Abstract

The behaviour of the fatigue crack propagation under the repeated mode II loading was investigated using the rolled plate specimens with a fatigue precrack. Tests on the alminium alloys (7075-T 6, 2017-T 4) and the mild steel (SS 400) were conducted, and the macroscopic crack paths and the microscopic fracture surfaces were examined. In these tests under the repeated mode II loading to the precrack, two modes of the fatigue crack growth were observed ; the mode I crack growth and the mode II crack growth. In 2017-T 4 specimens, the mode II crack growth was always observed while in SS 400, only the mode I crack growth was observed. However, in 7075-T 6 specimens, the mode I growth was observed in low ΔK_II and the mode II growth in high ΔK_II.