Viscoplastic modeling of dynamic fracture events in reactor pressure vessel steels

Abstract

The Heavy-Section Steel Technology Program at the Oak Ridge National Laboratory under the sponsorship of the U.S. Nuclear Regulatory Commission is continuing to improve the understanding of conditions that govern the initiation, rapid propagation, arrest, and ductile tearing of cracks in reactor pressure vessel steels. Nonlinear rate-dependent effects in crack run-arrest events in ductile materials are being investigated through the development and application of viscopalstic-dynamic finite-element analysis techniques. This paper describes a portion of these studies wherein various viscoplastic constitutive models, dynamic crack-propagation algorithms, and proposed nonlinear fracture criteria are being evaluated through their use in the general-purpose ADINA finite-element computer program. The predictive capabilities of the nonlinear techniques are being examined by comparing analytical and experimental results for the crack-arrest tests of large nonisothermal plate specimens. Values of the fracture parameters calculated by elastodynamic and viscoplastic dynamic techniques are compared to assess the impact of including visocplastic effects in the computational models. Recent studies are described that examine the convergence problems associated with energy-based fracture parameters in viscoplastic-dynamic fracture applications. Alternative techniques that have potential for achieving convergent solutions for the fracture parameters in the context of viscoplastic-dynamic models are discussed.