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At least 343 records · Page 19

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NASA NTRS1985

The reactions of cobalt, iron and nickel in SO2 atmospheres Similarities and differences

The reactions of cobalt, iron and nickel in SO2 atmospheres are reviewed and compared. A mixed oxide-sulfide product layer is observed in all cases. Cobalt and nickel exhibit similar behavior. The observed rates are near the sulfidation rates, and the reaction rate is strongly influenced by the outward diffusion of metal through an interconnected sulfide network. A continuous interconnected sulfide is not observed in the oxide-sulfide scales formed on iron, and the reaction rates are more difficult to summarize. The differences and similarities among the three metals are explained in terms of the absence of scale-gas equilibrium and the ratio of the metal diffusivity in the corresponding oxide and sulfide.

Jacobson, N. S.↗

NASA NTRS1993

Internal strain analysis of ceramics using scanning laser acoustic microscopy

Quantitative studies of material behavior characteristics are essential for predicting the functionality of a material under its operating conditions. A nonintrusive methodology for measuring the in situ strain of small dimeter (to 11 microns) ceramic fibers under uniaxial tensile loading and the local internal strains of ceramics and ceramic composites under flexural loading is introduced. The strain measurements and experimentally observed mechanical behavior are analyzed in terms of the microstructural development and fracture behavior of each test specimen evaluated. Measurement and analysis of Nicalon silicon carbide (SiC) fiber (15 microns diameter) indicate that the mean elastic modulus of the individual fiber is 185.3 GPa. Deviations observed in the experimentally determined elastic modulus values between specimens were attributed to microstructural variations which occur during processing. Corresponding variations in the fracture surface morphology were also observed. The observed local mechanical behavior of a lithium alumino-silicate (LAS) glass ceramic, a LAS/SiC monofilament composite, and a calcium alumino-silicate (CAS)/SiC fully reinforced composite exhibits nonlinearities and apparent hysteresis due to the subcritical mechanical loading. Local hysteresis in the LAS matrices coincided with the occurrence of multiple fracture initiation sites, localized microcracking, and secondary cracking. The observed microcracking phenomenon was attributed to stress relaxation of residual stresses developed during processing, and local interaction of the crack front with the microstructure. The relaxation strain and stress predicted on apparent mechanical hysteresis effects were defined and correlated with the magnitude of the measured fracture stress for each specimen studied. This quantitative correlation indicated a repeatable measure of the stress at which matrix microcracking occurred for stress relief of each material system. Stress relaxation occurred prior to the onset of steady state cracking conditions. The relaxation stress occurred at 18.5 percent of the fracture stress in LAS and 11.0 percent of the yield stress in CAS/SiC. The relaxation stress ratio was dependent upon the dominant fracture mode of the LAS/SiC specimens. Relaxation stress ratios greater than 0.30 were observed for specimens which fractured due to shear at the fiber matrix interface; specimens which fracture due to tensile cracking had relaxation stress ratios less than 0.30. The stress relaxation ratio appeared to be a specific characteristic of the glass ceramic material. The measured stress relaxation for LAS indicated a measure of the inherent residual stresses in the material due to processing and suggested localized toughening mechanisms for brittle material structures.

Kent, Renee M.↗

NASA NTRS2020

Robustness and Behavior of Adjoint Calculations of Observation Impacts in Numerical Weather Prediction

Adjoint models are powerful tools that can be used to estimate the impact of observations on a chosen norm for numerical weather prediction forecasts. In this study, the Global Modeling and Assimilation Office (NASA/GMAO) Observing System Simulation Experiment framework is employed to investigate the behavior of the adjoint tool in an environment where the 'true' state of the atmosphere is fully known. This allows for the calculation of adjoint estimates of observation impact for very short forecast times including the zero-hour analysis state. The adjoint calculations using self-analysis verification can also be compared to adjoint calculations using the 'truth' as verification in order to characterize the robustness of adjoint estimations in the operational setting. Results from a experiments exploring various aspects of performance of the adjoint tool will be presented.

Prive, Nikki C.↗

NASA NTRS2014

Current Pressure Transducer Application of Model-based Prognostics Using Steady State Conditions

Prognostics is the process of predicting a system's future states, health degradation/wear, and remaining useful life (RUL). This information plays an important role in preventing failure, reducing downtime, scheduling maintenance, and improving system utility. Prognostics relies heavily on wear estimation. In some components, the sensors used to estimate wear may not be fast enough to capture brief transient states that are indicative of wear. For this reason it is beneficial to be capable of detecting and estimating the extent of component wear using steady-state measurements. This paper details a method for estimating component wear using steady-state measurements, describes how this is used to predict future states, and presents a case study of a current/pressure (I/P) Transducer. I/P Transducer nominal and off-nominal behaviors are characterized using a physics-based model, and validated against expected and observed component behavior. This model is used to map observed steady-state responses to corresponding fault parameter values in the form of a lookup table. This method was chosen because of its fast, efficient nature, and its ability to be applied to both linear and non-linear systems. Using measurements of the steady state output, and the lookup table, wear is estimated. A regression is used to estimate the wear propagation parameter and characterize the damage progression function, which are used to predict future states and the remaining useful life of the system.

