connecting rods materials

[Jersey Tom]

From personal experience I would not use aluminum as a bearing material. Galls up so damn easy, unless you use an MMC.

I'd be pretty iffy on using carbon fiber con rods. You'd have to do some wicked fiber layout, do it very repeatedly, and get some serious fatigue data in there. Beyond that I doubt you'll find a resin that will go up to engine temperatures and not transition to glass or straight up turn to liquid or burn.

Forged Titanium would probably be my choice, or something like 300M steel (S155 I believe for you English types). Titanium can have really high endurance limits, can be super light. Will stretch appreciably more than steel but you can account for this.

300M just by nature of being absurdly strong you can make fairly light/thin sections from.

[riff_raff]

"Do you know where i may find more information on the use or possiblility of carbon fibre conrods"

Connecting rod beams (in a 4 stroke engine) experince both tensile and compressive loads. While graphite fibers are great in tension, they are useless in compression. That is why they have not been used as a material for con rods. Also, the usual resin matrix materials (epoxy, polyimides, etc) don't perform very well in hot engine oil.

Some people have experimented (VW?) with filament wound fibers over a metal column, but there was no real benefit in the end.

[Jersey Tom]

I beg to differ. I've used carbon tubes (90% unidirectional or so) in compression and they're stellar.

[riff_raff]

Jersey Tom,

From Timoshenko: "Composite will break at the lesser of matrix collapse or fibre buckling."

Essentially, what that means is that a composite (ie. graphite reinforced epoxy) is really only as good as the matrix in compression. A good epoxy resin might achieve 15ksi in compression at engine operating temps. A more expensive polyimide resin might be 30% better.

An individual fiber looks "stellar" in compression as long as it doesn't buckle. But once you yield the resin matrix that keeps the fiber from buckling, the fiber will immediately also fail (in buckling).

[Belatti]

I know that Renault used titanium rods that worked well in F1 engines in the 90´s.

Bearings can have several layers (2-3 or even 4).
There are bearings of Al-Sn alloys, copper alloys, babbits and galvanics for some applications, but I really ignore what F1 bearings are made from.

Some technology I know is called Sputterlager, a layer of metal that is applied to the bearings evaporizing under very low absolute pressures plasm (like an electrodeposition).

[humble sabot]

That's known in english as either 'vapour deposition' or 'sputter deposition'.
It can be used to coat a surface in a very hard and slippery material, say, titanium nitride. Which i suppose could be useful in certain rod bearing applications, but, it will be a thin coating and anything like that relies in very large part on the toughness of the substrate. Aluminum anodising converts the surface of the aluminum to aluminum oxide, which is retarded-hard, but there are limits to how deep the anodising can go, and it can be worn through not all that much difficulty.

Forging does not increase strength, it improves the metal's grain structure. Which allows a higher fatigue limit.

that's assuming you designed your tooling properly

[Belatti]

...

Forging does not increase strength, it improves the metal's grain structure. Which allows a higher fatigue limit.

that's assuming you designed your tooling properly

WRONG!

I made an internship in a Federal Mogul piston plant, here in Argentina.
The tensile strength of Aluminum-Silicon alloys can grow from 22Kg/mm2 to almost 40Kg/mm2 by forging, with very small silicon grains in the metalographic microstructure (thus, this is a little difficult to achieve and the process must be well controled).

I learnt a lot there about road cars pistons tecnology, but still I ignore about F1 piston tec, any reply with information will be appreciated.

[riff_raff]

Belatti,

The endurance (fatigue) limit of any metal, especially Al alloys, is highly dependent upon the metal's microstructure. The endurance limit for a metal (the stress limit at which it can sustain an unlimited number of load cycles) is usually defined as the "knee" on its S-N curve. The endurance limit must be corrected for the magnitude of the load reversal (compression vs. tension) the metal structure will experience during its service life. This is referred to as its "R" value. And as I'm sure you're aware, the number of load cycles a connecting rod experiences can add up very quickly.

4-stroke connecting rod beams see a complete load reversal every other stroke. 2-stroke connecting rod beams are almost always in compression.

Take a look at the S-N curves for forged Al alloys here in MIL-HDBK-5H:

http://www.grantadesign.com/userarea/mil/mil5.htm

[Belatti]

Sorry riff_raff, you are right, I was not explicit enough...

What I meant to tell Humble Sabot was wrong was "Forging does not increase strength"

The improvement of metal's grain structure in forging, which allows a higher fatigue limit, is right.

Some facts for everyone better understanding:
- AL alloys theorically do not have fatigue limit (there is no "knee" on its S-N curve), AL will always fail due to this, no matter how little is S, that is why:
- AL alloys "practical" fatigue limit is usually calculated at N=5*10^8, wich is a "high enough" number of cycles (ej1: an F1 engine at 20000rpm for 416 hours and you´ll get N=5*10^8 cycles) (ej2: an road car engine at 6000rpm for 1388 hours -equivalent to 235.000km and you´ll get N=5*10^8 cycles)
- Steel alloys does have fatigue limit, usually calculated at N=1*10^6(there is "knee" on its S-N curve), any load applied < that the S value in the S-N curve, will -theorically- never brake the rod...

PS: thank you for the link!!!

[ss_collins]

There is a room in a country in Europe in which the designs for every engine in F1 is stored - particularly detailed are the con rods- the room is called Shanghai and I was allowed to look in the door - something even F1 teams are not allowed to do.

[ginsu]

sam, did you see the chalice of christ there too?

[Carlos]

ginsu - What did you imagine the best conrods were made of?

ss_collins - Actually sounds like F1 Shangri-La. Will you offer a little more detail, once RCE is on the magazine stands? Just a few details

[humble sabot]

Bellati, if you thought i meant what i think you thought i meant, perhaps your understanding in terms of breadth of application just didn't lead you to put certain 'two's and 'two's together. In the case of a con rod or a piston it will require very simple forging processes that would not leave any loopholes, if you will. There are however, many applications outside of those two in which it will take much engineering and effort to realise a structural improvement by forging versus simply cutting the shape out a of a block of billet, or casting the part. In some cases ya just plain can't make a structurally equivalent part by forging within a similar weight, and if you can, it might have to be done by hand, which isn't foolproof. Note; i am speaking very broadly here.

[ss_collins]

Carlos once the company involved clears the text I'll put it in the mag - its obviously related to this thread.

[Belatti]

humble sabot, what´s the problem then??...
for motor racing applications (wich is the subject we are talking about here...) forged pistons and rods are better (in strenght and fatigue limit terms)... any other application is world appart
are we even then?