Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “contact pressure”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

RAWINPROC: Computer program for decommutating, interpreting, and interpolating Rawinsonde meteorological balloon sounding data

The FORTRAN computer program RAWINPROC accepts output from NASA Wallops computer program METPASS1; and produces input for NASA computer program 3.0.0700 (ECC-PRD). The three parts together form a software system for the completely automatic reduction of standard RAWINSONDE sounding data. RAWINPROC pre-edits the 0.1-second data, including time-of-day, azimuth, elevation, and sonde-modulated tone frequency, condenses the data according to successive dwells of the tone frequency, decommutates the condensed data into the proper channels (temperature, relative humidity, high and low references), determines the running baroswitch contact number and computes the associated pressure altitudes, and interpolates the data appropriate for input to ACC-PRD.

Staffanson, F. L.↗
NASA NTRS1979

Acoustic levitation and manipulation for space applications

A wide spectrum of experiments to be performed in space in a microgravity environment require levitation and manipulation of liquid or molten samples. A novel acoustic method has been developed at JPL for controlling liquid samples without physical contacts. This method utilizes the static pressure generated by three orthogonal acoustic standing waves excited within an enclosure. Furthermore, this method will allow the sample to be rotated and/or oscillated by modifying the phase angles and/or the amplitude of the acoustic field. This technique has been proven both in our laboratory and in a microgravity environment provided by KC-135 flights. Samples placed within our chamber driven at (1,0,0), (0,1,0), and (0,0,1), modes were indeed levitated, rotated, and oscillated.

Wang, T. G.↗
NASA NTRS1995

Numerical Methodology For Full-Body TPS Sizing And Optimization For Access-To-Space Vehicles

This paper presents details of the methodology and numerical procedures developed at NASA Ames for full-body TEXAS sizing and optimization for Access to Space vehicle concepts. The core of the procedures is a robust implicit solver for one dimensional transient heat conduction in reusable multilayer TEXAS stackups. The solver includes an arbitrary number of material layers, contact resistances between materials, temperature and pressure dependent material and surface properties, numerous boundary-condition options, and self-adaptive time stepping. The solver is coupled with the Access-to-Space material database of 23 candidate TPS and structural materials and a thermal-environment database obtained from trajectory-based fullbody Navier-Stokes computations of the external flowfield. The thermal environment and material response are coupled through the use of T-type heat transfer coefficients. TIPS sizing and weight optimization are performed at every surface point on the vehicle based on sizing constraints which include material temperature limits, maximum backwall temperature, and cumulative interior heat flux. Typical results are presented for a lifting body concept with 10000 surface points, which required 35 minutes to compute on an SGI Indigo 2.

Milos, Frank S.↗
NASA NTRS2014

Demonstration of SiC Pressure Sensors at 750 C

We report the first demonstration of MEMS-based 4H-SiC piezoresistive pressure sensors tested at 750 C and in the process confirmed the existence of strain sensitivity recovery with increasing temperature above 400 C, eventually achieving near or up to 100% of the room temperature values at 750 C. This strain sensitivity recovery phenomenon in 4H-SiC is uncharacteristic of the well-known monotonic decrease in strain sensitivity with increasing temperature in silicon piezoresistors. For the three sensors tested, the room temperature full-scale output (FSO) at 200 psig ranged between 29 and 36 mV. Although the FSO at 400 C dropped by about 60%, full recovery was achieved at 750 C. This result will allow the operation of SiC pressure sensors at higher temperatures, thereby permitting deeper insertion into the engine combustion chamber to improve the accurate quantification of combustor dynamics.

Semiconductor↗
NASA NTRS1978

Investigations of lubricant rheology as applied to elastohydrodynamic lubrication

Measurements of lubricant shear rheological behavior in the amorphous solid region and near the liquid-solid transition are reported. Elastic, plastic and viscous behavior was observed. A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature.

Bair, S.↗
NASA NTRS1979

A rheological model for elastohydrodynamic contacts based on primary laboratory data

A shear rheological model based on primary laboratory data is proposed for concentrated contact lubrication. The model is a Maxwell model modified with a limiting shear stress. Three material properties are required: Low shear stress viscosity, limiting elastic shear modulus, and the limiting shear stress the material can withstand. All three are functions of temperature and pressure. In applying the model to EHD contacts the predicted response possesses the characteristics expected from several experiments reported in the literature and, in one specific case where direct comparison could be made, good numerical agreement is shown.

Bair, S.↗
NASA NTRS1976

Isothermal elastohydrodynamic lubrication of point contacts. IV - Starvation results

Previously developed basic theory for isothermal elastohydrodynamic lubrication of point contacts is used to study the effect of lubricant starvation on pressure and film thickness within the conjunction. A simple expression for the dimensionless inlet boundary distance is derived. This inlet boundary distance defines whether a fully flooded or a starved condition exists in the contact. Simple expressions for the minimum and central film thickness under starvation condition are presented. Contour plots of pressure and film thickness in and around the contact are shown in order to gain a better insight into what occurs in going from fully flooded to lubricant starvation condition. Theoretical predictions are compared with earlier results.

