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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 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Scale-dependent gravitational waves from a rolling axion

We consider a model in which a pseudo-scalar field σ rolls for some e-folds during inflation, sourcing one helicity of a gauge field. These fields are only gravitationally coupled to the inflaton, and therefore produce scalar and tensor primordial perturbations only through gravitational interactions. These sourced signals are localized on modes that exit the horizon while the roll of σ is significant. We focus our study on cases in which the model can simultaneously produce (i) a large gravitational wave signal, resulting in observable B-modes of the CMB polarizations, and (ii) sufficiently small scalar perturbations, so to be in agreement with the current limits from temperature anisotropies. Different choices of parameters can instead lead to a localized and visible departure from gaussianity in the scalar sector, either at CMB or LSS scales.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Dynamics and Stability of Rolling Viscoelastic Tires

Current steady state rolling tire calculations often do not include treads because treads destroy the rotational symmetry of the tire. We describe two methodologies to compute time periodic solutions of a two-dimensional viscoelastic tire with treads: solving a minimization problem and solving a system of equations. We also expand on work by Oden and Lin on free spinning rolling elastic tires in which they disovered a hierachy of N-peak steady state standing wave solutions. In addition to discovering a two-dimensional hierarchy of standing wave solutions that includes their N-peak hiearchy, we consider the eects of viscoelasticity on the standing wave solutions. Finally, a commonplace model of viscoelasticity used in our numerical experiments led to non-physical elastic energy growth for large tire speeds. We show that a viscoelastic model of Govindjee and Reese remedies the problem.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2016

Report on the Second ARM Mobile Facility (AMF2) Roll, Pitch, and Heave (RPH) Stabilization Platform: Design and Evaluation

One of the primary objectives of the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Climate Research Facility’s second Mobile Facility (AMF2) is to obtain reliable measurements of solar, surface, and atmospheric radiation, as well as cloud and atmospheric properties, from ocean-going vessels. To ensure that these climatic measurements are representative and accurate, many AMF2 instrument systems are designed to collect data in a zenith orientation. A pillar of the AMF2 strategy in this effort is the use of a stable platform. The purpose of the platform is to 1) mitigate vessel motion for instruments that require a truly vertical orientation and keep them pointed in the zenith direction, and 2) allow for accurate positioning for viewing or shading of the sensors from direct sunlight. Numerous ARM instruments fall into these categories, but perhaps the most important are the vertically pointing cloud radars, for which vertical motions are a critical parameter. During the design and construction phase of AMF2, an inexpensive stable platform was purchased to perform the stabilization tasks for some of these instruments. The first table compensated for roll, pitch, and yaw (RPY) and was reported upon in a previous technical report (Kafle and Coulter, 2012). Subsequently, a second table was purchased specifically for operation with the Marine W-band cloud radar (MWACR). Computer programs originally developed for RPY were modified to communicate with the new platform controller and with an inertial measurements platform that measures true ship motion components (roll, pitch, yaw, surge, sway, and heave). This platform could not be tested dynamically for RPY because of time constraints requiring its deployment aboard the container ship Horizon Spirit in September 2013. Hence the initial motion tests were conducted on the initial cruise. Subsequent cruises provided additional test results. The platform, as tested, meets all the design and performance criteria established for its use. This is a report of the results of those efforts and the critical points in moving forward

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Phonon Spectrum Engineering in Rolled-up Micro- and Nano-Architectures

We report on a possibility of efficient engineering of the acoustic phonon energy spectrum in multishell tubular structures produced by a novel high-tech method of self-organization of micro- and nano-architectures. The strain-driven roll-up procedure paved the way for novel classes of metamaterials such as single semiconductor radial micro- and nano-crystals and multi-layer spiral micro- and nano-superlattices. The acoustic phonon dispersion is determined by solving the equations of elastodynamics for InAs and GaAs material systems. It is shown that the number of shells is an important control parameter of the phonon dispersion together with the structure dimensions and acoustic impedance mismatch between the superlattice layers. The obtained results suggest that rolled up nano-architectures are promising for thermoelectric applications owing to a possibility of significant reduction of the thermal conductivity without degradation of the electronic transport.

