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

Abstract

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.

Keywords

Wood adhesive Bond line Fracture Ductility Green gluing Polyurethane 

Notes

Acknowledgments

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.

References

  1. 1.
    Anon (ASTM D 905-898) Standard test method for strength properties of adhesive bonds in shear by compression loading. Adhesives, vol 15.06. ASTM, PhiladelphiaGoogle Scholar
  2. 2.
    Anon (EN 302-1:2004) Adhesives for load bearing timber structures. Test methods. Determination of bond strength in longitudinal tensile shear strength. European Committee for Standardization (CEN), BrusselsGoogle Scholar
  3. 3.
    Baba MN (2011) Assessing the mode i interlaminar fracture toughness of wood laminated specimens—an experimental approach. Pro Ligno 7(3):10–17Google Scholar
  4. 4.
    Bergman RD, Simpson WT, Turk C (2010) Evaluating warp of 2 by 4 s sawn from panels produced through green gluing dimension lumber from small ponderosa pine logs. For Prod J 60(1):57–63Google Scholar
  5. 5.
    Boström L (1992) Method for determination of the softening behaviour of wood and the applicability of a nonlinear fracture mechanics model. Dissertation no TVBM-1012, Lund Institute of Technology, Division of Building Materials, Lund, SwedenGoogle Scholar
  6. 6.
    Conrad MPC, Smith GD, Fernlund G (2004) Fracture of wood composites and wood-adhesive joints: a comparative review. Wood Fiber Sci 36:26–39Google Scholar
  7. 7.
    Core Document of the COST Action E34 Bonding of Timber (2008) In: Dunky M, Källander B, Properzi M, Richter K, Van Leemput M (eds) WG 2 Green gluing. ISSN 1681-2808Google Scholar
  8. 8.
    da Silva LFM, de Magalhaes F, Chaves FJP, de Moura M (2010) Mode II fracture toughness of a brittle and a ductile adhesive as a function of the adhesive thickness. J Adhes 86(9):889–903Google Scholar
  9. 9.
    de Moura M, Oliveira JMQ, Morais JJL, Dourado N (2011) Mixed-mode (I plus II) fracture characterization of wood bonded joints. Constr Build Mater 25(4):1956–1962CrossRefGoogle Scholar
  10. 10.
    Gagliano JM, Frazier CE (2001) Improvements in the fracture cleavage testing of adhesively-bonded wood. Wood Fiber Sci 33(3):377–385Google Scholar
  11. 11.
    Gustafsson PJ, Enquist B (1988) Strength of wooden beam at right angle notch. Report TVSM-7042, Lund Institute of Technology Division of Structural Mechanics (in Swedish)Google Scholar
  12. 12.
    Hilleborg A (1991) Application of the fictitious crack model to different types of materials. Int J Fract 51:95–102Google Scholar
  13. 13.
    Holmberg S (1998) A numerical and experimental study of initial defibration of wood. Dissertation No TVSM-1010, Lund Institute of Technology Division of Structural Mechanics, Lund, SwedenGoogle Scholar
  14. 14.
    Li Y-N, Bažant ZP (1994) Eigenvalue analysis of size effect for cohesive crack model. Int J Fract 66(3):213–226CrossRefGoogle Scholar
  15. 15.
    Li S, Thouless MD, Waas AM, Schroeder JA, Zavattieri PD (2005) Use of Mode-I cohesive-zone models to describe the fracture of an adhesively-bonded polymer-matrix composite. Compos Sci Technol 65:281–293CrossRefGoogle Scholar
  16. 16.
    Li S, Thouless MD, Waas AM, Schroeder JA, Zavattieri PD (2006) Competing failure mechanisms in mixed-mode fracture of an adhesively bonded polymer-matrix composite. Int J Adhes Adhes 26:609–616CrossRefGoogle Scholar
  17. 17.
    Marzi S, Biel A, Stigh U (2011) On experimental methods to investigate the effect of layer thickness on the fracture behavior of adhesively bonded joints. Int J Adhes Adhes 31(8):840–850CrossRefGoogle Scholar
  18. 18.
    Maun K, Cooper G (1999) Re-engineering softwood for constructional use by wet (green) gluing. In: Berti S, Macchioni N, Negri M, Rachello E (eds) Eurowood technical workshop proceedings industrial end-uses of fast-grown species, Florence May 31st–June 1st, pp 47–59Google Scholar
  19. 19.
    Ormstad E (2005) Gluing sideboards from green Norway spruce. In: Källander B (ed) Proceedings of international conference/workshop green gluing of wood—process—products—market, Borås, April 7–8, 2005, pp 113–117Google Scholar
  20. 20.
    Petersson H, Källsner B, Ormarsson S (2005) Shape stability of laminated planks made of green-glued pairs of side boards. In: Källander B (ed) Proceedings of international conference/workshop green gluing of wood—process—products—market. Borås, April 7–8, 2005, pp 118–124Google Scholar
  21. 21.
    Pommier R, Elbez G (2006) Finger-jointing green softwood: evaluation of the interaction between polyurethane adhesive and wood. Wood Mater Sci 1:127–137CrossRefGoogle Scholar
