Acceleration stress effects on pilot performance and dynamic response
Acceleration stress effects on pilot performance and dynamic response
PILOT PERFORMANCE↗
SEARCH · Engineering Papers
Results for “Effective stress”
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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Tensile-stress effect on ferroelectric Barkhausen noise
Here, this study examines the effect of tensile stress on the ferroelectric properties of Pb(Zr 0.4 Ti 0.6 )O 3 thin film, with a focus on Barkhausen noise, observed for the first time under such conditions. Tensile stress significantly alters domain wall motions, affecting Barkhausen noise more than average polarization. Frequency analysis identifies grain boundaries as primary pinning sites, consistent across stress levels. A nonlinear relationship between stress, domain wall mobility, and polarization is found, where increased stress initially enhances pinning and polarization changes, but this effect diminishes at higher stress levels, indicating a shift in behavior.
36 MATERIALS SCIENCE↗
Characterization of Residual Stress Effects on Fatigue Crack Growth of a Friction Stir Welded Aluminum Alloy
An on-line compliance-based method to account for residual stress effects in stress-intensity factor and fatigue crack growth property determinations has been evaluated. Residual stress intensity factor results determined from specimens containing friction stir weld induced residual stresses are presented, and the on-line method results were found to be in excellent agreement with residual stress-intensity factor data obtained using the cut compliance method. Variable stress-intensity factor tests were designed to demonstrate that a simple superposition model, summing the applied stress-intensity factor with the residual stress-intensity factor, can be used to determine the total crack-tip stress-intensity factor. Finite element, VCCT (virtual crack closure technique), and J-integral analysis methods have been used to characterize weld-induced residual stress using thermal expansion/contraction in the form of an equivalent delta T (change in local temperature during welding) to simulate the welding process. This equivalent delta T was established and applied to analyze different specimen configurations to predict residual stress distributions and associated residual stress-intensity factor values. The predictions were found to agree well with experimental results obtained using the crack- and cut-compliance methods.
Newman, John A.↗
Unlocking the Dynamics of Ion Migration and Voltage Bias Stress Effects through Crystallite Engineering in Metal Halide Perovskites
Understanding the interplay between crystal engineering and the coupled electronic-ionic charge transport properties of metal halide perovskites remains a critical issue in the field. In this work, we developed an experimental approach to tune the crystallite orientation of methylammonium lead iodide (CH 3 NH 3 PbI 3 ) while maintaining their overall crystal structure. This approach allows us to selectively manipulate crystallite orientations to control out-ofplane ion migration and mitigate voltage bias stress effects in CH 3 NH 3 PbI 3 thin films. By employing advanced diffraction and spectroscopic techniques, we achieved a comprehensive characterization of the anisotropic crystallite properties in CH 3 NH 3 PbI 3 thin films with distinct preferred orientations. Our findings reveal that specific crystallite orientations, particularly those that limit halide ion migration pathways along the (200) crystallographic plane, significantly suppress out-of-plane ion migration. This suppression reduces hysteresis and alleviates voltage bias stress effects in CH 3 NH 3 PbI 3 solar cells, ultimately enhancing device stability and performance. These insights not only deepen our understanding of the relationship between crystallite orientation and device functionality but also highlight a promising strategy for regulating ion migration in MHP-based devices. This approach holds significant potential for advancing the stability and efficiency of perovskite solar cells and extending its applicability to other optoelectronic devices.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Gravitational radiation in the limit of high frequency. II - Nonlinear terms and the effective stress tensor.
HF vacuum gravitational field expansion, discussing nonlinear terms and effective stress tensor for gravitational waves localized energy
Isaacson, R. A.↗
Stress effects of high noise levels on lower body negative pressure experiments
Stress effects of high noise levels on lower body negative pressure experiments
Allen, R. E.↗
Thermal stress effects in intermetallic matrix composites
Intermetallic matrix composites develop residual stresses from the large thermal expansion mismatch (delta-alpha) between the fibers and matrix. This work was undertaken to: establish improved techniques to measure these thermal stresses in IMC's; determine residual stresses in a variety of IMC systems by experiments and modeling; and, determine the effect of residual stresses on selected mechanical properties of an IMC. X ray diffraction (XRD), neutron diffraction (ND), synchrotron XRD (SXRD), and ultrasonics (US) techniques for measuring thermal stresses in IMC were examined and ND was selected as the most promising technique. ND was demonstrated on a variety of IMC systems encompassing Ti- and Ni-base matrices, SiC, W, and Al2O3 fibers, and different fiber fractions (Vf). Experimental results on these systems agreed with predictions of a concentric cylinder model. In SiC/Ti-base systems, little yielding was found and stresses were controlled primarily by delta-alpha and Vf. In Ni-base matrix systems, yield strength of the matrix and Vf controlled stress levels. The longitudinal residual stresses in SCS-6/Ti-24Al-llNb composite were modified by thermomechanical processing. Increasing residual stress decreased ultimate tensile strength in agreement with model predictions. Fiber pushout strength showed an unexpected inverse correlation with residual stress. In-plane shear yield strength showed no dependence on residual stress. Higher levels of residual tension led to higher fatigue crack growth rates, as suggested by matrix mean stress effects.
