Device And Specimen Design And Experimental Study Of Ultrasonic Fatigue Testing

With the rapid development of modern science and technology,especially the development of material application in the fields of aerospace,transportation and medical treatment,people put forward higher requirements on the performance of materials and parts.Traditionally,metal materials have fatigue limit,and when the working load of parts is lower than the fatigue limit,the parts have infinite life.However,the research results of ultra-high cycle fatigue show that the fatigue fracture of parts still occurs after 107 cycles and the traditional fatigue disappears.Therefore,it is necessary to study the ultra-high cycle fatigue properties of materials.In order to obtain the S-N curve of material with more than 107 cycles,the conventional fatigue test method is time-consuming and laborious,or even impossible to complete.The application of ultrasonic fatigue test technology can quickly and accurately study the ultra-high cycle fatigue properties of materials.In this paper,starting from the design of ultrasonic fatigue tensile compression test specimens,the design of ultrasonic axial tensile compression section specimens is carried out on the basis of the theory of one-dimensional linear bar specimen vibration displacement differential equation and elastic wave theory.Matlab was used to calculate the geometric size of the specimen,and ANSYS Finite Element analysis software was used to analyze the stress and strain of the specimen.The modal analysis and harmonic response analysis of the specimen were carried out.Systematically describe the specimen processing method and the test process.Based on the concept of specific stiffness of material,a new design method of tensile specimen was proposed.In addition,the design interface of ultrasonic fatiguespecimens based on Matlab was proposed and designed for the problems of too many steps in the design of ultrasonic fatigue specimens and cumbersome calculation.The design procedure and method of ultrasonic tensile specimen are optimized greatly.The macroscopical and microcosmic morphologies of tensile specimens are analyzed,and the mechanism of ultrahigh cycle fatigue fracture and the way of crack initiation and propagation of aluminum alloy are systematically described.Basquin formula was used to predict the fatigue life of ultra-high cycle fatigue specimens,and the predicted s-n curve was compared with the actual S-N curve after the test,so as to improve and advance the S-N curve theory of aluminum alloy specimens.On the basis of referring to the existing torsional fatigue test methods,the theory and method of ultrasonic fatigue longitudinal and torsional composite test with ultrasonic torsional conversion device are explored.The working principle,design procedure and design method of the torsional converter are described in detail.The new torsional fatigue test method provides a new feasible scheme for ultrasonic fatigue torsion test,improves the conversion rate of torsional vibration and makes up for the single defect of ultrasonic torsion test method,which promotes the further study of ultrasonic fatigue torsion test.In the process of ultrasonic fatigue tensile pressure and longitudinal torsion test,the test device can run stably and each unit can work normally.Vibration form and stress analysis of specimen.The fatigue life is basically consistent with the simulation results.In this paper,the platform of ultrasonic fatigue test device has been built successfully,and the development of each parameter index has reached the expected goal.