Testing Load Control Method Of The Resonance Fatigue Crack Propagation Test Based On The Crack Length Measuring On The Real Time

In material fatigue test field, high frequency fatigue testing machine has been an important experimental equipment in the field of material fatigue test for its high work frequency, low energy consumption, short test time. To meet the first condition of thee high frequency fatigue test is:constant amplitude load loading and vibration in resonance point place. But for the linear time-varying and parameter slowly varying characteristics, the system can’t meet the two conditions and seriously affected the test accuracy and effectiveness. In order to realize the control for constant vibration load amplitude and inherent frequency tracking, this paper mainly do the following several aspects study:(1) Aim at the Testing load control system of the resonance fatigue crack propagation test based on the crack length measuring on the real time has an overall introduction, and briefly describes the working principle and the hardware.(2) Through the analysis of the system mechanism, the use of vibration mechanics principle to establish system mathematical model and modern control equation. The analysis of the system dynamic behavior includes stiffness changes with time, inherent frequency with crack change and amplitude changes with time and the research for system amplitude frequency characteristics.(3) Aim at the amplitude fuzzy PID control strategy on resonant fatigue expansion test was carried on concrete research; including two methods for amplitude fuzzy PID and self-adaptive fuzzy PID control strategy, and do the MATLAB/Simulink simulation.(4) Aim at the realization for test load control of the crack propagation, including the specific parameter design for Natural frequency tracking algorithm, amplitude fuzzy PID and the rule self-adaptive fuzzy PID,software design and the realization of the serial communication.(5) Completed two tests for the vibration load closed-loop control based on fuzzy PID and inherent frequency tracking, work out the results of the test error analysis.The paper formulated the suitable vibration load constant amplitude control strategy after the analysis of the high frequency fatigue testing machine dynamic characteristics. Make high-frequency fatigue testing machine meets the requirement of constant amplitude loading conditions and inherent frequency tracking, and improve the accuracy of the material fatigue test.