О способах идентификации нелинейного соотношения вязкоупругости Работнова по семейству кривых релаксации с учетом начальной стадии деформированиястатья
Статья опубликована в журнале из списка RSCI Web of Science
Аннотация:IDENTIFICATION OF THE RABOTNOV NON-LINEAR VISCOELASTICITY RELATION USING STRESS RELAXATION CURVES WITH ARBITRARY INITIAL STAGES OF DEFORMATIONА.V. KhokhlovAbstractThe Rabotnov nonlinear constitutive equation for non-aging elasto-viscoplastic materials containing two material functions is studied analytically to elucidate the set of basic rheological phenomena which it is able to simulate, to outline the areas of material functions influence, to indicate application field of the relation and to find the ways of its identification and fitting. General properties of the relaxation curves generated by the Rabotnov equation under arbitrary non-decreasing strain histories at initial stage of deformation up to a given strain level are investigated in uni-axial case assuming material functions of the relation are arbitrary. Influence of an initial stage shape and rise time influence on the properties of the theoretic relaxation curves are examined. Stress rate jump at final point of a an initial stage, monotonicity and convexity intervals of relaxation curves, their asymptotic behavior at infinity and conditions for convergence to zero of the deviation from the relaxation curve under instantaneous (step) deformation to the same strain level with time tending to infinity are examined. Effective general bounds have been obtained for differences of relaxation curves with different initial programs of deformation up to a given level and for their deviation from the relaxation curve under step loading via material functions and initial programs norms. As the rise time tends to zero, convergence of the relaxation curves family (with fixed strain level and initial stage shape) to the relaxation curve under step loading has been proved.The analysis reveals several characteristic features of the theoretic stress relaxation curves that can be employed as the relation applicability (or non- applicability) indicators which are convenient for check in relaxation tests. The ways of the relation identification are outlined.