Poisson's ratio for viscoelastic materials

Abstract

A technique for obtaining Poisson's ratio for materials undergoing large strains has been developed. The change in volume of a specimen is measured during a compression test which allows specimen volume to be obtained as a function of compressive strain in the specimen. Once volume changes have been obtained, Poisson's ratio may be computed from the volume changes by means of the relationships derived for large strains. The volume change is measured by compressing the specimen while it is submerged in mercury and simultaneously recording the mercury liquid level and crosshead movement of the testing machine. Readings were taken at time intervals large enough so that adequate time elapsed for near-equilibrium conditions to prevail. The reproducibility and accuracy of each of the pertinent dimensions and measurements were also carefully determined so that the error in the computed Poisson's ratio could be evaluated. Error analysis indicates that Poisson's ratio can easily be determined by this technique within an error of 0.005. Experimental results also indicate that values of Poisson's ratio that exceed 0.500 have been measured which may mean that this technique may be used to detect phase changes in the material.