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Catherine Froustey et al. / Procedia Structural Integrity 2 (2016) 1959–1966 Author name / Structural Integrity Procedia 00 (2016) 000–000

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In-situ infrared imaging and structural analysis of recovered aluminum samples subjected to the dynamic loading allowed one to link the collective behavior of defects (microshears) with strain localization and adiabatic shear failure. Two characteristic stages of defects kinetics are responsible for adiabatic shear failure: formation of solitary wave collective modes and the following transforming into the blow-up dissipative structure of damage localization and crack nucleation. 4. Conclusion The stages of dynamic shear instability and ASB formation in the condition of torsional Kolsky bar test were analyzed on the phase field model and representation of out-of-equilibrium free energy of solid with defects in the Ginzburg-Landau form that was found after statistical description of collective behavior of defects. Specific type of criticality (the structural-scaling transitions) in solid with defects in terms of two structural variables (defect induced strain as damage parameter and structural scaling parameter, which reflects the current susceptibility of solid to defect growth) allowed us to link characteristic stages of shear strain instability and ASB failure with generation of collective modes of defects. These modes, that have the nature of self-similar solutions of the damage evolution equation (auto-solitary waves for the shear strain instability stage and blow-up structures as the precursor of ASB failure), provides the scaling laws for multiscale microstructure rearrangement responsible for characteristic stages of the ASB formation. Optical, TEM and microdiffraction study of the adjacent areas at the ASB fracture surface in aluminum revealed the sub-grain refining, pronounced aspect ratio of sub-grains in the shear localization areas and supported the scaling laws of structure rearrangement related to the types of collective modes of defects. Transition to the ASB failure is linked to the formation of the dislocation-free grains providing triple-junction sub-grain structure, anomalous hardening leading to the blow-up kinetics of free (stored) energy release. Acknowledgements This study was supported by the Russian Science Foundation, project № 14-19-01173. References Austin, R. A., McDowell, D. L., 2011. A dislocation-based constitutive model for viscoplastic deformation of fcc metals at very high strain rates. Int. J. Plast. 27, 1–24. Bai, Y. L., 1982. Thermo-plastic instability in simple shear. J. Mech. Phys. Solids 30 (4), 195–207. Bai, Y., Dodd, B., 1992. Shear Localization: Occurrence Theories and Applications. Pergamon Press, Oxford, UK, pp. 375. Bak, P., Clifton, R. J., Duffy, J., Hartley, K. A., Shawki, T. G., 1984. On critical conditions for shear band formation at Batra, R. C., Chen, L., 2001. Effect of viscoplastic relations on the instability strain, shear band initiation strain, the strain corresponding to the minimum shear band spacing, and the band width in a thermoviscoplastic material. Int. J. Plast. 17, 1465–1489. Bronkhorst, C., Cerreta, E., Xue, Q., Maudlin, P., Mason, T., III, G. G., 2006. An experimental and numerical study of the localization behavior of tantalum and stainless steel. Int. J. Plast. 22 (7), 1304–1335. Cerreta, E., Frank, I., Gray, G., Trujillo, C., Korzekwa, D., Dougherty, L., 2009. The influence of microstructure on the mechanical response of copper in shear. Mater. Sci. Eng. A 501 (1-2), 207–219. Daridon, L., Oussouaddi, O., Ahzi, S., 2004. Influence of the material constitutive models on the adiabatic shear band spacing: MTS, Power Law and Johnson-Cook models. Int. J. Solids Struct. 41, 3109–3124. Giovanola, J.H., 1988. Adiabatic shear banding under pure shear loading . Part 1: direct observation of strain localization and energy dissipation measurements. Mechanics of Materials, 7, 59-71. Grady, D. E., Kipp, M. E., 1987. The growth of unstable thermoplastic shear with application to steady-wave shock compression in solids. J. Mech. Phys. Solids 35 (1), 95–119. high strain rates. Scripta Metall. 18 (5), 443–448. Lyapunova, E.A., Petrova, A.N., Brodova, I.G., Naimark, O.B., Sokovikov, M.A., Chudinov, V.V., Uvarov, S.V., 2012. Morphology of multiscale defect structures and plastic strain localization during impact perforation of A6061 alloy targets. Technical Physics Letters, 38, 13 20. Marchand, A., Duffy, J., 1998. An experimental study of the formation process of adiabatic shear bands in a structural steel. Journal of the Mechanics and Physics of Solids 36, 251-283. McDowell, D. L., 2010. A perspective on trends in multiscale plasticity. Int. J. Plast. 26 (9), 1280–1309.