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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Navier-Stokes prediction of large-amplitude delta-wing roll oscillations characterizing wing rock

High-incidence vortical flow about a 65-deg sweep delta wing undergoing static roll and large-amplitude, high-rate-of-roll oscillations is simulated numerically using the time-dependent, three-dimensional, Reynolds-averaged, Navier-Stokes equations. Turbulent computations are presented for static roll angles up through 42 degrees. The effects of roll angle on the vortex aerodynamics are discussed, and the solution accuracy is evaluated by comparison with experimental data. The effects of grid refinement and zonal boundary condition treatment on solution accuracy are assessed at zero roll angle. Numerical simulation of a forced periodic roll motion is also presented.

Chaderjian, Neal M.↗
NASA NTRS1996

Forced Rolling Oscillation of a 65 deg-Delta Wing in Transonic Vortex-Breakdown Flow

Unsteady, transonic, vortex dominated flow over a 65 deg. sharp-edged, cropped-delta wing of zero thickness undergoing forced rolling oscillations is investigated computationally. The wing angle of attack is 20 deg. and the free stream Mach number and Reynolds number are 0.85 and 3.23 x 10(exp 6), respectively. The initial condition of the flow is characterized by a transverse terminating shock which induces vortex breakdown of the leading edge vortex cores. The computational investigation uses the time accurate solution of the laminar, unsteady, compressible, full Navier-Stokes equations with the implicit, upwind, Roe flux difference splitting, finite-volume scheme. While the maximum roll amplitude is kept constant at 4.0 deg., both Reynolds number and roll frequency are varied covering three cases of forced sinusoidal rolling. First, the Reynolds number is held at 3.23 x 10(exp 6) and the wing is forced to oscillate in roll around the axis of geometric symmetry at a reduced frequency of 2(pi). Second, the Reynolds number is reduced to 0.5 x 10(exp 6) to observe the effects of added viscosity on the vortex breakdown. Third, with the Reynolds number held at 0.5 x 10(exp 6), the roll frequency is reduced to 1(pi) to complete the study.

Menzies, Margaret A.↗
NASA NTRS1996

Biomechanically Induced and Controller Coupled Oscillations Experienced on the F-16XL Aircraft During Rolling Maneuvers

During rapid rolling maneuvers, the F-16 XL aircraft exhibits a 2.5 Hz lightly damped roll oscillation, perceived and described as 'roll ratcheting.' This phenomenon is common with fly-by-wire control systems, particularly when primary control is derived through a pedestal-mounted side-arm controller. Analytical studies have been conducted to model the nature of the integrated control characteristics. The analytical results complement the flight observations. A three-degree-of-freedom linearized set of aerodynamic matrices was assembled to simulate the aircraft plant. The lateral-directional control system was modeled as a linear system. A combination of two second-order transfer functions was derived to couple the lateral acceleration feed through effect of the operator's arm and controller to the roll stick force input. From the combined systems, open-loop frequency responses and a time history were derived, describing and predicting an analogous in-flight situation. This report describes the primary control, aircraft angular rate, and position time responses of the F-16 XL-2 aircraft during subsonic and high-dynamic-pressure rolling maneuvers. The analytical description of the pilot's arm and controller can be applied to other aircraft or simulations to assess roll ratcheting susceptibility.

Smith, John W.↗
NASA NTRS1995

Resistance to Rolling in the Adhesive Contact of Two Elastic Spheres

For the stability of agglomerates of micron sized particles it is of considerable importance to study the effects of tangential forces on the contact of two particles. If the particles can slide or roll easily over each other, fractal structures of these agglomerates will not be stable. We use the description of contact forces by Johnson, Kendall and Roberts, along with arguments based on the atomic structure of the surfaces in contact, in order to calculate the resistance to rolling in such a contact. It is shown that the contact reacts elastically to torque forces up to a critical bending angle. Beyond that, irreversible rolling occurs. In the elastic regime, the moment opposing the attempt to roll is proportional to the bending angle and to the pull-off force P(sub c). Young's modulus of the involved materials has hardly any influence on the results. We show that agglomerates of sub-micron sized particles will in general be quite rigid and even long chains of particles cannot be bent easily. For very small particles, the contact will rather break than allow for rolling. We further discuss dynamic properties such as the possibility of vibrations in this degree of freedom and the typical amount of rolling during a collision of two particles.