Wright, P. K.↗
Engineered Edge Effect Stress Redistribution in Suspended Thin Film Stacks for Flatness Control
This paper presents the systematic study of edge effect stresses and interaction between thin film stacks to achieve flat suspended thin film structures. Finite element modeling (FEM) was used for rapid analysis of support structures on microshutter array (MSA) shutter blades. The design application aims to flatten the blades to provide ultra-high contrast to optical detectors using MSAs as field masks. This is the first comprehensive study of microscopic surface feature edge effect and film-to-film stress interaction in micro electromechanical systems (MEMS). This study demonstrates flattening of thin film stacks by stress redistribution by induced shear force at the edge of strategically designed reinforcement structures.
Thin Film MEMS↗
Residual stress effects on the impact resistance and strength of fiber composites
Equations have been derived to predict degradation effects of microresidual stresses on impact resistance of unidirectional fiber composites. Equations also predict lamination residual stresses in multilayered angle ply composites.
Chamis, C. C.↗
Stress effects on the energy barrier and mechanisms of cross-slip in FCC nickel
The energy barrier for homogeneous cross-slip of a screw dislocation in face-centered cubic (FCC) nickel is calculated using atomistic simulations as a function of the Escaig stress on the glide plane, the Escaig stress on the cross-slip plane, and the Schmid stress on the cross-slip plane. Two cross-slip mechanisms, Friedel-Escaig (FE) and Fleischer, are examined and their energy barriers are calculated for a large number of stress combinations. For each mechanism, the energy barrier as a function of three stress components can be reduced into a one-dimensional function of an effective stress. The stress domains in which FE and Fleischer mechanisms operate respectively are determined. Additionally, the FE mechanism dominates when the Escaig stress on the glide plane (in the direction that reduces the stacking fault width) is the largest stress component. Increasing the Schmid stress and Escaig stress (in the direction that expands the stacking fault width) on the cross slip plane promotes the Fleischer mechanism. The cross slip energy barrier functions obtained here can be used as input functions for computing cross slip rates in mesoscale dislocation dynamics simulations.
36 MATERIALS SCIENCE↗
Elimination of the bias-stress effect in ligand-free quantum dot field-effect transistors
Field-effect transistors (FETs) made from colloidal quantum dot (QD) solids commonly suffer from current–voltage hysteresis caused by the bias-stress effect (BSE), which complicates fundamental studies of charge transport in QD solids and the use of QD FETs in electronics. Here, we show that the BSE can be eliminated in n-channel PbSe QD FETs by first removing the QD ligands with a dose of H 2 S gas and then infilling the QD films with alumina by atomic layer deposition (ALD). The H 2 S-treated, alumina-infilled FETs have stable, hysteresis-free device characteristics (total short-term stability), indefinite air stability (total long-term stability), and a high electron mobility of up to 14 cm 2 V −1 s −1 , making them attractive for QD circuitry and optoelectronic devices. The BSE-free devices are utilized to conclusively establish the dependence of the electron mobility on temperature and QD diameter. We demonstrate that the BSE in these devices is caused by both electron trapping at the QD surface and proton drift within the film. The H 2 S/alumina chemistry produces ligand-free PbSe/PbS/Al 2 O 3 interfaces that lack the traps that cause the electronic part of the BSE, while full alumina infilling stops the proton motion responsible for the ionic part of the BSE. In conclusion, our matrix engineering approach should aid efforts to eliminate the BSE, boost carrier mobilities, and improve charge transport in other types of nanocrystal solids.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Bend-Test Results of the MISSE 7 Flexural Stress Effects Experiment After 1.5 Years of Space Exposure
Low Earth orbital environmental exposure can cause degradation of exterior spacecraft materials. Radiation and thermal exposure often result in bond-breaking and embrittlement of polymers, reducing mechanical strength and structural integrity. The Flexural Stress Effects Experiment (FSEE) was flown with the objective of determining the role of space exposure on the degradation of polymers under flexural stress. The FSEE samples were flown in a wake orientation on the exterior of International Space Station for 1.5 years. Twenty-three polyimide and fluorinated polymers with various coatings were flown: 11 bent over a 0.375-inch diameter holder and 12 over a 0.25-inch diameter holder. A non-standard bend-test procedure was used to determine the surface strain at which embrittled polymers crack. None of the control samples cracked, even under surface strains up to 19.7%, although one coating cracked. Of the 10 flight samples tested, seven indicated increased embrittlement through bend-test cracking at surface strains from 0.65% to 8.11%. Therefore, most of the tested polymers were embrittled due to space exposure, when compared to their control samples. The samples flown over the 0.375-inch holder were more embrittled than those on the 0.25-inch holder. Determination of the extent of space induced embrittlement of polymers is important for designing durable spacecraft.
