In these experiments, soft aluminium cylindrical specimens
were compressed between two platens. The lower platen
was a double-slotted block horn, tuned to a
longitudinal mode at 20 kHz, providing a uniform nominal
vibration peak amplitude of 8 lm on the platen surface.
The block horn was excited by a piezoelectric transducer
driven by an ultrasonic generator. The upper die was connected
to the cross-head of a Lloyd test machine which
provided a constant cross-head speed of 5 mm/min for
these experiments. A piezoelectric force transducer was
used to measure the static-oscillatory force response during
compression, and was mounted between the upper platen
and the cross-head as shown in Fig. 1. The oscillatory dis