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At least 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Relationship between the ideal tensile strength and the friction properties of metals in contact with nonmetals and themselves

The adhesion and friction properties of metals in contact with diamond, boron nitride, silicon carbide, manganese-zinc ferrite, and the metals themselves in vacuum was investigated. An estimate of the ideal uniaxial tensile was obtained in terms of the equilibrium surface energy, interplanar spacing of the planes perpendicular to the tensile axis, and the Young's modulus of elasticity. The coefficient of friction for metals was found to be related to the ideal tensile strength of metals. The higher the strength of the metal, the lower the coefficient of friction.

Miyoshi, K.↗
NASA NTRS1980

A film thickness analysis for line contacts under pure rolling conditions with a non-Newtonian rheological model

The non-Newtonian constitutive equation of Winer and Bair (1979) is applied to a conventional isothermal film thickness analysis of line contact lubrication of rolling elements providing dimensionless film thickness equations for four lubrication methods. The equations can be applied to high viscosity and rolling speed and low limiting shear stress cases where Newtonian methods are not applicable. This analysis is based on a reasonable range of limiting shear stress which is smaller than the Newtonian values for low viscosity lubricants.

Gecim, B.↗
NASA NTRS1980

The adhesion, friction, and wear of binary alloys in contact with single-crystal silicon carbide

Sliding friction experiments were conducted with various iron-base alloys (alloying elements were Ti, Cr, Ni, Rh, and W) in contact with a single-crystal silicon carbide (0001) surface in vacuum. Results indicate atomic size misfit and concentration of alloying elements play a dominant role in controlling adhesion, friction, and wear properties of iron-base binary alloys. The controlling mechanism of the alloy properties is an intrinsic effect involving the resistance to shear fracture of cohesive bonding in the alloy. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases as the solute-to-iron atomic radius ratio increases or decreases from unity. Alloys having higher solute concentration produce more transfer to silicon carbide than do alloys having low solute concentrations. The chemical activity of the alloying element is also an important parameter in controlling adhesion and friction of alloys.

Miyoshi, K.↗
NASA NTRS1980

Behavior of interdigitated back-contact solar cells

This paper presents experimental data concerning operation mechanisms of two versions of interdigitated back-contact solar cells: the tandem junction cell and the front-surface field cell. It is shown that a photogenerated forward bias at the front junction of a tandem junction cell is a critical parameter for cell performance which not only causes photogenerated carriers to migrate to the back junction, but also eliminates the reduction in photoresponse over back p(+) metallization regions. However, no similar light effects are observed in the performance of front-surface field cells. Finally, a discussion on mechanisms concerning the performance of front-surface field and tandem junction cells along with their merits is given.

Cheng, L. J.↗
NASA NTRS1980

High efficiency ultrathin coplanar back contact cells

Efforts to fabricate high efficiency, ultrathin coplanar back contact cells are described. Included is a description of design considerations, cell fabrication, and theoretical and experimental analyses of loss mechanisms. The results of these efforts has been the fabrication of a 11.8% AM0 efficient, 50 micron cell when measured at 25 C. Design and process changes required to increase the efficiency are indicated.

Storti, G.↗
NASA NTRS1980

Screenable silver and base metal solar cell contacts

The metallurgical soundness of the all-metal screenable thick film electrode system is established for silver and copper electrodes. Silver fluoride was identified as a successful etchant material and is found most effective in the liquid phase (435-460 C). Best results were achieved with the eutectic alloys of dopants and semiconductors. The air-fired silver inks were strongly adherent, rugged, and solderable, whereas the hydrogen-fired silver inks had very poor adhesion. A two-step firing process was devised in which copper inks containing silver fluoride were activated in a nitrogen atmosphere, with sintering done at the same or higher temperatures in hydrogen. Good solar cells were made using the copper paste back contacts demonstrating that the electrodes are not the limiting factors in efficiency.

