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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Creep of chemically vapor deposited SiC fibers

The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with neglible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

Dicarlo, J. A.↗
NASA NTRS1984

Engine cyclic durability by analysis and material testing

The problem of calculating turbine engine component durability is addressed. Nonlinear, finite-element structural analyses, cyclic constitutive behavior models, and an advanced creep-fatigue life prediction method called strainrange partitioning were assessed for their applicability to the solution of durability problems in hot-section components of gas turbine engines. Three different component or subcomponent geometries are examined: a stress concentration in a turbine disk; a louver lip of a half-scale combustor linear; and a squealer tip of a first-stage high-pressure turbine blade. Cyclic structural analyses were performed for all three problems. The computed strain-temperature histories at the critical locations of the combustor linear and turbine blade components were imposed on smooth specimens in uniaxial, strain-controlled, thermomechanical fatigue tests of evaluate the structural and life analysis methods.

Kaufman, A.↗
NASA NTRS1984

Elevated temperature biaxial fatigue

A three year experimental program for studying elevated temperature biaxial fatigue of a nickel based alloy Hastelloy-X has been completed. A new high temperature fatigue test facility with unique capabilities has been developed. Effort was directed toward understanding multiaxial fatigue and correlating the experimental data to the existing theories of fatigue failure. The difficult task of predicting fatigue lives for non-proportional loading was used as an ultimate test for various life prediction methods being considered. The primary means of reaching improved undertanding were through several critical non-proportional loading experiments. It was discovered that the cracking mode switched from primarily cracking on the maximum shear planes at room temperature to cracking on the maximum normal strain planes at 649 C.

Jordan, E. H.↗
NASA NTRS1985

Statement of contamination problem

Space station contamination information is given. There are five major areas in which there are task requirements: (1) potential contaminants need to be identified, i.e., both the sources and types of contaminants, (2) the scope and magnitude of contaminant effects need to be determined, i.e., toxicological effects, microbacteriological effects and impurities, (3) mathematical models for predictive methods need to be developed. (4) state-of-the-art and advanced technologies for monitoring contaminants and for methods of decontamination need to be identified, and (5) automated monitoring and control systems need to be designed.

Hoffler, W.↗
NASA NTRS1984

Review of recent research of interior noise of propeller aircraft

Publications on the topics of propeller source noise, airborne noise transmission, and passenger comfort response to noise and vibration are reviewed. Of the 187 publications referenced, 140 have appeared since 1978. Examples of research accomplishments are presented to illustrate the state of the art. Emphasis is on comparisons of theoretical and measured results, but the description of the theories is left to the references. This review shows that substantial progress has been made in understanding the characteristics of propeller noise, airborne noise, and passenger response, and in the development of prediction methods. Application of the technology to cabin noise control and possible future research directions are discussed.

Mixson, J. S.↗
NASA NTRS1985

Disturbance-wave interactions in flows with crossflow

The leading-edge region of swept wings is dominated by the crossflow instability, resulting in vortices that all rotate in the same sense. The effect of these possibly unsteady vortices on the behavior of other disturbances is examined, and a strong interaction between these and disturbances of half the dominating crossflow wavelength is predicted. According to theory, the interaction is of crossflow-crossflow type. The effect explains the anomalies found in the experimental observations of Saric and Yeates. Visually, they observe vortices at the wavelength predicted by linear theory; however, in their hot-wire measurements they find that the superharmonic dominates disturbance growth, eventually having three times the amplitude of the primary wave. In this case, the usual transition prediction methods would fail, clearly indicating the importance of studying interactions of this sort.

Reed, H. L.↗
NASA NTRS1985

Effect of surface configuration during solid particle impingement erosion

A study of the progression of erosion and its detrimental effects due to solid particle impingement requires a detailed understanding of the erosion process and morphology of real surfaces of ductile metals. A series of experiments was conducted to investigate the erosion characteristics of aluminum alloy surfaces during spherical glass bead and angular crushed glass particle impingement. The effects of particle shape on cylindrical surfaces and surfaces with pre-existing holes and slits were determined. An attempt was made to understand the relationship between erosion rate and pit morphology. Based on the experimental observations, an empirical relationship between erosion rate and volume loss is presented. This technique provides an improved prediction method for a wide spectrum of ductile materials.

