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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Low-Cost Phased Array Antenna for Sounding Rockets, Missiles, and Expendable Launch Vehicles

A low-cost beamformer phased array antenna has been developed for expendable launch vehicles, rockets, and missiles. It utilizes a conformal array antenna of ring or individual radiators (design varies depending on application) that is designed to be fed by the recently developed hybrid electrical/mechanical (vendor-supplied) phased array beamformer. The combination of these new array antennas and the hybrid beamformer results in a conformal phased array antenna that has significantly higher gain than traditional omni antennas, and costs an order of magnitude or more less than traditional phased array designs. Existing omnidirectional antennas for sounding rockets, missiles, and expendable launch vehicles (ELVs) do not have sufficient gain to support the required communication data rates via the space network. Missiles and smaller ELVs are often stabilized in flight by a fast (i.e. 4 Hz) roll rate. This fast roll rate, combined with vehicle attitude changes, greatly increases the complexity of the high-gain antenna beam-tracking problem. Phased arrays for larger ELVs with roll control are prohibitively expensive. Prior techniques involved a traditional fully electronic phased array solution, combined with highly complex and very fast inertial measurement unit phased array beamformers. The functional operation of this phased array is substantially different from traditional phased arrays in that it uses a hybrid electrical/mechanical beamformer that creates the relative time delays for steering the antenna beam via a small physical movement of variable delay lines. This movement is controlled via an innovative antenna control unit that accesses an internal measurement unit for vehicle attitude information, computes a beam-pointing angle to the target, then points the beam via a stepper motor controller. The stepper motor on the beamformer controls the beamformer variable delay lines that apply the appropriate time delays to the individual array elements to properly steer the beam. The array of phased ring radiators is unique in that it provides improved gain for a small rocket or missile that uses spin stabilization for stability. The antenna pattern created is symmetric about the roll axis (like an omnidirectional wraparound), and is thus capable of providing continuous coverage that is compatible with very fast spinning rockets. For larger ELVs with roll control, a linear array of elements can be used for the 1D scanned beamformer and phased array, or a 2D scanned beamformer can be used with an NxN element array.

Mullinix, Daniel↗
NASA NTRS1942

Comparison of Aileron Control Characteristics as Determined in Flight Tests of P-36, P-40, Spitfire, and Hurricane Pursuit Airplanes

The Army Air Force has made available several pursuit-type airplanes for quantitative investigation of their flying and handling qualities. One Item of special interest obtained from the results of the investigation is a comparison of the aileron control characteristics of the P-36, P-40, Hawker Hurricane, and Supermarine Spitfire airplanes. Figure 1 shows the design characteristics of the ailerons and the control sticks of the four airplanes. Aileron effectiveness may be expressed in terms of the helix angle generated by the wing tip in a steady roll. This angle is given by the expression pb/2V, where p is the rolling velocity, b the wing span, and V the true airspeed, expressed in consistent units. This quantity is convenient to use because, although it does not rep resent directly the rolling velocity of airplanes of different spans or airplanes operating at different speeds, it provides a satisfactory basis for computing the rate of roll and the time required to bank a given amount under any given set of conditions. The ratio of pb/2V obtained in any roll to the maximum value reached with full aileron deflection indicates the fraction of the maximum aileron travel that was reached. A complete discussion of this criterion for aileron effectiveness is given in reference 1. The aileron effectiveness of the various airplanes is compared in the following table on the basis of the response obtained with stick forces of 30 and 5 pounds. A force of 30 pounds is somewhat less than the greatest stick force exerted by the pilot. Repeated flight measurements have shown, however, that this force is a reasonable upper limit for maneuvering at high speeds.

