Theoretical Simulation of an Anomalous Response in a Torsional Oscillator

In a torsional oscillator, constructed by stretching a hollow cylindrical natural rubber member and connecting one end to a fly wheel and the other end to a fixed support, an anomalous behavior has been experimentally observed which is attributed to crystallization in the rubber. The anomalous behavior is observed when the rubber is stretched to more than 3.5 times its initial length and is characterized by a reduction in the period of the oscillator during stress relaxation. This indicates a gradual increase in the torsional rigidity of the rubber which can be explained by crystallization. Analyzing the response of the oscillator based on modeling the rubber as an incompressible isotropic elastic or viscoelastic material predicts a behavior opposite to that observed in the experiments. Using a model developed for characterizing mechanical response during crystallization in polymers, the anomalous behavior of the oscillator is reproduced.