Effect of applied stress amplitudes on the growth behavior of fatigue cracks in ultrafine grained Cu specimen with a small-holeThursday (28.05.2020) 11:10 - 11:30
Using ultrafine-grained copper processed by equal channel angular pressing, the growth mechanism of surface-cracks at high- and low-cycle fatigue regimes was studied by the constant and two-step stress amplitude tests. The crack growth direction depended on the location along the circumferential direction of the round bar specimen and on the applied stress amplitudes. A small blind hole as a crack starter was drilled on the surface where an intersection between the shear plane of the final pressing and the specimen surface makes an angle of 45° with respect to the loading axis. The crack from the hole grew with a 45° inclination to the loading axis at stress amplitudes above 180 MPa. At the stress amplitude less than 160 MPa, however, the crack grew perpendicular to the loading axis. The physical background of deferent crack path directions between high- and low-stresses was discussed in terms of the microstructural evolution caused by cyclic stressing and the morphological feature of surface damage around the crack paths.