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dc.contributor.authorKaiser, Michael Adamen_US
dc.description.abstractThe split Hopkinson bar test is the most commonly used method for determining material properties at high rates of strain. The theory governing the specifics of Hopkinson bar testing has been around for decades. It has only been the last decade or so, however, that significant data processing advancements have been made. It is the intent of this thesis to offer the insight of its author towards new advancements.

The split Hopkinson bar apparatus consists of two long slender bars that sandwich a short cylindrical specimen between them. By striking the end of a bar, a compressive stress wave is generated that immediately begins to traverse towards the specimen. Upon arrival at the specimen, the wave partially reflects back towards the impact end. The remainder of the wave transmits through the specimen and into the second bar, causing irreversible plastic deformation in the specimen. It is shown that the reflected and transmitted waves are proportional to the specimen's strain rate and stress, respectively. Specimen strain can be determined by integrating the strain rate. By monitoring the strains in the two bars, specimen stress-strain properties can be calculated.

Several factors influence the accuracy of the results, including longitudinal wave dispersion, impedance mismatch of the bars with the specimens, and transducer properties, among others. A particular area of advancement is a new technique to determine the bars dispersive nature, and hence reducing the distorting effects. By implementing numerical procedures, precise alignment of the strain pulses is facilitated. It is shown that by choosing specimen dimensions based on their impedance, the transmitted stress signal-to-noise ratio can be improved by as much as 25dB. An in depth discussion of realistic expectations of strain gages is presented, along with closed form solutions validating any claims. The effect of windowing on the actual strains is developed by analyzing the convolution of a rectangular window with the impact pulse.

The thesis concludes with a statistical evaluation of test results. Several recommendations are then made for pursuing new areas of continual research.

dc.publisherVirginia Techen_US
dc.rightsI hereby grant to Virginia Tech or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation.en_US
dc.subjectHopkinson Baren_US
dc.subjectHigh Strain-Rateen_US
dc.subjectImpact Testingen_US
dc.subjectWave Dispersionen_US
dc.subjectBar Impedanceen_US
dc.titleAdvancements in the Split Hopkinson Bar Testen_US
dc.contributor.departmentMechanical Engineeringen_US of Scienceen_US Polytechnic Institute and State Universityen_US
dc.contributor.committeechairWicks, Alfred L.en_US
dc.contributor.committeememberSaunders, William R.en_US
dc.contributor.committeememberWilson, Leonard T.en_US

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