Fracture Toughness of Parallel-Laminated Veneer

Fracture toughness (KIc) of parallel-laminated veneers (PLV), loaded normal to the glueline, was evaluated in relation to veneer thickness, grain orientation, and loading rate. The veneers were sawed from clear solid wood to thicknesses of 1/8, 1/16, and 1/32 inch with flat- and edge-grain orientations. Like-grain orientations were then laminated with 2.7 pounds of phenol formaldehyde resin per 1,000 square feet of glueline. Fracture toughness was tested for four orientations (RL, TL, TR, and RT) where the first letter of the mode designates the load direction and the second designates the expected direction of the crack with respect to the grain direction. Fracture toughness of the PLV was then compared to that of the original solid wood used for making the veneers. KIc values generally increased as veneer thickness decreased. PLV with a KIc exceeding that of the original clear wood can be constructed with thin veneers (1/32 in.); at that thickness, the apparent directional effect of solid wood disappears. The TL fracture orientation had the least variation and retained the highest percentage of fracture toughness of its solid. KIc was not significantly different for two testing rates, 0.004 and 0.04 inch per minute.

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