PSI - Issue 13

Yuta Suzuki et al. / Procedia Structural Integrity 13 (2018) 1221–1225 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1223

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Fig. 2 Configuration of crack arrest specimens

2.3. Evaluation result When evaluating the arrest characteristic of a material from the result of the arrest toughness tests, arrest toughness using the stress intensity factor is often adopted as an indicator. However, this arrest toughness is only an apparent crack propagation resistance value. Therefore, based on the accomplishment of Yanagimoto et al., local fracture stress was adopted (Yanagimoto et al., 2018). Considering the crack opening displacement and the position of crack arrest at the time of occurrence of fracture, local fracture stress was evaluated by the finite element analysis with Abaqus 6.14 (SIMULIA, 2014). In this analysis, the estimation of local fracture stress was carried out by evaluating stress in the vicinity of crack tip when crack arresting. Fig. 3 shows the local fracture stress based on the average grain size. As a result, it can be said that experimentally showed that the larger grain size is, the larger cleavage crack propagation resistance.

1000 1200 1400

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Estimated local fracture stress [MPa]

Fig. 3 Result of the estimated local fracture stresses

3. Calculation of absorbed energy

In fact, it is nearly impossible to obtain effective surface energy directly from cleavage crack propagation experiments because it is extremely fast and complicated phenomenon. Therefore, microscopic cleavage fracture surface simulated by a numerical model was employed to calculate energy absorption during cleavage crack propagation. The accomplishment of Aihara and Tanaka was unique attempt to model cleavage crack propagation in bcc solids (Aihara and Tanaka, 2011). However, the model had problems in reproducing the actual phenomenon because of simplification such as discretization by a single rectangular unit cell and evaluation of the stress intensity factor of crack front by superposition of approximate solutions. Therefore, Shibanuma et al. developed a new cleavage crack