Materials

Automated Material Deposition Chamber

AFRL materials scientists have acquired an automated deposition chamber (see figure on next page) that enables them to simultaneously or sequentially deposit solid-lubricant coatings onto target objectives from any of three deposition sources. The chamber also incorporates AFRLinvented technology entailing a hybrid, magnetron-assisted, pulsed-laser deposition (PLD) process. The scientists acquired the chamber to study protective solid-lubricant coatings capable of resisting wear and corrosion in (relatively) large friction components, including gears and bearings, and preventing static friction in microelectromechanical systems devices such as switches and connectors.

Posted in: Briefs, Materials
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Super-High-Strength Aluminum Alloy

AFRL researchers developed a superhigh- strength aluminum alloy that engineers can use to improve the capability and performance of aerospace components—cryogenic rocket engine components, in particular. They created an aluminum alloy with specific strength and ductility characteristics surpassing those of the alpha titanium alloy currently used in rocket engine turbopumps. The aluminum alloy also demonstrates less sensitivity to hydrogen embrittlement, is lighter weight, and is potentially less costly to manufacture than the titanium alloy.

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Recent Advances in Insensitive Munitions

AFRL scientists from the High Explosives Research and Development facility successfully developed, demonstrated, and transitioned a nextgeneration melt-castable explosive formulation. The new formulation, MNX-795, exhibits significantly improved insensitive munitions (IM) characteristics—a requirement for the formulation's intended use in the MK- 84 bomb.

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Geopolymers

The use of ceramics in an ancient culture is one measure of that society's overall technical sophistication. Combining the study of ancient ceramics with modern science and technology has led to the creation of new ceramics with superior properties. Victor Glukhovsky, a scientist working in the Ukraine half a century ago, researched differences in the durability of ancient cements and more modern concretes. His work ultimately led to the synthesis of various aluminosilicate binders from clays, feldspars, volcanic ashes, and slags. These binders exhibited properties superior to those of the cementitious materials in common use at that time. Decades after Glukhovsky's discoveries, Ukrainian builders continued to employ aluminosilicate binders in construction applications, confirming their outstanding durability.

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Composites Affordability Initiative

AFRL and Boeing have developed an innovative structural inspection technique for testing bonded structures. This technique provides materials engineers a first-time, validated, nondestructive capability to test for weak adhesive bonds and determine the minimum strength of adhesively bonded aerospace structures. The new method will enable aircraft designers to use bonded structures in a wider range of applications, and industry analysts predict it will provide both a 25% reduction in fabrication and assembly time and a 75% reduction in life-cycle costs.

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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.

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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.

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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.

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New Capability to Characterize the Mechanical Properties of Explosive Materials

Improved targeting accuracy and the long-standing desire to minimize collateral damage are causing current and future munitions to become much smaller. As munitions size decreases, the explosive materials packed within bomb cases begin to carry a significant portion of the structural loads experienced by the warhead. In an ongoing program effort to determine the mechanical properties of explosives and other energetic materials, scientists at AFRL's High Explosives Research and Development (HERD) facility (Eglin Air Force Base, Florida) acquired a miniaturized split Hopkinson pressure bar (MSHPB) (see Figure 1). Designed and built by Mr. Clive Siviour under the guidance of Drs. John Field, Bill Proud, and Stephen Walley (of the United Kingdom's University of Cambridge, Physics and Chemistry of Solids Group), the MSHPB is capable of strain rates up to 105 s-1 in material samples. AFRL's European Office of Aerospace Research and Development sponsored the project.

Posted in: Briefs, Materials, Materials properties, Hazardous materials
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Ceramic Matrix Composites Research

AFRL scientists characterized and evaluated the high-temperature mechanical behavior of fiber-reinforced ceramic matrix composite (CMC) materials used in aerospace structural applications. Researchers examined four principal characteristics of a porous matrix composite that General Electric developed for the aerospace industry. Their evaluations resulted in an increased understanding of the materials and their potential for applications in military and commercial aerospace products.

Posted in: Briefs, Materials, Research and development, Ceramics, Composite materials
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