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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Effects of strain rate on delamination fracture toughness of graphite/epoxy

The objective of this paper is to evaluate various experimental techniques and analysis methods for the characterization of interlaminar fracture toughness, and to determine the effects of strain rate on that property for a graphite/epoxy composite. Mode I interlaminar fracture was investigated by means of a double-cantilever beam (DCB) specimen for AS-4/3501-6 graphite/epoxy. Hinged tabs were used to insure unrestrained rotation at the free ends. Specimens were loaded at quasi-static deflection rates of up to 8.5 mm/s corresponding to crack extension rates of over 51 mm/s. Crack extension was monitored by means of strain gages mounted on the surface of the specimen, or a conductive-paint circuit attached to the edge of the DCB specimen. Continuous records were obtained of load, deflection, and crack extension for determination of the strain energy release rate. The latter was expressed as a power law of the crack extension velocity. Results indicate that the strain energy release rate increases with crack velocity by up to 28 percent for the range of rates considered.

Daniel, I. M.↗
DOE OSTI2026

Multi-physics Preconditioning for Thermally Activated Batteries

Thermal batteries, also known as molten-salt batteries, are single-use reserve power systems activated by pyrotechnic heat generation, which transitions the solid electrolyte into a molten state. The simulation of these batteries relies on multiphysics modeling to evaluate performance and behavior under various conditions. This paper presents advancements in scalable preconditioning strategies for the Thermally Activated Battery Simulator (TABS) tool, enabling efficient solutions to the coupled electrochemical systems that dominate computational costs in thermal battery simulations. We propose a hierarchical block Gauss-Seidel preconditioner implemented through the Teko package in Trilinos, which effectively addresses the challenges posed by tightly coupled physics, including charge transport, porous flow, and species diffusion. The preconditioner leverages scalable subblock solvers, including smoothed aggregation algebraic multigrid (SA-AMG) methods and domain-decomposition techniques, to achieve robust convergence and parallel scalability. Strong and weak scaling studies demonstrate the solver’s ability to handle problem sizes up to 51.3 million degrees of freedom on 2048 processors, achieving near sub-second setup and solve times for the end-to-end electrochemical solve. These advancements significantly improve the computational efficiency and turnaround time of thermal battery simulations, paving the way for higher-resolution models and enabling the transition from 2D axisymmetric to full 3D simulations.

25 ENERGY STORAGE↗
NASA NTRS1979

Temperature Measurement Aid

NASA's Ames Research Center has designed a simple but medically important device--one which holds temperature probes, called thermistors, to a person's skin without affecting the characteristics of the skin segment being measured. The device improves the accuracy of skin surface temperature measurements, valuable data in health evaluation. The need for such a device was recognized in the course of life science experiments at Ames. In earlier methods, the sensing head of the temperature probe was affixed to the patient's skin by tape or elastic bands. This created a heat variance which altered skin temperature readings. The Ames-developed thermistor holder is a plastic ring with tab extensions, shown in the upper photo on the chest, arm and leg of the patient undergoing examination. The ring holds the sensing head of the temperature probe and provides firm, constant pressure between the skin and the probe. The tabs help stabilize the ring and provide attachment points for the fastening tape or bands, which do not directly touch the sensor. With this new tool, it is possible to determine more accurately the physiological effects of strenuous exercise, particularly on the treadmill. The holder is commercially available from Yellow Springs Instrument Company, Inc., Yellow Springs, Ohio, which is producing the device under a NASA patent license.

Source record↗
NASA NTRS2005

Mechanically Biased, Hinged Pairs of Piezoelectric Benders

The upper part of the figure depicts an actuator that comprises two mechanically biased piezoelectric benders hinged together at their ends and equipped with tabs at their mid-length points for attachment to the relatively moving objects that are to be actuated. In the example of the figure, the attachment tabs are labeled to indicate that the actuator is used to drive a pump piston relative to a base plate. Actuators of this type could be used to drive low-power, small-volume pumps in consumer, medical, and aerospace applications, and to generate and measure linear displacements in such robotic applications as teleoperation and tactile feedback. Each bender is a bimorph a unitary plate that comprises an upper and a lower piezoelectric layer plus electrode layers. Benders may also be made of several layers arranged to produce the same effect at the lower operating voltages. As stated above, each bender is mechanically biased; it is fabricated to have a small permanent curvature (the bias curvature) in the absence of applied voltage. As on other bimorphs, the electrical connections on each bender are arranged so that an applied voltage of suitable polarity causes the upper layer to expand and the lower layer to contract. In this case, the net effect of applying the voltage is that the plate becomes more concave as viewed from below. Conversely, an applied voltage of the opposite polarity causes the plate to become less concave as viewed from below. The benders in a hinged pair are oriented with their bias curvatures concave inward, so that there is a bias distance between the attachment tabs. The two benders are connected electrically in parallel, with their connection polarities chosen so that an applied voltage of one polarity causes both benders to become more convex inward (more bent), while an applied voltage of the opposite polarity causes both benders to become less convex inward (less bent). An increase or decrease in bend is accompanied by an increase or decrease in distance between the attachment tabs; this increase or decrease is the linear displacement desired for actuation. Because the displacement can be either positive or negative relative to the bias distance, depending on the polarity of the applied voltage, the overall stroke achievable for a given magnitude of applied voltage is double the stroke achievable in the absence of mechanical bias. Each hinged pair can be regarded as a unit cell that can serve as a building block for a larger actuator: Multiple unit cells can be stacked (mechanically connected in series), as shown in the lower part of the figure, and electrically connected in parallel to multiply the overall stroke achievable at a given applied voltage.

