Radial Inertia Effects in Kolsky Bar Testing of Extra-soft Specimens
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Impact responses of extra-soft materials, such as ballistic gelatins and biological tissues, are increasingly in demand. The Kolsky bar is a widely used device to characterize high-rate behavior of materials. When a Kolsky bar is used to determine the dynamic compressive response of an extra-soft specimen, a spike-like feature often appears in the initial portion of the measured stress history. It is important to distinguish whether this spike is an experimental artifact or an intrinsic material response. In this research, we examined this phenomenon using experimental, numerical and analytical methods. The results indicate that the spike is the extra stress from specimen radial inertia during the acceleration stage of the axial deformation. Based on this understanding, remedies in both specimen geometry and loading pulse to minimize the artifact are proposed and verified, and thus capture the intrinsic dynamic behavior of the specimen material.
KeywordsKolsky bar Impact testing Radial inertia effect Extra-soft material
This research was supported by US Army Research Laboratory (ARL) through a collaborative research agreement with Purdue University. The authors wish to thank Dr. Michael Scheidler of ARL for his efforts in the proofreading of the analytical modeling work.
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