On Interconversion of Various Material Functions of PMMA

The interconversion between various linear viscoelastic functions for Poly (methyl) methacrylate (PMMA) is explored. With the availability of four time or frequency-dependent material functions (shear, bulk, uniaxial and Poisson) on the same material, various material functions are computed using the correspondence principle of the linearized theory of viscoelasticity through the use of standard relations. Computed material functions are evaluated against the directly measured properties and the limitations imposed on successful interconversion due to the experimental errors in the underlying physical data are explored.It is observed that the differences between the computed and measured functions were larger than suggested by experimental error. The results intimates the need to thoroughly re-examine the applicability of time-temperature superposition principle often employed to develop 'master curves' for viscoelastic functions, especially with respect to the glassy domain.