PSI - Issue 33

Toru Yagi et al. / Procedia Structural Integrity 33 (2021) 1225–1234 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 12 Crack extension and normalized dynamic stress intensity factor of (a) three-point bending model and (B) tensile model

3.2. Proposal New pop-in mechanism described by the superposition of tunnel crack model on FEM is proposed in this study. It is the simplified model which consists of the superposition of d obtained by FEM analysis and of tunnel crack shape model that is developed to simulatye actual crack driving force of section notch specimens. The core part of this model is the consideration of the closure effect by the side ligaments. Fig. 13 (a) is the schematic image of this model. The black curve is the d value obtained from the FEM analysis and the read shaped area is the amount of the closure effect of the side ligament. The red curve is the actual d value described by this mechanism. Fig. 13 (b) is the schematic image of the fracture surface of the specimen. The closure effect of side ligament is calculated by the equations (4)-(6) and the amount of the effect strongly depends on the width of local brittle zone. Fig. 14 shows the schematic image of the fracture surface of the specimen with the local brittle zone.

Fig. 13 (a) schematic image of P-Vg curve of actual d and (b) is image of fracture surface of specimen closure = 2( closure1 + closure2 ) closure1 = ∫ ∫ ( √ 2 ) 3 2 ∙ 1 + 1 ( ) 2 ∙ (− Y ) −√ 2 − 2 + 0 0

(4) (5)