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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 1,333 records · Page 74
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Dynamic testing of thin-walled composite box beams in a vacuum chamber

Vibration characteristics of thin-walled composite box beams are measured in a rotating environment in a 10-ft diameter vacuum chamber. Symmetric and antisymmetric layup beams are fabricated out of graphite/epoxy prepreg material using an autoclave molding technique. These are excited using piezoelectric ceramic elements and responses are measured using strain gages and accelerometers. First three natural modes are identified using spectrum analyzer over a range of rotational speeds up to 1000 rpm. Measured frequencies and mode shapes (displacement as well as strain) are correlated satisfactorily with calculated finite element results.

Chandra, Ramesh↗
NASA NTRS1989

Investigation of test methods for measuring compressive strength and modulus of two-dimensional carbon-carbon composites

An experimental evaluation has been conducted to ascertain the the usefulness of two techniques for measuring in-plane compressive failure strength and modulus in coated and uncoated carbon-carbon composites. The techniques involved testing specimens with potted ends as well as testing them in a novel clamping fixture; specimen shape, length, gage width, and thickness were the test parameters investigated for both coated and uncoated 0/90 deg and +/-45 deg laminates. It is found that specimen shape does not have a significant effect on the measured compressive properties. The potting of specimen ends results in slightly higher measured compressive strengths than those obtained with the new clamping fixture. Comparable modulus values are obtained by both techniques.

Ohlhorst, Craig W.↗
NASA NTRS1990

High-temperature tensile properties of fiber reinforced reaction bonded silicon nitride

Measurements of tensile properties of unidirectional silicon carbide fiber-reinforced reaction-bonded silicon nitride (SiC/RBSN) composite specimens were carried out in air at 25, 1300, and 1500 C, using a new testing technique and a specially designed gripping system that minimizes bending moment and assures that failure always occurred in the gage section. The material was found to display metallike stress-strain behavior at all temperatures tested, and a noncatastrophic failure beyond the matrix fracture. The tensile properties were found to be temperature dependent, with the values of the ultimate tensile strength decreasing with temperature, from 543 MPa at 25 C to 169 at 1500 C.

Jablonski, David A.↗
NASA NTRS1991

A review of ice accretion data from a model rotor icing test and comparison with theory

An experiment was conducted by the Helicopter Icing Consortium (HIC) in the NASA Lewis Icing Research Tunnel (IRT) in which a 1/6 scale fuselage model of a UH-60A Black Hawk helicopter with a generic rotor was subjected to a wide range of icing conditions. The HIC consists of members from NASA, Bell Helicopter, Boeing Helicopter, McDonnell Douglas Helicopters, Sikorsky Aircraft, and Texas A&M University. Data was taken in the form of rotor torque, internal force balance measurements, blade strain gage loading, and two dimensional ice shape tracings. A review of the ice shape data is performed with special attention given to repeatability and correctness of trends in terms of radial variation, rotational speed, icing time, temperature, liquid water content, and volumetric median droplet size. Moreover, an indepth comparison between the experimental data and the analysis of NASA's ice accretion code LEWICE is given. Finally, conclusions are drawn as to the quality of the ice accretion data and the predictability of the data base as a whole. Recommendations are also given for improving data taking technique as well as potential future work.

Britton, Randall K.↗
NASA NTRS1991

Results of a sub-scale model rotor icing test

A heavily instrumented sub-scale model of a helicopter main rotor was tested in the NASA Lewis Research Center Icing Research Tunnel (IRT) in September and November 1989. The four-bladed main rotor had a diameter of 1.83 m (6.00 ft) and the 0.124 m (4.9 in) chord rotor blades were specially fabricated for this experiment. The instrumented rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The model rotor was exposed to a range of icing conditions that included variations in temperature, liquid water content, and median droplet diameter, and was operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed) and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracings, and ice molds. The sensitivity of the model rotor to the test parameters, is given, and the result to theoretical predictions are compared. Test data quality was excellent, and ice accretion prediction methods and rotor performance prediction methods (using published icing lift and drag relationships) reproduced the performance trends observed in the test. Adjustments to the correlation coefficients to improve the level of correlation are suggested.

