PSI - Issue 2_A

Toshiyuki Meshii et al. / Procedia Structural Integrity 2 (2016) 704–711 Toshiyuki Meshii and Kenichi Ishihara / Structural Integrity Procedia 00 (2016) 000–000

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The tendency that J s of 0.5T SE(B) is larger than that of 1T CT, which often appeared in the past experiences, was obtained. 5. Fracture toughness test The dimensions of the fracture toughness test are shown in Fig. 7 and Fig. 8. Fracture toughness test was conducted in accordance with ASTM E1921. After inserting a fatigue crack into the specimen, the crack length a satisfied ASTM’s requirement of a / W = 0.45 to 0.55; the crack length was in the range of 0.496 to 0.504.

Fig. 7 Dimensions of 0.5T SE(B) specimen

Fig. 8 Dimensions of 1T CT specimen

Precracking was performed with two discrete steps which satisfied the requirement of the standard that precracking can be performed by using at least two discrete steps. Fatigue precrack was inserted with loads corresponding to K max = 22 and 19 MPam 1/2 for the 1st and 2nd stages, respectively, which satisfied the requirement of the standard 25 and 20 MPam 1/2 . For each discrete step, the reduction in P max for any of these steps was 18.7 %, which satisfied the suggestion if the standard the reduction in P max for any of these steps be no greater than 20 %. The maximum force P max and the minimum force P min ratio R = P min / P max was applied, and the load frequency was 10 Hz. In fracture toughness test, the loading rate was controlled to be 1.2 MPam 1/2 /s, which is very small in the specified range of 0.1 to 2.0 MPam 1/2 /s. The test specimen temperature was maintained to be in the range of 20  1 °C for 30/(25/ B )+15 minutes, which satisfied ASTM requirement of 20  3 °C and 30/(25/ B ) minutes. Test results are summarized in Table 2. Here, in Table 2,  and  denotes the average and standard deviation of each value, respectively. 2  /  % is a reference value intended to represent the magnitude of data scatter. It is seen from Table 2 that 2  /  of K J c were in the range of 26.1 to 49.2 % for all the specimens. Considering that the guideline for 2  /  given in ASTM E1921 for K J c is 56(1  20/  ) % and was in the range of 44.2 to 44.8 % for the data in Table 2, it was concluded that the scatter in the K J c data summarized in the table is acceptable. In addition, it can be said that a very small scatter in K J c was realized from the current test data. It is also seen that all of the test results were satisfied ASTM E1921 requirements of M  30 ( M = b 0  YS / J : b 0 is the length of specimen ligament W a ).