Effect of specimen size on bending fatigue behavior of a new kind of micro-alloyed forging steel

The three-point-bending fatigue behaviors of a new kind of Nb + V micro-alloyed forging steel for truck front axle have been studied by hydraulic servo fatigue testing machine. The effects of specimen size on the fatigue behavior and its origin have been considered. The S-N curves were plotted and the fatigue cracked surfaces were analyzed by SEM. The results showed that the specimen size has a significant influence on three-point-bending fatigue limit. The three-point-bending fatigue limit of specimen increased with decreasing the specimen size. There is little effect of specimen size on the morphology of fatigue fractured surfaces. The reasons for this specimen size effect are that there exist stress gradient in specimen for three-point-bending fatigue test and that the stress gradient in a smaller specimen is larger than that in a larger one.