Improvement of fatigue strength of the plate with a hole

In this paper plane bending fatigue tests have been performed to investigate the effect of die-pressing on fatigue strength of specimens with a central circular hole notch. The main results obtained in this study are as follows: (1) By applying a die-press chamfering method, the fatigue limit of notched specimen increases with 63% higher than that of specimen without chamfering; The increment obtained by the above method is over 4 times of the increment obtained by the machining chamfering method. (2) The fatigue strength enhancing may attribute to the work-hardening and compressive residual stress that suppress the fatigue crack initiation and early stage propagation. (3) Though non-propagating micro-crack is not observed on the specimen without die-pressing chamfering the existence of the non-propagating micro-cracks in the specimen with die-press chamfering are observed.