Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “cohesiveness”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The use of analytical surface tools in the fundamental study of wear

This paper reviews the various techniques and surface tools available for the study of the atomic nature of the wear of materials. These include chemical etching, X-ray diffraction, electron diffraction, scanning electron microscopy, low-energy electron diffraction, Auger emission spectroscopy analysis, electron spectroscopy for chemical analysis, field ion microscopy, and the atom probe. Properties of the surface and wear surface regions which effect wear such as surface energy, crystal structure, crystallographic orientation, mode of dislocation behavior, and cohesive binding are discussed. A number of mechanisms involved in the generation of wear particles are identified with the aid of the aforementioned tools.

Buckley, D. H.↗
NASA NTRS1978

Microparticle accelerator of unique design

A microparticle accelerator has been devised for micrometeoroid impact and cratering simulation; the device produces high-velocity (0.5-15 km/sec), micrometer-sized projectiles of any cohesive material. In the source, an electrodynamic levitator, single particles are charged by ion bombardment in high vacuum. The vertical accelerator has four drift tubes, each initially at a high negative voltage. After injection of the projectile, each tube is grounded in turn at a time determined by the voltage and charge/mass ratio to give four acceleration stages with a total voltage equivalent to about 1.7 MV.

Vedder, J. F.↗
NASA NTRS1978

NDT of DC-10 graphite-epoxy rudder

The results of visual and ultrasonic nondestructive tests (NDT) on a DC-10 rudder constructed of Thornel 300/5208 graphite-epoxy are presented. A viscous couplant was used for both contact pulse-echo ultrasonics and the Fokker bondtester. Attention is given to the stiffness of cohesive bond structures (the rudder is assembled primarily in a basic six-ply pattern), and to possible delamination. A piezoelectric transducer is employed to sense changes in impedance and signal amplitude. In all, four rudder units were evaluated. The main problems found in the units were porosity and cracking. It is noted that rudder unit four was able to be sufficiently cured to permit static tests on all rib, spar, and skin panel interfaces.

Hagemaier, D. J.↗
NASA NTRS1978

The puzzling moons of Mars

Viking Orbiter observations of Phobos and Deimos are presented with attention to physical dimension and surface features. Both satellites are approximately 1.4 times as long as they are wide; Phobos having a length of 27 km, while Deimos is half that size. In addition, both satellites are tidally locked, as is earth's moon, and are held together by cohesive forces as well as by gravity. Phobos and Deimos are both heavily cratered, and Phobos has deep (30 m) grooves in the vicinity of its largest crater, Stickney; indicating surface fracturing under meteorite impact. The craters on Deimos are largely filled with a fine-grained substance, probably crater ejecta.

Veverka, J.↗
NASA NTRS1979

Friction and wear characteristics of iron-chromium alloys in contact with themselves and silicon carbide

Sliding friction experiments were conducted with various iron-chromium alloys in contact with (1) themselves, (2) single crystal silicon carbide disks, and (3) single crystal abrasive grit of silicon carbide. Results indicate the coefficients of friction for the alloys sliding against themselves are between those for pure iron and pure chromium, and are only slightly different with 1, 5, 9, 14, and 19 weight percent chromium in iron. The wear is due, primarily, to shearing, or tearing fracture, of the cohesive bonds in the bulk metal and plowing of the bulk by lumps of wear debris. There are only slight differences in the coefficients of friction for the various alloys when sliding on silicon carbide. The coefficient of friction for the alloys are higher than those for pure iron and pure chromium. Alloy hardening observed in the alloys plays a dominant role in controlling the abrasive friction and wear behavior of the alloys.

Miyoshi, K.↗
NASA NTRS1978

The mechanics of ringed basin formation

The study investigates the mechanics of ring formation in lunar basins by collapse or slumping. Two classes of models are presented in order to broaden the range of plausible mechanisms involved. Extrusion flow models which assume a weak layer underlying a strong layer as well as plastic flow models which assume a continuous decrease of cohesion strength with depth are considered. In both classes, strength or resistance to deformation decreases with depth. If this decrease is rapid enough, in either set of models, at least one concentric fault scarp forms. The ratio between the scarp radius and the crater radius varies between 1.2 and about 2.7 depending on the model, and is thus in the range of observed radius ratios.

