Do standard delamination tests relate to planar delamination growth?

R.C. Alderliesten, H.J. den Ouden

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

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Abstract

Delamination growth in fibre reinforced polymer composites is generally evaluated with experiments that have been standardized for quasi-static load conditions. These tests characterize unidirectional delamination growth in mode I (DCB), mode II (ELS or ENF) of mixed mode conditions (MMB). However, little attention is paid in literature to the applicability of these tests to in-service delamination problems that are generally characterized by planar delamination growth. In this study, the relation between planar delamination growth, induced by transverse quasi-static indentation loading, and these unidirectional delamination tests was investigated. To that aim, prior planar delamination growth tests reported in literature, performed at EPFL, were analysed to identify up to what extent this planar growth could be correlated to the concepts of strain energy release and strain energy density. Once this appeared to successful, an experimental setup was designed to measure the delamination boundary during the transverse indentation loading of planar delamination specimens made of nontransparent carbon fibre reinforced polymer composites. With that set-up, quasi-static and fatigue planar delamination growth experiments were performed, and delamination contours could be successfully captured. While the quasi-static tests revealed limited growth, evaluation with numerical simulations revealed that the indentation force required to extend the delamination quasi-statically would cause damage to the specimen. This is attributed to the increasing length of the delamination contour when delaminations expand, which is not the case with standard unidirectional specimen. With the fatigue tests, however, delamination growth was achieved, but interestingly enough two phases were observed; first the delamination propagated in a planar fashion, while at some point in time work did not exceed an apparent threshold. Instead of no growth, however, the delamination still increased but then in a transverse manner. What makes this study of particular interest, is that the strain energy density as criterion could capture the strain energy offered (work) along the entire delamination contour, while the strain energy release rate described the resistance to delamination growth. This latter observation is in agreement with the original concept employed by Griffith when he formulated the basis of linear elastic fracture mechanics. This presentation present the experiments performed, the analysis of results, and will conclude with a proposal how to relate standard unidirectional tests to planar growth, considering that these standard tests contain little to no information on transverse phenomena with respect to strain energy density (work) and strain energy release (dissipation).
Original languageEnglish
Title of host publicationProceedings of the 20th European Conference on Composite Materials: Composites Meet Sustainability
Subtitle of host publicationVol 4 – Modeling and Prediction
EditorsAnastasios P. Vassilopoulos , Véronique Michaud
Place of PublicationLausanne
PublisherEPFL Lausanne, Composite Construction Laboratory
Pages174-181
Number of pages8
ISBN (Electronic)978-2-9701614-0-0
Publication statusPublished - 2022
Event20th European Conference on Composite Materials: Composites Meet Sustainability - Lausanne, Switzerland
Duration: 26 Jun 202230 Jun 2022
Conference number: 20

Conference

Conference20th European Conference on Composite Materials
Abbreviated titleECCM20
Country/TerritorySwitzerland
CityLausanne
Period26/06/2230/06/22

Keywords

  • Delamination
  • Unidirectional
  • Planar
  • Physics
  • Fracture Mechanics

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