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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Predicting Mechanical Properties from Microstructure Images in Fiber-Reinforced Polymers Using Convolutional Neural Networks

Evaluating the mechanical response of fiber-reinforced composites can be extremely time-consuming and expensive. Machine learning (ML) techniques offer a means for faster predictions via models trained on existing input–output pairs and have exhibited success in composite research. This paper explores a fully convolutional neural network modified from StressNet, which was originally used for linear elastic materials, and extended here for a non-linear finite element (FE) simulation to predict the stress field in 2D slices of segmented tomography images of a fiber-reinforced polymer specimen. The network was trained and evaluated on data generated from the FE simulations of the exact microstructure. The testing results show that the trained network accurately captures the characteristics of the stress distribution, especially on fibers, solely from the segmented microstructure images. The trained model can make predictions within seconds in a single forward pass on an ordinary laptop, given the input microstructure, compared to 92.5 h to run the full FE simulation on a high-performance computing cluster. These results show promise in using ML techniques to conduct fast structural analysis for fiber-reinforced composites and suggest a corollary that the trained model can be used to identify the location of potential damage sites in fiber-reinforced polymers.

Sun, Yixuan (ORCID:0000000311093380)↗
NASA NTRS1966

Rugged microelectronic module package supports circuitry on heat sink

Rugged module package for thin film hybrid microcircuits incorporated a rigid, thermally conductive support structure, which serves as a heat sink, and a lead wire block in which T-shaped electrical connectors are potted. It protects the circuitry from shock and vibration loads, dissipates internal heat, and simplifies electrical connections between adjacent modules.

Johnson, A. L.↗
NASA NTRS1974

Research on wood bending in a macrosonic field

Woodworking often requires the wood to be bent into different shapes. In view of the fact that macrosonic waves compress and expand the medium through which they are being propagated we assumed that wood subjected to the action of these waves during the bending process would have enhanced plasticity as a result of the loosening-up that takes place in it, as well as of the reduction in effort. To this effect, the bending of wood plasticized in a macrosonic field was studied. This bending took place under good conditions, and structural analyses conducted with the aid of an electron microscope proved initial premises to be corrent. Applied on an industrial scale, this procedure would contribute to improving the technology of wood bending as well as to eliminating factory spoilage.

Filipovici, J.↗
NASA NTRS1975

Development program to produce mullite fiber insulation

Processing methods were utilized to form a mullite fiber-Kaowool felt. The formation of a blended felt using the Rotoformer wet-laying method was successful. Felt products were evaluated for tensile strength, thermal stability, thermal conductivity and structural integrity at 1259 C and 1371 C. Textile processing methods failed in an attempt to form a yarn from staple and multifilament mullite fiber due to fiber damage through mechanical handling. The refractoriness of pure Kaowool ceramic fiber is improved with additions of 30% or greater mullite fiber.

Long, W. G.↗
NASA NTRS1978

Advanced composites wing study program, volume 2

The study on utilization of advanced composites in commercial aircraft wing structures was conducted as a part of the NASA Aircraft Energy Efficiency Program to establish, by the mid-1980s, the technology for the design of a subsonic commercial transport aircraft leading to a 40% fuel savings. The study objective was to develop a plan to define the effort needed to support a production commitment for the extensive use of composite materials in wings of new generation aircraft that will enter service in the 1985-1990 time period. Identification and analysis of what was needed to meet the above plan requirements resulted in a program plan consisting of three key development areas: (1) technology development; (2) production capability development; and (3) integration and validation by designing, building, and testing major development hardware.

