get back to work....

 

I never hurt the bottom end of my cheap DSS long rod 306 kit with forged I beams and the stock cast crank for 6 years and multi ten second passes.

 

material there made with .... and rpm , i read once a chev 350 at 6000 rpm the pull on the rod was around 2000 pounds on the exh stroke and the engine builder article stated thris causes most failures , the pinching of the pin is intrusting but considering press pin use for years in oem i dought any harmonics well any extra harmonics are generated,,its kinda llike a roller tip rocker it really doesnt have revolutions... a correct arch on the tip of a rocker arm would achieve the same effect

 

Just looking at the rods' geometry, an I Beam rod is stronger in the direction you are describing. An H Beam rod is more resistant to bending the other way (sideways). I'd have to run some FEA to see which does better in torsion.

 

It would be interesting to see what you find.

 

I sketched up three cross-sections. I-Beam, H-Beam, and Pauter-style X-Beam. All profiles were sketched inside a 1"X2" rectangle. Web thickness was tailored to each design to yield an equal cross-sectional area (read: weight) between the three. The outcome was three 6" long beams that weighed exactly 1.571lbs each. The playing field is level.

(Note: I tossed in the X-Beam just for laughs )

Results:
Torsion: Twisting the beam.
In the torsion test, the I-Beam and X-Beam rods were almost identical. Both were about 20% stronger than the H-Beam. I expected the I-Beam and H-Beam to be close, but I didn't expect the X-Beam to compete. Perhaps I should take this rod seriously................... ON TO TEST #2!

Bending: Simulating buckling with crankshaft rotation.
This is where the I-Beam really shines. It was 1.5 times stronger than the H-Beam and 2 times stronger than the X-Beam (ha! there we go!). This type of load is important because the rod is free to buckle in this direction (nothing stopping it except itself). This is the direction I-Beams are always loaded in the construction industry. They're one of the most efficient profiles for this type of loading.

Bending: Simulating sideways buckling.
H-Beam wins hands down here. It was 2.6 times stronger than the I-Beam and 3.7 times stronger than the X-Beam (hahaha!). However, I'm not sure how much force is really exerted in this direction because both the rod bearing and piston try to keep it from buckling this way. Has anyone ever had rods bend this way apart from a catastrophic event?

Tension: Pulling apart.
I didn't simulate this situation because, unless your profile is generating some crazy stress concentrations as it transfers force into the big or small end, the strength of the beam will always be a function of cross-sectional area and material strength. Cross-sectional area was constant in this test, so all three would have performed the same.

One profile that I didn't test was the other style of X-Beam which is basically an I-Beam with a slight H-Beam relief in each side. Howards offers this rod for the Duramax. There is a heck of a lot of material to work with in those diesel rods, so I guess they might as well just go ahead and mill out random areas. I don't think there's quite enough material to do this with a normal I-Beam though. I'd expect it to fall somewhere between the I and H-Beams in buckling since it's kind of an average of both.

So there you have it. I'll get some pictures of the tests up soon.

 

Wow. Now this is exactly the type of information I was hoping for, and amazingly, how I imagined the results might be.
Thank you very much, JGTurbo.

 

In the 2007 Oliver connecting rods catalog there is a section and discussion about thier design and why they have an I-beam. It includes a FEA model pic and some info. I was going to post it but pretty sure it is to big.

JGT turbo thanks for posting up your findings, a few questions: what FEA software did you use? I assume this was a simple static analyis evaluating different cross sections of rods? How did you constrain the model?

I will see if i can post up the info I found some how....

 

Centrifuge:If you shoot me an email I'll make sure it gets attached to this thread. Shoot me a PM about it if you want it done.

Besides that, I wanted to throw a few things in here

1)If you're running bushed pins and not binding does the I-beam's extra strength really matter when it comes to rotational torque
2)Certain engines offset the rod compared to the piston's center line. The one that comes to mind for me is the 4.3L v6 Chevy. In this case it may be more prudent to use pins.
3)How come we never see a tubular connecting rod? I mean I realize that being multi-piece has its flaws but either a boxed or a DOM based connecting rod may be able to give significant strength for a set weight and allow hybridizing of materials if done correctly
4)Speaking of hybridizing materials, even though the expansion rates would differ how come we don't see people doing something like TI caps and steel beams? The weight savings from that alone would be noticable.

 

Exactly. I used Inventor Professional 2011. I prefer Solidworks, but Inventor is a little easier to come by. Yes, it was just a simple static analysis. In all three tests I constrained one end of the beam and loaded the other end. Not an exact model of what's going on inside the engine, but it's a good tool for comparison.

 

how about metal matrix rods like the jager rods? light weight with strength, expensive though and near impossible to come by at the moment.
interesting thought behind them though...

 

+1 on the metal matrix composite rods! They'd be light as aluminum and almost as strong as steel. However, the most popular matrix is aluminum so I'd wonder if they would display the same longevity issues as regular aluminum rods. How about this material for a set of rods (390ksi !): http://www.matweb.com/search/DataSheet.aspx?MatGUID=de22e04486ff4598a26027abc48e6382

Here are a few videos of the tests I ran. They're pretty basic.
http://youtu.be/HWCI1s5hCKE
http://youtu.be/tA_qVoOP33U
http://youtu.be/ELcacoGv_rs
http://youtu.be/5DxqmnIdLEw

 

Some other interesting videos.

http://youtu.be/uTpRfREYa9Q
http://youtu.be/KtdHYKFCX5A
http://youtu.be/KtdHYKFCX5A

 

It's interesting to see which plane most of the flexing and bending is taking place in with these computer sims.

 

Cosmos works is good for basic stuff quick and easy, I have a seat of that on my home computer. I would love to do some dynamic modeling of systems at different RPMs, temps etc. Thanks for posting up the videos!

 

Hey Guys,

This is a good read regarding FEA and connecting rod design. Take a look, i think it is sound information from a company who is known for great connecting rods (Oliver). I have a set of their rods in my SBC.

sorry for the quality, i had to make it small enough to attach

 

Just a comment, The company located in Dearborn, Michigan has used the "H" Beam Manufacturers Rods in the majority of their Research Engines the last few years. As was said, both rods are an excellent design. The "H" Beam Manufacturers Rods could be ordered and received in 6 weeks vs 9 months for the "other guys" custom rods. The "I" Beam Manufacturers Rods cost a lot more when the word "prototype" is used.

Most of what you read anymore is Advertising hype "my rod is better than your rod"

I guess I go more by a statement like "Nearing our 50th anniversary, the name "Cxxxxxxx" is synonymous with connecting rods. Cxxxxxxx has won more races in virtually every format of motor-sports than any rod manufacturer in the world.

Aluminum Rods have also been around a long time. Mickey Thompson, BME, etc but some of the new guys are designing exceptional aluminum connecting rods.

I would say, do your research and then buy the best that you can afford.

Tom Vaught