PSI - Issue 13

Yuki Nishizono et al. / Procedia Structural Integrity 13 (2018) 1817–1827 —‹ ‹•Š‹œ‘‘ Ȁ –”—…–—”ƒŽ –‡‰”‹–› ”‘…‡†‹ƒ ͲͲ ሺʹͲͳͺሻ ͲͲͲ – ͲͲͲ

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Fig. 9. Arrhenius type temperature dependence of steel A. (Analysis condition: flat crack front, crack velocity = 300 m/sec const.)

4. Main experiments In order to evaluate ca in high range, the authors used the test specimen whose planer size is four times the test specimen in the preliminary experiments. The experiments are denoted “Main experiments” in this paper. The authors applied a four-point reverse bend processing to the test specimen after the press notch processing because a brittle crack is less likely to be initiated from a press notch tip at high test temperature. The detailed FEA results required for selecting the test conditions of press notch processing and four-point reverse bend processing are not introduced in this paper. 4.1. Results of main experiments Test specimen used was the small-scale tapered specimen with 5 mm depth press notch, as shown in Fig. 10. The notch processing B in Fig. 10 is a process of applying a four-point reverse bend of 395 kN, which is determined by limit load concept (Norman E. Dowling, 1993), after processing 15 mm depth machining notch and 5 mm depth press notch at room temperature. Temperature of test specimen was controlled steadily by using Hydrofluoroether and liquid nitrogen, and measured by a temperature history recording equipment. Temperature of test specimen was kept within the aimed temperature ±2°C for at least 15 minutes (Fig. 11). Table 6 shows the test conditions and results. Fig. 11 shows the fracture surfaces of specimen No.1 and No.3 respectively, and the longest crack lengths from press notch tips were measured as a .

Fig. 10. Configuration of tapered three-point bend test specimen used in the main experiments.