13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- Figure 1. Concept for developing simulation method. 2. Simulation method for correlating ductile crack growth resistance with mechanical properties (Macroscopic approach) First attention in this study, that is macroscopic approach, was paid to developing a simulation method for correlating ductile crack initiation and extension properties (CTOD-R curve) with mechanical properties that could be obtained by laboratory tests. One of the authors has already proposed the numerical simulation model [1]. The ductile crack initiation from crack-tip is in accordance with local strain criterion [1-4], and the subsequent crack extension triaxiality dependent damage criterion [1]. This model can predict a CTOD-R-curve only from two types of ductile properties and stress-strain curve of steel; one is a resistance of ductile crack initiation estimated with critical local strain for ductile cracking from the surface of notch root obtained with notched bend specimen, and the other one is a stress triaxiality dependent ductility obtained with circumferentially notched round-bar specimens. In this chapter, the applicability of this model to prediction of CTOD-R curve of a cracked component of high strength steel is demonstrated. 2.1. Mechanical properties controlling ductile crack growth resistance The steels used in this study are steels A, B and C. The steels A and B have almost the same yield stress and work hardening, whereas the steel C has higher strength and lower work hardening as shown in Figure 1. Table 1 summarizes the strength properties of all the steels used. Two types of the ductile properties, which are critical local strain and stress triaxiality dependent ductility, of all the steels that would control ductile crack growth resistance of cracked components were measured. To measure a critical local strain (!p tip) cr , static 3-point bending tests were conducted using V-notched Charpy specimen. Typical shear mode ductile cracking was observed, which implies that the local strain criterion can be applicable to the steels used. By means of FE-analysis, a critical equivalent plastic strain (!p tip) cr at crack-tip element was estimated. Another ductile property of the steels, that is stress triaxiality dependent critical local strain (!p)cr , was examined by conducting tensile test as well as FE-analysis for round-bar specimens with circumferential notch. (!p)cr as a function of stress triaxiality were estimated on the middle of the notch-root section where ductile cracking occurred in experiments. The details of the method of experiments and FE-analysis are described in the literature [1]. Figure 2 summarizes the obtained two types of the ductile properties. The (!p tip) cr and tress triaxiality dependent critical local strain (!p)cr for the steel C are lower than those for steels A and B. From these results, ductile crack growth resistance for the steel C can be supposed to be the lowest. Micro-structural ! characteristics Mechanical properties Structural performance Crack Crack High pressure pipe Steel framed structure
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