Influence of Wood Grain Direction on Linear Welding

Wood grain orientation differences in the two surfaces to be bonded yield bondlines of different strengths in linear wood welding. End-grain-to-end-grain welds of good strength were obtained for both beech and oak woods. The tendency to defibration in end-grain-to-end-grain welding indicated that for wood densities higher than or equal to the density of beech wood, end-grain-to-end-grain welding is possible and yields sufficient joint strength. A higher density seemed to yield a stronger joint. Wood pieces having other grain directions were also vibration welded. These were: (1) with the grain perpendicular to the wood longitudinal grain direction, (2) with the grain of both wood pieces at 45 degrees to the wood longitudinal grain direction and (3) with the grain of both wood pieces at 45 degrees to the wood longitudinal grain direction but at 90 degrees to each other to form a fishbone-like pattern. The first of these yielded results comparable to end-grain-to-end-grain welding. The other two yielded much lower strength of the joints, indicating that fibre orientation in the interphase composite formed during welding had considerable influence on joint strength. These differences in joint strength have been explained by the very marked effect that anisotropy of the interphase composite has on fibre/matrix composites. (C) Koninklijke Brill NV, Leiden, 2009