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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Analytical techniques of pilot scanning behavior and their application

The state of the art of oculometric data analysis techniques and their applications in certain research areas such as pilot workload, information transfer provided by various display formats, crew role in automated systems, and pilot training are documented. These analytical techniques produce the following data: real-time viewing of the pilot's scanning behavior, average dwell times, dwell percentages, instrument transition paths, dwell histograms, and entropy rate measures. These types of data are discussed, and overviews of the experimental setup, data analysis techniques, and software are presented. A glossary of terms frequently used in pilot scanning behavior and a bibliography of reports on related research sponsored by NASA Langley Research Center are also presented.

Harris, R. L., Sr.↗
NASA NTRS1986

The behavior of fuel-lean premixed flames in a standard flammability limit tube under controlled gravity conditions

Fuel-lean flames in methane-air mixtures from 4.90 to 6.20 volume percent fuel and propane-air mixtures from 1.90 to 3.00 volume percent fuel were studied in the vicinity of the limit for a variety of gravity conditions. The limits were determined and the behavior of the flames studied for one g upward, one g downward, and zero g propagation. Photographic records of all flammability tube firings were obtained. The structure and behavior of these flames were detailed including the variations of the curvature of the flame front, the skirt length, and the occurrence of cellular instabilities with varying gravity conditions. The effect of ignition was also discussed. A survey of flame speeds as a function of mixture strength was made over a range of lean mixture compositions for each of the fuels studied. The results were presented graphically with those obtained by other researchers. The flame speed for constant fractional gravity loadings were plotted as a function of gravity loadings from 0.0 up to 2.0 g's against flame speeds extracted from the transient gravity flame histories for corresponding gravity loadings. The effects of varying gravity conditions on the extinguishment process for upward and downward propagating flames were investigated.

Wherley, B. L.↗
NASA NTRS1986

Fiber Composite Sandwich Thermostructural Behavior: Computational Simulation

Several computational levels of progressive sophistication/simplification are described to computationally simulate composite sandwich hygral, thermal, and structural behavior. The computational levels of sophistication include: (1) three-dimensional detailed finite element modeling of the honeycomb, the adhesive and the composite faces; (2) three-dimensional finite element modeling of the honeycomb assumed to be an equivalent continuous, homogeneous medium, the adhesive and the composite faces; (3) laminate theory simulation where the honeycomb (metal or composite) is assumed to consist of plies with equivalent properties; and (4) derivations of approximate, simplified equations for thermal and mechanical properties by simulating the honeycomb as an equivalent homogeneous medium. The approximate equations are combined with composite hygrothermomechanical and laminate theories to provide a simple and effective computational procedure for simulating the thermomechanical/thermostructural behavior of fiber composite sandwich structures.

Chamis, C. C.↗
NASA NTRS1986

Temperature dependent nonlinear metal matrix laminae behavior

An analytical method is described for computing the nonlinear thermal and mechanical response of laminated plates. The material model focuses upon the behavior of metal matrix materials by relating the nonlinear composite response to plasticity effects in the matrix. The foundation of the analysis is the unidirectional material model which is used to compute the instantaneous properties of the lamina based upon the properties of the fibers and matrix. The unidirectional model assumes that the fibers properties are constant with temperature and assumes that the matrix can be modelled as a temperature dependent, bilinear, kinematically hardening material. An incremental approach is used to compute average stresses in the fibers and matrix caused by arbitrary mechanical and thermal loads. The layer model is incorporated in an incremental laminated plate theory to compute the nonlinear response of laminated metal matrix composites of general orientation and stacking sequence. The report includes comparisons of the method with other analytical approaches and compares theoretical calculations with measured experimental material behavior. A section is included which describes the limitations of the material model.

Barrett, D. J.↗
NASA NTRS1985

The relation between the Type A behavior pattern, pacing, and subjective workload under single- and dual-task conditions

Twenty Type A and 20 Type B subjects performed two discrete tasks alone and together. Half of the subjects performed paced versions of both tasks; half, unpaced versions. Workload ratings were obtained for all subjects under single- and dual-task conditions using eight bipolar adjective scales. Under single-task conditions there was a significant interaction between behavior pattern and pacing on one of the tasks. This interaction indicated that Type A subjects responded more rapidly under unpaced conditions than did Type B subjects, although there was little difference between the groups under paced conditions. Under dual-task conditions, Type A subjects responded more rapidly than did Type B subjects regardless of pacing. There was one significant interaction between behavior pattern and task on one of the workload scales.

