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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 NTRS1991

Conical Euler methodology for unsteady vortical flows about rolling delta wings

A conical Euler methodology was developed to study unsteady vortex-dominated flows about rolling highly swept delta wings undergoing either forced or free-to-roll motions. The flow solver of the code involves a multistage Runge-Kutta time-stepping scheme which uses a finite-volume spatial discretization of the Euler equations on an unstructured grid of triangles. Results are presented for a 75-deg swept sharp-leading-edge delta wing at a freestream Mach number of 1.2 and at alpha = 10, 20, and 30 deg. At the 10 and 20 deg, forced harmonic analyses indicate that the rolling moment coefficients provide a positive damping which is verified by free-to-roll calculations. In contrast, at 30 deg, a forced harmonic analysis indicates that the rolling moment coefficient provides a negative damping at the small roll amplitudes. A free-to-roll calculation for this case produces an initially divergent response, but as the amplitude of motion grows with time, the response transitions to a wing-rock type of limit cycle oscillation.

Lee, Elizabeth M.↗
NASA NTRS1949

Investigation at low speeds of the effect of aspect ratio and sweep on rolling stability derivatives of untapered wings

A low scale wind tunnel investigation was conducted in rolling flow to determine the effects of aspect ratio and sweep (when varied independently) on the rolling stability derivatives for a series of untapered wings. Test results indicate that when the aspect ratio was held constant, an increase in the sweepback angle caused a significant reduction in the damping in roll at low lift coefficients for only the higher aspect ratios that were tested. This result was in agreement with available swept wing theory which indicated no effect of sweep for aspect ratios near zero. The result of the linear theory that the damping in roll is independent of lift coefficient and that the yawing moment and lateral force due to rolling are directly proportional to the lift coefficient was found to be valid for only a very limited lift coefficient range when the wings were highly swept. For such wings, the damping was found to increase in magnitude and the yawing moment due to rolling, to change from negative to positive at moderate lift coefficients. The effect of wing tip suction, not acounted for by present theory, was found to be very important with regard to the yawing moment due to rolling, particularly for low aspect ratio swept wings. An empirical means of correcting present theory for the effect of tip suction is suggested.

Goodman, Alex↗
NASA NTRS1993

A study of roll attractor and wing rock of delta wings at high angles of attack

Wing rock is a high angle of attack dynamic phenomenon of limited cycle motion predominantly in roll. The wing rock is one of the limitations to combat effectiveness of the fighter aircraft. Roll Attractor is the steady state or equilibrium trim angle (phi(sub trim)) attained by the free-to-roll model, held at some angle of attack, and released form rest at a given initial roll (bank) angle (phi(sub O)). Multiple roll attractors are attained at different trim angles depending on initial roll angle. The test facility (Vigyan's low speed wind tunnel) and experimental work is presented here along with mathematical modelling of roll attractor phenomenon and analysis and comparison of predictions with experimental data.

Niranjana, T.↗
NASA NTRS1993

Judging rolling wheels: Dynamic and kinematic aspects of rotation-translation coupling

Four experiments were carried out to investigate observers' abilities to judge rolling motions. The experiments were designed to assess whether two important aspects of such motions are appreciated: the kinematic coupling of rotation and translation, and the dynamic effects of gravity. Different motion contexts of rolling wheels were created using computer-generated displays. The first experiment involved wheels rolling down an inclined plane. Observers spontaneously appreciated the anomaly of wheels that failed to accelerate, but they were not able to differentiate between different acceleration functions. Moreover, their judgements were almost exclusively based on the translation component of the rolling motion, neglecting the rotation component. In a second experiment it was found that observers could accurately estimate the perimeter of various objects. Thus, their inability to consider rotation information is not attributable to misperceptions of the geometry of wheels. In a third experiment the finding that rolling wheels appear to overrotate was replicated; however, findings from this experiment also showed, together with those from a fourth experiment, that observers are able to make very accurate judgments about translation-rotation coupling in rolling wheels when information is provided about the orientation of the wheel and the texture of the surface on which it rolls.

