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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Poisson’s ratio of eTPU molded bead foams in compression via in situ synchrotron X-ray microtomography

In situ synchrotron X-ray microtomography was used to characterize the bulk deformation behavior by computing the Poisson's ratio of expanded thermoplastic polyurethane (eTPU) molded bead foams used in footwear midsole during compression. Quantitative data on morphological characteristics were obtained using an iterative image processing workflow. Image correlation on the 4D datasets using DVC was performed to calculate the volumetric and axial strain to estimate the Poisson ratio. Strain maps from DVC showed the influence of variability in ligament thickness distribution on the global mechanical behavior exhibited which dominated the response seen in these bead foams. Lastly, our results showed a strong correlation between Poisson ratio and distribution of ligament thickness in foams.

36 MATERIALS SCIENCE↗
NASA NTRS1990

Postbuckling of long thick plates in compression including higher order transverse shearing effects

Aluminum plates of various length/width ratios loaded in compression are examined analytically in terms of buckling and postbuckling for comparison with classical theory. The plates are considered to be subjected to longitudinal compressive displacement with no edge stress and are assumed to be simply supported at the side edges. The average longitudinal direct stresses are computed to plot characteristic curves by means of the following theories: 3D flexibility, higher-order shear deformation, first-order shear deformation, and classical von Karman. The 3D flexibility approach yields the lowest results with more unknowns than the higher-order shear-deformation method. The 3D flexibility approach is considered to be the most accurate, and it is shown that the calculated resultants and displacements tend to vary when consideration is given to the effects of transverse shear.

Stein, Manuel↗
NASA NTRS1991

Contraction ratio effects in a generic sidewall compression scramjet inlet - A computational and experimental investigation

Computed and experimental data on a generic three-dimensional sidewall compression scramjet inlet with a leading edge sweep of 45 degrees at Mach 20 are presented. A three-dimensional Navier-Stokes code was adapted to perform preliminary parametric studies leading to the present configuration. Following the design phase, the code was then employed as an analysis tool to provide a better understanding of the flow field and the experimental static and pitot pressure data. The model possessed 240 static pressure orifices distributed on the forebody plane, sidewalls, and cowl and was tested in the 31 Inch Mach 10 facility at the NASA Langley Research Center. Pitot rakes were employed to map the entrance and exit planes. The contraction ratio was observed to have a dominant effect on the inlet shock structure and performance; these effects are the emphasis of the present report. In addition to pressure measurements, oil flows were used for further visualization and comparison with computation.

Holland, Scott D.↗
NASA NTRS1988

Truss-core corrugation for compressive loads

A corrugated panel structure for supporting compressive loads is described which includes curved cap strips separated by truss-core web segments. The truss-core web segments are formed from first and second flat panels with a corrugated filler in between them. The corrugated filler extends in the direction of the compressive load. As a result, all components of the panel structure have a compressive load carrying capability resulting in a high strength-to-weight ratio when the compressive load is limiting. Application to rocket and aircraft structures is suggested.

Randall C Davis↗
DOE OSTI2021

1D kinetic study of pinch formation in a dense plasma focus: Transition from collisional to collisionless regimes

Here, the pinch-formation stage of a deuterium dense plasma focus, and associated “shock-flash” neutron yield, is studied using 1D kinetic simulations considering a plasma column with initial pressure P, initial radius R, and the compression to be driven by a constant current I. The relative behavior of the compression is shown to be similar for fixed ratios of the characteristic ion mean free path to the radius of the plasma column at stagnation, $λ_{st}/R_{st}$. This dimensionless parameter is shown to scale like $I^4/(P^3R^5)$. The compression ratio, $R/R_{st}$, is found to be a minimum when $λ_{st}/R_{st} ≈$ 1 and is the largest in the collisionless limit where $λ_{st} \gg R_{st}$. This behavior is in contrast to the analogous planar pinch where R/Rst decreases from one constant for λst/Rst$\ll$1 to a smaller constant for $λ_{st}/R_{st} \gg$ 1. The yield in the collisionless regime is shown to fall between the two well-known $I^4$ scaling laws. Furthermore, this regime exhibits qualities that potentially make it appealing for radiography applications, such as increased localization in time and space of the neutron formation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1991

Flux compression measurements in sintered bulk Ba2YCu3O7

Trapping of magnetic fields and subsequent flux compression have been realized in sintered bulk Ba2YCu3O7 superconductors at 77 K. The field is trapped in two interconnected holes of 0.95-cm and 0.52-cm diameter, respectively. By inserting a superconducting plunger with a diameter of 0.93 cm into the larger hole, the trapped flux is compressed into the smaller hole, where the flux density is measured with a Hall probe. The ratio of the areas available for the magnetic flux before and after compression is 3.7. Deviations from this compression ratio are observed to increase as the trapped field is increased, demonstrating penetration of magnetic flux into the interior of the superconductor. Using a simple extension of the critical state model, the authors demonstrate how the flux compression technique can be used to test the validity of the model and also to calculate the critical current density of the superconductor directly from the measurements.

