and ultrasonic block horn amplitudes. Although the actual
values of mean stress reduction and amplitude of oscillating
stress are dependent on these parameters, the resulting
profile of the stress–strain relationship exhibited a consistent
pattern of a linear reduction followed by a linear
increase in oscillating stress amplitude in all of the tests.
Specimen temperature was also recorded, using two
embedded thermocouples located in the specimen close to
the interface and close to the centre of the specimen. During
static and ultrasonic compression tests no significant
rise in surface or bulk temperature was recorded.
Clearly the measured stress–strain relationships deviate
considerably from the definition of oscillatory stress superposition
described earlier. Although, as in Kirchner et al.
[8] and other studies, the path of the mean oscillatory stress
is consistent with oscillatory stress superposition, the oscillatory
stress amplitude response is inconsistent with this
mechanism and the maximum stress does not follow the
path of the static stress curve.
The FE model is therefore developed to assess how a significant
reduction in the coefficient of friction during
applied ultrasonic oscillation affects the estimated stress–
strain relationship. Comparison with the experimentally
derived stress–strain data can provide some initial assessment
of the possible occurrence of interfacial fiction
changes.