Stress-dependent opening- and shear-mode propagation behavior of fatigue cracks in ultrafine-grained Cu fabricated by equal channel angular pressing. (January 2021)

• Record Type: Journal Article
• Authors: Goto, M.; Yamamoto, T.; Han, S.Z.; Kim, S.; Kitamura, J.; Yakushiji, T.; Ahn, J-H.; Takanami, R.; Utsunomiya, T.; Lee, J.
• Is Part Of: International journal of fatigue. Volume 142(2021)
• Publication Date: 2021-01
• Subjects: Equal channel angular processing -- Fatigue -- Crack propagation -- Copper -- Mixed mode; Materials -- Fatigue -- Periodicals; Materials -- Fatigue; Periodicals; 620.1122
• DOI: 10.1016/j.ijfatigue.2020.105978
• Languages: English
• ISSNs: 0142-1123

Abstract

Highlights: At σa ≥ 180 MPa, the crack path was inclined 45° to the loading axis. At σa ≤ 160 MP, the crack path was nearly perpendicular to the loading axis. The change in crack path was caused by the different growth thresholds between modes I and II. The threshold of the applied stress amplitude for mode II growth was σa = 160 MPa. Abstract: Constant and two-step stress amplitude tests were conducted to study the surface crack growth mechanism of ultrafine-grained copper processed by equal channel angular pressing (ECAP) in high- and low-cycle fatigue regimes. The crack growth direction varied depending on the location on the circumference of the round bar specimen and applied stress amplitude. On the surface where an intersection between the shear plane of final pressing and the specimen's surface made an angle of 45° with respect to the loading axis, the crack grew with a 45° inclination to the loading axis at stress amplitudes ≥ 180 MPa. At stress amplitudes < 160 MPa, the crack grew nearly perpendicular to the loading axis. The physical background of various crack growth directions at high and low stresses is discussed based on the microstructural evolution caused by cyclic stressing and mixed-mode deformation at the crack tip.