acoustic phonon energy spectrum↗
NASA NTRS2015

Relation Between Residual and Hoop Stresses and Rolling Bearing Fatigue Life

Rolling-element bearings operated at high speed or high vibration may require a tight interference fit between the bore of the bearing and shaft to prevent rotation of the bearing bore around the shaft and fretting damage at the interfaces. Previous work showed that the hoop stresses resulting from tight interference fits can reduce bearing lives by as much as 65 percent. Where tight interference fits are required, case-carburized steel such as AISI 9310 or M50 NiL is often used because the compressive residual stresses inhibit subsurface crack formation and the ductile core inhibits inner-ring fracture. The presence of compressive residual stress and its combination with hoop stress also modifies the Hertz stress-life relation. This paper analyzes the beneficial effect of residual stresses on rolling-element bearing fatigue life in the presence of high hoop stresses for three bearing steels. These additional stresses were superimposed on Hertzian principal stresses to calculate the inner-race maximum shearing stress and the resulting fatigue life of the bearing. The load-life exponent p and Hertz stress-life exponent n increase in the presence of compressive residual stress, which yields increased life, particularly at lower stress levels. The Zaretsky life equation is described and is shown to predict longer bearing lives and greater load- and stress-life exponents, which better predicts observed life of bearings made from vacuum-processed steel.

Fatigue↗
DOE OSTI2012

Universality of the Volume Bound in Slow-Roll Eternal Inflation

It has recently been shown that in single field slow-roll inflation the total volume cannot grow by a factor larger than e{sup S{sub dS}/2} without becoming infinite. The bound is saturated exactly at the phase transition to eternal inflation where the probability to produce infinite volume becomes non zero. We show that the bound holds sharply also in any space-time dimensions, when arbitrary higher-dimensional operators are included and in the multi-field inflationary case. The relation with the entropy of de Sitter and the universality of the bound strengthen the case for a deeper holographic interpretation. As a spin-off we provide the formalism to compute the probability distribution of the volume after inflation for generic multi-field models, which might help to address questions about the population of vacua of the landscape during slow-roll inflation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Polarization Amplitude-Based Method of Determining the Bearing and Roll Angles of an Object in Motion from Orthogonal Circularly Polarized Signals of a Radio Beacon

The possibility of determining the bearing and roll angles of an object in motion is investigated based on orthogonal left- and right-hand circularly polarized signals simultaneously radiated by a radio beacon from two points with the known coordinates spatially spaced in the horizontal plane. The bearing and roll angles are determined onboard the object in motion using a two-channel receiving system based on polarization amplitude-based processing of resultant vector signals received in a linear polarization basis.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Recrystallization and Grain Growth Simulations for Multiple-Pass Rolling and Annealing of U-10Mo

A simulation model of recrystallization and grain growth has been developed to investigate grain structure evolution during deformation and heat treatment in polycrystalline U-10wt% Mo (U-10Mo) fuel. Experimentally obtained U-10Mo microstructures were used as input for closed loop simulations of multiple rolling, intermediate heating and final annealing process. FEM calculations of deformation and Potts Model simulations of recrystallization and grain growth were used to iteratively inform each subsequent stage of simulation. Furthermore, the model was then applied to predict the grain structure evolution during multiple-pass hot rolling of U-10Mo, and benchmarked against experimentally observed U-10Mo recrystallization behavior. The results showed that our model was able to capture the coupling between deformation and recrystallization as a function of microstructure, including particle stimulated nucleation and recrystallization nucleation on grain boundaries. Additionally, we have achieved reasonable quantitative agreement with U-10Mo recrystallization and grain growth behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Microstructural Evolution on Sagging Behavior of Cold-Rolled Aluminum Foil During the Brazing Thermal Cycle

Effect of microstructural evolution on sagging behavior of aluminum foil was investigated during the brazing thermal cycle. During the brazing thermal cycle, the sagging behavior consists of three stages: slight sagging stage, accelerative sagging stage and slow sagging stage. The sagging of cold-rolled aluminum foil mainly occurs in the accelerative sagging stage, which is governed by recovery under external stress in the sagging test. The coarse recrystallized grain is responsible for the slow sagging stage by reducing grain boundary sliding. Increasing cold-rolled reduction and addition of final annealing heat treatment can improve sagging resistance by shortening recovery process during the brazing thermal cycle. Dissolution of dispersoids has few effects on sagging deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Very Hard Corrosion-Resistant Roll-Bonded Cr Coating on Mild Steel in Presence of Graphite

