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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Procedure for pressure contact on high-power semiconductor devices free of thermal fatigue

To eliminate thermal fatigue, a procedure for manufacturing semiconductor power devices with pure pressure contact without solid binding was developed. Pressure contact without the use of a solid binding to avoid a limitation of the maximum surface in the contact was examined. A silicon wafer covered with a relatively thick metal layer is imbedded with the aid of a soft silver foil between two identically sized hard contact discs (molybdenum or tungsten) which are rotationally symmetrical. The advantages of this concept are shown for large diameters. The pressure contact was tested successfully in many devices in a large variety of applications.

Knobloch, J.↗
NASA NTRS1982

Touch Sensor Responds to Contact Pressure

Optical tactile sensor for mechanical hands senses contact pressure via change in light reflected from an elastic covering. Pressure against a cell cover causes distortion, which changes internal reflection of light. Change is sensed by detector, and output signal informs operator of contact. The greater the pressure and distortion, the greater the change in light reflection.

Bejczy, A. K.↗
NASA NTRS1975

Pressure contact sounding data for NASA's Atmospheric Variability Experiment (AVE 2)

The basic rawinsonde data are described at each pressure contact from the surface to sounding termination for the 54 stations participating in the AVE 2 pilot experiment. Soundings were taken at three-hour intervals from stations within the United States east of about 105 degrees west longitude. Methods of data reduction and estimates of data accuracy are discussed. Examples of the data records produced are shown. The AVE 2 pilot experiment was conducted as part of NASA's program to better understand and establish the extent of applications for meteorological satellite sensor data through correlative ground truth experiments and to provide basic experimental data for use in studies of atmospheric scales-of-motion interrelationships.

Fuelberg, H. E.↗
NASA NTRS1975

Pressure Contact Sounding Data for NASA's Atmospheric Variability Experiment (AVE 3)

The basic rawinsonde data are described at each pressure contact from the surface to sounding termination for the 41 stations participating in the AVE III measurement program that began at 0000 GMT on February 6 and ended at 1200 GMT on February 7, 1975. Soundings were taken at 3-hour intervals during a large period of the experiment from most stations within the United States east of about 105 degrees west longitude. Methods of data processing, change in reduction scheme since the AVE II pilot experiment, and data accuracy are briefly discussed. An example of contact data is presented, and microfiche cards of all the contact data are included in the appendix. The AVE III project was conducted to better understand and establish the extent of applications for meteorological satellite sensor data through correlative ground truth experiments and to provide basic experimental data for use in studies of atmospheric scales of-motion interrelationships.

Fuelberg, H. E.↗
NASA NTRS1976

Analysis of contact pressures attainable using indentors which are bodies of revolution

The elastic behavior of a conical indentor with a rounded tip pressed against a flat anvil has been analyzed. It is found that when the radius of contact extends beyond the rounded tip, the contact radius increases much more rapidly as the pressure increases than it does for the case of a fully spherical or parabolic tip. Consequently, the pressure achieved for a rounded conical tip for a given applied force is considerably less than for a spherical or parabolic tip.

Ruoff, A. L.↗
NASA NTRS1980

SSME turbopump bearing analytical study

Three shuttle pump bearings operating under severe overspeed and shut-down conditions are evaluated. The specific parameters investigated include outer race stresses, cage stresses, cage-race drag, bearing heating, and crush loading. A quasi-dynamic version of the BASDAP computer code was utilized which involved the calculation of ball-race forces (inner and outer), contact pressures, contact dimensions, and contact angles as a function of (1) axial load, (2) radial load, and (3) centrifugal load on the bearing. Generally, radial loads on the order of 13,300 N (3000 pounds) per bearing or 26,700 N (6000 pounds) per bearing pair, could be expected to cause severe problems to any of the bearings with a 17,800 N (4000 pounds) axial load. Further, when possible temperature excursions are considered, even a load of 8900 N (2000 pounds) may be excessive. However, high momentary radial loads with a 3800 N (850 pounds) axial load would not be anticipated to cause catastrophic failure of the fuel pump bearing.

