Withdrawal Properties of Glued, Round, Mortise and Tenon Joints Using Greenwood Shrinkage as a Clamping Pressure

Glued mortise and tenon joints are often used in joints for furniture such as chairs. However, such joints are not sufficiently resistant to withdrawal forces because of the difficulty of applying a clamping pressure to the surfaces being glued. Therefore, some reinforcement, such as the use of dowel-type fasteners, is necessary. In this study, we discussed the applicability of the shrink-fit method used in green woodworking to strengthen glued round mortise and tenon joints. The test specimens were assembled using wet mortise members and air-dried tenon members with polyvinyl acetate resin emulsion adhesive. Withdrawal tests on joint specimens of four hardwood species were conducted to study the reinforcing effects of the shrink fit on the withdrawal performance of the mortise and tenon joints. The proposed shrink-fitted glued round mortise and tenon joint exhibited sufficient withdrawal strength equivalent to that of the joint glued with epoxy resin adhesive. After applying four humidity cycles to simulate seasonal variations in moisture content, withdrawal strength did not decrease significantly. The proposed joint could withstand the withdrawal force to some extent after adhesion was fractured by shear force.