13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Quantitative analysis of microcracks ensemble induced by shock-wave loading of metallic targets (vanadium and iron). Elena Lyapunova*, Oleg Naimark, Sergey Uvarov Institute of continuous media mechanics, 614013 1, Akademic Korolev St., Perm, Russia * Corresponding author: lyapunova@ icmm.ru Abstract Results of analysis of microstructure evolution of metallic samples (vanadium and iron) subjected to shock-wave loading are presented. The influence of loading velocity both on predominant mechanisms of structure deformation and fracture as well as regularities of microcracks ensemble evolution is investigated. Keywords shock-wave loading, spall, microstructure analysis 1. Introduction Understanding the material behavior under shock-wave loading has been paid a much attention for several decades because of its both practical and theoretical issues. Experimental results obtained till nowadays reveal highly complicated character of spall fracture. Changes of microstructure of material is one of the key factors among others, which reveals in nucleation, growing and coalescence of microcracks and microvoids, recrystallization processes, ets. It is not trivial problem to consider several microstructure mechanisms, for example nucleation and growing of recrystallized grains and evolution of defects (cracks, microvoids). Different kinetic models of metal behavior under dynamic loading usually use quantitative parameters characterizing size, shape or orientation of defects (microcracks or microvoids) in order to describe the role of microstructure. However there is still a big gap between experimental data and modeling results since the lack of complex information about kinetics of fracture and defect distribution corresponding to different loading rates. In the current work results of experiments on shock-wave loading of metallic targets are presented and microdefects evolution regularities during spall formation are discussed. 2. Experiment Shock-wave loading of flat metallic samples was carried out one stage gas gun. Using of coarse-grained vanadium and polycrystalline iron as a target material allowed us to investigate deformation and fracture behavior of single crystallites (on vanadium samples) as well as typical polycrystalline metal behavior (iron samples). Dimensions of cylindrical samples and corresponding mean grain size are presented in table 1. In order to obtain different loading conditions, velocity of accelerated plate-projectile was varied in the interval 230… 375 m/s which is slightly above the velocity at which spallation occurs. Analysis of spall surface and inner microstructure changes was made with using of SEM (Quanda 600) and digital optical microscope Hyrox 7700. Preparation for investigation of inner microstructure included mechanical polishing and etching of sample sections made along the loading direction. Table 1. Dimensions of samples Material Diameter, mm Thickness, mm Mean grain size Vanadium 200 5 4 mm Iron 200 10 50 mkm
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