Effect of Glue-line Flexibility on Cleavage Fracture Toughness of Wood-Epoxy Resin Bond System

The paper concerns with effect of the mechanical properties of glue-line on the cleavage fracture toughness of wood-epoxy resin bond systems. Tensile stress-strain relations of the resin films flexibilized with polysulfide in various grades were tested at a range of head speed 0.09 mm/min to 180 mm/min and temperature 20℃ to 60℃. Resins containing 20 to 40 parts per hundred of resin (phr) behaved like elasto-plastic material and that of 60 phr like rubber. Numerical analysis of stress distribution in cleavage fracture toughness test specimens of wood-flexibilized epoxy resin bond system was made by using the values of mechanical properties of resin films obtained above. Less stress concentration was found on the tip of a crack in thicker and more flexible glue-line. Higher stress concentration was found on thinner and more rigid glue-line arid on lower density adherend. Test results on cleavage fracture toughness G_ of wood-epoxy resin bond specimens showed clearly that increasing flexibility and thickness of glue-line could effectively improve cleavage fracture toughness of wood-glue bond system.
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