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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 721 records · Page 40
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Reevaluation of the stress-life relation in rolling-element bearings

Four groups of 12.7 millimeter diameter vacuum-degassed AISI 52100 balls were tested, each at a maximum Hertz stress in the range of 4.5 times 10 to 9th power to 6.0 times 10 to 9th power N/m2. Tests were run in the five-ball fatigue tester at a contact angle of 30 deg and a shaft speed of 10,000 rpm. The 10 percent fatigue lives at the four stress levels indicated that fatigue life is inversely proportional to maximum Hertz stress raised to the power of 12. This result agrees with a survey of the literature which suggests that a stress-life exponent of approximately 12 is typical of vacuum-processed bearing steels rather than the exponent of 9 which has been generally accepted by the bearing industry.

Parker, R. J.↗
NASA NTRS1972

Effect of residual stresses induced by prestressing on rolling element fatigue life

A mechanical prestress cycle suitable to induce compressive stress beneath the surface of the inner race of radially loaded 207-size bearings was determined. Compressive residual stress in excess 0.69 x 10 to the 9th power N/sq m (100,000 psi), as measured by X-ray diffraction, were induced at the depth of maximum shearing stress. The prestress cycle consisted of running the bearings for 25 hours at 2750 rpm at a radial load which produced a maximum Hertz stress of 3.3 x 10 to the 9th power N/sq m (480,000 psi) at the contact of the inner race and the heaviest loaded ball. Bearings subjected to this prestress cycle and subsequently fatigue tested gave a 10 percent fatigue life greater than twice that of a group of baseline bearings.

Parker, R. J.↗
NASA NTRS1972

An elastic analysis of stresses in a uniaxially loaded sheet containing an interference-fit bolt

The stresses in a sheet with an interference-fit bolt have been calculated for two sheet-bolt interface conditions: a frictionless interface and a fixed (no-slip) interface. The stress distributions were calculated for various combinations of sheet and bolt moduli. The results show that for repeated loading the local stress range is significantly smaller if an interference bolt is used instead of a loosely fitting one. This reduction in local stress range is more pronounced when the ratio of bolt modulus to sheet modulus is large. The analysis also indicates that currently used standard values of interference cause yielding in the sheet.

Crews, J. H., Jr.↗
NASA NTRS1972

Experimental and theoretical investigation of stress wave attenuation in fiber reinforced composites.

The propagation of an initialrcidrical pressure pulse through a linear elastic fiber reinforced composite medium is analysed, both experimentally and analytically. In the experiment, tests were performed on plates with single and multiple circular inclusions embedded in a matrix of lower characteristic impedance. Sharp compression pulses were generated at an edge of the plate. Strain gages were mounted on various positions of the plate to determine the attenuation of the transient stress in the fiber reinforced composite. The qualitative analytical treatment is based on the methods of propagating stress discontinuities. Computer programs were written to numerically determine the changes in the shape of the leading wave front and the stresses immediately behind it. Experimental results for the attenuation of stress wave on steel-aluminum and steel-brass fiber-matrix composites compared very well with the computed analytical results when the applied pressure is generated by small explosive charges. The results did not compare well when the applied pressure is generated by projectile impact.

Yang, J. C. S.↗
NASA NTRS1972

A dynamic polariscope for stress wave analysis.

A polariscope for the study of the propagation of stress waves in birefringent sheets is described. Sensitive, fast-responding photomultiplier tubes, a laser light source, and a multiple channel oscilloscope were used for the simultaneous recording of the stress-optic data at several points of the target following impact. A method of separation of stresses and the computation of displacement, strain, and stress is given.

Kinslow, R.↗
NASA NTRS1972

Attenuation of stress waves in single and multi-layered structures

Analytical and experimental studies were made of the attenuation of the stress waves during passage through single and multilayer structures. The investigation included studies on elastic and plastic stress wave propagation in the composites and those on shock mitigating material characteristics such as dynamic stress-strain relations and energy absorbing properties. The results of the studies are applied to methods for reducing the stresses imposed on a spacecraft during planetary or ocean landings.

