Materials

High-Strain-Rate Tests of Epoxy/Aluminum-Powder Composites

Initial tests have been performed in a continuing experimental study to determine selected mechanical properties, at high strain rates, of an epoxy and of composite materials consisting of the epoxy filled with aluminum powders. These composites are examples of the large variety of polymer-matrix/particlefilling composites in general, which are widely used in military and civilian applications. The properties of such composites can be tailored for specific applications through appropriate choices of constituent materials, the proportions of the constituent materials, and the sizes of the particles. Especially in aerospace structural applications, the composites are exposed to complex, temporally varying loads. Therefore, the mechanical properties of such composites’ high strain rates are of increasing importance.

Posted in: Briefs, Materials
Read More >>

High-Temperature Resins for Composite Materials

Improved, readily processable thermosetting polymer resins are being developed for use as matrix materials in composite-material structures in applications in which there are requirements for thermal stability and hot-wet performance. Heretofore, the development and utilization of polymer resins for such applications have been limited by adverse characteristics that include (1) toxicity of many of the chemicals used to make the resins; (2) poor performance during fires (excessive flame and smoke, dripping, and generation of hazardous substances); (3) significant absorption of water in humid environments, linked to delamination during rapid heating; and (4) in the cases of many of the polymers suitable for use at the highest temperatures, difficulties in the use of newer, less expensive fabrication techniques.

Posted in: Briefs, Materials
Read More >>

Making Ultra-Hydrophobic Textured Silicone-Rubber Surfaces

Silicone-rubber surfaces microscopically textured in such a manner as to render them ultra-hydrophobic have been fabricated by a method in which breath figures are utilized. Originally, “breath figures” signified fog-like patches formed by condensation of microscopic droplets of water from air exhaled onto cooler surfaces. Now, “breath figures” refers more generally to patches formed by condensation, whether from natural breath or artificial sources. The essence of the method is to use a breath figure to form a pattern of microscopic, approximately hemispherical pits (each pit corresponding to a condensed water droplet) on the surface of a layer of polystyrene, then use the pitted polystyrene surface as a template to cast the silicone rubber having a surface pattern of nanometer- or micron-sized pillars corresponding to the pits.

Posted in: Briefs, Materials
Read More >>

Alloys for Nozzles of Hypersonic Wind Tunnels

Alloys are being developed for nozzles of hypersonic wind tunnels to be used in testing components of future hypersonic missiles, aircraft, and space transportation systems. The nozzle components made from these alloys will be required to retain sufficient strength to withstand stresses of as much as 600 MPa at throat surface gas temperatures as high as 1,700 K while resisting erosion and oxidation by impinging hypersonic flows of air and possibly other gases. In some applications, back-side cooling or film/transpiration cooling may be used to reduce the temperature rises in nozzles. Alternatively, in some applications, nozzles may be used, without active cooling, in either of two heat-sink modes. In one mode, exposure time would be limited in order to limit the maximum temperature rise. In the other mode, denoted the self-limiting heat-sink mode, a nozzle throat would be exposed long enough to come into thermal equilibrium with the gas, and, hence, the nozzle throat material must be chosen to withstand the maximum surface gas temperature (e.g., 1,700 K) for an indefinite time.

Posted in: Briefs, Materials
Read More >>

Improved Dielectric-Breakdown Property of POSS-Filled Epoxy

A n experimental study has shown that the AC short-term dielectric breakdown potential of material specimens consisting of polyhedral oligomeric silsesquioxane (POSS) nanoparticles dispersed within an epoxy matrix exceeds the AC short-term dielectric breakdown potential of equal-thickness specimens of the neat epoxy. This finding is consistent with results of prior studies in which it was found that inorganic nanoparticle fillings yielded improvements in electrical, mechanical, or thermal properties.

Posted in: Briefs, Materials
Read More >>

Low-Water-Permeability Encapsulants for Acoustic Sensors

Afamily of improved encapsulating materials for protecting underwater acoustic sensors has been invented. These materials could also be used for encapsulation or protective coating of marine hardware in general. These materials are formulated to exhibit ultra-low permeability by water, to be acoustically transparent or nearly transparent, and to be amenable to curing in place on the objects to be protected. Previously, none of the available underwater- acoustic-sensor-encapsulating material had all of these desired properties in combination.

Posted in: Briefs, Materials
Read More >>

Castable, Relatively Stiff Acoustic-Damping Materials

A recently invented family of acoustic-damping materials offers advantages over prior acoustic-damping materials:

Posted in: Briefs, Materials
Read More >>

Self-Lubrication of Hot YSZ-Ag-Mo Nanocomposite Coatings

An experimental study has been performed to learn about the physical and chemical mechanisms of self-lubrication of coatings that comprise nanostructured composites of yttria-stabilized zirconia (YSZ), silver, and molybdenum. These and other YSZ-based nanocomposite coatings have received increasing attention in recent years because they offer a combination of hardness, toughness, resistance to wear, and low-friction C properties that make them attractive for reducing wear and friction and increasing the lifetimes of hot, sliding components of mechanical systems. In addition to the excellent mechanical and thermal stability of the basic YSZ ceramic material, the nanocomposite structures of these coatings, consisting of combinations of amorphous and crystalline phases, provide a “chameleon” surface adaptation, in which different phases turn into lubricants in response to different test environments, contact loads, sliding speeds, and temperatures. Moreover, proper sizing of nanocrystalline grains can restrict crack sizes and create large volumes of grain boundaries, thereby increasing the toughness and contact-load-bearing capabilities of these coatings.

Posted in: Briefs, Materials, Lubricants, Coatings Colorants and Finishes, Composite materials, Nanomaterials, Wear
Read More >>

Innovations Pertaining to Carbon-Based Materials

Some notable innovations in the design and manufacture of carbonbased materials have been made in a continuing program of basic research on carbon- based materials for use in propulsion systems of aircraft and spacecraft. The research has ranged over diverse topics that have included fabrication of carboncarbon composite-material components, protection of carbon against oxidation, microelectromechanical devices, and surface- tension phenomena.

Posted in: Briefs, Materials, Composite materials, Aircraft, Spacecraft
Read More >>

Polymeric “Smart” Skin Materials

"Smart” skin materials based, variously, on polymers, dendrimers, carbon nanotubes, and/or other tailored molecular components are being developed for use as conformal coating surfaces of mechanical structures, including those of aircraft, to impart enhanced functionality to the coated surfaces. As used here, “smart” signifies that a material so characterized exhibits a useful physical response (e.g., a change in color) to a change in some aspect of its environment (e.g., temperature or pressure) or to a control or actuation signal. It is envisioned that smart skin materials could be used for diverse purposes, including sensing surface flow conditions and altering surface optical properties to enable detection, concealment, or display. It is further envisioned that smart skin materials could be integrated with microscopic electronic, optoelectronic, electro-optical, and microelectromechanical devices to obtain smart skins exhibiting even more varieties and higher degrees of functionality.

Posted in: Briefs, Materials, Coatings Colorants and Finishes, Smart materials
Read More >>