Research on Several Problems in the Characterization of Lightweight Cellular Materials by Low-Impedance Hopkinson Pressure Bar

Abstract

There are great challenges in studying the dynamic mechanical behavior of lightweight cellular materials by using the traditional split Hopkinson pressure bar (SHPB) system because of the unique microstructure of such materials. To overcome these challenges, we present in this article a new experimental framework for dynamic loading tests of low-strength cellular materials from the elastic stage to the densification stage. Nylon is utilized as the compression bar in the SHPB system, and its low elastic modulus can cause larger displacement during dynamic loading. Meanwhile, polymethyl methacrylate (PMMA) inserts are attached to the bar end to prevent plastic deformation in that part, and a data correction method is employed to reduce the error caused by inserts. For the problem of wave dispersion during propagation in nylon bars, we use the in situ test method for dispersion correction to obtain more accurate results. We test a closed-cell aluminum foam by this modified SHPB test method and get ideal results. The test results of the aluminum foam show that its mechanical behavior is insensitive to the strain rate at the elastic stage and plastic collapse stage but sensitive to the strain rate at the beginning of the densification stage.