Fracture of discontinuous wood-adhesive bonds

This paper examines the effect of resin droplet diameter and droplet spacing on the Mode I fracture toughness of a discontinuous Douglas Fir-liquid phenol–formaldehyde bond, using Double Cantilever Beam specimens. The modification of a flexographic printing technique allowed the deposition of droplets of known diameter and spacing onto wood substrates. Experiments showed that the fracture toughness is proportional to the resin droplet diameter, inversely proportional to the droplet spacing, and relatively independent of the amount of resin applied. These findings are in agreement with a developed analytical model. Additionally, the fracture toughness of the discontinuously bonded specimens can equal the fracture toughness of the substrates, despite area coverage of only 50%.