That's nothing to do with the flat ends. It's the material and temper of the Spring unit.
Broken springs tend to show a typical stress fracture normally just after the first coil.
In reality its not that simple:-
https://pearl.plymouth.ac.uk/bitstream/handle/10026.1/2300/DANIEL%20GERHARDUS%20HATTING.PDF?sequence=1
Broken springs tend to show a typical stress fracture normally just after the first coil.
In reality its not that simple:-
https://pearl.plymouth.ac.uk/bitstream/handle/10026.1/2300/DANIEL%20GERHARDUS%20HATTING.PDF?sequence=1