Piezo-driven Design And Analysis Of High-frequency Fatigue Test Control Mechanism

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 fatigue test on the subject, and test subject’s fatigue life. Now, there are two kinds of fatigue testing machine: fatigue testing machine driven by electromagnetic and fatigue testing machine driven by electro hydraulic servo, due to the restrictions of systems impedance reluctance, operating frequencyof them is lower than200Hz generally, they have bad amplitude controlling ability, bad resonance stabilization, and the loading accuracy is not high, they are not suitable to do high frequency fatigue test on small 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 and performance research, use circular bimorph piezo electric vibrator as the driving source, develop a fatigue testing machine to test materials or parts with small amplitude, high frequency load, and do the corresponding research on design theory, dynamic analysis modeling, analysis and simulation, and prototype measurement, the main contents are as following:Establish vibration mode of the circular piezoelectric bimorph vibrator,solve the first order vibration modal and the corresponding natural frequency; Solve the deflection formula at the center of piezoelectric bimorph vibrator; apply the finite element software to do the modal analysis of piezoelectric vibrator;measure the impedance characteristics of the piezoelectric vibrator’s natural frequency and deflection at the center of piezoelectric bimorph vibrator;compare the above three results to verify the reasonable theoretical model and the reasonable solving process.Discussed the overall scheme of piezoelectric driven high frequency fatigue testing machine to determine its pre load adjustment mechanism of the type being analyzed and tested to determine the kind of shape and material tensile fatigue test article focuses on the analysisrequired; on fatigue testing machine composed of a piezoelectric load preset adjustment mechanism, spring loaded mechanism and the base was designed; and analyzes the various component parts of a preload adjustment mechanism with spring loaded mechanism and its main role, and ultimately determine its material and specification.Based on piezoelectric vibrator works in fatigue testing machine and combined with the piezoelectric fatigue testing machine is designed in this paper the parameters of the actual demand determines the driving power. Design the main circuit structure of electric drive, select the suitable microprocessor and IGBT drive mode. And through the analysis of the inverter unit three forms and comparison, the selection of full bridge inverter. In order to improve the output efficiency of drive power supply, on the impedance matching. Analysis and design of the driving power of the main control program and the interrupt service routine. Piezoelectric fatigue testing machine and determine the parameters of each main components in thesystem, determine the technical requirements of the data acquisition device, and the matching software is designedBy simplifying the application focus quality standard established the dynamic model ofpiezoelectric fatigue testing machine, and according to the Newton’s second law, establishedits mechanical system movement differential equation, and solving the steady state responseand specimen under maximum load; To calculate the stiffness of the piezoelectric vibrator, rectangular plate spring stiffness, weight of the quality of the mass and stiffness of the specimens; Analyses the resonant frequency of the driving type fatigue testing machine and the specimen under maximum load and the calculation of several important parameters of the relationship between. In accordance with table5.5structural parameters of the established finite element model of fatigue testing machine and the entity model, solving each order modal vibration mode and corresponding natural frequency, determines the frequency of230.4Hz14order vibration mode as the main mode; By changing the thickness of the plate spring fatigue testing machine and farmar mass thickness, studied the changes of these parameters on its mainmodal frequencies, the results show that under the premise of without changing the driving voltage RMS, thickness and weight plate spring mass increases, the quality of will cause themain modal frequencies significantly larger; Validation when its work in main modal frequency, specimen under load stability, at the same time frame small amplitudes; By changing the thickness of the plate spring fatigue testing machine and farmar mass thickness, respectively in four different driving voltage test prototype effect on the specimen under dynamic load,the largest prototype various parameters were analyzed on the influence of the maximum dynamic load acting on the specimen, the variation law and reason.