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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 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

A technique for the optical analysis of deformed telescope mirrors

The NASTRAN-ACCOS V programs' interface merges structural and optical analysis capabilities in order to characterize the performance of the NASA Goddard Space Flight Center's Solar Optical Telescope primary mirror, which has a large diameter/thickness ratio. The first step in the optical analysis is to use NASTRAN's FEM to model the primary mirror, simulating any distortions due to gravitation, thermal gradients, and coefficient of thermal expansion nonuniformities. NASTRAN outputs are then converted into an ACCOS V-acceptable form; ACCOS V generates the deformed optical surface on the basis of these inputs, and imaging qualities can be determined.

Bolton, John F.↗
NASA NTRS1987

Thermally induced stresses and deformations in angle-ply composite tubes

Cure-induced uniform temperature change effects on the stresses, axial expansion, and thermally-induced twist of four specific angle-ply tube designs are discussed with a view to the tubes' use as major space structure components. The stresses and deformations in the tubes are studied as a function of the four designs, the off-axis angle, and the single-material and hybrid reinforcing-material construction used. It is found that tube design has a minor influence on the stresses, axial stiffness, and axial thermal expansion characteristics, which are more directly a function of off-axis angle and material selection; tube design is, however, the primary influence in the definition of thermally-induced twist and torsional stiffness characteristics. None of the designs is free of thermally induced twist.

Hyer, M. W.↗
NASA NTRS1987

Tracking and pointing maneuvers with slew-excited deformation shaping

It is shown in this paper how it is possible to shape the slew-excited structural response of a deformable vehicle undergoing agile attitude maneuvers, so that the required fully corrected slew torque profiles can be computed on-line in closed form, and with the same bandwidth as required for the rigid body case. This is accomplished by simultaneously applying maneuver-dependent structural force controls of progressively smaller amplitudes, at the cost of progressively higher signal processing complexity of slew torque and structural force command generation.

Dwyer, Thomas A. W., III↗
NASA NTRS1987

The interpretation of crustal dynamics data in terms of plate motions and regional deformation near plate boundaries

The focus of the research was in two broad areas during the most recent 6 month period: the nature and dynamics of time-dependent deformation along major seismic zones, including the influence of irregularities in fault geometry on the earthquake cycles, and the processes contributing to the state of stress and rates of strain in plate interior regions. The principal findings of the research to date are described.

Solomon, Sean C.↗
NASA NTRS1987

The evaluation of a deformable diffraction grating for a stigmatic EUV spectroheliometer

A high-efficiency, extreme ultraviolet (EUV) imaging spectrometer is constructed and tested. The spectrometer employs a concave toroidal grating illuminated at normal incidence in a Rowland circle mounting and has only one reflecting surface. The toroidal grating has been fabricated by a new technique employing an elastically-deformable sub-master grating replicated in a spherical form and then mechanically distorted to produce the desired aspect ratio of the toroidal surface for stigmatic imaging over the selected wavelength range. The fixed toroidal grating used in the spectrometer is then replicated from this surface. Photographic tests and initial photoelectric tests with a two-dimensional, pulse-counting detector system verify the image quality of the toroidal grating at wavelengths near 600 A. The results of these tests and the basic designs of two instruments which could employ the imaging spectrometer for astrophysical investigations in space are described; i.e., a high-resolution EUV spectroheliometer for studies of the solar chromosphere, transition region, and corona; and an EUV spectroscopic telescope for studies of non-solar objects.

Timothy, J. G.↗
NASA NTRS1988

An internal variable constitutive model for the large deformation of metals at high temperatures

The advent of large deformation finite element methodologies is beginning to permit the numerical simulation of hot working processes whose design until recently has been based on prior industrial experience. Proper application of such finite element techniques requires realistic constitutive equations which more accurately model material behavior during hot working. A simple constitutive model for hot working is the single scalar internal variable model for isotropic thermal elastoplasticity proposed by Anand. The model is recalled and the specific scalar functions, for the equivalent plastic strain rate and the evolution equation for the internal variable, presented are slight modifications of those proposed by Anand. The modified functions are better able to represent high temperature material behavior. The monotonic constant true strain rate and strain rate jump compression experiments on a 2 percent silicon iron is briefly described. The model is implemented in the general purpose finite element program ABAQUS.

Brown, Stuart↗
NASA NTRS1988

Unified constitutive model for single crystal deformation behavior with applications

Single crystal materials are being used in gas turbine airfoils and are candidates for other hot section components because of their increased temperature capabilities and resistance to thermal fatigue. Development of a constitutive model which assesses the inelastic behavior of these materials has been studied in 2 NASA programs: Life Prediction and Constitutive Models for Engine Hot Section Anisotropic Materials and Biaxial Constitutive Equation Development for Single Crystals. The model has been fit to a large body of constitutive data for single crystal PWA 1480 material. The model uses a unified approach for computing total inelastic strains (creep plus plasticity) on crystallographic slip systems reproducing observed directional and strain rate effects as a natural consequence of the summed slip system quantities. The model includes several of the effects that have been reported to influence deformation in single crystal materials, such as shear stress, latent hardening, and cross slip. The model is operational in a commercial Finite Element code and is being installed in a Boundary Element Method code.

