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  • aging airplanes.  (1)
  • multiple scales  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Mechanics of time-dependent materials 3 (1999), S. 263-278 
    ISSN: 1573-2738
    Schlagwort(e): fuzzy constraint method ; multiple scales ; non-equilibrium statistical thermodynamics ; polymers ; unified relaxation spectrum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract The molecular relaxation mechanisms of polymers withmulti-scale units of motion in glassy, rubbery and melt states areproposed based upon a fuzzy constraint method and non-equilibriumstatistical thermodynamics. The entanglement effects due to cohesiveforce and steric hindrance are expressed quantitatively in terms of amembership function. The micro-Brownian motion of a polymer chain isgoverned by the Langevin equation, which accounts for viscous force,nonuniform tension, entanglement constraint force and random force.Perturbation solutions have been established for different time and sizescales. The solutions account for the effects of both intramolecular andintermolecular interactions in the relaxation process. The unifiedrelaxation spectrum over many orders of time scale is a naturalconsequence of macromolecular structure, which satisfies thetime-temperature equivalence in the form of the Arrhenius equation atlow and high temperatures and in the form of the WLF equation near theglass transition temperature. The barrier model, the normal mode theory,the retraction and reptation theories can be taken as special casescorresponding to different scales.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    International journal of fracture 85 (1997), S. 185-200 
    ISSN: 1573-2673
    Schlagwort(e): multiple site damage ; widespread fatigue damage ; aging airplanes.
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau
    Notizen: Abstract This paper presents a methodology for predicting the thresholds of multiple site damage and widespread fatigue damage in fuselage lap slices. Widespread fatigue damage is a type of multiple cracking that reduces the airframe residual strength to a level below the damage tolerant requirement. The MSD threshold refers to the point in the lifetime of an airplane when two adjacent collinear fatigue cracks can linkup at the allowable stress. The WFD threshold is the point in time when linkup of a primary crack created from accidental damage and secondary cracks created from fatigue can result in a catastrophic failure. The methodology presented in this paper combines results from residual strength analysis and fatigue crack growth testing to determine these thresholds. In particular, a displacement compatibility approach is adopted to calculate residual strength in curved stiffened panels tested in the laboratory. The laboratory experiments also include fatigue testing of full-scale panels containing a debonded lap slice. Based on this methodology, the threshold of widespread fatigue damage for these laboratory panels, adjusted to zero minimum-stress cycling, is between 32,000 and 40,000 cycles, and the threshold of multiple site damage is about 70,000 cycles.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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