Damos, D.↗
NASA NTRS1985

Eye-scan behavior in a flight simulation task as a function of level of training

The present study explored eye-scan behavior as a function of level of subject training. Oculometric (eye-scan) measures were recorded from each of ten subjects during training trials on a CRT-based flight simulation task. The task developed for the study incorporated subtasks representative of specific activities performed by pilots, but which could be performed at asymptotic levels within relatively short periods of training. Changes in eye-scan behavior were examined as initially untrained subjects developed skill in the task. Eye-scan predictors of performance on the task were found. Examination of eye-scan in proximity to selected task events revealed differences in the distribution of looks at the instruments as a function of level of training.

Comstock, J. R., Jr.↗
NASA NTRS1986

Composite sandwich thermostructural behavior - Computational simulation

Computational methods have been developed for simulating the thermomechanical behavior of composite sandwiches, in which the analyses with several levels of progressive sophistication were used in conjunction with composite hygrothermomechanical theory. The sophistication levels include: (1) three-dimensional detailed finite element modeling of the honeycomb, the adhesive, and the composite faces; (2) three-dimensional finite element modeling assuming a homogeneous core; (3) laminate theory simulation; and (4) simple equations for predicting the equivalent properties of the honeycomb core. These levels have been packaged into a procedure embedded in a computer code streamlined for the simulation of the composite sandwich hygrothermal and structural behavior. It is shown that in order to properly simulate the thermomechanical response of the composite sandwich, all the honeycomb thermal and mechanical properties must be used.

Chamis, C. C.↗
NASA NTRS1986

A comparison of the fracture behavior of thick laminated composites utilizing compact tension, three-point bend, and center-cracked tension specimens

An experimental study of the effects of specimen configuration and laminate thickness on the fracture behavior of notched laminated composites is presented. The behavior of (0/+, 45/90)ns, (0/90)ns and (0/+, - 45)ns graphite/epoxy T300/5208 laminates was studied. When fracture toughness was computed at the failing load of the center-cracked tension specimen, laminate thickness significantly influenced fracture toughness. If fracture toughness was computed at the interception of the 5 percent secant line with the load-COD record, fracture toughness was found to be independent of both laminate thickness and specimen configuration. Defined in this manner, fracture toughness can be physically interpreted as an indicator of the onset of significant notch-tip damage.

Harris, C. E.↗
NASA NTRS1986

Bimodal quasi-oscillatory and spectral behavior in Scorpius X-1

Exosat observations of Sco X-1 obtained using the Xe and/or Ar detectors for a total of about 80,000 s during four runs on August 24-27, 1985 are reported and analyzed. Two modes of quasi-periodic oscillations (QPOs) corresponding to the quiescent and active states of Sco X-1 and to two modes of spectral behavior are identified and characterized, confirming the findings of Priedhorsky (1985) and Middleditch and Priedhorsky (1986). In the quiescent state, the QPO frequency is about 6 Hz and is anticorrelated with intensity, and the spectral hardness ratio (14-21 vs 2-7 keV) varies steeply with intensity; in the active state, QPO frequency is correlated with intensity and varies from 10 to 20 Hz, and the spectral-hardness-ratio/intensity curve is flatter. Previous observations of bimodal behavior in other bands are summarized, and theoretical models proposed to explain them are discussed.

Priedhorsky, W.↗
NASA NTRS1986

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. II - Low cycle fatigue behavior

The low cycle fatigue (LCF) properties of a single-crystal nickel-base superalloy Rene N4, have been examined at 760 and 980 C in air. Specimens having crystallographic orientations near the 001, 011, -111, 023, -236, and -145 lines were tested in fully reversed, total-strain-controlled LCF tests at a frequency of 0.1 Hz. At 760 C, this alloy exhibited orientation dependent tension-compression anisotropies of yielding which continued to failure. Also at 760 C, orientations exhibiting predominately single slip exhibited serrated yielding for many cycles. At 980 C, orientation dependencies of yielding behavior were smaller. In spite of the tension-compression anisotropies, cyclic stress range-strain range behavior was not strongly orientation dependent for either test temperature. Fatigue life on a total strain range basis was highly orientation dependent at 760 and 980 C and was related chiefly to elastic modulus, low modulus orientations having longer lives. Stage I crack growth on 111 planes was dominant at 760 C, while Stage II crack growth occurred at 980 C. Crack initiation generally occurred at near-surface micropores, but occasionally at oxidation spikes in the 980 C tests.

Gabb, T. P.↗
NASA NTRS1986

The cyclic stress-strain behavior of PWA 1480 at 650 deg C

The monotonic plastic flow behavior of several single crystal nickel-base, superalloys has been shown to vary significantly with crystallographic orientation. In the present study, the cyclic plastic flow response of one such alloy, PWA 1480, was examined at 650 deg C in air. Single crystal specimens aligned near several crystallographic directions were tested in fully reversed, total-strain-controlled low cycle fatigue tests at a frequency of 0.1 Hz. The cyclic stress-strain response and general cyclic hardening behavior was analyzed as a function of crystallographic orientation and inelastic strain range.

