Hello,

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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