Modulus recovery kinetics end other insights into the Payne effect for filled elastomers

The nonlinear viscoelastic behavior of filled elastomers is examined in det ail using a variety of samples including carbon-black filled natural rubber s and fumed silica filled silicone elastomers. New insights into the Payne effect are provided by examining the generic results of sinusoidal dynamic and constant strain rate tests conducted in true simple shear both with and without static strain offsets. The effect of deformation history is explor ed by probing the low amplitude modulus recovery kinetics resulting from a perturbation by a large strain deformation such as a sinusoidal pulse or th e application or removal of a static strain. It is found that a static stra in has no effect on either the fully equilibrated dynamic (storage and loss ) moduli or the incremental stress-strain curves taken at constant strain r ate. The reduction in low amplitude dynamic modulus and subsequent recovery kinetics due to a perturbation is found to be independent of the type of p erturbation. Modulus recovery is complete but requires thousands of seconds , and is independent of the static strain. The results suggest that deforma tion sequence is as critical as strain amplitude in determining the propert ies, and that currently available theories are inadequate to describe these phenomena. The distinction between fully equilibrated dynamic response and transitory response is critical and must be considered in the formulation of any constitutive equation to be used for design purposes with filled ela stomers.