Natalia Saveleva

The results of study of the behavior of natural materials (quartzite, sandstone, andesite) under quasi-static, dynamic loading and low-speed indentation (10-3-103 1/s) are presented. The experimental conditions made it possible to preserve fragmented samples and to analyze the statistics of the preserved fragments by size (mass). During the research, a system of laboratory sieve and an HR202i electronic scales with a measurement error of 0.0001 g were used. The method of processing fragment photographs allowed us to establish the number and mass of fragments on sieves with cell sizes up to 0.063-0.05 mm, not less than 99% of the sample weight and minimize measurement error. The obtained cumulative distributions of fragments by mass N(mf) show a change in the shape of the inflection and a shift of the inflection point toward smaller scales with increasing strain rate. The data analysis reflects the similarity of the statistics of fragmentation according to the power law and asymptotic fracture modes with multiple ruptures obtained according to the brittle fracture scenario. It is shown that specimens fracture occurs according to different scenarios depending on loading conditions and is associated with a change in the rate of transition from one stage of crack appearance(or accumulation of stress states, defective structure) to another (crack formation and complete fragmentation). It has been found that the formation of fragments is of an “automodel” nature.

Mechanisms of structural relaxation are linked with the metastability of nonequilibrium potential of solid with defects and the generation of collective modes of defects responsible for the plastic strain and damage localization. It is shown that spatial-temporal dynamics of collective modes (auto-solitary and blow-up dissipative structures) provide the anomalous relaxation ability of nonlinear system “solid with defects” in the conditions of the specific type of criticality – structural-scaling transition. These modes have the nature of self-similar solutions of evolution equations for damage parameter (defect-induced strain) and represent the “universality class” providing the four power law for a steady plastic front, splitting of an elastoplastic shock wave front, and elastic precursor decay kinetics. Wide-range constitutive equations reflecting the linkage between defect-induced mechanisms and structural relaxation are used in the numerical simulation for shock wave loading of metals and ceramics in the comparison with experiments.

The paper presents the results of numerical simulation of plate impact loading for an aluminum alloy AMg6 to clarify thermodynamic and kinetic aspects of the transition from elastic to plastic fronts. This transition is connected with the metastability of out-of-equilibrium potential that reflects the type of criticality of solid with mesodefects—the structural-scaling transition. The modeling of mesodefects kinetics allowed one to establish the connection with mechanisms of defect induced structural relaxation responsible for the elastic precursor decay in metals. It was shown that transition from elastic to plastic fronts is realized due to the free energy release with kinetics related to metastability decomposition.

Full wave profiles were monitored by the laser interferometry method by means of a VISAR laser Doppler velocimeter under shock-wave loading of samples of AMg6 aluminum alloy. Analysis of these...

Формирование упругопластических фронтов и откольное разрушение в сплаве АМг6 при ударных воздействиях

This paper reports on the modeling of the behavior of a 5056 aluminum alloy plate target subjected to shock wave loading using the structural-statistical model that links multiscale defect kinetics, relaxation properties (plasticity) and the kinetics of damage-failure transition related to the generation of multiscale collective modes of defects (solitary waves in a defect ensemble in the case of plastic relaxation) and blow-up collective modes as a precursor of damage-failure transition. The important part of the numerical study is the identification of material parameters using the data of quasi-static and dynamic tests for aluminum alloy samples and the verification of the model and the identification procedure in the course of the simulation of plate impact loading of the aluminum alloy target.

Specific features in the deformation of polycrystalline vanadium under shock-wave loading conditions have been studied by experimental and theoretical methods. Analysis of the full wave profiles was...