Gabb, T. P.↗
NASA NTRS1986

On the pilot's behavior of detecting a system parameter change

The reaction of a human pilot, engaged in compensatory control, to a sudden change in the controlled element's characteristics is described. Taking the case where the change manifests itself as a variance change of the monitored signal, it is shown that the detection time, defined to be the time elapsed until the pilot detects the change, is related to the monitored signal and its derivative. Then, the detection behavior is modeled by an optimal controller, an optimal estimator, and a variance-ratio test mechanism that is performed for the monitored signal and its derivative. Results of a digital simulation show that the pilot's detection behavior can be well represented by the model proposed here.

Morizumi, N.↗
NASA NTRS1987

Elevated temperature tension, compression and creep-rupture behavior of (001)-oriented single crystal superalloy PWA 1480

Tensile and compressive flow behavior at various temperatures and strain rates, and tensile creep rupture behavior at 850 and 1050 C and various stresses were studied for (001)-oriented single crystals of the Ni-base superalloy PWA 1480. At temperatures up to 760 C, the flow stress is insensitive to strain rate and of greater magnitude in tension than in compression. At temperatures of 800 C and above, the flow stress decreases continuously with decreasing strain rate and the tension/compression anisotropy diminishes. The second stage creep rate and rupture time exhibited power law relationships with the applied stress for both 850 and 1050 C, however with different stress dependencies. The stress exponent for the steady state creep rate was about 7 at 1050 C, but much higher at 850 C, about 12. Directional coarsening of the gamma' phase occurred during creep at 1050 C, but not at 850 C.

Hebsur, Mohan G.↗
NASA NTRS1987

Cockpit management and Specific Behavioral Objectives (SBOs)

One of the primary tools used to accomplish the task of effective training is the specific behavioral objective (SBO). An SBO is simply a statement which specifically identifies a small segment of the final behavior sought, and a little more. The key word is specific. The company pinpoints exactly what it is it wants the pilot to do after completing training, and what it should evaluate from the point of view of both the program and the pilot. It tells the junior crewmember exactly, specifically, what he should monitor and support insofar as the management function is concerned. It gives greater meaning to the term second in command. And finally, it tells the supervisory pilot exactly what he should observe, evaluate, and instruct, insofar as the management function is concerned.

Mudge, R. W.↗
NASA NTRS1987

Fatigue damage interaction behavior of PWA 1480

The fatigue damage interaction behavior of PWA 1480 single crystal alloy has been experimentally established for the two-level loading case in which a block of low-cycle fatigue loading is followed by high-cycle fatigue loading to failure. A relative life ratio N1/N2 (where N1 and N2 are the low- and high-cycle fatigue baseline lives, respectively) of approximately 0.002 was explored to assess the interaction behavior. The experimental results thus far show evidence of a loading order interaction effect to a similar degree of detriment as has been observed in polycrystalline materials. Current generation single crystal alloys in general, and PWA 1480 in particular, contain pores; indeed, it was observed in all cases that specimen failure initiated from pores connected with or immediately below the surface. Detailed fractographic and metallographic studies are currently being made to assess the nature of the porosity in terms of its effect on fatigue life.

Mcgaw, Michael A.↗
NASA NTRS1987

Effects of fiber motion on the acoustic behavior of an anisotropic, flexible fibrous material

The acoustic behavior of a flexible fibrous material was studied experimentally. The material consisted of cylindrically shaped fibers arranged in a batting with the fibers primarily aligned parallel to the face of the batting. This type of material was considered anisotropic, with the acoustic propagation constant depending on whether the dirction of sound propagation was parallel or normal to the fiber arrangement. Normal incidence sound absorption measurements were taken for both fiber orientations over the frequency range 140 to 1500 Hz and with bulk densities ranging from 4.6 to 67 kg/cu m. When the sound propagated in a direction normal to the fiber alignment, the measured sound absorption showed the occurrence of a strong resonance, which increased absorption above that attributed to viscous and thermal effects. When the sound propagated in a direction parallel to the fiber alignment, indications of strong resonances in the data were not present. The resonance in the data for fibers normal to the direction of sound propagation is attributed to fiber motion. An analytical model was developed for the acoustic behavior of the material displaying the same fiber motion characteristics shown in the measurements.

Dahl, Milo D.↗
NASA NTRS1986

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity, at room temperature. Clusters or crystallines with sizes to 150 nm and a diffused honeycomb-shaped structure are produced on sizes to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures to 750 C. Contaminants can come from the bulk of the alloys to the surface upon heating and impart to the surface oxides at 350 C and boron nitride above 500 C. The oxides increase friction while the boron nitride reduces friction drastically in vacuum.

Miyoshi, K.↗