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  • STRUCTURAL MECHANICS  (4)
  • 25.85.Ge  (2)
  • Chemical Engineering  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Mass resolved angular distribution in helium ion induced fission of233U (1992)
    Springer
    The European physical journal 342 (1992), S. 299-301 
    Details
    ISSN: 1434-601X
    Keywords: 25.85.Ge ; 25.85.Ee
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mass resolved fission fragment angular distribution was measured in the 28.5 MeV alpha induced fission of233U using recoil catcher technique and direct gamma spectrometry. The angular distribution of 8 fission products were obtained. The angular anisotropies of asymmetric fission products were found to be higher than those of symmetric products indicating a correlation between the fragment angular distribution and the mass distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01291513
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Fragment angular momenta in low and medium energy fission of242Pu (1987)
    Springer
    The European physical journal 327 (1987), S. 225-229 
    Details
    ISSN: 1434-601X
    Keywords: 25.85.Ge ; 25.85.Ec
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Independent isomeric yield ratios of128Sb were determined radiochemically in the thermal neutron induced fission of241Pu and 34 MeV alpha particle induced fission of238U, both involving the same compound nucleus (242Pu). Fragment angular momenta estimated from the measured isomer ratios using the statistical model analysis showed significantly larger fragment angular momenta in the medium energy fissioning system compared to the low energy fissioning system. This has been attributed to the effect of higher excitation energy and angular momentum in the entrance channel leading to increased fragment temperature, moments of inertia and angular velocity. An attempt was made to calculate the fragment angular momentum in the medium energy fission using the Fermi gas model for the fissioning nucleus, taking into account the multichance fission, saddle shapes of the fissioning nuclei and the angular velocity components of the fissioning nuclei both along and orthogonal to the fission axis. The calculated angular momenta agree well with the experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01292412
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Phenolic triazine (PT) resins. I. Gelation phenomenon studied by calorimetric, mechanical, and dielectric techniques (1989)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 29 (1989), S. 1488-1491 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Gelation phenomenon in thermoset polymers is an area of extreme importance from the processing point of view. Gel point (GP) has traditionally been detected using rheological and mechanical techniques. We wish to report the use of dielectric and especially calorimetric techniques for detecting GP. Using a particular thermoset system, we have compared the calorimetric, dielectric, and mechanical techniques and shown how to define GP in terms of time and temperature. As a matter of convenience, we have briefly defined the gelation phenomenon in thermosets, its significance and measurement, and a critical evaluation of the techniques for detecting GP.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760292010
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Phenolic triazine (PT) resins. II: Cure characterization by dynamic melt rheology and its comparison to DSC (1990)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1171-1174 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new approach involving dynamic melt rheology i.e. dynamic mechanical analysis in a molten inert matrix, is presented for studying the cure of thermoset resins. The degree of cure by dynamic melt rheology has been correlated with that from differential scanning calorimetry, DSC (correlation coefficient = 0.87) and the lack of an excellent correlation is attributed to the uncertainties with the DSC method at higher cure levels. A kinetic expression with appropriate constants, “E, A, and n” from our new approach is presented for predicting the time-temperature dependence of the degree of cure. Advantages of dynamic melt rheology are discussed in relationship to conventional dynamic mechanical and DSC methods.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760301810
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    Paper (German National Licenses)
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  • 5
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    Inverse dynamics of adaptive structures used as space cranes (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: As a precursor to the real-time control of fast moving adaptive structures used as space cranes, a formulation is given for the flexibility induced motion relative to the nominal motion (i.e., the motion that assumes no flexibility) and for obtaining the open loop time varying driving forces. An algorithm is proposed for the computation of the relative motion and driving forces. The governing equations are given in matrix form with explicit functional dependencies. A simulator is developed to implement the algorithm on a digital computer. In the formulations, the distributed mass of the crane is lumped by two schemes, vz., 'trapezoidal' lumping and 'Simpson's rule' lumping. The effects of the mass lumping schemes are shown by simulator runs.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Intelligent Material Systems and Structures (ISSN 1045-389X); 1; 50-75
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    A numerical method for determination of source time functions for general three-dimensional rupture propagation (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A method to determine the displacement and the stress on the crack plane for a three-dimensional shear crack of arbitrary shape propagating in an infinite, homogeneous medium which is linearly elastic everywhere off the crack plane is presented. The main idea of the method is to use a representation theorem in which the displacement at any given point on the crack plane is written as an integral of the traction over the whole crack plane. As a test of the accuracy of the numerical technique, the results are compared with known solutions for two simple cases.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-162139
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    A mathematical basis for the design and design optimization of adaptive trusses in precision control (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A mathematical basis for the optimal design of adaptive trusses to be used in supporting precision equipment is provided. The general theory of adaptive structures is introduced, and the global optimization problem of placing a limited number, q, of actuators, so as to maximally achieve precision control and provide prestress, is stated. Two serialized optimization problems, namely, optimal actuator placement for prestress and optimal actuator placement for precision control, are addressed. In the case of prestressing, the computation of a 'desired' prestress is discussed, the interaction between actuators and redundants in conveying the prestress is shown in its mathematical form, and a methodology for arriving at the optimal placement of actuators and additional redundants is discussed. With regard to precision control, an optimal placement scheme (for q actuators) for maximum 'authority' over the precision points is suggested. The results of the two serialized optimization problems are combined to give a suboptimal solution to the global optimization problem. A method for improving this suboptimal actuator placement scheme by iteration is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: Joint U.S./Japan Conference on Adaptive Structures; Nov 13, 1990 - Nov 15, 1990; Maui, HI; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Optimal actuator placement in adaptive precision trusses (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Actuator placement in adaptive truss structures is to cater to two needs: displacement control of precision points and preloading the elements to overcome joint slackness. Due to technological and financial considerations, the number of actuators available is much less than the degrees of freedom of precision points to be controlled and the degree of redundancy of the structure. An approach for optimal actuator location is outlined. Test cases to demonstrate the effectiveness of the scheme are applied to the Precision Segmented Reflector Truss.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 92-2344 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 13, 1992 - Apr 15, 1992; Dallas, TX; United States
    Format: text
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    NASA TECHNICAL REPORTS
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