Development of a damage mechanics based limit strain concept using an enhanced Rousselier model

Several incidents in the past showed the risks of environmental caused accidents, which exceed the design limits of power plant components. According to technical standards, for the evaluation of safety margins usually stress based criteria are used. These criteria are unable to fully utilize the high deformation capabilities of most materials used for power plant components. To overcome this disadvantage, a proposal for a strain based structural integrity assessment (SIA) concept will be made. The proposed SIA concept is based on damage mechanics simulations using an enhanced Rousselier model. Therefore, three extensions were made to the standard Rousselier model. First, the integration of an additional term allowing the prediction of failure under shear stress conditions developed by Nahshon and Hutchinson is presented. Second, the extension with a kinematic term using a back-stress tensor to the Rousselier model to properly describe very low cyclic loading behavior will be described. For the description of the back stress tensor, models developed by Drucker/ Prager, Armstrong/ Frederick and Chaboche are used. Third, the plasticity behavior at low stress triaxialities was improved by replacing the von Mises plasticity law by a Hosford like yield criterion. The extensions were evaluated with a large experimental program using a ferritic and an austenitic steel. For the derivation of the limit strain concept, the different influences of stress triaxiality, component size, non proportional loading and multiple loading on the limit strains are investigated experimentally and numerically. (C) 2018 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the ECF22 organizers.