Re: Am I looking at this wrong?
Not totally Tim. Your theory about absorbing the energy is true in circumstances such as the technology in new cars. They make them fold up real easy so your body doesn't see the full impact loads. Aircraft seats are designed to collapse in a bottoming type crash to prevent spinal compression injuries. But let's get back to the issue of ultimate tensil and ultimate yield.
Let's just say for conversation purposes we pull some numbers out of the air ( I got no data books here at home...) that 4130 tubing has a yield strength of 75,000 ksi and an ultimate tensil strength of 130,000ksi. Let's pretend that 1026 DOM mild steel tubing has a yield strength of 50,000 ksi and an ultimate tensil strength of 90,000 ksi.
You crash and roll your car and generate 65,000ksi load on the material. If it's made from 4130, you don't even notice any damage. If it's made from 1026 that sucker is gonna be bent. Now you crash your car and generate 110,000 ksi load on the material. If it's 4130 you've exceded the yield strength and it's now bent. If it's 1026 you have exceded the ultimate tensil strength and it is no longer just bent, It's broken! Using 1026 tubing will shear just like you saw in the photos I posted except at much lower loads than 4130.
The problem with racing organizations frowning on 4130 in the cockpit has more to do with how it is welded than anything else. If you don't stress relieve the weld areas on 4130 it becomes hard and the fatigue life of the welded joint is severely limited. This can be eliminated by heating the welded area to a dull orange glow and cool slowly. Most fabricators don't bother with this since it is time consuming. If you look closely at the pictures I posted you will notice that the weld did not fail. Just the material outside the weld. That's because the welded area is harder than the rest of the structure because it was not stress relieved after weld.
Best,
Dave