Effective use of metallic Z-pins for composites’ through-thickness reinforcement

Beene M'membe*, Mehdi Yasaee, Stephen R. Hallett, Ivana K. Partridge

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

41 Citations (Scopus)
107 Downloads (Pure)


Z-pins offer effective through-thickness reinforcement for laminated composites. Various studies have however, shown that metal Z-pins are less effective at bridging Mode I delaminations than carbon-fibre composite Z-pins, due to poor interfacial bonding with the laminate. This is exacerbated by high thermal mismatch between the metallic Z-pins and the laminate. This study investigates inserting metallic Z-pins at angles offset from the laminate normal, to improve the Mode I bridging in composites. The effects on the apparent fracture toughness under pure and mixed Mode I/II loads using single pin specimens is investigated. Results show that, unlike orthogonally inserted metal Z-pins, inclined Z-pins exhibit high energy absorption throughout the mixed mode range. Double Cantilever Beam (DCB) tests show that the inclined metal Z-pins increase the Mode I apparent fracture toughness by a factor of 2 compared to traditional carbon fibre Z-pins. In End Loaded Split (ELS) tests, the Mode II apparent fracture toughness of inclined stainless steel Z-pins, although less than their uninclined equivalent, is greater than that of carbon fibre Z-pins.

Original languageEnglish
Pages (from-to)77-84
Number of pages8
JournalComposites Science and Technology
Early online date28 Feb 2019
Publication statusPublished - 3 May 2019

Structured keywords

  • Bristol Composites Institute ACCIS
  • Composites UTC


  • Fracture toughness
  • Inclined insertion
  • Metal Z-pins


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