R. J. Deigan J. J. Dlubac
Code 7451, Ship Acoustics Directorate, Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000
The accurate determination of the complex moduli of viscoelastic materials is of great importance for the efficient design of many noise control devices. It is often the case that a design, in conjunction with its acoustic performance requirements, leads to a narrow band of acceptable dynamic modulus for the viscoelastic material. In such cases knowledge of the accuracy and reliability of the measurement apparatus is essential. Dynamic complex shear modulus is measured at Carderock Division Naval Surface Warfare Center (CDNSWC) with the Dynamic Mechanical Thermal Analyzer (DMTA), manufactured by Polymer Laboratories. An attempt to quantify the absolute accuracy of the DMTA measurement has been made through the consideration of errors including the accuracy of the beam solution used to infer the complex modulus, compliance of the sample mounts, measurement noise, temperature control, thermal stress, Poisson effects, and the implementation of time-temperature superposition. With these considerations, an ad hoc error analysis is implemented to quantify absolute error bounds expected for DMTA measurements of a hypothetical material. These results are of direct interest to the ASA Committee on Standards S2WG79, ``Characterization of the Dynamic Properties of Viscoelastic Polymers,'' which has initiated round-robin testing among committee participants. CDNSWC results from the DMTA tests of three round-robin materials will be presented.