Phillips, William H.↗
NASA NTRS2015

Superelastic Ball Bearings: Materials and Design to Avoid Mounting and Dismounting Brinell Damage in an Inaccessible Press-fit Application-: Detailed Analysis - II

Rolling element bearings utilized in precision rotating machines require proper alignment, preload, and interference fits to ensure overall optimum performance. Hence, careful attention must be given to bearing installation and disassembly procedures to ensure the above conditions are met. Usually, machines are designed in such a way that bearings can be pressed into housings or onto shafts through the races without loading the rolling elements. However, in some instances, either due to limited size or access, a bearing must be installed or removed in such a way that the load path travels through the rolling elements. This can cause high contact stresses between the rolling elements and the races and introduces the potential for Brinell denting of the races. This paper is a companion to the Part I paper by the authors that discusses material selection and the general design philosophy for the bearing. Here, a more in-depth treatment is given to the design of a dent-resistant bearing utilizing a superelastic alloy, 60NiTi, for the races. A common bearing analysis tool based on rigid body dynamics is used in combination with finite element simulations to design the superelastic bearing. The primary design constraints are prevention of denting and avoiding the balls riding over the edge of the race groove during a blind disassembly process where the load passes through the rolling elements. Through an iterative process, the resulting bearing geometry is tailored to improve axial static load capability compared to a deep-groove ball bearing of the same size. The results suggest that careful selection of materials and bearing geometry can enable blind disassembly without damage to the raceways, which is necessary in the current application (a compressor in the International Space Station Environmental Control and Life Support System), and results in potential design flexibility for other applications, especially small machines with miniature bearings.

metals↗
NASA NTRS2018

Time-Varying Manual Control Identification in a Stall Recovery Task Under Different Simulator Motion Conditions

This paper adds data to help the development of simulator motion cueing guidelines for stall recovery training by identifying time-varying manual control behavior in a stall recovery task under different simulator motion conditions. A study was conducted with seventeen general aviation pilots in the NASA Ames Vertical Motion Simulator. Pilots had to follow a flight director through four stages of a high-altitude stall task. A time-varying identification method was used to quantify how pilot manual control parameters change throughout different stages of the task in both roll and pitch. Four motion configurations were used: no motion, generic hexapod motion, enhanced hexapod motion and full motion. Pilot performance was highest for the enhanced hexapod and full motion configurations in both roll and pitch, and the lowest without motion. In the roll axis, the pilot position gain did not significantly change throughout the stall task, but was the lowest for the condition with no motion. The pilot roll velocity gain was significantly different between motion conditions, the largest difference being found close to the stall point. The enhanced hexapod motion condition had the highest pilot roll velocity gain. In the pitch axis, the pilot position gain was significantly different between time segments but not between motion conditions. The pilot pitch velocity gain was highest for the full motion condition and increased close to the stall point, but did not change significantly for the other motion conditions. Overall, pilot control behavior under enhanced hexapod motion was most similar to that under full aircraft motion. This indicates that motion cueing for stall recovery training on hexapod simulators might be improved by using the principles behind the enhanced hexapod motion configuration.

manual control↗
NASA NTRS2020

Evaluation of Low Cost, User-Centered Alerting Devices for the Mitigation of Flight Crew Spatial Disorientation

