PSI - Issue 2_A

Kiminobu Hojo et al. / Procedia Structural Integrity 2 (2016) 1643–1651 Hojo, Ogawa, Hirota et al. / Structural Integrity Procedia 00 (2016) 000–000

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to the condition of -95°C. No ductile crack growth by the coupled model at -125°C (not shown in Fig. 5) and -95°C occurred. At -50°C the distribution by (1) is very steep ( m =87). Figure 6 is σ W - K J relationof Beremin model and the coupled model at each temperature. K J relates to loading or applied displacement. σ W of Beremin model saturates earlier than lower temperature. Saturation of σ W is caused by saturation of the stress adjacent to the crack tip even when loading or displacement increases. At -125°C the specimens broke at K Jc =57-131 MPa √ m, which corresponds to σ W =1700-1900 MPa. This range is less than the saturation value of σ W =2300 MPa. This is true of the condition of -95°C. On the other hand, at -50°C, K Jc is in 225-430 MPa √ m, and σ W is in the saturated region for the larger K Jc region. As a result, the gradient of Weibull distribution of σ W becomes very steep in this region. For the smaller side of K Jc , the gradient of Weibull distribution in the case (1) looks similar. It may suggest the parameter m is independent of temperature, at least in the range of -125 °C to -50°C. The coupled model makes the σ W – K Jc curve increase. The curves of the coupled model deviate at K Jc =260-280 MPa √ m, which corresponds to σ W =2200MPa (-125°C), 2100MPa(-95°C), and 1900 MPa (-50°C), just before saturation of σ W. These do not affect σ Wc at -125°C and -95°C, but affect largely at -50°C. As a result the coupled model correlates Weibull distribution of σ Wc only at -50°C. However the correlation may be too much because the slope of the Weibull distribution in Fig.5 is too gentle. Figure 7 shows the relation between K Jc and temperature. Beremin and the coupled model can predict the fracture tests at -125 and -95°C, but the upper bound of K Jc at -50 °C is not precisely predicted. Further investigation is needed.

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lnln 1/(1- P f )

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Beremin Model(-125℃) Beremin Model(-95℃)

CT, Beremin Model(-125℃) CT, Coupled Model(-125℃) CT, Beremin Model(-95℃) CT, Coupled Model(-95℃) CT, Beremin Model(-50℃) CT, Coupled Model(-50℃) CT, Beremin Model(-50℃, m=87)

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Fig. 6. σ W – K J relation from Beremin and Coupled model

Fig. 5. Failure probability- σ W from Beremin model and Coupled model

Fig. 7 Relation between K Jc and temperature by the simulation models and fracture toughness test