Plastic zones and fatigue-crack closure under plane-strain double slip

The results of a systematic investigation involving forward and reversed plastic zones for a growing fatigue crack under plane-strain double-slip conditions are presented. The study focuses on plasticdeformation fields outside the small-scale yielding regime. The size of the macroscopic forward plastic zone is found to be nearly proportional to the square of the applied-stress intensity over the critical resolved shear stress. The size of the forward plastic zone is also found to depend on the angles of the two microscopic slip directions with respect to the crack line. When the microscopic slip directions are kept symmetric about the crack-line normal, and the angle between them is varied, the forward plastic zone sizes hardly vary. However, when the angle between the slip lines is kept constant, and both planes are simultaneously rotated, the forward plastic zone sizes vary by a factor of three. The ratio of the reversed plastic zone size to the forward plastic zone size is also found to be dependent on the orientation of the microscopic slip planes. The ratio varies when the angle between the microscopic slip planes is changed, or when the orientations of both planes are rotated simultaneously. Stationary cracks are generally found to have larger reversed plastic zones than fatigue cracks, and the difference is attributed to crack closure.