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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 sources NASA NTRS DOE OSTI

NASA NTRS1973

Effect of artificial gravity on thermoregulation, respiratory metabolism and intermediary metabolism of animals

Metabolic alterations in animals exposed to radial acceleration are reported. Temperatures in acutely stressed animals dropped profoundly in correlation with decreased food consumption. Repeated exposure of the acutely stressed animal caused a decrease in hypothermic response whereas deceleration or reduction of G load did not significantly change body temperatures. Adrenal corticosteroids affected significantly the animal's recovery rate. No changes occured in body temperature patterns of chronically centrifuged animals after full adaptation; their respiratory rate increased very significantly in terms of CO2 output as did their glucose uptake by muscle tissues and their insulin responsiveness or sensitivity.

Oyama, J.↗

NASA NTRS1981

Fatigue crack growth in 7475-T651 aluminum alloy plate in hard vacuum and water vapor

Compact specimens of 25 mm thick aluminum alloy plate were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Crack growth rates were determined at frequencies of 1 Hz and 10 Hz in hard vacuum and laboratory air, and in mixtures of water vapor and nitrogen at water vapor partial pressures ranging from 94 Pa to 3.8 kPa. A significant effect of water vapor on fatigue crack growth rates was observed at the lowest water vapor pressure tested. Crack rates changed little for pressures up to 1.03 kPa, but abruptly accelerated at higher pressures. At low stress intensity factor ranges, cracking rates at the lowest and highest water vapor pressure tested were, respectively, two and five times higher than rates in vacuum. Although a frequency was observed in laboratory air, cracking rates in water vapor and vacuum are insensitive to a ten-fold change in frequency. Surfaces of specimens tested in water vapor and vacuum exhibited different amounts of residual deformation. Reduced deformation on the fracture surfaces of the specimens tested in water vapor suggests embrittlement of the plastic zone ahead of the crack tip as a result of environmental interaction.

Dicus, D. L.↗

NASA NTRS1989

Detection of potential space station control/structure interaction with CO-ST-IN

The NASA Lewis Research Center is concerned with the potential of interaction between space station controllers and the solar PV array structures. The models required to handle this problem are very large, and automated methods were developed for the transfer of data between structural dynamic and control system analysis software. These methods emphasize the need to achieve accurate coupled analysis results while using as small a model as possible. Specific tools which help the analyst in this regard include modal order techniques, the use of mode acceleration to calculate internal loads and stresses and the transfer of Craig-Bampton components to reduce problems associated with modal sufficiency. These techniques were applied to a space station model with 366 modes below 1 Hz. Attitude control, and alpha and beta joint control were simulated. The inclusion of alpha and beta joint controllers is important when examining overall space station dynamics. An initial choice of control parameters does indicate a potential for control/structure interaction during reboost. As expected this is exacerbated by increasing the rate gain and decreasing the hysteresis of the reaction control system (RCS) in order to improve rigid body performance.

Carney, Kelly↗

NASA NTRS1991

Analysis of Spacelab 3 residual acceleration data

A data reduction plan is being developed to efficiently process residual acceleration data, making such data more accessible to principal investigators of low-gravity experiments. Accelerometer data collected during the Spacelab 3 mission is being processed using a prototype version of this plan. The plan addresses various aspects of acceleration data analysis: the identification of disturbances that are intolerable to experiments, the investigation of acceleration orientations, the definition and characterization of the background acceleration corresponding to a given experiment time line, the isolation and examination of particular significant disturbances, and the identification of disturbance sources. Acceleration magnitude, frequency, and orientation are discussed: transient accelerations can have magnitudes as large as 0.01 g with frequency components no greater than 0.001 g. These accelerations fluctuate rapidly in orientation. The occurrence of disturbance sources in an orbiter is tentatively identified as a random process, whereas the response of the orbiter to given accelerations is considered deterministic. The need to continue monitoring of residual accelerations in orbiting space laboratories is stressed.

