Cyclic creep of polymers and polymer-matrix composites

The paper provides a state-of-the-art review of the current understanding regarding the long-term response of polymer-matrix composites subjected to cyclic loading conditions. Typically, under such conditions, the behavior of polymeric systems is characterized by much higher creep rates than those observed in the cases of static loading. In this paper, research accomplishments in the subject area are discussed. New experimental results are presented regarding the cyclic-creep response of a composite system consisting of a thin-film piezoelectric polymer polyvinylidene fluoride (PVDF) with thin metallic layers deposited on both surfaces of the polymer. This composite was tested under the conditions of tensile static stresses with superimposed sinusoidal oscillations. As a result, considerable acceleration of creep rates has been recorded as the mean stresses, vibration amplitudes, and frequencies of oscillations tended to increase. These effects were observed even within the linear viscoelastic deformation range at room temperature: however, the acceleration of cyclic-creep rates tended to decrease below the freezing temperature. In general, as indicated in the conclusion, the problem of cyclic creep in polymeric systems is far from being well understood and requires further studies.