H-Beam Vs I-Beam conrods...

[Kagetsu]

Probably a little general a question, I've always been under the impression that the H Beam conrod has a greater load capacity in the centre (where the majority of the force is located) and distributed across a larger area in comparison to I beam conrods. I've been hearing however, a lot of people (who probably don't know much about much really) claiming there is little to no difference in strength and that the weight saving of the I beam conrods is far more substantial.
Can anybody clear up these myths? I've not really seen anything firm in proof for either case, so I just don't know.

[ed]

yeah, ive not got a reference, but my money would be on I beams...

theres not a lot of side/side load to take advantage of the design of the H beam, but there is a lot of front/back (for want of a better description) load associated with the continual acceleration/deceleration of the rod on that axis - which is where the I beam is more strongly designed. the 'exactly on axis' compressive/tensile differences would be minimal id think - and would come down more to individual material, style of fabrication and finishing

slightly lighter as you say as well

but the argument has been going on for a while now, and i dont think there is a universal answer.

thats my 2c

[ed]

oh, and i forgot to add that obviously the compression/tensole loads on a conrod are almost never 'on axis' down the guts of the rod, and again, the I beam is MUCH better designed to distribute this load

[Kagetsu]

I just re-arranged my search through google, and actually ended up coming up with some interesting information (funny what happens when you put I beam and H beam around different ways.

Firstly this one from another forum:
http://forums.hybridz.org/showthread.php?t=109350
Lots of information on other sites too, plus constructive arguements.

This one has more information on materials and general uses.
http://www.hotrod.com/techarticles/c...nnecting_rods/

A nice little PDF on the two types (H Beam/I Beam).

[ed]

http://em-ntserver.unl.edu/Mechanics...0Rods%20VI.htm

[Kagetsu]

I actually seem to be getting a different picture from all of these then what I'd previously thought. Maybe it's better to use I beam 'rods.

[ed]

look at any aluminium rod

THAT is the shape you need. an aluminium rod will be made in the strongest possible mechanical configuation. apply that back to your steel rod

[joecoolmk2]

don't forget that rods are getting pushed and pulled up and down. if they haven't got sufficient strength on the sides they could snap out to the side. as an example look at a paper airplane. a normal piece of paper would folp around and not fly unless it is folded to angles to give it strength.

basically what i'm saying is an i beam can be as strong as an h beam, but needs more metal to do so, therefore the h beam is stronger than an i beam of the same weight.

[clubagreenie]

depends which way the load is acting as to how 'strong' something is

and in an engine, the i beam has the material in the right spots

[brett_celicacoupe]

look at any aluminium rod

THAT is the shape you need. an aluminium rod will be made in the strongest possible mechanical configuation. apply that back to your steel rod

ahhh but alloy doesnt behave exactly like steel under compression and tension.


if you want to make an accurate comparison then you will need to do (or find on google) a comparison with I-beams and H-beams with identical cross sectional area.


if you could be arsed doing a bending moment diagram and failure cals for both beams then i think youll find the H-beam will be able to withstand more shear force..... meaning it wont 'bow' under comp loading


however...... predicting the compression beam strength required for the front-rear and side-side direction of a engine can be difficult.

so it basically comes down to where the most likely place of fail is and then 'beef' that region up


but dont forget that weight and production costs need to be taken into consideration by car makers. nearly all stock production cars run I beam but that may be just because of the strength:cost ratio being better than H-beams. similarily, the engineers may be able to acheive equal compression rigidity with a lighter desing (H-beam)

if the product was made by a reputable brand that have made quality parts then i'd say just go with the 'new' design. it was obviously made like that for a reason, but hopefully not just as a sales gimmick

[oldcorollas]

to my uneducated mind, it depends on the relative magnitudes of the bending forces on the rods (from high rpm, and the inertia of the beam of the rod), and the magnitude of the tensile/compression forces.

metal is far stronger in compression that tension.
many rod failures occur due to tension (or a combination of bending and tension) from high RPM.
some fail from bending and compression loads.

it seems unlikely that withouth a significant bending moment, a rod will fail in pure compression.... or pure tension for that matter (since the rpm/bending force magnifies the tensile forces at the edge of the rods..

for high RPM.. look at F1 rods. wiiiiide base to reduce the magnitude of the tensile force at the edge of the rod resulting from the bending forces from RPM.

[Hiro]

Just thought I'd let people know, I'm actually doing a project on stress analysis of automotive conrods for my advanced CAD subject (using 4AFE and 7AFE conrods as a model base). I'll try and get my hands on some I-beam conrods too, I'll let everyone know what the results are when I get them

[Kagetsu]

That'd be excellent if you could. Just generally H vs I beam. I'm still leaning towards the H beam design.

[oldcorollas]

Hiro, i'd be very keen to know what kind of combination loading regimes you will be using too (ie, bend, stretch, compress, side load etc)

[Hiro]

Hiro, i'd be very keen to know what kind of combination loading regimes you will be using too (ie, bend, stretch, compress, side load etc)

If I model it right, it'll be a mechanism with a cyclic pressure load applied to the piston, so with the right restraints all the proper loadings should be present.

[brett_celicacoupe]

it would be interesting if you could compare a H beam and I beam with the same cross sectional area. same material as well.

although probly not possible

[kingmick]

If your guys really want to know why not just email or ring people like John sydney{race engine builder for supercars} or Cosworth even Hendrick motorsport, much easyer and you find out why they use certain Rods.
V8 supercar have been using Oliver{very very expensive} I-beams for a few years now because they have a low rev limit and they can handle 1000km's before being thrown in the bin. They use the I-beams to lower rotating mass as thats all they can do with there rev limit, they make everything lighter{rotating mass} to help spinup to point that matches the strength needed with some saftey margin to get the 1000kms or so till the $30k+ freshen up.
Dosnt matter which is better its more a cost thing to most people, i cant see many people on here{myself included on my own engines} spending $4000+ on a set of top quality I-beam rods!

Email some of the big engine builders, im sure one of them will tell you there reasons.

One for Stew, i have somewere and ill find it of were there developing the rods using the fracture line of the steel for the big End join, to get more strength.

[ed]

PM me the emails of these engine builders mick

cheers mate
ed

[kingmick]

look them up or ill have a look for them tommorro slacko

[ed]

lol - you have em already - just PM me - ive got bags to pack! going to churmanny