PSI - Issue 2_A

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

2234

5

Table2.Average grain size and yield stress

Steel

SA1 231 41.9

SA2 279 53.1

SA3 325 17.7

Yield stress @RT [MPa] Average grain size[μm]

OIM analysis map

It is known on brittle fracture that sheer lip is formed by ductile fracture of uncracked side-ligament which is caused by stress relaxation near the surface of steel plate. In our study, we made side groove on test pieces in order to restrain side-ligament which caused crack closure effect, because our study aimed at the evaluation of effective surface energy as material resistance for cleavage fracture. Besides, we used embrittlement bead to promote the crack initiation, based on many preliminary experiments. Referring to WES TS2816 (2015), we conducted three-point bending tests as a kind of crack arrest test. Each test was conducted, maintained a consistent temperature. We looked for temperature conditions in which crack arrested. An example of fracture surface is shown in Fig.4(b). Succeed test results were as follows. Macroscopic arrest toughness � �� was calculated under the calculation of WES TS2816 (2015) by measuring initial crack length a 0 , crack initiation load value P 0 and crack length value a a . The calculation was conducted as follows. � �� � �� � ��√� �� � ��� �� ����� � � � �� � ����� � � � � � �� � � � � √ �� � ��� � � � �� � � � � � � � � � � � � � (2) ���� � ����� � �� � �������� � � ����� � ����� √��� � �� ��� ��� � �� (3) ���� � � � � � � � � ������� � � ������ � � ������ � � ������ � ����� (4) From some temperature conditions, we successfully obtained the relationship between temperature and arrest toughness as is shown in Fig5.

305 mm

crack length

Side groove

x

Embrittlment bead

W=76 mm

y

S=250 mm

z

30 mm

20 mm

y

(a)three-point bending test

(b)an example of fracture surface

Fig.4. three-point bending test and an example of fracture surface