Snow, Kate E.↗
Hydrostatic Stress Effect On the Yield Behavior of Inconel 100
Classical metal plasticity theory assumes that hydrostatic stress has no effect on the yield and postyield behavior of metals. Recent reexaminations of classical theory have revealed a significant effect of hydrostatic stress on the yield behavior of notched geometries. New experiments and nonlinear finite element analyses (FEA) of Inconel 100 (IN 100) equal-arm bend and double-edge notch tension (DENT) test specimens have revealed the effect of internal hydrostatic tensile stresses on yielding. Nonlinear FEA using the von Mises (yielding is independent of hydrostatic stress) and the Drucker-Prager (yielding is linearly dependent on hydrostatic stress) yield functions was performed. In all test cases, the von Mises constitutive model, which is independent of hydrostatic pressure, overestimated the load for a given displacement or strain. Considering the failure displacements or strains, the Drucker-Prager FEMs predicted loads that were 3% to 5% lower than the von Mises values. For the failure loads, the Drucker Prager FEMs predicted strains that were 20% to 35% greater than the von Mises values. The Drucker-Prager yield function seems to more accurately predict the overall specimen response of geometries with significant internal hydrostatic stress influence.
Allen, Phillip A.↗
Constitutive and Stability Behavior of Granular Materials Under Very Low Effective Stresses
The study of the behavior of granular materials such as sand is of great importance to the understanding of the response of foundations resting on surface and near-surface soil deposits. A clear understanding of the behavior of such materials can also provide insights into other related issues where low effective stresses are encountered such as liquefaction. The main sources of the constitutive and stability properties of cohesionless granular materials is interparticle friction, which in turn under low confinement stress levels is strongly affected by gravitational body forces under terrestrial (1 gravity) conditions. Under moderate-to-high stress levels, the influence of gravity on the behavior of experiments may not be pronounced and therefore the test results in a terrestrial environment may be acceptable for engineering purposes. However, the conduct of experiments on granular materials under very low stress levels and under quasi-static conditions can only be performed in a microgravity environment. A series of displacement-controlled cyclic triaxial compression experiments were performed in a SPACEHAB module on the Space Shuttle during the STS-79 mission to Mir in September, 1996, and the STS-89 mission in January, 1998. The experiments were conducted on six right cylindrical specimens 75 mm in diameter and 150 mm long at effective confining pressures of 0.05, 0.52 and 1.30 kPa. The results show very high peak strength friction angles in the range of 47.6 to 70.0 degrees, which are mainly due to overconsolidation and grain interlocking effects. It was observed that the residual strength levels were in the same range as that observed at higher confining stress levels. The dilatancy angles were unusually high in the range of 30 to 31 degrees. All specimens display substantial initial stiffnesses and elastic moduli during unloading and reloading events, which are nearly an order of magnitude higher than conventional theories predict. A periodic instability phenomenon which appears to result from buckling of multiple internal arches and columnar systems, augmented by stick-slips was observed in the experiments. Computed Tomography (CT) measurements revealed valuable data about the internal fabric and the specimens deformation patterns. Uniform diffuse bifurcation with multiple radial shear bands was observed in the specimens tested in a microgravity environment. In the axial direction, two major conical surfaces were developed. Spatial nonsymmetrical deformations were observed in specimens tested in terrestrial laboratory.
