Split Hopkinson Bar Method Using Viscoelastic Stress Bars.

Abstract

The split Hopkinson bar (SHB) method has been widely used to study mechanical behavior of materials at high strain rates. In this paper, we present a new kind of SHB technique to study dynamic behavior of materials having low characteristic impedance, such as polymers or composite materials. To enable better matching of characteristic impedance between specimens and stress bars, polymethyl methacrylate (PMMA) bars, which are considered to be viscoelastic, and whose viscoelastic properties were determined in advance through preliminary experiments, are used as the input and output stress bars. In this method, the wave analysis of the stress pulses is executed in the frequency domain. Strain histories of the PMMA stress bars resulting from a SHB test are resolved into frequency components by the fast Fourier transform, and mean stress and strain of the specimen are subsequently determined as functions of frequency. Employing the Fourier inverse transformation, the stress-strain relation of the specimen can be obtained. It is found that the proposed SHB method provides reasonable estimations of the dynamic properties of materials having low impedance, such as polymers.