Shear strain distribution in PRF and PUR bonded 3-ply wood sheets by means of electronic laser speckle interferometry

The distribution of shear strain across a 3-ply wood sheet bonded with PRF and PUR, respectively, was measured by means of electronic laser speckle interferometry. Owing to the higher shear modulus of PRF compared to PUR, shear strains were more evenly distributed in PRF bonded specimens than in PUR bonded specimens. However, considering the different shear moduli of earlywood and latewood bands in the core layer of the 3-ply sheet, it is concluded that shear stress is distributed more evenly along PUR bond lines compared to PRF bond lines. Since it is less prone to stress concentrations, PUR should provide more durable adhesive connections than stiff adhesives such as PRF.