Dear Yichau.Liu,
Regarding blade fatigue and tower buckling, FAST can be used to calculate the reaction loads that would lead to blade or tower failure, but the actual failure event is not generally modeled directly e.g. see: Making fault - #2 by Jason.Jonkman.
Please see the “Simulating Special Events” Section of the “Controls” Chapter of the old FAST User’s Guide (nwtc.nrel.gov/system/files/FAST.pdf) for information on how to simulate various electrical faults.
Best regards,