13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- Figure 13. Load - displacement curves obtained by experiment and simulation for notched micro-tensile specimen. Figure 14. Comparison between simulated and observed ductile damage evolution for notched micro-tensile specimen. 3.3 Effect of micro-structural morphology on mechanical properties It is demonstrated that the developed simulation model can well simulate ductile cracking behaviors regardless of surface or inside of a specimen, namely regardless of global triaxial stress conditions. Therefore, effect of micro-structural characteristics of two-phase steel on the macro-scopic ductile properties i.e., critical local strain and stress triaxiality dependent ductility which were found to control ductile crack growth resistance of a cracked component could be expected to be able to predict on the basis of the meso-scopic simulation method. Simulation model to estimate those macro-scopic ductility are proposed as given in Figure 15; (a) is 3-point bend specimen with sharp crack for critical local strain and (b) is tensile RVE (Representative Volume Element) under constant stress triaxiality for stress triaxiality dependent ductility, which controls macro-scopic ductile crack initiation and extension, respectively. (a) Random type (b) Layered type (a) For critical local strain (b) For stress triaxiality dependent ductility Figure 16. Type of morphology of micro-structure Figure 15. Models for simulating the effect of micro-structural characteristics of two-phase steel on ductility. 0 20 40 60 80 100 0 0.05 0.1 0.15 0.2 Experiment Simulation (Micro-structural model) Load, P (N) Displacement, u (mm) Level 1 Level 2 Ferrite Pearlite Void/Micro-crack(No stiffness)! Level 1! Level 2! Experiment Simulation Ferrite Pearlite 0.25! 0.3! 0.3! 0.1R! Second phase! (Unit : mm)! Rigid body! 8! 2! 0.25! Matrix phase! 1! 1/2 model! 0.3! 0.3! 0.25! ! ! ! ! ! (Unit : mm)! RVE! Second phase! Matrix phase!
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