AFRL Proves Feasibility of Plasma Actuators

AFRL is laying the groundwork for the development of revolutionary hypersonic aerospace vehicles (see Figure 1). Accordingly, AFRL engineers are examining the feasibility of replacing an air vehicle's traditional, mechanically or electrically actuated flight control surfaces (e.g., wing flaps) with plasma actuators that require no moving parts and are therefore potentially less expensive and more reliable. As part of the laboratory's Boundary Layers and Hypersonics program, the engineers conducted a wind tunnel test to evaluate the feasibility of using plasma actuators for airframe flight control.

Posted in: Briefs, Mechanical Components

Composites Design and Structural Analysis Tool

AFRL researchers developed a unique design and structural analysis tool for composite materials, and they subsequently transitioned their product to manufacturers of helicopters and other rotorcraft. The new tool, the B-Spline Analysis Method (BSAM), makes it quicker and less expensive to characterize and predict the behavior of flaws or damage in the structures used to build these aircraft. AFRL developed the technology in coordination with the University of Dayton Research Institute (UDRI) and the United Technologies Research Center (UTRC) and then transitioned it to Sikorsky Aircraft Corporation.

Posted in: Briefs, Materials

Corrosion Suppression Technologies and Techniques

Members of AFRL's Air Force Corrosion Prevention and Control Office (AFCPCO) teamed with corrosion experts from Warner Robins Air Logistics Center to assess environmentally induced damage to systems and equipment subjected to extended operations in Southwest Asia (SWA). The purpose of the ongoing assessment effort is to observe the effects of sand and dust intrusion on Air Force (AF) weapons systems and sensitive support equipment (see figure), analyze sands from various locations, and compare corrosion prevention and control policies and inspection requirements from prewar to present-day operations. As the investigation proceeds, team members are providing progressive and alternative approaches to corrosion prevention and control, wet and dry cleaning, and aircraft maintenance tasks performed in rigorous environmental conditions.

Posted in: Briefs, Materials

Enhanced Blast-Resistant Windows

AFRL entered into a Cooperative Research and Development Agreement (CRADA) with Dlubak Technologies, Inc., of Freeport, Pennsylvania, to pursue ongoing research in blast-resistant window and glazing technologies. Dlubak Technologies—a 50-year-old glass manufacturing company—provided fullscale window and frame products (see Figure 1) to AFRL for blast mitigation testing at AFRL's Sky Ten Range, Tyndall Air Force Base, Florida.

Figure 1. Test specimens installed on blast response reaction structure at Sky TenDuring recent conflicts, the US has seen a dramatic increase in terrorist bombings as instruments of warfare. AFRL engineers and scientists are actively exploring blast mitigation technologies that will help minimize the casualties caused by explosive attacks targeting buildings and expeditionary structures. Blast mitigation technology is particularly important, since flying glass and wall debris created by the detonation cause the vast majority of blast-related injuries and fatalities.

Research performed under this CRADA has produced a successful blastresistant window that uses protective glazing in conjunction with a perimeteranchored laminate. For these state-ofthe- art windows, Dlubak Technologies fabricates glass with a polymer laminate layer that extends beyond the glass edges. Installers anchor these "laminate tails" in the window frame using one of several techniques. Dlubak is already marketing LAMLOK, its patent-pending laminate-locking system, for commercial sale, due in part to product performance demonstrated during AFRL research trials conducted under this CRADA. Throughout the effort, AFRL researchers studied various LAMLOK systems, including a polyvinyl butyral hinged-style window system for postblast emergency exit and another variation for use in standard window frames having either flat or curved glass panels. Based on the research results, Dlubak created an improved version of the interlocking mechanism employed for standard window frames. The CRADA is intended both to facilitate further blast-resistant window research and to promote future investigations of related technologies.

In addition to engaging in the blastresistant window research, AFRL engineers and scientists are investigating several systems designed to prevent wall fragments from penetrating a building's interior. As a result of this wall debris research, AFRL pioneered various techniques for retrofitting concrete block walls with blast-resistant polymers.1 Engineers can retrofit existing walls either by spraying or troweling the material onto the wall surface or by installing prepared façade panels to cover the existing surface. These alternatives allow engineers to better match the most suitable application method to the specific need, a determination that normally depends upon factors such as wall area, manpower skills, equipment availability, and budgetary resources. As part of an additional project focused on examining the blast resistance of insulated concrete products widely used in concrete construction, researchers are also evaluating the benefits of polymers for blast protection in new construction (as a stay-in-place concrete form).

