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Interest in accurate measurements of the time-dependent Poisson's ratio of polymers arises because it is a component commonly needed in stress analysis and it appears in most theories predicting the behavior of filled materials and composites. Because of the paucity of data and the difficulties in determining [...](t) experimentally, it has been customary in the past to treat [...](t) as a constant. This is unsatisfactory theoretically and inadequate for accurate work.

An apparatus has been constructed that enables us to measure tensile relaxation modulus, E(t), and time-dependent Poisson's ratio, [...](t), simultaneously on the same specimen under the same experimental condition. The apparatus, which contains several novel features, is essentially in working condition. Experiments will be made on a series of selected polymers.

We hope to be able to determine the bulk relaxation modulus, K(t), and the shear relaxation modulus, G(t), from measurements of E(t) and [...](t). A method for solving the appropriate convolution integrals to determine K(t) and G(t) is already available. It would be desirable to compare the calculated G(t) and K(t) with direct measurements. The latter are very difficult. Direct measurements of G(t) will be made in a torsional relaxometer on the same specimen but not under identical conditions. Nevertheless, these data will be useful as a check on our measurements and our method of calculation.

This work will allow a comparison to be made between shear and bulk relaxation via the spectral functions. The measurements will ultimately form the basis for the development of a theory of bulk relaxation in polymeric materials.

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