Walker, K. P.↗
NASA NTRS1988

The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

The creep properties of silicon nitride containing 6 wt percent yttria and 2 wt percent alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation epsilon dot varies as sigma sup n, was determined to be 2.00 + or - 0.15 and the true activation energy was found to be 692 + or - 25 kJ/mol. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

Todd, J. A.↗
NASA NTRS1987

Closed-form analysis for elastic deformations of multilayered strands

Closed-form solutions are developed for elastic deformation characteristics of multilayered strands under tensile and torsional loads. These analytical results are successfully applied to obtain expressions for the effective extensional and torsional moduli of rigidity for the strands. Finally, a simple design criterion is established for 'nonrotating' cables.

Kumar, K.↗
NASA NTRS1988

Free-streamline analysis of deformation and dislodging by wind force of drops on a surface

Free-streamline theory is used to analyze the deformation and dislodging by wind pressure of drops of liquid adhered by surface tension to a solid surface. The critical Weber number for droplets to be dislodged is determined as a function of advancing and receding contact angle. Graphical results for drop shape are in good agreement with observation.

Durbin, P. A.↗
NASA NTRS1988

Electro optical performance of an improved deformable mirror device

The design, fabrication, and performance of an improved 128 x 128 deformable mirror device (DMD) are discussed. The present DMD consists of a monolithically formed array of cantilever beams which are electrostatically deflected by an underlying MOS transistor address matrix. In contrast to an earlier version, the improved DMD on-chip address circuitry supports a single video input to the chip, with all demux operations performed on-chip. The cantilever beams are formed by two layers of high-reflectivity aluminum alloy. The dynamic range of the DMD in the Fourier plane at the Nyquist frequency has been determined at greater than 45 dB.

Wu, Wen R.↗
NASA NTRS1988

Deformational models of rifting and folding on Venus

Features of presumed tectonic origin on Venus are reviewed, and lithospheric strength envelopes are derived based on laboratory measurements of the deformational properties of crustal and subcrustal rocks, extrapolated to conditions appropriate to Venus. Models for rifting and folding are developed that use this lithospheric structure and take into account both brittle and ductile yielding as well as finite elastic strength. For both rifting and folding, structures with characteristic widths and spacings are predicted whose size depends on the thickness of the lithosphere, density contrast, and elastic properties of the layer. Finally, the model predictions are compared with the widths and spacings of observed tectonic features, and it is concluded that they are consistent with a relatively strong mantle layer separated from a thin brittle surface layer by a ductile lower crust. These results allow constraints to be placed on the crustal thickness and thermal gradient on Venus.

Banerdt, W. Bruce↗
NASA NTRS1988

Coherent optical correlator using a deformable mirror device spatial light modulator in the Fourier plane

Attention is given to experimental results for a binary phase-only filter implementation's correlation operations, using the deformable mirror device (DMD) spatial light modulator as the Fourier plane filter. These results demonstrate the basic capabilities of the DMD in an image correlator system which, in combination with the potential 8-kHz frame rate for 128 x 128 DMDs, can constitute a very high speed pattern recognition system. The DMD has the further capability of operating in the analog mode.

Florence, James M.↗
NASA NTRS1988

Modeling surface deformations at complex strike-slip plate boundaries

Two new versions of the physical base-traction model of Li and Rice (1987) have been developed to study the loading processes and surface deformation near plate boundaries with geometric complexities, including a shallow creeping fault segment and two subparallel faults. Predictions of surface velocity and surface slip rate for the region between the San Andreas fault and the Pacific coast at the latitude of the Parkfield-Cholame segment using model parameters based on geologic, geodetic, and seismic considerations were found to be in good agreement with contemporary geodetic field data (not used in constrainning model parameters). Also, predicted surface velocity for the Salton Sea-Coachella Valley area were fit to recently derived contemporary geodetic data and very large baseline interferometry data, althoug here the model parameters are not well constrained.

Li, Victor C.↗
NASA NTRS1988

The effect of hydrogen on deformation substructure, flow and fracture in a nickel-base single crystal superalloy

The room temperature flow and fracture of a nickel-base single crystal gamma/gamma-/prime superalloy in the presence and absence of hydrogen is explored. The procedure of hydrogen-charging employed in this study provides a very high and uniform hydrogen concentration of the order of 5000 at.-ppm in the material. It is shown that the most compelling hydrogen-induced changes in deformation behavior are enhanced dislocation accumulation in the gamma matrix and extensive cross-slip of super-dislocations. The explanation of these changes is proposed. Both effects contribute to the increase of flow stress and the notable work hardening that occurs prior to fracture. Hydrogen enhanced strain localization in the gamma matrix leads to the dramatic loss of ductility and premature cracking, which manifests as failure macroscopically parallel to the 100-plane-oriented faces of gamma-prime precipitates. On the microscale, cracking, while limited to the gamma matrix, occurs parallel to multiple 111-plane-oriented slip systems.

Dollar, M.↗
NASA NTRS1987

A nonlinear viscoelastic constitutive equation - Yield predictions in multiaxial deformations

Yield stress predictions of a nonlinear viscoelastic constitutive equation for amorphous polymer solids have been obtained and are compared with the phenomenological von Mises yield criterion. Linear viscoelasticity theory has been extended to include finite strains and a material timescale that depends on the instantaneous temperature, volume, and pressure. Results are presented for yield and the correct temperature and strain-rate dependence in a variety of multiaxial deformations. The present nonlinear viscoelastic constitutive equation can be formulated in terms of either a Cauchy or second Piola-Kirchhoff stress tensor, and in terms of either atmospheric or hydrostatic pressure.

Shay, R. M., Jr.↗