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    Item type:Publication, Access status: with files ,
    Structural health monitoring of carbon fiber reinforced polymers and carbon nanotube modified adhesive joints via electrical resistance measurement
    (2018-09)
    Augustin, Till
    ;
    Fiedler, Bodo
    ;
    Fiedler, Bodo
    This thesis deals with damage detection via electrical resistance measurements on carbon fiber reinforced polymers and on carbon nanoparticle modified adhesive joints. Silver nanoparticle based ink is printed onto carbon fiber reinforced polymers and onto prepregs and mechanical tests with simultaneous electrical resistance measurements demonstrate the possibility to detect delaminations and inter-fiber failures. In addition, impact damage detection is demonstrated for plate specimens as well as for an omega stringer. On carbon nanotube modified epoxy based adhesive joints, electrical resistance measurements show the possibility of accurate detection and localization of impact damages and damages developing in cyclic tests.
    Publicationtype: Doctoral Thesis
      630  2750
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    Item type:Publication, Access status: with files ,
    Mikrostrukturelle Betrachtung des Einflusses von Poren auf die mechanischen Eigenschaften von faserverstärkten Kunststoffen
    (Tutech Innovation GmbH, 2014)
    Liebig, Wilfried
    ;
    Schulte, Karl
    ;
    Fiedler, Bodo
    The subject of this work is the investigation of the influence of voids on the mechanical properties of fibre-reinforced polymers (FRP) under compression. To specify the damage accumulation of FRP in the presence of voids, the complex three dimensional structure of the composite including several voids were analysed and a reduced mechanical model composite was derived. The reduced model consists of the matrix system and a unique void, which is squeezed between two fibres by using an injection method. The experimental investigation of the model composite included the description of the stress- and strain behaviour of the matrix using photoelasticity and digital image correlation technology. Additionally, a numerical examination of a parameterised model composite and an analytical study of the stability of a single fibre was conducted. As a result of the experimental investigation of the model composite consisting of ten fibres embedded in a matrix, the failure initiation and propagation could be observed. Supported by the findings from the numerical examination and the analytical study, the most impact on the failure initiation has the foundation of the fibre as well as the bonding between fibre and matrix. Both facts are leading to a premature fibre-matrix debonding with ongoing loss of stability of the fibre finally resulting in fibre kinking. Because of the rearrangement of stresses further overloaded fibres failed. Additional studies on transparent glassfibre reinforced polymers including a unique void showed, that the gained experience made on the examination of the model composite could be transferred to real existed composites.
    Publicationtype: Doctoral Thesis
      765  1096