Israelsson, U. E.↗
DOE OSTI2022

Crack width control and mechanical properties of low carbon engineered cementitious composites (ECC)

Engineered Cementitious Composites (ECC) have superior properties with high tensile ductility and tight crack width compared to conventional concrete. The properties of ECC are significantly influenced by the material composition which can be tailored to enhance the sustainability of ECC. Towards this goal, recycled crumb rubber (CR) and silica fume (SF) were used to tailor the properties of a polypropylene-fiber reinforced ECC with a low carbon binder based on limestone calcined clay cement (LC3) in this study. Crumb rubber was found to be effective in enhancing strain-hardening performance and reducing the width of the multiple microcracks. However, a loss of compressive strength was accompanied by an increasing amount of CR. While silica fume or lower w/b ratio enhanced the compressive strength, the crack width of ECC increased at higher SF content or lower w/b. The underlying mechanisms of these trends were traced to the alteration of the matrix fracture toughness and fiber/matrix interfacial bond. Rubber particle bridging was found to contribute to crack width control. Finally, the combined use of the LC3 green binder and CR led to a lowering of the embodied and operational carbon footprint of ECC.

36 MATERIALS SCIENCE↗
NASA NTRS1993

An experimental parametric study of geometric, Reynolds number, and ratio of specific heats effects in three-dimensional sidewall compression scramjet inlets at Mach 6

The effects of the decrease in the ratio of specific heats have been investigated in generic 3D sidewall compression scramjet inlets with leading-edge sweep angles of 30 and 70 degrees. The effects of a decrease in ratio of specific heats were seen by comparing data from two facilities in two test gases: in the Langley Mach 6 CF4 Tunnel in tetrafluoromethane and in the Langley 15-Inch Mach 6 Air Tunnel in perfect gas air. In addition to the simulated real gas effects, the parametric effects of cowl position, contraction ratio, leading-edge sweep, and Reynolds number were investigated in the 15-Inch Mach 6 Air Tunnel. The models were instrumented with a total of 45 static pressure orifices distributed on the sidewalls and baseplate. Surface streamline patterns were examined via oil flow, and schlieren videos were made of the external flow field. The results of these tests have significant implications to ground based testing of inlets in facilities which do not operate at flight enthalpies.

Holland, Scott D.↗
NASA NTRS1996

Performance Analysis of Two Early NACA High Speed Propellers with Application to Civil Tiltrotor Configurations

The helicopter industry is vigorously pursuing development of civil tiltrotors. One key to efficient high speed performance of this rotorcraft is prop-rotor performance. Of equal, if not greater, importance is assurance that the flight envelope is free of aeroelastic instabilities well beyond currently envisioned cuise speeds. This later condition requires study at helical tip Match numbers well in excess of 1.0. Two 1940's 'supersonic' propeller experiments conducted by NACA have provided an immensely valuable data bank with which to study prop-rotor behavior at transonic and supersonic helical tip Mach numbers. Very accurate 'blades alone' data were obtained by using nearly an infinite hub. Tabulated data were recreated from the many thrust and power figures and are included in two Appendices to this report. This data set is exceptionally well suited to re-evaluating classical blade element theories as well as evolving computational fluid dynamic (CFD) analyses. A limited comparison of one propeller's experimental results to a modem rotorcraft CFD code is made. This code, referred to as TURNS, gives very encouraging results. Detailed analysis of the performance data from both propellers is provided in Appendix A. This appendix quantifies the minimum power required to produce usable prop-rotor thrust. The dependence of minimum profile power on Reynolds number is quantified. First order compressibility power losses are quantified as well and a first approximation to design air-foil thickness ratio to avoid compressibility losses is provided. Appendix A's results are applied to study high speed civil tiltrotor cruise performance. Predicted tiltrotor performance is compared to two turboprop commercial transports. The comparison shows that there is no fundamental aerodynamic reason why the rotorcraft industry could not develop civil tiltrotor aircraft which have competitive cruise performance with today's regional, turboprop airlines. Recommendations for future study that will insure efficient prop-rotor performance to well beyond 400 knots are given.

