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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature.

Cullers, Cheryl L.↗
NASA NTRS1987

Effect of thermal history on mechanical properties of polyetheretherketone below the glass transition temperature

The effect of thermal history on the tensile properties of polyetheretherketone neat resin films was investigated at different test temperatures (125, 25, and -100) using four samples: fast-quenched amorphous (Q); quenched, then crystallized at 180 C (C180); slowly cooled (for about 16 h) from the melt (SC); and air-cooled (2-3 h) from the melt (AC). It was found that thermal history significantly affects the tensile properties of the material below the glass transition. Fast quenched amorphous films were most tough, could be drawn to greatest strain before rupture, and undergo densification during necking; at the test temperature of -100 C, these films had the best ultimate mechanical properties. At higher temperatures, the semicrystalline films AC and C180 had properties that compared favorably with the Q films. The SC films exhibited poor mechanical properties at all test temperatures.

Cebe, Peggy↗
NASA NTRS1973

Glass transition temperatures of liquid prepolymers obtained by thermal penetrometry

Thermal penetrometry is experimental technique for detecting temperature at which frozen prepolymer becomes soft enough to be pierced by weighted penetrometer needle; temperature at which this occurs is called penetration temperature. Apparatus used to obtain penetration temperatures can be set up largely from standard parts.

Potts, J. E., Jr.↗
NASA NTRS1973

A simplified ductile-brittle transition temperature tester

The construction and operation of a versatile, simplified bend tester is described. The tester is usable at temperatures from - 192 to 650 C in air. Features of the tester include a single test chamber for cryogenic or elevated temperatures, specimen alining support rollers, and either manual or motorized operation.

Arias, A.↗
NASA NTRS1987

Growth kinetics of the (001) face of TGS below the ferroelectric transition temperature

The growth rates of the (001) face of triglycine sulfate (TGS) from aqueous solutions were measured at 33.55 C in an apparatus which produced a laminar flow of solution past the crystal. The data of growth rate as a function of relative supersaturation were compared with the results of two well-known models: the Burton-Cabrera-Frank (1951) surface diffusion model and the birth-and-spreading growth model. Both models produced good fits to the growth rate data. However, on the basis of the qualitative aspects of the experimentally-observed growth, it is suggested that the correct growth model for these crystals is the Burton-Cabrera-Frank model.

Reiss, D. A.↗
NASA NTRS1988

Effect of fluoride doping on the transition temperature of YBa2Cu3O(6.5+delta)

The effects of F content on the Tc of superconducting YBa2Cu3F(x)O(6.5+delta-0.5x) (x = 0.0165-1.65) prepared by the solid-state reaction method (Bandsahl and Sandkuhl, 1988) are investigated experimentally. The results are presented in tables and graphs and characterized. Tc is found to increase steadily from 90.8 to 93.4 K as x is increased from 0.0165 to 0.066, but to decrease as x is further increased (Tc = 90.3 K at x = 1.65). The structure of the samples with x = 0.066 or lower is found to be single-phase perovskite.

Bansal, Narottam P.↗
NASA NTRS1990

Chiral interface at the finite temperature transition point of QCD

The domain wall between coexisting chirally symmetric and broken symmetry regions is studied in a saddle point approximation to the effective three-flavor sigma model. In the chiral limit the surface tension varies in the range ((40 to -50)MeV)(exp 3). The width of the domain wall is estimated to be approximately or equal to 4.5 fm.

Frei, Z.↗
NASA NTRS1990

The superconducting state of the high-transition temperature superconductors: Experimental basis

Experiments on the high-T(sub c) cuprate superconductors continue to narrow the possible theoretical explanations of the phenomenon. Experimental evidence to date points to a BCS-like state, with pairs in singlet s-states, the familiar gap in the excitation spectrum, type 2 behavior in a magnetic field and a normal state with fermi liquid origins. Several other features of the superconducting state in the cuprates, however, appear to differ from those of conventional alloy superconductors (these relate to the detailed structure of the gap and to the nature of the coupling mechanism). Recent experiments have helped clarify what these differences are, and together with the earlier experiments, they now impose still stronger constraints on theories of these superconductors. These and other developments will be reviewed.

Little, W. A.↗
NASA NTRS1991

Microwave properties of high transition temperature superconducting thin films

Extensive studies of the interaction of microwaves with YBa2Cu3O(7-delta), Bi-based, and Tl-based superconducting thin films deposited in several microwave substrates were performed. The data were obtained by measuring the microwave power transmitted through the film in the normal and the superconducting state and by resonant cavity techniques. The main motives were to qualify and understand the physical parameters such as the magnetic penetration depth, the complex conductivity, and the surface impedance, of high temperature superconducting (HTS) materials at microwave frequencies. Based on these parameters, the suitability of these HTS thin films is discussed for microwave applications.

Gordon, W. L.↗
NASA NTRS1991

The superconducting state of the high-transition temperature superconductors: Experimental basis

Experiments on the high-T(sub c) cuprate superconductors continue to narrow the possible theoretical explanations of the phenomenon. Experimental evidence to date points to a BCS-like state, with pairs in singlet s-states, the familiar gap in the excitation spectrum, Type 2 behavior in a magnetic field, and a normal state with fermi liquid origins. Several other features of the superconducting state in the cuprates, however, appear to differ from those of conventional alloy superconductors (these relate to the detailed structure of the gap and to the nature of the coupling mechanism). Recent experiments have helped clarify what these differences are, and together with the earlier experiments, they now impose still stronger constraints on theories of these superconductors. These and other developments are reviewed.

Little, W. A.↗
NASA NTRS2002

High-Glass-Transition-Temperature Polyimides Developed for Reusable Launch Vehicle Applications

Polyimide composites have been traditionally used for high-temperature applications in aircraft engines at temperatures up to 550 F (288 C) for thousands of hours. However, as NASA shifts its focus toward the development of advanced reusable launch vehicles, there is an urgent need for lightweight polymer composites that can sustain 600 to 800 F (315 to 427 C) for short excursions (hundreds of hours). To meet critical vehicle weight targets, it is essential that one use lightweight, high-temperature polymer matrix composites in propulsion components such as turbopump housings, ducts, engine supports, and struts. Composite materials in reusable launch vehicle components will heat quickly during launch and reentry. Conventional composites, consisting of layers of fabric or fiber-reinforced lamina, would either blister or encounter catastrophic delamination under high heating rates above 300 C. This blistering and delamination are the result of a sudden volume expansion within the composite due to the release of absorbed moisture and gases generated by the degradation of the polymer matrix. Researchers at the NASA Glenn Research Center and the Boeing Company (Long Beach, CA) recently demonstrated a successful approach for preventing this delamination--the use of three-dimensional stitched composites fabricated by resin infusion.

Chuang, Kathy↗