@IPOFreakSir, Yes you can use Flexi FD in AUSF Bank for applying in IPO. It will only break if you you got allotment and you do not have the allotment amount free in your Savings account.
This are the points I got from AU Bank in an Email:
1) While applying for ASBA, the lien will be marked on linked sweep-in (Flexi) FD balance.
2) If required, the AU Savings/Current Account balance will also be considered for ASBA lien marking.
3) On successful allotment, debit from AU Current/Savings Account will be initiated first and wherever required (by EOD) the linked sweep-in (Flexi) FD balance will be utilised.
Hope this clarifies your doubt.