Kannel, J. W.↗
NASA NTRS1988

Thermal contact conductance of pressurized surfaces

Thermal vacuum testing has demonstrated the feasibility of the concept of pressurizing contact surfaces for the transfer of waste heat on the Space Station. Data show a thin inflatable bladder design to provide a greater contact conductance than an expandable bellows approach, with substantially less interface volume to transfer the same amount of heat. Extended vacuum testing of the Radiator-to-Thermal Bus assembly indicated a continual increase of conductance as the interface was maintained at 150 psi for a 100-hour period.

Voss, Fred E.↗
NASA NTRS1995

Contact and pressure balance structures in two-fluid cosmic-ray hydrodynamics

The role of cosmic-ray-modified contact discontinuities and pressure balance structures in two-fluid cosmic-ray hydrodynamics in one Cartesian space dimension are investigated by means of analytic and numerical solution examples, as well as by weakly nonlinear asymptotics. The fundamental wave modes of the two-fluid cosmic-ray hydrodynamic equations in the long-wavelength limit consist of the backward and forward propagating cosmic-ray-modified sound waves, with sound speed dependent on both the cosmic-ray and thermal gas pressures; the contact discontinuity; and a pressure balance mode in which the sum ofthe cosmic ray and thermal gas pressure perturbations is zero. The pressure balance mode, like the contact discontinuity is advected with the background flow. The interaction of the pressure balance mode with the contact discontinuity is investigated by means of the method of multiple scales. The thermal gas and cosmic-ray pressure perturbations satisfy a linear diffusion equation, and entropy perturbations arising from nonisentropic initial conditions for the thermal gas are frozen into the fluid. The contact discontinuity and pressure balance eigenmodes both admit nonzero perturbations in the thermal gas, whereas the cosmic-ray-modified sound waves are isentropic. The total entropy perturbation is shared between the contact discontinuity and pressure balance eigenmodes, and examples are given in which there is a transfer of entropy between the two modes. In particular, N-wave type density disturbances are obtained which arise as a result of the entropy transfer between the two modes. A weakly nonlinear geometric optics perturbation expansion is used to study the long timescale evolution of the short-wavelength entropy wave and the thermal gas sound waves in a slowly varying, large-scale background flow. The weakly nonlinear geometric optics expansion is also used to generalize previous studies of squeezing instability for short-wavelength sound waves in the two fluid model, by including a weakly nonlinear wave steepening term that leads to shock formation, as well as the effect of long time and space dependence of the background flow. Implications of cosmic-ray-modified pressure balance structures and contact discontinuities in models of the interaction of traveling interplanetary shocks and compression and rarefraction waves with the solar wind termination shock are briefly discussed.

Webb, G. M.↗
NASA NTRS2000

Friction and Wear Properties of Selected Solid Lubricating Films: Magnetron-Sputtered and Plasma-Assisted, Chemical-Vapor-Deposited Diamondlike Carbon Films - Part 3

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of magnetron-sputtered diamondlike carbon (MS DLC) and plasma-assisted, chemical-vapor-deposited diamondlike carbon (PACVD DLC) films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of L-2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7x10(exp -7) Pa), humid air (relative humidity, approx.20 percent), and dry nitrogen (relative humidity, <1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the DLC films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the DLC films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 10(exp -6) cu mm/N-m or less, respectively. MS DLC films and PACVD DLC films met the criteria in humid air and dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction were greater than the criterion, 0.3. In sliding contact with 440C stainless steel balls in all three environments the PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) than the MS DLC films. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart DLC film.

