Impedance Matching between the Bars of the Polymeric SHPB Technique and the Specimen : Experimental and Analytical Studies

Abstract

High polymers or composite materials with lightness and formability have widely been used in various industries. It is well known that these materials show the viscoelastic behavior; the deformation remarkably depends on the time or strain rate. It is, therefore, very important to understand the dynamic behavior technologically. To this end, the split Hopkinson pressure bar techniques using polymeric materials (polymeric SHPB technique) have been used as a method of evaluating the compressive impact characteristics of various viscoelastic materials. However, the accuracy of the method depends on the specimen geometry and mechanical properties of test materials. In this research, therefore, a method of calculating the experimental strain waveform obtained by the polymeric SHPB technique is proposed. The calculations of reflection and transmission at interfaces are considered based on the one-dimensional theory in the frequency domain. The amplitude of reflected strain pulse and the stresses at both interfaces of the specimen are analyzed by changing the mechanical impedance of the specimen. The uniform deformation within the specimen is required in the polymeric SHPB technique. Moreover, the appropriate amplitude of the reflected and the transmitted strain pulses should be measured. Next, polymeric SHPB tests are carried out by using some specimens. The complex compliances of the specimens, which are the ratio of the strain to stress in the frequency domain, are determined, and a mechanical model are identified. It is shown that the actual polymeric SHPB tests should be performed based on the appropriate impedance matching between the specimen and input/output bars studied by the numerical experiments.