A Fractographic Study of Low Cycle Fatigue

Abstract

Low cycle fatigue fracture surfaces of an aluminum alloy (17S-T4) and a low carbon steel were studied fractographically to throw some light on the transition of the fracture surface topography form the static type characterized by dimples to the fatigue type characterized by striations. The mechanism of formation of the tire tracks was also studied in detail by mean s of stereographic technique, matching technique and panoramic pictures taken by scanning electron microscope, and it is concluded that the tire tracks are impressions made by protrusions or edges on the mating fracture surface each time repeated stress was applied. Some examinations were also made on the mechanism of formation of the striations and the results suggested the validity of the model proposed by Laird and Smith. Finally, measurements were made of the striation spacing with notched specimens of aluminum alloy, and the results were summarized fairly successfully in terms of stress intensity factor calculated by taking account of the stress concentration due to notch effect.