• Besson, Jacques
• Osipov, Nikolay
• Quilici, Stéphane
• Feld-Payet, Sylvia
• Tuham, Amar El Ouazani

Abstract

Ductile failure prediction is essential to avoid integrity loss for structures or to control crack propagation during forming process. One of the main difficulties is the prediction of complex crack paths. This study proposes a non local extension of a local Gurson-Tvergaard-Needleman (GTN) ductile damage model at finite strains able to capture cup-cone or slant fracture. The proposed model is based on an implicit gradient formulation which enables to solve the problem of spurious strain and damage localization. The model integrates two different material characteristic lengths which are used to separately regularize damage by void growth and damage by void nucleation. After parameter fitting based for a pipe line steel, conditions to obtain converged solutions are studied which can be used to select the mesh size in the localization band. With the appropriate mesh design, it has been possible to study the effect of the values of the characteristic lengths on the formation of cup-cone fracture and slant fracture. It is observed that, for a given specimen size, larger characteristic lenghts favor flat crack advance. By the same token, for given material lengths, size effects can be predicted with small specimens being more prone to flat fracture. This paves the way to a more direct determination of material lengths by using homothetic specimens so as to obtain different crack paths.

Topics

• impedance spectroscopy
• crack
• steel
• forming
• void