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September 16, 2016

Thesis defense of Vincent Mac Donald

of Centre des Matériaux

Thesis defense of Vincent Mac Donald

Vincent Mac Donald will defend his thesis, wich is called

" Determination of a fracture criterion for cold worked and stress relieved Zircaloy-4 fuel cladding tubes with hydride blister, during a reactivity initiated accident"

on septembre, the 16th at 1.30pm

in Amphithéatre Jean Talairach (Neurospin) CEA Saclay 91191 Gif/Yvette

abstract : This study deals with the determination of a fracture criterion for hydrided, cold worked and stress relieved Zircaloy-4 fuel cladding tubes with hydride blister, during a reactivity initiated accident. Two types of fracture profiles were identified, depending on the temperature, thanks to a bibliographical study, mechanical tests and fracture profiles analysis : brittle fracture at 25°C, and ductile fracture at 350°C. At 25°C, brittle fracture was studied by a global analysis in elasto-plastic fracture mechanic. Numerical simulations were performed by a finite element method with the CAST3M code, based on mechanical tests on fuel cladding tubes with blisters. Crack tip J-integral calculations were carried out to identify a mean fracture toughness of 13,8 +/- 3,1 MPa.m1/2. At 350°C, internal pressure combined to axial tensile tests were performed on Zircaloy-4 fuel cladding tubes with hydride blisters, at stress biaxialities corresponding to those of a RIA. It was observed a ductile fracture for tubes with and without blister. It was shown that hoop strain at failure decreases when blister thickness increases, and that stress biaxiality has no effect on cladding tubes bearing a thick blister. A ductile fracture model based on the GTN model was employed and a nucleation of voids due to shear stress was introduced, based on the Lode parameter. Stress triaxiality and Lode parameter were assessed in numerical simulations to understand some experimental observations.

Thesis defense in Materials - MINES ParisTech - MINES ParisTech

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