PSI - Issue 2_A

Takuhiro Hemmi et al. / Procedia Structural Integrity 2 (2016) 2230–2237 Author name / Structural Integrity Procedia 00 (2016) 000–000

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Uncracked ligament

Tear-ridge

� � � ��

Cleavage plane

(a)

Optical microscope photograph of tear ridge

(b)

Energy absorption by ductile fracture of tear-ridge in the model

Fig.2.Tear ridge formation in brittle fracture surface and assumed energy absorbing mechanism It is known that one of the most effective factor on arrest toughness is grain size. By using the model, we attempted parametric study evaluated the relationship between grain size and effective surface energy by changing grain size �� � 20, 25, 40μm . The result of micro model parametric study was as follows.

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1

20 25 40 Grain size[μm]

Cumulative probability

0

2000 4000 6000 8000 10000

Effective surface energy γ[J/m 2 ]

Fig.3.Grain size and effective surface energy distribution The graph above shows that the smaller grain size is, the smaller effective surface energy is. Empirically, it is known that the smaller grain size is, the larger the arrest toughness is. Considering Therefore, the model cannot respect the actual behavior and this inconsistence suggests that the expression of effective surface energy should be

investigated in detail. 3. Crack arrest tests

For the purpose of crystallizing the issues about the relationship between grain size and arrest toughness mentioned in previous section, we conducted three-point bending tests, a types of crack arrest tests, for three kind of steel plates (SA1,SA2,SA3). They have different grain size but nearly the same chemical conditions. These chemical compositions were shown in Table1 and yield stress and average grain size were shown in Table2. EBSD maps were obtained from OIM analysis software, TSL Solutions(2011).

Table1. Chemical composition of tested material

mass%

Steel

C

Si

Mn

P

S

Al

N

O

SA1 SA2 SA3

0.10 0.10 0.10

0.20 0.19 0.20

1.51 1.50 1.50

0.010 0.010 0.010

0.003 0.003 0.003

0.027 0.028 0.028

0.0031 0.0029 0.0030

0.001 0.001 0.001