Fault Estimation↗

NASA NTRS1976

Ruby laser induced emission from NO2

Two different types of emission from excited NO2 were observed using pulsed ruby laser light at 6943 A. The first type of fluorescence was seen in the near IR and results from the single photon excitation of NO2 from the ground 2-A1 state. By observing the emission as a function of time an unexpected behavior was observed in the near IR and could be explained by a consecutive deactivation mechanism, wherein a secondary species is preferentially detected. A second type of emission recently observed in the blue spectral region is weaker and is due to a multiphoton process. The intensity of the blue emission is a function of the cube of the laser intensity at low pressures and approaches the square at high pressures. This variation is attributed to simultaneous deactivation of the excited NO2 intermediate by collision (square) and by anti-Stokes Raman scattering off of the excited NO2 (cube).

Hakala, D. F.↗

NASA NTRS1989

Metal matrix composite micromechanics: In-situ behavior influence on composite properties

Recent efforts in computational mechanics methods for simulating the nonlinear behavior of metal matrix composites have culminated in the implementation of the Metal Matrix Composite Analyzer (METCAN) computer code. In METCAN material nonlinearity is treated at the constituent (fiber, matrix, and interphase) level where the current material model describes a time-temperature-stress dependency of the constituent properties in a material behavior space. The composite properties are synthesized from the constituent instantaneous properties by virtue of composite micromechanics and macromechanics models. The behavior of metal matrix composites depends on fabrication process variables, in situ fiber and matrix properties, bonding between the fiber and matrix, and/or the properties of an interphase between the fiber and matrix. Specifically, the influence of in situ matrix strength and the interphase degradation on the unidirectional composite stress-strain behavior is examined. These types of studies provide insight into micromechanical behavior that may be helpful in resolving discrepancies between experimentally observed composite behavior and predicted response.

Murthy, P. L. N.↗

NASA NTRS1990

Quasi-periodic oscillations in GX 17 + 2

X-ray observations of GX 17 + 2 were made in March and April, 1988 with the Large Area Counter of the Ginga satellite. The source was observed in the flaring, normal, and horizontal branches. Quasi-periodic oscillations (QPOs) were oberved in all three of these branches. The relationship between QPO behavior and the X-ray spectral properties of GX 17 + 2 is examined. Continuous variation of QPO behavior is observed as GX 17 + 2 moves from the normal to flaring branch, indicating that the normal-branch QPO and the flaring-branch QPO are probably one physical phenomenon. This QPO behavior is similar to that observed in Sco X-1. Also, it is found that GX 17 + 2 is an example of the Z-type sources defined by Hasinger et al. (1989).

Penninx, W.↗

NASA NTRS2013

The First Pulse of the Extremely Bright GRB 130427A: A Test Lab for Synchrotron Shocks

Gamma-ray burst (GRB) 130427A is one of the most energetic GRBs ever observed. The initial pulse up to 2.5 s is possibly the brightest well-isolated pulse observed to date. A fine time resolution spectral analysis shows power-law decays of the peak energy from the onset of the pulse, consistent with models of internal synchrotron shock pulses. However, a strongly correlated power-law behavior is observed between the luminosity and the spectral peak energy that is inconsistent with curvature effects arising in the relativistic outflow. It is difficult for any of the existing models to account for all of the observed spectral and temporal behaviors simultaneously.

Pulse↗

NASA NTRS2017

Analysis of High-order Social Interaction of Female Mice on the International Space Station

Social interactions are adaptive responses to environmental pressures that have evolved to facilitate the success of individual animals and their progeny. Quantifying social behavior in social animals is therefore one method of evaluating an animal's health, wellbeing and their adjustment to changes in their environment. The interaction between environment and animal can influence numerous other physiological and psychological responses that may enhance, deter or shift an animals social paradigm. For this study, we utilized flight video from the Rodent Research Hardware and Operations Validation mission (Rodent Research-1; RR1) on the International Space Station (ISS). Female mice spent 37 days in microgravity on the ISS and video was captured during the final 33 days. In a previous analysis of individual behavior, we also reported an observed spontaneous ambulatory behavior which we termed circling or 'race tracking,' and we anecdotally observed an increase in group organization around this behavior. In this analysis we further examined this behavior, and other social interactions, to determine if (1) animals joining in on this behavior were induced by other cohort members already participating in this circling behavior, (2) rates of joining varied by number already participating.

