Welding of thermally modified wood and thermal modification of the welded wood: Effects on the shear strength under climatic conditions

Abstract

This work investigated how thermal modification affects the shear strength of welded joints under different climatic conditions. The order of the thermal modification, before or after the welding, was investigated for its effect on the shear strength of the welded wood. Two groups of thermally modified specimens were prepared in a laboratory kiln under controlled conditions, one thermally modified before welding and the other after welding of the specimens. The shear strength of the specimens were measured at four different moisture contents of 10%, 12%, 16%, and 18%, and the results for the two different approaches were compared. Moreover, observations of the X-ray computed tomography scanning and digital microscopy were used to study the density profile and the structural details of the welded joints. The results showed that thermal treatment of the wood either before or after welding had a negative influence on the shear strength, and the modes of failure of the joints in mechanical tests were in most cases brittle. In the weld interface of the wood modified before welding, a rigid material similar to charcoal was produced as a result of the further degradation of wood by welding pressure and frictional motion. Welding of wood before thermal modification, however, yielded thicker and more densified joints with less susceptibility to higher moisture variations than the joints obtained by welding the thermally modified wood.

Evaluation of the interface of Eucalyptus specimens welded by rotary friction

“…As the temperature increases, the wood polymers soften, mainly hemicelluloses, which are more susceptible to high temperatures (Vaziri and Sandberg 2021). At 140 ºC, the DSC thermograms show a first relative minimum (exothermic) hump assigned to the complete evaporation of free and adsorbed water present in the wood (Esteves and Pereira 2009).…”

Effects of Dowel Rotation Welding Conditions on Connection Performance for Chinese Fir Dimension Lumbers

“…Traditional furniture and architectural joints, like mortise and tenon, round dowel joints, metal connectors, and glue joints, while prevalent, face challenges like complex production processes, significant wood loss, metal corrosion, and low efficiency [16][17][18][19][20][21]. In order to solve these problems, wood welding technology, as an emerging environmentally friendly and efficient connection technology, has attracted the attention of researchers and industry [22][23][24][25][26]. Since wood welding technology was first proposed by Suthoff [27], it has experienced the development of various technologies from linear friction welding to rotary friction welding, ultrasonic wood welding, and laser wood welding [22,[28][29][30][31].…”

Influence of biological pretreatment of wooden dowels on strength of rotary welded joints

“…The poor water resistance of welded joints is based on the uneven swelling of the welded joint, which causes strong stresses in the welded joint (Vaziri et al 2019). Thermal modification in vibration welding affects a significant reduction in shear strength (Vaziri and Sandberg 2021). In vibration welding, the strength of the welded joint is twice that of unmodified wood (Boonstra et al 2006).…”