Abstract
The indications of a high quantity of cracks from non-destructive testing measurements were determined in a root cause analysis as hydrogen flakes positioned in segregated zones in the base material of pressure vessels of Belgian nuclear power plants. Because of the laminar and quasi-laminar orientations of this hydrogen flakes with an inclination up to 16° to the pressure retaining surface the crack tips undergo predominantly mixed-mode loading conditions under internal pressure and the induced stress and strain fields of the single crack tips influence each other. In a former paper, the failure behavior of crack fields under mixed mode loading conditions was investigated at RT (Room Temperature) and −100°C, the upper shelf and the lower transition phase of the steel 22NiMoCr3-7, respectively. In this paper, the failure behavior of crack fields is investigated for many different levels of material toughness (from to upper shelf to the lower shelf region) on experiments with different artificial manufactured crack fields. Therefore, numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure the Rousselier model is used and the Beremin model to calculate the probability of cleavage fracture. To account the sensitivity for low stress triaxiality damage by shear loading, the damage mechanics model was enhanced with a term to account for damage evolution by shear. For numerical simulations in the transition region of brittle-to-ductile failure a coupled damage mechanics model (enhanced Rousselier & Beremin) will be used. In this paper, the current state of the ongoing research project is presented.
