Composites and Unsrpung weight 1

[blackaluminum]

This is a fairly general question that I would really appreciate some feedback on.

The automotive industry is inundated with carbon/composite parts (mostly glass with carbon over for looks) to give that real performance feel and look. Why is there little demand for actual suspension structure upgrades that could not only reduce unsprung weight but improve performance in more than just looks. Suspension components (struts, hubs, tie-rods, a-arms) are simple in design and easy to upgrade or even supply as high end OEM.

Has anyone here come across anything in this arena yet? I would love to get into this segment with anyone interested. I definitely see a market for this stuff.

 

[evelrod]

This is just my take on all this, but...

I see, at least in the present time frame, an extremely complicated route to DOT approval for any such venture due in part to the rough and tumble applications of street vehicles. As to performance/race applications...Considering the presumed weight advantage is mostly a myth as it relates to production based race cars and all the formula types already have such parts...

There is also the cost factor, the 800 lb. $ in the corner! Cost would certainly limit your market, not saying that such a limited market might still be there. I see the production costs as only the 'tip of the iceberg'!

Rod

 

[cibachrome]

The world is overflowing with claims of superior this, that, or something other for these types of parts. Yet, a vehicle manufacturer must certify that the parts meet or exceed all standards of the time and anticipate what the foreseeable misuse of these parts and materials must be. You say they are better but can you prove it to me without me having to run tests, write reports, inspect your manufacturing facility, run legal discoveries and still save time and money? Better yet, do a person-in-the-street survey and find out the answer to your own question. A majority of the public could care less about your 'plastic' parts. And these are the buyers of my car. Oh, just wait until a courtroom lawyer asks you you why your company was so careless that it turned his client into a vegetable and wants $500 million in punative damages. Your company will cut & run, mine will get stuck with the tab. By the way his client used your composite upper control arm for a boomerang and it came back and hit him in the shorts. He was high on E85 at the time.

Next question...

 

[blackaluminum]

I really appreciate the feedback on this subject.

I assumed that we would all understand R&D is a large part of any new idea. I'm sure many people have been burned by "crazy" ideas such as this throughout the years in the automotive industry like that crazy aluminum stuff that dominates all cast parts and pump assemblies and body panels and heating cooling in the industry and those "weird" vinyls and plastics that line all cars in the industry and have made them safer, lighter and more comfortable. I could go on.

The point is: The data is there. Tons of it. Aerospace frames, industrial structures, chemical resistance ability, shock resistance, vibration control capability, acoustic absorption; the list goes on.

Nobody wanted airbags in cars when they were introduced either; oh the lawsuits, oh the burns on unsuspecting drivers, oh the horror of a misfire.

Now find a car without one.

People want mileage, performance and safety. I'd say people do care a lot about the 'plastic' parts.

 

[patprimmer]

I thought some Chevrolet Corvettes already had some carbon fibre suspension parts.

I think Aramid Fibre pulp is used quite a bit in gaskets and brake pads.

Regards

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[GregLocock]

Every car company I have worked for has a test that runs something like this:

drive the car into a 5 inch kerb at 30 mph

repeat three times

Now drive it back to the workshop, under control.





Cheers

Greg Locock

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[Tmoose]

I screw up often enough that I have come to really like materials with isotropic properties that fail first by yielding, but can then handle more than 10% elongation, and can be repaired by welding.

Any one of those pretty much rules out composite materials.

 

[patprimmer]

Well they certainly rule out carbon fibre reinforcement.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tmoose]

From a widely distributed and broadly applied US Department of Defense directive - "Brittle material shall not be used except where approved for a particular application or where its suitability is proven by mechanical shock tests. Brittle material is material showing less than ten percent elongation in two inches for the standard tensile test."

Their definition of shock test is likely a bit more severe than a curb strike, but............

 

[patprimmer]

There is also a large dependency on structure, as Aramid fibre can be brittle, but is used extensively in armour.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

I'm not saying you can't make suspensions out of composites - Pat's suggestion of Kevlar to hold the thing together once it has deformed is a good one. But, Tmoose's criteria is spookily similar to our rule of thumb for ductility.

For a racing car then this criteria could be relaxed a little - but even at F1 levels of research and development some of those cool black or yellow and black suspension arms have steel 'cores'. Naming no names...

Bear in mind that for racing cars the advantage of being able to jump kerbs with confidence far outweighs the hard to quantify advantage of a lower unsprung mass.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[FoMoCoMoFo]

You meant to say street cars in that last sentence, Did'nt you ?

 

[patprimmer]

Sorry. I was not advocating Aramid for suspension components as even though with correct structure it is tough enough for armour, it only works in tension and is really poor in compression as the fibres fibrillate.

I cannot imagine a suspension member where both compression and tension load bearing is not required.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Front lower control arm on a 2WD Ford Territory could be safely designed as a tension member, I think. I was thinking more of using carbon fibre to provide most of the strength and stiffness, but kevlar to provide the ultimate structural integrity.

Cheers

Greg Locock

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[patprimmer]

What would happen if you went backwards over a kerb.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Sure. But that is not the purpose of the test.

The test is a rough and ready approximation to real world failures. If a significant number of customers suddenly started failing tension struts by buckling them, we'd investigate why and introduce another test to cover it. That's how these tests are created - and why even the absurd ones are still used.

Cheers

Greg Locock

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[Neubaten]

Well, my company works into suspension parts for the major european OEMs, and, actually, some of our oldest families of products, the link rods, have a composite/plastic/hybrid version.Mainly, french car manufacturers have a taste for them.

They are not A security parts, but they are plastic, nevertheless. They have advantages from the manufacturing point of view (no multiple step forming/processing required, no welding, etc...), but from the functional as well. Noise reduction, as an example, which is a pain in the ass for the metallic ones. They work both compression and extension, and the plastic seems to have a good fatigue behaviour, specially in the unions, where the metallic ones have weldings.

But apart from this simple linking parts, where plastic works, I see further use of composites very complicated, as the majority of the parts suffer not only tension or compression, but torsion as well, and most of them require thin walls or small sections. I can picture that the only future could be specifically developed composites with hard and ductile fibres orientated specifically and a matrix that could work nicely at both compression and extension.

 

[GregLocock]

"They are not A security parts"

That's not a phrase that I've come across, how do you define that?





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Neubaten]

I'm saying it without checking it, but I think it is a classification derived from the Renault Institute, and says something like "A" security parts are the ones whose breakage implies that the vehicle has to stop, or implies a risk that the driving could be seriously affected.

 

[jandreas]

Has anyone here come across anything in this arena yet?

The engineering and units costs are too high for most road-going cars?