ABSTRACT
Unlike ductile metals, brittle materials have small failure strains (<1%) and hence if the loading is too fast, as in a conventional SHPB test, the specimen may fail in a non-uniform manner (i.e., the front portion of the sample may be shattered while the back portion of the sample remains intact.). To achieve accurate measurements in SHPB tests, one has to make sure that the dynamic loading is slow enough so that the specimen is experiencing an essentially quasi-static load, and thus the deformation of the specimen is uniform. As a rule of thumb, it takes the loading stress wave to travel in the specimen 3-4 rounds for the stress to achieve such an equilibrium state. The pulse-shaping technique was proposed to slow down the loading rate and thus to minimize the so-called inertial effect associated with the stress wave loading (Frew et al., 2001). Another problem in conventional SHPB tests is that the specimen will be subjected to multiple loading due to the reflection of the wave at the impact end of the incident bar. A momentumtrap technique was proposed to ensure single pulse loading and thus enables valid post-mortem analysis of the recovered specimen (Nemat-Nasser et al., 1991). Other advancements in SHPB can be found in a recent review (Field et al., 2004).
