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At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

2012 SRNL-EM Vane Rheology Results

The vane method has been shown to be an effective tool in measuring the yield stress of both settled and mixed slurries in laboratory bench scale conditions in supporting assessments of both actual and simulant waste slurries. The vane has also been used to characterize dry powders and granular solids, the effect of non-cohesive solids with interstitial fluids and used as a guide to determine if slip is present in the geometries typically used to perform rheological flow curve measurements. The vane has been extensively characterized for measuring the shear strength in soils in both field and laboratory studies. The objectives for this task are: Fabricate vane instrument; Bench top testing to further characterize the effect of cohesive, non-cohesive, and blends of cohesive/non-cohesive simple simulants; Data from measurement of homogenized and settled bed of Kaolin sludge and assessment of the technology. In this document, the assessment using bench scale measurements of non-cohesive materials (beads) and cohesive materials (kaolin) is discussed. The non-cohesive materials include various size beads and the vane was assessed for depth and deaeration (or packing) via tapping measurements. For the cohesive (or non-Newtonian) materials, flow curves and yield stress measurements are performed using the vane and this data is compared to the traditional concentric cylinder flow curve measurement. Finally, a large scale vane was designed, fabricated, and tested with the cohesive (or non-Newtonian) materials to determine how a larger vane performs in measuring the yield stress and flow curve of settled cohesive solids.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Coiled Tube Gas Heaters For Nuclear Gas-Brayton Power Conversion

This project developed an alternative design for heat exchangers for application to heating supercritical carbon dioxide (S-CO 2 ) or air for power conversion. We have identified an annular coiled tube bundle configuration–where hot sodium enters tubes from multiple vertical inlet manifold pipes, flows in a spiral pattern radially inward and downward, and then exits into an equal number of vertical outlet manifold pipes–as a potentially attractive option. The S-CO 2 gas or air flows radially outward through the tube bundle. Coiled tube gas heaters (CTGHs) are expected to have excellent thermal shock, long-term thermal creep, in-service inspection, and reparability characteristics, compared to alternative options. CTGHs have significant commonality with modern nuclear steam generators. Extensive experience exists with the design, manufacture, operation, in-service inspection and maintenance of nuclear steam generators. The U.S. Nuclear Regulatory Commission also has extensive experience with regulatory guidance documented in NUREG 0800. CTGHs leverage this experience and manufacturing capability. The most important difference between steam generators and gas-Brayton cycles such as the S-CO 2 cycle is that the heat exchangers must operate with counter flow with high effectiveness to minimize the pinch-point temperature difference between the hot liquid coolant and the heated gas. S-CO 2 -cycle gas heaters also operate at sufficiently elevated temperatures that time dependent creep is important and allowable stresses are relatively low. Designing heat exchangers to operate in this regime requires configurations that minimize stresses and stress concentrations. The cylindrical tubes and cylindrical manifold pipes used in CTGHs are particularly effective geometries. The first major goal of this research project was to develop and experimentally validate a detailed, 3-D multi-phase (gas-solid-liquid) heat transport model for CTGHs, using methods similar to earlier UCB multi-scale models for PCHEs, which will enable optimization of CTGH designs with respect to the number of manifold pipes, S-CO 2 and sodium circulating power, and other design parameters. CTGHs are relatively novel because the tubes loaded in compression as well as the manifold pipes which form the tube sheets. The second major goal of the experimental and modeling effort was to optimize the assembly and heat treatment of the tube-to-tubesheet joints, using a novel tapered joint configuration, and to develop diffusion-bonded joints with high shear strength and creep resistance, as has been done in other applications for tapered plugs. The project would also conduct creep testing of these tubesheet joints in pressurized furnaces under prototypical conditions of stress and temperature, however this was not feasible due to numerous hinderances. Detailed microstructural investigations was conducted on the diffusion bond interface, while the bond strength was evaluated by tensile testing. The mechanical testing quantified the overall strength of the bond and measured the pull out force as well as long term behavior, which complemented the microstructural analysis and gave a complete understanding of the diffusion bond.

30 DIRECT ENERGY CONVERSION↗
NASA NTRS1972

Weld-brazing - a new joining process

A joining process designated weld brazing which combines resistance spot welding and brazing has been developed. Resistance spot welding is used to position and align the parts as well as to establish a suitable faying surface gap for brazing. Fabrication is then completed by capillary flow of the braze alloy into the joint. The process has been used successfully to fabricate Ti-6Al-4V titanium alloy joints using 3003 aluminum braze alloy. Test results obtained on single overlap and hat-stiffened structural specimens show that weld brazed joints are superior in tensile shear, stress rupture, fatigue, and buckling than joint fabricated by spotwelding or brazing. Another attractive feature of the process is that the brazed joints is hermetically sealed by the braze material.

