13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 3. Results – Mechanical tests and fractography The results obtained on Charpy specimens and on CT specimens, tested along the T (transverse) – L orientation are reported in Fig. 2. A shift of the ductile to brittle transition temperature (DBTT) measured at 41J appears in Fig. 2a when comparing the as-received and the aged conditions. This shift is of about 39°C. Similarly the fracture toughness determined on CT20 specimens is lowered by aging (Fig. 2b and c). In these figures we have also reported the probabilities to fracture for 5%, 63% and 95% determined from the master curve (MC) analysis [8, 9]. The temperature To at which KJC = 100MPa m1/2 is shifted from – 124°C in the as-received condition to – 91°C in the aged condition. The scatter in the aged material is much wider than in the as-received material. In particular it is noticed that the MC analysis is unable to describe this large scatter. Figure 2. a) Charpy tests in as-received and aged (450°C – 5000 h) conditions; b) Fracture toughness, KJC (thickness) determined on CT 20 mm thick specimens as a function of temperature in the as-received material; c) Fracture toughness KJC on CT20 mm thick specimens in the aged (450°C – 5000 h) condition. The probabilities Pr = 5%, 63%, 95% determined from the Master Curve (MC) are also drawn. Fracture surface examination of Charpy and CT specimens tested at relatively low temperature showed the presence of elongated zones aligned along the L direction (Fig. 3a) in which the fracture a) b) c)
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