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Micromechanical modeling of the ductile damage with a cohesive-volumetric approach: application to the irradiated UO2

​Noé Brice Nkoumbou Kaptchouang has defended his thesis​ on 16th December 2019 in Montpellier, France

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Research Unit > IRSN/PSN-RES/SEMIA/LPTM

Authors > Noé Brice Nkoumbou Kaptchouang

Publication Date > 16/12/2019

Summary

​This work is interrested in simulating the local cracking of uranium dioxide during a postulated Reactivity Initiated Accident (RIA). More specifically, the present work addresses the modelling and the simulation of crack initiation and propagation in ductile materials which failed by void nucleation, growth and coalescence. One of the current research frameworks on crack propagation is the use of the cohesivevolumetric approach where the crack growth is modelled as decohesion of two surfaces in a continuum material. In this framework, the material behavior is characterized by two constitutive relations - the volumetric constitutive law relating stress and strain, and a traction-separation law across a two-dimensional surface embedded in the three-dimensional continuum. One specific idea to developed the cohesive model for ductile materials consist in determining the traction separation based on the behavior of a continuouslydeforming unit cell failing by void growth and coalescence. Following this method, the present work proposes a cohesive model for ductile materials based on a micromechanical approach. The strain localization band prior to ductile failure is modelled as a cohesive band and the Gurson-Tvergaard-Needleman plasticity model (GTN) is used to describe the behavior of the cohesive band and to derive a corresponding traction separation law. The numerical implementation of the model has been performed using a multi-domain finite element approach where cohesive models are introduced as mixed boundary conditions between each volumetric finite element. The cohesive-volumetric approach is applied to simulate the brittle-ductile cracking of porous uranium dioxide fuels under postulated accident conditions.


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