Rao, P. V.↗
NASA NTRS1985

Performance degradation of helicopter rotor in forward flight due to ice

This study addresses the analytical assessment of the degradation in the forward flight performance of the front rotor Boeing Vertol CH47D helicopter in a rime ice natural icing encounter. The front rotor disk was divided into 24 15-deg sections and the local Mach number and angle of attack were evaluated as a function of azimuthal and radial location for a specified flight condition. Profile drag increments were then calculated as a function of azimuthal and radial position for different times of exposure to icing, and the rotor performance was re-evaluated including these drag increments. The results of the analytical prediction method, such as horsepower required to maintain a specific flight condition, as a function of icing time have been generated. The method to illustrate the value of such an approach in assessing performance changes experienced by a helicopter rotor as a result of rime ice accretion is described.

Korkan, K. D.↗
NASA NTRS1986

Measuring Hole Elongation in Bolted Joints

Measurement does not affect joint parameters. Verification of analytical and strength-prediction methods for bolted composite joints based generally on data obtained experimentally from double-lap-joint specimens. In mechanically fastened joints, stresses maximal at fastener holes. Ability to measure accurately hole elongations without affecting joint parameters provides better understanding of elastic and plastic behavior of joint material leading to failure mechanisms in mechanically fastened joints required for design of more-efficient, lightweight composite joints.

Wichorek, G. R.↗
NASA NTRS1983

Turbine Engine Hot Section Technology (HOST)

A two-day workshop on the research and plans for turbine engine hot section durability problems was held on October 25 and 26, 1983, at the NASA Lewis Research Center. Presentations were made during six sessions, including structural analysis, fatigue and fracture, surface protective coatings, combustion, turbine heat transfer, and instrumentation, that dealt with the thermal and fluid environment around liners, blades, and vanes, and with material coatings, constitutive behavior, stress-strain response, and life prediction methods for the three components. The principal objective of each session was to disseminate the research results to date, along with future plans, in each of the six areas. Contract and government researchers presented results of their work.

Source record↗
NASA NTRS1985

Elevated temperature biaxial fatigue

A 3 year experimental program for studying elevated temperature biaxial fatigue of a nickel based alloy Hastelloy-X has been completed. A new high temperature fatigue test facility with unique capabilities has been developed. Effort was directed toward understanding multiaxial fatigue and correlating the experimental data to the existing theories of fatigue failure. The difficult task of predicting fatigue lives for nonproportional loading was used as an ultimate test for various life prediction methods being considered. The primary means of reaching improved understanding were through several critical nonproportional loading experiments. The direction of cracking observed on failed specimens was also recorded and used to guide the development of the theory. Cyclic deformation responses were permanently recorded digitally during each test. It was discovered that the cracking mode switched from primarily cracking on the maximum shear planes at room temperature to cracking on the maximum normal strain planes at 649 C. In contrast to some other metals, loading path in nonproportional loading had little effect on fatigue lives. Strain rate had a small effect on fatigue lives at 649 C. Of the various correlating parameters the modified plastic work and octahedral shear stress were the most successful.

Jordan, E. H.↗
NASA NTRS1986

Commentary on the 1985 NASA/Vanderbilt Symposium on Future Hypervelocity Flight Requirements

The discussion, started in Semiannual Status Report Number 1, on aerothermal problems of hypervelocity flight and experiments that may lead to significant improvements in analytical/computational predictive methods, continues. The commentary is based on presentations made by speakers at a symposium on this subject held in December 1985. Symposium participants focused on the serious deficiencies that exist in knowledge of real-gas, nonequilibrium thermochemical-kinetic processes, catalytic processes, surface and shock slip, gas/surface interaction, boundary layer transition, and vortical leeside flows under hypervelocity conditions. Programs of laboratory research and computations leading toward in-flight experiments were recommended. Feasibility of appropriate measurement techniques for the flight environment was assessed and problems for study in that area identified. A synopsis of the oral presentations is given.

