Effects of failure mode II on crack initiation and crack propagation steps using multilevel fatigue loading test

To evaluate the effects of mode II on the crack initiation and propagation stages, the effects in the fatigue threshold region under a mixed-mode I+II loading state was experimentally investigated. In the case of mixed-mode I + II, during the crack initiation stage, as the loading application angle (θ) increased, cracks occurred in the lower load owing to the effects of mode II, while the crack propagation rate decreased. The effects of mode II were experimentally investigated in the crack propagation stage by means of multilevel loading direction variation. Following mixed-mode I+II (0°→θ→ 60°), as the load application angle increased, the fatigue crack propagation rate decreased, as did the fatigue crack propagation rate, which occurred later. Following mixed-mode I + II in case of(θ =75°), the fatigue crack propagation rate was found to increase, while the fatigue life decreased. © 2017 The Korean Society of Mechanical Engineers.