| In recent decades,with the continuous progress and development of human science and technology,especially in the fields of aerospace,rail transit and machinery manufacturing,the requirements for operating speed and service life of structures and mechanical equipment have increased exponentially.Since World War II,the problem of very high cycle Fatigue in the mechanical field has gradually emerged.Due to the low vibration frequency of the traditional fatigue test method in the past,it takes a huge amount of time and cost to measure the fatigue life law of parts with a service life of 109.The traditional fatigue test method is used to draw the S-N curve.The use of ultrasonic fatigue testing will have a huge improvement in time and cost control.Under the background and problems mentioned above,this paper takes the theoretical design and working environment of the specimen in the ultra-high cycle fatigue test as the breakthrough point,combined with the ultrasonic fatigue device,the evolution of the test process,and the ultrasonic fatigue test system at home and abroad.The summary and analysis of the aluminum alloy 7075-T6 specimens were carried out to optimize the design and ultrasonic fatigue tests.The main researches in this paper are as follows:(1)In view of the data collection requirements of the ultrasonic fatigue test system,this paper develops an ultra-high cycle fatigue test measurement and control system with integrated recording and detection functions,which can meet the system resonant frequency,processing time,ambient temperature and test piece during the test.The dynamic detection and recording requirements of the maximum displacement greatly improve the measurement accuracy and test time,laying a foundation for subsequent tests.(2)In this paper,the geometric dimensions of the specimen are calculated analytically through the ultra-high cycle fatigue theory,and the finite element analysis and structural optimization design are carried out using Ansys Workbench to analyze the dimensional parameters of the specimen and the natural frequency of the specimen and the minimum section of the specimen.From the correlation diagram and sensitivity diagram between the maximum stress values,it can be obtained that there is a linear relationship between the dimensions of the specimen and the system resonant frequency.(3)In this paper,the size of the actual processed specimen is measured by the surface profile micrometer,and the data is analyzed by SPSS software,and the specific equation of the multiple linear regression equation is obtained.According to the regression equation,the resonance length and diameter of the specimen are changed to make the ultrasonic fatigue test.The overall resonance frequency of the system reaches 20 k Hz,eliminating the influence of machining errors on the test resonance frequency.(4)In this paper,ultrasonic fatigue tests were carried out on 7075T-6 aluminum alloy specimens under 9 different maximum stresses.By comparing the fatigue life law SN curve,the reliability of the ultrasonic fatigue measurement and control software system and test device was verified.The fractures of the specimens were observed macroscopically and microscopically,and the fracture mechanism of ultra-high cycle fatigue and the mode of crack initiation and propagation were analyzed. |
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