An essential aspect of developing novel bio-adhesives is ensuring sufficient bond strength. Currently, bond strength is typically assessed using stress-based criteria derived from lap-shear tests, such as those specified in EN 302-1. However, this method provides limited insight into bond performance and cannot reliably predict behaviour in other joint configurations or structural components. A more comprehensive approach involves fracture-mechanical characterisation of the wood-adhesive bond line through measurement of its cohesive law, commonly referred to as the traction–separation (σ–δ) law. This allows for detailed analysis of both strength and fracture energy release rates under various loading modes. The most relevant modes of loading for wood products are mode I (opening/tension), mode II (sliding/shear), and mixed-mode loading. These parameters can be implemented in Finite Element (FE) models using Cohesive Zone Modelling (CZM) to simulate crack growth, enabling strength predictions across a range of wood products, such as bed slats in furniture applications or glulam finger joints in structural applications. This modelling approach, requiring a mixed-mode I–II cohesive zone model, was successfully applied in the 1990s to conventional adhesives such as resorcinol–phenol and polyvinyl acetate, and it is now highly relevant for guiding the development of wood-based bio-adhesives. In parallel research, experimental cohesive laws have been derived from Double Cantilever Beam (DCB) specimens subjected to pure bending moments under varying mode I/II conditions. In the present study, these experimentally obtained parameters are implemented in a COMSOL-based FE model to simulate crack growth. The predicted crack propagation and fracture resistance are then compared with experimental results to validate the model.
Keywords: cohesive zone model, finite element method, fracture mechanics
Authors
Joran van Blokland
Swedish University of Agricultural Sciences, Division of Wood Science and Technology, Uppsala, Sweden
Cléa Franchon
Department of Materials Science and Engineering, Uppsala University, Sweden, United Kingdom
E. Kristofer Gamstedt
Department of Materials Science and Engineering, Uppsala University, Sweden, United Kingdom
Sara Florisson
Department of Materials Science and Engineering, Uppsala University, Sweden, United Kingdom
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