Viscoelastic Material Characterization Relative to Constitutive and Failure Response of an Elastomer

摘要

This program sought to determine the time-dependent (viscoelastic) response of an elastomer at various temperatures to be able to construct the uniform master relaxation response, from which the mechanical responses under a wide range of prescribed load or deformation histories may be deduced at any reference temperature. Particular attention was devoted to the precision with which the loads and deformations could be determined. Strain measurements were taken for monitoring purposes by means of the digital image correlation method. Because of the desire to determine the time-dependent Poisson behavior, digital image correlation was attempted in both the axial and transverse directions. While consistent data were obtained for strain monitoring in the axial direction, the precision with which lateral strains could be determined over long periods of time was not sufficient to specify the volumetric or bulk behavior in the rubbery domain. The report is divided into several parts, namely a summary of linear viscoelasticity principles, the delineation of the experimental requirements, and verification of the test method's precision. In this context, it is of interest to note that test machine precision was found to be insufficient to prescribe axial strains on the uniaxial specimens of below about 1-2%. However, a 2%-strain prescription was still able to render the essentially linearly viscoelastic behavior of the material. The time- temperature superposition method provided a master relaxation function for the elastomer and determined its glass transition temperature to be near -50 degrees C. The range of modulus values measured over a temperature-reduced time range of 15 decades varied by a factor of about 12-15. By usual standards of polymer behavior in the transition range this is not a very large variation, though not abnormally small, especially if one considers that the full range of the glass-to-rubber transition has not been captured.