Dominik, C.↗
NASA NTRS1995

Resistance to Rolling in the Adhesive Contact of Two Elastic Spheres

For the stability of agglomerates of micron sized particles it is of considerable importance to study the effects of tangential forces on the contact of two particles. If the particles can slide or roll easily over each other, fractal structures of these agglomerates will not be stable. We use the description of contact forces by Johnson, Kendall and Roberts, along with arguments based on the atomic structure of the surfaces in contact, in order to calculate the resistance to rolling in such a contact. It is shown that the contact reacts elastically to torque forces up to a critical bending angle. Beyond that, irreversible rolling occurs. In the elastic regime, the moment opposing the attempt to roll is proportional to the bending angle and to the pull-off force P(sub c). Young's modulus of the involved materials has hardly any influence on the results. We show that agglomerates of sub-micron sized particles will in general be quite rigid and even long chains of particles cannot be bent easily. For very small particles, the contact will rather break than allow for rolling. We further discuss dynamic properties such as the possibility of vibrations in this degree of freedom and the typical amount of rolling during a collision of two particles.

Dominik, C.↗
NASA NTRS1996

An Initial Examination of Roll-Lateral Coordination Motion Requirements in Flight Simulation

A piloted simulation that examined the effects of uncoordinated roll-lateral motion cues from a coordinated math model was conducted. The vehicle model represented a typical helicopter with satisfactory handling qualities in the roll-lateral axes. The task was a two-degree-of-freedom horizontal sidestep, where the pilot controlled lateral position through roll angle. The motion platform commands were varied via two motion control system gains. One gain reduced the ratio between platform roll angle to math model (and thus visual) roll angle. The other gain was placed on how much lateral platform movement would result from platform roll attitude in an attempt to align the apparent gravity vector vertically relative to the pilot. Gains from one to zero were examined in both axes. Thus, the true 1:1 motion case, where the motion cues matched the visual cues was evaluated. Pilots subjective ratings of motion fidelity matched well against an earlier developed motion fidelity criteria. Significant differences were noted in the fixed-base versus motion base configurations.

Schroeder, Jeffery A.↗
NASA NTRS1998

Spatial coding of eye movements relative to perceived earth and head orientations during static roll tilt

This purpose of this study was to examine the spatial coding of eye movements during static roll tilt (up to +/-45 degrees) relative to perceived earth and head orientations. Binocular videographic recordings obtained in darkness from eight subjects allowed us to quantify the mean deviations in gaze trajectories along both horizontal and vertical coordinates relative to the true earth and head orientations. We found that both variability and curvature of gaze trajectories increased with roll tilt. The trajectories of eye movements made along the perceived earth-horizontal (PEH) were more accurate than movements along the perceived head-horizontal (PHH). The trajectories of both PEH and PHH saccades tended to deviate in the same direction as the head tilt. The deviations in gaze trajectories along the perceived earth-vertical (PEV) and perceived head-vertical (PHV) were both similar to the PHH orientation, except that saccades along the PEV deviated in the opposite direction relative to the head tilt. The magnitude of deviations along the PEV, PHH, and PHV corresponded to perceptual overestimations of roll tilt obtained from verbal reports. Both PEV gaze trajectories and perceptual estimates of tilt orientation were different following clockwise rather than counterclockwise tilt rotation; however, the PEH gaze trajectories were less affected by the direction of tilt rotation. Our results suggest that errors in gaze trajectories along PEV and perceived head orientations increase during roll tilt in a similar way to perceptual errors of tilt orientation. Although PEH and PEV gaze trajectories became nonorthogonal during roll tilt, we conclude that the spatial coding of eye movements during roll tilt is overall more accurate for the perceived earth reference frame than for the perceived head reference frame.