spacefligh↗

NASA NTRS2017

Evaluation of CVI SiC/SiC Composites for High Temperature Applications

Silicon carbide fiber reinforced silicon carbide (SiC/SiC) composites are candidate materials for various high temperature turbine engine applications because of their high specific strength and good creep resistance at temperatures of 1400 C (2552 F) and higher. Chemical vapor infiltration (CVI) SiC/SiC ceramic matrix composites (CMC) incorporating Sylramic-iBN SiC fiber were evaluated via fast fracture tensile tests (acoustic emission damage characterization to assess cracking behavior), tensile creep testing, and microscopy. The results of this testing and observed material behavior degradation mechanisms are reviewed.

testing↗

NASA NTRSDate not supplied

Surface Pressure Results for the NATO AVT-298 SWiFT Configuration in the National Transonic Facility

A high Reynolds number wind tunnel test of the Swept Wing Flow Test (SWiFT) configuration was conducted in the National Transonic Facility at the NASA Langley Research Center during the summer of 2023. The test campaign was the culmination of an international collaboration under the NATO AVT-298 research task group. The main objective of the test was to investigate Reynolds number scaling effects on the low-speed stability & control characteristics of the SWiFT model. Surface pressure results corroborate the force & moment results and help to provide more insight into the observed flow behavior. The effect of angle of attack and Reynolds number on the low-speed surface pressure results are analyzed particularly around the leading edge of the model. The onset and progression of flow separation on the wings particularly near the wing crank is also investigated, as well as the cause of an observed double-stall behavior. Finally, the transonic results showed a slight forward movement of the shock location with decreased shock strength as Reynolds number was increased. The data acquired from the test will ultimately help improve computational aerodynamic analysis and design tools for application to future BWB-type vehicle configurations.

NATO AVT-298↗

NASA NTRSDate not supplied

Surface Pressure Results for the NATO AVT-298 SWiFT Configuration in the National Transonic Facility

NATO AVT-298↗

NASA NTRS2010

International Space Station Common Cabin Air Assembly Condensing Heat Exchanger Hydrophilic Coating Failures and Lessons Learned

The ability to control the temperature and humidity of an environment or habitat is critical for human survival. These factors are important to maintaining human health and comfort, as well as maintaining mechanical and electrical equipment in good working order to support the human and to accomplish mission objectives. The temperature and humidity of the International Space Station (ISS) United States On-orbit Segment (USOS) cabin air is controlled by the Common Cabin Air Assembly (CCAA). The CCAA consists of a fan, a condensing heat exchanger (CHX), an air/water separator, temperature and liquid sensors, and electrical controlling hardware and software. The CHX is the primary component responsible for control of temperature and humidity. The CCAA CHX contains a chemical coating that was developed to be hydrophilic and thus attract water from the humid influent air. This attraction forms the basis for water removal and therefore cabin humidity control. However, there have been several instances of CHX coatings becoming hydrophobic and repelling water. When this behavior is observed in an operational CHX, the unit s ability to remove moisture from the air is compromised and the result is liquid water carryover into downstream ducting and systems. This water carryover can have detrimental effects on the cabin atmosphere quality and on the health of downstream hardware. If the water carryover is severe and widespread, this behavior can result in an inability to maintain humidity levels in the USOS. This paper will describe the operation of the five CCAAs within in the USOS, the potential causes of the hydrophobic condition, and the impacts of the resulting water carryover to downstream systems. It will describe the history of this behavior and the actual observed impacts to the ISS USOS. Information on mitigation steps to protect the health of future CHX hydrophilic coatings and potential remediation techniques will also be discussed.

Balistreri, Steven F.↗

NASA NTRS2013

International Space Station Common Cabin Air Assembly Condensing Heat Exchanger Hydrophilic Coating Operation, Recovery, and Lessons Learned

The ability to control the temperature and humidity of an environment or habitat is critical for human survival. These factors are important to maintaining human health and comfort, as well as maintaining mechanical and electrical equipment in good working order to support the human and to accomplish mission objectives. The temperature and humidity of the International Space Station (ISS) United States On-orbit Segment (USOS) cabin air is controlled by the Common Cabin Air Assembly (CCAA). The CCAA consists of a fan, a condensing heat exchanger (CHX), an air/water separator, temperature and liquid sensors, and electrical controlling hardware and software. The CHX is the primary component responsible for control of temperature and humidity. The CCAA CHX contains a chemical coating that was developed to be hydrophilic and thus attract water from the humid influent air. This attraction forms the basis for water removal and therefore cabin humidity control. However, there have been several instances of CHX coatings becoming hydrophobic and repelling water. When this behavior is observed in an operational CHX in the ISS segments, the unit s ability to remove moisture from the air is compromised and the result is liquid water carryover into downstream ducting and systems. This water carryover can have detrimental effects on the ISS cabin atmosphere quality and on the health of downstream hardware. If the water carryover is severe and widespread, this behavior can result in an inability to maintain humidity levels in the USOS. This paper will describe the operation of the five CCAAs within the USOS, the potential causes of the hydrophobic condition, and the impacts of the resulting water carryover to downstream systems. It will describe the history of this behavior and the actual observed impacts to the ISS USOS. Information on mitigation steps to protect the health of future CHX hydrophilic coatings as well as remediation and recovery of the full heat exchanger will be discussed.