Miyoshi, Kazuhisa↗
NASA NTRS2000

Friction and Wear Properties of Selected Solid Lubricating Films: Ion-Plated Lead Films - Part 2

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of ion-plated lead films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7 x 10(exp -7 Pa), humid air (relative humidity, approx. 20 percent), and dry nitrogen (relative humidity, less then 1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the ion-plated lead films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the ion-plated lead films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 1(exp -6) cu mm/N.m or less, respectively. The ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen, where the coefficient of friction was higher than the criterion. Both the lead film wear rate and the ball wear rate met that criterion in all three environments. Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead films in contact with 440C stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart lead.

Miyoshi, Kazuhisa↗
NASA NTRS2019

Characterization of Flat-Plate Heat Pipe Functionality for Fuel Cell Application

For many exothermic systems such as proton exchange membrane (PEM) fuel cells, cooling is necessary to maintain consistent and uniform operating temperatures which are generally in the range of 60 to 80°C. A potential solution is a heat pipe employing the principle of conduction in combination with a phase change. The purpose of this study was to fully characterize the operation of a heat pipe with unique geometry designed for fuel cell heat removal at operating temperatures up to 100°C and to assess the suitability of the resulting performance for cooling system integration. Test variables consist of cold sink thermal contact conductance coefficient improving material usage, heat rejection temperature, contact pressure and area, heat pipe orientation, operational hours, and variability between units. The test results showed that heat pipe performance improves through increased condenser and heat sink contact pressure, thermal contact coating usage, greater condenser area utilization, and colder heat sink temperature. Higher initial heat pipe temperature and greater age or operation time reduce the heat pipe capabilities. Placing the condenser lower than the evaporator is the only heat pipe orientation that affects evaporator plate temperature. Condensing fluid in the lower section reduces heat transfer capacity as that orientation requires liquid water to transport by wicking against gravity.

Smith, Phillip J.↗
NASA NTRS1989

Surface modification of Monel K-500 as a means of reducing friction and wear in high-pressure oxygen

A study is conducted of the tribological characteristics of Monel K-500 during rubbing in a high pressure oxygen atmosphere, upon surface treatment by ion-implanted oxygen, chromium, lead, and silver, as well as electrolyzed chromium and an electroless nickel/SiC composite. The electrolyzed chromium dramatically increased total sample wear, while other surface treatments affected sample wear only moderately. Although the ion-implant treatments reduced the average coefficient of friction at low contact pressure, higher contact pressures eliminated this improvement.

Gunaji, Mohan↗
NASA NTRS1986

Ignition of metals and alloys in gaseous oxygen by frictional heating

The ignition of metals and alloys have been investigated by rotating the end of a hollow cylinder against an identical stationary cylinder on a common axis (frictional heating) in gaseous oxygen. A ranking criterion that measures the resistance of metals and alloys to ignition is discussed. It consists of the power per unit area required for ignition conveniently expressed as the product of contact pressure P and average linear velocity ALV. Data are presented that demonstrate that materials that are high in nickel and copper require greater P-ALV products for ignition (more resistant to ignition) than materials that are high in iron. Aluminum and titanium alloys are shown to require the lowest P-ALV products for ignition. The effects of varying surface velocity, contact pressure, coefficient of friction, and oxygen pressure on P-ALV products required for ignition are discussed. The results indicate that P-ALV product required for ignition increases as surface velocity increases, as contact pressure decreases, and as the coefficient of friction decreases. Increasing oxygen pressure will cause the P-ALV product required for ignition to decrease at low pressures and increase at high pressures. In some cases, the relative ranking of materials based on P-ALV products will also change as conditions are varied. The data presented in this paper are from a development program to determine the merits of using such a dynamic test method for ranking materials for oxygen service. The results to date have indicated that more testing is required before this method can be made into a standard test. The data presented do show some of the major parameters affecting the ignition of materials when exposed to frictional heating. The repeatability of the data at any set of conditions have not been thoroughly investigated.