NASA Discipline Neuroscience↗
NASA NTRS2011

Rolling-Element Fatigue Testing and Data Analysis - A Tutorial

In order to rank bearing materials, lubricants and other design variables using rolling-element bench type fatigue testing of bearing components and full-scale rolling-element bearing tests, the investigator needs to be cognizant of the variables that affect rolling-element fatigue life and be able to maintain and control them within an acceptable experimental tolerance. Once these variables are controlled, the number of tests and the test conditions must be specified to assure reasonable statistical certainty of the final results. There is a reasonable correlation between the results from elemental test rigs with those results obtained with full-scale bearings. Using the statistical methods of W. Weibull and L. Johnson, the minimum number of tests required can be determined. This paper brings together and discusses the technical aspects of rolling-element fatigue testing and data analysis as well as making recommendations to assure quality and reliable testing of rolling-element specimens and full-scale rolling-element bearings.

Vlcek, Brian L.↗
NASA NTRS2011

Rolling-Tooth Core Breakoff and Retention Mechanism

Sampling cores requires the controlled breakoff of the core at a known location with respect to the drill end. An additional problem is designing a mechanism that can be implemented at a small scale that is robust and versatile enough to be used for a variety of core samples. This design consists of a set of tubes (a drill tube and an inner tube) and a rolling element (rolling tooth). An additional tube can be used as a sample tube. The drill tube and the inner tube have longitudinal holes with the axes offset from the axis of each tube. The two eccentricities are equal. The inner tube fits inside the drill tube, and the sample tube fits inside the inner tube. While drilling, the two tubes are positioned relative to each other such that the sample tube is aligned with the drill tube axis and core. The drill tube includes teeth and flutes for cuttings removal. The inner tube includes, at the base, the rolling element implemented as a wheel on a shaft in an eccentric slot. An additional slot in the inner tube and a pin in the drill tube limit the relative motion of the two tubes. While drilling, the drill assembly rotates relative to the core and forces the rolling tooth to stay hidden in the slot along the inner tube wall. When the drilling depth has been reached, the drill bit assembly is rotated in the opposite direction, and the rolling tooth is engaged and penetrates into the core. Depending on the strength of the created core, the rolling tooth can score, lock the inner tube relative to the core, start the eccentric motion of the inner tube, and break the core. The tooth and the relative position of the two tubes can act as a core catcher or core-retention mechanism as well. The design was made to fit the core and hole parameters produced by an existing bit; the parts were fabricated and a series of demonstration tests were performed. This invention is potentially applicable to sample return and in situ missions to planets such as Mars and Venus, to moons such as Titan and Europa, and to comets. It is also applicable to terrestrial applications like forensic sampling and geological sampling in the field.

Badescu, Mircea↗
NASA NTRS2012

Analysis of Roll Steering for Solar Electric Propulsion Missions

Nothing is more vital to a spacecraft than power. Solar Electric Propulsion (SEP) uses that power to provide a safe, reliable, and, most importantly, fuel efficient means to propel a spacecraft to its destination. The power performance of an SEP vehicle s solar arrays and electrical power system (EPS) is largely influenced by the environment in which the spacecraft is operating. One of the most important factors that determines solar array power performance is how directly the arrays are pointed to the sun. To get the most power from the solar arrays, the obvious solution is to point them directly at the sun at all times. Doing so is not a problem in deep space, as the environment and pointing conditions that a spacecraft faces are fairly constant and are easy to accommodate, if necessary. However, large and sometimes rapid variations in environmental and pointing conditions are experienced by Earth orbiting spacecraft. SEP spacecraft also have the additional constraint of needing to keep the thrust vector aligned with the velocity vector. Thus, it is important to analyze solar array power performance for any vehicle that spends an extended amount of time orbiting the Earth, and to determine how much off-pointing can be tolerated to produce the required power for a given spacecraft. This paper documents the benefits and drawbacks of perfectly pointing the solar arrays of an SEP spacecraft spiraling from Earth orbit, and how this might be accomplished. Benefits and drawbacks are defined in terms of vehicle mass, power, volume, complexity, and cost. This paper will also look at the application of various solar array pointing methods to future missions. One such pointing method of interest is called roll steering . Roll steering involves rolling the entire vehicle twice each orbit. Roll steering, combined with solar array gimbal tracking, is used to point the solar arrays perfectly towards the sun at all points in the orbit, while keeping the vehicle thrusters aligned in the velocity direction. Roll steering is particularly attractive for a recently proposed mission that involves a spiral trajectory from low Earth orbit (LEO) to the Earth-Moon Lagrange Point 1 (E-M L1). During the spiral, the spacecraft will spend over 300 days experiencing the full spectrum of near-earth environments and solar array pointing conditions. An extensive study of the application of SEP (and roll steering) to this spiral mission is included, highlighting the ultimate goal of reduced vehicle cost and mass. Tools used for this analysis include the Systems Power Analysis for Capability Evaluation (Refs. 1 and 2) (SPACE) electrical power systems code, and SEP trajectory simulation tools developed at NASA Glenn Research Center.

