AN EDUCATIONAL VISUALIZATION TECHNIQUE FOR KOLSKY (SPLIT HOPKINSON) BAR.pdf

November/December 2003 EXPERIMENTAL TECHNIQUES 35 N TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TECHNIQUES by M. Vural and D. Rittel AN EDUCATIONAL VISUALIZATION TECHNIQUE FOR KOLSKY (SPLIT HOPKINSON) BAR The present paper introduces a simple educationaltechnique that allows the design of a variety of cre-ative and instructive experiments in the areas ofone dimensional wave motion in solids and dynamic behavior of materials. The technique is essentially based on the Kolsky (split Hopkinson) pressure bar setup. However, instead of electronic data acquisition tools, it uses a block of plasticine (modeling clay) as the basic tool to capture, visu- alize and quantify the displacement (or stress) waves, thus making the physical process of transient wave propagation easily conceivable particularly for the students. When cou- pled with the elementary theory of stress wave propagation in long bars the technique is shown to be capable of provid- ing useful information about the average flow stress of ma- terials at varying strain rates. INTRODUCTION The propagation of elastic waves in solids has long been an area of interest because stress waves provide a powerful tool for studying the mechanical properties of solids and also due to the fact that the understanding of high-strain-rate behav- ior of materials has become increasingly important from an σT , σTR Wheatstone Bridge σI , σRStriker Strain Gage 1 Incident Bar Transmission Bar Stopper Plasticine Oscilloscope Wheatstone Bridge Strain Gag 2 Fig. 1: Schematic of the Kolsky pressure bar setup used in the experiments engineering point of view.1 Bertram Hopkinson2 was among the first to investigate experimentally the propaga- tion of stress pulses in long bars on a laboratory scale. His apparatus, which has be- come known as the Hopkin- son pressure bar, is an appli- cation of the simple theory of stress propagation of elastic pulses in a cylindrical bar where