Modelling and simulation of disc brake contact analysis and squeal
This thesis proposes a new methodology of predicting squeal using the finite element
method in which three validation stages are established. A detailed 3-dimensional
finite element model of a real disc brake is not only validated through modal analysis
at the components and assembly levels but also through contact analysis where static
contact pressure distribution and its contact area match with the experimental results.
The main key issue in this research is the refinement of contact interface model of
the friction material. Having assumed a smooth and flat surface (or perfect contact
interface) in the past, current research considers a real surface topography of which
measurementsa re carried out in order to obtain a realistic contact interface model. It
is found that with the refined disc brake model, a good correlation is achieved
between the predicted results and experimental ones on the contact pressure
distribution and contact area at the piston and finger pads.
Complex eigenvalue analysis that is available in ABAQUS software package is used
as the main tool to predict squeal generation. Prediction of squeal occurrence is
limited to a frequency range of I kHz to 8 kHz. Simulations of disc brake squeal are
performed at different friction characteristics with the inclusion of friction damping
for the perfect contact interface and real contact interface models. It is shown that the
real contact interface model predicts squeal occurrences much better than the perfect
contact interface model by considering the effect of negative u-v slope and friction
damping. Comparison between complex eigenvalue analysis and dynamic transient
analysis using a reduced FE model is also made for different contact schemes. It is
found that using small sliding with Lagrange multiplier contact scheme predicted
results in both analyses in a good agreement.
Wear effects on instability of the disc brake assembly are also simulated. The results
show that with the inclusion of wear, unstable frequencies are predicted to appear
and disappear as wear progresses even though similar boundary conditions and
operating conditions are imposed to apparently the same disc brake model. This
phenomenon may explain the fugitive nature of squeal behaviour.