Finite element simulations were developed using a commercial
finite element code, ABAQUS, with implicit solution.
Half of the cylinder specimen was meshed using 2D
axi-symmetric 4-node elements. The platens were assumed
to be rigid bodies, modelled by an analytical rigid surface.
The material properties of aluminium, derived from prior
compression tests, were; Young’s modulus 69 GPa, yield
stress 60 MPa and Poisson’s ratio 0.33. A coefficient of friction
of 0.25 for the dry surface was used in the model. To
investigate the effects of a change in the coefficient of friction
numerically, another model was created where the
coefficient of friction of 0.25 was used during static compression
and changed to 0.001 at the onset of ultrasonic
excitation. The boundary conditions simulated the constant
speed of the upper platen, which was set to 5 mm/
min and the oscillation of the lower platen at 20 kHz and
8 lm as in the experiments. To allow for manageable computational
time whilst ensuring that the effects of the
change in interface friction could be evaluated, the ultrasonic
excitation was applied for very short intervals in
the FE models. The numerical stress–strain curves were
derived from the FE models.