微磨粒对超声空化冲击波衰减作用研究

Attenuation Effect of Micro-abrasive Particles on Ultrasonic Cavitation Shock Waves

目的研究超声加工过程中微磨粒对冲击波的影响。方法建立功率超声振动加工下的空化泡动力学方程,以及空化泡溃灭产生冲击波的数学模型,进而建立冲击波在微磨粒与水混合介质中的传播模型。使用六阶Runge-Kutta方法对数学模型进行求解,得到空化泡半径随时间的变化规律,以及空泡内部压强随空化泡半径变化的规律。结果当空泡半径被压缩至1μm左右时,空泡内部压强可达1000 MPa。通过对距离空泡壁1.5R_(0)处的冲击波压力进行求解发现,冲击波的压力仅需0.07μs就可从初始的1000 MPa迅速衰减至80 MPa。通过比较纯水介质与混合介质(SiO_(2)微磨粒与水)中冲击波传播速度的结果发现,加入SiO_(2)微磨粒会使冲击波的最大速度由2976 m/s降至2681 m/s,降低率约为10%。通过钛钽合金的功率超声振动加工实验验证了数值结果。对比分析了加入SiO_(2)微磨粒前后钛钽合金表面结构和三维表面形貌,发现微磨粒的加入导致材料表面空化坑的投影面积下降了12.5%。结论证实微磨粒对冲击波的传播起到了明显的衰减作用,是对材料表面产生作用的主要因素。该研究在超声加工领域具有理论意义和工程价值。

The effect of cavitation shock waves during power ultrasonic vibration machining can be produced.The presence of micro-abrasive particles can enhance the machining efficiency and impact the propagation of shock waves.The work aims to investigate the mechanism of micro-abrasive particles on shock waves during power ultrasonic vibration machining.By utilizing the Gilmore-Akulichev equation,the bubble dynamic equation under power ultrasonic vibration machining and the mathematical model of shock waves generated by the collapse of bubble were established.Subsequently,a propagation model for shock waves in the mixed medium of micro-abrasive particles and water was developed.The mathematical model was solved by the sixth-order Runge-Kutta method,providing insights into the dynamic evolution of bubble radius and the internal pressure of the bubble.The results indicated that a bubble with an initial radius of 8μm exhibited nonlinear oscillations under the effect of the ultrasonic field.After a series of oscillations,the change in radius gradually diminished over time,indicating a convergence towards equilibrium between the pressure inside the bubble and the surrounding environment.When the bubble radius decreased from 8μm to 3μm,the pressure on the bubble wall remained relatively stable.Upon compression approximate to 1μm,the internal pressure of the bubble could reach 1000 MPa,surpassing the ambient pressure.Consequently,the cavitation bubble rebounded outward,compressing the surrounding water and generating a shock wave that propagated radially.By solving the shock wave pressure at a distance of 1.5R_(0) from the cavitation wall,it was found that the shock wave pressure rapidly decreased from the initial 1000 MPa to 80 MPa within a short time of 0.07μs,covering a propagation distance of 17μm.Comparing the shock wave propagation speed in a pure water medium with that in a mixed medium of SiO_(2)micro-abrasive particles and water,it was discovered that the addition of SiO_(2)micro-abrasive particles reduced the maximum speed of the shock wave from 2976 m/s to 2681 m/s,resulting in a reduction rate of 10%.Subsequently,power ultrasonic vibration processing experiments were conducted on Ti-Ta alloy to validate the aforementioned numerical results.Through a comparative analysis of the surface structure and three-dimensional surface morphology of the Ti-Ta alloy before and after the addition of SiO_(2)micro-abrasive particles,it was observed that the number of cavitation pits decreased from 34 to 21.This indicated that the addition of SiO_(2)micro-abrasive particles reduced the occurrence of cavitation pits.The software ImageJ was utilized to measure the projected area of cavitation pits with diameter greater than 1μm on the Ti-Ta alloy surface.The results showed that the addition of SiO_(2)micro-abrasive particles led to a decrease in the projected area of cavitation pits from 497.132μm^(2) to 434.84μm^(2),corresponding to a reduction rate of 12.5%.This reduction rate was in line with the 10%calculated by the model,demonstrating consistency.The observed discrepancy mainly arose from the uneven distribution of SiO_(2)micro-abrasive particles in the machining area during the machining due to factors such as gravity,resulting in varying obstacles to the shock wave.This study confirms that micro-abrasive particles effectively attenuate the propagation of shock waves and become a key factor affecting the material surface.The findings of this research hold both theoretical significance and practical value in the field of ultrasonic processing.