The influence of inelastic deformations on the reverse thermoelastic transformation start temperature in shape memory alloys | Mekhanika | kompozitsionnykh | materialov i konstruktsii
> Volume 25 > №1 / 2019 / Pages: 3-18

The influence of inelastic deformations on the reverse thermoelastic transformation start temperature in shape memory alloys

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Abstract:

The first part of the article presents experimental data indicating that the temperature of the onset of reverse martensitic or rhombohedral phase transformation in titanium nickelide in the absence of stresses increases with increasing initial phase-structural deformation of the material. This effect can not be described in the framework of the known model of nonlinear deformation of shape memory alloys in phase and structural transformations, since according to the constitutive relations of this theory, the change in the temperature of the onset of the reverse transformation is proportional to the convolution of stress deviators and initial phase-structural deformations, which turns into zero at zero stress. This effect is not described in the framework of most known phenomenological models of SMAs thermomechanical behavior.In this paper, to describe the effect under consideration, it is proposed to add to the expression for the Gibbs potential of the SMA a nonadditive term that is a function of the invariant of the phase-structure deformation deviator. According to this assumption, using the formalism adopted in rational thermodynamics, as a consequence of the first and second laws of thermodynamics, expressions were obtained for the temperature of the onset of an inverse thermoelastic phase transition containing a term that does not vanish at zero stress. The question of the sign of this term is analyzed.The formulation of the coupled energy balance equation taking into account the change in the expression for the Gibbs potential is also obtained. By comparison with the experimental data, the sign of the Gibbs potential additional term derivative and the values of the additional constants of the proposed model are determined. The question of the effect of the proposed change in the model on the values of the characteristic temperatures of direct thermoelastic phase transformation is discussed.

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