Melosh, H. J.↗
NASA NTRS1978

An investigation into the role of plastic failure in crater modification

The mechanical stability of an impact crater is analyzed in this paper via a quasi-static, axisymmetric slip line theory of plasticity. The yield model incorporated is Mohr-Coulomb and a simplified rectangular profile is used for the transient cavity. The degree of stability (or instability) is described as a function of internal friction angle, depth/diameter ratio, and a dimensionless parameter. To match the observed slumping of large lunar craters the cohesion strength of the lunar surface material must be low (less than 20 bars) and the angle of internal friction must be less than 2 deg. It is not implausible that these failure strength characteristics are realized by freshly shocked rock.

Mckinnon, W. B.↗
NASA NTRS1979

Asteroidal regoliths

A physical model is developed for the evolution of regoliths on small bodies and applied to the asteroid and meteorite parent bodies. The model considers global deposition of that fraction of cratering ejecta that is not lost to space. In addition, it is applied to cases of both strong, cohesive bodies and to bodies of weak, unconsolidated materials. It is found that large, strong asteroids generate surficial regoliths of a few kilometers depth while strong asteroids smaller than 10-km diameter generate negligible regoliths. In conclusion, it is noted that the theory that substantial regoliths are produced predominantly by blanketing differs from earlier hypotheses that asteroidal regoliths might be thin or absent and that short surface exposure of asteroidal materials is due chiefly to erosion rather than blanketing.

Housen, K. R.↗
NASA NTRS1980

Adhesion, friction, and wear of binary alloys in contact with single-crystal silicon carbide

Sliding friction experiments, conducted with various iron base alloys (alloying elements are Ti, Cr, Mn, Ni, Rh and W) in contact with a single crystal silicon carbide /0001/ surface in vacuum are discussed. Results indicate atomic size misfit and concentration of alloying elements play a dominant role in controlling adhesion, friction, and wear properties of iron-base binary alloys. The controlling mechanism of the alloy properties is as an intrinsic effect involving the resistance to shear fracture of cohesive bonding in the alloy. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases as the solute-to-iron atomic radius ratio increases or decreases from unity. Alloys having higher solute concentration produce more transfer to silicon carbide than do alloys having low solute concentrations. The chemical activity of the alloying element is also an important parameter in controlling adhesion and friction of alloys.

Miyoshi, K.↗
NASA NTRS1979

Eolian sedimentation on earth and Mars - Some comparisons

Eolian sediments on earth are mostly formed from quartz. The quartz particles originally came from a granitic source. With respect to eolian sediments on Mars, it appears that an entirely different set of criteria must apply, but some critical parameters can be usefully compared. Impact experiments with basalt in eolian abrasion devices suggest that basalt sand-sized particles fragment rapidly to produce silt and clay-sized detritus. Cohesive forces must be more effective on Mars since the gravitational contribution to the bond/weight ratio is lower. Compared to the terrestrial situation, both larger and smaller particles can be expected to make significant contributions to eolian sediments on Mars. The low gravity and the high speed of moving particles and the relative weak rock material of which they are composed will allow large-scale fine particle production.

Smalley, I. J.↗
NASA NTRS1979

Recent developments in liquid-metal embrittlement

The paper reviews developments in liquid-metal embrittlement of the past 7 years including data on cyclic loading. Embrittlement by solid and liquid metals and by hydrogen has many common features, although the mechanism of embrittler transport differs. Fracture may occur in each type of embrittlement by environmentally assisted shear and by reduced cohesion; embrittlement under cyclic loading has been widely observed, with stress level, temperature, and substrate alloy composition and grain size being the major variables. The degree of embrittlement between any combination of environment (i.e. hydrogen, liquid metal, or solid metal) and substrate depends upon the strength of the interaction with the substrate, the kinetics of embrittler transport, the mutual solubility of embrittler and substrate, and a large number of test and microstructural conditions. A method of calculating the most significant of these variables and the strength of interaction was reviewed and predictions of embrittlement in previously untested couples were made.

