Theoretical Representations of the Thermokinetics of Thermal Destruction of Polymers
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 6, November, 2020
HEAT CONDUCTION AND HEAT TRANSFER IN TECHNOLOGICAL PROCESSES THEORETICAL REPRESENTATIONS OF THE THERMOKINETICS OF THERMAL DESTRUCTION OF POLYMERS É. M. Kartashov
UDC 539.3
A generalized theory of the thermokinetics of the process of thermal destruction of polymer materials has been developed in the context of the kinetic thermofluctuating concept based on unification of a number of independent approaches, namely, structurally kinetic (for describing elementary acts of the destruction process), mechanical (for describing the local stress at the crack tip), thermodynamic (for calculating the value of safe stress). The developed model concepts are based on experimental data relating to accumulation of disturbances in loaded samples; on force disturbances and ruptures of bonds in the vicinity of the crack tip; on submicroscopic cracks and their characteristics; fractographic investigations of the rupture face; and on the kinetic of growth of a main crack. A generalized formula of the rate of crack growth is given, the tensor of stresses at the crack tip in the conditions of mechanical and thermal loadings is calculated, the main parameters and limiting characteristics on mechanical and thermal loading of a polymer sample are calculated, a theoretical relation of the time dependence of strength in the case of a purely thermal loading in the full interval of thermal loadings from a safe to a critical one and at the stage of athermal growth of the crack has been suggested. Numerical experiments are presented. Keywords: time dependence of strength, longevity curve, full interval of thermal loadings; safe, critical, and limiting characteristics, parameters of the process of thermal destruction. Introduction. The modern constructional and functional polymer materials representing a collection of micro- or nanostructural elements are called structurally sensitive materials [1]. Their creation on the basis of nanotechnologies is an important direction of the development of the modern material science. Such materials have unique physicomechanical and thermophysical properties allowing one to use them in constructions subjected to high-intensity external effects [2]. An important stage in the creation and use of the indicated materials is the development of mathematical models for desorbing the behavior of these materials in a wide range of variation of external effects. The general methodology of constructing such models is far from being resolved. This refers in the first place to the processes of thermal destruction of materials in the course of action of intense heat fluxes on solid bodies. The indicated direction of investigations constitutes the content of the problem of thermal strength, the importance of which increased in recent decades in connection with the creation of powerful energy radiators and their use in technological operations. There is an enormous quantity of publications that describe these processes in the nuclear power eng
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