Materials and Structures

, Volume 46, Issue 3, pp 421–434 | Cite as

Fracture characterisation of green-glued polyurethane adhesive bonds in Mode I

Original Article


Unseasoned (green) spruce timber side boards of size 25 × 120 × 600 mm were flatwise-glued with a one-component PUR adhesive. Glued pairs of boards were then kiln-dried to 12 % moisture content. A special small-scale specimen for testing the fracture properties of the adhesive bond in Mode I was developed in order to evaluate the adhesive bond properties. The complete force versus deformation curve, including both the ascending and the descending parts, could be obtained with these small-scale specimens, enabling the strength and fracture energy of the bond line to be calculated. In addition, the fractured specimens were examined by scanning electron microscope. Results show that both the tensile strength and the fracture energy of the green glued PUR adhesive bonds were equal to those of the dry glued bonds. The methodology developed and used in the present study gives new possibilities for analysis of the mechanical behaviour of wood adhesive bonds, and particularly of their brittleness and its correlation with the type of fracture path. This is in sharp contrast to the use of standardised test methods (e.g. EN 302, ASTM D905) with specimens having relatively large glued areas. Using such types of specimens, it is not possible to obtain the complete force versus deformation response of the bond. In addition, when using such test methods, failure takes place in the wood or in the fibres near the bond, thus making it impossible to obtain detailed information about the bond line characteristics.


Wood adhesive Bond line Fracture Ductility Green gluing Polyurethane 



The financial support from the Foundation Centre for Building and Living with Wood (CBBT) and from the Knowledge Foundation (KK-stiftelsen), which made this research possible, is hereby gratefully acknowledged.


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Copyright information

© RILEM 2012

Authors and Affiliations

  • Magdalena Sterley
    • 1
    • 2
  • Erik Serrano
    • 1
    • 2
  • Bertil Enquist
    • 2
  1. 1.SP Technical Research Institute of SwedenStockholmSweden
  2. 2.Linnaeus UniversityVäxjöSweden

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