The National Aeronautics and Space Administration (NASA) is conducting research into technologies which have the potential to reduce flight crew Spatial Disorientation (SD). While flight deck technology has advanced rapidly over the past fifty (50) years, the reported occurrences of flight crew SD have not decreased. The Cost-Effective Devices for Alerting Research (CEDAR) effort has focused on the identification and development of low cost, user-centered alerting solutions for the purpose of mitigating the occurrence of flight crew SD. This effort seeks to evaluate both existing technologies as well as new and emerging technologies which have a viable path to implementation in commercial aviation within the next five (5) years. This research is intended to develop a proof-of-concept for real-time SD mitigation which could eventually be utilized to improve safety in future air transport operations. NASA has partnered with the United States Naval Aeromedical Research Unit in Dayton, OH (NAMRU-D) to conduct flight crew SD research utilizing their Disorientation Research Device (DRD), dubbed “The Kraken”. This high-tech simulator features never-before-seen capabilities for side-by-side commercial aviation flight crew SD research, and is capable of re-creating the forces necessary to induce SD illusions in a safe and repeatable manner. Prototype SD mitigation solutions were incorporated into this simulator for scenario-based testing and evaluation using airline pilots within a contextually representative operational environment. SD mitigation technology prototypes designed to provide haptic feedback for both alerting and guidance, as well as innovative visual and aural alerting displays were evaluated. In December 2014, as a result of analyzing eighteen (18) loss-of-control events, the Commercial Aviation Safety Team (CAST) recommended research into flight deck technologies that have potential to mitigate the problems and contributing factors that lead to flight crew loss of airplane state awareness (ASA) and conditions likely to produce SD. The aviation community (government, industry and academia) have been charged with conducting research into cost-effective, user-centered flight deck alerting systems to alert flight crews; especially for the two conditions that produced SD (sub-threshold rolls and the somatogravic illusion). Somatogravic illusions are defined as illusions in which “there is a false perception of attitude on exposure to a force vector that differs in direction and/or magnitude from the normal gravitational force”. The sub-threshold roll illusion (aka the “leans” illusion) is a false sensation of roll attitude. A prolonged roll of less than two degrees becomes physiologically imperceptible to the pilot, and can lead to an incorrect perception of aircraft orientation. The sub-threshold roll illusion forms the entry point for the “graveyard spiral”, a maneuver in which the pilot’s corrective action (based on their false perception of aircraft orientation) causes the aircraft to spiral down into the ground. In both of these SD illusions, it is when the pilot attempts to correct the aircraft’s attitude (based on a false perception of its state) that problems arise, sometimes with lethal consequences.

Ronald J Daiker↗
DOE OSTI2019

Silica Development For Sidewall Compounds

Tire tread is the single largest contributor to tire rolling resistance. Because of this, most developments to improve tire rolling resistance have focused on the incorporation of precipitated silicas into the tread compounds. However, still approximately 50% of the tire rolling resistance is attributed to the energy dissipation of non-tread components. The next largest contributor to rolling resistance after the tread is the sidewall, which contributes to about 20% of the tire rolling resistance. For this reason, the sidewall is an excellent candidate to achieve additional fuel efficiency improvements by taking advantage of the known reduction in hysteresis obtained when using silica in place of carbon black. The sidewall is a compound rich in natural rubber which needs to have good weathering, tear, abrasion, fatigue, and ozone-induced cracking resistance. Hysteresis improvements cannot be achieved at the expense of resistance to these degradative forces. Initial studies showed that treated silica can deliver reduced hysteresis, but the impact on other key performance properties required further investigation. Results are presented here showing the effect of partially replacing carbon black with treated silica in a sidewall model formulation. Emphasis is placed in reducing hysteresis while maintaining other performance properties.

Dos Santos Freire, Lucas↗
DOE OSTI2022

Multichannel pumps and applications of same

A push-pull micropump includes one or more pairs of channels configured to transfer one or more fluids, each channel pair having an aspiration channel and an injection channel; and an actuator configured to engage the one or more pairs of channels, wherein the actuator comprises a plurality of rolling members and a driving member configured such that when the driving member rotates, the plurality of rolling members rolls along the one or more pairs of channels to cause individually the one or more fluids to transfer through each channel pair simultaneously at different flowrates or the same flowrate, depending upon actuated lengths of the aspiration and injection channels of each channel pair, wherein an actuated length of a channel is defined by a length of the channel along which the plurality of rolling members rolls during a full rotation of the driving member.

