Fatigue Property Study Of 16Mn Steel Including Smooth And Welding Joint In Ultra-high Cycle Fatigue Range

With the development of industrial technology, a lot of industry components were affected by high speed cycle of loading. The working life of the component already needs to endure 109 cycles even higher in the military service. Using the routine fatigue test technology is unable to adjust to the request of development of industrial. Thus the fatigue property of metallic materials in the UHCF range tends to be an important subject in the mechanical design to ensure the long term safety of the mechanical structures.Since performing experiments of the ultra-high-cycle regime in the range of 107-1010 cycles using a conventional fatigue testing method is very time consuming and expensive, in this paper, a kind of acceleration fatigue test technique, called the ultrasonic fatigue testing, was developed and studied. The design of ultrasonic fatigue equipment is an important question which makes people puzzled a long time. So, I fist introduce the experiment equipment called HJ-II ultrasonic peening machine which was developed by our team, and make a detail about the core technique-the designing of the hardware circuit of DSP.A the same time , ultrasonic fatigue specimen must be designed very precisely ,so I did the job and designed the shape and dimension by accurately deducing. At last I used the specimen which is made of 16Mn to do the ultrasonic fatigue test. As a result of the test I got an S-N curve which is different from the traditional one. It is a curve which is declined continuously. So I made an important conclusion which is that it is too dangerous to design a structure which only can endure 107 cycles, but were used in the situation where the loading were 109 cycles.In addition, I inspect the macro shape of the fracture section by electronic microscope, and found that the crack always originate inside. It is just as the same as the main idea about the law of which the crack originate. It is that the crack of material will originate inside or in the semi-surface in which there is a lot of defect when the material is exerted super high cycle loading.