Sager, Frank E.↗
NASA NTRS1985

Simulation study of an automatic trim system for reducing the control forces on a light twin after an engine failure

An automatic trim system for reducing the control forces after an engine failure on a light twin has been investigated on the Langley General Aviation Simulator. The system schedules open-loop trim tab deflections as a function of differential propeller slipstream dynamic pressure and freestream dynamic pressure. The system is described and the airplane-system static and dynamic characteristics are documented. Three NASA research pilots evaluated the effectiveness of the system for takeoff and landing maneuvers. A variety of off-nominal system characteristics were studied. The system was judged to be generally beneficial, providing a 2 to 3 point improvement in pilot rating for the tasks used in the evaluations.

Stewart, E. C.↗
NASA NTRS1996

U-Groove aluminum weld strength improvement

Though butt-welds are among the most preferred joining methods in aerostructures, their strength dependence on inelastic mechanics is generally the least understood. This study investigated experimental strain distributions across a thick aluminum U-grooved weld and identified two weld process considerations for improving the multipass weld strength. The extreme thermal expansion and contraction gradient of the fusion heat input across the groove tab thickness produces severe peaking, which induces bending under uniaxial loading. The filler strain-hardening decreased with increasing filler pass sequence, producing the weakest welds on the last pass side. Current welding schedules unknowingly compound these effects which reduce the weld strength. A depeaking index model was developed to select filler pass thicknesses, pass numbers, and sequences to improve depeaking in the welding process. The intent is to combine the strongest weld pass side with the peaking induced bending tension to provide a more uniform stress and stronger weld under axial tensile loading.

Verderaime, V.↗
NASA NTRS1995

U-groove aluminum weld strength improvement

Though butt-welds are among the most preferred joining methods in aerostructures, their strength dependence on inelastic mechanics is generally the least understood. This study investigated experimental strain distributions across a thick aluminum U-grooved weld and identified two weld process considerations for improving the multipass weld strength. The extreme thermal expansion and contraction gradient of the fusion heat input across the groove tab thickness produces severe peaking which induces bending under uniaxial loading. The filler strain-hardening deceased with increasing filler pass sequence, producing the weakest welds on the last pass side. Current welding schedules unknowingly compound these effects which reduce the weld strength. A de-peaking index model was developed to select filler pass thicknesses, pass numbers, and sequences to improve de-peaking in the welding process. Intent is to combine the strongest weld pass side with the peaking induced bending tension to provide a more uniform stress and stronger weld under axial tensile loading.

Verderaime, V.↗
NASA NTRS1989

Emergency egress fixed rocket package

A method of effecting the in-flight departure of an astronaut from a shuttle craft, and apparatus is presented. A plurality of removeable compartment covers are provided, behind which rocket assemblies are stowed. To actuate the system, the astronaut pulls off a tab from one of the compartments which exposes a cannister having a lanyard with a hook. The lanyard extends around a spring biased sleeve with a safety lever preventing rocket ignition until the hook is moved by the astronaut. Upward movement of the hook allows the trigger mechanism to actuate the system resulting in the rods projecting out of the hatch. When the lanyard becomes taut, a lanyard elongation detector transmits a signal to the firing mechanisms to fire the rocket.

Allen, Margaret A.↗
NASA NTRS1945

Wind-Tunnel Tests of a 1/6-Scale Model of Republic XF-12 Vertical Tail Incorporating a De-Icing Air Duct

A 1/6-scale model of the Republic XF-12 vertical tail with stub fuselage, stub horizontal tail, and a de-icing air duct was tested in the Langley stability tunnel. The investigation consisted of a study of the effects of the duct, with and without air flow, on the aerodynamic characteristics of the model. The model tested was a revision of a model previously tested in the Langley stability tunnel. The revised model differed from the original model in that it incorporated a de-icing air duct, included a dorsal fin, and had a larger stub fuselage. A comparison of data obtained form tests of the original and revised models was made. The results of the investigation indicated that the air duct had very little effect on the aerodynamic characteristics of the model. A small change occurred in the variation of rudder hinge-moment coefficient with angle of attack but it is believed that this change can be corrected by a properly applied spring tab.

