Steel or aluminium for bodyshells?

[squizzler]

I've read a few things in print, none of which I have to hand, however online I've found this article which looks to be from the supplier's in-house magazine - so naturally espousing their own processes!

Interesting read. Steel bodyshells sound very attractive, especially in light of the thinner walls which would be even more relevant to vehicles in UK structure gauge where every mm of internal width counts. Thinner coach walls also means thinner dead lights - and bigger windows! As those who ride Reynolds framed bicycles like to say, "steel is real"!

Thanks to all for their contributions. This is an area far too often overlooked by us "hobbyists" so it's good to learn things about an area in which I can only claim the knowledge that I've acquired from others. Anyone remember articles many years ago by Roger Ford which discussed the use of Computer Aided Design (CAD) to allow virtual structure testing before any metal was cut? Old hat now but I remember being impressed by the concept at the time.

I did not take Modern Railway in those days but agree that more coverage on the mechanical design of both vehicles and structures would be nice. For example this thread was started from a brief reference to steel bodies in MR coverage of the ICE 4, but the article did not elaborate further.

 

[DarloRich]

I understand that most modern passenger coaches or multiple units in the UK are built from aluminium. However Modern Railways has recently discussed the new DB ICE 4 (formerly ICx) and makes reference to its steel body shells.

Intuition suggests that steel is a retrograde step in being a denser material than aluminium and can be prone to corrosion. I note the length of the ICE4 coach is 28m so maybe steel is chosen due to the greater bending forces? Fire resistance? Does the large production run favour designing for steel? Or is it due to designing for production such as factories or plant capable of this order being those equipped for working in steel, or having sunk costs in steel tooling that can be amortised in the ICE 4 order?

So is the ICE 4 an aberration or is steel likely to be favoured for future UK rolling stock?

bluntly, as a passenger, I don't care if the train is made out of cheese as long as it is comfortable, has enough seats and runs on time!

With a business hat on I want the cheapest build costs and the fastest route to in service hand over and the final milestone payment in my account.

 

[TwistedMentat]

Maybe for small parts, but carbon fibre/kevlar in quantities required for structural bodywork is probably currently far too expensive for something where there isn't that much of a weight saving, whereas their use in aircraft construction can create large through-life running-cost savings despite a higher acqusition cost.
Then there are low quantity premium uses, e.g. racing/sports cars, cycles, certain military vehicles etc..

This is why I referenced the near future stuff around low temperature curing and such. There is some interesting stuff on the horizon that could change the equations.

Of course nothing concrete yet but I'd be surprised if the major manufacturers were ignoring it.

 

[hwl]

This is why I referenced the near future stuff around low temperature curing and such. There is some interesting stuff on the horizon that could change the equations.

Of course nothing concrete yet but I'd be surprised if the major manufacturers were ignoring it.

My bet would be resin infusion with closed moulds for smaller parts such as doors is as big as it gets.
I can't see composite bodyshells for a very long time as the value equation is different to aircraft.

 

[Taunton]

My bet would be resin infusion with closed moulds for smaller parts such as doors is as big as it gets.
I can't see composite bodyshells for a very long time as the value equation is different to aircraft.

BR actually built one in 1962, 55 years ago. And it's survived on a preservation line

http://www.eastsomersetrailway.com/stock.php?num=S1000S

 

[Emblematic]

My bet would be resin infusion with closed moulds for smaller parts such as doors is as big as it gets.
I can't see composite bodyshells for a very long time as the value equation is different to aircraft.

Hanvin 200 (Korea) already proved the use of carbon composites for train bodies, albeit not in a production train. Bombardier has used glued-on composite panels on it's Talent trains for some time. Cab ends have been formed of composite materials for ages - even the venerable HST has a a GRP cab shell. We're constantly seeing novel materials such as foamed metal sandwich panels appearing on the market, so I'd be surprised if we don't see a bigger variety of materials and construction being used in future.

 

[hwl]

Hanvin 200 (Korea) already proved the use of carbon composites for train bodies, albeit not in a production train. Bombardier has used glued-on composite panels on it's Talent trains for some time. Cab ends have been formed of composite materials for ages - even the venerable HST has a a GRP cab shell. We're constantly seeing novel materials such as foamed metal sandwich panels appearing on the market, so I'd be surprised if we don't see a bigger variety of materials and construction being used in future.

I was meaning for additional parts to what are being made with composites today. Bombardier /Alstom use fiberglass inner ends on plenty of stock too.