Potter, J. L.↗
NASA NTRS1986

Supersonic wing-body inteference at high angles of attack with emphasis on low aspect ratios

A systematic NASA data base for cruciform wing-body combinations has been analyzed to extract the values of the wing and body interference factors. The fin planforms vary in aspect ratio from 0.5 to 2.0, the Mach number from 2.5 to 4.5, and the angle of attack from 0 deg to 40 deg. Sufficient data are available to permit interpolation with respect to fin aspect ratio, taper ratio, Mach number, and angle of attack. The data base described in this paper can be used in an engineering prediction method to determine the normal force of planar wing-body combinations and for scaling the effects of body radius-fin semispan ratio.

Nielsen, J. N.↗
NASA NTRS1986

Creep of chemically vapour deposited SiC fibres

The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with negligible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

Dicarlo, J. A.↗
NASA NTRS1985

The performance characteristics of simulated ice on rotorcraft airfoils

Attention is given to the results of NASA-sponsored rotorcraft icing research which was aimed at the formulation of a predictive method for the computation of performance penalties due to rotor and airfoil icing. Parametric simulated ice test results obtained in wind tunnels are compared with those of other investigations. These comparisons indicate that proper design of simulated ice shapes can adequately represent ice on airfoil sections, with incremental lift, drag, and pitching moments matching those generated in icing wind tunnels.

Flemming, R. J.↗
NASA NTRS1986

Unsteady forces on counter-rotating propeller blades

Unsteady forces experienced by counter-rotating propeller blades are examined in this paper. A fully coupled vortex lattice model of counter-rotation is used to obtain a quasi-steady solution to the propeller loadings, and an unsteady Sears (1941) analysis provides an estimate of the unsteady loads from the quasi-steady results. The vortex lattice method predicts the overall performance of counter-rotation well, based on comparisons of measured and predicted results. The effects of propeller spacing and blade number on the unsteady loadings are investigated. The peak-to-peak variation about the mean of the unsteady loads on the rear propeller varied from 9 percent for a 2 x 2 counter-rotation system to 2 percent for an 8 x 8 system.

Lesieutre, D. J.↗
NASA NTRS1986

Navier-Stokes computations of lee-side flows over delta wings

Solutions to the Navier-Stokes equations for the flow over delta wings are computed with emphasis on the separated vortical flows developing on the lee side at high angles of attack. A recently developed implicit algorithm is used which employs upwind differencing for the pressure and convection terms and central differencing for the shear stress and heat transfer terms. Solutions to both the three-dimensional equations and the approximate conical flow equations are compared parametrically with an extensive experimental data base at supersonic speeds. The computations indicate that the conical flow approximation provides results in close agreement with the three-dimensional equations, even to angles of attack as high as 20 degrees. Good agreement with experimentally measured pressures and vapor screen photographs is obtained for the conditions investigated. The method predicts the classical pattern of vortical flow over a delta wing and transition to other flow patterns as the leading edge sweep angle and leading edge normal Mach number are varied.

Thomas, J. L.↗
NASA NTRS1986

Noise radiation directivity from a wind-tunnel inlet with inlet vanes and duct wall linings

The acoustic radiation patterns from a 1/15th scale model of the Ames 80- by 120-Ft Wind Tunnel test section and inlet have been measured with a noise source installed in the test section. Data were acquired without airflow in the duct. Sound-absorbent inlet vanes oriented parallel to each other, or splayed with a variable incidence relative to the duct long axis, were evaluated along with duct wall linings. Results show that splayed vans tend to spread the sound to greater angles than those measured with the open inlet. Parallel vanes narrowed the high-frequency radiation pattern. Duct wall linings had a strong effect on acoustic directivity by attenuating wall reflections. Vane insertion loss was measured. Directivity results are compared with existing data from square ducts. Two prediction methods for duct radiation directivity are described: one is an empirical method based on the test data, and the other is a analytical method based on ray acoustics.

Soderman, P. T.↗