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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Finite element stress analysis of a notched coupon specimen for in-plane shear behaviour of composites

The results of a linear elastic, plane stress finite element investigation of the stress distribution in a double V-notched coupon specimen are presented for an isotropic material (steel) and five graphite/polyimide laminates: (0), (90), (0/90)s, (plus or minus 45)s and (0/90/plus or minus 45)s. Stress contours, stress profiles, and stress concentration factors are presented for specimens loaded through rigid fixtures. It is shown that the finite element analysis predicts a region of essentially uniform pure shear in the central portion of the specimen for all laminates considered. Stress concentrations vary considerably with laminate configuration. The influences of elastic fixtures and thermal stresses on the stress distribution in (0) laminates are also investigated. The (0) laminate is predicted to exhibit maximum pure shear in the center of the test section for both rigid and elastic fixtures. It is concluded that the specimen is a practicable candidate for use as a composite shear specimen.

Herakovich, C. T.↗
NASA NTRS1993

Design and test of a magnetic thrust bearing

A magnetic thrust bearing can be employed to take thrust loads in rotating machinery. The design and construction of a prototype magnetic thrust bearing for a high load per weight application is described. The theory for the bearing is developed. Fixtures were designed and the bearing was tested for load capacity using a universal testing machine. Various shims were employed to have known gap thicknesses. A comparison of the theory and measured results is presented.

Allaire, P. E.↗
NASA NTRS1993

Fixtures Hold Nuts During Tightening Of Bolts

Two fixtures designed for use on cross-head of tensile testing machine simplify adjustments of crosshead to accommodate specimens of various lengths. Two cagelike fixtures hold pairs of nuts, preventing nuts from turning while bolts are tightened. Enable one person acting alone to tighten bolts.

Gyekenyesi, John Z.↗
NASA NTRS1989

Evaluation of the resiliency characteristics of several candidate Solid Rocket Booster O-ring materials

Resiliency tests have been conducted in order to evaluate O-ring sealing response in the revised Space Shuttle SRBs, giving attention to the effects of temperature and gap-opening rates. Additional testing was conducted to ascertain O-ring responses to simulated SRB field-joint deflections. All tests employed a face-seal fixture mounted on a servohydraulic apparatus. The Viton candidate O-ring material tracked the gap-opening rate better at higher temperatures and lower gap-opening rates; it was also the only material inert to the calcium grease employed. Heaters must be used to maintain the 70 F minimum temperature at which the Viton O-ring will track the required gap opening rate.

Lach, C. L.↗
NASA NTRS1992

The NASA/Industry Design Analysis Methods for Vibrations (DAMVIBS) Program - Boeing helicopters airframe finite element modeling

Finite-element modeling of the airframe vibration of the Army/Boeing CH-47D helicopter is conducted with comparisons to experimental data in an effort to improve the design process. A NASTRAN FEM is developed that is fully representative of the test configuration and includes the support fixture, shakers, and the aircraft/shaker suspension system. The analysis is conducted with specific attention given to the prediction of reasonable forced amplitudes throughout the airframe. Reasonable correlation is noted between the FEM and experimental results, although improved correlation can be obtained by including more accurate damping values and secondary effects such as stringer shear loading. It is shown that the general stress model does not provide an adequate dynamic analysis on which to base design improvements. A more detailed model is required that emphasizes highly detailed helicopter elements and employs a finer mesh particularly in the description of the mass distribution.

Gabel, R.↗
NASA NTRS1976

High Temperature Strain Gage Calibration Fixture

An apparatus and method are described for calibrating high temperature strain gases which serve for both dead weight and constant deflection measurements. A cantilever support arm allows the test unit to slide into a furnace while one end is subjected to bending strain either by hanging weights upon it or by deflecting it with a push rod. The dual nature of the fixture permits both tests to be run without change of the test specimen or removal from the furnace.

Vranas, T.↗
NASA NTRS1973

Multi axes vibration fixtures

A simplified technique and apparatus are described for testing the effects of vibration on various material specimen. Particular attention was given to tests along the orthogonal vibrational planes in order to prove the strength of the item under extraordinary conditions to which it will be subjected.

