Design And Analysis Of Piezoelectric-driven High Frequency Fatigue Testing Machine

The main failure of the parts under alternating loads is fatigue failure. Currently,the main effective mean to prevent fatigue failure of materials or parts is to do fatiguetest on the subject, and test subject’s fatigue life. Now, there are two kinds of fatiguetesting machine: fatigue testing machine driven by electromagnetic and fatigue testingmachine driven by electro-hydraulic servo, due to the restrictions of system’simpedance reluctance, operating frequency of them is lower than200Hz generally,they have bad amplitude controlling ability, bad resonance stabilization, and theloading accuracy is not high, they are not suitable to do high-frequency fatigue test onsmall and hard and brittle specimen.This paper is based on the National Natural Science Foundation project named“piezoelectric-driven high-frequency fatigue testing structure design theory andperformance research”, use circular bimorph piezo-electric vibrator as the drivingsource, develop a fatigue testing machine to test materials or parts with smallamplitude, high-frequency load, and do the corresponding research on design theory,dynamic analysis modeling, analysis and simulation, and prototype measurement, themain contents are as following:Establish vibration mode of the circular piezoelectric bimorph vibrator,solve thefirst-order vibration modal and the corresponding natural frequency; Solve thedeflection formula at the center of piezoelectric bimorph vibrator; apply the finiteelement software to do the modal analysis of piezoelectric vibrator；measure theimpedance characteristics of the piezoelectric vibrator’s natural frequency anddeflection at the center of piezoelectric bimorph vibrator; compare the above threeresults to verify the reasonable theoretical model and the reasonable solving process.Discuss the general scheme of piezoelectric-driven high-frequency fatiguetesting machine, include design of exciting method,pre-load adjustment mechanism,loading mode and tested specimen, drive loads preliminary calculation and testsystem’s requirements, design preset load adjusting mechanism, the elastic loader and the machine base.Establish the dynamic model of the piezoelectric-driven high-frequency fatiguetesting machine, according to Newton second law, establish the system’s differentialequation group of mechanical motion, solve the steady-state response and Maximumload on specimens, calculate stiffness of circular piezoelectric bimorph vibrator,rectangular spring plate and tested specimen,calculate the quality of the weight mass;analysis their effect on resonant frequency of fatigue testing machine and maximumload on specimens.According to the structural parameters in Table4.3, build the solid model offatigue testing machine, build the finite element model of prototype, solve thevibration modals and the corresponding natural frequencies, determine the14thVibration mode is main vibration for the fatigue testing machine, the workingfrequency is330.4Hz;by changing the thickness of spring plate and mass of loader,study the impaction of these different parameters on its main modal natural frequency.The result shows that: when the thickness of spring plate and the mass of loaderincrease, the natural frequencyofmain vibration mode will vary significantly; verifythat: when the fatigue testing machine works in frequency of main vibration modal,load on specimen is stable, while the frame of fatigue testing machine has littlevibration. By changing the thickness of spring plate and mass of Loader, test themaximum dynamic load on the specimen when prototypes work in four differentdriving voltages, analyze the impaction of different parameters on maximum dynamicload acting on the specimen, From the test results, the maximum dynamic load actingon the specimen becomes larger as the increment of the in mass of the elastic loaderand the driving voltage. By adjusting the two parameters, meet the requirements ofload table of fatigue testing,meet the different requirements of load acting onspecimen.