Hecht, Heiko↗
NASA NTRS2007

Free-to-Roll Testing of Airplane Models in Wind Tunnels

A free-to-roll (FTR) test technique and test rig make it possible to evaluate both the transonic performance and the wingdrop/ rock behavior of a high-strength airplane model in a single wind-tunnel entry. The free-to-roll test technique is a single degree-of-motion method in which the model is free to roll about the longitudinal axis. The rolling motion is observed, recorded, and analyzed to gain insight into wing-drop/rock behavior. Wing-drop/rock is one of several phenomena symptomatic of abrupt wing stall. FTR testing was developed as part of the NASA/Navy Abrupt Wing Stall Program, which was established for the purposes of understanding and preventing significant unexpected and uncommanded (thus, highly undesirable) lateral-directional motions associated with wing-drop/rock, which have been observed mostly in fighter airplanes under high-subsonic and transonic maneuvering conditions. Before FTR testing became available, wingrock/ drop behavior of high-performance airplanes undergoing development was not recognized until flight testing. FTR testing is a reliable means of detecting, and evaluating design modifications for reducing or preventing, very complex abrupt wing stall phenomena in a ground facility prior to flight testing. The FTR test rig was designed to replace an older sting attachment butt, such that a model with its force balance and support sting could freely rotate about the longitudinal axis. The rig (see figure) includes a rotary head supported in a stationary head with a forward spherical roller bearing and an aft needle bearing. Rotation is amplified by a set of gears and measured by a shaft-angle resolver; the roll angle can be resolved to within 0.067 degrees at a rotational speed up to 1,000 degrees/s. An assembly of electrically actuated brakes between the rotary and stationary heads can be used to hold the model against a rolling torque at a commanded roll angle. When static testing is required, a locking bar is used to fix the rotating head rigidly to the stationary head. Switching between the static and FTR test modes takes only about 30 minutes. The FTR test rig was originally mounted in a 16-ft (approximately 4.0-m) transonic wind tunnel, but could just as well be adapted to use in any large wind tunnel. In one series of tests on the FTR rig, static and dynamic characteristics of models of four different fighter airplanes were measured. Two of the models exhibited uncommanded lateral motions; the other two did not. A figure of merit was developed to discern the severity of lateral motions. Using this figure of merit, it was shown that the FTR test technique enabled identification of conditions under which the uncommanded lateral motions occurred. The wind-tunnel conditions thus identified were found to be correlated with flight conditions under which the corresponding full-size airplanes exhibited uncommanded lateral motions.

Capone, Francis J.↗
DOE OSTI2018

Recrystallization Behavior and Super-Elasticity of a Metastable β-Type Ti-21Nb-7Mo-4Sn Alloy During Cold Rolling and Annealing

Based on the d-electron alloy design theory, a new metastable β-type titanium alloy for biomedical applications, Ti-21Nb-7Mo-4Sn (wt.%) was designed in this article. This theory predicted this alloy was a metastable single β-type titanium alloy with low elastic modulus at room temperature, and the β-phase transition (β to α″) would be easy to occur during the cold rolling. The evolution of microstructure and mechanical properties of this alloy during cold rolling plus annealing were investigated by means of x-ray diffraction, optical microscope, transmission electron microscope and mechanical properties test. The results indicate that only β phase can be identified in this alloy before cold rolling, while a large amount of lath martensite (α″ phase) appears after cold rolling due to stress-induced martensitic transformation, which is in accordance with the prediction of the d-electron alloy design theory. The recrystallization nucleation occurs preferentially in the martensite lath region during the subsequent annealing process, and this region forms a large number of nano-crystals and microcrystals, showing that cold rolling plus annealing can become a new process for refining grains. Compared with casting and cold rolling samples, the annealing materials at 923 K for 10 min have excellent comprehensive mechanical properties with lower elastic modulus (58 GPa) and higher elastic recovery rate (35.39%).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural Analysis and Texture Evolution of the CVCEDed AZ31 Magnesium Alloy by Hot Rolling

Grain refinement is one of the important methods to improve the performance of magnesium alloy sheets. This paper attempts to prepare the billets of AZ31 magnesium alloy sheets by continuous variable cross-section direct extrusion (CVCDE) and then prepare sheets by rolling. The results show that the average grain size of the sheets rolled from extruded products by CVCDE with 2 interim dies reduced by 30% and the tensile strength increased by 12.6% compared with the sheets rolled from extruded products by traditional extrusion (CE), which is related to the dislocation multiplication in the corresponding conditions. The high dislocation density hinders the plastic deformation of the material, which is one of the internal factors that cause the increase in the strength of the material and the decrease in the plasticity. In addition, the basal surface of a lot of grains of the sheets rolled from extruded products by CVCDE with 2 interim dies is parallel to the RD-TD plane and the strength of texture is high. Meanwhile, the value of average Schmid factor of the sheets rolled from extruded products by CVCDE with 2 interim dies along the rolling direction is lowest, which result in lower plasticity. The above research provides a new idea for the development of high-performance magnesium alloy sheets.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Contradictory Feature Size Effects in the Tensile Yield Strength of Cu Sheets Produced Using Different Sequences Involving Annealing, Rolling, and Grinding