Harvey, S. T.↗
NASA NTRS1981

Large modal survey testing using the Ibrahim time domain /ITD/ identification technique

The ability of the ITD identification algorithm in identifying a complete set of structural modal parameters using a large number of free-response time histories simultaneously in one analysis, assuming a math model with a high number of degrees-of-freedom, has been studied. Identification results using simulated free responses of a uniform rectangular plate, with 225 measurement stations, and experimental responses from a ground vibration test of the Long Duration Exposure Facility (LDEF) Space Shuttle payload, with 142 measurement stations, are presented. As many as 300 degrees-of-freedom were allowed in analyzing these data. In general, the use of a significantly oversized math model in the identification process was found to maintain or increase identification accuracy and to identify modes of low response level that are not identified with smaller math model sizes. The concept of a Mode Shape Correlation Constant is introduced for use when more than one identification analysis of the same structure are conducted. This constant quantifies the degree of correlation between any two sets of complex mode shapes identified using different excitation conditions, different user-selectable algorithm constants, or overlapping sets of measurements.

Ibrahim, S. R.↗
NASA NTRS1981

Hardware survey for the avionics test bed

A survey of maor hardware items that could possibly be used in the development of an avionics test bed for space shuttle attached or autonomous large space structures was conducted in NASA Johnson Space Center building 16. The results of the survey are organized to show the hardware by laboratory usage. Computer systems in each laboratory are described in some detail.

Cobb, J. M.↗
NASA NTRS1982

Transit Thermal Control Design for Galileo Entry Probe for Planet Jupiter

A totally passive design was completed for the thermal control of the Galileo entry probe during its transit to the planet Jupiter. The design utilizes radio isotope heater units, multilayer insulation blankets and a thermal radiator in conjunction with a design conductance support structure to achieve both the required storage and critical initial planet atmosphere entry temperatures. The probe transit thermal design was completed and verified based on thermal vacuum testing of a prototype probe thermal test model.

Haverly, George C.↗
NASA NTRS1981

Present growth technology of silicon germanium alloys and possible advantages of microgravity growth

The growth technology of Silicon-germanium (Si-Ge) alloys and the possible advantages of growth in microgravity is reviewed. The Si-Ge alloys have a continuous variation of bandgap energy from the germanium bandgap to the silicon bandgap. The unusual two slope behavior of Eg versus composition is due to the differences in the conduction band structure between Si and Ge. Below 17% (atomic), the germanium band structure dominates; and above it, the bands are "silicon like". It is found that the growth of Si-Ge alloys in microgravity is very attractive. In particular, the float zone method, in which a liquid zone of controlled starting composition, used to grow a large amount of useful alloy crystal. Large temperature gradients and relatively flat growth interfaces are necessary to obtain homogeneous crystal growth.

Stafsudd, O. M.↗
NASA NTRS1982

The NASA Radar Remote Sensing Program

The NASA radar remote sensing program is structured to conduct scientific research for earth and planetary exploration using the microwave spectrum. The program began in 1966 and has since developed a complement of radar sensors for satellite, aircraft and ground-based platforms which have been used in both land and oceanic research. Basic measurements of radar scattering coefficient signatures are carried out with airborne and ground-based scatterometers. SAR imagery is being used for geological, hydrological, geographical, and agricultural microwave remote sensing research. For oceanic investigations, altimeters are used for ocean topography experiments and scatterometers for ocean wind and current research. Future satellite radar instruments being proposed include SIR-B, SAMEX, FIREX, TOPEX and a Scatterometer Experiment.

Carver, K. R.↗
NASA NTRS1983

Stability, vibration and passive damping of partially restrained imperfect columns

A theoretical and experimental study of slender tubular columns for possible use in space structures is conducted in the presence of partial rotational end restraints. Explicit formulas are derived for computing the buckling load and the lowest natural frequency of perfectly straight uniform elastic members with rotational end restraints possessing linear moment-rotation characteristics. An exact solution in the form of a transcendental equation, and a numerical solution using second-order finite-differences are also presented. The presence of an initial imperfection is also incorporated into the numerical procedure. Vibration tests are conducted on an imperfect tubular steel member in the absence of an axial load. A damping concept consisting of a string-mass assembly is explored. Three passive damping configurations involving combinations of three lead shots were investigated. The three lead shot configurations provided considerably greater damping than the single lead shot.

