The Influence of Overlap Length on Adhesive Joint Strength

Audrey G. Zink, Robert W. Davidson, Robert B. Hanna


The influence of overlap length on the strength and failure mode of bonded wood double lap joints was investigated in this study. The overlap lengths ranged from 12.7 mm (0.5 in.) to 44.45 mm (1.75 in.) in 6.35-mm (1/4-in.) increments. The side members were 50.8 mm (2 in.) long, and the center member was 88.9 mm (3.5 in.) long. All joint members were 25.4 mm x 25.4 mm (1 in. x 1 in.) in cross section. The type of wood was yellow-poplar (Liriodendron tulipifera), and the joints were loaded in double shear. The strength of the joint was found to increase slightly with increased overlap length. The failure mode of the joints shifted from cleavage of the side members for the shortest overlap lengths, to a combination of side splits and forward shear failures for the intermediate overlaps, to center splits for the longest overlap lengths studied. While the joint strength trends observed for the double lap wood joints were consistent with previous work on other materials and similar conditions, the failure modes with the wood adherends were different from any other studies to date.


Double lap joints;joint strength;adhesive connections;failure mode

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