Lotus Elise Service Notes page 28

Lotus Service Notes Section TDM
BM.1 - GENERAL DESCRIPTION
The body panels of the Lotus Elise are constructed of composite materials, with the external panels not
being required to contribute to chassis rigidity. The panels are attached to the aluminium chassis and/or other
body panels either by elastomeric polyurethane adhesive, or in the case of the front and rear clamshells, are
bolted on for ease of dis-assembly and access to chassis parts. The major panels are manufactured by the
VARI (Vacuum Assisted Resin Injection) process, using a low profile resin and are of a nominal 2 mm thick-
ness. The windscreen frame incorporates foam beams to create closed box sections for optimum strength and
a 'crash structure' bonded to the front of the chassis incorporates longitudinal box sections to provide specific
crush characteristics and absorb crash impact by progressive collapse. This structure also acts as a mounting
and duct for the engine cooling radiator which is mounted horizontally on its top surface.
BM.2 - LOTUS COMPOSITE BODY FEATURES
Composite structures have the ability to absorb high impact loads by progressive collapse, with impact
damage being localised. In vehicle accidents this feature protects the occupants from injurious shock loads
and greatly reduces the danger of entrapment by deformation of steel body panels. This behaviour also
facilitates repair by either replacing the damaged bonded or bolt on panels, and/or integrating a replacement
section with the undamaged area, using recognised approved methods which restore the panel to its original
condition without residual strain or distortion.
The manufacturing process enables the thickness of composite mouldings to be varied in order to pro-
vide efficient structures of high strength and low weight. Composites will not corrode, so the strength of
composite components is retained regardless of age, unless physical damage is sustained. On the Elise, the
body construction utilises a single moulding for the whole of the nose and front wings, and a second one piece
moulding for the whole of the rear body aft of the doors. These two mouldings are fixed using threaded
fasteners to permit easy removal for access to chassis or powertrain components, or to allow simple and
economic accident repair. Other composite mouldings include the door shells, sills, front compartment lid,
windscreen frame and rear bulkhead, some panels being bonded to the aluminium alloy chassis with an
elastomeric adhesive.
The outer surface of a composite panel is sealed by a thin layer of 'gel coat'. If the panel is deflected
beyond its limits of flexibility the gel coat will be overstressed and cracks will result, although the panel will
return to its original shape. A steel panel similarly treated would become dented or deformed. The cracking
may be confined to the surface gel coat with no reduction in panel strength, but if the damage is more severe
the composite structure below the gel coat may be weakened. Localised repairs can be made in either case.
Gel cracks may not appear immediately after overstressing, because the effect can be masked by the flexibil-
ity of the paint finish which covers the gel coat, and in some instances can take as long as three months to
appear. Causes of gel cracks include:
Vehicle collision;
Sitting, leaning heavily or pushing on the body or any composite panel;
Knocking doors against obstructions when opening;
Dropping objects onto a panel;
Allowing unrestrained items to roll about in a luggage compartment;
Closing the bonnet or boot lid onto projecting objects, e.g. luggage or tools;
Applying excessive force to parts attached to composite panels e.g. mirrors, locks, aerial etc. (action
by vandals).
Incorrect jacking.
BM.3 - BODYCARE
The acrylic enamel paint finish of the Elan is extremely resistant to all normal forms of atmospheric
attack. Following the simple maintenance procedure summarised below will help retain the gloss, colour and
protective properties of the paint throughout the life of the vehicle. However, car finishes are not immune to
damage, and amongst the more common causes of deterioration are:
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