Figure 2. Test specimens exposed to 1,000 lb detonation at 75 ftAFRL has state-of-the-art facilities for conducting blast protection research activities. The lab's Range Operations and Support Group has two reaction structures at Sky Ten, each with the capability to simultaneously expose up to eight windows and/or wall systems to a 1,000 lb TNT charge (see Figure 2). Researchers monitor and control the blast from a master control board that provides over 100 channels for recording critical scientific data during and after the detonation. In addition, high-speed digital and traditional video cameras record the event to provide researchers with yet another tool for analyzing results.

Dr. Robert Dinan, Mr. Jeff Fisher (Applied Research Associates), and Ms. Mindy Cooper (General Dynamics), of the Air Force Research Laborator y's Materials and Manufacturing Directorate, wrote this article. For more information, visit http://www.afrl.af.mil/techconn_index.asp. Reference document ML-H-05-36.


1 Anderl, T., Dinan, R., and Porter, J. "Blast Protection Elastomer Coating." AFRL Technology Horizons®, vol 4, no 3 (Sep 03): 13. http://www.afrlhorizons.com/Briefs/ Sept03/feature1.html.

Posted in: Briefs, Materials

Friction Stir Welding of Aerospace Materials

AFRL scientists are studying a unique metal joining process— friction stir welding (FSW)—for building major structural assemblies. FSW is a solid-state welding process that forces a spinning tool along the joint line, heating the abutting components by friction and producing a weld joint formed by strong plastic mixing (stirring) of the two components' constituent materials. FSW promises to be a highly efficient and cost- effective alternative to the conventional fusion welding routinely used for joining structural alloys on military and civilian aircraft.

Bright-field TEMs of the 7050-T7451 subgrain structure (left) and coarsened precipitates in the grain interior and along the grain boundaries and PFZ of a friction-stir-welded joint (right)Some of the important advantages FSW offers over fusion welding include the ability to weld structural aluminum alloys (particularly alloys in the 7xxx series), better retention of baseline material properties, fewer welding defects, lower residual stresses, and improved dimensional stability of the welded structure. The material that flows around the tool undergoes extreme levels of plastic deformation, and a very recrystallized grain structure forms in the center of the weld. This region of the weld, commonly referred to as the nugget zone, is part of the weld's heat-affected zone (HAZ). The surrounding material, which constrains the nugget metal and undergoes deformation via the spinning tool's passage, comprises the remainder of the HAZ and experiences much lower plastic strains. Because the FSW process does not melt or recast the welded material, microstructural material transformations occur during the weld's cooldown— essentially taking place in the material's solid state.

FSW may also produce significant economic advantages. The process joins aluminum alloys fairly rapidly— about 4 mm/sec—with low heat input and without the costly shielding gases and filler materials required in fusion welding processes. The aerospace industry also uses substantial quantities of fasteners to join metallic structures— literally millions of fasteners in fabricating a large cargo or passenger aircraft. Thus, eliminating fasteners in aerospace structures by incorporating FSW joints would provide manufacturers considerable cost and weight savings.

Researchers from AFRL's Metals, Ceramics, and Nondestructive Evaluation Division friction-stir-welded a number of aerospace aluminum alloys, including 7050-T7451, an alloy widely used in military and commercial aircraft manufacturing, to assess the effects of the process on microstructure and mechanical properties. Optical microscopy and transmission electron microscopy (TEM) examination of the welded joint's weld-nugget region showed that FSW transforms the initial millimeter-sized, pancake-shaped grains to fine, 1-5 μ dynamically recrystallized grains. The TEM examination also demonstrated that the FSW process redissolves the strengthening precipitates in the weld-nugget region. Furthermore, in the HAZ, the FSW process preserved the initial grain size and increased both the size of the strengthening precipitates and that of the precipitatefree zone (PFZ) by a factor of five (see figure). The AFRL team was the first to explain the continuous dynamic recrystallization process in friction stir welds.

The team also performed a series of mechanical tests on friction-stir-welded aluminum alloys. To stabilize the welded material, the test samples first underwent a postweld heat treatment (120°C for 24 hrs to create an as-welded [as-FSW] +T6 temper). As expected of any weldment, tensile specimens loaded transverse to the weld direction exhibited a slight reduction in strength level and an elongation in the as-FSW condition and also revealed that the fracture occurred in the HAZ.