Flemming, Robert J.↗
NASA NTRS1990

Axial-torsional fatigue: A study of tubular specimen thickness effects

A room-temperature experimental program was conducted on AISI type 316 stainless steel to determine the effect of wall thickness on the cyclic deformation behavior and fatigue life of thin-wall, tubular, axial-torsional fatigue specimens. The following experimental variables were examined in this study: the depth of the surface work-hardened layer produced in specimen machining, and the effects of strain range and axial-torsional strain phasing. Tubular fatigue specimens were fabricated with wall thicknesses of 1.5, 2.0, and 2.5 mm. One as-fabricated specimen from each wall thickness was sectioned for microstructural examination and microhardness measurement. A specimen of each wall thickness was tested at each of three conditions - high strain range in-phase, low strain range in-phase, and low strain range out-of-phase - for a total of nine axial-torsional fatigue experiments. The machining-induced work-hardened zone, as a percentage of the gage section material, was found to have a minimal effect on both deformation behavior and fatigue life. Also, little or no variation in fatigue life or deformation behavior as a function of wall thickness was observed. Out-of-phase fatigue tests displayed shorter fatigue lives and more cyclic hardening than in-phase tests.

Bonacuse, Peter J.↗
NASA NTRS1990

Optical measurement of unducted fan flutter

A nonintrusive optical method is described for flutter vibrations in unducted fan or propeller rotors and provides detailed spectral results for two flutter modes of a scaled unducted fan. The measurements were obtained in a high-speed wind tunnel. A single-rotor and a dual-rotor counterrotating configuration of the model were tested; however, only the forward rotor of the counterrotating configuration fluttered. Conventional strain gages were used to obtain flutter frequency; optical data provided complete phase results and an indication of the flutter mode shape through the ratio of the leading- to trailing-edge flutter amplitudes near the blade tip. In the transonic regime exhibited some features that are usually associated with nonlinear vibrations. Experimental mode shape and frequencies were compared with calculated values that included centrifugal effects.

Kurkov, Anatole P.↗
NASA NTRS1990

Modal analysis of UH-60A instrumented rotor blades

The dynamic characteristics of instrumented and production UH-60A Black Hawk main rotor blades were measured, and the results were validated with NASTRAN finite element models. The blades tested included pressure and strain-gage instrumented blades, which are part of the NASA Airloads Flight Research Phase of the Modern Technology Rotor Program. The dynamic similarity of the blades was required for accurate data collection in this program. Therefore, a nonrotating blade modal analysis was performed on the first 10 free-free modes to measure blade similarities. The results showed small differences between the modal frequencies of instrumented and production blades and a close correlation with the NASTRAN models. This type of modal testing and analysis is recommended as a standard procedure for future instrumented blade flight testing.

Hamade, Karen S.↗
NASA NTRS1991

In-space experiment on thermoacoustic convection heat transfer phenomenon-experiment definition

The definition phase of an in-space experiment in thermoacoustic convection (TAC) heat transfer phenomenon is completed and the results are presented and discussed in some detail. Background information, application and potential importance of TAC in heat transfer processes are discussed with particular focus on application in cryogenic fluid handling and storage in microgravity space environment. Also included are the discussion on TAC space experiment objectives, results of ground support experiments, hardware information, and technical specifications and drawings. The future plans and a schedule for the development of experiment hardware (Phase 1) and flight tests and post-flight analysis (Phase 3/4) are also presented. The specific experimental objectives are rapid heating of a compressible fluid and the measurement of the fluid temperature and pressure and the recording and analysis of the experimental data for the establishment of the importance of TAC heat transfer process. The ground experiments that were completed in support of the experiment definition included fluid temperature measurement by a modified shadowgraph method, surface temperature measurements by thermocouples, and fluid pressure measurements by strain-gage pressure transducers. These experiments verified the feasibility of the TAC in-space experiment, established the relevance and accuracy of the experimental results, and specified the nature of the analysis which will be carried out in the post-flight phase of the report.

