Mode I Interlaminar Fracture Toughness of FRP-Timber Joints Connected by Epoxy and Polyurethane

This paper presents an experimental study of mode Ⅰ interlaminar fracture toughness of FRP-timber joints bonded with epoxy (EP) and polyurethane (PUR) adhesives. The flax and glass fabrics were used in the FRP parts of the joints. Laminated veneer lumber (LVL) was utilized as the timber element in the current research against the background that engineered wood products have been widely applied in modern timber buildings. The double cantilever beam (DCB) test was conducted to evaluate the fracture toughness of LVL-FRP joints from the perspectives of failure mode, strain energy release rate, and crack propagation path. The effects of the fibre and adhesive type on the fracture toughness of LVL-FRP joints were analyzed statistically. The results indicate that the joints bonded with polyurethane showed a significantly higher energy release rate than those bonded with epoxy. As the crack length increased, the energy release rate increased, regardless of fibre and adhesive types. When the adhesive was epoxy, LVL-glass FRP had at least 44.4% higher fracture toughness than LVL-flax FRP. Regarding the joints connected by polyurethane, wood failure and fiber-tearing failure were the main failure modes in LVL-flax FRP and LVL-glass FRP joints, respectively; no significant difference in the fracture toughness was observed.