Yang, J. C. S.↗
NASA NTRS1974

Plane-stress fracture of compact and notch-bend specimens

Thin-gaged or high toughness materials containing cracks usually fail in a ductile manner with nominal failure stresses approaching the ultimate strength of the material. For such materials, a two-parameter fracture criterion was developed. An equation which related the linear elastic stress-intensity factor, elastic nominal stress, and two material parameters was previously derived and has been used as a fracture criterion for surface- and through-cracked specimens under tensile loading. This two-parameter fracture criterion was rederived in a more general form and was extended to compact and notch-bend fracture specimens. A close correlation was found between experimental and predicted failure stresses.

Newman, J. C., Jr.↗
NASA NTRS1974

Ultrasonic measurement of stress in railroad wheels and in long lengths of welded rail

The failure of high speed emergency braking is discussed for railroad wheels and track. It is shown that high compressive residual stresses exist in the rims of new wheels which generate excessive heat, reducing the stress levels. Thermal stresses that build up in continuous lengths of welded track are reported and nondestructive methods of measuring stresses in thick steel are presented for identification, replacement, or adjustment before hazardous failures occur.

Clotfelter, W. N.↗
NASA NTRS1974

Experimental evaluation of stresses in cylindrically hollow (drilled) balls

An experimental stress analysis was undertaken to evaluate stresses within cylindrically hollow (drilled) bearing balls proportioned for 40, 50, and 60 percent mass reductions. Strain gage rosettes were used to determine principal strains and stresses in the steel ball models statically loaded in various orientations. Results are reported for 127 mm OD balls under 44,500 N loads. Similitude considerations permit these results to be applied to calculate stresses in actual size drilled bearing balls proportioned to these mass reductions.

Nypan, L. J.↗
NASA NTRS1974

A study of RSI under combined stresses

The behavior of typical rigidized surface insulation material (RSI) under combined loading states was investigated. In particular, the thermal stress states induced during reentry of the space shuttle were of prime concern. A typical RSI tile was analyzed for reentry thermal stresses under computed thermal gradients for a model of the RSI material. The results of the thermal stress analyses were then used to aid in defining typical combined stress states for the failure analysis of RSI.

Kibler, J. J.↗
NASA NTRS1974

A test procedure for determining the influence of stress ratio on fatigue crack growth

A test procedure is outlined by which the rate of fatigue crack growth over a range of stress ratios and stress intensities can be determined expeditiously using a small number of specimens. This procedure was developed to avoid or circumvent the effects of load interactions on fatigue crack growth, and was used to develop data on a mill annealed Ti-6Al-4V alloy plate. Experimental data suggest that the rates of fatigue crack growth among the various stress ratios may be correlated in terms of an effective stress intensity range at given values of K max. This procedure is not to be used, however, for determining the corrosion fatigue crack growth characteristics of alloys when nonsteady-state effects are significant.

Fitzgerald, J. H.↗
NASA NTRS1974

Vibration and stress analysis of soft-bonded shuttle insulation tiles. Modal analysis with compact widely space stringers

An efficient iterative procedure is described for the vibration and modal stress analysis of reusable surface insulation (RSI) of multi-tiled space shuttle panels. The method, which is quite general, is rapidly convergent and highly useful for this application. A user-oriented computer program based upon this procedure and titled RESIST (REusable Surface Insulation Stresses) has been prepared for the analysis of compact, widely spaced, stringer-stiffened panels. RESIST, which uses finite element methods, obtains three dimensional tile stresses in the isolator, arrestor (if any) and RSI materials. Two dimensional stresses are obtained in the tile coating and the stringer-stiffened primary structure plate. A special feature of the program is that all the usual detailed finite element grid data is generated internally from a minimum of input data. The program can accommodate tile idealizations with up to 850 nodes (2550 degrees-of-freedom) and primary structure idealizations with a maximum of 10,000 degrees-of-freedom. The primary structure vibration capability is achieved through the development of a new rapid eigenvalue program named ALARM (Automatic LArge Reduction of Matrices to tridiagonal form).

