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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Surface topographical changes measured by phase-locked interferometry

An electronic optical laser interferometer capable of resolving depth differences of as low as 30 A and planar displacements of 6000 A was constructed to examine surface profiles of bearing surfaces without physical contact. Topological chemical reactivity was determined by applying a drop of dilute alcoholic hydrochloric acid and measuring the profile of the solid surface before and after application of this probe. Scuffed bearing surfaces reacted much faster than virgin ones but that bearing surfaces exposed to lubricants containing an organic chloride reacted much more slowly. The reactivity of stainless steel plates, heated in a nitrogen atmosphere to different temperatures, were examined later at ambient temperature. The change of surface contour as a result of the probe reaction followed Arrhenius-type relation with respect to heat treatment temperature. The contact area of the plate of a ball/plate sliding elastohydrodynamic contact run on trimethylopropane triheptanoate with or without additives was optically profiled periodically. As scuffing was approached, the change of profile within the contact region changed much more rapidly by the acid probe and assumed a constant high value after scuffing. A nonetching metallurgical phase was found in the scuff mark, which was apparently responsible for the high reactivity.

Lauer, J. L.↗
NASA NTRS1988

Performance of lightweight nickel electrodes

The NASA Lewis Research Center is currently developing nickel electrodes for nickel-hydrogen (Ni-H2) batteries. These electrodes are lighter in weight and have higher energy densities than the heavier state-of-the-art (SOA) sintered nickel electrodes. In the present approach, lightweight materials or plaques are used as conductive supports for the nickel hydroxide active material. These plaques (fiber and felt, nickel plated plastic and graphite) are commercial products that are fabricated into nickel electrodes by electrochemically impregnating them with active material. Evaluation is performed in half cells structured in the bipolar configuration. Initial performance tests include capacity measurements at five discharge levels, C/2, 1.0C 1.37C, 2.0C and 2.74C. The electrodes that pass the initial tests are life cycle tested in a low Earth orbit regime at 80 percent depth of discharge. Different formulations of nickel fiber materials obtained from several manufacturers are currently being tested as possible candidates for nickel electrodes. One particular lightweight fiber mat electrode has accumulated over 3000 cycles to date, with stable capacity and voltage. Life and performance data of this electrode were investigated and presented. Good dimensional stability and active material adherence have been demonstrated in electrodes made from this lightweight plaque.

Britton, Doris L.↗
NASA NTRS1988

Performance of lightweight nickel electrodes

The NASA Lewis Research Center is currently developing nickel electrodes for nickel-hydrogen (Ni-H2) batteries. These electrodes are lighter in weight and have higher energy densities than the heavier state-of-the-art (SOA) sintered nickel electrodes. In the present approach, lightweight materials or plaques are used as conductive supports for the nickel hydroxide active material. These plaques (fiber and felt, nickel plated plastic and graphite) are commercial products that are fabricated into nickel electrodes by electrochemically impregnating them with active material. Evaluation is performed in half cells structured in the bipolar configuration. Initial performance tests include capacity measurements at five discharge levels, C/2, 1.0C, 1.37C, 2.0C and 2.74C. The electrodes that pass the initial tests are life cycle tested in a low earth orbit regime at 80 percent depth of discharge. Different formulations of nickel fiber materials obtained from several manufacturers are currently being tested as possible candidates for nickel electrodes. One particular lightweight fiber mat electrode has accumulated over 3000 cycles to date, with stable capacity and voltage. Life and performance data of this electrode were investigated and presented. Good dimensional stability and active material adherence have been demonstrated in electrodes made from this lightweight plaque.

Britton, Doris L.↗
NASA NTRS1992

Progress in the development of lightweight nickel electrode for aerospace applications

The NASA Lewis Research Center is currently developing nickel electrodes for nickel-hydrogen (Ni-H2) cells and batteries. These electrodes are lighter in weight and have higher specific energy than the heavy sintered state of the art nickel electrodes. In the present approach, lightweight materials or plaques are used as conductive supports for the nickel hydroxide active material. These plaques (fiber, felt, and nickel plated plastic) are fabricated into nickel electrodes by electrochemically impregnating them with active material. Initial performance tests include capacity measurements at five discharge levels, C/2, 1.0C, 1.37C, 2.0C, and 2.74C. The electrodes that pass the initial tests are life cycle tested at 40 and 80 percent depths of discharge (DOD). Different formulations of nickel fiber materials obtained from several manufacturers are currently being tested as possible candidates for nickel electrodes. Over 7,000 cycles of life cycle testing have been accumulated at 40 percent DOD, using the lightweight fiber electrode in a boiler plate Ni-H2 cell with stable voltage.

