PSI - Issue 2_A

Takehisa Yamada et al. / Procedia Structural Integrity 2 (2016) 2206–2213 Author name / Structural Integrity Procedia 00 (2016) 000–000

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(a)

(b)

Fig. 12 Limit characteristic of ductile crack initiation for different materials. (a) relationships between ε ’ p and η ; (b) relationships between ( ε ’ p ) -n and η .

6. Summary

• From the tensile tests using notched round bar specimens of SM400B, HT780 and A2024-T351, it was found that the relationships between ε ’ p and η at ductile crack initiation are dependent on materials. • The processes of ductile crack initiation are considered to be different between steels such as SM400B and HT780, and A2024-T351 from the cross section observations. It is supposed that the ductile fracture of steels is caused by the coalescence of voids generated and grown during deformation. On the other hand, the one of A2024-T351 is supposed to be caused by the rapid growth and coalescence of micro voids at a stage of deformation. • As for steels such as SM400B and HT780, ductile crack initiation is considered to be caused by shear fracture between grown voids and Mohr – Coulomb fracture criterion was applied to the evaluation of ductile crack initiation limit. As a result, it was found that strain hardening exponent could be a new parameter and ductile crack initiation limit of steels could be evaluated by a single master curve. References Bai, Y., Wierzbicki, T., 2010. Application of extended Mohr-Coulomb criterion to ductile fracture, International Journal of Fracture, 161, 1–20. Bai, Y., Teng, X., Wierzbicki, T., 2009. On the application of stress triaxiality formula for plane strain fracture testing, Journal of Engineering Materials and Technology, 131, 2 (2009). Beese, A. M., Luo, M., Bai, Y., Wierzbicki T., (2010). Partially coupled anisotropic fracture model for aluminum sheets, Engineering Fracture Mechanics, 77, 1128–1152. Enami, K., 2005. The effects of compressive and tensile prestrain on ductile fracture initiation in steels, Engineering Fracture Mechanics, 72, 1089–1105. Johnson, G. R., Cook, W. H., 1985. Fracture characteristics of three metals subjected to various strains, strain rates, temperatures and pressures, Engineering Fracture Mechanics, 21, 1, 31–48. Mutoh, Y., Sakamoto, I., Nakagawa, T., 1985. Ductile fracture in type 304 stainless steel weldments, Japan Welding Society, 3, 4, 869–874 (in Japanese). Otsuka, A., Miyata, T., Nishimura, S., Ohashi, M., 1981. Ductile fracture, cleavage fracture and ductile-brittle transition in low strength steels, Transactions of the Japan Society of Mechanical Engineers, Series A, 47, 415, 286-294 (in Japanese). Rice, J. R., Tracy, D. M., 1969. On the ductile enlargement of voids in triaxial stress fields, Journal of the Mechanics and Physics of Solids, 17, 201 – 217. Yamada, T., Yamashita, Y., 2011. Ductile crack initiation behavior of prestrained steels, Proceeding of the ASME 2011 Pressure Vessels & Piping Division Conference, PVP2011, PVP2011-57294.