Why not Aluminium?

Yes, why can’t we make a train bogie in aluminum instead of steel? Well, aluminum is lighter than steel, it’s a great material for aeronautics. But trains are an application requiring a very high resistance to fatigue because it must bear shocks and very strong constraints. If a crack is to appear in the aluminum it will propagate more quickly than in steel. It means Al would break more quickly than steel, so more research needs to be undertaken into alloys involving Aluminum to replace steel. As railways are mostly interesting in topographically flat countries, weight is not a so important issue for trains than it is for aircrafts in terms of energy consumption.

Still, Aluminum managed to have its own business class seat in trains. Why? A new version of French TGV has been designed to have two stairs, which implied more weight. It is called TGV Duplex. But as for the A380 aircraft, for which the runway strength was a restriction, the railway strength was the limitation for the TGV Duplex too: one set of wheels could not concentrate more than 17 tons ½.

   

So which part of the train has been “aluminized”?

Is it the bogies? No, as safety was involved, it was not the priority for Alstom, the TGV manufacturer. It’s the structure itself which used aluminum and finally the challenge was won.

But why are we talking about it?

Actually, these last three days I’ve been traveling with my classmates to visit some material process industries and it was one of the things I learned which I would like to share with you. It was really nice. Firstly, because it is a great opportunity to get closer to my friends secondly, because it is a very instructive way to learn.

What is harder – rails or wheels?

It was also during this trip that I discovered that in France, railways are made of harder steel than steel’s wheels. The reason is simple: with the shear, both rail and wheel get damaged. But the softer steel will be damaged first and it is easier to replace a wheel than a rail. It seems to be logic, but in Great Britain, the system is working the other way round; train wheels are consuming the rails and that’s why the railway has a worse quality than the French one.