You have to engineer such a structure from 2 perspectives. IN the roll over situation, deformation needs to be limited to protect the occupants.  An element of energy absorption is also needed.

THe crash structure on an elise is mostly bothered with the later.  It works by absorbing energy through its own destruction. It is entirely outside of the "safety cell" so it doesnt really matter if the structure is destroyed in the process.

A roll structure has the difficult job of both roles. Primarily energy absorbtion is sacrificed for sheer strength to protect the safety cell, but some absorption is necessary.

There is no reason why a composite roll over protection system isn't doable. As proven in F1 and certain other high level motorsport, it is possible with the research and development.

Problem of that is the cost and man hours to get it right.

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Yeah, I have a VX220 which has the same crash structure.  I've looked at some vanes for the centre 'box' part to help flow for the rad but done very little with it so far.

Yes I've worked quite closely with one. I had to redesign one here to fit a bigger radiator, and to improve cooling efficiency as unfortunately the stock ones aren't very conducive to getting air to flow through the radiator. They are an interesting design though, and they actually serve 3 functions. They are a crash box, a radiator shroud, and a support for the front bodywork, all in one neat little unit. Pig heavy for what they are, as is the entire Lotus package. 

Ah right, have you seen them?  Quite an interesting part in how its made.

No no I know. I was just talking about the use of composites in impact/collision and safety structures. 

The exige crash box is just on the front so doesn't cover roll over events.

Lotus Exige has a composite 'crash box' too. Can definitely be done, but it's certainly not something I would be doing before completing an engineering degree. 

Just another car to look at is the Mclaren P1 GTR which doesn't have a cage as it's carbon monocoque already meats FIA roll over regs

Although I have dropped the idea now, I was thinking "outside the tubular box". Perhaps trying to integrate another structure into the existing bodywork so that the extra strength is hidden away. Maybe bonding a new composite structure to the existing GRP. It must be possible, but I now understand that it is a complex and skilled job and not for a beginner like me.

You can prevent the "shattering  /shards" problem by simply using outer layers of Kevlar/CF mix ...   Also using a semi-flexible resin in the outer layers will help keep the structure less prone to fracturing into dangerous parts. (in effect constructing a much more flexible "bag" that can contain the CF "splinters" in case of a catastrophic structural failure)

Metal tubes (Aluminium Alloys or steel) that are kept at a level of hardness/toughness where you ensure that they are ductile, under the loads from a rollover or medium impact chrash, will mean thet they have to be heavy compared to similar strenght tubing that will take the impacts, but may crack at joints and also present dangerous edges.

So in metal roll-cages it is also a balance  ... done properly CF/Kevlar/Twaron should make exellent light weight safety cages.   (No F1 car has anything but composite "safety tubs")

To make it really efficient, one has to think outside the "tubular box" in my opinion, and construct a "cage"/ "tub" that takes advantage of the properties of a purpose built composite construction.

(Stiffness in the right directions - impact absorbance in the correct directions - anchor points reinforced with regards to the forces acting on them in both a chrash and a roll .. It can be done .. even hand built, and I would think that even severely overengineered for safety, it will still be as light as a steel cage, and can probably be incorporated into the inside cabin structure in a much less intrusive way ..

But you will really have to know how to engineer it ...

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