Pederson, Dylan, M.↗
DOE OSTI2016

Rolled-up transformer structure for a radiofrequency integrated circuit (RFIC)

A rolled-up transformer structure comprises a multilayer sheet having a rolled configuration comprising multiple turns about a longitudinal axis. The multilayer sheet comprises more than one conductive pattern layer on a strain-relieved layer, including a first conductive film and a second conductive film separated from the first conductive film in a thickness direction. The first conductive film comprises an even number of primary conductive strips, where each primary conductive strip has a length extending in the rolling direction, and the second conductive film comprises an even number of secondary conductive strips, where each secondary conductive strip has a length extending in the rolling direction. In the rolled configuration, turns of the primary conductive strips and turns of the secondary conductive strips wrap around the longitudinal axis. The primary conductive strips serve as a primary winding and the secondary conductive strips serve as a secondary winding of the rolled-up transformer structure.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Minimizing thickness variation in monolithic U-10Mo fuel foil and Zr interlayer during hot rolling: A microstructure-based finite element method analysis

Low-enriched uranium alloyed with 10 wt. % molybdenum (U-10Mo) has been identified as a promising alternative to highly enriched uranium fuel for the United States’ high performance research reactors. The monolithic U-10Mo fuel plate consists of a metallic U-10Mo fuel foil with a 25 µm Zr interlayer and a relatively thick cladding of aluminum alloy 6061. The Zr interlayer is typically applied during the hot co-rolling process, and this process dictates the uniformity of the Zr interlayer. Thickness variation observed in the U-10Mo and Zr interlayer has been attributed to several sources: the initial grain size of the U-10Mo castings, can materials, rolling temperature, inhomogeneous molybdenum content, and porosity in the cast U-10Mo. This thickness variation limits the ability to meet the dimensional specification; thus, a better understanding of the factors causing the nonuniform thickness is needed. In this work, we used a novel, microstructure-based finite element method to model the hot rolling process to address these concerns. Grain microstructures in U-10Mo were tessellated and explicitly considered in the finite element model. Each grain was assigned a random material property to mimic the grain strength variations induced by different grain orientations. Simulations were performed using six steel can thicknesses, four grain sizes, and with or without a Zr interlayer to investigate the influences of those variables on the thickness nonuniformity. The simulation results showed that a thinner steel can and finer U-10Mo grain size reduce thickness variations in both the U-10Mo fuel foil and Zr interlayer. The direct findings from the simulations and analysis can be used to optimize the hot rolling schedule, reduce fabrication defects, and meet the dimensional specifications. The proposed microstructure-based finite element model can be also coupled with experimental microstructure characterization data, images, and models to simulate multi-pass hot rolling.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of Residual Stress and Distortion of Cold-Rolled Bearing Ring from Annealing to Quenched-Tempered Heat Treatment