Harris, Franklin D.↗
NASA NTRS2013

Granular Media-Based Tunable Passive Vibration Suppressor

and vibration suppression device is composed of statically compressed chains of spherical particles. The device superimposes a combination of dissipative damping and dispersive effects. The dissipative damping resulting from the elastic wave attenuation properties of the bulk material selected for the granular media is independent of particle geometry and periodicity, and can be accordingly designed based on the dissipative (or viscoelastic) properties of the material. For instance, a viscoelastic polymer might be selected where broadband damping is desired. In contrast, the dispersive effects result from the periodic arrangement and geometry of particles composing a linear granular chain. A uniform (monatomic) chain of statically compressed spherical particles will have a low-pass filter effect, with a cutoff frequency tunable as a function of particle mass, elastic modulus, Poisson fs ratio, radius, and static compression. Elastic waves with frequency content above this cutoff frequency will exhibit an exponential decay in amplitude as a function of propagation distance. System design targeting a specific application is conducted using a combination of theoretical, computational, and experimental techniques to appropriately select the particle radii, material (and thus elastic modulus and Poisson fs ratio), and static compression to satisfy estimated requirements derived for shock and/or vibration protection needs under particular operational conditions. The selection of a chain of polymer spheres with an elastic modulus .3 provided the appropriate dispersive filtering effect for that exercise; however, different operational scenarios may require the use of other polymers, metals, ceramics, or a combination thereof, configured as an array of spherical particles. The device is a linear array of spherical particles compressed in a container with a mechanism for attachment to the shock and/or vibration source, and a mechanism for attachment to the article requiring isolation (Figure 1). This configuration is referred to as a single-axis vibration suppressor. This invention also includes further designs for the integration of the single-axis vibration suppressor into a six-degree-of-freedom hexapod "Stewart"mounting configuration (Figure 2). By integrating each singleaxis vibration suppressor into a hexapod formation, a payload will be protected in all six degrees of freedom from shock and/or vibration. Additionally, to further enable the application of this device to multiple operational scenarios, particularly in the case of high loads, the vibration suppressor devices can be used in parallel in any array configuration.

Dillon, Robert P.↗
NASA NTRS1991

Data volume reduction for single-look polarimetric imaging radar data

An 8-b quantization scheme to reduce the data volume for single-look complex scattering matrix data measured by polarimetric imaging radar systems is described. The scattering matrices are not symmetrized before compression, thereby retaining information about background noise and system effects. The data volume is reduced by a factor of 3.2. It is shown, with measured data, that the signal to quantization noise ratio for the compression scheme is more than 35 dB for the cross-polarized channels, and more than 45 dB for the copolarized channels.

Van Zyl, Jakob J.↗
DOE OSTI2020

Meso-scale modeling and damage analysis of carbon/epoxy woven fabric composite under in-plane tension and compression loadings

The mechanical properties and damage behaviors of carbon/epoxy woven fabric composite under in-plane tension and compression are studied at the meso-scale level through experiment and simulation. An efficient representative volume element (RVE) modeling method with consistent mesh, high yarn volume fraction and realistic geometry is proposed. The material constitutive laws with plasticity, tension-compression asymmetry and damage evolution are established for the three components - yarn, matrix and interface, respectively. Significantly different mechanical properties and damage evolutions are observed depending on loading conditions and initial geometry characteristics. It shows a non-linear stress-strain curve with clear transition region and intensive damage in tension, while a quasi-linear behavior up to facture is observed in compression with little damage prior to final fracture. Furthermore, compared to the constant Poisson's ratio with straining in compression, a dramatic increase in Poisson's ratio appears in tension. Simulation shows damage mechanisms including transverse damage, matrix damage and delamination, which all play critical roles in the property evolution. In particular, the rapid damage accumulation after elastic deformation destroys the strong bonds and causes the easy deformation of transverse yarns which results in the transition region and large Poisson's ratio in tension. All the mechanical behaviors and damage evolutions are well captured and explained with the current RVE model.

42 ENGINEERING↗
NASA NTRSDate not supplied

Some Design Considerations for Two-Dimensional, Mixed-Compression Inlets for Mach 2.5 to 3.5.

A computational design study was performed to explore design factors for two-dimensional, mixed-compression inlets designed for cruise conditions at Mach 2.5, 2.75, 3.0, 3.25, and 3.5 and their influence on the aerodynamic performance of the inlets. The design factors included the split of external and internal compression, capture aspect ratio, throat section and subsonic diffuser geometry, and location and rates of porous bleed regions. The performance of the inlet was measured by the total pressure recovery, cowl wave drag, bleed flow rates, and total pressure distortion at the engine face. The results provide useful information for the design of inlets for future supersonic aircraft.

