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Taking into account transport mechanisms in the fissuring of heterogeneous materials: application to the operating lifespan of nuclear power stations

​Lionel Bichet has defended his thesis on 30th January 2017, in Montpellier (France).

Document type > *Mémoire/HDR/Thesis

Keywords >

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

Authors > BICHET Lionel

Publication Date > 30/01/2017

Summary

During their confinement in a nuclear power plant, the mechanical properties of the constitutive materials of concrete change as a result of ageing. This is due to the transportation of chemical species at the microscopic level of the media. Firstly, this can be modelled with average equations. The Fick laws represent the evolution of chemical diffusion and the Fourier laws, the transportation of heat at a mesoscopic level. In this research, we will consider thermal evolution on a fractured media.


This thermomechanical problem is solved with a staggered method. The mechanical contribution used an approach based on multi-bodies system linked with cohesive zone models. The thermal problem is based on the approximation of the heat transfer equation at the cohesive interface. This approach has been implemented and validated. The description of the heat trough the interface is composed with the definition of an homogenized conductivity and the local damage parameter.


In order to optimize the computational cost with a good agreement of the crack propagation, a criterion is proposed for sizing a representative elementary volume (REV). The eigenerosion method is used, validated and extended to heterogeneous media. Two studies are carried out on the morphological properties on a cementious media. As a result of those studies, a minimal size for a REV is defined.


Crack spread under thermal loads are investigated on a media representing the concrete of the containment of a nuclear power station. The ageing effects are taken into account as an initial damage between the mortar and the aggregates. These parameters are expressed in terms of rate of initial damage. A study is proposed for different values of this rate. As assumed, the development of multi-cracks is linked with the rate of initial damage and the creation of thermal border is proposed.


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