Mechanism Study On Betula Wood Dowel Rotation Welding Into Larch And Enhanced Mechanism Of Treating With CuCl₂

In this paper,welded joints specimens were manufactured by rotation welding with Betula wood dowel and Larch substrate.The pullout resistance and chemical groups and components of welded joints specimens were analysed to study the rotation welding mechanism and the enhancement mechanism of wood dowel treated with CuCl2 solution.The conclusions are as follows:(1)The optimized parameters of Betula wood dowel welded into Larch were welded depth 30mm,welded rotation 2400rpm,and the moisture content 2%and 12%for Betula wood dowel and Larch substrate,and welded time 3s.(2)The nonlinear regression could fit the temperature distribution of the welding interface for both untreated and treated groups.The linear relation was existed between the highest temperature of the welding interface and welded depth for the untreated group,while for treated group,two stages of linear and nonlinear relation were existed.(3)The mechanism of Betula wood dowel welded into Larch was that fiber was covered by the molten materials of pyrolysed hemicellulose and amorphous materials in the welding interface during the rotation friction process.Wood constituents could be pyrolysed by the friction heat generated from rotation welding to form a lot of oxygen-containing materials,most of them were C-O materials.With the extension of welded time,welding interface materials were pyrolysed deeper,but the rate of pyrolysis decreased which indicated that the pyrolysis of hemicellulose and cellulose might occur in the prior period of welding process.(4)The samples treated with CuCl2 of welded time 3s showed the best pullout resistance and the rupture occurred in the wood dowel.With the extension of welded time,pullout resistance of treated samples decreased.Pullout resistance of welded time 3s was showed the smallest variability and the best reliability.(5)The enhancement mechanism of wood dowel treated with CuCl2 was that acid hydrolysis of hemicellulose and cellulose of wood dowel might occur during immersion which may promote the formation of molten materials by the depolymerization and pyrolysis of wood constituents.And the decreased of glass transition temperature of cellulose might promoted the formation of molten materials.With the pyrolysis of cellulose and hemicellulose,the pyrolysis of lignin might occur because the increment of lignin was insufficient.With the same welded time,the content of oxygen-containing materials with treated samples was higher than untreated samples,which might indicate more pyrolysis and molten reactions occurred in the treated welding interface.