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lighter car leaf springs
2

lighter car leaf springs

lighter car leaf springs

(OP)
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: superior spring (leaf spring) materials to 17-7 ch900 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

RE: lighter car leaf springs

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

Quando Omni Flunkus Moritati

RE: lighter car leaf springs

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.

RE: lighter car leaf springs

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

RE: lighter car leaf springs

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.)

RE: lighter car leaf springs

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.

RE: lighter car leaf springs

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

RE: lighter car leaf springs

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

RE: lighter car leaf springs

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


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: lighter car leaf springs

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

RE: lighter car leaf springs

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.

RE: lighter car leaf springs

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.

RE: lighter car leaf springs

Quote (JStephen)

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!

RE: lighter car leaf springs

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.

RE: lighter car leaf springs

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.

RE: lighter car leaf springs

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


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: lighter car leaf springs

(OP)
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.





RE: lighter car leaf springs

"Will contact Flex-com about the sideways load / stress on the springs."

If this quest for light weight is driven by racin' , then a panhard bar would not spend the entire 70 lb weight loss, if its side loading was not objectionable.

RE: lighter car leaf springs

A panhard rod would be capable of better side-to-side axle location and remove the obligation of absorbing side loads from the leaf springs ... but if you do that, make sure the panhard and the leaf springs aren't both trying to do that job differently, thus binding up against each other. The panhard should be as long as possible, as horizontal as possible at nominal ride height, and with its pivots at the same height as the leaf springs, and it might be advisable to arrange for some sideways compliance (intentional sideways clearance, soft bushings, etc) in the way the leaf springs attach at the pivots at both ends. This way the leaf springs don't have to take up side load. They'll still have to absorb axle-wrap loading from accelerating and braking, and fore/aft locating-the-axle load between the axle and the fixed pivot.

One thing to be mindful of is that conventional leaf springs are built with multiple thin leaves partly because this causes the leaves to rub against each other a bit when the axle moves around, which adds some (frictional) damping to the system in a direction that the normal hydraulic dampers can't fully absorb. This helps dampen out oscillatory axle-wrap, which would otherwise lead to all sorts of axle-hop and other bad stuff. I don't know if composite springs would be able to be constructed in that manner and survive. (It also adds to the rough ride that conventional leaf springs are notorious for, but that's another matter.)

All of those loads can also be taken up by linkages, and with less axle-wrap and deflection than leaf-spring setups have, so that if you get the geometry right, the axle-wrap doesn't happen in the first place. And by the time you're done all that, you might as well do ALL of the axle locating with a linkage, and toss the leaf springs in the trash and put in a set of coil-over shocks!

The Corvette independent setup doesn't have any of these issues since the wheel spindles are fully located by the linkage, the hydraulic damper is responsible for all the damping, and the spring only has to be a spring in one direction of movement.

RE: lighter car leaf springs

Stephen (Mechanical) wrote -
"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."

A broken spring, whether leaf or coil, almost certainly will show the crack initiated from a badly rusted area.

Up here in Massachusetts the roads are salted pretty aggressively in the winter. Modern car bodies suffer somewhat less than in the old days, probably because there are warrantees requiring no perforation for X miles and Y years.
GM says this "All body and sheet metal components are warranted against rust-through corrosion for a minimum of 6 years/100,000 miles (whichever comes first). "

I think it is significant there is no mention of suspension parts or brake lines or even frames. This is confirmed by A peek under late model US trucks around here that sometimes reveals the body is going to outlast the rust ravaged nether regions. A rusted leaf (or coil) spring is far more vulnerable to fatigue cracks.

RE: lighter car leaf springs

RE leaf springs not rusting to the failure point: There are a lot of owners of boat trailers in salt water service who would disagree with that premise. Even well rinsed after use you are lucky to get much past 3 or 4 years.

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