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F. V. Antunes et alii, Frattura ed Integrità Strutturale, 25 (2013) 54-60; DOI: 10.3221/IGF-ESIS.25.09 54 Special Issue: Characterization of Crack Tip Stress Field Effect of crack propagation on crack tip fields F.V. Antunes, A.G. Chegini CEMUC, Department of Mech Eng, University of Coimbra, Rua Luís Reis Santos, Pinhal de Marrocos, 3030-788 Coimbra, Portugal L.M. Correia, A.L. Ramalho CEMUC, Escola Superior de Tecnologia do Instituto Politécnico de Castelo Branco, Av. do Empresário, 6000 - 767 Castelo Branco, Portugal A BSTRACT . Crack closure influences fatigue crack growth rate and must be included in the design of components. Plasticity induced crack closure is intimately linked with the crack tip plastic deformation, which becomes residual as the crack propagates. The objective here is to study numerically the effect of crack propagation on crack tip fields. The transient effect observed at the beginning of crack propagation is linked to the hardening behavior of material. The effect of mesh refinement is studied, and a singular behavior is evident, which is explained by the sharp crack associated with mesh topology, composed of a regular pattern of square elements. The plastic zone size measured perpendicularly to crack flank in the residual plastic wake is quantified and compared with literature models. Finally, the removal of material at the first node behind crack tip with load cycling was observed for plane strain state and some hardening models in plane stress state. K EYWORDS . Plasticity induced crack closure; Crack tip; Plastic deformation. I NTRODUCTION rack closure is a phenomenon which consists of the contact of the fracture surfaces during a portion of the load cycle. This contact affects the local stress and plastic deformation fields near the crack tip, and therefore, the intrinsic micromechanisms responsible for fatigue propagation (cyclic plastic deformation, oxidation, creep, etc.). According to Elber’s understanding of crack closure [1], as the crack propagates due to cyclic loading, a residual plastic wake is formed. The deformed material acts as a wedge behind the crack tip and the contact of fracture surfaces is forced by the elastically deformed material. Plasticity induced crack closure (PICC) is intimately related with the monotonic and reversed plastic deformation occurring at the crack tip. The forward or monotonic plastic zone is constituted by the material near the crack tip undergoing plastic deformation during loading. Major parameters are the maximum load, the stress state and the isotropic component of hardening. On the other hand, the reversed plastic zone is formed by the material near the crack tip undergoing compressive yielding during unloading. The amplitude of stress intensity factor,  K, the stress state and the kinematic hardening are expected to have a major influence on reversed plastic deformation. However, the plastic deformation at a Gauss point is a complex phenomenon, occurring progressively as the crack tip approaches it, depending on the hardening model, loading parameters and finite element mesh, among other parameters. The main objective here is to study numerically the effect of crack propagation on crack tip fields. The effect of mesh refinement, stress state and hardening model are considered. The numerical simulations were performed with a three- dimensional elasto-plastic finite element program (DD3IMP) that follows a fully implicit time integration scheme. C