Performance Study And Structure Improvement Of Electromagnetic Resonance Type High Frequency Fatigue Testing Machine

Electromagnetic resonance type fatigue testing machine is a kind of testing machine based on resonance principle to test the fatigue performance of metal or non-metal materials.Because of its advantages of low energy consumption,high efficiency and convenient control,it has a wide application prospect in engineering practice.In particular,because the tester is based on the resonance principle,it consumes almost no energy in theory during the alternating load test on the specimen.Compared with the traditional electro-hydraulic servo technology,the energy-saving effect reaches more than 98%,and the working time required can generally be saved at least twice.The fatigue testing machine based on electromagnetic resonance technology,like other equipment and tool technology,is developing rapidly in the direction of higher,better and larger.It is mainly reflected in the amplitude,frequency range,applicable specimen type,tester structure and intelligent work control.With the continuous development of technology,people have higher requirements for the performance of the test machine,such as higher working frequency,wider range of specimens and greater amplitude,etc.This paper applies the theory and technology of dynamics and electromagnetic resonance to study the performance of electromagnetic resonance type high frequency fatigue testing machine,and expand and improve the function and structure of the testing machine.The research object breaks through the traditional 300 Hz high-frequency range and the more single application limitation,and this paper mainly carries out the following aspects of research work:(1)Based on the theory of vibration mechanics,the dynamic characteristics of the testing machine were analyzed.According to the structure of the fatigue testing machine,a three-degree-of-freedom forced vibration system model of the testing machine was established,and the system was solved to obtain the expressions of motion amplitudes of each participating part of the testing machine.Based on the above work,the conditions of the ideal working condition of the tester are proposed through theoretical analysis;the solution formula of the system’s inherent frequency is calculated,and the influencing factors of the inherent frequency and the influencing law are analyzed to obtain the formula.Finally,the influence law of each parameter of the testing machine on the inherent frequency is verified by simulation and test.(2)In order to improve the performance of the tester,the tester can be applied to the test tasks of different complex shape specimens,such as conducting tests of three-point bending and crankshaft bending fatigue.For the first time,the installation position of force transducer is analyzed and studied,mainly the dynamic force error of the test machine with the transducer installed at the excitation end is studied theoretically,and is the first to be tested and applied in China,which provides strong theoretical support for the expansion of the application of electromagnetic resonance technology.According to the structure of the sensor mounted on the excitation end and the fixed end of the test machine,a four-degreeof-freedom linear system was established and solved respectively,and the expression of the amplitude of the reference part was obtained;according to the expression of the force value of the sensor and the specimen,the expression of the dynamic force error was obtained,and its influencing factors were analyzed by the expression of the dynamic force error,which provided a reference basis for the subsequent dynamic force calibration;then the test was conducted to The real force of the specimen was measured and compared with the actual force measured by the sensor,and the dynamic force error was obtained to verify the accuracy of the correction formula.Finally,the installation position and usage of the accelerometer are discussed to provide a scientific and reasonable method for dynamic force calibration.(3)In order to expand the function of the testing machine,the shaker assembly was innovatively designed and the shaker function of the testing machine was verified through tests.Simulation analysis of the vibration system installed with the shaker assembly was carried out to obtain the resonant frequency and vibration type of the system,and the theoretical maximum acceleration of the shaker was calculated;theoretical analysis of the vibration system was carried out to obtain the relationship between the acceleration of the shaker and the magnitude of the excitation force;finally,test tests were conducted on the test machine installed with the shaker assembly to verify the feasibility of the shaker and the correctness of the theoretical analysis.(4)According to the problems occurred during the commissioning of the testing machine,the structure of the testing machine was improved from its existing structure.According to the Zener model of the support structure of the testing machine,a new solution is proposed,and the vibration isolation performance of the original support structure and the support structure with rubber mats in series is compared and analyzed,and the latter has better performance;a new support structure is designed and simulated to verify its vibration isolation performance,which provides new ideas for the design of vibration isolation structures in other industries.Through the phenomenon of force-time curve amplitude fluctuation during the test of the test machine,the causes were analyzed and improvement measures were proposed to solve the problem of resonance of the excitation system of the test machine.