Rogers, Melissa J. B.↗

NASA NTRS2008

Structural Benchmark Creep Testing for the Advanced Stirling Convertor Heater Head

The National Aeronautics and Space Administration (NASA) has identified the high efficiency Advanced Stirling Radioisotope Generator (ASRG) as a candidate power source for use on long duration Science missions such as lunar applications, Mars rovers, and deep space missions. For the inherent long life times required, a structurally significant design limit for the heater head component of the ASRG Advanced Stirling Convertor (ASC) is creep deformation induced at low stress levels and high temperatures. Demonstrating proof of adequate margins on creep deformation and rupture for the operating conditions and the MarM-247 material of construction is a challenge that the NASA Glenn Research Center is addressing. The combined analytical and experimental program ensures integrity and high reliability of the heater head for its 17-year design life. The life assessment approach starts with an extensive series of uniaxial creep tests on thin MarM-247 specimens that comprise the same chemistry, microstructure, and heat treatment processing as the heater head itself. This effort addresses a scarcity of openly available creep properties for the material as well as for the virtual absence of understanding of the effect on creep properties due to very thin walls, fine grains, low stress levels, and high-temperature fabrication steps. The approach continues with a considerable analytical effort, both deterministically to evaluate the median creep life using nonlinear finite element analysis, and probabilistically to calculate the heater head s reliability to a higher degree. Finally, the approach includes a substantial structural benchmark creep testing activity to calibrate and validate the analytical work. This last element provides high fidelity testing of prototypical heater head test articles; the testing includes the relevant material issues and the essential multiaxial stress state, and applies prototypical and accelerated temperature profiles for timely results in a highly controlled laboratory environment. This paper focuses on the last element and presents a preliminary methodology for creep rate prediction, the experimental methods, test challenges, and results from benchmark testing of a trial MarM-247 heater head test article. The results compare favorably with the analytical strain predictions. A description of other test findings is provided, and recommendations for future test procedures are suggested. The manuscript concludes with describing the potential impact of the heater head creep life assessment and benchmark testing effort on the ASC program.

Krause, David L.↗

NASA NTRS2016

Model-Based Fatigue Prognosis of Fiber-Reinforced Laminates Exhibiting Concurrent Damage Mechanisms

Prognostics of large composite structures is a topic of increasing interest in the field of structural health monitoring for aerospace, civil, and mechanical systems. Along with recent advancements in real-time structural health data acquisition and processing for damage detection and characterization, model-based stochastic methods for life prediction are showing promising results in the literature. Among various model-based approaches, particle-filtering algorithms are particularly capable in coping with uncertainties associated with the process. These include uncertainties about information on the damage extent and the inherent uncertainties of the damage propagation process. Some efforts have shown successful applications of particle filtering-based frameworks for predicting the matrix crack evolution and structural stiffness degradation caused by repetitive fatigue loads. Effects of other damage modes such as delamination, however, are not incorporated in these works. It is well established that delamination and matrix cracks not only co-exist in most laminate structures during the fatigue degradation process but also affect each other's progression. Furthermore, delamination significantly alters the stress-state in the laminates and accelerates the material degradation leading to catastrophic failure. Therefore, the work presented herein proposes a particle filtering-based framework for predicting a structure's remaining useful life with consideration of multiple co-existing damage-mechanisms. The framework uses an energy-based model from the composite modeling literature. The multiple damage-mode model has been shown to suitably estimate the energy release rate of cross-ply laminates as affected by matrix cracks and delamination modes. The model is also able to estimate the reduction in stiffness of the damaged laminate. This information is then used in the algorithms for life prediction capabilities. First, a brief summary of the energy-based damage model is provided. Then, the paper describes how the model is embedded within the prognostic framework and how the prognostics performance is assessed using observations from run-to-failure experiments

Prognostics↗

NASA NTRS2005

Impact of Device Scaling on Deep Sub-micron Transistor Reliability: A Study of Reliability Trends using SRAM

As microelectronics are scaled in to the deep sub-micron regime, users of advanced technology CMOS, particularly in high-reliability applications, should reassess how scaling effects impact long-term reliability. An experimental based reliability study of industrial grade SRAMs, consisting of three different technology nodes, is proposed to substantiate current acceleration models for temperature and voltage life-stress relationships. This reliability study utilizes step-stress techniques to evaluate memory technologies (0.25mum, 0.15mum, and 0.13mum) embedded in many of today's high-reliability space/aerospace applications. Two acceleration modeling approaches are presented to relate experimental FIT calculations to Mfr's qualification data.

