| Heterogeneous components with complex profiles,such as engine turbine blades,aircraft wings,and irregular grinding tools with irregular cavities,are widely used in fields such as aerospace and weapon equipment.Due to their application background,these heterogeneous components need extremely high requirements for surface accuracy,fatigue strength,and other surface properties.The complexity of their profiles easily leads to limited machining space.Power ultrasonic vibration machining is not constrained by the workpiece configuration due to its force on the material coming from the fluid flow.A large number of small bubble nuclei in the liquid undergo growth,oscillation,and collapse under the action of ultrasonic positive and negative pressure,and generate a series of secondary effects such as micro jets and shock waves,which affect the surface of the material.At present,a large number of scholars have conducted extensive research on cavitation bubble observation,secondary effects of cavitation,and cavitation erosion.However,there is still insufficient research on the synergistic mechanism of micro abrasive particles under power ultrasonic cavitation.Based on this,this article clarifies the theory of power ultrasonic cavitation,and uses mathematical modeling,simulation calculation,and experimental research to study the mechanism of ultrasonic cavitation effect on materials.Based on the complexity of ultrasonic cavitation environment,a precision ultrasonic machining micro displacement platform driven by piezoelectric ceramics is proposed and designed.The main research work and achievements are as follows:（1）The mechanism of power ultrasonic cavitation and micro abrasive particles is explored.The relationship between heterogeneous nucleation and cavitation phenomenon is explained,and the cavitation threshold that causes the fracture of liquid medium molecules and the occurrence of cavitation phenomenon is calculated.It is found that as the initial radius of the bubble increases,the cavitation threshold of the liquid medium also decreases continuously.The mechanism of the effect of power ultrasonic cavitation on materials is explored.A bubble dynamics model considering micro abrasive particle disturbance in abrasive suspension has been established.It is found that the disturbance of micro abrasive particles would suppress the vibration of bubbles.The larger the initial radius of bubbles,the lower their oscillation expansion amplitude,and the longer their oscillation cycle.The motion state of micro abrasive particles in cavitation phenomenon is studied in this article.（2）In order to better control the micro cutting stroke on materials under the synergistic effect of micro abrasive particles in power ultrasonic cavitation,a precision ultrasonic machining micro displacement platform driven by piezoelectric ceramics is proposed and designed.The stacked piezoelectric ceramics are used as the driving device of the precision ultrasonic machining micro displacement platform.The displacement is amplified by the bridge amplification mechanism based on the triangular amplification principle.The theoretical amplification ratio is 24.65.Using Workbench to carry out finite element analysis,the simulation amplification ratio is 25.03,and the error is within a reasonable range.The maximum stress of the flexure hinge is analyzed by finite element method,which is far less than the allowable stress of spring steel,meeting the bearing requirements.（3）The motion state of micro abrasive particles under power ultrasonic cavitation is explored.Using Fluent for analysis,it is found that there is periodic variability in the flow field pressure and velocity vector of the liquid flow in the cavitation effect.A fluid shape resembling vortex appears in the flow field,which drives micro abrasive particles to perform micro cutting on the surface of the workpiece.The cutting effect is positively correlated with velocity.The velocity of micro abrasive particles in the flow field is decomposed into impact velocity perpendicular to the surface of the workpiece（Y-axis）and shear velocity along the surface of the workpiece（X-axis）,and the values are negatively correlated with the distance between its position and the tool head.In the area close to the tool head,due to the alternating nature of positive and negative pressures,the velocity of micro abrasive particles continues to increase over time.By analysis of the motion state of micro abrasive particles near the edge of the tool head,it is found that the shear velocity is greater than the impact velocity,and the shear effect of micro abrasive particles is more obvious,which is beneficial to the finishing of material surface.（4）The constitutive relationship of materials under power ultrasonic cavitation from a microscopic perspective is studied.Considering the scale effect and using the strain gradient plasticity theory,a constitutive model has been constructed to describe the stress changes of titanium tantalum alloy from a microscopic perspective.Using a universal testing machine and Hopkinson rod,quasi-static tensile tests and dynamic compression tests are conducted on the material.By fitting the stress-strain curve,the initial yield stress in the Johnson Cook model is928.6MPa,the hardening index is 0.6,and the strain rate strengthening coefficient is 0.025.And the Johnson Cook curve describing material behavior from a macro perspective has been analyzed and compared with the constitutive equation curve from a micro perspective.It is found that when considering material scale effects,the stress of Ti-Ta alloy under the synergistic effect of power ultrasonic cavitation and micro abrasive particles increased by about 13%compared to when not considering scale effects.（5）Power ultrasonic cavitation test has been carried out.The effects of abrasive content and ultrasonic amplitude on the natural frequency and resonance amplitude of the material are investigated.It is found that the natural frequency of the material increased,then decreased,and then remained unchanged with the increase of abrasive content.When the abrasive content is 10wt.%and the ultrasonic amplitude is 50%,the natural frequency of the material reaches the peak of 46.32 Hz.With the increase of abrasive content,the resonance amplitude of the material decreases,then increases,and then remains unchanged.When the abrasive content is constant,the resonance amplitude of the material increases firstly and then decreases with the increase of ultrasonic amplitude,and when the amplitude is 60%,the maximum resonance amplitude of the material is 0.1789m·s-2.The variation of surface hardness and grain size of materials in abrasive suspension with ultrasonic amplitude,distance between workpiece and tool head,and ultrasonic action time is analyzed by orthogonal test in abrasive suspension.It is found that the ultrasonic time has an obvious effect on the surface hardness and the surface grain size.When the ultrasonic amplitude is 60%,the distance between the tool head and the workpiece is 1mm,and the modification lasted for 10min,the surface hardness of the material is the highest,and the surface grain refinement is the most obvious.It is considered that the grain refinement of the surface layer of the material is an important factor affecting the improvement of the surface hardness.By comparison,it is found that the grain refinement and the fluctuation of grain size in abrasive suspension are significantly better than those in water environment.Therefore,the surface modification of the material can be realized by the power ultrasonic cavitation effect through the regulation of the process parameters. |
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