This study investigates the correlation between the residual stress and distortion behavior of a cold-rolled ring from the annealing to quenching-tempering (QT) process. Due to the cold-rolled process, the external periphery of the bearing ring experiences a compressive residual stress. To relieve the residual stress, cold-rolled rings are annealed at 700 °C which is higher than the starting temperature of recrystallization. When cold-rolled rings are annealed at 700 °C for 15 min, the compressive residual stress is reduced to zero and the outer diameter of the annealed ring becomes larger than that of a non-annealed sample, which is unrelated to annealing time. Simultaneously, the roundness and taper deviation do not obviously change compared with those of non-annealed sample. The stress relaxation during the annealing process was attributed to the recovery and recrystallization of ferrite. Annealing has a genetic influence on the following QT heat treatment, wherein the lowest residual stress is in the non-annealed cold-rolled ring. From the annealing to QT process, the deviation of the outer diameter, roundness, and taper increased with annealing time, a large extend than that of non-annealed samples.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Properties of Rolled AZ31 Magnesium Alloy Sheet Fabricated by Continuous Variable Cross-Section Direct Extrusion

Rolling is currently a widely used method for manufacturing and processing high-performance magnesium alloy sheets and has received widespread attention in recent years. Here, we combined continuous variable cross-section direct extrusion (CVCDE) and rolling processes. The microstructure and mechanical properties of the resulting sheets rolled at different temperatures from CVCDE extrudate were investigated by optical microscopy, scanning electron microscope, transmission electron microscopy and electron backscatter diffraction. The results showed that a fine-grained microstructure was present with an average grain size of 3.62 μm in sheets rolled from CVCDE extrudate at 623 K. Dynamic recrystallization and a large strain were induced by the multi-pass rolling, which resulted in grain refinement. In the 573-673 K range, the yield strength, tensile strength and elongation initially increased and then declined as the CVCDE temperature increased. The above results provide an important scientific basis of processing, manufacturing and the active control on microstructure and property for high-performance magnesium alloy sheet.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Development and Characterization of a Novel Ti-Modified High-Si Medium-Mn Steel Possessing Ultra-High Strength and Reasonable Ductility After Hot Rolling

The present work systematically correlates the strength–ductility relationship of a Ti-Si-modified Fe-Mn-Al-C steel with its microstructural characteristics such as grain size, type and morphology of precipitates, and the transformation-induced plasticity (TRIP) effect during hot deformation. The Ti-Si-modified multicomponent steel developed through melting and casting route is subjected to thermo-mechanical processing such as hot forging (at 1373 K) and subsequent hot rolling (at 1173 K). An excellent combination of ultra-high tensile strength (UTS ~ 1700 ± 20 MPa), reasonable ductility (elongation ~ 11%) and high work hardening behavior (n ~ 0.89) is achieved in the hot-rolled specimen as compared to the hot-forged one (UTS ~ 824 ± 9 MPa, n ~ 0.07) with negligible change in the elongation. The better tensile properties of the hot-rolled specimen in contrast to the hot-forged one are due to the combined effects of grain refinement during rolling, twin–twin interactions, precipitation strengthening by mixture of hexagonal structured Ti{sub 3}(Al,Si)C{sub 2} and Mn-Al-Si-rich carbide precipitates and most significantly the enhanced TRIP effect. The lower critical resolved shear stress value of martensitic transformation instigates the TRIP effect during tensile testing which resulted in the increased hardness and strength of the hot-rolled specimen. The above observation offers a strong support to the proposition that TRIP effect is the dominant plasticity-enhancing mechanism activated during the deformation of the low-stacking fault energy (~ 12.2 mJ/m{sup 2}) Si-Ti-modified, medium-Mn multicomponent steel employed in the present investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Heat Treatment and Combination of Cold Rolling and Heat Treatment on Microstructure and Mechanical Properties of Titanium Alloy Ti6Al2V2Zr1.5Mo

