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

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 degrees with respect to the loading axis, the crack grew with a 45 degrees 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.

Automated summary

Research showed that the surface crack growth direction of ultrafine-grained copper is influenced by the location on the specimen circumference and the stress amplitude in high- and low-cycle fatigue regimes. Under certain conditions, cracks grow inclined or perpendicular to the loading axis, with a significant difference in the angle with respect to the loading axis.