Hamrock, B. J.↗
NASA NTRS1977

Low-pressure low-temperature molding process

Use of expanding rubber mandrel allows for bonding of graphite/epoxy laminated parts in oven instead of expensive autoclave. Heavy-duty two-piece aluminum mold limits deflection. Manipulation of resin contact by precise control of mandrel-generated pressure eliminates complex bleeder system.

Bowman, E. L.↗
DOE OSTI2025

Low fractional volume superconductivity in single crystals of Pr{sub 4}Ni{sub 3}O{sub 10} under pressure

Magnetotransport measurements of P⁢r4⁢N⁢i3⁢O10 single crystals performed under externally applied pressures up to 73 GPa in diamond anvil cells with either KBr or Nujol oil as pressure media yield signatures of superconductivity with a maximum onset temperature of approximately 31 K. True zero resistance was not observed, consistent with a nonpercolating superconducting volume fraction. Magnetization measurements provided corroborating evidence of superconductivity, with a pressure-dependent diamagnetic signal occurring below the onset temperature, and an estimate from the absolute value of the susceptibility suggests a superconducting volume fraction on the order of 10%. We observe sample to sample variations in the magnitude and pressure dependence of 𝑇𝑐 as well as a dependence on the configuration of electrical contacts on a given sample. Possible causes of this behavior may be significant inhomogeneities in the pressure and/or damage to the samples induced by the pressure media as well as inhomogeneities in the crystals themselves. The results imply that our as-grown P⁢r4⁢N⁢i3⁢O10 single crystals are not bulk superconductors but that there is a minority structure present within the crystals that is indeed superconductin

Chen, Xinglong↗
NASA NTRS1966

Fluid pressure balanced seal

A seal which increases in effectiveness with increasing pressure is presented. The seal's functional capability throughout both static and dynamic operation makes it particularly useful for sealing ball valve ports. Other features of the seal include the ability to seal two opposed surfaces simultaneously, tolerance of small misalignments, tolerance of wide temperature ranges, ability to maintain positive sealing contact under conditions of internal or external pressurization, and ability to conform to slight irregularities in seal or surface contours.

Marsh, H. W.↗
NASA NTRS2010

Meniscus Shapes in Detached Bridgman Growth

In detached Bridgman crystal growth, most of the melt is in contact with the ampoule wall, but the crystal is separated from the wall by a small gap, typically 1-100 micrometers. A liquid free surface, or meniscus, bridges across this gap at the position of the melt-crystal interface. Meniscus shapes have been calculated for the case of detached Bridgman growth in cylindrical ampoules by solving the Young-Laplace equation. Key parameters affecting meniscus shapes are the growth angle, contact angle of the meniscus to the ampoule wall, the pressure differential across the meniscus, and the Bond number, a measure of the ratio of gravitational to capillary forces. In general, for specified values of growth and contact angles, solutions exist only over a finite range of pressure differentials. For intermediate values of the Bond number, there are multiple solutions to the Young-Laplace equations. There are also cases where, as a function of pressure differential, existence intervals alternate with intervals where no solutions exist. The implications of the meniscus shape calculations on meniscus stability are discussed.

Volz, M. P.↗
DOE OSTI2020

Autoclave grid-to-rod fretting wear evaluation of a candidate cladding coating for accident-tolerant fuel

In pressurized water reactors (PWRs), water flow induced vibrations cause contact and rubbing between the fuel rods and the supporting grid, a phenomenon known as Grid-to-Rod-Fretting (GTRF). GTRF may produce progressive wear damage on the fuel claddings leading to subsequent leakage of radioactive fission products. Various accident-tolerant fuel (ATF) concepts are being developed for higher resistance to the high temperature steam and one approach is to apply a cladding coating. Here, fretting wear behavior of a candidate Cr-coating was investigated using a unique bench-scale autoclave testing rig mimicking the environment in an industrial full-assembly PWR simulator. The contact was under a realistically low load (~0.5 N) lubricated by deionized water at a temperature of 204 °C under a pressure of 20-23 bars. Results demonstrated that the Cr-coating significantly improved the cladding's wear resistance when tested against a commercial ZIRLO grid with or without pre-oxidization. In addition, the Cr-coating also reduced wear on the non-oxidized ZIRLO grid but slightly increased the wear on the pre-oxidized grid.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Benchmarking Solid-State Batteries Containing Sulfide Separators: Effects of Electrode Composition and Stack Pressure

Integrating sulfide separators into solid-state batteries (SSBs) containing high energy cathodes typically requires one or more materials and engineering solutions including: (i) applying interfacial coatings to mitigate electrolyte decomposition, (ii) applying high stack pressures to form robust solid-solid contacts, and (iii) using alloying anodes to avoid Li dendrite formation. Despite the promise of these approaches, a lack of standardized testing protocols makes it difficult to directly compare results among different studies. To address this problem, the present work benchmarks the performance of SSBs containing β-Li 3 PS 4 (LPS) separators and composite cathodes. By systematically varying the anode/cathode composition and stack pressure, this work demonstrates that cathode design is a major bottleneck for solid-state cells cycled at low rates (<100 µA cm -2 ). Operando stack pressure measurements show that, while mechanical confinement generally promotes higher active material utilization and cycling stability, this strategy alone does not address interfacial reactivity between LPS and high voltage cathodes. Here, these results also demonstrate that stress evolution during cycling is dominated by volume changes at the Li metal anode. Finally, we show that FeS 2 cathodes with moderate operating voltages (<3 V vs Li/Li + ) exhibit superior cycling performance compared to high voltage cathodes by facilitating formation of stable cathode/electrolyte interfaces.

