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. 2. Typical d transition in the press-notched bend test and the ideal d transition. Analysis condition: T = -60 °C , flat crack front, crack velocity = 300 m/sec const., crosshead displacement = 3 mm.

Fig. 1. Low correlation between ca and ca−PB in the Arrhenius type temperature dependence (Kawabata et al., 2017).

Fig. 3. Schematic configuration of press-notched bend test specimen and tapered three-point bend test specimen. 3.2. Results of preliminary experiments Test specimen used was the small-scale tapered specimen with 5 mm depth press notch, as shown in Fig. 4. Temperature of test specimen was controlled steadily by using ethanol and frozen carbon dioxide. Test temperature was kept within the aimed temperature ± 2 °C for at least 10 minutes. Table 5 shows the test conditions and results. Brittle cracks were initiated and arrested in all test specimens although some test results are invalid due to significant ductile cracks, where plastic strain is applied in a wide range of the ligament. The brittle crack arrested positions were visualized by heat-tint (Fig. 5), the longest crack lengths from press notch tips were measured as . Fig. 6 shows a strong relationship between test temperature and arrested crack length. Given the influence of the dispersion of brittle fracture initiation, these results suggest that the dynamic crack driving force decreases monotonically with crack propagation.

Fig. 4. Configuration of tapered three-point bend test specimen used in the preliminary experiments.