Using auxiliary adherends to eliminate need for grain control in fracture testing of adhesively bonded wood

Proper crack growth in the investigation of adhesive failure in bonded wood joints requires laborious grain control. By adding auxiliary adherends, this paper introduces and evaluates a novel sample geometry that enables fracture energy characterization of wood veneer-adhesive systems. The proposed method was applied to three wood species to test three commonly used wood adhesives. The proposed sample geometry successfully identified differences in fracture energies associated with the use of different adhesives on the same wood species and offered comparable success rate as grain control method. More importantly, for sawn and planed veneers that were without lathe checks common in rotary-peeled veneers, the success rate was even higher than that of rotary peeled veneers, indicating the significance of our proposed method to wood adhesion. We further explored the effects of crack propagation both parallel and perpendicular to wood grain orientation and designed wax strip specimens to understand rising R-curve behavior observed in certain species.