Manufacturing & Prototyping

Structural/Radiation-Shielding Epoxies

Pendant aliphatic groups are incorporated as integral parts of molecular structures. A development effort was directed toward formulating epoxy resins that are useful both as structural materials and as shielding against heavy-ion radiation. Hydrogen is recognized as the best element for absorbing heavy-ion radiation, and high- hydrogen-content polymers are now in use as shielding materials. However, high- hydrogen-content polymers (e.g. polyethylene) are typically not good structural materials. In contrast, aromatic polymers, which contain smaller amounts of hydrogen, often have the strength necessary for structural materials. Accordingly, the present development effort is based on the concept that an ideal structural/heavy-ion-radiation-shielding material would be a polymer that contains sufficient hydrogen (e.g., in the form of aliphatic molecular groups) for radiation shielding and has sufficient aromatic content for structural integrity.

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Modal Vibration Analysis of Large Castings

Massive objects can be tested in situ, without precisely controlling boundary conditions. The art of experimental modal vibration analysis (MVA) has been extended to apply to large castings. This extension was made to enable the use of experimental MVA as a relatively inexpensive, simple means of assessing the internal structural integrity of tread shoes of crawler transporters used to move spacecraft to the launch pad at Kennedy Space Center. Each tread shoe is made from cast iron and weighs about a ton (has a mass ≈907 kg). The present extended version of experimental MVA could also be applied to other large castings. It could be especially useful to manufacturers as a means of rapidly discriminating against large castings that contain unacceptably large concentrations of internal defects.

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Laser Ablation Increases PEM/Catalyst Interfacial Area

Increased interfacial area is expected to result in improved fuel-cell performance. An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/electrode assembly.

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Diamond Machining of an Off-Axis Biconic Aspherical Mirror

Complex shapes can be produced at relatively low costs. Two diamond-machining methods have been developed as part of an effort to design and fabricate an off-axis, biconic ellipsoidal, concave aluminum mirror for an infrared spectrometer at the Kitt Peak National Observatory. Beyond this initial application, the methods can be expected to enable satisfaction of requirements for future instrument mirrors having increasingly complex (including asymmetrical), precise shapes that, heretofore, could not readily be fabricated by diamond machining or, in some cases, could not be fabricated at all.

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Alternative Packaging for Back-Illuminated Imagers

Electrical contacts are made accessible from the back side. An alternative scheme has been conceived for packaging of silicon- based back-illuminated, back- side-thinned complementary metal oxide/semiconductor (CMOS) and charge-coupled-device image-detector integrated circuits, including an associated fabrication process. This scheme and process are complementary to those described in “Making a Back- Illuminated Imager With Back-Side Connections” (NPO-42839), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), page 38.

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Improved Photoresist Coating for Making CNT Field Emitters

This technique could contribute to development of cold cathodes for diverse applications. An improved photoresist-coating technique has been developed for use in the fabrication of carbon-nanotube- (CNT)- based field emitters of the type described in “Fabrication of Improved Carbon- Nanotube Field Emitters” (NPO-44996), NASA Tech Briefs, Vol. 32, No. 4 (April 2008), page 50. The improved photoresist- coating technique overcomes what, heretofore, has been a major difficulty in the fabrication process. This technique is expected to contribute to the realization of high-efficiency field emitters (cold cathodes) for diverse systems and devices that could include gas-ionization systems, klystrons, flat-panel display devices, cathode-ray tubes, scanning electron microscopes, and x-ray tubes.

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Composite Layer Manufacturing With Fewer Interruptions

An improved version of composite layer manufacturing (CLM) has been invented. CLM is a type of solid freeform fabrication (SFF) — an automated process in which a three-dimensional object is built up, point-by-point, through extrusion of a matrix/fiber composite-material precursor. The elements of SFF include (1) preparing a matrix resin in a form in which it will solidify subsequently, (2) mixing fibers and matrix material to form a continuous preimpregnated tow (also called “towpreg”), and (3) dispensing the towpreg from a nozzle onto a base while moving the nozzle to form the dispensed material into a series of patterned layers of controlled thickness.

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