Bales, T. T.↗
NASA NTRS1976

Results of investigations conducted in the LaRC 4-foot unitary plan wind tunnel leg no. 1 using the 0.010-scale 72-OTS model of the space shuttle integrated vehicle (IA94A)

Aero-loads investigations were conducted on the updated configuration-5 space shuttle launch vehicle at Mach numbers 2.50, 3.50, and 4.50. Six-component vehicle forces and moments, base and sting-cavity pressures, elevon hinge moments, wing-root bending and torsion moments, and normal shear force data were obtained. Full simulation of updated vehicle protuberances and attach hardware was employed. Various elevon deflection angles were tested, with two different forward orbiter-to-external-tank attach-strut configurations. The entire vehicle model 72-OTS was supported by means of a balance mounted in the orbiter through its base and suspended from an appropriate sting for the specific tunnel.

Nichols, M. E.↗
NASA NTRS1979

Thermal stress analysis of ceramic gas-path seal components for aircraft turbines

Stress and temperature distributions were evaluated numerically for a blade-tip seal system proposed for gas turbine applications. The seal consists of an abradable ceramic layer on metallic backing with intermediate layers between the ceramic layer and metal substrate. The most severe stresses in the seal, as far as failure is concerned, are tensile stresses at the top of the ceramic layer and shear and normal stresses at the layer interfaces. All these stresses reach their maximum values during the deceleration phase of a test engine cycle. A parametric study was carried out to evaluate the influence of various design parameters on these critical stress values. The influences of material properties and geometric parameters of the ceramic, intermediate, and backing layers were investigated. After the parametric study was completed, a seal system was designed which incorporated materials with beneficial elastic and thermal properties in each layer of the seal. An analysis of the proposed seal design shows an appreciable decrease in the magnitude of the maximum critical stresses over those obtained with earlier configurations.

Kennedy, F. E.↗
NASA NTRS1980

An airborne Doppler Lidar

A pulsed CO2 Doppler Lidar, developed for airborne measurements of atmospheric wind fields, is described. In-flight tests show that the device can be successfully utilized in the detection and measurement of mountain-wave turbulence and wind shear, and in the generation of time histories of wind-field variations in smooth flight. This Lidar is in the process of being configured for measurement of the atmospheric flow fields surrounding severe convective storms.

Dimarzio, C. A.↗
NASA NTRS1981

Pulsed Doppler lidar for the detection of turbulence in clear air

A pulsed C02 Doppler lidar system is described and demonstration tests in ground-based and airborne flight operations are discussed. As a ground-based system, it can detect wind shears in thunderstorm gust fronts to a range of 6 km. When in the airborne configuration, the lidar can detect clear air turbulence in advance of the aircraft encountering clear air turbulence. The data provided by the lidar included turbulence location and intensity with intensity being indicated by the measured spectral width which is proportional to the wind gust velocity.

Weaver, E. A.↗
NASA NTRS1983

The effect of matrix properties and fiber properties on impact failure mechanics

The low-velocity impact problem in graphite/epoxy composite sheets must be solved before large amounts of that material can be used in commercial aircraft. Many of the low-velocity impacts that affect aircraft parts occur during normal ground operations and maintenance. Service equipment and tools have masses above 1 kg, and at velocities of less than 3 m/s can impact structural parts with energies higher than composites can endure without degradation of stiffness or strength. Simple solutions were developed for large-mass, low-velocity impacts which can be modeled as quasi-static events. Static test data and impact data show that the fiber properties control the impact energy which can be absorbed before penetration. Matrix shear strength and peel resistance control the extent of delamination. Comparison of results from tough matrix and brittle matrix composites show that although tough matrices reduce the extent of delamination, they lead to more fiber damage in the contact area.

Elber, W.↗
NASA NTRS1983

Low velocity transverse impact behavior of 8-ply, graphite-epoxy laminates

This work discusses the behavior of eight-ply, quasi-isotropic, graphite epoxy laminates subjected to low velocity transverse impact loading. Large deflection theory of plates was used to predict the load-deflection characteristics during the impact event. The impact model considered that the indentation, flexural and shear stiffnesses could be represented by three-equivalent springs in series. The analysis of static and dynamic impact loading test-data concluded that the membrane parameter, beta, used in flexural stiffness relation was proportional to the square of the coefficient of restitution, e, of the impactor. Use of beta=0.443 e-squared was made in load-deflection relations to consider the drop in plate stiffness due to delamination. The results of impact tests up to impact velocity 5.3 m/sec. were found in close agreement with the predictions.

