Abstract:

A double step precracking technique is suggested for gaining an original crack which will be accepted as a genuine short crack. An optimum precracking program under falling amplitude fatigue loadis proposed which can, in combination with the double step precracking technique, reduce the stress intensity range K to below the threshold valve K （defined for long racks in engineering）, and can effectively shorten precracking time. A method of locating crack tip on the specimen surface is presented to make identification of the crack tip convenient and accurate.