Ojalvo, I. U.↗
NASA NTRS1975

Application of experimental stress analysis techniques to speed ball bearings

The object of the project was to determine experimentally the stress distribution in cylindrically hollow and spherically hollow balls. Ball models several times actual bearing ball size were fabricated. Strain gage rosettes will be mounted on the outside and inside surfaces of the models at specific locations and orientations. The models were subjected to a range of static loads simulating actual ball-race contact loads experienced in high-speed bearings operating at DN values from 2 to 4 million. The strain gages were read, and the principal strains determined for each load setting. Principal stresses were calculated and dimensionless stress coefficients determined to permit the evaluation of stresses in hollow balls of any size and load of geometrically similar configuration.

Nypan, L. J.↗
NASA NTRS1975

Psychological stress measurement through voice output analysis

Audio tape recordings of selected Skylab communications were processed by a psychological stress evaluator. Strip chart tracings were read blind and scores were assigned based on characteristics reported by the manufacturer to indicate psychological stress. These scores were analyzed for their empirical relationships with operational variables in Skylab judged to represent varying degrees of situational stress. Although some statistically significant relationships were found, the technique was not judged to be sufficiently predictive to warrant its use in assessing the degree of psychological stress of crew members in future space missions.

Older, H. J.↗
NASA NTRS1975

Stress relaxation and mechanical properties of RL-1973 and PD-200-16 silicone resin sponge materials

Stress relaxation tests were conducted by loading specimens in double-lap shear to a preselected strain level and monitoring the decay of stress with time. The stress relaxation response characteristics were measured over a temperature range of 100 to 300 K and four strain levels. It is concluded that only a slight amount of stress relaxation was observed, and the stiffness increased approximately two orders of magnitude over the range of temperatures.

Saylak, D.↗
NASA NTRS1975

Stresses in a webbed ball

An experimental stress analysis was undertaken to evaluate stresses within cylindrically hollow reinforced webbed bearing balls proportioned for a 50 percent mass reduction. Strain gage rosettes were used to determine principal strains and stresses in the steel ball models, which were statically loaded in various orientations. Results are reported for 127 mm (5 in.) outside diameter balls under 44,500 N (10,000 lb) loads. Similitude considerations permit these results to be applied to calculations of stresses in actual size drilled bearing balls proportioned to these mass reductions.

Nypan, L. J.↗
NASA NTRS1974

Thermal stresses in chemically hardening elastic media with application to the molding process

A method has been formulated for the determination of thermal stresses in materials which harden in the presence of an exothermic chemical reaction. Hardening is described by the transformation of the material from an inviscid liquid-like state into an elastic solid, where intermediate states consist of a mixture of the two, in a ratio which is determined by the degree of chemical reaction. The method is illustrated in terms of an infinite slab cast between two rigid mold surfaces. It is found that the stress component normal to the slab surfaces vanishes in the residual state, so that removal of the slab from the mold leaves the remaining residual stress unchanged. On the other hand, the residual stress component parallel to the slab surfaces does not vanish. Its distribution is described as a function of the parameters of the hardening process.

Levitsky, M.↗
NASA NTRS1974

An experimental evaluation of the stresses in drilled balls

Stresses in dimensionally similar large models of 40-, 50- and 60-percent mass reduction cylindrically hollow 'drilled' bearing balls were experimentally evaluated with flat strain gage rosettes. Dimensionless principal stress coefficients were calculated and were applied to estimate the bending stresses in the drilled balls of three series of full-scale bearing experiments. Stresses were highest when the applied load approached the edge of the hole, and ranged up to almost 620 million Newtons per sq m at the bore.

Nypan, L. J.↗