Going beyond yield to the plastic region means PERMANENT DEFORMATION. The shape changes. If the shape changes, and the chassis gets faster (this never happens) that would mean that the chassis was the wrong shape to start with. So we are to believe that chassis are designed wrong, in hopes that they will be bent into a shape that works better? This is just absurd.
Bending in use is simply not controllable, which is why high level competitors cycle through frames so much more often than recreational racers. Bending means the chassis is compromised. In other words, just because a chassis bends, does not mean it is designed to function at its best after bending. It is meant to perform at its best BEFORE it bends. Bending is an unfortunate side effect of use at a high level (curbs, etc). As we know in motor sports, it is the consumables that really cost. But at high levels of competition, EVERTYHING is a consumable. A frame is no different than a tire.
That said, as the paper Nick posted explains, if you can return a chassis to its original shape (straighten it), it will perform well again. But high level competitors, factory teams, etc, so not have time to mess with that, so they just change chassis often.
No they are just made from different alloys of steel iām sureā¦ Even heard of some chassisā using heat treated material or being heat treated after welding. As far as karts go, different steels make a drastic difference in how they handle and feel.
TJ, four ātypesā of heat treatment?
Normalizing
Soaking at Critical Temperature
Quencihng
Tempering
Those are different phases of heat treatment for steels, but they are all parts of the same process. There is also nitriding and/or carburizing for low carbon alloy steelsā¦this is the sort of thing they do to make bearing races and rolling elements hardā¦
Sorryā¦I donāt buy that they are doing ā4 types of heat treatmentā on a kart chassis. I specify HT for rotating machinery components, and it is expensive. Kart chassis are not expensive.
Yes. Max-effort cornering/curb hopping induces plastic strain. Not much, not everywhere, but enough to measure and enough to really cut down fatigue lives. Highest stress zone is exactly where you think it is, not helped by the thickness transition at the weld.
I believe thereās also BKW (lightly cold worked) and BK (cold finished as drawn) but they werenāt offered.
They didnāt want to use different sizes, available but not preferred.
Heat treatment doesnāt effect the flex, it does effect the Yield Point.
So Iām going to posit a hypothesis (additional to my own post i refound below). A kart is always under some load, through its own weight and the quite substantial (proportionally) weight of its driver (or the drivers lead in @tjkoyenās case ). In part of cornering, some part of the kart is entering the plastic region, maybe only slightly, and the load of the weight of the driver is bending it back again (plus the going left and right as we do on most kart tracks). This back and forth hardens the frame over time and also deforms part of it. Itād be interesting to just go round left hand corners for a race length and see if the frame deformed (bent) in that direction. Itād have to be a typical kart surface, not a dirt oval, that relies on the kart keeping a wheel up to be fast.
So by using hardened tubing, designers are moving the yield point to have the kart only just go over it for the given tire engine combo.
I donāt believe this to be true. Springback/flex (whatever you want to call it) are proportional to yield strength. Which is a by product of different heat treatments. Been awhile since I was in my college material science book, so Iām only 80% positive on that. Someone Iām sure will fact check me.
Or notā¦ Modulus of Elasticity seems relatively unaffected by heat treatments or chemical composition in steels. So this leads to rabbit hole #2. What then is affecting axle stiffness? I think we also beat that to death in another thread.
Anyone remember the old Kart Mini chassis (Brazil) and their range of axles? They had a crazy range of axles based on different heat treatments, seemingly localized to various positions on the axle (multiple areas with different coloration). That was a next level head scratcherā¦
I never noticed that, but the Kart Mini guys really ripped in Rotax back in the day. Gabby Chavez was one of their drivers along with a few other really good South Americans.
From what I heard the founder of Kart Mini knows a lot about karts, donāt know if heās still alive. There are some saying they want to start to sell in Europe in the future
Catching air or hopping karts tends to do that. 
). In part of cornering, some part of the kart is entering the plastic region, maybe only slightly, and the load of the weight of the driver is bending it back again (plus the going left and right as we do on most kart tracks). This back and forth hardens the frame over time and also deforms part of it. Itād be interesting to just go round left hand corners for a race length and see if the frame deformed (bent) in that direction. Itād have to be a typical kart surface, not a dirt oval, that relies on the kart keeping a wheel up to be fast.
I think we also beat that to death in another thread.
