薄壁结构高频超声应力场COMSOL仿真及试验研究

High-frequency Ultrasound Vibration Stress Field of Aircraft Thin-Walled Structures Based on COMSOL Simulations

为了深入研究高频超声振动(high-frequency ultrasound vibration,HFUV)对飞机薄壁结构激光焊接微熔池的影响机理,借助COMSOL软件,建立了激光微熔池模型,开展了旁触式单振源模式下振幅、超声加载位置等参数对熔池声压作用规律的仿真计算,分析了超声空化效应和声流效应的产生条件,并试验验证了超声功率对接头微观组织以及生成相的影响。结果表明,高频超声振动使得激光微熔池内部声压产生正负交替变化,温度场更加均匀,有利于空化泡的形成、闭合和超声空化效应的产生,降低残余应力;超声加载位置、超声振幅与熔池输入声压成正比,超声加载位置每靠近熔池10 mm,熔池声压增大2~3倍,每增大4μ倍的振动幅值,熔池输入声压增大10 Pa;超声振动对熔池主要起搅拌作用,当振幅>7μm、加载位置到熔池距离<60 mm时可产生声流效应,距离<15 mm时,影响机制则以空化效应为主;随着辅加超声振动场强度的增大,焊缝组织的晶粒度呈单调增加的趋势,即组织随超声功率的增加逐渐细化。

The laser molten pool model was built to research the influence of high-frequency ultrasound vibration(HFUV)on aircraft thin-walled structures using the COMSOL software.The acoustic pressure of the laser molten pool was simulated,which considered the position and number of sources,with side-touch single vibration sources.Subsequently,we analyzed the conditions of the ultrasound cavitation effect and the acoustic streaming effect.The results indicate that,firstly,the positive and negative acoustic pressures alternate with HFUV,and this phenomenon favors the formation and collapse of cavitation bubbles.Secondly,the distance and amplitude of the ultrasound are directly proportional to the acoustic pressure of the molten pool.The acoustic pressure of the molten pool will enlarge 2-3 fold with each 10 mm decrease in the distance,which will enlarge by 10 Pa with each 4μm increase in the amplitude.Thirdly,HFUV primarily acts as a blender toward the molten pools.The acoustic streaming effect will appear when the amplitude is higher than 7μm and the distance is lower than 60 mm.The ultrasound cavitation effect will appear when the distance is lower than 15 mm.Fourthly,the acicularα′-martensite content is more intense,orientation and arrangement are more cluttered,besides,the acicularα′-martensite average length is shorter because of ultrasonic vibration and radiation pressure.