crack, crack up, crack up to be

crack :

• crack a book as snacks
• The glass cracked. (broken partially but still connected?)
• The cracked cake is crispy and tasty.
• The poor programmer tried hard to crack a code to gain success, but failed.

crack up:

• break down
• burst out (laughing)

crack up to be:
The out-of-date actress is not the beauty she was cracked up to be anymore.


[ref]
http://www.thefreedictionary.com/crack