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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Evaluation of long-duration exposure to the natural space environment on graphite-polyimide and graphite-epoxy mechanical properties

Experiment AO175 involved passive exposure (on oblique leading and trailing faces of LDEF) of carbon-fiber reinforced laminates of epoxy, bismaleimide, and polyimide resins. Post-flight evaluation included: optical examination of exposed surfaces, panel weight and distortion measurements, ultrasonic c-scan inspection, and conventional mechanical testing of coupons machined from the panel.

Vyhnal, Richard F.↗
NASA NTRS1989

Characterization of quantum well structures using a photocathode electron microscope

Present day integrated circuits pose a challenge to conventional electronic and mechanical test methods. Feature sizes in the submicron and nanometric regime require radical approaches in order to facilitate electrical contact to circuits and devices being tested. In addition, microwave operating frequencies require careful attention to distributed effects when considering the electrical signal paths within and external to the device under test. An alternative testing approach which combines the best of electrical and optical time domain testing is presented, namely photocathode electron microscope quantitative voltage contrast (PEMQVC).

Spencer, Michael G.↗
NASA NTRS1991

Ultrasonic velocity technique for monitoring property changes in fiber-reinforced ceramic matrix composites

A technique for measuring ultrasonic velocity was used to monitor changes that occur during processing and heat treatment of a SiC/RBSM composite. Results indicated that correlations exist between the ultrasonic velocity data and elastic modulus and interfacial shear strength data determined from mechanical tests. The ultrasonic velocity data can differentiate strength. The advantages and potential of this nondestructive evaluation method for fiber reinforced ceramic matrix composite applications are discussed.

Kautz, Harold E.↗
NASA NTRS1989

Influence of dissolved hydrogen on aluminum-lithium alloy fracture behavior

The objective of this work is to study the effects of dissolved hydrogen on the mechanical properties of 2090 and 2219 alloys. Prior to mechanical testing, potentiostatic and potentiodynamic tests were performed using NaCl/HCl solutions varying in pH from 1.5 to 7.5 (3.5 pct NaCl in deionized water). After analysis of the potentiodynamic curve for each solution, several potentiostatic experiments were conducted for various times (from 10 minutes to several hours) with a cathodic overpotential of 300 mV. These experiments were performed to select charging conditions. It is shown that the fracture of L-S and T-S orientations proceeds via slipping of layers in the S-T direction. The T-S and L-S orientations fractured with substantially higher propagation energy that the L-T and T-L orientations, due in large part to the extensive delamination propagation of the fracture.

Rivet, F. C.↗
NASA NTRS1991

Ultrasonic velocity technique for monitoring property changes in fiber-reinforced ceramic matrix composites

A technique for measuring ultrasonic velocity was used to monitor changes that occur during processing and heat treatment of a SiC/RBSM composite. Results indicated that correlations exist between the ultrasonic velocity data and elastic modulus and interfacial shear strength data determined from mechanical tests. The ultrasonic velocity data can differentiate strength. The advantages and potential of this nondestructive evaluation method for fiber reinfoced ceramic matrix composite applications are discussed.

Kautz, H. E.↗
NASA NTRS1992

Effects Of B On Intergranular Hot Cracking In Ni Alloys

Report describes experiments on role of boron on solidification of 718-type nickel/chromium/iron superalloys containing niobium and relative intergranular segregations of boron, sulfur, and phosphorus in alloys. Ten alloys studied by use of light and scanning electron microscopy (SEM), energy-dispersive x-ray analysis, transmission electron microscopy (TEM) with energy-dispersive analysis of thin-film specimens, mechanical tests for susceptibility to microfissuring, differential thermal analysis (DTA), scanning Auger microscopy, and Gleeble thermal analysis.

Thompson, Raymond G.↗
NASA NTRS1992

Evaluation of long-duration exposure to the natural space environment on the mechanical properties of carbon-reinforced epoxy and polyimide composites

Experiment AO175 involved passive exposure of carbon-fiber reinforced laminates of epoxy, bismaleimide, and polyimide resins. The post-flight evaluation includes the following: optical examination of exposed surfaces and polished cross-sections; panel weight and distortion measurements; ultrasonic c-scan inspection; and conventional mechanical testing of coupons machined from the panels.

Vyhnal, Richard F.↗
NASA NTRS1991

NASA MSFC hardware in the loop simulations of automatic rendezvous and capture systems

Two complementary hardware-in-the-loop simulation facilities for automatic rendezvous and capture systems at MSFC are described. One, the Flight Robotics Laboratory, uses an 8 DOF overhead manipulator with a work volume of 160 by 40 by 23 feet to evaluate automatic rendezvous algorithms and range/rate sensing systems. The other, the Space Station/Station Operations Mechanism Test Bed, uses a 6 DOF hydraulic table to perform docking and berthing dynamics simulations.

Tobbe, Patrick A.↗
NASA NTRS1993

Six degree of freedom active vibration damping for space application

Work performed during the period 1 Jan. - 31 Mar. 1993 on six degree of freedom active vibration damping for space application is presented. A performance and cost report is included. Topics covered include: actuator testing; mechanical amplifier design; and neural network control system development and experimental evaluation.

Haynes, Leonard S.↗
NASA NTRS1991

Mechanical and analytical screening of braided composites for transport fuselage applications

The mechanics of materials progress in support of the goal of understanding the application of braided composites in a transport aircraft fuselage are summarized. Composites consisting of both 2-D and 3-D braid patterns are investigated. Both consolidation of commingled graphite/PEEK and resin transfer molding of graphite-epoxy braided composite processes are studied. Mechanical tests were used to examine unnotched tension, open hole tension, compression, compression after impact, in-plane shear, out-of-plane tension, bearing, and crippling. Analytical methods are also developed and applied to predict the stiffness and strengths of test specimens. A preliminary study using the test data and analytical results is performed to assess the applicability of braided composites to a commercial aircraft fuselage.

