抄録
Almost all of fatigue crack growth in the stmcture occurs under the mode I loading. However in some structures, the fatigue may occur not only under the pure mode I condition but also in the shear and torsion conditions. Under such conditions, the mixed mode fatigue crack growth may occur. In this paper, mode II+III fatigue test is conducted using a single-axis testing machine. After the test, the fracture surface is observed using SEM and the characteristic feature of the mixed mode fatigue surface is observed. The contact between fatigue crack surfaces could be avoided. The crack growth direction is compared with that predicted by Erdogan-Sih critedon and the maximum shear stress criterion. The maximum shear stress criterion predicts the fatigue crack growth direction very well. The three-dimensional FEM analysis is carried out and stress intensity factors, KII and KIII, are evaluated. The crack growth rate is evaluated and is compared with that of mode I condition. It is found that the mixed mode fatigue crack growth rate is nearly same with that of mode I fatigue.
