Relaxation response of polyurethane elastomers

Abstract

AbstractThe transient extension relaxation modulus E(t) and the lateral contraction ratio vr(t) for a polyurethane elastomer have been simultaneously measured in the transition region from the glassy to the rubbery consistencies of the material. The differential moiré method was used in these measurements and yielded simultaneous values of the longitudinal extension and the lateral contraction principal strains of the tension specimen. Composite curves of E(t) and vr(t) reduced to a standard temperature were obtained by applying the method of reduced variables. The time factors KT in both curves were coincident and they followed the WLF equation. The shear and bulk modulus characteristic functions were determined from the extension modulus and lateral contraction ratio functions. The values of the lateral contraction ratio in relaxation were determined by using data of the extension relaxation modulus along the whole viscoelastic range and the initial value of the lateral contraction ratio at the rubbery state and applying an indirect method. The results obtained by the indirect method coincided with the experimental values. The shear modulus function was evaluated from the extension relaxation modulus and the lateral contraction ratio functions and compared with the shear dynamic compliance determined by Landel. The experimental data indicated that a linear relationship holds between the lateral contraction ratio in relaxation and the bulk modulus along the whole response spectrum. The same relationship was previously shown to hold for a series of various polymeric substances.