Abstract:
In
heavy-duty disc brake systems, braking is a transient, non-linear and
asymmetrical thermo-mechanical process. Surface cracking, rather than wear, is the
major factor limiting the brake disc's life. The disc material (cast-iron), heat transfer
boundary conditions and pad-disc frictional reactions are characteristically non-linear
and
asymmetrical during the friction process. Non-uniform deformation and surface
cracks in brake discs result from the accumulation of excessive residual stress/strain.
During braking processes, many factors affect the distributions of the residual
stress and strain in discs, and hence the propagation of the surface cracks. The disc
material, structure and boundary conditions are three of the crucial aspects. From the
structure, a brake disc could be either solid or ventilated. In practice, solid structures
always have higher anti-cracking performance than the same class of ventilated
designs. However solid discs cost more material and have lower cooling efficiency.
This thesis
presents an improved finite element analysis for heavy-duty disc
brakes and identifies
design improvements. As the friction pads slide against the
disc's surfaces
continuously, the thermal and mechanical loads are functions of time
and
spatial coordinates. A 3-D asymmetrical finite element model was developed to
achieve more accurate simulations of the thermo-mechanical behaviour of brake discs
during braking processes. A non-linear inelastic material model for cast-iron was
employed in the FE model. Permanent plastic stress and strain fields were predicted
and
analysed for multi-stop drag operations. The residual stress/strain fields in the
discs are
investigated to understand the differences between solid and ventilated discs
in terms of the
cracking resistance ability. Several engineering solutions are
recommended for
optimising the performance of the disc brake system. _
The thesis is
organized in five chapters. Chapter One introduces the
background concepts about the commercial disc brake system. In this part, the brake
structure, material and previous researches are reviewed. The goals for this
investigation are also summarised at the end of this chapter. Chapter Two introduces
the
general finite element modelling knowledge, procedures and the modelling
boundary conditions and material models. Chapter Three presents an analysis of the
disc brakes thermo-mechanical behaviour and the
affecting factors. Chapter Four is
focused on the residual stress field
prediction and cracking behaviour analysis. The
project conclusions and further research recommendations are presented in Chapter
Five.