Issue 38

R. Shravan Kumar et alii, Frattura ed Integrità Strutturale, 38 (2016) 19-25; DOI: 10.3221/IGF-ESIS.38.03 19 Focussed on Multiaxial Fatigue and Fracture Stress-state dependent cohesive model for fatigue crack growth R. Shravan Kumar, I.S. Nijin, M. Vivek Bharadwaj, G. Rajkumar, Anuradha Banerjee Department of Applied Mechanics, Indian Institute of Technology Madras, Chennai-36, India anuban @ iitm.ac.in A BSTRACT . In the cohesive framework, a stress-state dependent cohesive model, combined with an irreversible damage parameter has been used in simulation of fatigue crack growth initiation and continued growth. The model is implemented as interface elements and plane strain simulations of crack initiation and growth under cyclic loading are performed. The stress- state of neighboring continuum elements is used in the traction-separation behavior of the cohesive elements. The model is shown to be able to reproduce the typical initiation life as well as fatigue crack growth curves. Further, the effect of the cohesive fatigue parameter on the initiation life and crack growth rates is established. K EYWORDS . Cohesive zone model; Fatigue; Triaxiality; Stress state. Citation: Shravan Kumar, R., Nijin, I. S., Vivek Bharadwaj, M., Rajkumar, G., Anuradha Banerjee, Stress-state dependent cohesive model for fatigue crack growth, Frattura ed Integrità Strutturale, 38 (2016) 19- 25. Received: 15.05.2016 Accepted: 15.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION rogressive growth of microstructural damage under sub-critical loads makes fatigue one of the most critical modes of failure. Over the years, diverse approaches have been adopted with the objective of better prediction of fatigue failure. Classical approaches such as Paris law that are based on finding empirical relations between the amplitude of the stress intensity factor and the crack growth rate, firstly, are predictive only for crack growth under very idealized conditions but also lack the ability to predict the initiation life of a fatigue crack near a stress-concentrator. Safe operation and life assessment of ageing components and structures, thus, require not only a better understanding of the factors that influence the initiation and growth of damage under cyclic loading but also development of predictive models that account for these effects. As an alternative to classical fracture mechanics based characterization of fatigue crack growth, the cohesive zone model (CZM) has been receiving increasing attention for modeling fatigue damage growth ahead of a macroscopic crack [3-5]. More recently, a stress-dependent model that is able to incorporate the dominant role of stress-states in prediction of failure due to fatigue damage has been proposed [2]. In this model, the constitutive behavior of the process zone was described by a stress-state dependent traction-separation law that was combined with an irreversible damage parameter, whose evolution was based on continuum damage laws requiring two fatigue model parameters. While the model was able to capture the typical features of fatigue failure under uniaxial and proportionate bi-axial loads, the implementation of the model, determination of the model parameters and its validation with experimental data on fatigue crack growth was left as a future task. P