What would be the effects of an expiration date on currency?
A bill with an expiration date does not become worthless suddenly. Clearly its value would decrease over time until, just before the expiration date, it was next to worthless. Think about it: how much would you pay for a $1 bill that expires in 5 minutes? Certainly a lot less than you would for one that expires in 6 months.

This constantly changing value would make it hard to use as a medium of exchange. Whenever buying or selling something, one would have to look not just at the face value of the bill, but also at the expiration date, to be able to calculate its real value. People would probably start carrying calculators next to their wallets.

Cattle (which obviously "expire") were once used as currency, so it certainly could work. But that does not mean it is ideal.