Britton, Doris L.↗
NASA NTRS1992

Global/local analysis of laminated composite plates using variable kinematic finite elements

A finite element modeling methodology is developed for the hierarchical, global/local analysis of laminated composite plates. The method incorporates a new variable kinematics, displacement-based, finite element that is developed using a multiple assumed displacement field approach. The variable kinematic elements provide a great degree of flexibility in defining the transverse (through thickness) variation of the assumed displacement field. The resulting finite element model permits different subregions of the computational domain to be described by different mathematical models. Enforcing displacement continuity along subregion boundaries requires only the specification of certain homogeneous essential boundary conditions, thus avoiding the inconvenience of multi-point constraints, penalty function methods, or special transition elements.

Robbins, D. H., Jr.↗
NASA NTRS2002

Thermomechanical Response Variability of Stiffened Composite Panels

A significant numerical simulation capability now exists for studying the various phenomena associated with the response, failure, and performance of multilayered composite panels and shells subjected to combined pressure, mechanical, and thermal loads. The phenomena involved cover a wide range of length scales from local to global structural response. The modeling approaches used for multilayered panels include micromechanical models, three-dimensional continuum models, quasi-three-dimensional models, and two-dimensional plate and shell models. Within each category a number of models with several levels of sophistication has evolved. The four categories are described in review papers. Despite the extensive literature cited in the afore-mentioned references, only a few studies have been reported on the effects of stiffness discontinuities, such as those associated with an abrupt stiffener termination or dropped plies, on the response of composite panel. Stiffener termination is often necessary in composite aerospace structures to satisfy detailed design requirements, and therefore an understanding and a prediction of its effect on the response and failure of composite panels are desirable. Such a prediction must take into account the fact that current measurement technology does not allow the accurate determination of the material parameters that are used in the analytical models.

Noor, Ahmed K.↗
NASA NTRS1942

Theory of Heat Transfer in Smooth and Rough Pipes

The heat transfer accompanying turbulent flow in tubes has been treated by a new theory of wall turbulence, and a formula for smooth tubes has been derived which is asymptotic at Re approaches infinity. It agrees very well with the data available to date. The formula also holds for the flow along a flat plate if lambda is based on the velocity far away. For rough tubes, the unit conductance is shown to be a function of kv*/upsilon; the two empirical constants (delta(r), n) which appear in equation (52) cannot yet be determined because of lack of experimental data.

Mattioli, G. D.↗
NASA NTRS2016

A Computationally-Efficient Inverse Approach to Probabilistic Strain-Based Damage Diagnosis

This work presents a computationally-efficient inverse approach to probabilistic damage diagnosis. Given strain data at a limited number of measurement locations, Bayesian inference and Markov Chain Monte Carlo (MCMC) sampling are used to estimate probability distributions of the unknown location, size, and orientation of damage. Substantial computational speedup is obtained by replacing a three-dimensional finite element (FE) model with an efficient surrogate model. The approach is experimentally validated on cracked test specimens where full field strains are determined using digital image correlation (DIC). Access to full field DIC data allows for testing of different hypothetical sensor arrangements, facilitating the study of strain-based diagnosis effectiveness as the distance between damage and measurement locations increases. The ability of the framework to effectively perform both probabilistic damage localization and characterization in cracked plates is demonstrated and the impact of measurement location on uncertainty in the predictions is shown. Furthermore, the analysis time to produce these predictions is orders of magnitude less than a baseline Bayesian approach with the FE method by utilizing surrogate modeling and effective numerical sampling approaches.

Warner, James E.↗
NASA NTRS1988

Temperature effect on stress concentration around circular hole in a composite material specimen representative of X-29A forward-swept wing aircraft

The theory of anisotropic elasticity was used to evaluate the anisotropic stress concentration factors of a composite laminated plate containing a small circular hole. This advanced composite was used to manufacture the X-29A forward-swept wing. It was found for composite material, that the anisotropic stress concentration is no longer a constant, and that the locations of maximum tangential stress points could shift by changing the fiber orientation with respect to the loading axis. The analysis showed that through the lamination process, the stress concentration factor could be reduced drastically, and therefore the structural performance could be improved. Both the mixture rule approach and the constant strain approach were used to calculate the stress concentration factor of room temperature. The results predicted by the mixture rule approach were about twenty percent deviate from the experimental data. However, the results predicted by the constant strain approach matched the testing data very well. This showed the importance of the inplane shear effect on the evaluation of the stress concentration factor for the X-29A composite plate.