Balistreri, Steven F.↗

NASA NTRS1992

Behavior of faulty double BJT BiCMOS logic gates

Logic Behavior of a Double BJT BiCMOS device under transistor level shorts and opens is examined. In addition to delay faults, faults that cause the gate to exhibit sequential behavior were observed. Several faults can be detected only by monitoring the current. The faulty behavior of Bipolar (TTL) and CMOS logic families is compared with BiCMOS, to bring out the testability differences.

Menon, Sankaran M.↗

NASA NTRS1997

On the Dramatic Spin-up/Spin-Down Torque Reversals in Accreting Pulsars

Dramatic torque reversals between spin-up and spin-down have been observed in half of the persistent X-ray pulsars monitored by the Burst and Transient Space Experiment (BATSE) all-sky monitor on the Compton Gamma Ray Observatory. Theoretical models developed to explain early pulsar timing data can explain spin-down torques via a disk-magnetosphere interaction if the star nearly corotates with the inner accretion disk. To produce the observed BATSE torque reversals, however, these equilibrium models require the disk to alternate between two mass accretion rates, with M+/- producing accretion torques of similar magnitude but always of opposite sign. Moreover, in at least one pulsar (GX 1+4) undergoing secular spin-down, the neutron star spins down faster during brief (approximately 20 day) hard X-ray flares-this is opposite the correlation expected from standard theory, assuming that BATSE pulsed flux increases with mass accretion rate. The 10 day to 10 yr intervals between torque reversals in these systems are much longer than any characteristic magnetic or viscous timescale near the inner disk boundary and are more suggestive of a global disk phenomenon. We discuss possible explanations of the observed torque behavior. Despite the preferred sense of rotation defined by the binary orbit, the BATSE observations are surprisingly consistent with an earlier suggestion for GX 1+4: the disks in these systems somehow alternate between episodes of prograde and retrograde rotation. We are unaware of any mechanism that could produce a stable retrograde disk in a binary undergoing Roche lobe overflow, but such flip-flop behavior does occur in numerical simulations of wind-fed systems. One possibility is that the disks in some of these binaries are fed by an X-ray-excited wind.

Nelson, Robert W.↗

NASA NTRS2010

Thin-Film Ferro Electric-Coupled Microstripline Phase Shifters With Reduced Device Hysteresis

This work deals with the performance of coupled microstripline phase shifters (CMPS) fabricated using BaxSr 1 -xTiO 3 (BST) ferroelectric thin films. The CMPS were fabricated using commercially available pulsed laser deposition BST films with Ba:Sr ratios of 30:70 and 20:80. Microwave characterization of these CMPS was performed at upper Kuband frequencies, particularly at frequencies near 16 and 18 GHz. X-ray diffraction studies indicate that the 30:70 films exhibit almost a 1:1 ratio between the in-plane and out-of-plane lattice parameters, suggesting that their cubics create strain -free films suitable for producing CMPS devices with reduced hysteresis in the paraelectric state. The quality of performance of the CMPS was studied based on their relative phase shift and insertion loss within the DC bias range of 0 to 400 V (i.e., E-field ranges within 0 to 53 V/micron). The performance of the CMPS was tested as a function of temperature to investigate their operation in the paraelectric, as well as in the ferroelectric, state (i.e., above and below the Curie temperature, respectively). The novel behavior discussed here is based on the experimental observation of the CMPS. This behavior, observed for the aforementioned cation ratio, highlights the relevance of good crystalline structure for high-quality CMPS.

Miranda, Felix A.↗

NASA NTRS1989

The unusual near-threshold FCG behavior of a single crystal superalloy and the resolved shear stress as the crack driving force

An investigation of the fatigue growth (FCG) behavior of PWA 1480 single crystal nickel base superalloy was conducted. Typical Paris region behavior was observed above a Delta-K of 8 MPa sq rt m. However, below that stress intensity range, the alloy exhibted highly unusual behavior. The behavior consisted of a region where the crack growth rate became essentially independent of the applied stress intensity. The transition in the FCG behavior was related to a change in the observed crack growth mechanisms.

Telesman, Jack↗