Cohesive zone modelling of mixed-mode crack growth in bio-based wood adhesive bonds

Mixed-mode I−II crack growth in a bio-based wood adhesive bondline was investigated using a three-dimensional finite-element model with a cohesive zone formulation. Cohesive parameters – including strengths, onset displacements and fracture energies – were obtained directly from double cantilever beam experiments with uneven bending moments. These experimentally derived parameters were then implemented in the finite element model without any calibration to fit the global response, as the aim was to validate the modelling approach rather than to identify material parameters. The model reproduced stable delamination, captured the expected variation in fracture-process-zone size, provided insight into the distribution and magnitude of normal and shear stresses along the bondline from crack initiation through propagation, and showed good agreement with the global experimental response in opening-dominated (nominal Mode I) loading (phase angles ψ = 0° and 41°). In shear-dominated mixed-mode loading (ψ = 69°, 85° and 89°), fracture resistance was overpredicted, attributed to large fracture process zones and model simplifications. Overall, the results demonstrate that a relatively simple cohesive zone model, when driven by experimentally derived cohesive laws, can capture the key trends in mixed-mode fracture response of wood-adhesive bonds.