[SY-E6] FTMP-based Modeling and Simulations of Inhomogeneous Recovery-Triggered Accelerated Creep Rupture in Lath Martensite Structures
Against highly complex hierarchical material systems as in high Cr heat-resistant ferritic steels exhibiting inhomogeneous recovery-triggered accelerated creep rupture, the present study tackles a series of problems about their practically-feasible multiscale modeling and simulations based on FTMP. The targeted system here is composed of martensite laths with high-dense dislocations (Scale A), lath blocks/packets (Scale B) embedded within a prior austenitic grain (Scale C). The objectives are (a)reproduction of the experimentally-observed accelerated degradation of the creep strength due to inhomogeneous recovery of the microstructures under relatively low stress conditions, and (b)identification of the minimal conditions for (a) to occur, focusing on the interactions between Scales A and B. Creep analyses, considering the interior high-dense dislocations evaluated by the spontaneously-evolved incompatibility tensor field in Scale B, are conducted for single lath block models first. They exhibit pronounced local instability due to local recovery brought about by the interaction incompatibility field. Thus-developed models are further combined to construct single packets and embedded packet models, respectively, and the same series of analyses are performed on them. The fluctuating incompatibility field in Scale A, concurrently enhanced by the interaction term, is demonstrated to promote the local recovery. We further clarify the contributions of the projection directions of the incompatibility tensor in evaluating the Scale A dislocation density. The projection to the slip plane normal direction is turned out to play exclusively-dominant roles, implying the critical contribution of the climb-related elementary processes to the enhanced localized recovery. An attempt is also made to replace the above recovery model to improve the consistency of the current approach.