Research On The Inherent Frequency Tracking Technology Of Resonant Material Fatigue Test System

Resonant high-frequency fatigue testing machine is a metal material testing machine based on the resonance theory.It is a magnetic and resonant machine to test metal material.We mainly use it to determine the tensile and compressive fatigue performance of metals and alloys in room temperature.The testing machine is characterized by high load,high-frequency and low consumption.Due to these characteristics,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 accuracy controlling of vibration load and the real-time tracking of natural frequency during the change of the stiffness of the specimen.In this paper,the real-time natural frequency tracking method has been studied.To achieve this goal,this paper's study is as follows:1.According to the analysis of the resonant high-frequency fatigue testing machine's structure and vibration,The system mathematical model has been obtained.Next,the excited spring,the main vibration spring of system and the standard CT specimens were analyzed in ANSYS for so calculating its stiffness,on the basis,the relationship of specimen stiffness and system natural fi-equency with the crack length had been obtained.By combining these calculations with measured experiment data of the crack's length over time,then the fitting function of the system natural frequency changing with time is got.In the end,the frequency changing rate the system is got by solving first derivative.2.The frequency tracking algorithms of the resonant high-frequency fatigue testing system have been studied,then a modified climbing method,a adaptive search algorithm and a area optimization algorithm based on crack length to track the systemic natural frequency have been proposed.In addition,the advantages and disadvantages of the three algorithms are compared by theory and experiment.3.The sine wave generator,the signal acquisition module and designing the human-computer interaction of hardware and software of the high-frequency fatigue testing machine are designed.4.The following three experiments in a experimental platform were completed:a.Sweeping frequency of multiple standard CT specimen in the case of the same length of their crack.b.Comparing the three frequency tracking algorithms.c.Measuring the crack length during the fatigue test.Furthermore,the obtained experimental data are analyzed.In this paper,the analysis and research of natural frequency,frequency tracking algorithm,sine wave signal generator,data acquisition modules of the high-frequency fatigue testing machine are made.It makes a contribution to the technology development for the fatigue test.