Benz, F. J.↗
NASA NTRS1987

Structural and preliminary thermal performance testing of a pressure activated contact heat exchanger

A contact heat exchanger concept is being developed for use onboard Space Station as an interface device between external thermal bus and pressurized modules. The concept relies on mechanical contact activated by the fluid pressure inside thin-walled tubes. Structural testings were carried out to confirm the technology feasibility of using such thin-walled tubes. The test results also verified the linear elastic stress analysis which was used to predict the tube mechanical behaviors. A preliminary thermal testing was also performed with liquid Freon-11 flowing inside tubes and heat being supplied by electrical heating from the bottom of the contact heat exchanger baseplate. The test results showed excellent agreement of test data with analytical prediction for all thermal resistances except for the two-phase flow characteristics. Testing with two-phase flow inside tubes will, however, be performed on the NASA-JSC test bed.

Lee, C. Y.↗
NASA NTRS1990

Effect of metallic coatings on the thermal contact conductance of turned surfaces

An experimental investigation was conducted to determine the degree to which the thermal contact conductance at the interface of contacting Aluminum 6061 T6 surfaces could be enhanced through the use of vapor-deposited metallic coatings. Three different coating materials (lead, tin, and indium) were evaluated using four different thicknesses for each coating material. The results verified the existence of an optimum coating thickness, shown to be in the range of 2.0 to 3.0 microns for indium, 1.5 to 2.5 microns for lead, and 0.2 to 0.5 microns for tin. The enhancement factors for thermal contact conductance were found to be on the order of 700, 400, and 50 percent, respectively. Based upon the experimental data, the hardness of the coating materials appears to be the most significant parameter in ranking the substrate and coating material combinations; however, additional experimental data are needed to substantiate this hypothesis. Finally, it was apparent that the thermal contact conductance enhancement effect was greatest at low contact pressures and decreased significantly with increases in the contact pressure.

Kang, T. K.↗
NASA NTRS1997

Unique Tuft Test Facility Dramatically Reduces Brush Seal Development Costs

Brush seals have been incorporated in the latest turbine engines to reduce leakage and improve efficiency. However, the life of these seals is limited by wear. Studies have shown that optimal sealing characteristics for a brush seal occur before the interference fit between the brush and shaft is excessively worn. Research to develop improved tribopairs (brush and coating) with reduced wear and lower friction has been hindered by the lack of an accurate, low-cost, efficient test methodology. Estimated costs for evaluating a new material combination in an engine company seal test program are on the order of $100,000. To address this need, the NASA Lewis Research Center designed, built, and validated a unique, innovative brush seal tuft tester that slides a single tuft of brush seal wire against a rotating shaft under controlled loads, speeds, and temperatures comparable to those in turbine engines. As an initial screening tool, the brush seal tuft tester can tribologicaly evaluate candidate seal materials for 1/10th the cost of full-scale seal tests. Previous to the development of the brush seal tuft tester facility, most relevant tribological data had been obtained from full-scale seal tests conducted primarily to determine seal leakage characteristics. However, from a tribological point of view, these tests included the confounding effects of varying contact pressures, bristle flaring, high-temperature oxidation, and varying bristle contact angles. These confounding effects are overcome in tuft testing. The interface contact pressures can be either constant or varying depending on the tuft mounting device, and bristle wear can be measured optically with inscribed witness marks. In a recent cooperative program with a U.S. turbine engine manufacturer, five metallic wire candidates were tested against a plasma-sprayed Nichrome-bonded chrome carbide. The wire materials used during this collaboration were either nickel-chrome- or cobaltchrome-based superalloys. These tests corroborated full-scale seal test results and provided insight into previously untested combinations. As the cycle temperature for improved efficiency turbine engines increases, new brush seal materials combinations must be considered. Future brush seal tuft testing will include both metallic and ceramic bristles versus commercial and NASA-developed shaft coatings. The ultimate goal of this work is to expand the current data base so that seal designers can tailor brush seal materials to specific applications.

Fellenstein, James A.↗