The heat treatment and cold rolling combinations have been carried out on titanium alloy Ti6Al2V2Zr1.5Mo, and microstructure evolution and mechanical behavior have been studied. Solution treatment below the β-transus temperature, followed by air cooling, resulted in higher microhardness/strength as compared to the same with water quenching. A sudden drop in microhardness/strength is observed in sample solution heat-treated above β-transus temperature followed by air cooling. The former is attributed to the additional presence of fine secondary α-phase formed by dynamic aging during air cooling as compared to water-quenched samples which did not have fine secondary α-phase. Solution treatment above β-transus temperature resulted in Widmanstatten microstructure with no significant fine secondary α in air-cooled samples. Among the studied conditions of cold rolling (CR), gain in strength of the alloy from annealed condition is significant with first 15% reduction and thereafter it is marginal for 30% reduction. Initiation of cracks at the edges has been observed in 30% CR. The microstructure of cold-rolled samples confirms the fragmentation of α-plates with the presence of high dislocation density. Heat treatment of cold-rolled samples resulted in significant reduction in strength from the as-cold-rolled conditions. The marginally lower strength than the as-received (annealed) or heat-treated alloy samples is due to the recrystallization in CR samples and the formation of Widmanstatten microstructure in air-cooled samples. The alloy does not have fine secondary α or regions with large dislocation density in this condition. The microstructure in the samples heat-treated (with air cooling) below as well as above β-transus temperature (after CR) is similar to air-cooled samples (without prior CR) with heat treatment above β-transus temperature. This indicates the reduction in recrystallization temperature with cold working, which is substantiated with the reduction in strength as well.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interaction of Strain Refined Precipitates and Recrystallized Grains in Nb-Ti Microalloyed Steel during Continuous Casting, Hot-Core Heavy Reduction Rolling, and Reheating Process

Hot-core heavy reduction rolling (HHR{sup 2}) is an energy-saving process that directly rolls continuously cast slabs at the end of solidification that have a large temperature gradient. Here, we elucidated the interaction of strain refined precipitates and recrystallized grains in Nb-Ti microalloyed steel during continuous casting, hot-core heavy reduction rolling, and reheating process. Furthermore, theoretical models were established to calculate recrystallization driving force and pinning force at temperatures in the range of 850-1300 °C by a two-stage interrupted compression test using a Gleeble-3800 thermomechanical simulator. The study indicated that a random dispersion of strain refined precipitates with a size range of ~ 6-10 nm was obtained in the hot-core heavy reduction rolled slab, which was different from the coarse and uneven distribution of precipitates in a conventional slab. Upon reheating, the austenite grains in the hot-core heavy reduction rolled slab were significantly refined and evenly distributed along the thickness direction. This is attributed to the random dispersion of strain refined precipitates formed in the HHR{sup 2} process.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Efficient rolling texture predictions and texture-sensitive properties of α-uranium foils

Here, finite element (FE) analysis was used to simulate the strain history of an α-uranium foil during cold-rolling, with the sheet modeled as an isotropic elastoplastic continuum. The resulting strain history was then used as input for a viscoplastic self-consistent (VPSC) polycrystal plasticity model to simulate crystallographic texture evolution. Mid-plane textures predicted via the combined FE→VPSC approach show alignment of the (010) poles along the rolling direction (RD), and the (001) poles along the normal direction (ND) with a symmetric splitting along RD. The surface texture is similar to that of the mid-plane, but with a shear-induced asymmetry that favors one of the RD split features of the (001) pole figure. Both the mid-plane and surface textures predicted by the FE→VPSC approach agree with published experimental results for cold-rolled α-uranium plates, as well as predictions made by a more computationally intensive full-field crystal plasticity based finite element model. α-uranium foils produced by cold-rolling must typically undergo a final recrystallization anneal to restore ductility prior to their final application, resulting in significant texture evolution from the cold-rolled plate deformation texture. Using the texture measured from a foil in the final recrystallized state, coefficients of the thermal expansion and elastic stiffness tensors were calculated using a thermo-elastic self-consistent model, and the anisotropic yield loci and flow curves along the RD, TD, and ND were predicted using the VPSC code.

36 MATERIALS SCIENCE↗