The present work discusses the development of very hard Cr and Cr-carbide coating by roll bonding of Cr powder on a mild steel followed by annealing at 800, 1000, 1100 and 1200 °C with and without the presence of graphite powder packing in argon environment. In addition, the effect of a roll skin pass of 5% prior to the application of coating was studied. The presence of graphite allows diffusion of both carbon and Cr in the mild steel substrate, leading to the formation of Cr-carbide on the outer surface, making the surface very hard (VHN ~ 1800). Depending on the annealing temperature and processing condition, diffusion layer thickness of Cr is found to be in the range of 10-250 μm with Cr content of 12.5-15 wt.% across the diffusion layer. Excellent stable passivity of the coated surface is observed in 0.2 N H{sub 2}SO{sub 4}, which is comparable to a highly passivating 304 stainless steel, and very low corrosion rate of the coating is observed as compared to the substrate mild steel.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Corrosion Inhibition of Cold-rolled Low Carbon Steel with Pulse Fiber Laser Ablation in Water

This study aims at the use of a fiber laser for modifying the surface properties of cold-rolled low carbon steel via a pulse laser ablation technique in water. The effect on the corrosion behavior of the fiber laser-treated metal surface was investigated in NaCl and HCl environments. Electrochemical tests showed significant improvement in the corrosion resistance of the laser-treated sample in NaCl, with an increase in open-circuit potential (OCP) from − 0.65 to − 0.60 V and an inhibition efficiency of 89.22% as obtained from the impedance study. Such improvement was less significant in an acidic environment. Lower corrosion rates of 20.9 mpy and 5.819 × 10{sup 3} mpy were obtained for the laser-treated samples in neutral and acidic electrolytes, respectively, than the corrosion rates obtained for the as-received samples (33.2 mpy and 11.98 × 10{sup 3} mpy). Morphological analysis indicated a passive film built by spherical grains of regular size on the metal surface after laser treatment. The corrosion inhibition effects in NaCl were evident by the nonexistence of the common corrosion products of lepidocrocite and crystalline structures that were seen on as-received samples; only polyhedral crystals with micrograins grown on them were seen covering the laser-treated surface. Therefore, the laser treatment using a fiber laser source improved the corrosion resistance of cold-rolled low carbon steel.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Scale Spallation During Coiling on the Electrochemical and Pickling Behavior of a Hot-Rolled Dual-Phase Steel

Tertiary oxide scale consists of magnetite and hematite, and in dual-phase steel strips were observed after the exit of final rolling stand in a thin slab casting rolling (TSCR) mill. Microscopic observation confirmed that these scales cracked and spalled off from many places of surface during coiling causing a non-uniform oxide layer on the steel surface. The present work discusses the synergistic effect of such non-uniform oxide layer and run-out-table cooling water on the electrochemical behavior of the dual-phase steel. The electrochemical response was assessed with the help of dynamic and linear polarization tests considering cooling water as electrolyte. The presence of non-uniform scale produced high cathodic (scaled zone) to anodic (spalled-off zone) area ratio that eventually led to extensive pitting corrosion in the present steel. Furthermore, the pickling behavior of the steel was also studied in detail. It was observed that the steel surface, with spalled-off area of about one-tenth of total surface area, corroded preferentially 3-4 times faster at spalled-off area than that of the uniformly pickled surface. The characterization study was performed using scanning electron microscopy, confocal laser 3D scanning microscopy, x-ray diffraction and Raman spectroscopy in order to establish the reasons for pitting corrosion due to the scale spallation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Combined Rolling–ECAP on Ultrafine-Grained Structure and Properties in 6063 Al Alloy

