Dynamic Properties Of Electromagnetic Resonance Fatigue Testing System

Electromagnetic resonance high-frequency fatigue testing machine is a testing system for measuring the fatigue properties of materials, which is based on the resonance theory. Because of high working frequency, short testing time, low energy consumption and low cost, it has been widely applied in scientific research and teaching in universities, research institutes and industrial departments, etc. In recent years, with the improvement of manufacturing and testing technology, as well as the development and practical application demand of new materials, the accuracy and reliability of the testing results by fatigue testing machine have drawn more and more attention of relevant researchers. Currently, testing tools and methods for the static force calibration of fatigue testing machine are relatively mature and the dynamic force calibration is still in its developing stage. Therefore, in order to improve the calibration precision of fatigue testing machine, we must accurately model the fatigue testing system, and perform systematic theoretical analysis and simulations on the dynamic characteristics of the system. The main contents of the thesis are as follows:(1)Taking the electromagnetic resonance fatigue testing machine GBQ-100as an example, this thesis establishes finite element models of the whole fatigue testing machine. Through modal and harmonic response analysis, the natural frequencies of the testing machine and the corresponding vibration shapes are obtained. The influence of different factors, such as the vibration mass, the specimen stiffness and the whole machine stiffness, on the natural frequency are analyzed.(2)Based on the working principle of electromagnetic resonance fatigue testing machine and mechanical vibration theory, a linear three-degree-of-freedom mechanical vibration model of fatigue testing machine is established, the vibration mass movement rule is expressed, and the elastic deformation law and the natural frequency solving equation of the vibration system are given The natural vibration frequencies are obtained with numerical calculations and the effects of vibration mass and specimen stiffness on the natural frequency are illustrated. In the end, according to the force-transferred equation between the sensor and the specimen, the expression of dynamic force error are proposed and influence factors of the error are analyzed, which can provide a theoretical reference for dynamic force calibration.(3) The thesis analyzes the factors resulting in the coaxiality error of the fatigue testing machine and its influence on the testing force. Here, coaxiality error is divided into two parts:geometric coaxiality error caused by the uncoaxial of the upper and lower fixture and force coaxiality error of the specimen. Under a linear elastic condition, the geometric and the force coaxiality errors are connected by the combinational deformation theory of solid mechanics so as to obtain the expressions of force coaxiality error and dynamic force error, which can provide a recommended testing bar dimention during the certification process and reference for dynamic force calibration. Theoretically speaking, this result also makes different test data due to different concepts of coaxiality between the production and measurement departments comparable.