Wikswo, John P.↗
DOE OSTI2021

Collaboration on SBIR/TTO Phase II Project for Optical QC Device and Collaboration on SBIR/TTO Phase II-b Project for Advanced Quality Inspection Device Development: Cooperative Research and Development CRADA Number CRD-16-00652 (Final Report)

The overall goal of this program is to develop and commercialize a turnkey quality control solution for the entire PEM fuel cell manufacturing process including membrane, gas diffusion layers, catalyst, and assembled systems. This quality control solution is unique to each customer’s specific needs but includes a suite of in-line quality control systems for roll-to-roll manufacturing that can target thin, transparent membrane as well as opaque membrane, catalyst, and GDLs. The Phase II developed the CPNUVV system for thin, transparent membrane that operates using polarized filters to enhance defect resolution and determine thickness. However, PEM material manufacturers want a complete, turnkey solution for all components of the PEM fuel cell. In the Phase IIB, Mainstream will partner with NREL, and transition reflectance technology NREL developed (US Patent 9,234,843) to operate in real-time on a web-line to develop a total solution to PEM quality control. The device will identify and mark defects as well as monitor materials thickness in real-time to improve line efficiency and to reduce waste. The research performed at NREL under this CRADA increases the basis of knowledge about optical inspection methods, how they perform with regards to fuel cell component materials, and how they can be implemented in in-line, real-time configurations to provide quality inspection for roll-to-roll (R2R) manufacturing. Methods explored were found to be sensitive to catalyst loading in electrodes on both membrane and gas diffusion media substrates and to membrane thickness, across a broad range of thickness. The latter capability is novel and now patented and provides a previously unstudied and undemonstrated capability for R2R manufacturing of membranes.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2023

High Throughput Laser Processing for Enhanced Battery Performance and Manufacturing

For widespread adoption of electric vehicles, lithium-ion batteries (LiBs) need to achieve energy densities of >275 Wh/kg, cell costs less than $100/kWh, and charge to more than 80% capacity within 15 minutes. Recently, it has been shown that introducing a secondary pore network in thick battery electrodes enables higher extracted capacity without a severe reduction in charge/discharge rate performance. Secondary pore networks consisting of ordered arrays of microstructures reduce tortuosity of Li+-ion transport deep into the thick electrodes, diminishing detrimental concentration gradients within the cell. Ultrafast (femtosecond)-pulsed laser ablation is a promising method to introduce such micro pores or channels in thick battery electrodes as it allows for precise control of pattern geometries, results in minimal damage to the electrode, and can be introduced into existing roll-to-roll electrode manufacturing lines. We have explored laser patterning to create secondary pore networks in a variety of battery electrode materials for both anode and cathode applications and characterized the laser-material interaction parameters. In addition, advanced materials characterization techniques (SEM-EDS, XRD) were used to explore whether ultrafast laser ablation affects the remaining electrode materials' morphology and structure. Furthermore, we have translated lab-scale laser ablation to high-throughput roll-to-roll processing at industrially relevant scales. Finally, we worked with Argonne National Laboratory, developers of the battery cost-analysis package BatPac, to estimate the additional manufacturing costs (CapEx and OpEx) for incorporation of laser-ablation processing to current battery electrode manufacturing. We estimate that ultrafast laser processing will add only -$1kWh, which for considerable improvements in cell performance, creates a compelling case for industry adoption.

battery↗
DOE OSTI2018

Correlation Between Structure and Properties of Low-Carbon Cu-Ni-Mo-Ti-Nb Ultrahigh-Strength Steel

Low-carbon Cu-Ni-Mo-Ti-Nb steel having more than 1700 MPa tensile strength and good low-temperature impact toughness was successfully designed and processed for automobile, defence and structural applications. The steel was thermomechanical controlled processed at a different finish rolling temperatures (750-850 °C) and cooled at two different conditions: air cooling and water quenching. Evolutions of microstructure and precipitates were thoroughly characterised to understand the effect of different factors, such as steel composition, finish rolling temperature and cooling rate on the mechanical properties. The results indicate that the steel processed at 750 °C finish rolling temperature (FRT) followed by water quenching has exhibited superior tensile properties with a yield strength of 1034-1449 MPa, the tensile strength of 1598-1726 MPa and total elongation of 10-13%. Such an ultrahigh-strength level is primarily attributed to the combined effect of lower bainite dominated microstructure along with precipitation hardening. The satisfactory low-temperature toughness is promoted by low finish rolling temperature and higher amount of misorientation offered by the boundaries within the lower bainite.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Electron backscatter and X-ray diffraction studies on the deformation and annealing textures of austenitic stainless steel 310S

