In order to compare the measured effects of superimposed
ultrasonic excitation of the lower platen with a
numerical model, the FE model initially adopted a coeffi-
cient of friction for a dry surface condition and the value
was constant for static and ultrasonic compression intervals.
Fig. 5(a) therefore shows the predicted stress–strain
relationship for a short interval of ultrasonic excitation
where the effect is merely the superposition of an oscillatory
stress on a static stress as defined earlier. In the
expanded part as in Fig. 5(b) it can clearly be seen that