Fedro, Mark J.↗
NASA NTRS1993

Improved measurement of thermal effects on microstructure

The objectives were to introduce a simple methodology which could be used to replace the time-consuming and expensive conventional methods of metallographic and quantitative analysis of thermal treatment effect on microstructure. Metallurgical analysis continually calls for the evaluation of thermal treatment effects on microstructure. This commonly demands metallographic sample preparation and microscopic examination, which are time absorbing and costly. These drawbacks are burdensome when large numbers of samples must be levied fast. Mechanical testing can sometimes be substituted, but sample size and shape frequently make these methods impractical. The experiment described here is ideal for the microstructural evaluation of lamp filaments and other wire samples such as copper wire which can be conveniently coiled.

Rastani, Mansur↗
NASA NTRS1992

Development of a four-frequency selective surface prototype spacecraft antenna

NASA-JPL's four-frequency telecommunication system design entails the creation and integration of a frequency-selective surface (FSS) subreflector into the high-gain antenna subsystem. The FSS design, which incorporates a periodic array of conducting elements on a kevlar/polymer composite structure, will be able to multiplex S, X, Ku, and Ka frequency-band wavelengths. Accounts are presented of the FSS's development, mechanical testing, and electrical testing.

Hickey, Gregory S.↗
NASA NTRS1993

Hydrogen tolerance of a Ti3Al-based alloy

The Ti-24Al-11Nb (Ti-24-11) alloy heat-treated to the fine basketweave microstructure was shown previously to be hydrogen-tolerant. In order to assess its limit of hydrogen tolerance, the tensile, creep, fracture toughness, and sustained-load crack growth behaviors of this alloy were studied as a function of hydrogen content. The mechanical test results indicated that the fine basketweave microstructure was tolerant to hydride embrittlement for hydrogen contents up to about 1500 wppm. On the other hand, hydrogen charging experiments indicated that the Ti-24-11 alloy was severely cracked and pulverized under zero load when the hydrogen content exceeded 3000 wppm. X-ray diffraction results revealed that the dichotomous behaviors might be due to the formation of face-centered cubic (fcc) delta-type hydrides at higher hydrogen contents but face-centered tetragonal (fct) gamma-type hydrides at lower hydrogen contents.

Chan, Kwai S.↗
NASA NTRS1993

Investigation of low cost material processes for liquid rocket engines

The development of low cost material processes is essential to the achievement of economical liquid rocket propulsion systems in the next century. This paper will present the results of the evaluation of some promising material processes including powder metallurgy, vacuum plasma spray, metal spray forming, and bulge forming. The physical and mechanical test results from the samples and subscale hardware fabricated from high strength copper alloys and superalloys will be discussed.

Nguyentat, Thinh↗
NASA NTRS1953

Some problems on the theory of creep

The term creep of metals is applied to the phenomenon in which, at temperatures beyond a certain limit, the metal subjected to a load slowly undergoes deformation with time. For the case of steel, the creep phenomenon must be taken into account at temperatures above 400 degrees C. Very slow deformations for a prolonged period are cumulative and lead either to inadmissible changes in the dimensions of a structural part or to its failure. The theory of creep constitutes part of the mechanics of dense media and the mechanical formulation of the problem may be given as the following: a body is subjected to the action of a given system of forces, or initial displacements are prescribed on its surface. It is required to find the stress distribution in the body and the changes or its deformations with time. For the solution of the problem of creep as thus formulated, a mechanical theory of creep is required. Such theory must necessarily bear an external, overall character based, not on the investigation of microprocesses, but on the results of mechanical tests.

METALS - CREEP↗
NASA NTRS1995

Revealing Slip Bands In A Metal-Matrix/Fiber Composite

Experimental procedure includes heat treatments and metallographic techniques developed to facilitate studies of deformation of metal-matrix/fiber composite under stress. Reveals slip bands, indicative of plastic flow occurring in matrix during mechanical tests of specimens of composite.

Lerch, Bradley A.↗
NASA NTRS1993

Laser Welding Dissimilar Reflective Alloys

This project, jointly sponsored by Rocketdyne and CSTAR, involves the development of laser joining of materials which have heretofore been impractical to bond. Of particular interest are joints between stainless steel and copper and also aluminum 6061 to aluminum 2219. CSTAR has a unique opportunity in this area since both the process and development and diagnostics are of interest to industry. Initial results using the pulse tailored laser welding technique developed in CLA for joining crack sensitive materials have proven promising for the aluminum joints based upon metallurgical and electronic microprobe analysis. A declaration of success requires additional mechanical testing. A CW technique has been applied to the stainless-copper joining with some preliminary success. These joints are of significant interest for aeronautics and rocket propulsion applications and the project is expected to continue.

Mccay, M. H.↗
NASA NTRS1995

Space-flight experience and life test performance of a synthetic hydrocarbon lubricant

An alternative wet lubricant known as Pennzane(TM) SHF X-2000 is recommended for some spaceflight bearing systems. The performance characteristics between Pennzane(TM) SHF X-2000 and Bray 815Z were compared. The life tests showed excellent performances with continuous operation approaching three years in conservative operating environments. Space flight performance data are provided for several of the tested mechanisms which are operating in-orbit since February 1994.

Bialke, Bill↗