Testing viscoelastic solids

Abstract

An apparatus and method for testing viscoelastic solids, such as tire cord. The apparatus includes: holding means, pretension means, first and second displacement generators, and mechanical-electrical transforming means. The holding means holds the material in a predetermined position. The pretension means applies tension during testing. The first displacement generator has an eccentric means for applying cyclic displacement. The second displacement generator applies cyclic displacement to the material co-directional with that applied by the first displacement generator, but of smaller amplitude and higher frequency. The mechanical-electrical transforming means transforms mechanical motion into electrical signals, such as a stress signal, a strain signal and a differentiated strain signal. The apparatus may also include means for differential testing of duplicate material samples wherein one sample is subjected to cyclic displacement of both the first and second displacement generators, and the other sample is subjected to cyclic displacement of the first displacement generator only. The apparatus may further include integrating means for integration of a stress-strain hysteresis loop. The method includes: applying a basic substantially sinusoidal strain wave having superimposed a cyclic strain wave of smaller amplitude and higher frequency than the basic strain wave to the material, with resulting stress developed in the material; transforming the resultant strain into an electrical strain signal having a strain wave form; transforming the resulting stress into an electrical composite stress signal having a composite stress wave form; and determining cyclic changes in that component of the composite stress signal resulting from the superimposed strain wave as a function of the basic strain wave.