Yeh, Hsien-Yang↗
NASA NTRS1988

Stress concentration around circular hole in a composite material specimen representative of the X-29A forward-swept wing aircraft

The theory of anisotropic elasticity was used to evaluate the anisotropic stress concentration factors of a composite laminated plate containing a small circular hole. This advanced composite material was used to manufacture the X-29A forward swept wing. Observe that the usual isotropic material stress concentration factor is three. However, for composite material, it was found that the anisotropic stress concentration factor is no longer constant, and that the locations of maximum tangential stress points could shift by changing the fiber orientation with respect to the loading axis. The analysis showed that through the lamination process, the stress concentration factor could be drastically reduced, and therefore the structural performance could be improved. Both the mixture rule approach and the constant strain approach were used to calculate the stress concentration factor. The results predicted by the mixture rule approach were about 20 percent deviate from the experimental data. However, the results predicted by the constant strain approach matched the testing data very well. This showed the importance of the inplane shear effect on the evaluation of stress concentration factor for the X-29A composite plate.

Yeh, Hsien-Yang↗
NASA NTRS1976

Interaction between an elastic circular inclusion and two symmetrically placed collinear cracks

The paper investigates the fracture toughness of a flat large elastic cracked plate containing an elastic circular inclusion, using the plane stress crack-tip stress intensity factor as a criterion for fracture. In this plane stress geometry, each of the two collinear finite cracks is located on either side of the elastic circular inclusion and the geometry is subjected to uniform stresses at infinity. The analysis is based on the two-dimensional theory of elasticity by using the Muskhelishvili complex variable approach. Numerical calculations are reported for the case of simple tension normal to the crack direction and show the variation of the stress intensity factor with the configuration and elastic properties of the plate and the inclusion.

Hsu, Y. C.↗
NASA NTRS1985

Control plate for shock-boundary layer interaction

Paper describes tests and computations for a relatively unique technique to greatly reduce/eliminate the separation region for shock-boundary layer interactions. A number of studies have shown that the usual effects of such interactions include increased local heating and wall pressures, thickening of the boundary layer and a decrease in the momentum of the flow and, for stronger waves, flow separation. This flow situation is particularly prevalent in supersonic and hypersonic inlets where severe performance degradation can occur due to flow separation. High performance engine design generally requires a uniform entering flow field with little stagnation pressure loss. Previous approaches to the problem involved primarily active devices (e.g., suction or blowing); the present paper considers a passive device. The boundary layer separation control technique considered herein involves the placement of an embedded plate in the outer portion of the boundary layer and parallel to the wall. This control plate is situated such that the incident shock impinges upon and reflects from its surface, thus greatly lessening the pressure gradient in the low momentum near wall region.

Goodman, W. L.↗
NASA NTRS1985

Probabilistic Structural Analysis of SSME Turbopump Blades: Probabilistic Geometry Effects

A probabilistic study was initiated to evaluate the precisions of the geometric and material properties tolerances on the structural response of turbopump blades. To complete this study, a number of important probabilistic variables were identified which are conceived to affect the structural response of the blade. In addition, a methodology was developed to statistically quantify the influence of these probabilistic variables in an optimized way. The identified variables include random geometric and material properties perturbations, different loadings and a probabilistic combination of these loadings. Influences of these probabilistic variables are planned to be quantified by evaluating the blade structural response. Studies of the geometric perturbations were conducted for a flat plate geometry as well as for a space shuttle main engine blade geometry using a special purpose code which uses the finite element approach. Analyses indicate that the variances of the perturbations about given mean values have significant influence on the response.

Nagpal, V. K.↗
NASA NTRS1986

Nondestructive evaluation of adhesive bond strength using the stress wave factor technique

Acousto-ultrasonic nondestructive evaluation has been conducted to evaluate the adhesive bond strength between rubber and steel plates using the stress wave factor (SWF) measurement technique. Specimens with different bond strength were manufactured and tested using the SWF technique. Two approaches were used to define the SWF. One approach defines the SWF as the signal energy and the other approach defines the SWF as the square root of the zero moment of the frequency spectrum of the received signal. The strength of the rubber-steel adhesive joint was then evaluated using the destructive peel strength test method. It was observed that in both approaches higher values of the SWF measurements correspond to higher values of the peel strength test data. Therefore, these results show that the stress wave factor technique has the potential of being used in quality assurance of the adhesive bond strength between rubber and steel substrates.

