Issue 38

R. Fincato et alii, Frattura ed Integrità Strutturale, 38 (2016) 231-236; DOI: 10.3221/IGF-ESIS.38.31 231 Focussed on Multiaxial Fatigue and Fracture Numerical modelling of ductile damage mechanics coupled with an unconventional plasticity model R. Fincato, S. Tsutsumi University of Osaka, Japan fincato@jwri.osaka-u.ac.jp , http://orcid.org/0000-0002-2345-6790 tsutsumi@jwri.osaka-u.ac.jp , http://orcid.org/0000-0002-2345-6791 A BSTRACT . Ductility in metals includes the material’s capability to tolerate plastic deformations before partial or total degradation of its mechanical properties. Modelling this parameter is important in structure and component design because it can be used to estimate material failure under a generic multi-axial stress state. Previous work has attempted to provide accurate descriptions of the mechanical property degradation resulting from the formation, growth, and coalescence of microvoids in the medium. Experimentally, ductile damage is inherently linked with the accumulation of plastic strain; therefore, coupling damage and elastoplasticity is necessary for describing this phenomenon accurately. In this paper, we combine the approach proposed by Lemaitre with the features of an unconventional plasticity model, the extended subloading surface model, to predict material fatigue even for loading conditions below the yield stress. K EYWORDS . Unconventional plasticity; Ductile damage; Subloading surface; Cyclic loading. Citation: Fincato,R., Tsutsumi, S., Numerical modelling of ductile damage mechanics coupled with an unconventional plasticity model, Frattura ed Integrità Strutturale, 38 (2016) 231-236. Received: 13.05.2016 Accepted: 20.06.2016 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 he degradation of material properties, which results from the initiation of cavities and microcracks induced by large plastic deformations, has been widely studied. Material failure results from microscopic material impurities, which cause the formation and coalescence of microvoids that eventually produce cracks during deformation. Modelling this mechanism is important in many industrial processes for creating optimized reliable designs for structures and components. There are two main models for the elastoplastic framework [1, 2]: Gurson’s void growth model [3] and Lemaitre’s model [4, 5], often referred as continuum damage mechanics. Gurson’s model is based on void growth, where the plastic yield is inversely proportional to the amount of imperfections; as the porosity increases the material loading decreases. Further studies by Needleman and Tvergaard [6], Koplic and Needleman [7], and Ohata and Toyota [8] extended the damage evolution concept by introducing material parameters to model the acceleration of the degradation of mechanical properties. Lemaitre’s theory describes damage as an internal variable and models its evolution with a dissipative potential T