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At least 1,351 records · Page 75

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NASA NTRS1981

Hybridized polymer matrix composites

Design approaches and materials are described from which are fabricated pyrostatic graphite/epoxy (Gr/Ep) laminates that show improved retention of graphite particulates when subjected to burning. Sixteen hybridized plus two standard Gr/Ep laminates were designed, fabricated, and tested in an effort to eliminate the release of carbon (graphite) fiber particles from burned/burning, mechanically disturbed samples. The term pyrostatic is defined as meaning mechanically intact in the presence of fire. Graphite particulate retentive laminates were constructed whose constituent materials, cost of fabrication, and physical and mechanical properties were not significantly different from existing Gr/Ep composites. All but one laminate (a Celion graphite/bis-maleimide polyimide) were based on an off-the-shelf Gr/Ep, the AS-1/3501-5A system. Of the 16 candidates studied, four thin (10-ply) and four thick (50-ply) hybridized composites are recommended.

London, A.↗

NASA NTRS1981

An investigation of adhesive/adherend and fiber matrix interactions

Research during the report period focused on continued scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) of lap shear samples and flatwise tensile specimens and on the surface characterization of TiO2, Ti 6-4, and Ti powders with particular emphasis on their interaction with primer solutions of both polyphenylquinoxaline and LaRC-13 polyimide. The use of SEM and XPS in the analysis of Ti 6-4 adherend surfaces is described as well as differences in Ti 6-4 surface composition after different chemical pretreatments. Analysis of fractured surfaces is used to established the failure mode. The surface acidity of Ti 6-4 coupons can be established by reflectance visible spectroscopy using indicator dyes.

Beck, B.↗

NASA NTRS1979

High density circuit technology

Polyimide dielectric materials were acquired for comparative and evaluative studies in double layer metal processes. Preliminary experiments were performed. Also, the literature indicates that sputtered aluminum films may be successfully patterned using the left-off technique provided the substrate temperature remains low and the argon pressure in the chamber is relatively high at the time of sputtering. Vendors associated with dry processing equipment are identified. A literature search relative to future trends in VLSI fabrication techniques is described.

Wade, T. E.↗

NASA NTRS1981

An endochronic theory for transversely isotropic fibrous composites

A rational methodology of modelling both nonlinear and elastic dissipative response of transversely isotropic fibrous composites is developed and illustrated with the aid of the observed response of graphite-polyimide off-axis coupons. The methodology is based on the internal variable formalism employed within the text of classical irreversible thermodynamics and entails extension of Valanis' endochronic theory to transversely isotropic media. Applicability of the theory to prediction of various response characteristics of fibrous composites is illustrated by accurately modelling such often observed phenomena as: stiffening reversible behavior along fiber direction; dissipative response in shear and transverse tension characterized by power-laws with different hardening exponents; permanent strain accumulation; nonlinear unloading and reloading; and stress-interaction effects.

Pindera, M. J.↗

NASA NTRS1980

Positron annihilation studies of moisture in graphite-reinforced composites

The positron lifetime technique of monitoring absorbed moisture is applied to several composites, including graphite/polymides which are candidates for high-temperature (over 260 C) applications. The experimental setup is a conventional fast-slow coincidence system wherein the positron lifetime is measured with respect to a reference time determined by the detection of a nuclear gamma ray emitted simultaneously with the positron. From the experiments, a rate of change of positron mean lifetime per unit mass of water can be determined for each type of specimen. Positron lifetime spectra are presented for a graphite/polyimide composite and for a pure polyimide.

Singh, J. J.↗

NASA NTRS1980

Status of high-temperature laminating resins and adhesives

High-temperature polymers now being developed as adhesives and composite matrices are reviewed, including aromatic polyimides, polybenzimidazoles, polyphenylquinoxalines, nadic end-capped imide oligomers, maleimide end-capped oligomers, and acetylene-terminated imide oligomers. The mechanical properties of laminates based on these resins are reported together with preliminary test results on the adhesive properties for titanium-to-titanium and composite-to-composite lap shear specimens.

Hergenrother, P. M.↗

NASA NTRS1980

Characterization of aging effects of LARC-160

Specimens of freshly prepared polyimide precursor resin LARC-160 and resin aged at room temperature up to 45 days were characterized by high-pressure liquid chromatography and several different thermal analyses. Graphite reinforced composites were then fabricated from fresh and aged resin and tested to determine if changes observed by these techniques were significant. It was found that resin aging resulted in greater flow during processing and poorer composite isothermal stability. However, aging did not affect the room-temperature flexural or short-beam-shear strengths of the composites.

Young, P. R.↗

NASA NTRS1981

Experimental simulation of space plasma interactions with high voltage solar arrays

Operating high voltage solar arrays in the space environment can result in anomalously large currents being collected through small insulation defects. Tests of simulated defects have been conducted in a 45-cm vacuum chamber with plasma densities of 100,000 to 1,000,000/cu cm. Plasmas were generated using an argon hollow cathode. The solar array elements were simulated by placing a thin sheet of polyimide (Kapton) insulation with a small hole in it over a conductor. Parameters tested were: hole size, adhesive, surface roughening, sample temperature, insulator thickness, insulator area. These results are discussed along with some preliminary empirical correlations.

