lighter car leaf springs 2

[plutogamer]

To replace the leaf springs on a car, to reduce the overall mass. Would beryllium copper be strong enough, manage the same loads and stresses as steel, be similar mass to titanium and cheaper than titanium?
thread404-321076 gave some information (below) but not all the answers.
titanium … yield stress equivalent to spring steel, lower elastic modulus, lower stress, can be deflected more than steel.
beryllium copper … yield stress and elastic modulus similar to titanium, cheaper and more available, more corrosive than titanium.
Delrin?
Thanks

 

[rb1957]

and nastier for people to work with ... we're trying to get rid of beryllium

Quando Omni Flunkus Moritati

 

[JStephen]

I thought beryllium copper would be similar in mass to steel, actually, or maybe heavier. I also had the impression that it would be kinda like just building them out of gold, too.

I'm not a car designer. But I would expect them to look at composites or else change leaf springs to something other than leaf springs if they wanted to really save weight on that item.

 

[MikeHalloran]

Fiberglass springs have been tried, on Corvettes of all things, and I think on Novas. FRP has the advantage that you can put the strength only where you need it, so it's possible to minimize their mass. They don't have very good damping, relative to a laminated steel spring.

Like most other things, spring design is complex enough that it's not really possible to make a blanket statement about any one material being superior to all others, because there are so many variable other than material involved in any particular application.



Mike Halloran
Pembroke Pines, FL, USA

 

[Artisi]

My thinking, as manufacturer's are always looking to trim ever cent out of their manufacturing cost, it seems reasonable to expect they would in all cases use the most cost effective method / material. Therefore it would seem what is currently used is the best.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Tmoose]

If we are talking about Hotchkiss Leaf spring suspension they are pretty porky, and take up a lot of space, especially with a beam axle, but it's simplicity and low cost seem to keep it alive.

Some Studebaker owners report that using flex-a-form springs save a whopping 70-90 lbs (at the end of the car that already is too light).
50 vs 8 lbs each. 2 required. Cost supposedly not much more than steel.

http://www.flex-form.com/products.asp

Life generically proven in Corvettes at both ends since 1984 (optionally since 1980?). Supposedly no Corvette composite spring has been replaced due to fatige failure.

 

[Lou Scannon]

One nice thing about using a much lighter material for a traditional, Hotchkiss-style leaf spring (not so much the transverse, e.g. Corvette style) is, the unsprung mass is greatly reduced, since the mass of a traditional laminated leaf spring is heavily concentrated toward the central, i.e. unsprung part.

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[drawoh]

plutogamer,

Beryllium copper is a nifty material for springs because it has the yield stress of spring steel, and the elastic modulus of bronze. This means you can bend it more. This is a useful quality in optical fixtures, and on electrical connector contacts.

Beryllium copper is mostly copper, so I would expect it to be heavier than steel. I would wonder about the fatigue qualities of any non-ferrous material, although car springs may be loaded sufficiently that this does not matter.

--
JHG

 

[GregLocock]

On that last point, a leaf spring designer is very concerned about fatigue, particularly in a multileaf design, and especially if it has a second stage.

The SAE leaf spring handbook is an invaluable resource even now, since it explains the many subtleties.



Cheers

Greg Locock


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[tbuelna]

As others noted, composite leaf springs are a well established technology. For a metal automotive suspension leaf spring, titanium or high-strength alloy steel would provide a better combination of mass and fatigue life. As noted above, the high copper content of BeCu alloys results in high density, and also much lower specific modulus properties (elastic modulus/mass density)than alloy steel or titanium alloy. Even though most high-strength BeCu alloys contain less than 2% Be, they are still quite expensive on a $/lb basis.

Regards,
Terry

 

[GregLocock]

Ti would need special attention paid to contacts as it tends to gall. The OP needs to establish the figure of merit for materials in his application.

Cheers

Greg Locock


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[tbuelna]

True, titanium does tend to experience surface galling when subject to contact with titanium or other metal surfaces under high local bearing pressures. Titanium is also highly "notch sensitive", which means a Ti leaf spring would likely need to have some sort of surface protection from impact damage due to rocks/road debris.

Obviously, every leaf spring material has certain benefits and limitations. One benefit of both BeCu and Ti is that they have natural corrosion resistance. Or from an aesthetics standpoint, just imagine how beautiful a polished BeCu leaf spring would look.

 

[JStephen]

I've seen lots of sheet metal rust out on cars and trucks, but never have seen leaf springs that rusted out. So that's pretty much a cosmetic problem.

I suspect with copper or titanium springs, you'd start having cases where people came out of the Walmart only to find their springs had been stolen.

 

[tbuelna]

I suspect with copper or titanium springs, you'd start having cases where people came out of the Walmart only to find their springs had been stolen.

Actually, what you said is sad but true. I live in southern California, and a few months back a co-worker of mine had the catalytic converter stolen from his Toyota 4Runner during broad daylight while it was sitting in the company parking lot. A used catalytic converter is worth far less than a pair of BeCu or Ti leaf springs!

 

[jwhit]

BeCu would probably work well, however, as others have alluded to, BeCu can be nasty. I worked with it in BeCu and BeNi alloys plus Be powder 40 yrs ago and have the lungs to prove it. The good news is that they have blood tests now that can tell if your are extra sensitive to it. Point is, it wouldn't be worth screwing with in my opinion.

 

[plutogamer]

You all might be interested in this.
Received a quote for fibre glass leaf springs, from mark@flex-form.com
Here is the data sent to him:

http://classic-carshow.com/cars/Vauxhall/Cresta/PC-653

dry weight: 2796lb/1.248ton (1268kg)
Mark must think fibre glass has enough load bearing and tensile strength.

 

[GregLocock]

Yup, there is no doubt that glassfibre leaf springs are feasible, and in a given application may even be excellent.

Cheers

Greg Locock


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[BrianPetersen]

The last couple generations of Corvette have used leaf springs made of composite materials. It works there. One thing to note is that the Corvette relies on that spring to act only as a spring; it serves no function in guiding the path of the wheels as the suspension moves - unlike traditional Hotchkiss beam-axle suspension - so the loading conditions will be different.

I still wonder what vehicle the original poster wants to retrofit. It can't be a late model car; beam axles and leaf springs went out of favor in the 1970's. Pickup trucks still use them, but among all the places to save weight in a pickup truck there must be 100 places more advantageous and less safety-critical than this one. If it's for a vintage car, using anything but steel leaf springs isn't period-correct for an original restoration and if it is for a resto-mod, the path to better handling characteristics usually involves replacing the beam-axle and leaf-spring arrangement with something completely different and using coil springs. Substituting composite leaf springs for a Hotchkiss axle won't make that suspension arrangement's other faults magically go away.

 

[GregLocock]

Critically important to the above, the Corvette's springs are designed for large productio runs and are analysed and tested intensively before they are released. Similarly with other designs (they have been used in the UK fr light commercial vehicles for about 30 years).

This is vastly different to a one-off job, where the choice, crudely, is between a fragile product and a heavy one.

Cheers

Greg Locock


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[plutogamer]

Thankyou for the comments.
GregLocock:
"serves no function in guiding the path of the wheels as the suspension moves"
Noted, thankyou. Will contact Flex-com about the sideways load / stress on the springs.

BrianPetersen:
"what vehicle"

http://classic-carshow.com/cars/Vauxhall/Cresta/PC...

"there must be 100 places more advantageous and less safety-critical than this one"
the idea is to save weight on everything possible. Things considered are fibre glass body panels, alloy wheels, plastic petrol tank. Being true to the period with unseen parts is not relevant as the body will be unmodified.