Using DMA to Simultaneously Acquire Young's Relaxation Modulus and Time-dependent Poisson's Ratio of a Viscoelastic Material

A method to obtain the Young's relaxation modulus and time-dependent Poisson's ratio simultaneously by using DMA is developed with the assumption of constant bulk modulus instead of constant Poisson's ratio. The constant bulk modulus is then calculated by either instantaneous response or the equilibrium response of the time-dependent Poisson's ratio. The modulating Young's moduli and characteristic times that measured by DMA are corrected analytically by using the developed formulas. The time-dependent Poisson's ratio is then obtained from the corrected modulating Young's moduli and the constant bulk modulus. As an application example, the method is applied to the DMA measurement of an epoxy molding compound (EMC). Although the correction to Young's relaxation modulus is very small, the viscoelastic Poisson's ratio varies significantly over time from 0.4 to 0.496, and can’t be assumed as a constant.