Ross, B.↗
NASA NTRS1980

An all-plated, low cost contact system for silicon solar cells

The plating sequences Pd-Cr-Cu and Pd-Ni-Cu are demonstrated. The surface was sensitized with a 50 A-thick Pd layer obtained from an immersion bath. After 15 min heating at 400 C in N2, a thin barrier layer of either Cr or Ni was deposited from electroless baths operated at temperatures around 90 C. The sintering process was repeated, and a thin copper layer of 500 A was deposited by electroless means. An electrolytic copper bath was used to build the copper layer to 3-4 micron thicknesses. Cells with good I-V curves were obtained, and the all-plated contacts had good adhesion. Preliminary cost estimates show that the process costs approximately 12 cents per watt excluding the cost of the masking procedure.

Tanner, D. P.↗
NASA NTRS1981

Parallelism maps for optically contacted etalons

A measurement technique is described that is capable of producing accurate numerical maps of the parallelism defect of optically contacted Fabry-Perot etalons. A photoelectric raster scan of the etalon transmission intensity distribution is performed at each of three closely spaced etalon tunings, one at maximum on-axis and two at the half-maxima on-axis positions. Simple data manipulation gives numerical or contour maps of the parallelism defect. Results demonstrating the effect of mechanical constraints on etalon parallelism are presented

Killeen, T. L.↗
NASA NTRS1982

Non-contacting power transfer device

A transformer for coupling AC electrical energy from a stationary element to a rotating element without the use of sliding contacts is described. The transformer is of the rotary type and includes a ferrite core and two primary windings which are stationary with respect to a seconary winding which rotates within an annular cavity adjacent an axial bore in the core. The core is comprised of two cup type core halves. Electrical connection to the secondary winding is made through a split bobbin assembly which couples to a coaxial shaft assembly located in the axial bore. The electrical coupling to the coaxial shaft assembly is made through a continuous transverse channel connecting the axial bore with the annular cavity. The transverse channel forms a single air gap; however, it is not open directly to free space but is shielded by the magnetic permeable material of the core halves.

Studer, P. A.↗
NASA NTRS1982

The dryout region in frictionally heated sliding contacts

Some conditions under which boiling and two-phase flow can occur in or near a wet sliding contact are determined and illustrated. The experimental apparatus consisted of a tool pressed against an instrumented slider plate and motion picture sequences at 4000 frames/sec. The temperature and photographic data demonstrated surface conditions of boiling, drying, trapped gas evolution (solutions), and volatility of fluid mixture components. The theoretical modeling and analysis are in reasonable agreement with experimental data.

Hendricks, R. C.↗
NASA NTRS1982

Line-profile and continuum variations of the contact binary SV Centauri

A total of five high and ten low dispersion UV spectra of the interacting contact binary SV Centauri obtained between 1979 and 1982 are analyzed. The low resolution observations cover the whole phase range, while a few selected phases were observed in high dispersion. The UV data were complemented with optical photometric and spectroscopic observations, in order to determine the tructure and absolute dimensions of the system. The profiles of prominent UV resonance and metastable lines undergo drastic changes with phase angle and time. Their overall appearance indicates relatively strong mass loss from the system, exhibiting pronounced variations of the stellar wind. The far UV continuum distribution suggests the presence of a luminous hot radiation source with maximum emission in the soft X-ray range, which is most apparently seen during the first quadrature phase, while it is weakest close to primary minimum. The case exchange and mass loss process as well as the evolutionary stage of SV Centauri are discussed.

Rahe, J.↗
NASA NTRS1981

Alignment of fluid molecules in an EHD contact

Dichroic infrared emission spectra have been obtained from an operating elastohydrodynamic contact under conditions showing unequivocally that the molecules of the fluid are aligned under shear flow in the bulk of the fluid and that the extent of the alignment is increased by the presence of an additive in a small concentration. This work applied particularly to polyphenyl ether and to 1,1,2-trichloroethane as the additive, but similar results have been obtained with polycyclohexyls and the same additive. The observation of two separate glass transitions for the polycyclohexyl solution is an indication of the occurrence of a phase separation in the Hertzian inlet zone. A model has been developed to explain the effect of these phenomena and their relation to traction.

