Etude de l'influence de l'entaille sur les champs de déformations dans le domaine plastique pour des aciers ductiles et peu ductiles

Abstract : Usually, a structure is dimensionned in term of admissible stress. Unusually, we dimensionned in term of displacement (deflection/range for the cases of wood gathering) or strain (concept of admissible strain). By convention, admissible strain have the value of 1 %. The fact to take strain as parameter which governed the fracture allow a better caracterization of the structure behaviour in the elastoplastic case behaviour. Moreover, it allow to take in account of strain hardening capacity of the material. Finite elements computation may be used to prevent important strain that we may encounter in function of the applied load. Thoses computations are often realized in elasticity. However, presence of notches or sharps angles will breed stress concentration which will may cause a premature fracture (fracture occurs when applied stress is lower than yield stress) by the creation of a plasticity zone in vicinity of geometrical discontinuity. Then, we propose to define a new criteria of fracture in term of critical local strain versus local strain field in notch tip. For that, we carried out fractures tests on C.T. specimens (obtained from a few ductile steel) and K.T. specimens (obtained from a ductile steel). Next, we formulate the problem as following : in function of the notch geometry, defined by the notch radius, the depth and the notch angle, we examine elastoplastic strains distributions in notch tip. From this distribution, we define the concept of notch strain intensity factor, which critical value will be used a fracture criteria
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Gaêl Angot. Etude de l'influence de l'entaille sur les champs de déformations dans le domaine plastique pour des aciers ductiles et peu ductiles. Autre. Université Paul Verlaine - Metz, 1997. Français. ⟨NNT : 1997METZ019S⟩. ⟨tel-01777204⟩

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