PSI - Issue 42

Takumi Ozawa et al. / Procedia Structural Integrity 42 (2022) 730–737 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Fracture toughness test Fracture toughness tests were conducted under the LC conditions which are identified by Bayesian optimization and recommended in ISO standard. Fig. 9 shows the pictures of experiment. Fig. 10 shows the results of fracture toughness test. As shown in Fig. 10(a), the LC identified by Bayesian optimization achieved a straight crack. On the other hand, the fracture toughness value of the LC was twice or more higher than that of ISO recommended as shown in Fig. 10(b). As mentioned in Chapter 1, a traditional LC decrease fracture toughness value by half or more, therefore, the authors believe the LC maintains the fracture toughness value. In conclusion, the authors are of the view that we found the LC condition for achieving a straight fatigue precrack while maintaining the fracture toughness value. 4. Conclusion The authors operated Bayesian optimization for investigating the characteristics of ideal LC condition. As a result, it was found that ideal LC condition needs compression area with 500 to 700 mm 2 and distance from the future notch tip with 2 to 6 mm. Other parameters, such as aspect ratio and corner dimensions did not have much effect on the objective function. Based on the analysis result, the authors determined the LC condition for experiment and conducted fracture toughness test. The proposed LC condition achieved a straight fatigue precrack and the critical CTOD was twice or more higher than that of traditional one. The authors concludes that the characteristics of the ideal LC condition is found.

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Fig. 9. Pictures of experiment: (a) LC process; (b) Fracture toughness test.

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Fig. 10. Results of fracture toughness test: (a) Fatigue precrack; (b) Fracture toughness value.