THE CHOICE OF RELAXATION IN DESCRIBING MECHANICAL CHARACTERISTICS OF HIGH TEMPERATURE AREA OF DISSIPATIVE LOSS IN THE SPECTRUM OF INTERNAL FRICTION

Abstract

The analysis of experimental internal friction spectrum tgδ - f(T) shows that monocrystalline metallic materials possess the simplest spectrum. For those materials, dissipation of a part of the energy of external power impact exists in a form of internal friction background. The background increases slightly and monotonously at homologous temperatures θ < 0.2 ÷ 0.4, and it increases exponentially at θ ˃ 0.4. Taking into consideration the fact that monocrystalline systems may contain defects in the form of disturbance, and the concentration of point defects related to implantation atoms is minimal, one can suppose that this monocrystalline system consists of one aggregate subsystem having flat defects. Different analytical functions, which are often used in describing the inelasticity phenomenon, were studied as relaxation cores for describing the inelastic response of such subsystem in the area of increasing relaxation background of dissipative loss. It is shown that Rabotnov’s, Rzhanitsin’s and Havriliak-Negami’s cores don’t satisfy the asymptotic conditions for the convergence of series with positive values of incoming characteristics. In this case they cannot be used as relaxation functions describing the response of the aggregative subsystem in the temperature range which is higher than homologous temperature 0.4. Description of the viscoelastic response of the high-temperature background internal friction and, accordingly, of the temperature-frequency change of shear modulus is possible only when using Maxwell’s or Kolrausсh’s function which transforms into Maxwell’s function only at a single value of fractionality parameter.

Keywords

• internal friction
• inelasticity
• relaxation
• core relaxation