PSI - Issue 13

Atsuhisa Kitade et al. / Procedia Structural Integrity 13 (2018) 1845–1854 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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2.4. Prediction formula of critical stress

From the above results, it was found that there was a mechanism that more plastically deformed load was applied to the coarse grain portion. Therefore, it was suggested that it is necessary to incorporate the maximum value of the effective crystal grain size into the model. Moreover, it can be said that each small MA does not always works as a critical pile-up site of dislocations. The orientation gap to neighbor grain has to be focused more for establishment of the accurate fracture modelling. 3. Finite element method analysis for DWTT test In this section, we analyze the model that predicts the toughness of the DWTT test, which is generally used as the pipeline quality assurance test. In this paper, we show that the model can be correctly constructed for the TMCP steel manufactured under the rolling condition of "850-75" mentioned in Chapter 2. Fig. 10 shows the FEM model analyzed. The fulcrums support is located on both sides, the hammer is an elastic body, the test piece is assumed to be an elastoplastic body, and the upper part of the test piece is press notched. The initial speed of the hammer is 7 mm/s. The flowchart of this analysis is shown in Fig.11. Detailed dimensions are shown in Fig.12. Mesh division of the vicinity of the propagation part was made sufficiently fine as shown in Fig.13. Press notch process was calculated by implicit method and dynamic crack propagation by impacting was calculated by explicit method. 3.1. Coupling model for brittle and ductile fracture

Fig. 10 General of FEM model

Fig. 11 Flow chart of this analysis

Fig. 12 Detailed dimensions of FEM analysis

Fig. 13 Mesh division along crack line