Vibrocreep and Cyclic Damage of Polymers

Abstract

The paper concerns the time-dependent response of polymer systems subjected to superimposed static and cyclic loads. An overview of recent experimental results regarding the cyclic creep response of two polymers, Nylon 6/6 and polyvinylidene fluoride (PVDF) is presented. It is shown that both materials have demonstrated accelerated creep rates due to cyclic loading effects. This phenomenon, defined as “vibrocreep”, is essentially nonlinear, since the material response under combined static and cyclic loads does not represent a simple superposition of the responses to static and fully reversed cyclic loads applied separately. Further, a nonlinear constitutive model, describing the interaction between creep and cyclic damage evolution in polymers is formulated. This constitutive model combines the concepts of linear viscoelastic theory of hereditary type with damage characterization using a damage function. It is shown that the damage function depends on the number of loading cycles and can be determined experimentally. In the paper, experimental results validating the developed constitutive model are presented.