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

1649

7

parameters of GTN models from NT and CT specimens seem similar, but the parameter set from CT specimen could not predict the load-clip gage displacement relation of NT specimen.

(a) Normal model of GTN model

(b) Cell model of GTN model

(c) Rousselier model

Fig. 3. Stress contours of normal and Cell model of GTN model and Rousselier model

CT-44 CT-45 CT-46 CT-51 CT-52 CT-53 CT-54

3.5

3.5

CT-44 CT-45 CT-46 CT-51 CT-52 CT-53 CT-54

3.0

3.0

2.5

2.5

2.0

2.0

1.5

CT-44 (FEA) CT-45 (FEA) CT-46 (FEA) CT-51 (FEA) CT-52 (FEA) CT-53 (FEA) CT-54 (FEA)

1.5

CT-44 (FEA) CT-45 (FEA) CT-46 (FEA) CT-51 (FEA) CT-52 (FEA) CT-53 (FEA) CT-54 (FEA)

1.0

1.0

0.5

0.5

Ductile crack growth (mm)

Ductile crack growth (mm)

0.0

0.0

-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

-0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5

Thickness direction x/t

Thickness direction x/t

(a) GTN model (b) Rousselier model Fig. 4. Comparison between ductile crack growth distribution along the crack front from the fracture test and FEA.

When the larger displacement was applied to the FE model of CT specimen, some elements were crashed and the calculation was not converged. A larger sized mesh model with 0.1mm was produced to avoid this kind of behavior and the parameters were determined by the same procedure as mentioned above. Table 6 shows the parameters of GTN model. q 1 , q 2 , and q 3 were fixed to 1.5, 1, and 2.25, respectively for the case of the 0.1mm mesh model.

Table 6 Parameters of GTN model from CT specimens (-50°C)

f F

f c

ε N

S N

f N

f 0

1.0 × 10 -10

0.196

0.001

0.424

0.108

0.037

4.2. Coupled model

From the test results of CT specimens at -125°C, Weibull parameters m and σ u were determined as 35 and 2005MPa, respectively. On the assumption that m is constant regardless of temperature, Weibull distribution of Weibull stress were calculated at -95°C and -50°C using Beremin model and the coupled model with GTN model. Figure 5 shows the comparison between three kinds of Weibull distribution of σ Wc ; (1) σ Wc by Beremin model with its own m , (2) σ Wc by Beremin model with m =35 (from the tests at -125°C) , and (3) σ Wc by the coupled model with m =35. The results of -95°C are the nearly same among three cases. This means that m at -125 °C is applicable