| High-frequency fatigue testing machine is a metal material testing machine based on the resonance theory. It is used to measure the fatigue property of tension and compression of material and its alloy under the normal temperature, it can realize high-load, high-frequency, low-consumption, so the experiment time is shortened, the experiment cost is reduced, it is one of main testing equipments of our industrial development. So far, the main problem existed in the high-frequency fatigue testing machine is the system control in the process of the changing of sample stiffness. The concise dynamic model of system must be built in order to realize the aim. This thesis mainly deals with the theoretical analysis, simulation and experimental research of dynamic characteristics of system. Main contents of the thesis are listed as follows:1. Put forward a cantilever beam model of standard compact tension sample, the formula of stiffness of sample is set up from stress function, at last, the influence of dimension and material of sample to stiffness is analyzed.2. The modal and harmonic of sample are analyzed by the ANSYS software, the natural frequency of sample and the natural frequency change along the crack length when crack extends are calculated.3. The working principle of high-frequency fatigue testing machine is introduced, the dynamic model of system is built when the crack don't appear in the sample; The natural frequency, vibrating amplitude and sample maximum amplitude of small damper system are analyzed; At last, the dynamic characteristics of system is simulated.4. The dynamic equation of time-varying crack extending system is built; the relationship of crack length and time is recorded by on-line fatigue crack monitor system, based on the experiment data, the natural frequency and sample maximum amplitude of system is analyzed when the crack appears in the sample.5. The experiment platform based on virtual instrument is built, the identification of unknown parameter of system is operated, besides, the change trend of stiffness, natural frequency and sample maximum amplitude with crack length and time is verified.The analytical and research work on dynamic characteristics of high-frequency fatigue testing machine in the thesis, provides a theoretical basis for the high-precision control of frequency and load of high-frequency fatigue tester and contribute the development of the fatigue test technology. |
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