Stress localization in BCC polycrystals and its implications on the probability of brittle fracture

The evaluation of the reliability of pressure vessels in nuclear plants relies on the evaluation of failure probability models. Micromechanical approaches are of great interest to refine their description, to better understand the underlying mechanisms leading to failure, and finally to improve the prediction of these models. The main purpose of this paper is to introduce the stress heterogeneities arising within the polycrystal in a probabilistic modeling of brittle fracture. Stress heterogeneities are evaluated from Finite-Element simulations performed on a large number of Statistical Volume Elements. Results are validated both on the measured averaged behavior and on the averaged stresses measured by neutron diffraction in five specific orientations. A probabilistic model for brittle fracture is then presented accounting for the carbide distribution and the stress distribution evaluated previously inside an elementary volume V0. Results are compared to a “Beremin type” approach, assuming a homogeneous stress state inside V0.

► Intergranular stress distributions in a bainitic steel.
► Comparison of local mean stress field with neutron diffraction results.
► Application of the local stress distribution in a brittle fracture model.