Influence Of Ultrasonic Strengthening On The Fatigue Property Of Different Material

With the development of modern science and technology, requirements of mechanical equipment parts for the performance and working life have become more and more stringent. Not only the basic life requirements, but also the complex environment must be able to adapt to. Therefore the improvements of the aeronautical material are particularly important.The classical fracture mechanics theory suggests that the fatigue property of materials and surface processing technology have an inseparable relation. Good surface integrity can improve the fatigue performance of materials and reduce the crack initiation. The surface compressive stress can also extend the fatigue life of materials and prevent the expansion of the crack. Therefore on the basis of the existing materials and manufacturing processes, improving the material processing technology to increase the material reliability becomes a very effective mean of research in engineering application.In this paper, we take the relevant research in the China aviation industrial as the background and the three aviation materials of 2D12 aluminum alloy, 30CrMnSiNi2 A steel and TC6 titanium alloy as the research object. Use ultrasonic rolling processing to replace the original grinding processing and analyze the static and fatigue properties of three kinds of typical metal materials. This paper studies the application feasibility of the ultrasonic rolling processing and the fatigue effect on the three kinds of material so that we can accumulate valid data and establish the theoretical basis for the application of ultrasonic strengthening technology in aviation materials' processing.The study adopts a relatively stable machining parameters on the basis of a large number of trials.We divided the three kinds of materials into two groups.One is under turning + grinding processing, the other is under turning + ultrasonic rolling processing.Then use metallographic microscope, X-ray diffraction, hardness meter and scanning electron microscopy(SEM) to analyze the surface integrity differences between the polishing and ultrasonic rolling processing. Tensile and fatigue tests of three kinds of materials have been done to analyze the influence of ultrasonic rolling processing on fatigue performance of the three materials.Research shows that, the high frequency vibration in the process of ultrasonic rolling processing can make the grain on the surface occur plastic deformation to produce a plastic flow area then lead to grain refinement. Relative to the grinding, ultrasonic rolling processing can introduce higher surface residual compressive stress.We can see from the tensile test data that the ultrasonic rolling processsing has no particularly significant influence on the conventional mechanical properties of the sample, but the plasticity of three materials after ultrasonic rolling processing are reduced.The fatigue test results show that the fatigue life of 2D12 aluminum alloy and 30CrMnSiNi2 A steel has highly improved after ultrasonic rolling preocessing due to the improvement of the surface morphology and the introduction of high residual stress which can make the crack inititation and propagation process become more difficult. However, the fatigue life of TC6 titanium alloy decreases, the further research shows that the two-phase titanium alloys have a special crystal structure and phase composition so that it can make the micro-cracks generating easily in the processing.The decrease of the ductility after the plastic deformation make the crack propagation rate become faster which make the fatigue life of material decrease finally.