25 ENERGY STORAGE↗
NASA NTRS1991

Improved compression molding technology for continuous fiber reinforced composite laminates. Part 2: AS-4/Polyimidesulfone prepreg system

AS-4/polyimidesulfone (PISO2) composite prepreg was utilized for the improved compression molding technology investigation. This improved technique employed molding stops which advantageously facilitate the escape of volatile by-products during the B-stage curing step, and effectively minimize the neutralization of the consolidating pressure by intimate interply fiber-fiber contact within the laminate in the subsequent molding cycle. Without the modifying the resin matrix properties, composite panels with both unidirectional and angled plies with outstanding C-scans and mechanical properties were successfully molded using moderate molding conditions, i.e., 660 F and 500 psi, using this technique. The size of the panels molded were up to 6.00 x 6.00 x 0.07 in. A consolidation theory was proposed for the understanding and advancement of the processing science. Processing parameters such as vacuum, pressure cycle design, prepreg quality, etc. were explored.

Baucom, Robert M.↗
NASA NTRS1978

Elastohydrodynamic lubrication of elliptical contacts for materials of low elastic modulus. II - Starved conjunction

The study evaluates the effect of lubricant starvation on minimum film thickness in starved elliptical elastohydrodynamic conjunctions for materials of low elastic modulus. Lubricant starvation is studied simply by moving the inlet boundary closer to the center of the conjunction. A simple expression is presented for the dimensionless inlet boundary distance; this inlet boundary distance defines whether a fully flooded or a starved condition exists in the conjunction. A formula for the minimum film thickness under the starvation condition is derived. Contour plots of the pressure and film thickness in and around the contact are presented for both the fully flooded and starved lubrication conditions. It is shown that the inlet pressure contours become less circular and that the film thickness decreases substantially with increasing starvation severity.

Hamrock, B. J.↗
DOE OSTI2020

Effect of endoglucanase and high-pressure homogenization post-treatments on mechanically grinded cellulose nanofibrils and their film performance

In this study, the effects of mechanical grinding (G) assisted by endoglucanase (E) and high-pressure homogenization (H) post-treated cellulose nanofibrils (CNFs) and its film properties were investigated. Compared to only mechanical grinding, these two post-treatment processes improved the size uniformity of CNFs in width. Additionally, the crystallinity of GECNFs was increased by 4.3 % and the resulting film exhibited low oxygen permeability rate (6.33 mL/m 2 ·day). Moreover, the combination post-treatments of enzyme and homogenization improved the tensile strength and transparency of CNFs films from 132.31 MPa, 27.52 %– to 177.99 MPa, 61.75 %, respectively. Besides, a composite of acrylic resin ABPE-10 and GEHCNFs film under negative pressure improved the transparency (85.68 %) and water contact angle (104.11°) of film. This work also provides insight on the relationship between the CNFs morphology and their film properties, which can be used to improve the CNFs film performance and promote future applications of CNFs.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS2005

Promoted Metals Combustion at Ambient and Elevated Temperatures

Promoted combustion testing of materials, Test 17 of NASA STD-6001, has been used to assess metal propensity to burn in oxygen rich environments. An igniter is used at the bottom end of a rod to promote ignition, and if combustion is sustained, the burning progresses from the bottom to the top of the rod. The physical mechanisms are very similar to the upward flammability test, Test 1 of NASA STD-6001. The differences are in the normal environmental range of pressures, oxygen content, and sample geometry. Upward flammability testing of organic materials can exhibit a significant transitional region between no burning to complete quasi-state burning. In this transitional region, the burn process exhibits a probabilistic nature. This transitional region has been identified for metals using the promoted combustion testing method at ambient initial temperatures. The work given here is focused on examining the transitional region and the quasi-steady burning region both at conventional ambient testing conditions and at elevated temperatures. A new heated promoted combustion facility and equipment at Marshall Space Flight Center have just been completed to provide the basic data regarding the metals operating temperature limits in contact with oxygen rich atmospheres at high pressures. Initial data have been obtained for Stainless Steel 304L, Stainless Steel 321, Haynes 214, and Inconel 718 at elevated temperatures in 100-percent oxygen atmospheres. These data along with an extended data set at ambient initial temperature test conditions are examined. The pressure boundaries of acceptable, non-burning usage is found to be lowered at elevated temperature.

Engel, Carl D.↗