Lal, K. M.↗
NASA NTRS1986

One-Piece Force-Transducer Body

Rugged unit designed to operate in severe environment. Forcetransducer body designed for measurement of loads on specimens tested in hydrogen gas at temperatures up to 2,000 degree F (1,090 degree C). Body has symmetrical radial-shear-beam configuration and machined in one piece from bar stock.

Meyer, R. A.↗
NASA NTRS1991

Micromechanics of fatigue in woven and stitched composites

The goal is to determine how microstructural factors, especially the architecture of microstructural factors, control fatigue damage in 3D reinforced polymer composites. Test materials were fabricated from various preforms, including stitched quasi-isotropic laminates, and through-the-thickness angle interlock, layer-to-layer angle interlock, and through-the-thickness stitching effect weaves. Preforms were impregnated with a tough resin by a special vacuum infiltration method. Most tests are being performed in uniaxial compression/compression loading. In all cases to date, failure has occurred not by delamination, but by shear failure, which occurs suddenly rather than by gradual macroscopic crack growth. Some theoretical aspects of bridging are also examined.

Cox, B. N.↗
NASA NTRS1994

Buckling of composite beams (CDDF)

Presented are the results of an investigation of the twisting/warping deformation occurring in open-section composite beams. A series of C and L channels were manufactured using both hand layup and the innovative 'hot-drape forming' techniques. A transverse tip load was applied at the free end of the cantilevered open-section beams. The test setup allowed the tip load to be applied at various locations along the plane of and at the beam's shear center. Charts are included in this report depicting various angles of ply layups, loads applied, and load application points. A major verification resulting from this study is that the shear center of an open section composite beam can be altered, if not completely controlled, through laminate layup. Also, it was observed that the choice of the material system does not have an effect on the amount of deformation, as expected, and the material affects the location of an unsymmetric open section composite beam's true shear center. The results from this study have provided a foundation for further investigation into the apparent shifting of the shear center location in open-section composite beams.

Thompson, P.↗
NASA NTRS1995

Materials research for High Speed Civil Transport and generic hypersonics: Adhesive durability

This report covers a portion of an ongoing investigation of the durability of adhesives for the High Speed Civil Transport (HSCT) program. Candidate HSCT adhesives need to possess the high-temperature capability required for supersonic flight. This program was designed to initiate an understanding of the behavior of candidate HSCT materials when subjected to combined mechanical and thermal loads. Two adhesives (K3A and FM57) and two adherends (IM7/K3B polymeric composite and the titanium alloy Ti-6Al-4V) were used to fabricate thick adherend lap shear specimens. Due to processing problems, only the FM57/titanium bonds could be fabricated successfully. These are currently undergoing thermomechanical fatigue (TMF) testing. There is an acute need for an adhesive to secondarily bond polymeric composite adherends or, alternately, polymeric composites that remain stable at the processing temperatures of today's adhesives.

Allen, Mark R.↗
NASA NTRS1998

Experimental Study of a Nozzle Using Fluidic Counterflow for Thrust Vectoring

A static experimental investigation of a counterflow thrust vectoring nozzle concept was performed. The study was conducted in the NASA Langley Research Center Jet Exit Test Facility. Internal performance characteristics were defined over a nozzle pressure ratio (jet total to ambient) range of 3.5 to 10.0. The effects of suction collar geometry and suction slot height on nozzle performance were examined. In the counterflow concept, thrust vectoring is achieved by applying a vacuum to a slot adjacent to a primary jet that is shrouded by a suction collar. Two flow phenomena work to vector the primary jet depending upon the test conditions and configuration. In one case, the vacuum source creates a secondary reverse flowing stream near the primary jet. The shear layers between the two counterflowing streams mix and entrain mass from the surrounding fluid. The presence of the collar inhibits mass entrainment and the flow near the collar accelerates, causing a drop in pressure on the collar. The second case works similarly except that the vacuum is not powerful enough to create a counterflowing stream and instead a coflowing stream is present. The primary jet is vectored if suction is applied asymmetrically on the top or bottom of the jet.

Flamm, Jeffrey D.↗
NASA NTRS2018

Active Flow Control for Trailing Edge Flap Separation

Active flow control (AFC) in the form of sweeping jet (SWJ) excitation and discrete steady jet excitation is used to control the flow separation on an NACA 0015 semispan wing with a deflected, simple-hinged, trailing edge flap. This geometry has been the focus of several recent publications that investigated methods to improve the efficiency of sweeping jet actuators. In the current study, the interaction of the AFC excitation with the separated flowfields present at several flap deflection angles was examined. Previous studies with this model have been limited to a maximum flap deflection angle of 40°. The flap deflection range was extended to 60! because systems studies have indicated that a high-lift system with simple-hinged flaps may require larger flap deflections than the Fowler flaps found on most high-lift systems. The results obtained at flap deflection angles of 20°, 40°, and 60° are presented and compared. Force and moment data, Particle Image Velocimetry (PIV) data, and steady and unsteady surface pressure data are used to describe the flowfield with and without AFC. With a flap deflection of 60°, increasing the SWJ actuator momentum at the flap shoulder increased lift due to an increase in circulation but did not completely eliminate the recirculation region above the flap surface. AFC using the discrete steady jet actuators of this study increased lift as well but required more mass flow than the SWJ actuators and had a detrimental effect on lift at the highest mass flow level tested. PIV results showed that the angle between the excitation and the flap surface was not optimal for attaching the separated shear layer.

