A Novel Methodology for Non-Destructive Characterization of Polymers' Viscoelastic Properties

A procedure of non-destructive experimental tests aimed at determining the viscoelastic characteristics of the rubbers is described. After recalling the basic principles of viscoelastic theory, the experimental setup and the measurements necessary for the test are described. The procedure consists in hitting the surface of the object under test with a specially instrumented indenter. The techniques for processing the acquired signals to identify the characteristic starting and ending points of indentation in the time-histories are then illustrated. By analyzing separately the phases of the free drop of the indenter and the phase of contact between indenter and rubber, the main mechanical characteristics, such as stiffness and damping of both the instrumented indenter and the bulk of rubber under test are estimated. The methods of calculating the viscoelastic parameters of the rubber starting from the knowledge of the above mechanical parameters are then illustrated. The determined results, in terms of storage and loss moduli, are compared with those provided by classic DMA type tests. The qualitative agreement is excellent. The quantitative agreement falls in the scattering range typical for this kind of measurement. The paper is completed with a discussion of the main causes of measurement uncertainty.