PSI - Issue 13

Kejin Zhang et al. / Procedia Structural Integrity 13 (2018) 1047–1052 Kejin ZHANG / Structural Integrity Procedia 00 (2018) 000 – 000

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The stretch zone is a groove-like structure that yields and blunts when the crack tip receives opening stress. Due to the absence of the stretch zone, the cause of the brittle fracture of PH8 punched specimen is that the steel at the crack tip did not yield even though the shear crack tip received opening stress. The ease of sliding and yielding of the shear crack tip depends on dislocation mobility. It is thought that dislocation mobility at a certain position in a specimen varies depending on the thermal activation movement at that position and the magnitude of the stress triaxial degree determined by the specimen shape such as plate thickness, hole diameter, etc. From previous research [Reza et al. (2009)], it has been found that temperature and strain rate influence the thermal activation motion when steel receives a tensile loading, therefore it is thought that the shape, temperature, and strain rate can also influence the ductile-brittle transition. 5. Conclusions We studied the impact of shear-affected-zones in punched steel on their tensile properties. We compared tensile characteristics and failure mechanisms between specimens with SAZ and without SAZ. The conclusions are below: 1. For one of the punched specimens, tensile characteristics transitioned from ductile failure to brittle fracture. 2. For punched specimens, shear cracks caused by shear stress are initiated in the SAZ under tensile loading. The shear cracks may cause the steel tensile characteristics to transition from ductile failure to brittle fracture in steels with severe plastic strain localization such as PH8. 3. The strain rate is thought to affect the ductile-brittle transition in punched specimens also, just like in the general case of an un-holed specimen. References Hamada, S., Zhang, K., Zhang, J., Koyama, M., Yokoi, T., Noguchi, H., 2018a. Effect of shear-affected-zone on fatigue crack propagation mode, International Journal of Fatigue 116, 36-47. Hamada, S., Zhang, J., Zhang, K., Koyama, M., Tsuchiyama, T., Yokoi, T. and Noguchi, H., 2018b. Ductile-to-brittle transition in tensile failure due to shear-affected-zone with a stress-concentration source: A comparative study on punched-plate tensile-failure characteristics of precipitation-hardened and dual-phase steels. International Journal of Fracture, submitted for publication. Hosokawa, A., Wilkinson, D.S., Kang, J., Kobayashi, M., Toda, H., 2013. Void growth and coalescence in model materials investigated by high resolution X-ray microtomography: Influence of work hardening behavior on ductility, International Journal of Fracture 181, 51-66. Kaufman, J.G., 1970. Progress in fracture testing of metallic materials, in “ ASTM Special Technical Publication 463 (STP 463): Review of Developments in Plane Strain Fracture Toughness Testing ”. In: American Society for Testing and Materials, Philadelphia, PA, pp. 3 -21. Korsgren, P., Sperle, J.O., Trogen, H., 1989. Influence of shearing and punching on the fatigue strength of hot rolled steel sheet, Scandinavian Journal of Metallurgy 18, 203-210. Levy, B. S., Van Tyne, C. J., 2008. Failure During Sheared Edge Stretching, Journal of Materials Engineering and Performance 17, 842-848. McClintock, F.A., Kaplan, S.M., Berg, C.A., 1966. Ductile fracture by hole growth in shear bands, International Journal of Fracture Mechanics 2, 614-627. Reza, A., Robert, E., Reed-Hill, 2009. Physical Metallurgy Principles - 4 Version, Cengage Learning. Rogers, H.C., 1960. The tensile fracture of ductile metals, Transactions of the Metallurgical Society of AIME 218, 498-506. Sánchez, L., Gutiérrez-Solana, F., Pesquera, D., 2004. Fatigue behaviour of punched structural plates, Engineering Failure Analysis 11, 751-764.