Parang, M.↗
NASA NTRS1991

Dynamic stall effects and applications to high performance aircraft

Recent research conducted at the NASA Langley Research Center on the effects of large amplitude pitching motions on the aerodynamic characteristics of modern fighter aircraft configurations is highlighted. Wind tunnel tests were conducted on simple flat-plate wings to gain understanding of the complex flow phenomena during unsteady motions at high angles of attack. Studies then progressed to a representative modern fighter configuration. Using a computer controlled dynamic apparatus, tests were conducted to investigate effects of pitch rate and motion time history and to determine the persistence of unsteady effects. Data were also obtained in sideslip and with control surface deflections to investigate dynamic effects on lateral stability and available control power. Force and moment data were obtained using a 6-component internal strain-gage balance. To aid in the interpretation of the results, flow visualization using a laser light-sheet system was also obtained. Results of these tests are discussed, along with their implications on the maneuverability of future advanced airplanes designed to operate in the highly dynamic, high angle-of-attack environment.

Brandon, Jay M.↗
NASA NTRS1991

Comparison of analysis and experiment for dynamics of low-contact-ratio spur gears

Low-contact-ratio spur gears were tested in NASA gear-noise-rig to study gear dynamics including dynamic load, tooth bending stress, vibration, and noise. The experimental results were compared with a NASA gear dynamics code to validate the code as a design tool for predicting transmission vibration and noise. Analytical predictions and experimental data for gear-tooth dynamic loads and tooth-root bending stress were compared at 28 operating conditions. Strain gage data were used to compute the normal load between meshing teeth and the bending stress at the tooth root for direct comparison with the analysis. The computed and measured waveforms for dynamic load and stress were compared for several test conditions. These are very similar in shape, which means the analysis successfully simulates the physical behavior of the test gears. The predicted peak value of the dynamic load agrees with the measurement results within an average error of 4.9 percent except at low-torque, high-speed conditions. Predictions of peak dynamic root stress are generally within 10 to 15 percent of the measured values.

Oswald, Fred B.↗
NASA NTRS1991

Model rotor icing tests in the NASA Lewis icing research tunnel

Tests of a lightly instrumented two-bladed teetering rotor and a heavily instrumented sub-scale articulated main rotor were conducted in the NASA Lewis Research Center Icing Research Tunnel (IRT) in August 1988 and September and November 1989. The first was an OH-58 tail rotor which had a diameter of 1.575 m and a blade chord of 0.133 m, and was mounted on a NASA designed test rig. The second, a four bladed articulated rotor, had a diameter of 1.83 m with 0.124 m chord blades specially fabricated for the experiment. This rotor was mounted on a Sikorsky Aircraft Powered Force Model, which enclosed a rotor balance and other measurement systems. The models were exposed to variations in temperature, liquid water content, and medium droplet diameter, and were operated over ranges of advance ratio, shaft angle, tip Mach number (rotor speed), and weight coefficient to determine the effect of these parameters on ice accretion. In addition to strain gage and balance data, the test was documented with still, video, and high speed photography, ice profile tracing, and ice molds. Presented here are the sensitivity of the model rotors to the test parameters and a comparison of the results to theoretical predictions.

Flemming, Robert J.↗
NASA NTRS1989

Elevated temperature crack growth

Alloy 718 crack growth experiments were conducted to assess the ability of the selected path-independent (P-I) integrals to describe the elevated temperature crack growth behavior. These tests were performed on single edge notch (SEN) specimens under displacement control with multiple extensometers to monitor the specimen and crack mouth opening displacement (CMOD). The displacements in these tests were sufficiently high to induce bulk cyclic inelastic deformation of the specimen. Under these conditions, the linear elastic fracture mechanics (LEFM) parameter K does not correlate the crack growth data. The experimentally measured displacement gradients at the end of specimen gage length were used as the boundary conditions in elastic-plastic finite element method (FEM) analyses. These analyses were performed with a node release approach using CYANIDE, a GEAE FEM code, which included a gap element which is capable of efficiently simulating crack closure. Excellent correlation was obtained between the experimentally measured and predicted variation of stress and CMOD with crack length and the stress-CMOD loops for Alloy 718 tests conducted at 538 C. This confirmed the accuracy of the FEM crack growth simulation approach. The experimentally measured crack growth rate data correlated well the selected P-I integrals. These investigations have produced significant progress in developing P-I integrals as non-linear fracture mechanics parameters. The results suggest that this methodology has the potential of accurately describing elevated temperature crack growth behavior under the combined influence of thermal cycling and bulk elastic-inelastic deformation states.