Alshibli, Khalid A.↗
Hydrostatic Stress Effect on the Yield Behavior of Inconel 100
Classical metal plasticity theory assumes that hydrostatic stress has negligible effect on the yield and postyield behavior of metals. Recent reexaminations of classical theory have revealed a significant effect of hydrostatic stress on the yield behavior of various geometries. Fatigue tests and nonlinear finite element analyses (FEA) of Inconel 100 (IN100) equal-arm bend specimens and new monotonic tests and nonlinear finite element analyses of IN100 smooth tension, smooth compression, and double-edge notch tension (DENT) test specimens have revealed the effect of internal hydrostatic tensile stresses on yielding. Nonlinear FEA using the von Mises (yielding is independent of hydrostatic stress) and the Drucker-Prager (yielding is linearly dependent on hydrostatic stress) yield functions were performed. A new FEA constitutive model was developed that incorporates a pressure-dependent yield function with combined multilinear kinematic and multilinear isotropic hardening using the ABAQUS user subroutine (UMAT) utility. In all monotonic tensile test cases, the von Mises constitutive model, overestimated the load for a given displacement or strain. Considering the failure displacements or strains for the DENT specimen, the Drucker-Prager FEM s predicted loads that were approximately 3% lower than the von Mises values. For the failure loads, the Drucker Prager FEM s predicted strains that were up to 35% greater than the von Mises values. Both the Drucker-Prager model and the von Mises model performed equally-well in simulating the equal-arm bend fatigue test.
Allen, Phillip A.↗
The MISSE 7 Flexural Stress Effects Experiment After 1.5 Years of Wake Space Exposure
Low Earth orbit space environment conditions, including ultraviolet radiation, thermal cycling, and atomic oxygen exposure, can cause degradation of exterior spacecraft materials over time. Radiation and thermal exposure often results in bond- breaking and embrittlement of polymers, reducing mechanical strength and structural integrity. An experiment called the Flexural Stress Effects Experiment (FSEE) was flown with the objective of determining the role of space environmental exposure on the degradation of polymers under flexural stress. The FSEE samples were flown in the wake orientation on the exterior of International Space Station for 1.5 years. Twenty-four samples were flown: 12 bent over a 0.375 in. mandrel and 12 were over a 0.25 in. mandrel. This was designed to simulate flight configurations of insulation blankets on spacecraft. The samples consisted of assorted polyimide and fluorinated polymers with various coatings. Half the samples were designated for bend testing and the other half will be tensile tested. A non-standard bend-test procedure was designed to determine the surface strain at which embrittled polymers crack. All ten samples designated for bend testing have been tested. None of the control samples' polymers cracked, even under surface strains up to 19.7%, although one coating cracked. Of the ten flight samples tested, seven show increased embrittlement through bend-test induced cracking at surface strains from 0.70%to 11.73%. These results show that most of the tested polymers are embrittled due to space exposure, when compared to their control samples. Determination of the extent of space induced embrittlement of polymers is important for designing durable spacecraft.
Snow, Kate E.↗
Stress effects in multilayers
Calculations of interfacial stress in abrupt junctions and its effect on the defect state of the interface are examined.
Jesser, W. A.↗
Development of a standardized battery of performance tests for the assessment of noise stress effects
A set of 36 relatively independent categories of human performance were identified. These categories encompass human performance in the cognitive, perceptual, and psychomotor areas, and include diagnostic measures and sensitive performance metrics. Then a prototype standardized test battery was constructed, and research was conducted to obtain information on the sensitivity of the tests to stress, the sensitivity of selected categories of performance degradation, the time course of stress effects on each of the selected tests, and the learning curves associated with each test. A research project utilizing a three factor partially repeated analysis of covariance design was conducted in which 60 male subjects were exposed to variations in noise level and quality during performance testing. Effects of randomly intermittent noise on performance of the reaction time tests were observed, but most of the other performance tests showed consistent stability. The results of 14 analyses of covariance of the data taken from the performance of the 60 subjects on the prototype standardized test battery provided information which will enable the final development and test of a standardized test battery and the associated development of differential sensitivity metrics and diagnostic classificatory system.
Theologus, G. C.↗