Vibrational creep of polymer materials

Abstract

In the mechanics of deformed solids it is usually assumed that superposing small amplitude vibrations on a static load has no effect on the over-all characteristics of a material under strain. This hypothesis is reflected in the fact that the existing equations of state for the case of static loads with superposed small vibrations give deformation characteristics which differ little from the corresponding parameters of deformation processes taking place in the absence of excitations. At the same time, substantial changes in the deformation characteristics of a number of materials are observed under certain conditions after the application of alternating stresses of small amplitude. Reports on studies of creep of metals [1, 2], elastomers [3], and concrete [4] have been published, in which the fatigue curves obtained with small vibrations superposed on static loads lie above curves obtained for static loads corresponding to the maximum pulsating load level. Attempts have been made to explain this effect from the standpoint of the molecular-kinetic [3] and phenomenological [5] theories. Certain theoretical considerations and experimental data, discussed in this article, show that superposing a small dynamic component on a static load leads to an increase in the rate of creep of several polymer materials. This effect, which is due mainly to an increase in the polymer temperature as a result of dissipation of vibrational energy, differs from the “vibration effect” observed on elastomers by Slonimskii and Alekseev [3], in which the temperature rise due to the heat generated by vibrations plays no substantial part.