Technical Note Effect of micro-cavities on different plastic zones at the fatigue crack tip of a compact tension specimen Surajit Kumar Paul ⇑ R&D, Tata Steel Limited, Jamshedpur 831007, India article info Article history: Received 17 February 2016 Accepted 21 February 2016 Available online 27 February 2016 Keywords: Cyclic plastic zone Micro-cavities Monotonic plastic zone Ratcheting Crack Chaboche model abstract Knowledge of cyclic plastic deformation response at the fatigue crack tip is crucial to understand the nature of cyclic damage acting on the crack tip. Interaction between crack and defect is equally important to understand the cyclic damage progression at crack tip; however isotropic hardening model was adopted in all existing literatures. Isotropic hard- ening model is suitable to model only the monotonic plastic zone and unable to model the cyclic/reverse plastic zone. Kinematic hardening model is suitable to model the key cyclic plastic deformation responses like Bauschinger effect, ratcheting, and mean stress relax- ation. A non-linear kinematic hardening (Chaboche) model is used in this present investi- gation to represent the material’s cyclic stress–strain response accurately. Effect of micro-cavity positions (angle and distance from crack tip) and sizes on plastic zones near a crack tip is investigated in this study by two dimensional plane strain finite element model of a compact tension specimen. It is observed that the size and shape of the monotonic and cyclic plastic zones are affected by position and size of the micro- cavity. During asymmetric loading condition, the ratcheting strain accumulation direction is also affected by the position of micro-cavity. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Progression of plastic deformation and damage at the crack tip is commonly used to study the fracture behaviour of ductile materials. Similarly, advancement of cyclic plastic deformation and damage at the fatigue crack tip is generally used to investigate the fatigue fracture behaviour. Normally three zones are present at the fatigue crack tip: cyclic/reverse plastic zone, monotonic plastic zone and elastic zone. The cyclic plastic zone is surrounded by monotonic plastic zone and these two plastic zones are further surrounded by elastic zone. Among those three zones, cyclic plastic deformation and damage take place only in the cyclic plastic zone. Therefore, size, shape, deformation and damage modes in the cyclic plastic zone always become important in fatigue crack growth study. Recently number of experimental [1] and numerical [2–5] investigation has conducted to understand the cyclic deformation and damage modes in the cyclic plastic zone. Tong et al. [1–4] have concluded from continuum, visco-plastic and crystal plasticity based finite element analysis that ratcheting takes place in the cyclic plastic zone. Ratcheting can be defined as the progressive accumulation of permanent strain during asymmetric stress cycling. Paul and Tarafder [5] have also reported that accumulation of ratcheting strain in the cyclic plastic zone for R ratio – 1(R ratio is the ratio of minimum http://dx.doi.org/10.1016/j.engfracmech.2016.02.041 0013-7944/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Present address: School of Engineering, Deakin University, Pigdons Rd, Waurn Ponds, VIC 3217, Australia. Tel.: +61 431362497. E-mail address: paulsurajit@yahoo.co.in Engineering Fracture Mechanics 158 (2016) 13–22 Contents lists available at ScienceDirect Engineering Fracture Mechanics journal homepage: www.elsevier.com/locate/engfracmech