Fatigue behavior of medium carbon steel by symmetric bending ultrasonic frequency method

摘要

The S-N curves of medium carbon steel(MCS) are determined by the ultrasonic symmetric bending fatigue system (20 KHz).The results show that two S-N curves of MCS display the characteristic of "continually decreasing type" up to 109 cycles and exhibit no traditional horizontal plateau beyond 106 cycles.When the fatigue cycles are over 109,fatigue failure do occurs.By comparison of the two curves of 2mm thick and 5mm thick MCS,the results show that in the high-cycle stage(＜107cycles),size effect has an significant effect on fatigue Properties,and the ultra-high-cycle stage(＞107cycles),size effect has no significant impact on fatigue Properties.This can also be explained by the theory of crack initiation,in high cycle stage,fatigue crack initiation exists in the sample surface,and in ultra-high-cycle stage,fatigue crack initiation exists in internal initiation.