COUPLING CRYSTAL PLASTICITY WITH PHASE FIELD FRACTURE FOR CREEP DAMAGE FORMATION ANALYSIS IN AUSTENITIC AND FERRITIC STEELS

Accurate modelling and prediction of both statistical trends in damage formation and damage site initiation
is critical in both the design, microstructure optimization and lifetime management of components and
welded joints for nuclear power stations. This paper presents a coupling between a strain-gradient based
crystal plasticity formulation and a phase field fracture model to predict damage initiation sites, damage
propagation and void initiation statistics that match electron microscopy experimental results for grain
boundary damage from a 316H stainless steel creep test specimen. The interplay between the grain
misorientation and the presence of carbides at the grain boundaries is investigated. A range of novel
variations are incorporated into this approach that can isolate damage from varying mechanisms, including
slip, creep, and contributions from plastic or elastic deformation within the simulated microstructure. The
local effect of carbides, forming on specific grain boundary types, on void cavitation is included by using
a misorientation-dependent critical energy release rate. The direct comparison with electron backscatter
diffraction experiments clarifies what the most important damage mechanisms are and the quantitative
fracture energy reduction as a function of carbide density. The extension of this model to ferritic steel
microstructures is also explored.
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