The experts at Audi long ago abandoned the obsession with using a single material in lightweight design. With a mix of aluminum, steel, magnesium and carbon fiber-reinforced polymer (CFRP) they are establishing a new level in multi-material construction of the Audi Space Frame (ASF) for the next generation of the A8 – in keeping with the principle “the right material in the right place in the right amount”.
The company consistently applies new material technologies and designs that are directly beneficial to the customer – and not only in terms of weight. The upcoming flagship’s torsional rigidity – the critical parameter for precise handling and pleasing acoustics – surpasses its predecessor model’s rigidity value by up to 24 percent.
Innovative production process: The carbon rear panel in the new Audi A8
In terms of its overall dimensions, an ultra-high-strength, torsionally rigid rear panel made of CFRP is the largest component in the occupant cell of the new Audi A8, and it contributes 33 percent to the torsional rigidity of the total vehicle. To optimally absorb longitudinal and transverse loads as well as shearing forces, between six and 19 fiber layers are placed one on top of the other, ensuring a load-optimized layout. These individual fiber layers consist of tapes
50 millimeters (0.2 in) wide and can be placed individually in a finished layered panel, with any desired fiber angle and minimal trimming of the fibers. The innovative direct-fiber-layering process specially developed for this purpose makes it possible to entirely dispense with the normally needed intermediary step of manufacturing entire sheets of carbon fiber. Using another newly developed process, the layered panel is wetted with epoxy resin and cured within minutes.
A high-strength combination of hot-formed steel components make up the occupant cell, which comprises the lower section of the front bulkhead, the side sills, the B-pillars and the front section of the roof line. Some of these sheet metal blanks are manufactured in varying thicknesses by means of tailoring technologies – they’re tailor-made in other words – and others also undergo partial heat treatment. That reduces weight and increases the strength, especially in areas of the vehicle that are particularly critical for safety.
Aluminum components in the form of cast nodes, extruded profiles and sheets, elements characteristic of the ASF design, make up the biggest share of the new Audi A8 body, at 58 percent. And here too the competition of materials has been driving progress. New heat-treated cast alloys, for example, attain a tensile strength of over 230 MPa (megapascals). The corresponding yield strength in the tensile test is over 180 MPa, and for the profile alloys it is higher than 280 and 320 MPa – significantly higher values than seen previously.