Experimental and numerical characterization of a polymeric Hopkinson bar by DTMA

This paper is focused on the study of wave propagation in long Split-Hopkinson Pressure Bar (SHPB) setups made of polyethylene terephthalate (PET). The first step was the set up and the validation of an analytical formulation and of a FE model based on viscoelastic parameters, borrowed from literature; then, Dynamic-Mechanical Thermal Analysis (DTMA) has been conducted at different temperatures and frequencies, in order to obtain the storage and loss moduli of the real PET, as functions of the frequency. Experimental curves were shifted in order to extrapolate storage and loss master functions up to several kHz and to identify the stiffness and the damping parameters of a generalized Maxwell model. The obtained parameters were used to compute the attenuation factor and the wave number, which allows the analytical investigation of wave propagation in long bars. The proposed characterization method based on DTMA was applied to pressure waves experimentally measured on the SHPB made of PET; results were compared with the well-established “transfer function” method. Finally, an SHPB experiment was simulated using the FE model, in order to assess the impact of the proposed wave propagation analysis on the reconstructed stress-strain curve of a low impedance material.