PSI - Issue 13

Kazuki Shibanuma et al. / Procedia Structural Integrity 13 (2018) 1238–1243 Author name / Structural Integrity Procedia 00 (2018) 000–000

1242

5

Table 1 Chemical compositions of test steel [mass%]

C

Si

Mn

P

S

Al

N

O

0.14

0.41

1.45

0.017

0.003

0.027

0.0031

0.001

0,0 0,2 0,4 0,6 0,8 1,0

Area fraction

0,00

0,04

0,08

0,12

100  m

Grain size [mm]

(a) Optical micrograph

(b) Grain size distribution

Fig. 5. Employed test steel

The boundary conditions were defined based on the results of local stress distribution in the macroscopic finite element analysis simulating the test. An example of the comparisons between the results of the SEM observation and the model simulation is shown in Fig. 6. The crack propagation path in the actual fracture surface can be estimated by following river patterns on the cleavage planes. The results of the SEM observation showed complicated crack propagation behaviors such as micro branching and wraparound of cracks, see Fig. 6(a). On the other hand, the model simulation showed deviated or uneven crack propagation behavior accompanying with micro-branching and wraparound of cracks, see Fig. 6(b). That is, the result shows that the developed model successfully simulated the complicated cleavage crack propagation behaviors.

(a)

(b)

Fig. 6 Comparison of cleavage fracture surface morphology; (a) SEM observation; (b) Model simulation