DOI 10.1007/s10704-005-6024-y International Journal of Fracture (2005) 136:207–220 © Springer 2005 Simulation of fatigue crack propagation in ductile metals by blunting and re-sharpening VLADISLAV LEVKOVITCH 1,∗ , RAINER SIEVERT 2 and BOB SVENDSEN 1 1 Chair of Mechanics, University of Dortmund, D-44227 Dortmund, Germany 2 Federal Institute for Materials Research and Testing (BAM), Division V.2, Mechanical Behaviour of Materials, D-12200 Berlin, Germany ∗ Author for correspondence. (E-mail: vladislav.levkovitch@uni-dortmund.de) Received 28 June 2005; accepted in revised form 20 December 2005 Abstract. Laird and Smith [(1962). Philosophical Magazine 8, 847–857] proposed a plastic sliding-off mechanism for the stage II fatigue crack growth via striation formation. In their view, the fatigue crack extension results solely from the changing character of deformation at the crack tip during loading and unloading. In particular, the crack tip blunts during the loading stage and folds into a double notch during the unloading stage, resulting in striation formation. In order to verify Laird’s plastic blunting mechanism for ductile polycrystals as well as for ductile fcc single crystals, FE cal- culations were performed for a rectangular plate with an initially sharp crack under plane strain conditions. The plate was subjected to a fully reversed tension-to-pressure cyclic load perpendicular to the crack plane (Mode 1). In the single crystal case the crack propagation simulations were carried out for cracks with crack plane (001) for two different crack growth orientations [110] and [100]. No initial radius for the crack tip was assumed. The actual shape of the crack tip followed from an ini- tially sharp crack by repeated remeshing. To model the constitutive behavior typical for polycrystalline ductile metals, J 2 hypo-elasto-plasticity model with Armstrong–Frederick kinematic hardening was used. To model the constitutive behavior typical for ductile fcc single crystals, a geometrically nonlin- ear version of Cailletaud’s model based on the multiplicative elasto-plastic decomposition of the defor- mation gradient was implemented into the FE program ABAQUS. For simplicity, only octahedral slip systems were considered. Using repeated remeshing for severely distorted elements at the advancing crack tip, deformation patterns in the sense of Laird’s mechanism for fatigue crack propagation with striation formation were obtained in the case of the polycrystal simulation as well as in the case of the single crystal simulation for [110] crack growth direction. The simulation for [100] crack growth direction with the same stress level as for [110] direction also yielded crack extension by progressive large deformations but without striation formation. The dependence of the fatigue striation formation on the crack growth direction as predicted by the simulation of crack propagation in single crystals is verified by the experimental results of Neumann [(1974). Acta Metallurgica 22, 1155–1165] on pure copper single crystals. Key words: Crack propagation, fatigue, FE modeling, Laird, plastic blunting and re-sharpening, reme- shing, single crystal, striations. 1. Introduction In the case of cyclic loading, subcritical crack growth can occur if the stress intensity factor K is much lower than the fracture toughness K c . For most engineering alloys, the total crack resistance curve (i.e., plot of the crack growth rate da/dN versus the stress intensity factor range K = K max - K min on the logarithmic scale) exhibits a