The team also performed a series of mechanical tests on friction-stir-welded aluminum alloys. To stabilize the welded material, the test samples first underwent a postweld heat treatment (120°C for 24 hrs to create an as-welded [as-FSW] +T6 temper). As expected of any weldment, tensile specimens loaded transverse to the weld direction exhibited a slight reduction in strength level and an elongation in the as-FSW condition and also revealed that the fracture occurred in the HAZ.

AFRL researchers are expanding the knowledge of microstructure-property relationships, corrosion and failure modes, and life-cycle benefits in friction-stir-welded materials. They are also developing databases and process specifications so that manufacturers employing these FSW tools can consistently achieve desirable and predictable properties, enabling FSW to be qualified for use in the manufacture of major structural assemblies such as reusable cryotank applications for space.

Besides the AFRL activity, automotive, aerospace, and shipbuilding companies are also vigorously pursuing FSW technology to join not only aluminum alloys but also steels and, more recently, titanium alloys. Research is rapidly progressing in such areas as novel tool design, process parameter optimization, and FSW process modeling. As a result of these advances, FSW could soon produce joints with mechanical properties better than fusion-welded or mechanically fastened joints and provide cost-effective methods for repairing defects in metal surfaces.

Dr. Kumar V. Jata, Dr. Lee Semiatin, Dr. Reji John, and Dr. Peter S. Meltzer (General Dynamics), of the Air Force Research Laboratory's Materials and Manufacturing Directorate, wrote this article. For more information visit http://www.afrl.af.mil/techconn_index.asp. Reference document ML-H-06-01.

Posted in: Briefs, Materials

Intelligence Fusion System Tracks Mobile Targets

Current intelligence fusion systems are not accurately and quickly performing the intelligence, surveillance, and reconnaissance (ISR) fusion necessary for tracking moving targets that use camouflage, concealment, and deception to avoid detection. Combatant commanders require a more flexible and responsive capability to engage fleeting and mobile targets.

Posted in: Briefs, Information Technology

Integrated Aircraft Oxygen Sensor

Shortly after its takeoff from New York City on July 17, 1996, Trans World Airlines (TWA) Flight 800 exploded over the Atlantic Ocean and crashed. The accident investigation board determined that the center wing fuel tank caught fire and exploded. Although the ignition source remains unknown, it was unquestionably the presence of a combustible fuel/air mixture in the center wing fuel tank that caused the resulting


Posted in: Briefs, Materials

Multi-Fabric Switching Enables New Architectures for Military Systems

With multiple switched interconnects gaining momentum in the embedded space, selecting just one to address a wide range of military systems requirements is not easy.

Individually, switched fabrics such as Gigabit Ethernet (GbE), Serial RapidIO (SRIO), and PCI Express (PCIe) have their own particular technical merits, and each is poised to carve out a piece of the interconnect market. However, when combined in nextgeneration Serial Switched Backplanes (SSB) like VPX (VITA 46/48), multi-fabric switching can enable powerful new military architectures by leveraging 'best of breed' interconnect technology to address specific application requirements ( Figure 1).

Posted in: Articles, Articles, Electronics & Computers, Architecture, Embedded software, Switches, Military vehicles and equipment

Multicores Affect Algorithm Choices

Design engineers soon will need to bridge the growing gap between hardware reality and software capabilities in the highperformance computing (HPC) realm as the use of multicore microprocessors grows. If your software development or sourcing plans haven't anticipated these development situations, your applications may have a shorter life than you had planned.

The 2006 version of technical computing "reality" is an inexpensive dual-core processor from AMD or Intel on a desktop system, or a dual- or quad-core RISC processor from Sun or IBM running on a server. In 2007, we should expect to see inexpensive quad-core processors from AMD and Intel, and processors with up to eight or more cores in 2008. These small symmetric multiprocessing (SMP) systems will be a far cry from the proprietary $500,000+ SMP systems of a few years ago. This technology transition has big implications for the "democratization" of computing power. On the horizon are four- to eightcore systems that cost only a few thousand dollars and sit on the desk of every design engineer.

Posted in: Application Briefs, Application Briefs, Electronics & Computers, Mathematical models, Computer software / hardware, Systems engineering

Multi-Processor VME64x Computer With PowerPC Processor

Themis Computer (Fremont, CA) has introduced the TPPC64 multi-processor VME64x computer using IBM's 970FX Superscalar RISC processor. It can be configured with one or two 1.8-GHz PowerPC 970FX processors. The 970FX features VPX SIMD Vector Processing Units, bringing enterprise server-class processing power to bandwidth-intensive VME64x applications.

Posted in: Products, Products, Electronics & Computers