Stress-dependent opening- and shear-mode propagation behavior of fatigue cracks in ultrafine-grained Cu fabricated by equal channel angular pressing (vol 142, 105978, 2021)

•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.