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  • 1
    ISSN: 1432-2153
    Keywords: Shear stress and strain ; Partial dislocations ; Stacking faults
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics , Technology
    Notes: Abstract A mechanism responsible for the high speed shear relaxation immediately behind shock fronts is suggested. The shear stress generated by the shock front causes the growth of two-dimensional defects in the crystal lattice, known as stacking faults (SF). Increasing the SF concentration and area leads to the absorption of impact energy. A breach of the lattice symmetry due to the SF presence causes an additional shift in peaks of the x-ray diffraction pattern obtained from the shock compressed material. Thus pulse x-ray diffraction is the only method that experimentally measures both the dilatational and deviatoric components of the deformation, which takes place during shock wave passage.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0681
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Übersicht Ein semi-empirisches Modell zur Berechnung der Verdichtungswellengeschwindigkeit bei planarer Stoßeinwirkung auf Polyurethanschaumstoff wird aufgrund der Analyse einiger experimenteller Beobachtungen aufgestellt. Das Modell ermöglicht die Berechnung der infolge der Stoßverdichtung induzierten Wellengeschwindigkeit und Dichtenänderung. Die Vorhersagen des Modells werden mit Versuchsergebnissen verglichen und können als ausreichend eingestuft werden.
    Notes: Summary A semi-empirical model for calculating the velocity of the compaction wave which is transmitted into a polyurethane foam struck head-on by a planar shock wave is developed on the basis of some experimental observations. The compaction wave induced velocity and the induced density are determined. Predictions of the model are compared to experimental results and found to be satisfactory.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental facility was developed to obtain real-time, quantitative, x-ray diffraction data in laboratory plate impact experiments. A powder gun, to generate plane wave loading in samples, was designed and built specifically to permit flash x-ray diffraction measurements in shock-compression experiments. Spatial resolution and quality of the diffracted signals were improved significantly over past attempts through partial collimation of the incident beam and the use of two-dimensional detectors to record data from shocked crystals. The experimental configuration and synchronization issues are discussed, and relevant details of the x-ray system and the powder gun are described. Representative results are presented from experiments designed to determine unit cell compression in shock-compressed LiF single crystals subjected to both elastic and elastic-plastic deformation, respectively. The developments described here are expected to be useful for examining lattice deformation and structural changes in shock wave compression studies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3740-3747 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new model of fast operated dislocation source based on multiplication and motion of partial dislocations bounding the stacking fault is suggested. Stress-activated stretching of lateral branches of the partial dislocation bowed-out segment results in collapse of these branches with subsequent restoration of the "initial'' dislocation half-loop and generation of a "fresh'' partial dislocation loop, both capable to produce the next multiplication act. The multiplication results in the exponential increase of both dislocations and stacking faults concentration and is accompanied with the plastic deformation having a strain rate dε/dt∼2t/ΔT. The characteristic time of the process, ΔT, ranges from 10−9 to 10−10 s. The model explains the variations of x-ray diffraction pattern for the material undergoing shock compression, the shock-induced formation of twins, and shear bands and pre-fracture voids nucleation in the rarefaction wave. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2013-08-31
    Description: The speed capability of rolling element bearings has increased from speeds of less than two million DN to speeds of three million DN. The life and reliability of these bearings also increased where they are equal to, or greater than, those of bearings with limited speed capability. Design parameters must be carefully chosen and optimized based upon sophisticated bearing computer programs. Material and lubricant selection must be integrated into the bearing design. Bearing thermal management must be implemented through proper lubrication and cooling. Parameters which can be used to design, specify, and lubricate high speed bearings are discussed.
    Keywords: MECHANICAL ENGINEERING
    Type: NAS 1.15:87107 , E-2670 , NASA-TM-87107
    Format: application/pdf
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  • 6
    Publication Date: 2013-08-31
    Description: An analysis was performed to determine the effects of inner-ring speed and press fits on roller bearing fatigue life. The effects of the resultant hoop and radial stresses on the principal stresses were considered. The maximum shear stresses below the Hertzian contact were determined for different conditions of inner-ring speed and load, and were applied to a conventional roller bearing life analysis. The effect of mean stress was determined using Goodman diagram approach. Hoop stresses caused by press fits and centrifugal force can reduce bearing life by as much as 90 percent. Use of a Goodman diagram predicts life reductions of 20 to 30 percent. The depth of the maximum shear stress remains virtually unchanged.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-87165 , NAS 1.15:87165 , E-2516
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  • 7
    facet.materialart.
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    In:  CASI
    Publication Date: 2013-08-31
    Description: Traction drives are among the simplest of all speed-changing mechanisms. Because of their simplicity and their ability to smoothly and continuously adjust speed, they are excellent choices for many drive system applications. They have been used in industrial service for more than 100 years. Today's traction drives have power capacities which rival the best gear and belt drives due to modern traction fluids and highly fatigue-resistant bearing steels. This report summarizes methods to analyze and size traction drives. Lubrication principles, contact kinematics, stress, fatigue life, and performance prediction methods are presented. The effects of the lubricant's traction characteristics on life and power loss are discussed. An example problem is given which illustrates the effects of spin on power loss. Loading mechanism design and the design of nonlubricated friction wheels and rings are also treated.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-RP-1154 , NAS 1.61:1154 , E-2143
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  • 8
    facet.materialart.
    Unknown
    In:  CASI
    Publication Date: 2013-08-31
    Description: Gearing technology in its modern form has a history of only 100 years. However, the earliest form of gearing can probably be traced back to fourth century B.C. Greece. Current gear practice and recent advances in the technology are drawn together. The history of gearing is reviewed briefly in the Introduction. Subsequent sections describe types of gearing and their geometry, processing, and manufacture. Both conventional and more recent methods of determining gear stress and deflections are considered. The subjects of life prediction and lubrication are additions to the literature. New and more complete methods of power loss predictions as well as an optimum design of spur gear meshes are described. Conventional and new types of power transmission systems are presented.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-RP-1152 , NAS 1.61:1152 , E-2003 , AVSCOM-TR-84-C-15
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  • 9
    Publication Date: 2013-08-31
    Description: An analysis was performed to determine the effects of inner ring speed and press fit on the rolling element fatigue life of a roller bearing inner race contact. The effects of the resultant hoop and radial stresses on the principal stresses were considered. The maximum shear stresses below the Hertzian contact were determined for different conditions of inner ring speed, load, and geometry and were applied to a conventional ring life analysis. The race contact fatigue life was reduced by more than 90 percent for some conditions when speed and press fit were considered. The depth of the maximum shear stress remained virtually unchanged.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TP-2496 , E-2476 , NAS 1.60:2496
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  • 10
    Publication Date: 2013-08-31
    Description: Kinematic precision is affected by errors which are the result of either intentional adjustments or accidental defects in manufacturing and assembly of gear trains. A method for the determination of kinematic precision of gear trains is described. The method is based on the exact kinematic relations for the contact point motions of the gear tooth surfaces under the influence of errors. An approximate method is also explained. Example applications of the general approximate methods are demonstrated for gear trains consisting of involute (spur and helical) gears, circular arc (Wildhaber-Novikov) gears, and spiral bevel gears. Gear noise measurements from a helicopter transmission are presented and discussed with relation to the kinematic precision theory.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-TM-82887 , AVRADCOM-TR-82-C-10 , NAS 1.15:82887 , E-1191
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