Kim, K. S.↗
NASA NTRS1991

Comparison of Weibull strength parameters from flexure and spin tests of brittle materials

Fracture data from five series of four point bend tests of beam and spin tests of flat annular disks were reanalyzed. Silicon nitride and graphite were the test materials. The experimental fracture strengths of the disks were compared with the predicted strengths based on both volume flaw and surface flaw analyses of four point bend data. Volume flaw analysis resulted in a better correlation between disks and beams in three of the five test series than did surface flaw analysis. The Weibull (moduli) and characteristic gage strengths for the disks and beams were also compared. Differences in the experimental Weibull slopes were not statistically significant. It was shown that results from the beam tests can predict the fracture strength of rotating disks.

Holland, Frederic A., Jr.↗
NASA NTRS1990

A study of fracture mechanisms in ATD roller bearing

The purpose was to investigate how microstructures, especially anisotropy, affects internal stresses and the overall mechanical response of bearings. Samples with the stress axis along the aligned carbide direction possessed high modulus values compared to those with their axis perpendicular to the carbide stringers. The difference in the modulus was found to be more than a factor of two. A series of experiments was conducted on rolled samples to further investigate this effect; the two sets of results were consistent with each other. The degree of anisotropy of the microstructure in terms of the carbide and matrix orientations was determined using x-ray diffraction. The stress state determination was conducted using neutron diffraction. It was found that there was little variation in the distribution of the internal stresses amongst different samples, indicating that small changes in the processing and geometrical conditions did not result in significant variations in the internal stress. A nominal tensile hoop stress of 39 ksi was obtained for the inner raceway. Furthermore, during the course of the investigation, it was apparent that there was a need to determine the stress state induced by the shrink fitting process. Therefore, a series of experiments was conducted using strain gages to identify the stress distribution in a shrink fitting process in three different types of geometries. Correlations were obtained to estimate the highest stress values in the outer and inner groove geometry. A finite element program based on the ANSYS system was developed to compute the stress distribution in the inner raceway geometry. This analysis indicates that the highest tensile stress in the system occurs at the ID of the ring with a stress value of over 5 times that of the applied radial stress. Results from all these facets were correlated with one another. It appears that the material does not fail as a result of any one single factor, but results from a combination of the various factors investigated.

Zee, Ralph H.↗
NASA NTRS1990

Structural monitoring of filamentary composites using embedded fiber optics

The feasibility of monitoring overall integrity of structural components made of filamentary composites, by embedding optical fibers between lamina of a composite beam, is investigated using a beam constructed of Kevlar/epoxy cloth with embedded optical fibers aligned with the longitudinal axis of the beam. Phase changes were monitored in three different optical fibers as the composite beam was subjected to pure bending, and the strain response of the fibers was compared to the strain gage readings taken at the surface, showing a strong correlation between the phase change and the applied deformation.

Cashon, John L.↗
NASA NTRS1990

Buckling analysis and test correlation of hat stiffened panels for hypersonic vehicles

The paper discusses the design, analysis, and test of hat stiffened panels subjected to a variety of thermal and mechanical load conditions. The panels were designed using data from structural optimization computer codes and finite element analysis. Test methods included the grid shadow moire method and a single gage force stiffness method. The agreement between the test data and analysis provides confidence in the methods that are currently being used to design structures for hypersonic vehicles. The agreement also indicates that post buckled strength may potentially be used to reduce the vehicle weight.

Percy, Wendy C.↗
NASA NTRS1990

Spatial variability of rain rate and slant path attenuation distributions at 28 GHz in the mid-Atlantic coast region of the United States

Rain rate and corresponding estimated slant-path attenuation distributions derived from two years of measurements are presented for a network of nine rain-gage sites located in a region with extent 70 km N-S and 47 km E-W in the mid-Atlantic coast of the U.S. near the NASA Wallops Flight Facility, VA. The network average rain-rate distribution was compared with a previously measured 6-year average at one of the site locations. Agreement in rain rates was found to be within approximately 1 mm/h over the percentage range of 1-0.01 percent of the year, signifying the constancy of the rain-rate climatology for the region, and implying an ergodic rainfall process. Slant-path attenuation statistics were estimated at 28.56 GHz by interfacing the measured rain-rate distributions at each of nine site locations with Crane's (1980) global model.

Goldhirsh, Julius↗