Improving joint strength through controlled wood swelling

This study investigated how differential moisture content (MC) swelling can improve mortise-tenon joint durability without fasteners or adhesives. It quantifies swelling-induced stresses and determines optimal MC differences for pine and beech to maximize joint strength while minimizing cracking. The impact of this MC difference was evaluated using the finite element method. Both joint components were initially of equal nominal size. The mortise was assembled with the tenon at an equilibrium MC of 12%, with an initially lower MC (6%). The swelling of the tenon, caused by reaching equilibrium MC, and constrained within the mortise, induced internal stresses. With the same initial MC difference, beechwood exhibited greater moisture-induced strain (0.20 mm) than pinewood (0.16 mm). Localized stresses within the joint models reached 2.6 MPa for pinewood and 5.4 MPa for beechwood. These results suggest the potential for creating more durable joints eliminating the need for adhesives or fasteners. To minimize stress and prevent cracking, a maximum moisture content difference of 4% is recommended for pinewood joints and 5% for beechwood joints. This is particularly important when designing for zero clearance between mating parts. This study demonstrates the potential for leveraging wood's hygroscopicity to enhance furniture joint strength.