CMOS integrated circuits↗

NASA NTRS1992

Physical effects at the cellular level under altered gravity conditions

Several modifications of differentiated functions of animal cells cultivated in vitro have been reported when cultures have been exposed to increased or decreased inertial acceleration fields by centrifugation, clinorotation, and orbital space flight. Variables modified by clinorotation conditions include inertial acceleration, convection, hydrostatic pressure, sedimentation, and shear stress, which also affect transport processes in the extracellular chemical environment. Autocrine, paracrine and endocrine substances, to which cells are responsive via specific receptors, are usually transported in vitro (and possibly in certain embryos) by convection and in vivo by a circulatory system or ciliary action. Increased inertial acceleration increases convective flow, while microgravity nearly abolishes it. In the latter case the extracellular transport of macromolecules is governed by diffusion. By making certain assumptions it is possible to calculate the Peclet number, the ratio of convective transport to diffusive transport. Some, but not all, responses of cells in vitro to modified inertial environments could be manifestations of modified extracellular convective flow.

Todd, Paul↗

NASA NTRS2012

Accelerated Aging in Electrolytic Capacitors for Prognostics

The focus of this work is the analysis of different degradation phenomena based on thermal overstress and electrical overstress accelerated aging systems and the use of accelerated aging techniques for prognostics algorithm development. Results on thermal overstress and electrical overstress experiments are presented. In addition, preliminary results toward the development of physics-based degradation models are presented focusing on the electrolyte evaporation failure mechanism. An empirical degradation model based on percentage capacitance loss under electrical overstress is presented and used in: (i) a Bayesian-based implementation of model-based prognostics using a discrete Kalman filter for health state estimation, and (ii) a dynamic system representation of the degradation model for forecasting and remaining useful life (RUL) estimation. A leave-one-out validation methodology is used to assess the validity of the methodology under the small sample size constrain. The results observed on the RUL estimation are consistent through the validation tests comparing relative accuracy and prediction error. It has been observed that the inaccuracy of the model to represent the change in degradation behavior observed at the end of the test data is consistent throughout the validation tests, indicating the need of a more detailed degradation model or the use of an algorithm that could estimate model parameters on-line. Based on the observed degradation process under different stress intensity with rest periods, the need for more sophisticated degradation models is further supported. The current degradation model does not represent the capacitance recovery over rest periods following an accelerated aging stress period.

Celaya, Jose R.↗

NASA NTRS2011

Climate Change Impact Uncertainties for Maize in Panama: Farm Information, Climate Projections, and Yield Sensitivities

We present results from a pilot project to characterize and bound multi-disciplinary uncertainties around the assessment of maize (Zea mays) production impacts using the CERES-Maize crop model in a climate-sensitive region with a variety of farming systems (Panama). Segunda coa (autumn) maize yield in Panama currently suffers occasionally from high water stress at the end of the growing season, however under future climate conditions warmer temperatures accelerate crop maturation and elevated CO (sub 2) concentrations improve water retention. This combination reduces end-of-season water stresses and eventually leads to small mean yield gains according to median projections, although accelerated maturation reduces yields in seasons with low water stresses. Calibrations of cultivar traits, soil profile, and fertilizer amounts are most important for representing baseline yields, however sensitivity to all management factors is reduced in an assessment of future yield changes (most dramatically for fertilizers), suggesting that yield changes may be more generalizable than absolute yields. Uncertainty around General Circulation Model (GCM)s' projected changes in rainfall gain in importance throughout the century, with yield changes strongly correlated with growing season rainfall totals. Climate changes are expected to be obscured by the large inter-annual variations in Panamanian climate that will continue to be the dominant influence on seasonal maize yield into the coming decades. The relatively high (A2) and low (B1) emissions scenarios show little difference in their impact on future maize yields until the end of the century. Uncertainties related to the sensitivity of CERES-Maize to carbon dioxide concentrations have a substantial influence on projected changes, and remain a significant obstacle to climate change impacts assessment. Finally, an investigation into the potential of simple statistical yield emulators based upon key climate variables characterizes the important uncertainties behind the selection of climate change metrics and their performance against more complex process-based crop model simulations, revealing a danger in relying only on long-term mean quantities for crop impact assessment.

Maize↗

NASA NTRS1972

Reversed creep deformation behavior of metals.

It is shown that the creep deformation resistance of a variety of metals is reduced by repeated reversed deformation at temperatures above 0.4 Tm, where Tm is the absolute melting temperature of each metal. The reduction of creep deformation resistance due to stress reversals is most prominent at approximately 0.5 Tm where the average creep rate may increase by as much as a factor of twenty due to 50-100 stress reversals. Metallographic studies show that the observed acceleration of creep at high temperatures is in part due to the enhancement of grain boundary sliding as a result of gradual grain boundary migration toward planes of maximum shear stress during reversed creep deformation.