  22. 22.
    Properzi M, Pizzi A (2003) Comparative wet wood gluing performance of different types of glulam wood adhesives. Holz als Roh- und Werkstoff 61:77–78CrossRefGoogle Scholar
  23. 23.
    Seltman J (1995) Freilegen der Holzstruktur duch UV-Bestrahlung. Holz Roh Werkst 53:225–228CrossRefGoogle Scholar
  24. 24.
    Serrano E (2000) Adhesive joints in timber engineering. Modelling and testing of fracture properties. Dissertation Report TVSM-1012, Lund University, Department of Mechanics and Materials, Structural Mechanics. Lund, SwedenGoogle Scholar
  25. 25.
    Serrano E (2001) Glued-in rods for timber structures. An experimental study of softening behaviour. Mater Struct 34(238):228–234CrossRefGoogle Scholar
  26. 26.
    Serrano E (2004) A numerical study of the shear-strength-predicting capabilities of test specimens for wood-adhesive bonds. Int J Adhes Adhes 24(1):23–35CrossRefGoogle Scholar
  27. 27.
    Serrano R, Cassens D (2001) Reducing warp and checking in plantation-grown yellow-poplar 4 by 4’s by reversing part positions and gluing in the green condition. For Prod J 51(11/12):37–40Google Scholar
  28. 28.
    Serrano E, Enquist B (2005) Contact-free measurement and non-linear element analyses of strain distribution along wood adhesive bonds. Holzforschung 59:641–646CrossRefGoogle Scholar
  29. 29.
    Serrano E, Gustafsson PJ (2006) Fracture mechanics in timber engineering—strength analyses of components and joint. Mater Struct 40:87–96CrossRefGoogle Scholar
  30. 30.
    Shipsha A, Berglund LA (2007) Shear coupling effects on stress and strain distributions in wood subjected to transverse compression. Compos Sci Technol 67:1362–1369CrossRefGoogle Scholar
  31. 31.
    Simon F, Valentin G. (2000) In: Williams JG, Pavan A (eds) Damage and fracture of wood adhesive bonded joints under shear and opening loading, vol 27. European Structural Integrity Society, Elsevier, pp 285–296Google Scholar
  32. 32.
    Simon F, Valentin G (2003). In: Blackman RK, Williams JG, Pavan A (eds) Cohesive failure characterisation of wood adhesive joints loaded in shear, vol 32. European Structural Integrity Society, Elsevier, pp 305–316Google Scholar
  33. 33.
    Singh HK, Chakraborty A, Frazier CE, Dillard DA (2010) Mixed mode fracture testing of adhesively bonded wood specimens using a dual actuator load frame. Holzforschung 64(3):353–361CrossRefGoogle Scholar
  34. 34.
    Sterley M (2004) Green gluing of wood. Licentiate thesis. KTH Stockholm, Sweden. ISBN 91-7283-711-XGoogle Scholar
  35. 35.
    Sterley M, Gustafsson PJ (2005) Shear fracture properties of green-glued polyurethane wood adhesive bonds. In: Frihart Ch R (ed) Proceedings No 7230 of wood adhesives 2005, pp 221–229Google Scholar
  36. 36.
    Sterley M, Serrano E, Enquist B (2008) Fracture characterisation of green glued polyurethane adhesive bonds in Mode I. In: Csiha C (ed) Proceedings of final conference in COST action E34 bonding timber; enhancing bondline performance, pp 156–166. Sopron, Hungary, 6–7 MayGoogle Scholar
  37. 37.
    Sterley M, Serrano E, Enquist B (2009) Flat wise green gluing of Norway spruce for structural application. In: Proceedings of the international conference on wood adhesives, Lake Tahoe, Nevada, USA, September 28–30Google Scholar
  38. 38.
    Sterley M, Trey S, Lundevall Å, Olsson S (2012) Influence of cure conditions on the properties of a one component moisture cured polyurethane adhesive in the context of green gluing of wood. J Appl Polym Sci. doi: 10.1002/app.36895
  39. 39.
    Stigh U, Alfredsson KS, Andersson T, Biel A, Carlberger T, Salomonsson K (2010) Some aspects of cohesive models and modelling with special application to strength of adhesive layers. Int J Fract 165(2):149–162MATHCrossRefGoogle Scholar
  40. 40.
    Veigel S, Follrich J, Gindl-Altmutter W, Müller U (2012) Comparison of fracture energy testing by means of double cantilever beam-(DCB)-specimens and lap joint testing method for the characterization of adhesively bonded wood. Eur J Wood Wood Prod 70(1–3):3–10CrossRefGoogle Scholar
  41. 41.
    Wernersson H (1994) Fracture characterisation of wood adhesive joints. Dissertation TVSM 1006. Lund Institute of Technology Division of Structural Mechanics, SwedenGoogle Scholar
  42. 42.
    Xavier J, Morais J, Dourado N, de Moura M (2011) Measurement of Mode I and Mode II fracture properties of wood-bonded joints. J Adhes Sci Technol 25(20):2881–2895Google Scholar

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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