We studied the texture evolution of thermo-mechanically processed austenitic stainless steel 310S. This alloy was cold rolled up to 90% reduction in thickness and subsequently annealed at 1050 °C. At the early stages of deformation, strain-induced martensite was formed from deformed austenite. By increasing the deformation level, slip mechanism was found to be insufficient to accommodate higher deformation strains. Our results demonstrated that twinning is the dominant deformation mechanism at higher deformation levels. Results also showed that cold rolling in unidirectional and cross rolling modes results in Goss/Brass and Brass dominant textures in deformed samples, respectively. Similar texture components are observed after annealing. Thus, the annealing texture was greatly affected by texture of the deformed parent phase and martensite did not contribute as it showed an athermal reversion during annealing. Results also showed that when the fraction of martensite exceeds a critical point, its grain boundaries impeded the movement of austenite grain boundaries during annealing. As a result, recrystallization incubation time would increase. This caused an incomplete recrystallization of highly deformed samples, which led to a rational drop in the intensity of the texture components. - Highlights: •Thermo-mechanical processing through different cold rolling modes can induce different textures. •Martensite reversion is athermal during annealing. •Higher fraction of deformation-induced martensite can increase the annealing time required for complete recrystallization. •Annealing texture is mainly influenced by the deformation texture of austenite.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Elucidating the microscopic origin of electrochemical corrosion and electrical conductivity by lattice response to severe plastic deformation in Al-Mn-Si alloy

Highlights: • Al-Mn-Si specimens were underwent severe plastic deformation by CGP and cold-rolling and their combined routes. • Microscopical observations depicted particles' fragmentation and non-preferential distribution under heavy straining. • XRD analysis revealed dislocations annihilation and lattice swelling (d-spacing increase) due to dynamic recrystallization. • Polarization outputs disclosed direct correlation of corrosion behavior with dislocations density. • Four-point probe test proved that electrical conductivity was a function of lattice d-spacing. - Abstract: Al-Mn-Si specimens were underwent SPD by CGP, cold-rolling and their combined paths. Acquired OM and SEM micrographs revealed that random distribution of intermetallic precipitates beside their fragmentation under heavy imposed strains deteriorated particles’ influence on the electrochemical corrosion and inhibited pitting. Analysis of XRD patterns pointed out that post-rolling of CGPed sheets resulted in dynamic annihilation of dislocations and accordingly crystal lattice swelling (d-spacing increase) due to dynamic recrystallization. From polarization results, crystallites’ refinement along with density increment of sub-grain boundaries within structure as a consequence of SPD beside dislocation density enhancement accelerated corrosion. Outputs of four-point probe electrical conductivity examination indicated that apart from the employed processing, lattice compaction and atomic layers approach would limit the electrons’ mobility space and hence reduce the conductivity of material. In this regard, combined effects of CGP and rolling as employed dual-straining route on Al-Mn-Si alloy enhanced the electrical conductivity by d-spacing growth.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The influence of time dependent flight and maneuver velocities and elastic or viscoelastic flexibilities on aerodynamic and stability derivatives

