The proper term is stress? Since there is also compression.
My 3yo son usually ends up with really "tense" tracks if he manages to build a circle. The lever torque of the track length makes them bend a tiny bit, so there should be tension in the outer rail. The fittings are quite close fits.
FWIW you can get duplo track under enough tension that the tracks no longer have loose give and you can lift it up the entire track without it coming apart. It requires a bit of work to make a track like the one in OP
Don't the track pieces fit together loosely?
And aren't most Lego/Duplo pieces made of such hard and rigid plastic that they don't effectively bend at all?
So while it's still an interesting math problem about angles and lengths, I'm not sure the premise of "tension" is correct here.