Aluminium alloys might also work well, but what I need it to maximise the off-axis stiffness by making the bar thicker - it seems to me that the lower density of magnesium makes for a better part in this particular case. IE for the same weight as the current Ti bar, I could have a 23mm magnesium part. Realistically, I would go with a a 19mm bar and a pocket down the middle to keep stiffness while minimising weight.

Marco points out that the US army is using thick Magnesium plates on armoured vehicles - if they can take an RPG hit, Scissorhands should be quite harmless.

BTW: I don't think I have seen aluminium - lithium alloy, do you have a reference?

Alloy 2091

Chemical composition: Cu - 2.1, Li - 2.0, Zr - 0.10.

Alloy 2091 was developed to be a damage-tolerant alloy with 8% lower density and 1% higher modulus than 2024-T3, a major high-toughness damage-tolerant alloy currently used for most aircraft structures. Alloy 2091 is also suitable for use in secondary structures where high strength is not critical.

wrt armor
Thing is they are taking a single hit, not repeated flexing, Not saying its a definite "your gonna die" thing. But it might warrant some inspection during events, Same if you went to Al.

I still think a sandwich is really what your trying to achieve.
Think rather than a bar with pockets, a hollow block with a solid center. In terms of stiffness for weight thats really the ultimate, most high strength aerospace composites are done that way.
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Mechanical engineers build weapons, civil engineers build targets

I have also heard the army has used case hardened plate for armour, it seems to work alright too.
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YEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAH

I suggested a sandwich to Robert Woodhead when we were modelling various shaped bars in Solidworks and doing FEA on them. They didn't come out so well, but that was using the same material all the way through. I would guess that very stiff outer layers and a tough, light core would be a good starting point. Holding a sandwich together is a problem too.

The aim of the sandwich is to turn a "bending" load into a tensile load on the side opposite to the point of bending.
The core materials job is to pass the load to the other side with a minimum of deformation and weight. Its basically acting as a fulcrum to the lever of the skin material

Typically in aircraft they use honeycomb aluminium or nexcel/hexcel (basically impregnated nomex paper) for the core material with carbon fiber as the skins.

A typical thickness for an elevator or something like that is on the order of 20mm with 3-6 mm CF on each side.

By weight, a hollow bar is stiffer than a solid anyway. If your after the ultimate, perhaps an aluminium skin over a foamed aluminium core.
Weld the skin on over the core with a moderate amount of "preload" type clamping force to stop the core from rattling about in the middle.
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Mechanical engineers build weapons, civil engineers build targets

Finaly got some time to look at this properly
Great and extreamly informative guide I think ill get a printed copy to sit next to my other engineering texts and handbooks on my shelf i can see uses for me in non combat bot related interests.
It did however remind me why i was glad when i was done with my material science units hehehehe.
Love all the formulas

Thanks for all the effort in the guide.

Re quick printing in melb website lists the time to receive after printing in Australia quicker then Canada so they probably always print for this part of the would at a local printers
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Remember to trust me, I am an Engineer.

http://www.youtube.com/watch?v=rp8hvyjZWHs

The B&W version is 'cheap-as" but I really appreciate the expensive colour version - all Marco's diagrams are in colour and most of them are quite complex, even in colour. I have already off-set the cost in better designs and I am busy adding some extra pages of info to the next edition. Marco is very open to adding new content, so don't hold back on sharing.

Have you found any sources for the magnesium?
I'm after roughly a 400mm square plate ~40mm thick.
Might wind up just casting my own (mmmm exciting lol)
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Mechanical engineers build weapons, civil engineers build targets

I have not asked for a quote yet, but this place is supposed to be one of the best for small orders: http://www.metal-mart.com/HTML/MarkMetals.aspx