The advent of new structural concepts employing composites in primary load carrying aerospace structures in UAVs, MAVs, Boeing 787s, Airbus A380s, etc., necessitates the inclusion of flexibility as well as viscoelasticity in static structural and aero-viscoelastic analyses. Differences and similarities between aeroelasticity and aero-viscoelasticity have been investigated in [2]. An investigation is undertaken as to the dependence and sensitivity of aerodynamic and stability derivatives to elastic and viscoelastic structural flexibility and as to time dependent flight and maneuver velocities. Longitudinal, lateral and directional stabilities are investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings one of the critical static parameters is the velocity at which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. The influence of the twin effects of viscoelastic and elastic materials and of variable flight velocities on longitudinal, lateral, directional and spin stabilities are also investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are here extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings the critical parameter is the velocity at which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. This paper reports on analytical analyses and simulations of the effects of flexibility and time dependent material properties (viscoelasticity) on aerodynamic derivatives and on lateral, longitudinal, directional and spin stability derivatives. Cases of both constant and variable flight and maneuver velocities are considered. Analytical results for maneuvers involving constant and time dependent rolling velocities are analyzed, discussed and evaluated. The relationships between rolling velocity p and aileron angular displacement β as well as control effectiveness are analyzed and discussed in detail for elastic and viscoelastic wings. Such analyses establish the roll effectiveness derivatives (∂[p(t)])/(V{sub ∞}∂β(t)) . Similar studies involving other stability and aerodynamic derivatives are also undertaken. The influence of the twin effects of viscoelastic and elastic materials and of variable flight, rolling, pitching and yawing velocities on longitudinal, lateral and directional are also investigated. Variable flight velocities, encountered during maneuvers, render the usually linear problem at constant velocities into a nonlinear one.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Designing Low Tortuosity Electrodes through Pattern Optimization for Fast-Charging

The development of fast-charging technologies is crucial for expediting the progress and promotion of electric vehicles. In addition to innovative material exploration, reduction in the tortuosity of electrodes is a favored strategy to enhance the fast-charging capability of lithium-ion batteries by optimizing the ion-transfer kinetics. To realize the industrialization of low-tortuosity electrodes, a facile, cost-effective, highly controlled, and high-output continuous additive manufacturing roll-to-roll screen printing technology is proposed to render customized vertical channels within electrodes. Extremely precise vertical channels are fabricated by applying the as-developed inks, using LiNi 0.6 Mn 0.2 Co 0.2 O 2 as the cathode material. Additionally, the relationship between the electrochemical properties and architecture of the channels, including the pattern, channel diameter, and edge distance between channels, is revealed. The optimized screen-printed electrode exhibited a seven-fold higher charge capacity (72 mAh g -1 ) at a current rate of 6 C and superior stability compared with that of the conventional bar-coated electrode (10 mAh g -1 , 6 C) at a mass loading of 10 mg cm -2 . Finally, this roll-to-roll additive manufacturing can potentially be applied to various active materials printing to reduce electrode tortuosity and enable fast charging in battery manufacturing.

42 ENGINEERING↗
DOE OSTI2020

Modeling Arctic boundary layer cloud streets at grey-zone resolutions

To better understand how model resolution affects the formation of Arctic boundary layer clouds, we investigated the influence of grid spacing on simulating cloud streets that occurred near Utqiagvik (formerly Barrow), Alaska on 2 May 2013 and were observed by the Moderate Resolution Imaging Spectroradiometer (MODIS). The Weather Research and Forecasting model was used to simulate the clouds using nested domains with increasingly fine resolution ranging from a horizontal grid spacing of 27 km in the boundary-layer-parameterized mesoscale domain to a grid spacing of 0.111 km in the large-eddy-permitting domain. We investigated the model-simulated mesoscale environment, horizontal and vertical cloud structures, boundary layer stability, and cloud properties, all of which were subsequently used to interpret the observed roll-cloud case. Increasing model resolution led to a transition from a more buoyant boundary layer to a more shear-driven turbulent boundary layer. The clouds were stratiform-like in the mesoscale domain, but as the model resolution increased, roll-like structures, aligned along the wind field, appeared with ever smaller wavelengths. A stronger vertical water vapor gradient occurred above the cloud layers with decreasing grid spacing. With fixed model grid spacing at 0.333 km, changing the model configuration from a boundary layer parameterization to a large-eddy-permitting scheme produced a more shear-driven and less unstable environment, a stronger vertical water vapor gradient below the cloud layers, and the wavelengths of the rolls decreased slightly. In this study, only the large-eddy-permitting simulation with gird spacing of 0.111 km was sufficient to model the observed roll clouds.

