Fatigue Behavior Of GCr15 Steel In Gigacycle Regime

Conventional fatigue design point considers that fatigue test as long as endure stress circulation of 107 cycles can meet the safety activity of the mechanism and engineering structure. But with the high-speed and large-scale development of modern mechanism in recent years, many mechanism and engineering structure still can take place fatigue failure in ultra-long life regime exceeding 107 ¹09 cycles. So conventional fatigue design standard and life prediction method already don't meet the activity acquire of mechanism equipment in ultra-long life regime. The study of test method and fatigue behavior in ultra-long life regime already becomes an important task that the fatigue researchers must face.Fatigue behavior in ultra-long life regime (about 10⁷～10¹⁰ cycles) of high strength bear steel- GCr15 is studied by using the conventional rotary bending test and axial load test mainly and by using ultrasonic fatigue test secondly. Specifically explain as follows:The fatigue crack initiation place and vicinal mark are observed by SEM and OM in detail. The fatigue crack initiation mechanism of GCr15 bear steel is analyzed and can be classified into two crack initiation mechanisms, one is called surface crack initiation mechanism, and the other is called internal crack initiation mechanism.The material' fatigue S-N curve in three tests is obtained and analyzed. Simultaneously, rotate bent test data is better followed by the weibull distribution and the material' fatigue P-S-N curve in rotary bending test is obtained.Prediction method of SEV is adopted to estimate the maximum inclusion size and the fatigue strength of GCr15 bear steel is estimated by the Murakami equation.Through the calculation of stress intensity factor-â–³K_ini in crack initiation place, the fracture mechanics condition of crack initiation and propagation is analyzed.Through the comparison of the test results in rotary bending test conventional axial load test and ultrasonic fatigue test, the equivalence of rotary bending and conventional axial load fatigue strength is realized and the character of fatigue S-N curve and the crack initiation mechanism is influenced by the some factors, such as ultrasonic load frequency and temperature.The feasibility of test method in ultra-long life regime is discussed and the appliance range of the conventional fatigue test method and the ultrasonic fatigue test method is analyzed.Finally, on the base of work generalization, the research thinking and direction in the future is suggested.