 

[Emblematic]

I was meaning for additional parts to what are being made with composites today. Bombardier /Alstom use fiberglass inner ends on plenty of stock too.

There's definitely moves to increase the use of composites - in fact there was a whole EU project targetting regulatory obstacles to structural composites in trains, take a look at http://www.refresco-project.eu/

 

[D365]

bluntly, as a passenger, I don't care if the train is made out of cheese as long as it is comfortable, has enough seats and runs on time!

Cheese wouldn't be very good in an accident

 

[Firesprite]

In the next 15 to 20 years, I see complete body shells being produced on large 3d printers.

 

[HSTEd]

Did you mean a hundred thousand pounds??

No, a hundred thousand dollars because the price of aluminium given was in dollars.

 

[DerekC]

Cheese wouldn't be very could in an accident

Subject to mouse damage as well.

 

[edwin_m]

Cheese wouldn't be very could in an accident

You prevent the accident by applying the Swiss cheese model of safety.

 

[Taunton]

I was meaning for additional parts to what are being made with composites today. Bombardier /Alstom use fiberglass inner ends on plenty of stock too.

Again, this has been done for the last 60 years. The white upper cab roof on some old DMUs was unpainted fibreglass (and others were painted black). It mirrored comparable roof domes on double deck buses made the same way at the same time.

Mk 2 stock introduced fibreglass doors in the 1960s. This is what enabled the move from plain doors to wraparound end doors, which would have been too heavy in steel.

 

[HSTEd]

Carbon fibre costs are dropping all the time ofcourse.

It might be feasible to build composite monocoque carriages sooner than you might expect.

 

[dubscottie]

Carbon fibre costs are dropping all the time ofcourse.

It might be feasible to build composite monocoque carriages sooner than you might expect.

Carbon fibre, while strong, is still brittle. Hit it in the right spot and it shatters. (Look at the amount of shrapnel you get after a minor shunt in F1)

There is fire safety issues as well.

Unless someone has a eureka moment, composite bodies for heavy rail are decades away.

 

[HSTEd]

Carbon fibre, while strong, is still brittle. Hit it in the right spot and it shatters. (Look at the amount of shrapnel you get after a minor shunt in F1)

But aren't F1 components designed to shatter like that to absorb energy, after all they are designed to be absolutely as light as possible to win the race. Operation survivability after an accident is a minor concern.

There is fire safety issues as well.

Carbon fibre is surprisingly difficult to ignite though, about the only thing that can would be a massive pooled diesel fire - at which point the vehicle and everyone in it is dead anyway.

 

[D365]

Subject to mouse damage as well.

You prevent the accident by applying the Swiss cheese model of safety.

I appreciate both of you having the decency to look past my glaring mistake!

 

[squizzler]

Carbon fibre costs are dropping all the time ofcourse.

It might be feasible to build composite monocoque carriages sooner than you might expect.

I suspect if done it would involve composite panels glued onto a metal framework, which Airbus did for their planes when moving from aluminium to composites.

Ecologically I am not sure if composite construction offers any advantage. Sure, there will be some reduction in energy consumption during the lifetime of the vehicle, but composites are not readily recycled whereas metals are.

 

[edwin_m]

But aren't F1 components designed to shatter like that to absorb energy, after all they are designed to be absolutely as light as possible to win the race. Operation survivability after an accident is a minor concern.

Bending rather than shattering would absorb more energy. That's why modern train ends tend to contain metal honeycomb structures - won't make much different in a train-to-train collision but reduces the severity of say hitting an HGV on a level crossing.

 

[Emblematic]

Carbon fibre, while strong, is still brittle. Hit it in the right spot and it shatters. (Look at the amount of shrapnel you get after a minor shunt in F1)

There is fire safety issues as well.

Unless someone has a eureka moment, composite bodies for heavy rail are decades away.

Carbon fibre itself is not at all brittle - it can be woven into fabric, and lifts in high rise buildings now use carbon fibre ropes. It's the other materials in the composite that determine the brittleness or other properties. In applications where very high stiffness, strength and low weight are demanded, toughness and durability can be sacrificed. In everyday applications such as aircraft parts, I doubt very much whether the composite parts are any less strong and durable that their metal counterparts.
As to fire - well composites are already widely used in train interiors, and in non-structural external parts. The plastics used in composites for these materials - typically phenolic or epoxy resins - are very fire resistant and don't sustain combustion. Aircraft have far higher requirements for fire resistance, and it's not proved an obstacle there.

