Fracture resistance of wood adhesive bonds: Experimental insights into the J-integral approach using acoustic emission testing

Acoustic emission (AE) measurements were used to detect the onset of crack initiation and propagation, as well as to monitor crack front advancement during fracture resistance tests on wood-adhesive bonds. In parallel, digital image correlation (DIC) was employed as an independent technique to also monitor crack front progression. These measurements were conducted with the aim of further adapting and developing the J-integral approach for fracture characterisation of wood and wood-adhesive joints. In this method, double cantilever beam (DCB) specimens are loaded under pure bending moments to determine R-curves and cohesive laws. Tests were performed on European beech wood specimens bonded with a bio-based wood-lignin adhesive. The results show that AE can effectively identify the onset of crack initiation and propagation, supporting the characterisation and interpretation of R-curve and cohesive law data. Additionally, both AE-based localisation and DIC-derived strain fields can be used to estimate the cohesive zone length during crack growth.