13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- 4. Conclusions In the present paper, the newly developed fracture test equipment, techniques, and methodology based on moiré interferometry are presented in detail. Through real-time observation of fracture process around the crack tip and image acquisition of the moiré fringe at different loads, the magnitude of elastoplastic deformation and corresponding fracture parameters are extracted using the wave-front interference principle. In the test of TC11 finite specimen with through-thickness crack under mixed mode I-II loading, the duration from the beginning of loading to the ultimate fracture of specimen is relatively short, thereby causing difficulty in the determination of crack initiation moment. Moreover, no stable crack growth process is involved prior to the occurrence of unstable crack propagation. Concerning the common fracture mechanism on crack initiation, and the stable and unstable growth of metallic material, further investigation should be conducted to tell whether the size of crack tip plasticity zone on the surface can be adopted as a characteristic quantity of fracture. At the same time, the anomalous thickness effect of TC11 titanium alloy is reported, and the essence of this phenomenon is waiting to be uncovered. Acknowledgements The present work was supported by the National Natural Science Foundation of China (Grant nos. 61163048 and 11002066), the Aviation Science Foundation of China (Grant no. 2012ZF56027), and the Scientific Research Foundation of Key Laboratory of Nondestructive Testing, Ministry of Education (Grant no. ZD201129007). References [1] G.C. Sih, S. Tu, Z. Wang, Multiscaling Associated with structural and material integrity under elevated temperature. East China University of Science and Technology Press, Shanghai, 2006. [2] Z. Wen, Z. Yue, Fracture behaviour of the compact tension specimens of nickel-based single crystal superalloys at high temperatures. Mat Sci Eng A, 456(2007) 189-201. [3] S. Tu, F. Xuan, G. Wang, Recent progress in high temperature mechanical behavior of materials and structures. Chinese Journal of Solid Mechanics, 31(2010) 679-695. [4] H. Shi, X. Ma, T. Yu, Some new progresses on the research of creep and fatigue behaviors of high temperature structural materials. Chinese Journal of Solid Mechanics, 31(2010) 696-715. [5] S. Tu, F. Xuan, W. Wang, Some critical issues in creep and fracture assessment at high temperature. Acta Metallurgica Sinica, 45(2009) 781-787. [6] F. Erdogan, Fracture mechanics. Int J Solids Struct, 37(2000) 171-183. [7] A. Kotousov, Fracture in plates of finite thickness. Int J Solids Struct, 44 (2007) 8259-8273. [8] W. Guo, Three-dimensional analyses of plastic constraint for through-thickness cracked bodies. Engng Fract Mech, 62 (1999) 383-407. [9] T. Nakamura, D.M. Parks, Three-dimensional crack front fields in a thin ductile plate. J Mech Phys Solids, 38(1990) 787-812. [10] X.M. Kong, N. Schluter, W. Dahl, Effect of triaxial stress on mixed-mode fracture. Engng Fract Mech, 52(1995) 379-388. [11] H. Yuan, W. Brocks, Quantification of constraint effects in elastic-plastic crack front fields. J Mech Phys Solids, 46(1998) 219-241. [12] Y.R. Arun, R. Narasimhan, An experimental investigation of constraint effects on mixed mode
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