[mildchalupa]

Roughly 30k cycles is typical. You can certainly design a spring to have infinite life. But it requires reducing average deflection, aka more spring with less deflection per turn.

[bumby]

The article claims a 10k cycle limit for common-grade torsion springs (but again, I'm skeptical). You can design a spring to have infinite life. Still, you must constrain yourself to specific materials (steel and titanium being the most common) because most materials don't have an infinite life on an S-N curve.