Design And Experimental Study Of Ultrasonic Fatigue Tensile Samples And Bending Samples

In the past few centuries,the industries related to fields such as aerospace,transportation,and machinery manufacturing have undergone rapid development,thanks to the continuous improvement and perfection of science and technology.How to improve the performance of relevant mechanical structures and parts materials is the key to ensure the steady development of science and technology.In the traditional fatigue test research,the theory that the material has "infinite life" has been proved not to be suitable for the working condition under high frequency and low amplitude loading,and because the loading frequency of the traditional fatigue testing machine is too low,the ultra-high cycle fatigue test of the material cannot be completed in a short time,and the fatigue-life curve of the material cannot be drawn basically.Therefore,it is necessary to carry out ultrasonic fatigue test with low cost,short time and high efficiency.Building on this background,the paper provides a summary and analysis of the historical development of fatigue research,fatigue test equipment and fatigue test process,and builds a high-frequency fatigue test device which can be used for ultra-high cycle fatigue test of materials.It can realize high-frequency fatigue test of specimens under 20 k Hz load,greatly improve fatigue test efficiency and complete fatigue performance test of materials under corresponding working conditions.This paper designed an ultrasonic fatigue tensile specimen,and simplified the vibration model of the system to a circuit model using the equivalent circuit analysis method of mechanical-electrical analogy based on the principle of ultrasonic fatigue testing,and then the preliminary calculation of the size of the specimen is completed according to the frequency equation.The error caused by using catenary instead of circular arc in the transition section of dog-bone-shaped tensile specimen is calculated,and the size range of specimen is further refined.Combined with the actual processing details of the tensile specimen,Workbench software is utilized to dynamically optimize the size design,so that the resonance frequency and maximum stress of the actual processing specimen meet the requirements of the test.The software of ultrasonic fatigue tensile specimen design based on MATLAB is designed and developed to simplify the size design of ultrasonic fatigue tensile specimen.The structure of the bending specimen can be improved to realize the ultrasonic bending fatigue test.The improved method for calculating the resonant length of the ultrasonic fatigue bending specimen with single cantilever beam was described.The finite element software was employed to optimize the initial specimen size,ensuring that it meets the stress and strain requirements for high frequency fatigue testing.The general process of ultrasonic fatigue tensile and bending tests is given in this paper.The tensile and bending tests are carried out on the specimens machined from 6063 aluminum alloy.The S-N curves of the materials are drawn according to the test data,and the test scheme was verified for feasibility.The fracture morphology of the specimen was observed using an optical microscope,and the location of crack initiation was observed.