The feature size effect is significant research interest in the field of microforming. It is assumed that the size effect is influenced by the material preparation process. To verify this, the feature size effects associated with the tensile yield strength of Cu sheets with thicknesses ranging from 100 to 200 μm, produced using different sequences involving annealing, rolling, and grinding, were studied. Differing feature size effects were observed in the Cu specimens, and it was confirmed that the size effect was indeed influenced by the specimen preparation sequence. The tensile yield strengths of the annealed–ground–rolled and annealed–rolled specimens increased as the specimen thicknesses decreased. However, an opposing size effect was observed in the case of the annealed–rolled–annealed, annealed–ground, and annealed–rolled–ground specimens. The reduction ratio did not alter the trend associated with the size effect, but influenced the intensity of the size effect. It is believed that the reinforcement and erosion of the surface-hardened layer introduced during rolling resulted in the contradictory results.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Mechanical and Corrosion Properties of Hot-Rolled TiB{sub 2}/Ni Composites

To quickly prepare TiB{sub 2}/Ni composites at low temperatures, a method combining spark plasma sintering and hot rolling was used. This paper presents the preparation, microstructural and mechanical properties, strengthening mechanism and corrosion properties of TiB{sub 2}/Ni composites in detail. X-ray diffraction analysis shows that the texture degree of the TiB{sub 2}/Ni composites after hot rolling greatly differed from that of the as-rolled pure Ni samples. The addition of TiB{sub 2} particles limited grain growth in the Ni matrix and led to grain refinement. Dislocation strengthening, grain refinement strengthening and load transfer strengthening contributed to a 30% increase in the tensile strength compared to that of the as-rolled pure Ni. In addition, the strengthening mechanism of the mechanical property reinforcement was analyzed. The electrochemical test results demonstrate that the as-rolled pure Ni exhibited a lower corrosion current density and corrosion resistance than the other as-rolled TiB{sub 2}/Ni composites fabricated in this paper. This work demonstrates a new approach for fabricating composites in less time at lower preparation temperatures than conventional methods.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and mechanical properties development of micro channel tubes in extrusion, rolling and brazing

Highlights: • Rolling and brazing greatly affect the properties of micro-channel tubes (MCTs). • The properties of MCTs are investigated by the evolution of the microstructure. • Strength is decreased by 47% at 5%-rolling reduction ratio and 3-minute brazing. • Ductile fracture mode is observed by OM at failure of MCTs under inner pressure. - Abstract: In addition to extrusion, the post-processing of rolling and brazing has significant effect on the mechanical properties of multi-port tubes. The aluminum micro channel tubes, especially the seam welding zone in the internal webs, are investigated in terms of mechanical tests, microstructure characterization, and finite element analysis. The effect of the post-process of rolling are quantified by varying amount of rolling reduction ratios. Tensile strength and pressure bearing capacity are determined by tensile tests and burst pressure tests, respectively. The evolution of the microstructure within the seam wielding zone is characterized by Electron backscattered diffraction (EBSD) and optical microscopy (OM). The fracture profile observed by OM indicates ductile fracture mode. The pressure bearing capacity is reduced by ~47% at 5% reduction ratio of rolling followed by 3-minute brazing, where largest grains are obtained due to abnormal grain growth.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Hot Rolling of ZK60 Magnesium Alloy with Isotropic Tensile Properties from Tubing Made by Shear Assisted Processing and Extrusion (ShAPE)

In the present work, we utilized Shear Assisted Processing and Extrusion (ShAPE), a solid-phase processing technique, to extrude hollow tubes of ZK60 Mg alloy. Hot rolling was performed on these as-extruded tubes (after slitting them longitudinally) to thickness reductions of 37%, 68%, and 93% to investigate their viability as rolling feedstock material. EBSD analysis showed the formation of twinned grains in the ShAPE processed material and a gradual re-orientation of the basal texture parallel to the extrusion direction with each rolling step. Moreover, an equiaxed grain size of 5.15 ± 3.39 μm was obtained in the ShAPE extruded material, and the microstructure was retained even after 93% rolling reduction. The rolled sheets also showed excellent tensile strengths and no mechanical anisotropy, a critical characteristic for formability. The unique microstructures developed and their excellent mechanical properties, combined with the ease of scalability of the process, make ShAPE a promising alternative to existing methods for producing rolling feedstock material.

