Hopkinson Techniques for Dynamic Triaxial Compression Tests

A modified Hopkinson technique is developed to simultaneously load a sample in both the axial and radial directions. This is accomplished by using a composite incident-bar and a composite transmission-bar system. The incident-bar system consists of a large-diameter bar, followed by a small-diameter bar that fits inside a tube whose outside diameter is equal to that of the large bar. The transmission-bar system consists of a tube and a bar that fits inside the tube. The sample is placed inside a Teflon sleeve, and the Teflon sleeve is placed inside an aluminum sleeve. The Teflon sleeve is loaded during the test by the stress pulse traveling in the incident tube, producing a radial stress on the sample. The stress pulse traveling in the incident bar loads the sample that is sandwiched between the small-diameter incident and transmission bars. The radial stress is calculated from the hoop strain measured by a strain gauge placed on the outer surface of the aluminum sleeve. Mortar samples have been tested under a range of confining stresses and strain rates, and some of the results of these experiments are presented.