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    Item type:Publication, Access status: without files ,
    Friction-induced vibration of artificial hip joints
    (Wiley, 2009-12-01)
    Weiß, Cornelius
    ;
    Hothan, Arne
    ;
    Morlock, Michael
    ;
    Hoffmann, Norbert
    A hip replacement system is analysed with respect to its susceptibility to friction induced vibrations under laboratory conditions and in a pseudo-in vivo setup. The method of complex eigenvalue extraction within the framework of finite-element modelling and analysis is used to identify the geometric properties and system parameters that might lead to unstable sliding states. The approach presented reveals negatively damped eigenmodes for both the pseudo-in vivo setup and the not-implanted system under laboratory conditions without boundary conditions. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Publicationtype: Journal Article
      7
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    On the role of varying normal load and of randomly distributed relative velocities in the wavelength selection process of wear-pattern generation
    (Elsevier, 2007-12-15)
    Hoffmann, Norbert
    ;
    Misol, M.
    In systems with moving contacts, as e.g. automotive vehicles on dirt-roads, friction brakes, and of course railway vehicles moving on railway tracks, spatially periodic wear patterns may appear on the contact partners' surfaces. There is general agreement that the patterns are related to structural resonances. Using simple models with a moving point contact and an idealized wear model the present work first reviews some of the present understanding of wear-pattern generation. Then additional intuitively accessible explanations for the phenomena observed are developed and the effect of randomly specified relative velocities on the wavelength selection process is investigated. For this purpose the stability analysis of the surface evolution equation is pursued with the full, as well as with a reduced system, and a simple linear approach to deal with distributions of relative velocities is introduced. For fixed relative velocity the analysis yields an intuitively accessible picture of wear-pattern appearance or evanescence, as well as of wear-pattern motion. Based on these results it is shown, how dominant wavelengths are selected as a consequence of randomly distributed relative velocities.
    Publicationtype: Journal Article
      2
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    Effects of rate and state dependent friction on the stability of steady sliding
    (VDI Fachmedien, 2007)
    Hoffmann, Norbert
    ;
    Weiß, Cornelius
    The influence of LuGre-type friction on the fundamental mechanisms resulting in linear instability of steady sliding is investigated. Both a velocity-dependent kinetic friction coefficient as well as mode-coupling are considered. It turns out that the destabilizing effect of a kinetic friction coefficient that decreases with relative sliding velocity is reduced when the rate-dependent effects of LuGre-type friction are introduced and become more pronounced. Mode-coupling instability however seems to be much more robust with respect to underlying rate-dependencies.
    Publicationtype: Conference Paper
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