PSI - Issue 2_A

Teruhiro Yamaguchi et al. / Procedia Structural Integrity 2 (2016) 712–719 Author name / Structural Integrity Procedia 00 (2016) 000 – 000

716

5

5. Results of EP-FEA

5.1. Load P – crack mouth opening V g diagram P - V g diagram for full sized specimen obtained from experiment and EP-FEA are compared in Fig. 6. Solid line in Fig. 6 shows V g calculated from the elastic compliance given in ASTM E1820 (ASTM, 2006).

10 15 20 25 30

P kN

0 5

0

0.1

0.2

0.3

0.4

V g mm

Fig. 6 P - V g diagram for full sized specimen (25 x 25 mm)

As shown in Fig. 6, the linear slope of the FEA result was very close to the linear P - V g relationship calculated from the equations given in ASTM E1820 (ASTM, 2006), and the path of the P - V g diagrams for experiment and EP FEA are similar. Therefore, the EP-FEA result was considered to be valid. EP-FEA for miniaturized specimens were also conducted. P - V g diagrams for the miniaturized specimens whose specimen dimensions are 10 x 10, 3 x 3 and 2 x 2 mm. Though not shown, the linear slope of the FEA result was very close to the linear P - V g relationship calculated from the equations given in ASTM E1820 (ASTM, 2006). Therefore, the EP-FEA result was considered to be valid.

5.2. Determination of  22c for full sized specimen

The relationships between  22 measured at 4  t on the x 1 axis  22d and J FEA calculated from P - V g diagram for each load step are shown in Fig. 7. In Fig. 7, fracture toughness J c s obtained from experiments are indicated by stars.

Fig. 7 The relationship between  22d and J FEA (25 x 25 mm)

From this relationship, the critical value  22c and the yield stress  YS is equal to 3.82, and fracture toughness J c for miniaturized specimen is predicted from this  22c , described below.

5.3. Prediction of J c for miniaturized specimen

The relationships between  22d and J FEA are shown in Fig. 8. In Fig. 8, the value  22c /  YS = 3.82 indicates the predicted critical value. From Fig. 8 (a), it was predicted that the minimum fracture toughness for 10 x 10 mm is predicted as 59 N/mm because  22d exceeded the critical value  22c when J = 59 N/mm. The result for 3 x 3 mm (Fig. 8 (b)) shows that  22d is decreasing with increasing of J FEA after  22d exceeded the critical value  22c . From this result, it was predicted that cleavage fracture might not occur in fracture toughness test for 3 x 3 mm.