Stoloff, N. S.↗
NASA NTRS1980

Physical chemistry and evolution of salt tolerance in halobacteria

The cellular constituents of extremely halophilic bacteria not only tolerate high salt concentration, but in many cases require it for optical functioning. The characteristics affected by salt include enzyme activity, stability, allosteric regulation, conformation and subunit association. The salt effects are of two major kinds: electrostatic shielding of negative charges by cations at low salt concentration, and hydrophobic stabilization by salting-out type salts at high salt concentration. The composition of halobacterial proteins shows an excess of acidic amino acids and a deficiency of nonpolar amino acids, which accounts for these effects. Since the cohesive forces are weaker and the repulsing forces are stronger in these proteins, preventing aggregation in salt, these structures are no longer suited for functioning in the absence of high salt concentrations. Unlike these nonspecific effects, ribosomes in halobacteria show marked preference for potassium over sodium ions. To ensure the proper intracellular ionic composition, powerful ion transport systems have evolved in the halobacteria, resulting in the extrusion of sodium ions and their replacement by potassium. It is likely that such membrane transport system for ionic movements is a necessary requisite for salt tolerance.

Lanyi, J. K.↗
NASA NTRS1981

The 1980 Large space systems technology. Volume 2: Base technology

Technology pertinent to large antenna systems, technology related to large space platform systems, and base technology applicable to both antenna and platform systems are discussed. Design studies, structural testing results, and theoretical applications are presented with accompanying validation data. A total systems approach including controls, platforms, and antennas is presented as a cohesive, programmatic plan for large space systems.

Kopriver, F., III↗
NASA NTRS1981

Materials Processing in Space (MPS) program description

Insight is provided into the scientific rotationale for materials processing in space (MPS), and a comprehensive and cohesive approach for implementation and integration of the many, diverse aspects of MPS is described. The programmatic and management functions apply to all projects and activities implemented under MPS. It is intended that specific project plans, providing project unique details, will be appended to this document for endeavors such as the Space Processing Applications Rocket (SPAR) Project, the Materials Experiment Assembly (MEA) Project, the MPS/Spacelab (MPS/SL) Project, and the Materials Experiment Carrier (MEC) Payloads.

Source record↗
NASA NTRS1980

The adhesion, friction, and wear of binary alloys in contact with single-crystal silicon carbide

Sliding friction experiments were conducted with various iron-base alloys (alloying elements were Ti, Cr, Ni, Rh, and W) in contact with a single-crystal silicon carbide (0001) surface in vacuum. Results indicate atomic size misfit and concentration of alloying elements play a dominant role in controlling adhesion, friction, and wear properties of iron-base binary alloys. The controlling mechanism of the alloy properties is an intrinsic effect involving the resistance to shear fracture of cohesive bonding in the alloy. The coefficient of friction generally increases with an increase in solute concentration. The coefficient of friction increases as the solute-to-iron atomic radius ratio increases or decreases from unity. Alloys having higher solute concentration produce more transfer to silicon carbide than do alloys having low solute concentrations. The chemical activity of the alloying element is also an important parameter in controlling adhesion and friction of alloys.

Miyoshi, K.↗
NASA NTRS1981

An experimental investigation of silicon wafer surface roughness and its effect on the pull-strength of plated metals

Plated silicon wafers with surface roughness ranging from 0.4 to 130 microinches, subjected to tensile pull-strength tests, were analyzed. Results show that the measured pull-strength of plated metals decrease with increasing silicon surface roughness, effecting a weakening of the cohesive strength of the wafer, possibly caused by microcracks or 'etch pits' in the silicon surface. The mean value of pull-strength for all wafers plated with the Ni-Cu-Cu sequence exceeded the required 450 g/0.02 sq cm, and at Ra = 0.4 microinches, the mean pull-strength for the Ni-Cu-Cu and Ni-Cu wafers were 2290 and 850 g/0.02 sq cm, respectively. The development of standardized methods for measuring contact pull-strength is suggested. These results may have some bearing on solar cell arrays problems.

Spiers, G. D.↗