36 MATERIALS SCIENCE↗
DOE OSTI2018

An investigation of the microstructure and ductility of annealed cold-rolled tungsten

Tungsten is notoriously brittle metal at room temperature. Furthermore, contrary to most metals, plastic deformation increases ductility and recrystallization decreases ductility of tungsten. The fundamentals that govern this behavior have challenged academia and industry for decades. This paper focuses on understanding the controlling factors of ductility through a systematic investigation of the changes in microstructure and mechanical properties of cold-rolled tungsten that occur during annealing. Cold-rolled tungsten samples were annealed at temperatures up to 1400 °C, and mechanical testing and microstructural analysis was performed before and after annealing. Furthermore, a dislocation mobility model based on the Orowan equation was applied. The mechanisms of deformation are discussed within the context of deformed and annealed microstructures. The high fraction of low angle grain boundaries and high density of edge dislocations were found to be the most important factors for ductility. Although there were gradual changes in microstructure and mechanical properties, the ductility of cold-rolled tungsten was maintained up to 1300 °C. The material recrystallized when annealed above this temperature, had no ductility, and suffered brittle fracture. Microstructural characterizations of the as-rolled material revealed a typical BCC texture, with grains elongated in rolling direction and a large amount of edge dislocations and low angle grain boundaries. The level of texturing and the fraction of low angle grain boundaries diminished after recrystallization. It was found that, compared to the recrystallized material, as-rolled tungsten can accommodate over 7 orders of magnitude higher deformation velocity due to the high density of edge dislocations.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Calcium and zirconium as texture modifiers during rolling and annealing of magnesium–zinc alloys

Rolling experiments were carried out on a ternary Mg–Zn–Ca alloy and its modification with zirconium. Short time annealing of as-rolled sheets is used to reveal the microstructure and texture development. The texture of the as-rolled sheets can be characterised by basal pole figures with split peak towards the rolling direction (RD) and a broad transverse angular spread of basal planes towards the transverse direction (TD). During annealing the RD split peaks as well as orientations in the sheet plane vanish whereas the distribution of orientations tilted towards the TD remains. It is shown in EBSD measurements that during rolling bands of twin containing structures form. During subsequent annealing basal orientations close to the sheet plane vanish based on a grain nucleation and growth mechanism of recrystallisation. Orientations with tilt towards the TD remain in grains that do not undergo such a mechanism. The addition of Zr delays texture weakening. - Highlights: • Ca in Mg–Zn-alloys contributes to a significant texture weakening during rolling and annealing. • Grain nucleation and growth in structures consisting of twins explain a texture randomisation during annealing. • Grains with transverse tilt of basal planes preferentially do not undergo a grain nucleation and growth mechanism. • Zr delays the microstructure and texture development.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Slow-roll approximation in loop quantum cosmology

The slow-roll approximation is an analytical approach to study dynamical properties of the inflationary universe. In this article, systematic construction of the slow-roll expansion for effective loop quantum cosmology is presented. The analysis is performed up to the fourth order in both slow-roll parameters and the parameter controlling the strength of deviation from the classical case. The expansion is performed for three types of the slow-roll parameters: Hubble slow-roll parameters, Hubble flow parameters and potential slow-roll parameters. An accuracy of the approximation is verified by comparison with the numerical phase space trajectories for the case with a massive potential term. The results obtained in this article may be helpful in the search for the subtle quantum gravitational effects with use of the cosmological data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Stochastic disks that roll

We study a model of rolling particles subject to stochastic fluctuations, which may be relevant in systems of nano- or microscale particles where rolling is an approximation for strong static friction. We consider the simplest possible nontrivial system: a linear polymer of three disks constrained to remain in contact and immersed in an equilibrium heat bath so the internal angle of the polymer changes due to stochastic fluctuations. We compare two cases: one where the disks can slide relative to each other and the other where they are constrained to roll, like gears. Starting from the Langevin equations with arbitrary linear velocity constraints, we use formal homogenization theory to derive the overdamped equations that describe the process in configuration space only. The resulting dynamics have the formal structure of a Brownian motion on a Riemannian or sub-Riemannian manifold, depending on if the velocity constraints are holonomic or nonholonomic. We use this to compute the trimer's equilibrium distribution with and without the rolling constraints. Surprisingly, the two distributions are different. We suggest two possible interpretations of this result: either (i) dry friction (or other dissipative, nonequilibrium forces) changes basic thermodynamic quantities like the free energy of a system, a statement that could be tested experimentally, or (ii) as a lesson in modeling rolling or friction more generally as a velocity constraint when stochastic fluctuations are present. In the latter case, we speculate there could be a “roughness” entropy whose inclusion as an effective force could compensate the constraint and preserve classical Boltzmann statistics. Regardless of the interpretation, our calculation shows the word “rolling” must be used with care when stochastic fluctuations are present.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Effects of Rolling Reduction on Critical Current Density and Microstructure of Bi-2212 Wires

