毛竹销（钉）的高速旋转摩擦焊接性能研究

选取毛竹销钉替代木榫在1 500 r/min的情况下与榉木基材进行旋转摩擦焊接，对其抗拉强度和焊接机理进行研究。重点研究不同形状的预钻孔和不同榫径与孔径比值下的竹销钉焊接抗拉拔强度，并将其与木榫焊接和PVAc胶接的抗拉强度进行对比。结果表明:1）当采用恒定直径孔10/9、10/8、10/7、10/6 4种榫径/孔径比的焊接强度均高于PVAc胶接强度，但低于木荷榫和榉木榫的焊接强度，其中10/8的榫径/孔径比的焊接强度相对最高，达到了5.54 MPa；2）当采用渐变直径孔，竹销钉的焊接强度得到明显提高。其中10/8-6的榫径/渐变孔径比值取得了最高的焊接强度，达到6.42 MPa，比10/8比值的强度提高了15.6%，超过了木荷榫的焊接强度，但不及榉木榫的焊接强度；通过对竹销钉的焊接界面温度进行监测，发现焊接界面能在2 s内达到300℃以上的峰值高温，且维持了一定的高温时间（通常约2～3 s），随后随着竹销停止旋转摩擦，温度逐步下降；不同的榫径与孔径比值下，焊接界面的升温速率、峰值温度和高温持续的时间不同，它们是产生强度差异的主要原因；SEM观察结果显示，竹销旋转摩擦焊接界面由竹销或基材中的胞间层物质软化、熔化和流动并与作为增强材料的竹纤维包裹，形成了犹如“钢筋水泥土”结构般的致密、连续和坚固的焊接界面；FTIR分析结果表明，摩擦产生的高温会导致竹销中半纤维素发生一定程度的降解，纤维素的降级十分有限，木质素发生一定程度的缩合反应，木质素的含量相对提高。试验结果表明，将竹销钉代替木榫用于木材的旋转摩擦焊接是可行的。

Bonding Properties of Bamboo Dowel (Nail) Welded to Wood with High Speed Rotation

In this investigation,the moso bamboo (Phyllostachys pubescens) dowel was selected to replace the wood dowel welded with wood substrate by high-speed rotation,and the tensile strength and welding mechanism of bamboo dowel were studied.The results show that 1) for the cylindrical shape pre-drilled hole,the tensile strength of bamboo dowel welded joints of the dowel/hole diameter ratio of 10/9,10/8,10/7 and 10/6 were all higher than that of PVAc-glued joints,but lower than that of Schima dowel and Beech dowel rotational welded joints.And the welding strength of 10/8 dowel/hole diameter ratio was the highest which reached to 5.54 MPa.2) For the truncated conical shape pre-drilled hole,the welding effect was obviously enhanced.The welding strength of 10/8-6 dowel/hole diameter ratio reached to 6.42 MPa,which was even slightly higher than that of Schima dowel welding.The results of temperature monitoring and SEM showed that,due to the temperature-induced softening and flowing of some amorphous,cells-interconnecting polymer material (mainly lignin and hemicellulose) in the structure of the bamboo and the bamboo fibers (mainly vascular bundles) were wrapped to form a dense continuous bonding layer,similar to the reinforced cement soil,thus producing a good bonding effect.FT-IR analyses showed that the high temperature led to the degradation of some hemicelluloses and the relative content of lignin increased in the welding interface,and finally improved the bonding properties.The results showed that moso bamboo dowel as an excellent wooden material,was a good substitute for wood dowel in wood friction welding.