Revues

We provide a review of recent works about the Coupled Criterion (CC), originally developed to assess the initiation of a crack and thus overcome a main limitation of linear elastic fracture mechanics. This paper includes theoretical and implementation aspects of the CC, new fundamental developments such as extensions to 3D, dynamic aspects, nonlinearities or fatigue. It also focuses on confrontations between the CC and other fracture modeling approaches such as cohesive zone models or phase field approach for fracture. Originally developed in 2D, for linear elastic materials under the assumption of small deformations, the CC has now expanded and can be applied to a wide range of applications from macroscopic to atomic scale.

Doitrand, Aurélien

Engineering stress-strain curves are generated from tensile tests on semi-crystalline thermoplastics, which may exhibit non-linearity and/or peak stress associated with striction/necking phenomenon of the specimen at the macroscopic scale. This work addresses this state of deformed specimen, on an isotactic polypropylene, where irreversible strains have led to a variable cross-sectional area along the necked region. 3D images in this region, obtained through Synchrotron Radiation Computed Tomography with two high resolutions are exploited. The best resolution (1 pixel length = 0.05 μm) allowed better understanding of the morphology of several deformed spherulites within which polar fan arrangements are clearly detailed. Thanks to the dentification of the boundaries of spherulite patterns, with a 0.7 μm resolution, the longitudinal and transverse elongations of larger numbers of spherulites are measured. The evolution of the volumetric plastic strains due to cavitation at the spherulitic scale along the necked regions is comprehensively analysed. Volume changes at this scale are highlighted, consisting of an increase in the case of void growth followed by a decrease at large strains due to the collapse of elongated voids. The effects of these results on the establishment of reliable constitutive model are discussed. It is found that accounting for plastic dilation is necessary for the accuracy of constitutive models.

Laiarinandrasana, Lucien