Connecting Rod Tech.

[swampbuggy]

I will start by saying that I don’t want this topic to turn into a big argument about different beam designs, now my question at hand is In a 90 degree V-8 engine such as ( or similar to ) a NASCAR cup engine ( excluding the bolts ) what are the most highly stressed specific points of the rod and or the cap ? Thanks to any body who can give factual input, Mark H.

[panic]

In compression or tension?

[bentvalves]

google CFD connecting rod stress analysis.

[ptuomov]

Under tension, I’d say each rod section could be evaluated by the total piston assembly and rod section mass divided by the cross-sectional area of that rod section. So it depends on the rod design.

[panic]

AFAIK FEA only allows a single input in 1 plane = 1 test each for tension and compression.
The actual stress on each molecule of the rod depends in part on its vector.
In common understanding, the pin eye is subjected only to reciprocating forces, but the entire eye (and pin bushing, pin) also oscillates, with the top of the eye in direct opposition to the beam below the pin.
In similar complex fashion, each successive molecule down the length of the beam toward the crank begins to add a rotating load to it reciprocation, with the big end almost pure rotation (again, the bottom of the rod opposing the beam terminating in the big end).
However: the crank rotation acts both with and against rod big end rotation.
These factors suggest that rod ratio (and pin offset, where present) must be included in any simulation.
Tough question, impossible to quantify inputs TIKO.

[ptuomov]

“From what I’ve seen, the transitions between the beam and the big end and where the beam transitions to the small end, those two radii there definitely see the most stress in most of the cases I’ve looked at,” Stothers said.

https://nasaspeed.news/tech/engine/conn ... d-physics/

[digger]

AFAIK FEA only allows a single input in 1 plane = 1 test each for tension and compression.
The actual stress on each molecule of the rod depends in part on its vector.
In common understanding, the pin eye is subjected only to reciprocating forces, but the entire eye (and pin bushing, pin) also oscillates, with the top of the eye in direct opposition to the beam below the pin.
In similar complex fashion, each successive molecule down the length of the beam toward the crank begins to add a rotating load to it reciprocation, with the big end almost pure rotation (again, the bottom of the rod opposing the beam terminating in the big end).
However: the crank rotation acts both with and against rod big end rotation.
These factors suggest that rod ratio (and pin offset, where present) must be included in any simulation.
Tough question, impossible to quantify inputs TIKO.

FEA can simulate anything you want but the complexity and time goes up exponentially therefore most people break it down into a more manageable practical analysis that gives 98% of the answers to drive the engineering.

[digger]

Highest stress is in the bolts

[engineguyBill]

It is commonly stated that a connecting rod goes through the most stress as the piston goes through TDC on the exhaust stroke. Most high performance rod manufacturers should be able to provide you with test results that compare 'H' beam and 'I' beam rods, as well as various cap designs and rod bolt nomenclature.

[digger]

It is commonly stated that a connecting rod goes through the most stress as the piston goes through TDC on the exhaust stroke. Most high performance rod manufacturers should be able to provide you with test results that compare 'H' beam and 'I' beam rods, as well as various cap designs and rod bolt nomenclature.

Actually most engines the compressive rod stresses way out do the tensile stresses. Not the cases with an nascar rpm levels though.

The answer to the op question is depends on the exact rod geometry the transition rod little or big end to beam transition or the spot face under the bolt head on the cap are areas that show hot spots. You see many cheap rods with garbage cap geometry near the bolt spit gave yet these rods have been fea’d lol

[swampbuggy]

Digger please define the meaning of the word fea'd , excuse me if i seem dumb, Mark H.

[BCjohnny]

Highest stress is in the bolts

Always been an advocate of 'serrated' rod / cap designs, interlocking

While it doesn't completely eliminate the shear loads on the bolt, it at least vectors them through, say 45 deg, or such

[midnightbluS10]

Digger please define the meaning of the word fea'd , excuse me if i seem dumb, Mark H.

Finite Element Analysis. So he's said when that, process has been done, AFAIK. He making a noun into a verb. Using a word to describe itself or some such lol. He's using it to say they've been "Finite Element analyzed"

[panic]

FEA can simulate anything you want

Please explain input for crank rotation?

[bentvalves]

It would appear that I have confused CFD with FEA.

engine builder had an article on FEA not terribly long ago, worth a read.