PSI - Issue 33

Naoya Oie et al. / Procedia Structural Integrity 33 (2021) 586–597 Oie, N. / Structural Integrity Procedia 00 (2019) 000–000

588

3

� Weibull stress [MPa] shape parameter � scale parameter [MPa] � max principal stress [MPa] �

reference volume of a micro region such that it contains one microcrack [mm 3 ] � process zone (areas of the material that may contribute to failure) [mm 3 ] ���� critical Weibull stress [MPa] f fracture probability density function ���� probability of microcracks propagating through the material ���� probability of microcracks nucleated X distance from the notch tip to the initiation point of brittle fracture P ( x ) fracture probability that fracture will occur at a position ���� ��� integral form of ���� with respect to � stress triaxiality

Fig. 1. Cyclic bending test: (a) test specimen; (b) fracture appearance and SEM observation.

2. Experiments 2.1. Material

The steel sheet used was “SN490B” in Japan Industrial Standards (2012), which is the steel mainly used for structures in Japan. The chemical composition of the steel sheet is shown in Table 1. To adjust the toughness, the steel was tempered by two-phase quenching (750°C) and tempering (300°C) before being used in the test. The specimens used for the three-point bending test were taken in the rolling direction and at the mid-thickness.

Table 1. Chemical composition of the test steel mass [%]. C Si Mn P S Cu Mo

Nb

V

0.13 0.23 1.30 0.012 0.006

0.14

0.07 0.012 0.005

2.2. Three-point bending test The external shape of the three-point bending test was set so that W was twice B and S was four times W for all specimens according to the CTOD test standard based on ISO (2016). The test dimensions and notch length conditions for each of the eight types of specimens are shown in Table 2.