PSI - Issue 33

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

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1. Introduction The number of layers and size of structures, mainly steel frame structures, have been increasing over the years, as discussed by Haga (2006). Kato et al. (1969) pointed out that it was mainly only local buckling that was a problem in the fracture phenomena of structural members in those days. However, as the plate thickness of members has increased, the criteria for brittle fracture to occur have been met, and some cases of great damage have been observed due to the occurrence of brittle fracture in the event of a large earthquake, as reported by AIJ (1995). When it is difficult to prepare full-scale steel for fracture testing of structural members, fracture tests have been performed on reduced-scale steel. To correctly evaluate the brittle fracture properties of actual structural members, it is necessary to understand the effect of specimen size on the brittle fracture properties and to develop an approach for brittle fracture evaluation that is less sensitive to the specimen size. In recent years, the authors (proceedings to be published) have evaluated the effect of scale on brittle fracture properties. In the project, cyclic bending tests were performed on three types of columns and beams with equal scales of 4-2-1 until failure, as shown in Fig. 1(a). The energy absorbed up to failure, normalized by scale, showed that the energy absorbed decreased with increasing scale. However, the fracture surface showed that a ductile crack preceded brittle fracture, as shown in Fig. 1(b), indicating that the actual structure has both ductile and brittle fracture. In this study, we focus on the relationship between brittle fracture properties and geometrical shape. We performed this study based on three-point bending tests on several types of specimens with different specimen sizes and notch depths with the following objectives.  Evaluation of the scale effect on brittle fracture initiation properties  Verification of the applicability of the existing brittle fracture criterion  Proposal of a new accurate brittle fracture criterion

Nomenclature B

thickness of test specimens [mm] width of test specimens [mm] length of test specimens [mm]

W

L S

length of span in three-point bending test [mm] initial notch depth of test specimens [mm] curvature radius of test specimens [mm]

a 0

R

P load in three-point bending test [kN] � clip gauge opening displacement [mm] �������� critical quasi-CTOD [mm] �� critical stress intensity factor [N/mm 3/2 ] �� critical load [N] Y shape correction factor ν Poisson’s ratio g conversion factor �� yield stress [MPa] �� tensile stress [MPa] E Young’s modulus [MPa] , � � correction factor of plastic item � plastic component of � [mm] � (equivalent) plastic strain � true stress [MPa] ������� yield stress converted to true stress [MPa] n strain hardening index fracture probability of the entire material F