摘要
In order to clarify the differences of very high cycle fatigue(VHCF) behavior of nickel based superalloy IN718 with different loading frequencies,stress-controlled fatigue tests were carried out by using ultrasonic testing method(20 KHz) and rotary bending testing method(52.5 Hz),both at room temperatures,to establish stress versus cycles to failure(S-N) relationships.Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency,i.e.,the higher frequency produced an upper shift of the S-N curves.Fractographic analysis suggested that crack initiation and propagation behaviors had large differences:cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface,while in high-frequency tests,cracks mostly originated from a unique source of subsurface inclusions.Subsequently,frequency-involved modeling was proposed,based on the damage accumulation theory,which could well illustrate qualitatively those comparisons due to different loading frequencies.
In order to clarify the differences of very high cycle fatigue （VHCF） behavior of nickel based superalloy IN718 with different loading frequencies, stress-controlled fatigue tests were carried out by using ultrasonic testing method （20 KHz） and rotary bending testing method （52.5 Hz）, both at room temperatures, to establish stress versus cycles to failure （S-N） relationships. Results disclosed that cycles to failure at a given stress level increased with an increase of the applied frequency, i.e., the high- er frequency produced an upper shift of the S-N curves. Fractographic analysis suggested that crack initiation and propagation behaviors had large differences： cracks in low-frequency tests preferentially initiated from multiple sources on the specimen surface, while in high-frequency tests, cracks mostly originated from a unique source of subsurface inclusions. Subsequently, frequency-involved modeling was proposed, based on the damage accumulation theory, which could well illustrate qualita- tively those comparisons due to different loading frequencies.
基金
supported by the National Natural Science Foundation of China (Grant Nos. 10872105 and 51071094)
