PSI - Issue 19

Yoichi Yamashita et al. / Procedia Structural Integrity 19 (2019) 123–129 Yamashita et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Test conditions

CT specimens with and without insert-plates and also with and without stop hole are shown in Fig. 3. Fatigue crack growth rate tests were conducted under load-controlled with stress ratio of R =0.1. Test frequency was 5 – 15 Hz. For each specimen, after introducing the fatigue crack into the specimen without arrester and being installed the arresters, fatigue crack growth tests were started under apparent stress intensity factor range of 20 MPa √ m. If there is no restart of fatigue crack growth, the fatigue loading level increases step by step by each incrementation of 1x10 5 cycles until the fatigue crack growth restarted.

Fig.3. CT specimens used in fatigue crack growth tests.

3.3. Crack growth test results Figure 4 shows the relationship between fatigue crack growth rate, ⁄ , and apparent stress intensity factor range, ∆ . ∆ can be calculated using load range, ∆ , without considering the inserted plates and also stop hole based on the following equation (ASTM E647, 2015): ∆ = ∆ √ (2+ ) (1− ) 3⁄2 (0.886 + 4.64 − 13.32 2 + 14.72 3 − 5.6 4 ) . It has been found that fatigue crack growth rate of CT specimen with the arresters using the gourd-shaped-insert plates were lower than that without the arresters. Also apparent threshold stress intensity factor range to start the fatigue crack growth of CT specimens with the crack arresters was higher than that without arresters. From these results, the arresters showed the good performance for crack growth arrest and crack growth rate retardation. Fatigue crack growth rates of the specimens with arrester were 1/10 ~ 1/2 of those without arrester. And apparent threshold stress intensity factor range was increased by about 10~20 MPa√ through using only few gourd-shaped arresters. It has been found that the more numbers of crack arresters, the performance of crack growth arrest and crack growth rate retardation increase. The restart of the fatigue crack growth in CT specimen with stop hole at the crack tip cannot be found until apparent stress intensity factor range reached 40 MPa √ m in step by step load increasing test. However, once the fatigue crack growth restarts, the fatigue crack growth rate of the specimen with stop hole is almost as same as that without stop hole and the arresters as shown in Fig. 4. No crack growth retardation can be found in the specimen with stop hole. And to enable quantitative fatigue life assessment in fatigue design, fracture mechanics based-crack closure model with spring elements for the arrester has been developed. In Fig. 4, the curves are the predicted relationship