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Bykov D.L.,Central Scientific Research Institute for Engineering TsNIIMash | Konovalov D.N.,OT Kontakt Ltd. | Mel'nikov V.P.,The Federal Center for Dual Use Technologies Soyuz | Osavchuk A.N.,The Federal Center for Dual Use Technologies Soyuz
Mechanics of Solids | Year: 2010

The filled polymer materials exhibit viscoelastic properties in a wide time range including the millisecond range (~10-2-10 ms) characteristic of different shock loadings of structures made of these materials. We propose a method for the identification of the filled polymer material relaxation kernel in the millisecond time range; this method is based on a shock loading test of a cylindrical sample made of this material. In this test, the disk indenter acceleration is measured by using a piezotransducer. The test scheme does not impose any rigid constraints on the sample dimensions. In particular, it is possible to use samples of typical dimensions of the order of 10 cm, for which the conditions that the sample material is representative of the structure material are necessarily satisfied. The relaxation kernel parameters are identified by numerical minimization of the theoretically predicted indenter velocity deviation from the velocity-time dependence obtained by integrating the acceleration transducer readings. The minimization problem is solved by using a genetic algorithm. The problem of theoretical prediction of the indenter velocity is solved numerically by using a reduced computational scheme whose parameters are chosen from the minimum condition for the deviation from the prediction obtained in the framework of the detailed computational scheme. The use of the reduced computational scheme permits decreasing the computational costs by 3-4 orders of magnitude compared with the detailed computational scheme, which is a necessary condition for the practical applicability of the genetic algorithm in identification problems. We present examples of relaxation kernel identification in the range of 0.1-10ms from the results of the test where the disk indenter raised to the height of 1m falls on the sample end surface. © 2010 Allerton Press, Inc. Source


Bykov D.L.,Central Scientific Research Institute for Engineering TsNIIMash | Kazakov A.V.,Central Scientific Research Institute for Engineering TsNIIMash | Konovalov D.N.,OT Kontakt Ltd. | Mel'nikov V.P.,The Federal Center for Dual Use Technologies Soyuz | And 3 more authors.
Mechanics of Solids | Year: 2014

We present the results of a large series of experiments aimed at the study of laws of damage accumulation and fracture in highly filled polymer materials under loading conditions of various types: monotone, repeated, low- and high-cycle, with varying type of stress state, dynamic (in general, more than 50 programs implemented on specimens from one lot of material). The data obtained in these test allow one to make conclusions about the constitutive role of the attained maximum of strain intensity when estimating the accumulated damage in the process of uniaxial tension by various programs (in particular, an additional cyclic deformation below the preliminary attained strain maximum does not affect the limit values of strain and stress in the subsequent active extension), about the strong influence of the stress state on the deformation and fracture, about the specific features of the nonlinear behavior of the material under the shock loading conditions and its influence on the repeated deformation. All tests are described (with an accuracy acceptable in practical calculations, both with respect to stresses and strains in the process of loading and at the moment of fracture) in the framework of the same model of nonlinear viscoelasticity with the same set of constants. The constants of the proposed model are calculated according to a relatively simple algorithm by using the results of standard uniaxial tension tests with constant values of the strain rate and hydrostatic pressure (each test for 2–3 levels of these parameters chosen from the ranges proposed in applications, each loading lasts until the fracture occurs, and one of the tests contains an intermediate interval of total loading and repeated loading) and one axial shock compression test if there are dynamic problems in the applications. The model is based on the use of the criterion fracture parameter which, in the class of proportional loading processes, is the sum of partial increments of the strain intensity on active segments of the process (where the strain intensity is at its historical maximum) with the form of the stress state and the intensity of strain rates taken into account. © 2014, Allerton Press, Inc. Source


Bykov D.L.,Central Scientific Research Institute for Engineering TsNIIMash | Kazakov A.V.,Central Scientific Research Institute for Engineering TsNIIMash | Konovalov D.N.,OT Kontakt Ltd. | Mel'nikov V.P.,The Federal Center for Dual Use Technologies Soyuz | And 2 more authors.
Mechanics of Solids | Year: 2012

Determination of mechanical characteristics of filled polymer materials in shock wave processes is of interest in calculations of the strength of these materials. The standard computation methods are based on the use of the linear theory of viscoelasticity, where there is no distinction between the active and passive deformation processes. In the present paper, dynamical experiment and theoretical modeling are used to illustrate the important role played by the sharp decrease in the resistance of a filled polymer material in unloading (in the millisecond time range). The higher the degree of filling of this material, the more significant this effect is. © 2012 Allerton Press, Inc. Source


Rashkovskiy S.A.,Russian Academy of Sciences | Fedorychev A.V.,The Federal Center for Dual Use Technologies Soyuz | Milyokhin Y.M.,The Federal Center for Dual Use Technologies Soyuz | Klyuchnikov A.N.,The Federal Center for Dual Use Technologies Soyuz
International Journal of Energetic Materials and Chemical Propulsion | Year: 2010

Propellant stretching in combustion leads to an essential increase (up to 50% and more) in burn rate. Analysis of existing research regarding the influence of stretch deformations on propellant burn rate is carried out. It is shown that for composite solid propellants, the basic mechanism of increase in the burn rate under stretch conditions is detachment of the binder from particles of oxidizers, formation of additional burning surfaces, and change of structure in the burn zone. For a description of this effect, a rheological model of composite solid propellant is developed. The model takes into account a detachment of the binder from particles (oxidizers, coolers, metals, etc.) under action of stretch deformations. The criterion describing distinction in behaviors of propellant in stretch conditions with detachment of the binder from particles in comparison with a stretch of the same material without occurrence of internal defects is established. A method for experimental determination of the amount of defects arising in the propellant upon stretching is suggested based on analysis of the diagram of material stretch. A mathematical model of combustion of composite propellant under stretch conditions, taking into account a detachment of the binder from oxidizer particles, and the formation of an additional burning surface is developed. The model considers the heterogeneous structure of the propellant, the burn surface, and the gas phase. Analysis of ignition of the cracks formed on the binder-particle border as a result of detachment of the binder from particles in propellant stretch is carried out. When a burn rate shows little decrease with propellant stretch, an inverse effect can be observed under certain conditions. This effect is connected with incomplete burn-out of oxidizer particles on the propellant burn surface as a result of their detachment from the surface. Parametrical research of composite propellant combustion under the action of stretch deformations is carried out. Results of calculations are compared with well-known experimental data. Correlation between changes in propellant burn rate under stretch conditions and the parameters of the propellant stretch diagram without combustion is established. A method is developed that allows for predicting the change in propellant burn rate under stretch conditions by using the diagram of propellant stretch without combustion. © 2010 by Begell House, Inc. Source

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