MacLachlan, Robert↗
DOE OSTI2020

A 150-kW 99% Efficient All-Silicon-Carbide Triple-Active-Bridge Converter for Solar-Plus-Storage Systems

Solar-plus-storage systems could effectively mitigate the uncertainties of the photovoltaic (PV) generation and improve system reliability by adding an integrated battery energy storage system. As a three-port bidirectional isolated dc–dc converter with soft-switching capability, the triple-active-bridge (TAB) converter inherently matches the requirements of the solar-plus-storage system. However, challenges still remain in the TAB converter design to further improve system efficiency. In this article, the detailed design, implementation, and demonstration for a silicon carbide (SiC) 150-kW TAB converter are presented. Starting from a brief review of the TAB converter, the modulation scheme, power characteristics, and soft-switching region are analyzed. Then, the detailed design of the H-bridge converter building block is given. Here, to improve the system efficiency, a comprehensive characterization of the SiC gate driver with various external gate resistances is performed to address tradeoffs between switching loss and voltage overshoot during transients, as well as the thermal performance of the H-bridge building block. In addition, the design and characterization of the 20-kHz three-port transformer are also given. Comprehensive experimental studies are conducted on a full-power prototype to verify the proposed design. With a measured 99.1% peak efficiency, the proposed TAB converter can fulfill the requirements for solar-plus-storage applications.

14 SOLAR ENERGY↗
NASA NTRS1987

Rate effects on delamiantion fracture toughness of a toughened graphite/epoxy

The objective of this study was to determine the effects of loading rate on interlaminar fracture toughness of T300/F-185 graphite/epoxy composite, having an elastomer-modified epoxy resin matrix. Mode I interlaminar fracture was investigated by means of uniform width and width-tapered double cantilever beam (DCB) specimens. Hinged tabs were used to insure unrestrained rotation at the free ends. Specimens were loaded at quasi-static deflection rates of up to 8.5 mm/s corresponding to crack extension rates of up to 21 mm/s. Crack extension was monitored by means of strain gages mounted on the surface of the specimen. Continuous records were obtained of load, deflection, and crack extension for determination of the strain energy release rate. The latter was calculated by means of the area method and beam analysis method, and expressed as a power law of the crack extension velocity. Results indicate that the strain energy release rate decreases with crack velocity by over 20 percent over three decades of crack velocity.

Daniel, Isaac M.↗
NASA NTRS1991

Calorimetry of 25 Ah lithium/thionyl chloride cells

Heat flow measurements of 25-Ah lithium thionyl chloride cells provided a method to calculate an effective thermal potential, E(TP) of 3.907 V. The calculation is useful to determine specific heat generation of this cell chemistry and design. The E(TP) value includes heat generation by electrochemical cell reactions, competitive chemical reactions, and resistance heating at the tabs, connectors, and leads. Heat flow was measured while applying electrical loads to the cell in an isothermal calorimeter set at 0, 20, and 60 C.

Johnson, C. J.↗
NASA NTRS2012

Noise from a Jet Discharging Into a Duct and Its Suppression

The present study addresses unwanted high intensity noise sometimes encountered in engine test facilities. A simplified model-scale experiment is conducted for a circular jet discharging into a cylindrical duct. For the given configuration the unwanted noise is found to be primarily due to the duct resonance modes excited by the jet. When the "preferred mode". frequency of the jet matches a duct resonant frequency there can be a locked-in "super resonance". accompanied by a high intensity tone. However, even in the absence of a locked-in resonance, high levels of unwanted noise may occur due to the duct modes excited simply by broadband disturbances of the jet. Various methods for suppression of the noise are explored. Tabs placed on the ends of the duct are found ineffective; so are longitudinal fins placed inside the duct. A rod inserted perpendicular to the flow at different axial locations is also found ineffective; however, when there is a super resonance it is effective in suppressing the tone. By far the best suppression is achieved by a wire-mesh screen placed at the downstream end of the duct; placing it on the upstream end also works, however, there is some penalty at high frequencies due to impingement noise. The screen not only eliminates any super resonance but also the duct mode spectral peaks in the absence of such resonance. Apparently it works by dampening the velocity fluctuations at the pressure node and thereby weakening the resonance condition, for the simplified configuration under consideration.

Zaman, Khairul B. M. Q.↗
NASA NTRS1982

Compression fatigue behavior of composites in the presence of delaminations

Three different stacking sequences of a 64-ply layup were tested in an experimental investigation of the effect of idealized imbedded delaminations on the compression fatigue behavior of quasi-isotropic T300/5208 graphite-epoxy laminates. Postfailure examination of specimen cross sections revealed the absence of any fiber microbuckling, suggesting that the predominant failure mode was the propagation of imbedded delaminations in the tab region. One- and two-dimensional delaminations, respectively located across the entire width below the surface ply and buried one or four plies below the surface, were considered. A novel procedure employing minute, laser-drilled holes was successfully used in extending the application of diidobutane-enhaced radiography to buried delaminations.

Ramkumar, R. L.↗