Materials & Coatings

Progressive Failure Analysis of Composite Structures with FEA Software

A combination of analysis programs simulates the stochastic nature of fiber breakage in composites. The Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) is core technology in a software suite called ImMAC, developed at NASA’s John Glenn Research Center. An abbreviation for Integrated Multiscale Micromechanics Analysis Code, ImMAC is used in the design and analysis of advanced composite structures.

Posted in: Briefs

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Ceramic Paste for Patching High-Temperature Insulation

Repairs can be performed by use of simple techniques. A ceramic paste that can be applied relatively easily, either by itself or in combination with one or more layer(s) of high temperature ceramic fabrics, such as silicon carbide or zirconia, has been invented as a means of patching cracks or holes in the reinforced carbon-carbon forward surfaces of a space shuttle in orbit before returning to Earth. The paste or the paste/fabric combination could also be used to repair rocket-motor combustion chambers, and could be used on Earth to patch similar high-temperature structures.

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Protective Skins for Aerogel Monoliths

Viscous polymer precursors are applied, then polymerized before they can percolate in. A method of imparting relatively hard protective outer skins to aerogel monoliths has been developed. Even more than aerogel beads, aerogel monoliths are attractive as thermal-insulation materials, but the commercial utilization of aerogel monoliths in thermal-insulation panels has been inhibited by their fragility and the consequent difficulty of handling them. Therefore, there is a need to afford sufficient protection to aerogel monoliths to facilitate handling, without compromising the attractive bulk properties (low density, high porosity, low thermal conductivity, high surface area, and low permittivity) of aerogel materials. The present method was devised to satisfy this need.

Posted in: Briefs, TSP

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Fabrication of Polyimide-Matrix/Carbon and Boron-Fiber Tape

Production costs can be reduced and compression strengths increased. The term “HYCARB” denotes a hybrid composite of polyimide matrices reinforced with carbon and boron fibers. HYCARB and an improved process for fabricating dry HYCARB tapes have been invented in a continuing effort to develop lightweight, strong composite materials for aerospace vehicles. Like other composite tapes in this line of development, HYCARB tapes are intended to be used to build up laminated structures having possibly complex shapes by means of automated tow placement (ATP) — a process in which a computer controlled multiaxis machine lays down prepreg tape or tows. The special significance of the present process for making dry HYCARB for ATP is that it contributes to the reduction of the overall cost of manufacturing boron-reinforced composite-material structures while making it possible to realize increased compression strengths.

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Composite Elastic Skins for Shape-Changing Structures

Anisotropic stiffness properties can be tailored for specific applications. Composite elastic skins having tailorable mechanical properties have been invented for covering shape-changing (“morphable”) structures. These skins are intended especially for use on advanced aircraft that change shapes in order to assume different aerodynamic properties.

Posted in: Briefs, TSP

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Glass/Ceramic Composites for Sealing Solid Oxide Fuel Cells

Ceramic fillers in a glass contribute to strength and fracture toughness. A family of glass/ceramic composite materials has been investigated for use as sealants in planar solid oxide fuel cells. These materials are modified versions of a barium calcium aluminosilicate glass developed previously for the same purpose. The composition of the glass in mole percentages is 35BaO + 15CaO + 5Al2O3 + 10B2O3 + 35SiO2. The glass seal was found to be susceptible to cracking during thermal cycling of the fuel cells.

Posted in: Briefs, TSP

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Carbon-Nanotube-Carpet Heat-Transfer Pads

The compliance and high longitudinal thermal conductivity of carbon nanotubes are exploited. Microscopic thermal-contact pads that include carpetlike arrays of carbon nanotubes have been invented for dissipating heat generated in integrated circuits and similarly sized single electronic components. The need for these or other innovative thermal-contact pads arises because the requisite high thermal conductances cannot be realized by scaling conventional macroscopic thermal-contact pads down to microscopic sizes. Overcoming limitations of conventional thermal-contact materials and components, the carbon-nanotube thermal-contact pads offer the high thermal conductivities needed to accommodate the high local thermal power densities of modern electronic circuits, without need for large clamping pressures, extreme smoothness of surfaces in contact, or gap-filling materials (e.g., thermally conductive greases) to ensure adequate thermal contact. Moreover, unlike some conventional thermal-contact components, these pads are reusable.

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