HOPKINSON TECHNIQUES FOR DYNAMIC RECOVERY EXPERIMENTS

Novel techniques are introduced to render the classical split Hopkinson bar apparatus suitable for dynamic recovery experiments, where samples can be subjected to a single pulse of pre-assigned shape and duration, and then recovered without any additional loading, for post-test characterization; i.e., techniques for fully controlled unloading in Hopkinson bar experiments. For compression dynamic recovery tests, the new design generates a compressive pulse trailed by a tensile pulse (stress reversal), travelling toward the sample. Furthermore, all subsequent pulses which reflect off the free ends of the two bars (incident and transmission) are rendered tensile, so that the sample is subjected to a single compressive pulse whose shape and duration can also be controlled. For tension recovery experiments, the new design provides for trapping the compression pulse reflected off the sample, and the tensile pulse transmitted through the sample. In addition, a sample can be subjected to compression followed by tension, and then recovered, allowing the study of, e.g. the dynamic Bauschinger effect in materials.