6 Evaluating Path of Stress Triaxiality to Fracture of Thin Steel Sheet Using Stereovision 41 6.4 Conclusion A stereovision technique based on digital image correlation is applied to the evaluation of the stress triaxiality and fracture strain of thin steel sheet. A tensile testing specimen with notches made of high strength steel sheet is loaded and the surface displacements are measured from both sides of the specimen surface using two stereovision systems. Not only the in-plane strains but the through-thickness strains are evaluated from the measurement results of the displacements on the both surfaces of the specimen. The variation of the stress triaxiality at an evaluation point is evaluated from the measured strains. The fracture strain is also evaluated from the strain measurement results. Experimental results show that the stress triaxiality and the fracture strain of thin steel sheet can be evaluated by the surface strain measurement. The results can be utilized for simulating deformation and predicting fracture of a component made of thin steel sheet. References 1. Effelsberg, J., Haufe, A., Feucht, M., Neukamm, M., Du Bois, P.: On parameter identification for the GISSMO damage model. In: 12th International LS-DYNA Users Conference, pp. 1–12 (2012) 2. Ostuka, A., Miyata, T., Nishimura, S., Kimura, M., Mabuchi, M.: Effect of stress triaxiality on ductile fracture initiation of low strength steels. J. JSMS. 29(322), 717–723 (1979) 3. Bridgman, J., .W.: Studies in Large Plastic Flow and Fracture. Harvard University Press, Cambridge (1952) 4. Ma, N., et al.: Study on fracture prediction on advanced high strength steels. Trans. JASE. 47(2), 603–608 (2016) 5. Sato, K., et al.: Study on fracture prediction on advanced high strength steels. Trans. JASE. 45(6), 1099–1104 (2014) 6. Bai, Y., Wierzbicki, T.: Forming severity concept for predicting sheet necking under complex loading histories. Int. J. Mech. Sci. 50, 1012–1022 (2008) 7. Yonayama, S.: Measurement method for displacement and strain on two- and three-dimensional surface by using digital image correlation. Journal of the JSTP. 55(646), 979–983 (2014) 8. Kunio, T.: Introduction to Solid Mechanics. Baifukan, Tokyo (1977) S. Yoneyama 1995 BS Aoyama Gakuin University; 1997 MS Aoyama Gakuin University; 2000 PhD Tokyo Institute of Technology; 2000 Research Associate Wakayama University; 2004 Assistant Professor Osaka Prefecture University; 2007 Associate Professor Aoyama Gakuin University; 2015 Professor Aoyama Gakuin University.
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