Grain structure and mechanical properties of 6063 Al alloy subjected to one, two and three passes via combined rolling–ECAP at room temperature were investigated. The yield strength (196 MPa) and tensile strength (242 MPa) after three passes increased by 3.7 times and three times, respectively, relative to the initial annealed alloy (YS: 53 MPa, UTS: 82 MPa). Heat treatment comprising homogenizing annealing (600 °C, 15 min), water quenching from 520 °C and reheating to 100 °C before each pass led to ultrafine grains (600-800 nm) and high yield strength (245 MPa) and tensile strength (277 MPa). The three-pass combined rolling–ECAP process in conjunction with a suitable heat treatment is an effective way to form UFG structure and improved mechanical properties in 6063 Al alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Microstructure Refinement on Hardness Homogeneity of Aluminum Alloy 1100 Processed by Accumulative Roll Bonding

This work examines the effect of grain refinement via accumulative roll bonding (ARB) on the homogeneity of microstructure and hardness through the thickness of commercially pure aluminum AA1100 sheets. The use of 7 cycles of ARB was shown to produce homogeneous ultrafine-grained microstructure, reducing the grain size to 0.46 and 1.03 µm in normal direction and rolling direction, respectively. Examination by electron backscattered diffraction indicates that continuous dynamic recrystallization was the main mechanism for the formation of submicron equiaxed grains bounded with high-angle grain boundaries (HAGBs). The fraction of HAGBs increased gradually reaching a maximum of 71.6% after 7 cycles. Through-thickness hardness measurements using Vickers and nanoindentation tests show an increase from 43.5 Hv (0.85 GPa) for as-received sample to 63 Hv (1.1 GPa) after 7 cycles. The heterogeneity in hardness through the thickness of the as-received material was shown to restrain the evolution of uniform hardness across the sheet thickness with increasing ARB cycles. Tensile tests showed that the tensile strength is increased to 250 MPa, which is about 2 times its initial value. Owing to the high stacking fault energy of AA1100, strong dynamic recovery occurred with increasing ARB strain which was balanced with the strain hardening property of the material. This resulted in plastic instability at small strains and thus early necking during the tensile test.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Real-Time In Situ Neutron Diffraction Investigation of Phase-Specific Load Sharing in a Cold-Rolled TRIP Sheet Steel

Real-time in situ neutron diffraction was used to investigate the loading-direction dependence of phase-specific load sharing in a cold-rolled TRIP 780 sheet steel under tension at room temperature. A slightly lower yield stress and relatively faster initial strain hardening were observed for the tension along the rolling direction (RD), than those along the transverse direction (TD) and the diagonal direction (DD). In all three loading directions, the redistribution of inter-phase and inter-granular load sharing occurs upon the yields of the BCC matrix and the FCC phase. The FCC phase is found to yield earlier along the RD than those along the TD and DD. Based on the Hooke’s law and the rule of mixture, it is found that the lattice strains of BCC-(211)/FCC-(311) reflections via single peak fit are better representative of phase elastic strains than the strains calculated via the lattice parameters by Rietveld refinement. The quantitative evolution of phase-specific stress indicates a rapid strain hardening in the FCC phase after yielding during the RD tension. Possible mechanisms of the direction-dependent phase-specific load sharing are discussed in association with the different initial textures in the RD, DD and TD.

Yu, Dunji↗
DOE OSTI2018

Texture evolution and microcracking mechanisms in as-extruded and cross-rolled conditions of a 14YWT nanostructured ferritic alloy

Cr-stabilized nanostructured ferritic alloys (NFAs), dispersion strengthened by an ultra-high density of nanooxides, are attractive candidates for many nuclear energy applications due to their high-temperature strength, in-service stability and remarkable irradiation tolerance. However, typical NFA deformation processing paths lead to crystallographic texturing, formation of brittle microstructures and low toughness orientations, making fabricating components very difficult. In this paper, we characterize the dislocation-mediated deformation mechanisms that lead to the brittle texture component. The as-extruded bar is less brittle than the cross-rolled plate, which contains a large population of pre-existing cleavage microcracks. More generally, deformed ODS/NFAs are most often textured and have anisotropic low toughness orientations, even absent microcracks. However, cross-rolling produces a very high volume fraction of a plate normal {001}<110>-texture component, which constitutes the brittle cleavage system in iron. Finally, microcracks propagate along {001} low angle deformation induced subgrain boundaries in <110> directions after nucleating by the Cottrell mechanism.

36 MATERIALS SCIENCE↗