Dos Reis, Henrique L. M.↗
NASA NTRS1994

An integrated optical CO2 sensor. Phase 0: Design and fabrication of critical elements

Significant progress has been made toward all of the goals for the first phase of the project short of actual fabrication of a light path. Two alternative approaches to fabricating gold mirrors using the basic LIGA process were developed, one using electroplated solid gold mirrors and the second using gold plated over a nickel base. A new method of fabrication, the transfer mask process, was developed and demonstrated. Analysis of the projected surface roughness and beam divergence effects was completed. With gold surface with low surface roughness scattering losses are expected to be insignificant. Beam divergence due to diffraction will require a modification of the original design, but should be eliminated by fabricating mirrors 1000 mu m in height by 1000 mu m in width and using a source with an initial beam radius greater than 300 mu m. This may eliminate any need for focusing optics. Since the modified design does not affect the mask layout, ordering of the mask and fabrication of the test structures can begin immediately at the start of Phase 1.

Murphy, Michael C.↗
NASA NTRS1960

Thrust Characteristics of Multiple Lifting Jets in Ground Proximity

An investigation has been made to determine the thrust characteristics within ground proximity of a series of models which might represent vertical take-off-and-landing (VTOL) aircraft with multiple exit jet engines exhausting vertically downward beneath a lifting surface. Variations in simulated engine configurations were provided by a series of nozzle insert plugs in which the number of jet exits, located symmetrically on a fixed circle, was varied, or the diameter of the circle was varied for a given number of jet exits. represent lifting surfaces, and high-pressure air was used to simulate jet-engine exhaust. Plywood plates were used to The results of the investigation showed that increasing the number of exits, such that an annular jet configuration was approached, provided more favorable thrust characteristics within ground proximity than any other variation in the geometry of these multiple jets. Tests of a configuration with two nozzles approximating a fan-in-wing VTOL aircraft with fans located at different spanwise locations indicated that the augmentation in thrust within ground proximity was greater for the arrangement with the more inboard location of the nozzles.

Davenport, Edwin E.↗
NASA NTRS2004

Challenging Issues for On-orbit Calibration in the VIS and NIR

On-orbit calibration of Earth-observing sensors in the VIS and NIR spectral regions is usually performed using the sensors on-board devices such as internal lamp(s) or solar diffuser plate(s) to provide calibration parameters. For sensors with no (or with less reliable) on-board calibrators, lunar calibration or ground validation approaches are often used. Each of these has its own set of problems that need to be fully addressed in order to support high quality on-orbit calibration and characterization. Some science products, such as Ocean color, may impose more stringent requirements that demand greater calibration precision. This paper uses MODIS as an example to illustrate challenging issues involved in VIS and NIR on-orbit calibration. It focuses on the solar diffuser (SD) calibration approach, including the effects due to SD BRF, SD attenuation screen(s), and earthshine. The impact of optics (solar diffuser and scan mirror) on-orbit degradation, including changes in the sensor s response versus scan angle (RVS), on the calibration and subsequent data quality is also discussed.

Xiong, X.↗
NASA NTRS2006

User-Defined Material Model for Progressive Failure Analysis

An overview of different types of composite material system architectures and a brief review of progressive failure material modeling methods used for structural analysis including failure initiation and material degradation are presented. Different failure initiation criteria and material degradation models are described that define progressive failure formulations. These progressive failure formulations are implemented in a user-defined material model (or UMAT) for use with the ABAQUS/Standard1 nonlinear finite element analysis tool. The failure initiation criteria include the maximum stress criteria, maximum strain criteria, the Tsai-Wu failure polynomial, and the Hashin criteria. The material degradation model is based on the ply-discounting approach where the local material constitutive coefficients are degraded. Applications and extensions of the progressive failure analysis material model address two-dimensional plate and shell finite elements and three-dimensional solid finite elements. Implementation details and use of the UMAT subroutine are described in the present paper. Parametric studies for composite structures are discussed to illustrate the features of the progressive failure modeling methods that have been implemented.

Knight, Norman F. Jr.↗