Supersonic Inlet↗
DOE OSTI2021

Effect of nitric oxide and exhaust gases on gasoline surrogate autoignition: iso-octane experiments and modeling

Exhaust gas recirculation (EGR) is widely used in advanced internal combustion engines to reduce engine emissions as well as control combustion phasing. Among various species present in EGR gases, CO 2 and H 2 O are two major components that can thermally and chemically affect fuel autoignition. It is of fundamental interest to isolate the thermal and chemical effects of CO 2 and H 2 O on fuel autoignition, especially as such an effort has not been reported in the literature. Moreover, nitric oxide (NO) is known to exhibit strong chemical effects on fuel autoignition, which in turn affects engine combustion phasing. The effects of ultra-low NO addition (< 100 ppm) on fuel autoignition at low temperatures are also not well understood. Recognizing these problems, autoignition experiments of iso-octane (a major gasoline surrogate component) in air are performed in this study using a rapid compression machine at varying compressed pressures, equivalence ratios, dilution levels with an EGR gas analogue (consisting of CO 2 , H 2 O, O 2 , and N 2 ) and N 2 only, and varying amounts of NO addition. Furthermore, the thermal and chemical effects of the EGR gas analogue are isolated and evaluated by comparing the ignition delay time datasets of EGR and N2-only diluted cases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Elastic constants in monocrystalline tungsten under quasi-hydrostatic pressures to 11.3 GPa

Compressional (P) and shear (S) wave velocities of tungsten single crystals along the [100] and [110] directions were measured using ultrasonic interferometry at room temperature up to 11.3 GPa. Least-squares fitting of $V$$^{[100]}_{P}$, $V$$^{[100]}_{S}$, $V$$^{[110]}_{P}$, and pressure to finite strain (FS) equations yields the elastic constants: C 11 = 523.5(5) GPa, C 12 = 205.1(32) GPa, and C 44 = 160.8(4) GPa, along with their respective pressure derivatives: $C$$^{′}_{11}$ = 6.20(2), $C$$^{′}_{12}$ = 3.35(1), and $C$$^{′}_{44}$ = 1.65(6). Using the Voigt–Reuss–Hill approximation, the elastic moduli were derived as K S0 = 311.2(22) GPa and G 0 = 160.2(7)GPa, along with their respective pressure derivatives: $K$$^{′}_{S0}$ = 4.30(4) and $G$$^{′}_{0}$ = 1.56(1). The Debye temperature of tungsten was determined to be 380.7(8) K, showing good agreement with previous calorimetric measurements. The elastic anisotropy increases slightly from 1.01(1) at ambient pressure to 1.03(1) at 11.3 GPa, suggesting that tungsten remains nearly isotropic under compression. Poisson's ratio slightly increased from 0.281(3) to 0.288(3) with pressure. Additionally, Pugh's ratio decreased from 0.512(4) to 0.494(4), while Pettifor's ratio increased from 0.148(10) to 0.175(10) as pressure reached 11.3 GPa. These results suggest that tungsten is weakly ductile compared to the critical thresholds for ductile behavior (i.e., Pugh's ratio <0.6 and Pettifor's ratio >0, indicating ductile behavior), but that its ductility increases marginally under pressure.

Wang, Ran [Stony Brook University, NY (United Stat↗
NASA NTRS1993

The fundamentals and futures of removable mass storage alternatives

This article reflects my view of how the storage products have been introduced into the marketplace, where they came from, and where others will continue to come from in the future. My corporate goal is to be a resource for those searching for removable solutions to mass storage problems. My introduction to optical storage occurred a few months before signing a non-disclosure agreement with FileNet on 8 Aug. 1983. By 87 or 88, as the optical craze was getting more popular, I started looking for similar or complementary storage technologies. I am still looking and my research is constantly turning up new entrants into this field. Due to the scope of the coverage in this field, this article does not dwell on any single technology. The goal is to provide information that is not compiled in any other single source and focus on facts that are not commonly known. I have provided a few baseline assumptions to ensure the mathematical calculations remain consistent: (1) hard-copy 8.5 in x 11 in documents which are scanned at 200 dots per inch (dpi) and compressed at a ratio of 10:1 result in a document image which requires an average of 50 Kilobytes (KB) of storage; (2) an average ASCII page requires 2 KB of storage; (3) an average flle cabinet drawer can hold 2500 pieces of paper; (4) one GB of storage can hold an average of 20,000 document images (a reel of 6250 tape holds 180 Megabytes (MB)).

Kempster, Linda↗
NASA NTRS1953

Application of a Channel Design Method to High-Solidity Cascades and Tests of an Impulse Cascade with 90 Degrees of Turning

A technique is developed for the application of a channel design method to the design of high-solidity cascades with prescribed velocity distributions as a function of arc length along the blade-element profile. The technique is applied to both incompressible and subsonic compressible, nonviscous, irrotational fluid motion. For compressible flow, the ratio of specific heats is assumed equal to -1.0. An impulse cascade with 90 degree turning was designed for incompressible flow and was tested at the design angle of attack over a range of downstream Mach number from 0.2 to coke flow. To achieve good efficiency, the cascade was designed for prescribed velocities and maximum blade loading according to limitations imposed by considerations of boundary-layer separation.

Stanitz, John D↗