Bi-2212 Rutherford cables have been fabricated into flat racetrack coils and canted-cosine-theta dipole magnets. The performance gap between the magnets made with Rutherford cables and the “short-sample-limit” is about 30%. To better understand the influence of Rutherford cable processing on the strand performance, we studied three Bi-2212 wires with filament architectures of 37 × 18 and 55 × 18 and diameters of 0.8 and 1.0 mm. To simulate the deformation caused by cabling process, the three wires were rolled with thickness reductions ranging from 10% to 30%. The aspect ratios of rolled strands are between 1.29 and 2.05. The low aspect-ratio wire is also an interesting form for fabricating solenoid coils with higher packing density. The round and rolled strands were heat-treated under 50 bar and with maximum heat treatment temperatures of 885.5 °C and 890.5 °C. The rolling deformation reduced filament size uniformity, resulting in filament merging in fully heat-treated wires. It was found that rolling reduction reduced wire critical current density (JE) by 16 to 18%, but the JE decrease saturated at 15 to 20% of the thickness reduction. It is believed that the reduced JE results from the filament merging caused by rolling and non-uniform shrinking during overpressure heat treatment.

Bi-2212 wire↗
DOE OSTI2014

SU-E-J-56: Dosimetric Impact of Patient Roll Variability in Peripheral-Lung SBRT

Purpose: Positional variation about the patient longitudinal axis may introduce deleterious effects to clinical treatment plans, the effects of which are exacerbated by hypo-fractionated treatment regimens. Our goal is to evaluate the dosimetric impact of rotational setup error in stereotactic body radiation therapy (SBRT) for peripherally-located lung lesions. Methods: Six patients who had been treated for peripheral lung lesions using varying SBRT techniques were analyzed. Each patient's planning CT was processed using custom in-house software to simulate 1, 3, and 5 degree roll in both directions about their longitudinal axis. The original plan was fused and re-calculated. Agreement between planned and error-simulated dose distributions was quantified using 3%, 3mm criteria for the 3-dimensional gamma metric, and changes in target coverage and adjacent normal anatomy were also quantified. Results: Increased rotational setup error resulted in reduced target coverage, with changes in equivalent uniform dose ranging from −1.24% to −6.11% for simulated roll greater than or equal to 3 degrees, increasing with magnitude of error and skewed for roll directed toward the involved side. Changes to normal tissue metrics are linearly related to simulated roll, with rib D(1cc) changes ranging from −4.23% to 3.27% relative to the original treatment plan. Error-simulated dose distributions demonstrate agreement by the gamma metric in the planned target of 72.56%, 81.02%, and 99.52% for 5, 3, and 1 degree simulated roll scenarios, respectively. Corresponding agreement for the regional dose in excess of 50% of the maximum were 65.71%,70.77%, and 97.88%. Conclusion: This study suggests that the ability to detect and compensate for rotational positioning variations beyond a threshold level may improve care for patients with peripherally-located lesions beyond that which may be accomplished using only translational axes. Positional error of one degree of roll had little influence, though three or more degrees of error introduced significant discrepancy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Carbide Particle Redistribution in U10Mo Alloy during Hot Rolling Process

The influence of initial carbide particle distribution features on the evolution of particle and stringer distribution within U10Mo alloy during hot rolling was investigated in this study. This work will provide guidance to casting optimization work and identify actionable process changes to eliminate the surface features directly attributed to carbides. Various synthetic microstructure-based finite-element (FE) models were generated with consideration of different parameters (i.e., particle shape, particle volume fraction and particle distribution). Plane-strain compression loading was employed in the FE models to simulate hot rolling to 40% and 80% reductions. Stringer statistics analyses and two-point correlation functions were then performed with the simulated hot-rolling results. The results from stringer analyses show that stringer volume fraction substantially increases with increased rolling reduction for microstructure with particles distributed along grain boundaries, and that microstructures with elliptical particles may have slightly higher stringer volume fractions than those with circular particles. The results also show that the maximum stringer length can increase substantially with increased rolling reduction for microstructures with elliptical particles along grain boundaries, and that the microstructures with higher-aspect-ratio elliptical particles may have higher stringer volume fraction and higher maximum stringer length. Near-surface numbers of particles and particle volume fractions also increase with increased rolling reduction. The results from application of the two-point correlation function show that the particle shape (i.e., circular or elliptical) may not have significant influence on the overall shapes of the correlation curves, and that the correlation curves tend to show higher peaks at short distance and then gradually decrease for microstructures with higher particle volume fractions and particles distributed along grain boundaries.

36 MATERIALS SCIENCE↗