A new mechanism for the formation of ply wrinkles due to shear between plies

James S. Lightfoot*, Michael R. Wisnom, Kevin Potter

*Corresponding author for this work

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

121 Citations (Scopus)


The formation of out-of-plane ply deformation causes significant reductions in the mechanical properties of composites. In-plane fibre misalignments also cause reductions in the compressive strength, yet the origins of these defects are misunderstood. This paper presents a new mechanism for the formation of wrinkles, which is based upon the shear forces generated as a result of mismatches in the coefficient of thermal expansion of composite and tool, as well as the process of ply slippage that occurs during consolidation into radii. Using a U-shaped tool, defects in composite spars have been characterised using light microscopy, showing that the tool geometry and prepreg bridging leads to "instability sites," which lead to wrinkles up to 750 jam in height as well as in-plane misalignment of 00 plies of up to 50. Increasing the frictional shear stress through omission of release film prevents the formation of wrinkles, supporting the mechanism presented in this paper. (C) 2013 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)139-147
Number of pages9
JournalComposites Part A: Applied Science and Manufacturing
Publication statusPublished - Jun 2013


  • A. Prepreg
  • TOOL
  • D. Optical microscopy
  • E. Autoclave
  • B. Defects


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