Hierarchical Damage Simulation to Correlate Micro-structural Characteristics of Steel with Ductile Crack Growth Resistance of Component

摘要

The final goal of this study is to develop a method for estimating the effect of micro-structural characteristics of steel (especially two-phase steel) on ductile crack growth resistance of a structural component.For this purpose,hierarchical approach to link the micro-structural characteristics of steel and ductile crack growth resistance curve of a component is proposed.First attention is paid to reveal mechanical properties that control ductile crack growth resistance curve (CTOD-R curve),so that the R-curve could be numerically predicted only from those properties.It is shown from the observation of a mechanism for ductile crack growth that two types of "ductile properties" of steel associated with ductile damage can mainly influence CTOD-R curve; one is a resistance of ductile crack initiation estimated with critical local strain for ductile cracking from the surface of notch root,and the other one is a stress triaxiality dependent ductility obtained with circumferentially notched round-bar specimens.The damage model for numerically simulating the R-curve is proposed taking these two "ductile properties" into account,where ductile crack initiation from crack-tip is in accordance with local strain criterion,and subsequent crack growth triaxiality dependent damage criterion.This macroscopic simulation can correlate the mechanical properties of steel with CTOD-R curve of a component.The second approach is to develop a simulation method to predict the effect of micro-structural characteristics of two-phase steel on the two types of ductile properties that were found to be ductile crack growth controlling mechanical properties.To simulate meso-scale ductile damage behaviors,3D micro-structural FE-model is developed for analyzing the stress/strain localization behaviors by micro-structural strength mismatch and ductile damage model for reproducing damage evolution up to micro-void/micro-crack formation.This meso-scopic simulation can correlate micro-structural characteristics with mechanical properties of two-phase steel.Through the proposed hierarchical approaches,micro-structural morphology of two-phase steel to improve ductile crack growth resistance of a component can be discussed.