Can they send you jail for a federal student loan on defaul?

Only if you gave fraudulent info to get it, keep it, or obstruct collection of it.

Keep in mind that most student loans are federal government-backed financial aid, so there are enhanced penalties for those that abuse them.

Borrowers guilty of no crime can have their tax refunds and wages taken, without a court order, for defaulting on their federal student loans in the US.