Transverse Bonding of Slash Pine Joints

This paper deals with a study of the influence of wood structure on joint strength in transverse bonding. The study was confined to slash pine. The test specimens were selected by separating annual rings into earlywood and latewood components. To avoid problems associated with solvent-borne adhesives, a room-temperature curing epoxy resin was used. It has a solvent-free base, high solids, and low shrinkage characteristics. Two formulations were used–rigid adhesive and semi-rigid–to provide some degree of stress relief. Specimen size was 1/8 by 1/8 by 3-inch pieces of either earlywood or latewood. The specimens were bonded as butt-joint specimens and tested in tension to compare rigid vs- ductile adhesives. Both adhesives wetted the exposed wood surfaces. All joint failures were in cohesion within the adhesive. The location of failure did not differ among viscosity classes or between earlywood and latewood. The differences observed in tensile strength between earlywood and latewood joints were directly associated with the capacity of the adhesive-end wall and adhesive-lumen perimeter bonds to distribute stress. It was reported that for joints fabricated from untreated surfaces, the effect of adhesive age on joint strength was directly associated with bonding to the inner lumen walls.

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