Bestimmung ausgewählter mechanischer Eigenschaften sowie der monotonen und zyklischen interlaminaren Risszähigkeit von gewickelten und geflochtenen Kohlenstofffaserverbundwerkstoffen

Translated title of the contribution: Mechanical characterisation and interlaminar crack growth of braided and filament wound carbon fiber composites

Christian Schillfahrt

Research output: ThesisMaster's Thesis

Abstract

In contrast to the cost-intensive manual fabrication of fibre-reinforced composites, widely automated processing techniques allow massive savings in production time and costs. In particular the braiding technology offers a great potential for an efficient and automated manufacture of structures with complex shapes and high production rates. However, for the practical design of braided structures very simplified simulation methods are available due to the complex structural behavior of these composites. Thus, novel simulation approaches applying non-linear material models are relevant in regard to a material-optimized design. This requires the knowledge of several mechanical material properties, which are used as input parameters for meso-scale finite element modelling. Within the framework of this thesis, braided and filament wound unidirectional laminates made of carbon-fibre-reinforced epoxy resin were fabricated in order to determine the relevant mechanical properties. In an additional test series, rovings were rewound onto bobbins before being wound around the mandrel to simulate the effect of fibre damage during the braiding process on the relevant material properties. The mechanical characterization of all specimens was performed using tensile and compression tests both parallel and perpendicular to the fibre direction. To investigate the non-linear behavior of composites, further compression tests under dynamic transverse load conditions were carried out. Finally, the influence of fibre damage on the delamination behavior of the laminates was examined using fracture mechanical methods under monotonic and cyclic loading. The results of the monotonic tensile and compression tests performed with wound laminates reveals similar values for modulus and strength in fibre direction. For braided specimens in general lower values for modulus and strength were found. The moduli of laminates under transverse loading showed no significant differences. A thermoplastic yarn which was introduced merely for fabrication of braided laminates led, particularly in transverse tension testing, to increased strengths. Contrary to filament wound laminates, a distinct discontinuous crack growth (crack stop effects) during fracture mechanical testing was observed for the braided specimens, which can be attributed to the thermoplastic yarn. Therefore, significantly higher values for fracture toughness were found for the braided laminates. Due to the additional deflection of rovings in the filament winding process with bobbins, the fracture mechanical characterization of these laminates shows higher values compared to the conventionally filament wound specimens.
Translated title of the contributionMechanical characterisation and interlaminar crack growth of braided and filament wound carbon fiber composites
Original languageGerman
QualificationDipl.-Ing.
Supervisors/Advisors
  • Stelzer, Steffen, Co-Supervisor (internal)
  • Pinter, Gerald Gerhard, Supervisor (internal)
  • Wolfahrt, Markus, Supervisor (external)
Award date30 Mar 2012
Publication statusPublished - 2012

Bibliographical note

embargoed until 21-11-2016

Keywords

  • carbon fibre composites
  • unidirectional laminates
  • mechanical properties
  • interlaminar fracture toughness
  • winding
  • braiding
  • bobbin carrier
  • fibre damage
  • textile preforms
  • tensile test
  • compression test
  • nonlinear properties
  • delamination

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