Physics of the problem:
Air
dryer is widely used in heavy duty trucks to keep the moisture out of air, so
that air brakes work effectively. The unit is usually cylindrical block
weighing anywhere between 5-15 kg. In simple design it is mounted directly to
the frame with L-Shaped bracket as shown in the figure. It is not always
possible to mount the air dryer directly to the frame due to space claim/design
space availability. This makes design inferior compared to the frame mounted
design. As the bracket becomes cantilever as shown in the figure. It is
challenging to design a bracket to satisfy all structural requirements.
Design and Geometry:
The
design of the brackets is shown in the figure. It is mounted to the frame with
two M16 bolts. Assuming the material of the brackets as mild steel. The window
is provided to have access to the harness/coolant lines pass through along the
length of the frame rail. Gussets are welded to increase the stiffness and
increase the first natural frequency of the bracket. Assume the bracket
thickness as 6.35mm.
Modelling:
As the bracket is slender compared to thickness to width
and length ratio is high, this can be modelled as thin shell element. The
reason to model with shell element is it will reduce the modelling time which
in turn will reduce the computational cost. The default S4R first order reduced
integration elements will be used.
Assumptions:
- The material of is assumed to be isotropic and homogeneous.
- Nonlinear material properties are ignored
- Contact conditions between the frame rail and bracket is ignored in the initial analysis.
- No damping effects are considered
- Air dryer modeled as lumped mass.
Boundary conditions:
The bracket is
restrained at the bolt holes
Load Cases:
In practical
application the bracket is subjected to the random vibrations under different
load cases. As the loading is complicated and, even difficult to analyze even
though the design is simple. The load cases are simplified as static and
dynamic load cases. The static load is the amount of inertia-g’ the bracket will
be experienced when the resonance condition exist. It is difficult to predict
how much the inertia load for the initial design. So designers are left with
assuming the standard load cases based on the experience. On the similar note let’s
assume the bracket is subjected to 5g in x ,y and z directions. Also apply the
load in xy, yz conditions. This will be close to the real condition.
Acceptance criteria:
The stresses under inertia load cases are compared against
the endurance limit of the material.