Morrow, J.↗

NASA NTRS1973

Functional changes in systemic and regional (intracranial) circulation accompanying low accelerations

Functional changes in systemic and cerebral hemodynamics were studied with respect to vestibular stresses. The main types of responses, differing qualitatively with respect to the tolerance of test subjects to low accelerations (particularly to Coriolis accelerations), were established. This is of practical importance in the selection of aircraft and space pilots. The data presented sheds light on the physiological mechanisms of adaptation and disturbed compensation during vestibular stimulation. Further studies in this important field of aerospace medicine are outlined.

Usachev, V. V.↗

NASA NTRS1989

Derivation of improved load transformation matrices for launchers-spacecraft coupled analysis, and direct computation of margins of safety

Load and stress recovery from transient dynamic studies are improved upon using an extended acceleration vector in the modal acceleration technique applied to structural analysis. Extension of the normal LTM (load transformation matrices) stress recovery to automatically compute margins of safety is presented with an application to the Hubble space telescope.

Klein, M.↗

NASA NTRS2001

Improved Method Being Developed for Surface Enhancement of Metallic Materials

Surface enhancement methods induce a layer of beneficial residual compressive stress to improve the impact (FOD) resistance and fatigue life of metallic materials. A traditional method of surface enhancement often used is shot peening, in which small steel spheres are repeatedly impinged on metallic surfaces. Shot peening is inexpensive and widely used, but the plastic deformation of 20 to 40 percent imparted by the impacts can be harmful. This plastic deformation can damage the microstructure, severely limiting the ductility and durability of the material near the surface. It has also been shown to promote accelerated relaxation of the beneficial compressive residual stresses at elevated temperatures. Low-plasticity burnishing (LPB) is being developed as an improved method for the surface enhancement of metallic materials. LPB is being investigated as a rapid, inexpensive surface enhancement method under NASA Small Business Innovation Research contracts NAS3-98034 and NAS3-99116, with supporting characterization work at NASA. Previously, roller burnishing had been employed to refine surface finish. This concept was adopted and then optimized as a means of producing a layer of compressive stress of high magnitude and depth, with minimal plastic deformation (ref. 1). A simplified diagram of the developed process is given in the following figure. A single pass of a smooth, free-rolling spherical ball under a normal force deforms the surface of the material in tension, creating a compressive layer of residual stress. The ball is supported in a fluid with sufficient pressure to lift the ball off the surface of the retaining spherical socket. The ball is only in mechanical contact with the surface of the material being burnished and is free to roll on the surface. This apparatus is designed to be mounted in the conventional lathes and vertical mills currently used to machine parts. The process has been successfully applied to nickel-base superalloys by a team from the NASA Glenn Research Center, Lambda Research, and METCUT Research, as supported by the NASA Small Business Innovation Research Phase I and II programs, the Ultra Safe program, and the Ultra- Efficient Engine Technology (UEET) Program.

Gabb, Timothy P.↗

NASA NTRS1998

Simulation of Crack Propagation in Engine Rotating Components under Variable Amplitude Loading

The crack propagation life of tested specimens has been repeatedly shown to strongly depend on the loading history. Overloads and extended stress holds at temperature can either retard or accelerate the crack growth rate. Therefore, to accurately predict the crack propagation life of an actual component, it is essential to approximate the true loading history. In military rotorcraft engine applications, the loading profile (stress amplitudes, temperature, and number of excursions) can vary significantly depending on the type of mission flown. To accurately assess the durability of a fleet of engines, the crack propagation life distribution of a specific component should account for the variability in the missions performed (proportion of missions flown and sequence). In this report, analytical and experimental studies are described that calibrate/validate the crack propagation prediction capability ]or a disk alloy under variable amplitude loading. A crack closure based model was adopted to analytically predict the load interaction effects. Furthermore, a methodology has been developed to realistically simulate the actual mission mix loading on a fleet of engines over their lifetime. A sequence of missions is randomly selected and the number of repeats of each mission in the sequence is determined assuming a Poisson distributed random variable with a given mean occurrence rate. Multiple realizations of random mission histories are generated in this manner and are used to produce stress, temperature, and time points for fracture mechanics calculations. The result is a cumulative distribution of crack propagation lives for a given, life limiting, component location. This information can be used to determine a safe retirement life or inspection interval for the given location.

