The Hugoniot and Strength of Ultem 1000 Polyetherimide

Abstract

Parallel-plate impact studies using a single stage powder gun have been performed to investigate the shock and subsequent release behavior of the commercial polyetherimide polymer Ultem™ up to 13 GPa. Two different experimental configurations were used to observe both the shock and unloading behavior. In one configuration, the unloading was continuously tracked by observing transmitted wave profiles in the Ultem samples through a transparent interferometer window. In the other configuration, the unloading was inferred from observing stress wave reverberations in an elastic target plate resulting from impact by the Ultem sample. The loading behavior indicated by the two methods agreed very well and the resulting Hugoniot was represented by US = 2.42 + 1.61*uP. This study also demonstrated that the plate reverberation method of following the unloading response, though not observing the continuous unloading of the sample, agrees extremely well with the unloading response recorded using continuous data obtained using interferometry windows. The results are used to build a case that the strength τ of Ultem increases with shock stress from 0.03 to 0.08 GPa over the range investigated. Furthermore, an investigation of the ratio of the release wave velocity to the shock wave velocity indicates that a transition to bulk liquid (no strength) behavior is not achieved until Hugoniot strains exceed 0.35 for amorphous polymers such as Ultem.