Comparison of methods for determination of fracture toughness in a multi-directional CFRP laminate

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Abstract

Quasi-static tests were carried out on calibrated end loaded split (C-ELS) specimens to determine a critical initiation interface energy release rate or fracture toughness Gic. A multi-directional (MD) carbon fiber reinforced polymer (CFRP) laminate with a delamination between a unidirectional (UD) fabric ply with fibers oriented mainly in the 0?- direction and a plain balanced woven ply with tows oriented in the +45?/ - 45?- directions was considered. The Gic values from the non-precracked (NPC) specimens containing an artificial delamination were evaluated by means of an experimental compliance method (ECM), a beam theory (BT) method, as well as a two-dimensional finite element analysis (FEA) together with the area J-integral. In addition, the displacement extrapolation (DE) method and the virtual crack closure technique (VCCT) were used to determine the stress intensity factors Km (m = 1, 2) for each test. The stress intensity factors were normalized with a length scale L = 100 µm and used to calculate the phase angle ?. Finally, the obtained results were compared to critical initiation values which were obtained in a previous study from Brazilian disk (BD) tests for the same material and interface. The Gic value is a necessary property for predicting propagation of a delamination along the investigated interface. The aim of this paper is to examine the differences which occur as a result of using various methods to determine this value. Work is in progress to determine fracture resistance curves or R-curves. These curves relate the energy required for a delamination to propagate GiR to the delamination extension ?a and may be used to predict the delamination resistance to propagation.

Original languageEnglish
Pages (from-to)917-924
Number of pages8
JournalProcedia Structural Integrity
Volume28
DOIs
StatePublished - 2020
Event1st Virtual European Conference on Fracture, VECF 2020 - Virtual, Online
Duration: 29 Jun 20201 Jul 2020

Keywords

  • Delamination
  • Energy release rate
  • Fracture toughness
  • Laminate composite
  • Shear mode

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