Abstract
The Finite Element (F.E.) analysis of a grip system of a servo hydraulic machine used for high speed tensile testing of polymers is here presented. State-of-the- art dynamometers use a slack adaptor to allow the machine to accelerate, in order to reach the nominal tensile speed before the load is applied, so that the entire test is conducted at constant speed. In this case the sudden application of the load causes the onset of stress waves that can excite the system, causing it to oscillate at its natural frequency. This phenomenon, called “system ringing”, is here examined through the analysis of the frequencies characterizing the oscillations in the initial transient of the tensile test. It will be shown that this analysis can be a suitable tool for assessing what is the maximum strain rate achievable with a given equipment. We also show that the stress oscillations contain information that can be related to material properties and, consequently, can be used for their measurement through simple spectrum analyses. Some examples are reported for an easy determination of the Young modulus of a Polypropylene (PP) based compounds from the Fast Fourier Transform (FFT) of the force signal.

Keywords
polymers; high speed tensile tests; system ringing; FFT; strain rate

Cite this paper
M.Nutini, D.Sinnone, M.Vitali, Numerical investigation of System Ringing and Stress Oscillations in High Speed Tensile Test on Polymers , SCIREA Journal of Mechanical Engineering. Volume 3, Issue 1, February 2020 | PP. 1-19.

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