| In the past decade,power ultrasound technology has been widely used in the field of fatigue testing.Compared with the traditional fatigue test method using electrohydraulic servo or electromagnetic excitation as the excitation method,the ultrasonic fatigue test technology has the advantages of high frequency,short time,low energy consumption and high efficiency.As the core of power ultrasound technology,the ultrasonic fatigue vibration system using piezoelectric transducers as the excitation source has become a hot topic in the research of fatigue test equipment,and is gradually being applied to the detection of certain high-strength or long-life fatigue parts in the industrial field.In view of the above background,this paper takes the principle of power ultrasonic technology as an entry point to analyze and study the related issues of theory and design of ultrasonic fatigue vibration system based on longitudinal composite piezoelectric transducer.The main contents of this article are as follows:(1)Explain the constitution and realization principle of the ultrasonic fatigue vibration system,establish the longitudinal and transverse vibration models of the continuous vibrating body and solve the dynamic equations.On this basis,this paper analyzes the vibration principle of the horn-shaped longitudinal vibration specimen,symmetric cantilever bending vibration specimen and mosaic specimen,and gives the corresponding vibration mode function,frequency equation and amplification factor.The size of the theoretical design and finite element optimization.(2)Compare the characteristics of the three piezoelectric transducers commonly used in the ultrasonic field,and finally select the composite piezoelectric transducer as the excitation source;discuss the performance of the transducer at different joint positions,and select the front Installation form;establish composite transducer dynamic model and equivalent circuit model,analyze the relevant parameters of the transducer and its relationship with the size and material of the transducer;analyze the loss of the transducer from the perspective of hysteretic damping characteristic.(3)Design a new type of transducer that can realize the stepwise adjustment of resonance frequency,and its frequency adjustment range is 19 ~ 21 kHz.The piezoelectric ceramic part of the transducer is designed based on the characteristics of the piezoelectric material,with the front-rear vibration speed ratio and the electromechanical coupling coefficient of the transducer;a new transducer frequency adjustment scheme is proposed,and the size of the adjustment weight is designed by the finite element method And structure;design the transducer connection structure,protective cover structure and vibration isolation structure;design the horn structure that matches the transducer.Establish a finite element model of the new transducer,and analyze and verify the resonance frequency,amplification factor,electrical terminal impedance,etc.of the new transducer.(4)A new asymmetric force loading method is proposed,which can satisfy the loading of-500 ~ 500 MPa static stress and-500 ~ 500 MPa asymmetric stress.Design the dimensions of a new type of asymmetric force loading device and perform simulation verification.(5)The following tests are designed to verify the accuracy of the design of the ultrasonic fatigue vibration system: the displacement monitoring test verifies the accuracy of the design of the trumpet-shaped longitudinal vibration test piece and the symmetrical cantilever-shaped bending vibration test piece;Frequency change from the beginning of vibration to the occurrence of cracks;transducer impedance monitoring experiment to verify the feasibility and design accuracy of the new transducer frequency adjustment measures;flapping effect frequency estimation test to verify the estimation of ultrasonic vibration system based on flapping effect Feasibility. |
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