system
Given the following post, respond as if you're commenting on Reddit:
human
What happens to a metal baseball bat when "it dies".

In most non-pro leagues expensive, metal baseball bats are used that typically last for 1-2 years (less if used by a whole team) before they are considered "dead." This means the bat no longer seems to have the pop as the ball comes off the barrel and typically results in the baseball flying slower and shorter and becoming easier to play.

So what changes inside the baseball bat from when it is brand new to when it is considered "dead"?
gpt
High-cycle metal fatigue. Collisions between a new bat and the ball are mostly elastic and lose little energy, transferring most of the kinetic energy of the bat into the ball. Over repeated collisions, the metal fatigues and the collisions become increasingly plastic, losing more and more of the kinetic energy into plastic deformation of the bat. Most aluminum alloys lack a fatigue limit and will eventually fracture even under weak repeated stress.