 

[Emblematic]

Ecologically I am not sure if composite construction offers any advantage. Sure, there will be some reduction in energy consumption during the lifetime of the vehicle, but composites are not readily recycled whereas metals are.

It's a difficult one - recycling of metals is primarily done to reduce the huge energy cost in producing them from raw materials, but the recycling process is still energy intensive. Much of the content of composites has a much lower energy cost than even recycled metals, although glass and carbon fibres themselves are quite energy intensive. But you're correct, the used composites have very little value and are typically not recycled. There has been some investigation into recovery of used carbon fibre, but the process of removing the resins degrades the fibres and, so far, the product has been low quality and therefore of little value.

 

[Peter Mugridge]

But aren't F1 components designed to shatter like that to absorb energy, after all they are designed to be absolutely as light as possible to win the race. Operation survivability after an accident is a minor concern.

The F1 regulations require survivability first and foremost, just as the railway regulations do. There is also a mandatory minimum weight which an F1 car has to meet.

Shattering of the composites has as much to do with their nature as anything to do with the impacts.

I suspect we may well in the future see carbon fibre composite panels on carriage bodyshell sides in the form of being fixed to an underlying frame structure as mentioned in a post above, but less immediately likely for the ends of the carriages.

 

[Domh245]

The F1 regulations require survivability first and foremost, just as the railway regulations do. There is also a mandatory minimum weight which an F1 car has to meet.

Shattering of the composites has as much to do with their nature as anything to do with the impacts.

I suspect we may well in the future see carbon fibre composite panels on carriage bodyshell sides in the form of being fixed to an underlying frame structure as mentioned in a post above, but less immediately likely for the ends of the carriages.

It'd more likely be glass fibre if they are just panels being fixed to parts, you wouldn't need the strength that carbon provides so you may as well use the cheaper glass.

As for F1, components generally are made as light as possible, with ballast being added in strategic places (front wing, under the driver's seats, etc) to improve handling whilst coming up to minimum weight.

 

[Liam]

Carbon fibre, while strong, is still brittle. Hit it in the right spot and it shatters. (Look at the amount of shrapnel you get after a minor shunt in F1)

The F1 cockpit is also made of carbon fibre (and a few other materials) and does not shatter. Look at some of the major shunts (Kubica in Canada, Alonso in Melbourne last year spring to mind) where almost all the bodywork has gone, but the cockpit (or survival cell) is still very much intact.

 

[LOL The Irony]

This is why I referenced the near future stuff around low temperature curing and such. There is some interesting stuff on the horizon that could change the equations.

Of course nothing concrete yet but I'd be surprised if the major manufacturers were ignoring it.

The problem with Carbon Fibre is it's name. Carbon Fibre Re-enforced Plastic. If Aluminium has a low melting point... Basiaclly look at the 787's that had those battery fires. The Etheopian one is flying round with a metal plate over the burnt patch.

I have toyed with the idea of a Carbon Fibre bodied train though. But not a kevlar train. There is a massive design flaw with such a train. It would have to be painted red, have black Auto Union rings on the side and to start it, Gene Hunt would have to be present.

 

[LOL The Irony]

Carbon fibre, while strong, is still brittle. Hit it in the right spot and it shatters. (Look at the amount of shrapnel you get after a minor shunt in F1)

There is fire safety issues as well.

Unless someone has a eureka moment, composite bodies for heavy rail are decades away.

Most "minor" F1 shunts involve a broken off end plate or barge board. Somtimes a section of front wing. Not much else tbh. Fernando's crash was the last major one. But I have to agree CBRP is a LONG way off being used in heavy rail. The biggest advert against is Japan 2014.

 

[Brunel 1954]

I understand that whenever possible steel is used for bodyshells as in the case of an accident aluminium can burn if it is set on fire.

 

[najaB]

Basiaclly look at the 787's that had those battery fires. The Etheopian one is flying round with a metal plate over the burnt patch

If you're taking about ET-AOP then (a) the fire was severe enough that an Al frame would likely have been written off; and (b) I seem to remember that the repair method was building a new rear fuselage section and then cutting patches from it to match the burned sections of the incident aircraft.

 

[Domh245]

I understand that whenever possible steel is used for bodyshells as in the case of an accident aluminium can burn if it is set on fire.

I'm afraid that's a load of rubbish. Aluminium is non-combustible, it won't catch fire under almost all circumstances. It'll melt if it's hot enough, but at no point will it burst into flames.