Lotus 2004 Eleven Service Notes page 41

Lotus Service Notes
BQ.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 composite mouldings are manufactured
by one of several processes (see later) dependent on application, with a nominal thickness of 2.2 - 2.5 mm.
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.
BQ.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 con-
struction features an assembly of mouldings to form a single piece for the whole of the nose and front wings,
and a similar assembly for the whole of the rear body aft of the doors. These two 'clamshells' 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.
A composite panel may return to its original shape after deflection, but beyond a certain level of flexibility,
such treatment may result in the formation of surface cracks which may not be immediately apparent due to
the masking effect of the paint film. A steel panel similarly treated would become dented or deformed. The
cracking may be confined to the surface layer with no reduction in panel strength, but if the damage is more
severe the composite structure below the surface may be weakened. Localised repairs can be made in either
case. Possible causes of surface cracking 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;
- Fitting a front access panel or closing the engine cover onto projecting objects, e.g. luggage or tools;
- Applying excessive force to parts attached to composite panels e.g. mirrors, locks, aerial etc. (inc. action
byvandals).
- Incorrect jacking.
The composite body panels of the Elise are manufactured by one of several processes dependent on the
requirements of the panel concerned:
- The front and rear clamshells, sill panels, windscreen frame, door outer panels, hard top roof outer panel
and front crash structure are produced by Injection Compression System Resin Transfer Moulding (ICS-
RTM), whereby a mix of polyester resin and glass fibres is injected into a heated, chrome steel surfaced,
closed mould. After filling, the gap between the two halves of the mould is then reduced in order to com-
press the moulding and ensure complete material flow and consistent structural quality. Panel thickness
is a nominal 2.2 mm. The absence of the 'gel coat' used with other processes results in much greater
resistance to surface damage, and minimum surface preparation for before painting.
Section BQ
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