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Bell, V. L.

Publications and source records attributed to Bell, V. L..

At least 19 records

The potential for damage from the accidental release of conductive carbon fibers from aircraft composites

Carbon and graphite fibers are known to be electrically conductive. The rapidly accelerating use of carbon fibers as the reinforcement in filamentary composite materials brought up the possibility of accidental release of carbon fibers from the burning of crashed commercial airliners with carbon composite parts. Such release could conceivably cause widespread damage to electrical and electronic equipment. The experimental and analytical results of a comprehensive investigation of the various elements necessary to assess the extent of such potential damage in terms of annual expected costs and maximum losses at low probabilities of occurrence are presented. A review of NASA materials research program to provide alternate or modified composite materials to overcome any electrical hazards from the use of carbon composites in aircraft structures is described.

Bell, V. L.

Potential release of fibers from burning carbon composites

A comprehensive experimental carbon fiber source program was conducted to determine the potential for the release of conductive carbon fibers from burning composites. Laboratory testing determined the relative importance of several parameters influencing the amounts of single fibers released, while large-scale aviation jet fuel pool fires provided realistic confirmation of the laboratory data. The dimensions and size distributions of fire-released carbon fibers were determined, not only for those of concern in an electrical sense, but also for those of potential interest from a health and environmental standpoint. Fire plume and chemistry studies were performed with large pool fires to provide an experimental input into an analytical modelling of simulated aircraft crash fires. A study of a high voltage spark system resulted in a promising device for the detection, counting, and sizing of electrically conductive fibers, for both active and passive modes of operation.

Bell, V. L.

The potential for damage from the accidental release of conductive carbon fibers from aircraft composites

The paper considers the potential for damage from the accidental release of conductive carbon fibers from aircraft composites. The electrical conductivity of carbon and graphite fibers has led to electrical equipment damage from the inadvertent release of virgin fibers into the atmosphere; an accidental release of carbon fibers from filamentary composites from the burning of crashed commercial airliners could damage electrical and electronic equipment. The experimental and analytical results by NASA of the methods of assessing the extent of potential damage in terms of costs is presented; the NASA materials research program to provide alternate or modified composites to overcome electrical hazards of carbon composites in aircraft structures is described.

Bell, V. L.

Source of released carbon fibers

The potential for the release of carbon fibers from aircraft crashes/fires is addressed. Simulation of the conditions of aircraft crash fires in order to predict the quantities and forms of fibrous materials which might be released from civilian aircraft crashes/fires is considered. Figures are presented which describe some typical fiber release test activities together with some very preliminary results of those activities. The state of the art of carbon fiber release is summarized as well as some of the uncertainties concerning accidental fiber release.

Bell, V. L.

Process for preparing thermoplastic aromatic polyimides

A method of preparing insoluble thermoplastic aromatic polyimides is described, having uniquely low softening temperatures by reacting, in a suitable solvent, an aromatic dianhydride, and a meta-substituted aromatic diamine.

Bell, V. L.

Polyimide adhesives

A process was developed for preparing aromatic polyamide acids for use as adhesives by reacting an aromatic dianhydride to an approximately equimolar amount of an aromatic diamine in a water or lower alkanol miscible ether solvent. The polyamide acids are converted to polyimides by heating to the temperature range of 200 - 300 C. The polyimides are thermally stable and insoluble in ethers and other organic solvents.

Progar, D. J.

New diamine hardeners for epoxies

Stronger amine-cured polyepoxides can be obtained by using those diaminobenzophenones and diaminodiphenylmethanes that have amine groups located at ortho or meta positions to carbonyl or methylene groups joining two benzene rings.

Bell, V. L.

Novel aminobenzyl and imidobenzyl benzenes

Compounds are useful as intermediates for several classes of polymers. Amines can function as cross-linking agents for epoxide and urethane polymers, as well as intermediates for synthesis of thermally-stable addition-type polyimides. Imide derivatives can be obtained by reacting amines with certain monoanhydrides containing olefinic unsaturation.

Bell, V. L.

Process for preparing polyimide adhesives

High bonding strengths are obtained for metals and fiber-reinforced organic resin composites with no significant loss in thermo-oxidative stability of the adhesive resin.

Progar, D. J.

Diamine curing agents for polyurethanes

Three aromatic diamines have properties that make them promising candidates as curing agents for converting isocyanates to polyurethanes with higher adhesive strengths, higher softening temperatures, better toughness, and improved abrasion resistance.

Bell, V. L.

Polyimide adhesives

A process of preparing aromatic polyamide-acids for use as adhesives is described. An equimolar quantity of an aromatic dianhydride is added to a stirred solution of an aromatic diamine in a water or alcohol-miscible ether solvent to obtain a viscous polymer solution. The polymeric-acid intermediate polymer does not become insoluble but directly forms a smooth viscous polymer solution. These polyamic-acid polymers are converted, by heating in the range of 200-300 C and with pressure, to form polyimides with excellent adhesive properties.

Progar, D. J.

Preparing thermoplastic aromatic polyimides

Method prepares aromatic polyimides with significantly reduced glass-transition temperatures and without accompanying loss of high-level thermo-oxidative stability which has been typical. This has been made possible by use of diamine monomers with specific stereoisomeric features.

Bell, V. L.