Melton, LaTunia Pack↗
NASA NTRS2019

Test and Analysis Correlation for Sandwich Composite Longitudinal Joint Specimens

The NASA Composite Technology for Exploration (CTE) project is tasked with evaluating methods to analyze and manufacture composite joints for potential use in block upgrades to the Space Launch System (SLS) launch-vehicle structures such as the Payload Attach Fitting (PAF). To perform this task, the CTE project has initiated test and analysis correlation studies for composite joints under various loading conditions. Herein, NASA-developed numerical models are correlated with the experimental results from a series of tension tests. Pretest strain results matched the far-field test data well, but did not capture the nonlinear response in the vicinity of the joint. A refined pretest analytical model was modified to represent progressive failure of the specimens at failure locations observed during the experimental tests. The nonlinear strain response from this progressive failure model predicted the delamination failure load within 15% of the test data, but underpredicted the nonlinearity of the strain response. Further study of composite material models that account for the nonlinear shear response of fabric composites is recommended for the composite joint structures considered in this paper.

Mason, Brian H.↗
DOE OSTI2020

Discrepancy in the Critical State Void Ratio of Poorly Graded Sand due to Shear Strain Localization

The critical state (CS) concept is a theoretical framework that models the constitutive behavior of soils, including sand and other granular materials. It supports the notion of a unique postfailure state, where the soil ultimately experiences continuous shearing with no change in the plastic volumetric strain. However, the published literature has frequently noted the nonconvergence of sand specimens with different initial densities to a unique CS in the compression plane due to many factors such as specimen fabric, particle morphology, breakage, and grain size distribution. This paper examines the CS for poorly graded (uniform) glass beads and 3 different types of silica sands using 50 conventional triaxial compression (CTC) experiments, 12 oedometer tests, and in situ synchrotron microcomputed tomography (SMT) scans for 10 CTC experiments. The results of the 50 CTC experiments revealed a diffused CS zone in the compression plane, which was further examined using the in situ SMT scans. A thorough three-dimensional image analysis of the SMT scans accurately quantified the evolution of the local void ratio (elocal) versus axial compression within zones of intensive shearing toward the center of the specimen. The evolution of the void ratio was also measured using the entire volume of the specimen (eglobal). At the CS, the elocal/eglobal ratio was assessed to be ~1.25 when a single shear band developed within the scanned specimens and ~1.1-1.15 for specimens that failed via external bulging that was internally manifested by the development of multiple shear bands. This finding suggests that the CS zone in the compression plane can be attributed to the common wrong consideration of eglobal evolution in lieu of elocal within the developing shear bands. Furthermore, the lack of shear band development in uniaxial compression has made the results of the oedometer test reliable in quantifying the CS parameters in the compression plane.

58 GEOSCIENCES↗
DOE OSTI2020

Dark Energy Survey Year 3 results: cosmology with moments of weak lensing mass maps – validation on simulations

ABSTRACT We present a simulated cosmology analysis using the second and third moments of the weak lensing mass (convergence) maps. The second moment, or variances, of the convergence as a function of smoothing scale contains information similar to standard shear two-point statistics. The third moment, or the skewness, contains additional non-Gaussian information. The analysis is geared towards the third year (Y3) data from the Dark Energy Survey (DES), but the methodology can be applied to other weak lensing data sets. We present the formalism for obtaining the convergence maps from the measured shear and for obtaining the second and third moments of these maps given partial sky coverage. We estimate the covariance matrix from a large suite of numerical simulations. We test our pipeline through a simulated likelihood analyses varying 5 cosmological parameters and 10 nuisance parameters and identify the scales where systematic or modelling uncertainties are not expected to affect the cosmological analysis. Our simulated likelihood analysis shows that the combination of second and third moments provides a 1.5 per cent constraint on S8 ≡ σ8(Ωm/0.3)0.5 for DES Year 3 data. This is 20 per cent better than an analysis using a simulated DES Y3 shear two-point statistics, owing to the non-Gaussian information captured by the inclusion of higher order statistics. This paper validates our methodology for constraining cosmology with DES Year 3 data, which will be presented in a subsequent paper.

79 ASTRONOMY AND ASTROPHYSICS↗