A unified real time approach to characterizations of isotropic linear viscoelastic media from 1-D experiments without use of poisson's ratios

It is shown that for linear isotropic elastic and viscoelastic materials a single type of 1-D set of tension experiments supplies sufficient stress and strain data to completely characterize all moduli (including Young's, shear and bulk ones) and all compliances for isotropic viscoelastic media. This is accomplished directly in real time space without the use of integral transforms and/or Poisson's ratios and includes the complete history of loading and of displacements including their build ups. Additionally, several approaches to the determination of instantaneous moduli from 1-D quasi-static and dynamic experimental data are presented and evaluated. Unfortunately, none provided reliable instantaneous moduli based on quasi-static experiments. Three analytical and experimental procedures for properly describing the loading phase were investigated. The newly developed protocol based on accelerations rather than measured strains was found to be best suited to determine the loading times at which quasi-steady conditions are achieved. It is recommended as to protocol of choice to characterize the loading time history. A simple protocol for validating viscoelastic material linearity is developed demonstrating that the tested high polymer behaves linearly at strains in excess of 10%.