Lai, Hui-Wen↗
DOE OSTI2021

Investigation of main bearing operating conditions in a three-Point mount wind turbine drivetrain

Wear-related failures of spherical roller bearings in the main bearing position of three-point mount wind turbines have been higher than expected and can contribute to higher than anticipated operation-and-maintenance costs. In this paper, the operational conditions of such a main bearing—including measured axial displacement and velocity subject to the estimated axial loads—are described for an instrumented, commercial wind turbine. The field measurements suggest a maximum axial speed between the bearing rings that is less than 2 millimeters per second. It is estimated that the axial speed between the ring and rollers is approximately 25% of this value. When compared to a speed of rolling from approximately 200–352 millimeters per second, the measured axial sliding is therefore significantly less than 1% of the speed of rolling. Previous numerical studies of lubricant film formation in rolling contacts have shown that the effect of axial sliding starts to be noticeable only when this ratio exceeds 10%; therefore, the axial velocity represents only a small disturbance to the nominal pure rolling case, and the influence on oil film building can be neglected. A simple analytic model of the main bearing motion was also developed and demonstrated similar displacement and velocity characteristics.

17 WIND ENERGY↗
DOE OSTI2019

Effect of the Processing-Induced Morphology on the Mechanical Properties of Biodegradable Extruded Films Based on Poly(lactic acid) (PLA) Blends

Biodegradable films based on poly(lactic acid) blends were obtained by cast extrusion. Their tensile and fracture behavior was investigated and the effect of the processing conditions through the extrusion rolling speed on this behavior was analyzed. In uniaxial tensile tests, all films presented completely ductile behavior exhibiting a defined yield point, strain softening after this point and a plateau before fracture. Fracture behavior was determined through quasi-static fracture tests on deeply double edge notched tensile specimens. The film obtained at the lowest rolling speed exhibited completely ductile behavior hence, the Essential Work of Fracture methodology was applied to characterize its fracture. The film processed at intermediate rolling speed, on the other hand, presented ductile fracture or ductile instability depending on the ligament length and the film obtained with the highest rolling speed exhibited a transition regime fracture. In order to compare the fracture behavior of the different films, the J-integral at maximum load J{sub max} was adopted. Differences in the films fracture behavior were correlated to the processing-induced morphology.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Studies on Bio-acceptability of Thermo-Mechanically Processed Mg-4Li-0.5Ca Alloy and Its Microstructural Correlation

In this study, in vitro corrosion behavior of rolled Mg-4Li-0.5Ca (wt.%) alloy at three temperatures (250, 300 and 350 °C) with 75% reduction and subsequent short annealing at 200 °C for 10 min was systematically investigated. Microstructural evaluation, Mg{sub 2}Ca precipitation and defects like twins were characterized by an optical microscope, scanning electron microscope and x-ray diffraction. Micrographs reveal an increase in grain size and comparatively reduction in twins density population with an increase in hot rolling temperature and subsequent short annealing. In vitro corrosion tests like dynamic bio-corrosion immersion test, hydrogen evolution test and electrochemical linear polarization test were carried out in simulated body fluid. From in vitro corrosion tests, it is observed that the alloy rolled at 350 °C and subsequently short-annealed shows better bio-corrosion resistance than other hot-rolled and short-annealed alloys. This is due to low twins density and uniformly dispersed Mg{sub 2}Ca compound throughout the matrix.

36 MATERIALS SCIENCE↗