Bonacuse, P. J.↗

NASA NTRS1999

Simulation of Crack Propagation in Engine Rotating Components Under Variable Amplitude Loading

The crack propagation life of tested specimens has been repeatedly shown to strongly depend on the loading history. Overloads and extended stress holds at temperature can either retard or accelerate the crack growth rate. Therefore, to accurately predict the crack propagation life of an actual component, it is essential to approximate the true loading history. In military rotorcraft engine applications, the loading profile (stress amplitudes, temperature, and number of excursions) can vary significantly depending on the type of mission flown. To accurately assess the durability of a fleet of engines, the crack propagation life distribution of a specific component should account for the variability in the missions performed (proportion of missions flown and sequence). In this report, analytical and experimental studies are described that calibrate/validate the crack propagation prediction capability for a disk alloy under variable amplitude loading. A crack closure based model was adopted to analytically predict the load interaction effects. Furthermore, a methodology has been developed to realistically simulate the actual mission mix loading on a fleet of engines over their lifetime. A sequence of missions is randomly selected and the number of repeats of each mission in the sequence is determined assuming a Poisson distributed random variable with a given mean occurrence rate. Multiple realizations of random mission histories are generated in this manner and are used to produce stress, temperature, and time points for fracture mechanics calculations. The result is a cumulative distribution of crack propagation lives for a given, life limiting, component location. This information can be used to determine a safe retirement life or inspection interval for the given location.

P J Bonacuse↗

DOE OSTI2025

Operation at Reduced Atmospheric Pressure and Concept of Reliability Redundancy for Optimized Design of Insulation Systems

Electrified transportation is calling for insulation design criteria that is adequate to provide elevated levels of power density, power dynamics and reliability. Increasing voltage levels are expected to cause accelerated intrinsic and extrinsic aging effects which will not be easily predictable at the design stage due to a lack of suitable modeling. Designing reliable insulation systems would require finding solutions able to control accelerated aging due to an unpredictable increase of intrinsic stresses and the onset of extrinsic stresses as partial discharges. This paper proposes the concept of reliability redundancy for the insulation design of aerospace electrical asset components, which is also validated at lower-than-standard atmospheric pressure. The principle is that extrinsic-aging-free design might be achieved upon determining the aging stress or abnormal service stresses distribution and being sure that aging will not generate conditions that can incept extrinsic aging (partial discharges) during operation life. However, such information is never, in practice, fully available to insulation system designers. Hence, especially in critical applications such as electrified aircraft, aerospace, and combat ships a further level of reliability should be added to a partial-discharge-free design, which can consist of the use of corona-resistant materials and/or of life models able to consider the accelerated aging effect of partial discharges (or any other type of extrinsic-accelerated aging factor). Innovative life modeling considering both extrinsic and intrinsic aging stresses, insulating material testing to estimate model parameters, and a metric for quantifying the extent of corona (or partial discharge) resistance can lead to establishing feasibility and limit conditions for optimized or fully reliability-redundant design. It is shown in the paper that if an extrinsic-aging-free design is not feasible, and it is therefore replaced by a redundant design, a further level of reliability redundancy can be provided by effective condition monitoring plans.

Montanari, Gian Carlo↗

NASA NTRS1980

Long-time creep behavior of the niobium alloy C-103

The creep behavior of C-103 was studied as a function of stress, temperature, and grain size for test times to 19000 hr. Over the temperature range 827 to 1204 C and the stress range 6.89 to 138 MPa, only tertiary (accelerating) creep was observed. The creep strain epsilon can be related to time t by an exponential relation epsilon = epsilon(0) + K e raised to power (st) - 1), where epsilon (0) is initial creep strain, K is the tertiary creep strain parameter, and s is the tertiary creep rate parameter. The observed stress exponent 2.87 is similar to the three power law generally observed for secondary (linear) creep of Class I solid solutions. The apparent activation energy 374 kj/g mol is close to that observed for self diffusion of pure niobium. The initial tertiary creep rate was slightly faster for fine grained than for coarse-grained material. The strain parameter K can be expressed as a combination of power functions of stress and grain size and an exponential function of temperature. Strain time curves generated by using calculated values for K and s showed reasonable agreement with observed curves to strains of at least 4 percent. The time to 1 percent strain was related to stress, temperature, and grain size in a similar manner as the initial tertiary creep rate.

Titran, R. H.↗