rail thermometer

[erikem]

I had the materials class (required for everyone) and the solid mechanics class (one other EE weirdo in there, for whatever reason) as an elective, then it was all EE and math for the rest of my academic career. Those were fun things to think about, like, for instance, what are the differences when the rail is in, say, compression, as opposed to tension? Actually the deflection is easy to come up with, I think, in any case, except I don’t remember having to do anything with members other than in horizontal equilibrium, but then, it’s been a few decades, too.

Chuck,

Where did you go to college/university?

I got my BS-EECS from UC Bezerkeley in '76 and MSNE in '78. Had an interesting time in the lower division Materials Science class - lots of interesting stuff, though some of my EE classmates complained about having to learn the ins and outs of concrete. It was also amusing to note that one of the authors of the textbook used for the course, Craig Barret, went on to head Intel.

As far as rail heating - the heating will come from the inelastic bending of the steel (the hysteresis that Paul mentioned). The upper limit for rail heating an be estimated from rolling resistance - the heat losses from rolling resistance will be distributed among rail heating, wheel heating, journal bearing heating, etc.

Edit: Did some numbers off the top of my head, looks like the thermometer would have to be pretty sensitive to measure the temperature rise on stiff straight track - on the order of 0.1 degree F (or less) for a 10,000 ton train. Temperature rise for curved track would be higher due to increased wheel-rail friction losses.

[bpickering]

I recall that pennies left on the rail head were pretty darn hot after being flattened by the train.

Were the pennies placed there on a sunny day ? Are you sure that they weren’t warmed by the rail’s basic temperature, as opposed to the train’s wheels ? Once the pennies were flattened, they wouldn’t deform any more = not absorbing any more energy. Plus, being copper they would release the heat pretty quickly.

My recollection (this was pre-Amtrak) was that we did this at night and presumably the rail had a chance to cool down. If my less than perfect memory serves me, we were waiting for the southbound San Diegan at Anaheim and the pennies were overun by a northbound San Diegan.

FWIW, I’ve done a fair amount of track work at OERM in Perris, CA and am all too familiar with how hot steel can get in the hot sun.

Those pennies are being heated up by the flattening/deformation.

You can demonstrate the same effect by taking a paperclip and bending it back-and-forth until it breaks. The ends will be warm (even uncomfortably hot, if you did it quick-enough). The heat energy comes from the mechanical work you did in the bending; while a large fraction of said work goes into rearranging the atomic structure of the paperclip (or penny), a portion is turned into “heat” (i.e., vibrations of the atoms in-place).

Note that the pennies never really stop deforming as each subsequent car runs over them; it’s just that in each case, they have already been spread out/deformed, and subsequent deformations will have less material at any instant to flatten out further (only the material at the contact point between the rail and the wheel is being flattened out). Eventually, if the coin stays in place long-enough (perhaps several trains), it will

[ChuckCobleigh]

Chuck,

Where did you go to college/university?

I got my BS-EECS from UC Bezerkeley in '76 and MSNE in '78. Had an interesting time in the lower division Materials Science class - lots of interesting stuff, though some of my EE classmates complained about having to learn the ins and outs of concrete. It was also amusing to note that one of the authors of the textbook used for the course, Craig Barret, went on to head Intel.

As far as rail heating - the heating will come from the inelastic bending of the steel (the hysteresis that Paul mentioned). The upper limit for rail heating an be estimated from rolling resistance - the heat losses from rolling resistance will be distributed among rail heating, wheel heating, journal bearing heating, etc.

Edit: Did some numbers off the top of my head, looks like the thermometer would have to be pretty sensitive to measure the temperature rise on stiff straight track - on the order of 0.1 degree F (or less) for a 10,000 ton train. Temperature rise for curved track would be higher due to increased wheel-rail friction losses.

After getting what I thought was a useless degree and working in the broadcasting biz for a few years, I came back down from Hollyweird to SUDS (or SDSU) and did a BSEE about 30 years ago, then moved out to UCSD for grad school, then into defense contracting because I had educated myself out of show biz, though that was still the most fun part of life.

I suspect, based only on engineering experience and such, that rail heating due to the bending process is probably insignificant, even with respect to flange action. I am not curious enough to take an IR thermometer and do before and after measurements; we don’t have trains long enough or heavy enough down here to be interesting anyway.