Connecting rod internal or intrinsic (or spontaneous?) heat generation

[Tmoose]

A frequent poster on an automotive group joined in a discussion about connecting rods from engines in service showing some local discoloration presumably due to having been hot.

After the big ends and pin ends were discussed, and "we" moved to localized discoloration of the beam of the rod, the poster said this -
"But do not assume that heat is not generated locally on the beam of the rod. Heat is generated by the flexing of the rod -- it is not a theoretically rigid construct. If there are flaws or stress raisers that area can easily overheat and leave witness marks or color change."

I'm thinking that post may belong in an episode of "Big Bang Theory"

 

[CoryPad]

Easily proved or disproved using strain energy from deformation and surface energy during fracture. Adiabatic heating is a known condition too.

 

[tbuelna]

In order for a steel conrod beam to experience sufficient heating to produce a change in color to "straw" or "blue" from tempering, it would require a substantial amount of heat energy input. I cannot imagine there being enough hysteresis energy being created in the rod beam just from flexing to produce a temper change in the steel rod material. I also cannot see enough friction heat being created from sliding at the rod split face to do the same. The rod is cooled by oil splash, and it would not seem possible for the rod to get hot enough to produce a temper color change.

 

[Tmoose]

Hi Tbuelna,

The poster on the other group does get a bit esoteric at times.

thanks,

Dan T

 

[IRstuff]

Not only is it cooled by the oil, but if it got hot enough to discolor, I would think the oil trying to cool it probably would have cracked, and there would be tons of carbon deposits everywhere.

TTFN
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[Comcokid]

Any discoloration in the rod was likely there before the engine was assembled. Probably from machining operations and/or heat treatment of the rod during manufacture.

 

[RossABQ]

What is the context? Ultra-high-output racing engines or pedestrian street engines?