Sims, C. R.↗
NASA NTRS2006

Apparatus for Hot Impact Testing of Material Specimens

An apparatus for positioning and holding material specimens is a major subsystem of a system for impact testing of the specimens at temperatures up to 1,500 C. This apparatus and the rest of the system are designed especially for hot impact testing of advanced ceramics, composites, and coating materials. The apparatus includes a retaining fixture on a rotating stage on a vertically movable cross support driven by a linear actuator. These components are located below a furnace wherein the hot impact tests are performed (see Figure 1). In preparation for a test, a specimen is mounted on the retaining fixture, then the cross support is moved upward to raise the specimen, through an opening in the bottom of the furnace, to the test position inside the furnace. On one side of the furnace there is another, relatively small opening on a direct line to the specimen. Once the specimen has become heated to the test temperature, the test is performed by using an instrumented external pressurized-gas-driven gun to shoot a projectile through the side opening at the specimen.

Pawlik, Ralph J.↗
NASA NTRS1993

Effect of temperature and O-ring gland finish on sealing ability of Viton V747-75

As a part of the redesign project of the Space Shuttle solid rocket motor (SRM) following the Challenger accident, the field joint was redesigned to minimize the relative joint motion caused by internal motor pressurization during ignition. The O-ring seals and glands for the field joint were designed both to accommodate structural deflections and to promote pressure-assisted sealing. Tests were conducted in various face seal fixtures to evaluate the ability of Viton V747-75 O-rings to seal for a range of temperatures and surface finishes of the redesigned O-ring gland. The effect of surface finish on the sealing performance and wear characteristics of the O-rings was evaluated during simulated launch conditions that included low-frequency vibrations, gap openings, and rapid pressurizations. The effect of contamination on the sealing performance was also investigated. The O-rings sealed throughout the 75 deg F leak check test and for the seal tests from 50 deg F to 120 deg F for the range of surface finishes investigated. Although abrasions were found in the O-rings from pressurization against the rougher finishes, these abrasions were not detrimental to sealing. Below 50 deg F, Viton V747-75 O-rings were insufficiently resilient to track the test gap opening.

Lach, Cynthia L.↗
NASA NTRSDate not supplied

Segmented, Pleat-Folded and Rib-Supported Thin-Shell Composite Antenna Reflector

A new architecture scalable to sizes greater than 10 m for a deployable solid surface reflector antenna is presented. The design makes use of radially and circumferentially segmented thin-shell composite gores interconnected on the back side by a series of flexible shape memory composite elements. The reflector surface stows like an umbrella by creating serpentine-shaped pleats in the thin shell while being supported by a simple-hinged metering rib structure. A parametric study assessed how design features affect the deployed stiffness of the reflector and are used to identify a test matrix for manufacturing, foldability, and shape accuracy assessments. Various manufacturing tooling designs and dedicated folding fixtures were built to increase the fidelity and confidence of the test articles produced. An overview of the development effort is provided.

Deployable antennas↗
NASA NTRSDate not supplied

Segmented, Pleat-Folded and Rib-Supported Thin-Shell Composite Antenna Reflector

A new architecture scalable to sizes greater than 10 m for a deployable solid surface reflector antenna is presented. The design makes use of radially and circumferentially segmented thin-shell composite gores interconnected on the back side by a series of flexible shape memory composite elements. The reflector surface stows like an umbrella by creating serpentine-shaped pleats in the thin shell while being supported by a simple-hinged metering rib structure. A parametric study assessed how design features affect the deployed stiffness of the reflector and are used to identify a test matrix for manufacturing, foldability, and shape accuracy assessments. Various manufacturing tooling designs and dedicated folding fixtures were built to increase the fidelity and confidence of the test articles produced. An overview of the development effort is provided.

Deployable antennas↗
NASA NTRS1985

Swing-arm beam erector (SABER) concept for single astronaut assembly of space structure

Results are presented of tests conducted to evaluate a mobile work station/assembly fixture concept that would mechanically assist an astronaut in the on-orbit manual assembly of erectable truss-beams. The concept eliminates astronaut manual translation by use of a motorized work platform with foot restraints. The tests involved assembly of a tetrahedral truss-beam by a test subject in simulated zero gravity (neutral bouyancy in water). A three-bay truss-beam was assembled from 30 aluminum struts with quick-attachment structural joints. The results show that average on-orbit assembly rates of 2.1 struts per minute can be expected for struts of the size employed in these tests.