Razzaq, Z.↗
NASA NTRS1984

Radiation-conduction interaction in large space structures

The effects of a penumbra due to the long wave radiation emitted by the earth or to solar energy reflected from the earth on temperature distributions, deflections and stresses in plates are studied to determine their importance in the design of space structures. An examination of the state of stress in a thin plate exposed to the sun suggests that deflections are only slightly modified by the penumbra, but that stresses in the vicinity of the shadow line are more affected. Even with the smoothing due to the penumbra, these stresses should be considered in the design of space structures. A simple relationship is given by which albedo viewfactors can be easily derived from the direct viewfactor, thus simplifying the radiation analysis.

Emery, A. F.↗
NASA NTRS1985

Performance improvements of a highly integrated digital electronic control system for an F-15 airplane

The NASA highly integrated digital electronic control (HIDEC) program is structured to conduct flight research into the benefits of integrating an aircraft flight control system with the engine control system. A brief description of the HIDEC system installed on an F-15 aircraft is provided. The adaptive engine control system (ADECS) mode is described in detail, together with simulation results and analyses that show the significant excess thrust improvements achievable with the ADECS mode. It was found that this increased thrust capability is accompanied by reduced fan stall margin and can be realized during flight conditions where engine face distortion is low. The results of analyses and simulations also show that engine thrust response is improved and that fuel consumption can be reduced. Although the performance benefits that accrue because of airframe and engine control integration are being demonstrated on an F-15 aircraft, the principles are applicable to advanced aircraft such as the advanced tactical fighter and advanced tactical aircraft.

Putnam, T. W.↗
NASA NTRS1985

Multidisciplinary analysis and synthesis - Needs and opportunities

A comprehensive evaluation is conducted of structural analysis and synthesis opportunities which emerge through a multidisciplinary design program approach that simultaneously and interactively encompasses, in its determination of a given aircraft design, aerodynamics, structure, structural dynamics, materials, controls, and propulsion. In this way, it becomes possible to rapidly exploit technological advances in order to yield synergistic effects among configurational subsystems. The aircraft type presently considered as recipients of this treatment are commercial transports, high performance military aircraft, rotorcraft, and large space antennas, giving attention to common features among the multidisciplinary design tasks represented.

Tolson, R. H.↗
NASA NTRS1985

Large Modal Survey Testing Using the Ibrahim Time Domain Identification Technique

The ability of the ITD identification algorithm in identifying a complete set of structural modal parameters using a large number of free-response time histories simultaneously in one analysis, assuming a math model with a high number of degrees-of-freedom, has been studied. Identification results using simulated free responses of a uniform rectangular plate, with 225 measurement stations, and experimental responses from a ground vibration test of the Long Duration Exposure Facility (LDEF) Space Shuttle payload, with 142 measurement stations, are presented. As many as 300 degrees-of-freedom were allowed in analyzing these data. In general, the use of a significantly oversized math model in the identification process was found to maintain or increase identification accuracy and to identify modes of low response level that are not identified with smaller math model sizes. The concept of a Mode Shape Correlation Constant is introduced for use when more than one identification analysis of the same structure are conducted. This constant quantifies the degree of correlation between any two sets of complex mode shapes identified using different excitation conditions, different user-selectable algorithm constants, or overlapping sets of measurements.

Ibrahim, S. R.↗
NASA NTRS1987

Advanced long term cryogenic storage systems

Long term, cryogenic fluid storage facilities will be required to support future space programs such as the space-based Orbital Transfer Vehicle (OTV), Telescopes, and Laser Systems. An orbital liquid oxygen/liquid hydrogen storage system with an initial capacity of approximately 200,000 lb will be required. The storage facility tank design must have the capability of fluid acquisition in microgravity and limit cryogen boiloff due to environmental heating. Cryogenic boiloff management features, minimizing Earth-to-orbit transportation costs, will include advanced thick multilayer insulation/integrated vapor cooled shield concepts, low conductance support structures, and refrigeration/reliquefaction systems. Contracted study efforts are under way to develop storage system designs, technology plans, test article hardware designs, and develop plans for ground/flight testing.

Brown, Norman S.↗