The investigation of the initial stress-strain state influence on mechanical properties of viscoelastic bodies

We present a new general statement of the problem on steady-state oscillations of a non-uniform viscoelastic body, taking into account the residual stress-strain state. To derive it, we use the theory of complex modules and the correspondence principle which makes it possible to write down the problem for viscoelastic bodies in the same form as the corresponding elasticity problems by replacing the elastic characteristics with the complex functions of vibration frequency. To describe the viscoelastic behavior, we employ a three-parameter model of the standard viscoelastic body consisting of instantaneous and long-term modules, as well as relaxation time. On the basis of the statement proposed, we consider the model problems on vibrations of inhomogeneous viscoelastic rods and pipes taking into account the presence of both pre-stress and residual strain. Within the problem for the viscoelastic rod, we analyze the longitudinal oscillations and consider the pre-stress and residual strain as functions of the longitudinal coordinate. Regarding the problem for the viscoelastic pipe, we consider the plane stress-strain state and assume that the oscillations are excited by the radial load; the mechanical properties of the cylinder and the residual stress-strain state depend on the radial coordinate. The numerical solutions in both cases are based on the shooting method. For both models problems under study, we present and observe the results of the comparative analysis of the effect of pre-stress and residual deformations on the amplitude-frequency characteristics (AFC), based on the computational experiments. We also provide the analysis of such an influence of each factor on the most sensitive frequencies values. The study conducted shows that for both rod and pipe the residual strain fields have a significantly greater effect on the AFC than the pre-stress fields do. This conclusion correlates with the results obtained previously for elastic bodies.