Tech Briefs

Military Worth Analysis of New Concept Weapons

Weapon systems analysts traditionally conduct military worth analysis (MWA) to evaluate the warfighter payoff resulting either from the development and implementation of new assets or from the establishment of new concepts of employment for existing assets. Analysis scope ranges from the campaign level to the mission level and thus differs in magnitude, time frame, and level of detail (see Figure 1). While MWA can potentially evaluate hundreds of possible metrics, it typically includes parameters such as time to accomplish objectives, number of targets neutralized, amount of collateral damage, and volume of resources consumed (including dollars). As depicted in Figure 2, laboratory directors must consider both the analytically demonstrated payoff and the clear interest of the user community in making an informed investment decision; therefore, determining the MWA for a particular laboratory technology is vitally important.

Posted in: Briefs, Information Technology

Developing Condition-Based Maintenance

Like any manufacturing equipment, semiconductor fabrication systems have a finite lifetime. Technicians normally perform maintenance on these hardware systems according to preset schedules and regardless of actual need, which results in unnecessary equipment downtime and needless costs incurred as a result of lost production time and additional maintenance labor. AFRL scientists teamed with researchers from the University of New Mexico (UNM) to examine the feasibility of establishing prognostics for such expensive and valuable machinery and to devise a mechanism for scheduling equipment maintenance based on needs rather than calendar cycles. This so-called condition-based maintenance has the potential to increase equipment availability, improve productivity, enhance safety, and reduce expenses. The ultimate objective of the AFRL/UNM collaboration is to develop a data-driven prognostic system that provides advanced warning of failures, faults, and other error events that occur in complex systems.

Posted in: Briefs, Information Technology

Design of Lightweight and Durable Composite Structures

In the field of engineering design, "factors of safety" are derivatives of inadequate knowledge and therefore are a necessary, but costly, element of engineering design. Designing components with excessively high factors of safety is needless over design that results in partial loss of component functionality and increased costs to produce and use the component. To design components that incorporate rational factors of safety, engineers must have precise knowledge of both a component's performance requirements and the properties of its constituent materials during fabrication and while in service.

Posted in: Briefs, Materials

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