Connecting rod loading
Connecting rod loading
(OP)
When looking at the front or rear of a normal automotive or industrial piston engine, that is the vibration damper end or the flywheel end. In your opinion what sides of the rod see the most loading or stress, the right and left sides or the front and rear? Just curious of responses not asking things I don't know or understand. And if you want to get real involved use normal CCW as viewed at the flywheel end.
RE: Connecting rod loading
My comments are based on mag particle testing a bunch of engine parts when working in a specialty machine shop in the last millenium.
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I'd say down at the Crank shaft end, keeping the big end bore round at the exhaust stroke TDC is very difficult, and any geometry anomalies ( rod bolt head clearance notches etc) are likely to be the highest stressed areas ans subject to fatigue failures.
Fatigue failures of the ubiquitous I=beam shank were pretty rare, and likely to originate at a major surface defect, often man made, like filing or sawing notches in the I-beam to number the con rod. The orienation of the I-beam shape is doubtless convenient for forging a production part, but if the section properties needed more beef in the fore and aft direction, then they would have been forged as a different shape I believe.
Up by the wrist pin end failures were pretty rare indeed.
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Fred Carillo was a proponent of H-beam rods, but those may have had an advantage for machining from billets for custom lengths.
Their superb metallurgy and quality may have more do to with Carillo rods reputation for durablity as the choice of beam section choice.
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Under extreme boost ( and perhaps even more extreme detonation) or heavy doses of nitro or hydraulic locking or when valve heads break off and jam between the piston and cylinder head, when compression loading dominates and can be uniform or highly eccentric, almost anything can happen.
http://pics.tdiclub.com/members/drivbiwire/Blown%2...
https://www.bimmerboost.com/attachment.php?s=a890f...
https://ls1tech.com/forums/attachments/generation-...
http://www.grumpysperformance.com/rod2.jpg
http://s19529.pcdn.co/wp-content/uploads/2017/03/c...
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In the days before the availablity of high performance connecting rods, modifying stock con rods by various means was about the only choice.
Carefully done "Boxing" was a means to buy short term reliability.
http://image.carcraft.com/f/editorials/boxed-conne...
Mag particle inspection would often reveal problems developing in the welding, as might be expected.
RE: Connecting rod loading
Pattern failures in particular engines that I've seen aren't correlated to how close they are to the flywheel. They're more correlated to known deficiencies in oil distribution in the bottom end.
RE: Connecting rod loading
je suis charlie
RE: Connecting rod loading
As an example say the crankshaft is locked at say 45 degrees after TC on the power stroke, and there is some tons of pressure pushing on the piston. What do we see?
RE: Connecting rod loading
Cheers
Greg Locock
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RE: Connecting rod loading
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Connecting rod loading
The rod has a hinge at both ends. With the exception of hydrodynamic forces in the bearings, which in any healthy engine are going to be very low, there is no way for the piston or crankshaft to induce torque, and thus produce a bending load, in the rods.
RE: Connecting rod loading
Even these guys understand the subject matter a bit more.
http://blog.wiseco.com/wisecos-new-2000hp-capable-...
Since my simple example was not understood, just think of a hydraulic lock condition, that would be considered an extreme loading condition would it not?
So what side or sides of the rod is loaded the most?
RE: Connecting rod loading
The connecting rod is a two point load member owing to the swivel action of the bearings on each end so the the acts through those two centers with the exception of the side to side acceleration forces.
Under compression the rod is a column so the Euler column bending formulas can be used to calculate the additional bending forces that add to normal compression loading.
RE: Connecting rod loading
RE: Connecting rod loading
The only loading on the rod in that situation is pure axial. (Assuming the two bearings are frictionless) Yes the rod will eventually bend but that is a "column buckling" phenomenon.
To answer your original question, the sides of the rod facing away from the crank axis will experience the greater stresses, but that is a dynamic phenomenon - only present at speed.
je suis charlie
RE: Connecting rod loading
RE: Connecting rod loading
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Connecting rod loading
Be wary of making engineering judgments based on information provided by marketing personnel.. like a press release.
The rod is loaded in axial compression- there is no induced bending moment.
The bending you see in FEA plots and in failed parts is due to buckling, not a torque load. It's a different phenomenon.
RE: Connecting rod loading
je suis charlie
RE: Connecting rod loading
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Connecting rod loading
- is the pressure within the combustion chamber at any given crank angle constant?
- if the centre of gravity of the piston is not coaxial to the rod axis what happens under tensile inertia loads?