Investigations on the Failure Behavior of Specimens Containing Crack Fields Made by Additive Manufacturing

Abstract

Laminar and quasi-laminar orientations of hydrogen flakes with an inclination up to 16° to the pressure retaining surface were found in pressure vessels of Belgian nuclear power plants. Because of their orientation, these 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 under mixed-mode loading conditions was investigated at RT (Room Temperature) in the upper shelf and in the lower transition region of the steel 22NiMoCr3-7, respectively. In this paper, the failure behavior will be shown for many different levels of material toughness (beginning from upper shelf down to the lower shelf region) on experiments. Additionally numerical simulations are carried out with extended micromechanical based damage mechanics models. For the description of ductile failure mode the Rousselier model is used and the Beremin model to calculate the probability of cleavage fracture. To simulate 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.