Study On Pullout Resistance Of Compressed Wooden Dowel Rotary Friction Welding

Wood welding is an adhesive free connection,including linear friction welding and rotary friction welding.The rotary friction welding is that wooden dowel with high speed is inserted into a substrate with pre-drilled hole.In the rotary friction welding process,the temperature of the interface between high-speed rotating wooden dowel and the pre-drilled hole of the substrate rises,and the interface materials are determined to primarily come from the wooden dowel,and the interface material acts as an adhesive,thereby the wooden dowel and the substrate are joined together.In general,the wooden dowel is made of hardwood,and its strength is high.However,it still may be twisted during the rotation process,which affects the welded depth and pullout resistance.Although fast-growing poplar is a kind of hardwood,its mechanical properties are low due to its fast growth rate,but the strength and hardness of poplar can be improved by compression and thermal modification.The twisting would be avoided when compressed wood is used,and the per unit volume content of hemicellulose and lignin of compressed wood increases,which increases the content of molten material at the welding interface,thereby enhances pullout resistance of compressed wooden dowel rotary friction welding.The mechanical properties of wood can be increased by compressing the porous structure in the transverse direction after being softened.After compression,the compressed wood has a tendency to return to its original dimensions,therefore,it is necessary to fix permanently the compressive deformation through some pretreatment methods for uncompressed wood and post-treatment methods for compressed wood.The pretreatment with glycerin is a suitable process to fabricate the compressed wood and the post-treatment at high temperatures after densification is also one of common processes used to fix the compressive deformation.Northeast China poplar was firstly immersed in 50% volume concentration of glycerin for 24 h,then compressed under 150? to attain 60% compression ratio with different thermal modification time of 0.5 h,1 h and 2 h.This aim of this paper is to investigate the influence of thermal modification time and different wet/dry cycles on set recovery(SR)and mechanical properties of compressed poplar after pretreatment with glycerin.The mechanical properties include Brinell hardness(HB),hardness recovery(HR),modulus of elasticity(MOE),modulus of rupture(MOR)and ductility(D).It was found that the thermal modification time of 1 h can be more appropriate.The wooden dowel used for the pull-out test of rotary friction welding was made of the compressed wood.The influence of parameters on pullout resistance of compressed wooden dowel rotary friction welding were studied.The parameters include rotational speed,type of wood species,diameter of wooden dowel,welded depth,wood grain direction,the difference of the equilibrium moisture content between the substrate and the wooden dowel,and the difference of diameter between the wooden dowel and the pre-drilled hole of substrate.