted in: Briefs, Medical

Dielectric Coolants

The Joint Strike Fighter (JSF) is the Department of Defense's affordable next-generation strike aircraft designed to meet the needs of the Air Force (AF), Navy, Marines, and US allies. Currently in development by Lockheed Martin, the multimission, supersonic, JSF aircraft will provide all services with enhanced lethality and survivability and reduced vulnerability (see figure). The JSF's unique, multiple-variant design pushes the threshold of fighter technology far beyond current limitations. The AF variant of the technology takes multirole fighter performance to new levels, offering improved stealth, increased range on internal fuel, and advanced avionics. The JSF's advanced avionics, as well as its flight control, target acquisition, and other sophisticated electronic systems rely on high-performance coolants to ensure proper operation. Designers employ dielectric coolants to dissipate heat from high-energy electronic components and therefore consider these fluids critical to aircraft operation and safety.

Posted in: Briefs, Materials

Weapon Data Link Demonstration

One of the US Air Force's goals is to reduce the time needed to strike timesensitive targets, thus minimizing the adversary's perceived mobility advantage and leaving concealment as that enemy's primary defensive measure. One potential way to meet this challenge relies on a capability to redirect and update weapons with new target coordinates while they are in flight—a solution that requires weapons developers to outfit weapons with a data link enabling communications between warfighters operating in the air and on the ground. This Weapon Data Link (WDL) approach would allow the warfighter to directly communicate with and control air-launched weapons to strike moving or otherwise time-sensitive targets, while continually gathering information about the weapon's performance against those targets. The scenario could involve something as simple as a weapon communicating its position and system status back to the release aircraft, or something as complex as a weapon operating in the Global Information Grid (GIG), wherein a secondary ground/air controller assumes the weapon's control after a positive handoff from the release platform, with the weapon's sensor and video information autonomously distributed throughout the GIG.

Figure 1. Depiction of WDLAFRL engineers recently accomplished a critical step in demonstrating the WDL approach. Held at Langley Air Force Base (AFB), Virginia, the demonstration's primary objective was to show that two WDL terminals, connected to Tactical Air Control Party (TACP) laptop computers, could successfully transmit and receive J-series messages within a Link-16 network (see Figures 1 and 2). The network included a legacy Fighter Data Link (FDL) terminal provided by the 46th Test Squadron (Eglin AFB, Florida), two WDL terminals, and local aircraft equipped with Link-16 radios.

Engineers from AFRL and Rockwell Collins partnered to develop the 50 in3, software-defined WDL radio used in the demonstration. This radio provides multiple operators with the flexibility to port and upload communication waveforms. The device has three software waveforms loaded into its memory; the operator can switch between these waveforms as required. Although the test team limited this demonstration to Link-16 operation, future demonstrations will highlight the radio's capacity to receive and transmit ultra-high-frequency satellite communications and line-of-sight waveforms as well. The TACP Modernization program supplied the TACPCASS (Close Air Support System) software, laptop computers, and a trained operator. During the first part of the demonstration, one TACP computer generated target coordinates and transmitted them as J-series messages from one WDL terminal to the other. The TACP-CASS software on the second TACP computer interpreted and displayed the transmitted messages as target tracks. This test showed that messages generated by the TACP-CASS software could be correctly interpreted by the two networked WDL terminals and that this information could be shared between them. In the second phase of the demonstration, test engineers integrated the FDL terminal into the network. One of the TACP computers transmitted target information via Link-16 network protocol to the FDL terminal, which correctly interpreted and displayed the information on the Improved Multilink Translator and Display System (IMTDS). In the next phase, both computers correctly received, interpreted, and displayed target messages transmitted by the FDL terminal. In a final demonstration of system capability, several aircraft from Langley AFB joined the network for short periods of time, transmitting information that was subsequently displayed on both the TACP and IMTDS computers.

Figure 2. Setup of WDL demonstration equipmentAll demonstration participants gained valuable insight into using Link-16 networks for passing J-series messages between aircraft, weapons, and ground troops. The test team did not intend for the demonstration to provide an in-depth look at integrating weapons into battlefield networks. Rather, its purpose was to provide a rudimentary understanding of how an aircraft, weapon, and TACP could join and operate in an existing Link-16 network, while specifically demonstrating the capability of a software-defined WDL radio to transmit and receive J-series messages. The demonstration achieved its twofold purpose, both providing overall insight regarding the system and establishing the flexibility of a softwaredefined WDL radio in processing J-series messages within a representative network.

Ms. Michelle White, of the Air Force Research Laboratory's Munitions Directorate, wrote this article. For more information, contact TECH CONNECT at (800) 203-6451 or place a request at Reference document MN-H-05-14.


1 "China-America: The Great Game." Interview With Lt Gen Liu Yazhou. Eurasian Review of Geopolitics, Gruppo Editoriale L'Espresso/Cassan Press-HK, Jan 05.

Posted in: Briefs, Electronics & Computers, Data acquisition and handling, Personnel, Military aircraft

RASCAL Facility

AFRL's Radiation and Scattering Compact Antenna Laboratory (RASCAL) enables researchers to develop and evaluate advanced aperture technologies that support electronic warfare, radar, communication, and navigation— technologies supplementing a variety of applications as the "eyes and ears" of the warfighter. Current research efforts are concentrated on developing relatively small and inexpensive broadband, multifunctional antennas, as well as conformal and structurally integrated antennas for manned and unmanned air vehicles. Using the RASCAL facility, researchers can perform the necessary fabrication, simulation, testing, and measurement of aperture technologies.

Posted in: Briefs, Electronics & Computers, Antennas, Test facilities, Military aircraft