Design of an Innovative System for Wave Generation in Direct Tension–Compression Split Hopkinson Bar

The split Hopkinson bar is a well-known apparatus
for performing tests at high strain-rate on engineering
materials. The specimen is placed between two long bars and
quickly loaded by a pressure wave, which travels at sound
speed along the input bar, passes through the specimen, then
is partly reflected and partly transmitted to the output bar. In
the classical version, the input wave is generated by the
impact of a striker bar against the input bar at a given velocity.
In the direct version of the Hopkinson bar, the wave is
generated by pre-loading and releasing a portion of the input
bar. However, with this approach the rise time of the pressure
wave is usually longer respect to the classical version. In this
paper, an innovative wave generation system is presented,
which exploits the abrupt shear fracture of a thin brittle disc.
In this way, the rise time of the incident waves can be close to
that obtained by the classical impact-based Hopkison bars
(80 ls instead of 50 ls). Moreover, both tension and compression
tests can be carried out with the same experimental
system.