13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- Figure 7. TEM Stereo pair of dislocations in fatigued René 95 [30] showing that there are four narrow slip bands, three of which are overlapping. Such information can serve to develop physically accurate models. 7. Summary In this paper connecting the pioneering researches of Alan Cottrell and a current review of modern research results, we have demonstrated a critical role for localized strain concentrations in several deformation, fracture and fatigue processes. In all cases, the strain concentration arises from inhomogeneities in the microstructure including the dislocation substructure. The subject is not complete in that our understanding remains lacking in many important areas such as for PSB’s in precipitate-bearing alloys. Accurate assessment of the true precipitate and dislocation structure will provide a sound basis for numerical modelling of industrially important materials and should also improve our ability to develop fatigue-resistant structures. In most of the literature, the effects of slip mode have been largely ignored and studies in which slip mode is varied (e.g. by controlling stacking fault energy) would be of great value. Acknowledgements The authors express thanks to colleagues and students for their contributions to our knowledge over the years. A particular note of thanks goes to Professor Ashok Saxena in this regards and for his presenting this paper for us at the ICF13 meeting. References [1] S.D. Antolovich and R.W. Armstrong, Plastic Strain Localizations in Metals: Origins and Consequences, accepted for publication in Prog. Mater. Sci., to appear in 2013. [2] A.H. Cottrell, Theory of Dislocations, Prog. Met. Phys., 1, (1949), 77-126. [3] A.H. Cottrell, Dislocations and Plastic Flow in Crystals, Oxford University Press, Oxford, UK, 1953. [4] J.D. Eshelby, F.C. Frank and F.R.N. Nabarro, The Equilibrium of Linear Arrays of Dislocations, Philos. Mag., 42, (1951), 351-364. [5] R.W. Armstrong and T.R. Smith: Dislocation Pile-up Predictions for the Strength Properties of Ultrafine Grain Size FCC Metals, in: Processing and Properties of Nanocrystalline Materials Eds, C. Suryanarayana, J. Singh and F. H. Froes, TMS, Warrendale, PA., (1996) 345-352. [6] R.W. Armstrong and S.D. Antolovich: The Grain Size Dependence of Cleavage Cracking in -Iron, 18th European Conference on Fracture, Dresden, Germany, August 30-September 3, 2010. Published in conference proceedings. [7] A. H. Cottrell, Theory of Brittle Fracture in Steel and Similar Materials, Trans. TMS-AIME 212, (1958), 192-203. [8] R.W. Armstrong, Dislocation Pile-ups: from {110} Cracking in MgO to Model Strength Evaluations, Mater. Sci. Eng. A, 409, (2005) 24-31. [9] S.D. Antolovich and K.O. Findley, A New Look at Attractive/Repulsive Junctions and Cleavage Crack Formation in BCC Materials, Eng. Fract. Mech., 77, (2010), 201-216
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