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LIGHTWEIGHTING
AD&P; ∕ OCTOBER 2017
AUDI A8
4,144.7 pounds (German spec vehicle)
In 1994 Audi launched the A8 with the "Audi
Space Frame," with was a structure that consisted
of aluminum die castings and extrusions that
were wrapped with aluminum. But times have changed and the company itself admits that it
no longer has an "obsession with using a single material." That material: aluminum.
So for the new A8, the body structure consists of four materials: aluminum, steel, magne-
sium and carbon fiber-reinforced polymer (CFRP).
The last-named is rather significant. There is a rear panel made with CFRP that is the
largest component for the passenger cell (it is located behind the rear seat) that provides 33
percent to the torsional rigidity of the A8 (which, overall, is 24 percent more rigid than the
previous vehicle, which was launched in 2010). The part is engineered with 50-mm wide
tapes that are layered; depending on where they need strength, there are from six to 19
layers.
Hot-formed steel is used for the lower section of the front bulkhead, the side sills, the
B-pillars and the front section of the hood. Analogous to the layering of the CFRP, the steel
stampings are blanked so that there are varying gauges within a given component.
Magnesium is used to connect the front strut tower domes. It weighs 28 percent less than
the brace used in the previous-generation A8.
Aluminum is used in a variety of forms: cast nodes, extrusions and sheets. There is more
aluminum than any other material, at 58 percent of the body-in-white. They're using a
variety of aluminum alloys, including castings that have a tensile strength of more than 230
MPa and extrusions that are 280 and 320 MPa.
(It is worth noting that in order to put together this structure Audi, at its Neckarsulm plant,
is using 14 different joining processes, such as laser welding, grip-punch riveting, roller
hemming, adhesive bonding and more.)
This is the fourth generation Audi A8. It is a mixed
material construction, whereas the first generation,
back in 1994, was aluminum-intensive.
This carbon-fiber reinforced
polymer is located behind
the rear seat. It helps provide
additional structural rigidity
to the A8.
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