Lauer, J. L.↗
NASA NTRS1981

Analysis of starvation effects on hydrodynamic lubrication in nonconforming contacts

The effects of lubricant starvation on minimum film thickness, under conditions of a hydrodynamic point contact, are determined by numerical methods where: (1) starvation is effected by varying the fluid inlet level; (2) the Reynolds boundary conditions are applied at the cavitation boundary; and (3) zero pressure is stipulated at the meniscus or inlet boundary. Seventy-four cases were used to numerically determine a minimum-film-thickness equation, as a function of the ratio of dimensionless load to dimensionless speed for varying degrees of starvation. A film reduction factor was in turn determined as a function of the fluid inlet level, and a starved, fully-flooded boundary was defined along with an expression determining the onset of starvation. It is found that as the degree of starvation increases, the minimum film thickness decreases gradually until the fluid inlet becomes critical. The changes in the inlet pressure buildup due to changing the available lubricant supply are presented in the form of three-dimensional isometric plots.

Brewe, D. E.↗
NASA NTRS1982

Improved whisker pointing technique for micron-size diode contact

Pointed phosphor-bronze whiskers are commonly used to contact micron-size Schottky barrier diodes. A process is presented which allows pointing such wire and achieving the desired cone angle and tip diameter without the use of highly undesirable chemical reagents.

Mattauch, R. J.↗
NASA NTRS1982

Experimental stress analysis of a thin-walled pressurized torus loaded by contact with a plane

It is pointed out that pneumatic tires have a large effect on the overall landing characteristics of an aircraft. The dynamic response upon landing and steering are crucial to the safety of the vehicle and the occupants. The present investigation has the objective to compare experimentally determined strains on an inner tube in contact with a flat plate with numerical values obtained on the basis of a finite element prediction, taking into account an employment of the Structural Analysis of General Shells (STAGS). The obtained results suggest that the clamped boundary condition utilized in the STAGS calculation is not exactly simulated by the employed test setup.

Hill, D. E.↗
NASA NTRS1981

Thin foil silicon solar cells with coplanar back contacts

To fabricate 50 microns thick, coplanar back contact (CBC) silicon solar cells, wraparound junction design was selected and proved to be effective. The process sequence used, the cell design, and the cell performance are described. CBC cells with low solar absorptance have shown AMO efficiencies to 13%, high cells up to 14%; further improvements are projected with predictable optimization.

Ho, F.↗
NASA NTRS1981

The gridded back contact and its effect on solar cell performance

The effect of using gridded back contacts on silicon solar cells made with Al baked surface field (BSF) was experimentally investigated and found to result in a significant increase in conversion efficiency due to higher short-circuit current. An increase of 5 to 8% was noted for thin cells while a smaller increase was observed for standard thickness cells. Several possible explanatory mechanisms are suggested and summarized, including stress relief, incomplete BSF formation, improved back surface recombination velocity, and improved optical reflection off the back silicon-air interface.

Giuliano, M.↗
NASA NTRS1981

Large area, low cost space solar cells with optional wraparound contacts

Design parameters for two large area, low cost solar cells are presented, and electron irradiation testing, thermal alpha testing, and cell processing are discussed. The devices are a 2 ohm-cm base resistivity silicon cell with an evaporated aluminum reflector produced in a dielectric wraparound cell, and a 10 ohm-cm silicon cell with the BSF/BSR combination and a conventional contact system. Both cells are 5.9 x 5.9 cm and require 200 micron thick silicon material due to mission weight constraints. Normalized values for open circuit voltage, short circuit current, and maximum power calculations derived from electron radiation testing are given. In addition, thermal alpha testing values of absorptivity and emittance are included. A pilot cell processing run produced cells averaging 14.4% efficiencies at AMO 28 C. Manufacturing for such cells will be on a mechanized process line, and the area of coverslide application technology must be considered in order to achieve cost effective production.

Michaels, D.↗