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DEFINITION
Standard High strength Aluminium
steel steel alloy
Yield strength (MPa) 350 760 250
E-Modulus (MPa) 210000 210000 70000
Density (kg/m3) 7800 7800 2700
Unfair comparison!
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ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER III WHY USING ALUMINIUM 18 | 19
At equal strength:
• The aluminium beam is the
lightest, but has a lower stiffness
than the standard steel beam.
• The high-strength steel beam
ranks second for lightness, but its
stiffness is also the lowest!
• The aluminium solution is
about 60% lighter than the standard
steel one (0.42 vs. 1) and still
40% lighter than the high
strength steel one (0.42 vs. 0.71).
At equal stiffness:
• The aluminium beam is the
lightest, with 45% weight saved
(0.55 vs 1).
• The high strength steel beam
weighs the same as the standard
steel beam, because, based on
the same parent metal, both
materials have identical elastic
properties (E-modulus).
• Compared to the standard steel
beam, the aluminium one is
about 50% stronger, and the high
strength steel one about 120%.
Comparing an aluminium beam
designed for equal stiffness to a
standard steel beam and a high
strength metal beam designed for
equal strength to that standard
steel beam, only shows small
weight saving for aluminium
(0.55 vs. 0.71) but that comparison
is unfair, as the latter will
have a much higher strength
(1.54 vs. 1) and a much higher
stiffness (1 vs. 0.30).
Last but not least, we should
underline that further weight
optimisation is possible with aluminium
because:
• The above comparison is
based on a standard beam
design, the so-called “double T”
• Finite element modelling
allows a more precise definition
of most favorable section’s
geometry;
• These sections, even if very
complex, can easily be produced
with the aluminium extrusion
process.
• For parts where strength is the
leading criteria, high-strength
aluminium alloys can also be
used and provide further weight
savings
2.2. Durability
Some operators still fear problems
with aluminium trailer chassis
in heavy duty applications,
but they should know that the
lifespan is not material related if
properly designed.
Experienced manufacturers optimize
their design for the material
they use and are able to produce
aluminium chassis offering an
equivalent or longer lifespan but
at a much lower weight than
conventional models.
It is also important to underline
that aluminium vehicles often
operate in transport segments
where the load factors are the
highest (solid and liquid bulk,
public works etc…). In other
words, they are much more
intensively used than conven-
Unpainted aluminium patrol boat
(All American Marine)
19
EUROPEAN ALUMINIUM ASSOCIATION
tional ones, and this fact is taken
into account in the design of aluminium
vehicles.
Correctly used, aluminium alloys
have been developed to offer
optimum corrosion resistance in
all environments. Just one example:
the widespread use of
unpainted aluminium in marine
applications.
2.3. Stability
Achieving IRTE3 Class A4 tipping
stability standard for an aluminium
tipper chassis is no problem.
Aluminium, according to
tests carried out in the summer
of 2002 has no issues with flexing
and easily provides the equivalent
rigidity of steel.
Indeed, a full-aluminium vehicle,
significantly lighter than others,
passed the IRTE Class A test at 44
tonnes with its standard chassis,
reminding everyone that an
appropriate design leads to both
lightness and torsional stiffness.
3. Institute of Road Transport Engineers,
UK.
4. “Class A” standard states that a
trailer should be able to tilt sideways 7°
without falling with a fully loaded and
raised body.
Tipping stability test (STAS)
2.4. Diversity & functionality of semi-finished products,
castings and forgings
Vehicle designers and manufacturers
have a wide range of aluminium
alloy semi-finished products
from which to choose:
• Rolled semis: sheets, tread
plates (floor plates), pre-painted
sheets
• Extruded semis: hollow or solid
shapes, standard or customized
• Castings and forgings
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