PSI - Issue 6

Tonsho Fumiaki et al. / Procedia Structural Integrity 6 (2017) 269–275 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

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0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10

0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10

0.70 0.75 0.80 0.85 0.90 0.95 1.00 1.05 1.10

Specimen#5

Specimen#2

Specimen#3

a=60mm a=80mm

a=60mm a=80mm

a=60mm a=80mm

a=100mm a=120mm a=150mm Static Stress Intensity Factor Theory

a=100mm a=120mm a=150mm Static Stress Intensity Factor Theory

a=100mm a=120mm a=150mm Static Stress Intensity Factor Theory

0

10 20 30 40 50 60 Angle, θ [degree]

0

10 20 30 40 50 60 Angle, θ [degree]

0

10 20 30 40 50 60 Angle, θ [degree]

Fig. 10Comparison ofcircumferential stress

this modification of the crack tip stress field could account for the tendency of rapidly growing cracks in brittle materials to develop roughened fracture surfaces and to bifurcate into several branched cracks.Circumferential stress is calculated by stress conversion (8). = + 2 − − 2 2 − 2 (8) Fig.10 shows the results of calculation. Calculated is greater than that of theory on the whole, but no relation with the point where the crack branched is found. Much precise calculation with small size mesh is needed to get further information. Using 2 types of material, ESSO test were conducted. In the experiment, crack propagation velocity was measured and the point was observed where the crack starts bifurcation. FEM analysis is performed with the crack propagation velocity obtained by the experiment. Several theory on critical condition of crack branching was considered and from the results of analysis, it is shown that stress triaxiality tends to get bigger through the crack propagation. Critical condition for crack branching is thought to be max principal stress, 1 > 1500 and triaxiality, > 1.1~1.3 . Acknowledgements In this study, financial support from Fundamental Research Developing Association for Shipbuilding and Offshore, REDAS, is gratefully acknowledged. [1] T.Kawabata, N. Konda, K.Arimochi, H.Hirose, S.Muramoto, and S.Hirai: "Consideration on the Toughness Requirement to the Austenitic Weld Metal in the LNG Storage Tanks Subjected to a Partial Height Hydro Test", Materials Science Forum Vols. 638-642 (2010) pp 3679-3686. [2] E. Sharon, S. P. Gross, and J. Fineberg, "Local Crack Branching as a Mechanism for Instability in Dynamic Fracture", Phys. Rev. Lett. 74, 5096 (1995). [3] E.H Yoffe: "The Moving Griffith Crack", Philosophical Magazine,42(1951),739-750. [4] Y .J.Jia, B.Liu: “Crack Branching Characteristics at Different Propagation Speeds: From Quasi-Static to Supersonic Regime", J. Appl. Mech 81(12), 124501 (Oct 27, 2014). [5] H.Gao, “Surface Roughening and Branching Instabilities in Dynamc Fracture”, J. Mech. Phys. Solids Vol.41, No. 3(1993) pp.457-486 [6] T.Nishioka, Y. Negishi, H.Sumiii and T. Fujimoto : “Ultra High -Speed Photography and Moving Finite Element Analysis for Dynamic Crack Branching under Impact Loading”, Journal of the Society of Materials Science, Vol.61, No.11(2102) pp.894-899 6. Conclusion References