INITIATION AND GROWTH OF SURFACE CRACK UNDER TENSILE FATIGUE LOADING

The effect of fatigue crack initial life, N., on the shape of initial notch and stress ratio under the tensile loading for LY12R sheet specimens has been studied. A relation predicting fatigue life, in N_i=a+b△K_c has been obtained. The crack growth behavior for LY12R, three steels and a titanium alloy have also been analysed. The results show that the crack growth behavior is not sensitive for materials, dimension of specimens and loading condition so that the surface crack depth may be predicted by the empirical expresion, △a=f(△c). It was also found that the surface crack extension is controlled by. stress strength. factor when σ_(Nmax)/σ_y=0.9.