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Damage tolerance investigations of innovative metallic airframe structures

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The continuously expanding commercial air traffic of the last decades steadily increased 
 the demand for highly efficient... Weiterlesen
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The continuously expanding commercial air traffic of the last decades steadily increased 
 the demand for highly efficient aircraft which offer extended operation times
 while reducing costs and environmental impact at the same time. The associated design
 requirements for reduced structural weight and improved fatigue life represent
 the major challenges for todays aircraft structures and have significantly intensified
 the competition between metallic and composite airframe applications. New metallic
 design concepts try to face this competition by combining latest materials and
 innovative manufacturing methods, like high speed machining, laser beam welding
 or friction stir welding, which allows for possible savings with respect to structural
 weight and manufacturing costs. However, due to their integral characteristics, the
 damage tolerance behaviour of these new designs is generally inferior to the common
 differential design. Reliable estimations on the fatigue life of integrally stiffened
 structures consequently necessitate assessment methodologies that are capable to include
 additional manufacturing influences and offer numerical efficiency in order to
 be practical for parametric studies during airframe design.
 Therefore, the development and enhancement of simulation methods for efficient and
 reliable evaluation of cracks and crack growth represents the main objective of this
 thesis. Two simulation methods are implemented and investigated for this purpose,
 that are based on different approaches and intended for distinct applications. One
 method is based on analytical stress function expressions and enables a very efficient
 evaluation of the complete fatigue crack growth life of cracked airframe structures.
 The proposed approach in this context is generally based on plane assumptions and
 limited to pure mode I crack loading. In order to be able to additionally consider
 crack turning under mixed mode loading, a second simulation method is presented
 which implements an extended finite element framework for a mesh independent
 representation of cracks in two dimensions. The additional combination with the
 material force concept, as alternative crack state parameter, allows for automated
 simulations of crack growth under mixed mode loading without any need for remeshing
 Both simulation methods are validated based on different crack configurations and
 are applied for crack growth investigations of varying configurations of integrally
 stiffened panels under pure mode I and mixed mode loading conditions. In this
 context, a special focus is set on the influences of additional internal stresses that
 follow either from the applied manufacturing processes or an intentional prestressing
 of the stiffeners. Despite the general limitation to plane considerations, the proposed
 methods show a good accordance with experimental, theoretical and alternative
 numerical results. This demonstrates their capabilities to simulate fatigue crack
 growth and crack turning in integrally stiffened airframe structures and motivates
 further research with respect to a possible extension to three-dimensional problems.


Titel: Damage tolerance investigations of innovative metallic airframe structures
EAN: 9783736937741
ISBN: 978-3-7369-3774-1
Digitaler Kopierschutz: frei
Format: E-Book (pdf)
Herausgeber: Cuvillier Verlag
Genre: Technik
Anzahl Seiten: 288
Veröffentlichung: 10.06.2011
Jahr: 2011
Untertitel: Englisch
Dateigrösse: 11.7 MB