Watson, J. J.↗
NASA NTRS1972

Quick release acoustic sensor holding fixture

Quick-release spring holder secures acoustic sensor to test material surface eliminating adhesive bonding to test material and achieving acoustic emission evaluation from tensile tests. Reusability of sensors reduces test cost.

Mcmahon, W.↗
NASA NTRS2000

Piezoelectric Shunt Vibration Damping of F-15 Panel under High Acoustic Excitation

At last year's SPIE symposium, we reported results of an experiment on structural vibration damping of an F-15 underbelly panel using piezoelectric shunting with five bonded PZT transducers. The panel vibration was induced with an acoustic speaker at an overall sound pressure level (OASPL) of about 90 dB. Amplitude reductions of 13.45 and 10.72 dB were achieved for the first and second modes, respectively, using single- and multiple-mode shunting. It is the purpose of this investigation to extend the passive piezoelectric shunt-damping technique to control structural vibration induced at higher acoustic excitation levels, and to examine the controllability and survivability of the bonded PZT transducers at these high levels. The shunting experiment was performed with the Thermal Acoustic Fatigue Apparatus (TAFA) at the NASA Langley Research Center using the same F-15 underbelly panel. The TAFA is a progressive wave tube facility. The panel was mounted in one wall of the TAFA test section using a specially designed mounting fixture such that the panel was subjected to grazing-incidence acoustic excitation. Five PZT transducers were used with two shunt circuits designed to control the first and second modes of the structure between 200 and 400 Hz. We first determined the values of the shunt inductance and resistance at an OASPL of 130 dB. These values were maintained while we gradually increased the OASPL from 130 to 154 dB in 6-dB steps. During each increment, the frequency response function between accelerometers on the panel and the acoustic excitation measured by microphones, before and after shunting, were recorded. Good response reduction was observed up to the 148dB level. The experiment was stopped at 154 dB due to wire breakage from vibration at a transducer wire joint. The PZT transducers, however, were still bonded well on the panel and survived at this high dB level. We also observed shifting of the frequency peaks toward lower frequency when the OASPL was increased. Detailed experimental results will be presented.

Wu, Shu-Yau↗
NASA NTRS2011

Wedge and Conical Probes for the Instantaneous Measurement of Free-Stream Flow Quantities at Supersonic Speeds

Wedge and conical shaped probes for the measurement of free-stream flow quantities at supersonic speeds have been tested in both wind tunnel and flight. These probes have improved capabilities over similar ones used in the past. Through the use of miniature pressure sensors, that are located inside the probes, they are able to provide instantaneous measurements of a time-varying environment. Detailed herein are the results of the tests in NASA Langley Researcher Center s Unitary Plan Wind Tunnel (UPWT) at Mach numbers of 1.6, 1.8 and 2.0, as well as flight tests carried out at the NASA Dryden Flight Research Center (DFRC) on its F-15 aircraft up to Mach numbers of 1.9. In the flight tests the probes were attached to a fixture on the underside of the F-15 fuselage. Problems controlling the velocity of the flow through the conical probe, required for accurate temperature measurements, are noted, as well as some calibration problems of the miniature pressure sensors that impact the accuracy of the measurements.

Bobbitt, Percy J.↗
NASA NTRS2019

Experimental and Numerical Analysis of Skin-Stiffener Separation Using a Seven-Point Bend Configuration

Skin-stiffener separation in stiffened composite panels consists of a complex interaction between multiple scales of progressive damage and failure mechanisms. This work used a superposed cohesive element method of modeling resistance curve effects that represents the structural interface of a unidirectional tape skin and a fabric stiffener. Finite element models using cohesive elements with input properties obtained from tape-to-fabric interface characterization tests were compared to experimental results of a stable skin-stiffener separation characterization test using a seven-point bend fixture. This fixture deformed the stiffened panel specimens into a buckled configuration which induced mixed-mode interlaminar stress states at the skin-stiffener interface. The advantage of this fixture was the potential for more stable damage initiation and delamination growth compared to a stringer-stiffened panel under axial compression. Use of the superposed cohesive elements showed promise, but the characterization of interface material properties as input to the cohesive elements remains a crucial component to be investigated to ensure accurate prediction of skin-stiffener separation.

Kosztowny, Cyrus J. R.↗