Stillwell, R. P.↗

NASA NTRS1980

Analysis of aromatic polyamine mixtures for formulation of LARC-160 resin

An investigation was conducted to identify a potential substitute for the aromatic polyamine mixture, Jeffamine AP-22, currently used to formulate LARC-160 polyimide precursor resin. Jeffamine AP-22 was characterized by high pressure liquid chromatography and mass spectrometry. Eleven different aromatic amines in the mixture were isolated and identified. Subsequent liquid chromatographic analysis of nine additional commercially available aromatic polyamine mixtures identified three candidates that are similar in composition to AP-22.

Young, P. R.↗

NASA NTRS1981

Incorporation of metal related materials into electrically neutral polymers

Developments in the field of metal-containing polymers are reviewed with emphasis on neutral polymers incorporating dissolved metal salts, metal complexes, organometallic compounds, and metals. Polymer systems discussed include: polyamides, polyimides, polyalcohols, polyesters, polyacetylene, polyethylene, and polysiloxane. Most of the studies focus on the modification of polymer properties such as adhesive properties, thermal behavior, electrical conductivity, polymer flammability, and mechanical properties.

St. Clair, A. K.↗

NASA NTRS1982

High-Temperature Ultrafiltration Membrane

Ultrafiltration membrane with high-temperature capability prepared from polyimide soluble in organic solvent such as dimethylacetamide, made in single step by solution-casting phase inversion.

Sarbolouki, M. N.↗

NASA NTRS1983

Terminal Strip Facilitates Printed-Circuit Board Changes

Laminanted copper and polyimide terminal strip makes it easy to modify printed-circuit (PC) board, after board has been fabricated. When epoxied over conductors or insulating portion of PC board, strip provides series of solder-coated copper conductor pads to which integrated-circuit leads are soldered for functional changes. Terminal strips accommodate leads on dual inline IC package or as staggered single or multiple leads on planar mounted flatpacks.

Pinto, E. A.↗

NASA NTRS1983

A Solvent-Resistant, Thermoplastic Poly(imidesulfone)

Process for preparing thermoplastic poly(imidesulfone) results in material having excellent thermoplastic properties generally associated with polysulfones and excellent solvent resistance generally associated with polyimides. New thermoplastic, solvent-resistant polymer is used as molding resin, as adhesive, and as matrix resin for fiber reinforced composites.

St. Clair, T. L.↗

NASA NTRS1981

Experimental Simulation of the Interaction of Biased Solar Arrays with the Space Plasma

The phenomenon of unexpectedly large leakage currents collected by small exposed areas of high voltage solar arrays operating in a plasma environment was investigated. Polyimide (Kapton) was the insulating material used in all tests. Both positive bias (electron collection) and negative bias (ion collection) tests were performed. A mode change in the electron collection mechanism was associated with a glow discharge process and was found to be related to the neutral background density. Results indicate that the glow discharge collection mode does not occur in a space environment where the background density is considerably lower than that of the vacuum facility used.

Kaufman, H. R.↗

NASA NTRS1981

Hybridized polymer matrix composite

Under certain conditions of combined fire and impact, graphite fibers are released to the atmosphere by graphite fiber composites. The retention of graphite fibers in these situations is investigated. Hybrid combinations of graphite tape and cloth, glass cloth, and resin additives are studied with resin systems. Polyimide resins form the most resistant composites and resins based on simple novolac epoxies the least resistant of those tested. Great improvement in the containment of the fibers is obtained in using graphite/glass hybrids, and nearly complete prevention of individual fiber release is made possible by the use of resin additives.

Stern, B. A.↗

NASA NTRS1981

Thermomechanical response of Gr/Pi composites

The effects of temperature changes upon the stresses and strains in composite laminates having carbon fibers in a polyimide matrix were evaluated. Composites having laminae in which there were nonlinear stress-strain relations for stresses transverse to the fibers and for axial shear stresses were treated. Material properties were considered to be temperature dependent. Separately, the effects of laminae viscoelastic response were also treated. The results suggest that, for this material, nonlinearities due either to stress or time dependent effects do not appear to be of major practical importance for conventional high temperature composite structures.

Rosen, B. W.↗

NASA NTRS1980

High density circuit technology

Acquisition of polyimide materials for inter-metal dielectrics was obtained from three vendors, with considerable evaluation conducted on the Dupont PI2550 material. Experimental results indicate this material can be patterned using contact printing to line width far below 0.1 mils. Optimum line width is acquired using plasma etch equipment. Metal lift-off experiments on thermal evaporated films were optimized for application to sputtered deposited films. Alternate metal-lift-off experiments are proposed for future investigation. Dry processing equipment studies and future trends in VLSI fabrication techniques are on-going.

Wade, T. E.↗

NASA NTRS1982

Full-scale flammability test data for validation of aircraft fire mathematical models

Twenty-five large scale aircraft flammability tests were conducted in a Boeing 737 fuselage at the NASA Johnson Space Center (JSC). The objective of this test program was to provide a data base on the propagation of large scale aircraft fires to support the validation of aircraft fire mathematical models. Variables in the test program included cabin volume, amount of fuel, fuel pan area, fire location, airflow rate, and cabin materials. A number of tests were conducted with jet A-1 fuel only, while others were conducted with various Boeing 747 type cabin materials. These included urethane foam seats, passenger service units, stowage bins, and wall and ceiling panels. Two tests were also included using special urethane foam and polyimide foam seats. Tests were conducted with each cabin material individually, with various combinations of these materials, and finally, with all materials in the cabin. The data include information obtained from approximately 160 locations inside the fuselage.

Kuminecz, J. F.↗