THE EARLY STAGE OF FATIGUE CRACK-PROPAGATION

It is observed that an early stage fatigue crack propagates along the maximum shear direction rather than perpendicular to the maximum tensile stress direction. In the present paper, an analytical consideration is given concerning the effects of localized plastic deformation on the early stage of fatigue crack propagation. It is seen that the localized plastic deformation shields the local mode II stress intensity factor and leads the micro-crack to propagate along the maximum shear stress direction. In this analytical modeling, the localized plastic zone is modeled as an elliptical inclusion with eigenstrains where the Eshelby inclusion solution [Proc. R. Soc. A241, 376-396 (1957)] is employed.