Once you have your federal student loans there is no escaping repayment. They are non dischargeable and you can be pursued for non payment relentlessly and indefinitely. Defaulting on these loans is not a wise option as the consequences will resonate on many areas of your life and can cost you in more than just financial terms.
Whilst most other kinds of loans can be in default at 60 days overdue, federal student loans are not marked as in default until 270 days late, but once default is reached then the borrower becomes liable for the full amount of the loan plus interest.
One of the consequences of defaulting on a federal student loan is that you will no longer be eligible for any further federal loans, so defaulting on an undergraduate loan will close the door to federal funding for any postgraduate education plans you have in mind. It will also lose you the opportunity to receive deferment on other federal student loans you hold.
In addition it will severely damage your credit rating thus losing you any chance of obtaining auto loans, mortgage loans or personal loans, unless you use the services of a subprime lender.
One of the lesser known problems of student loan default is that it can cost you any professional licence which you hold which is necessary for your employment. Such licences can simply not be renewed, or they can be cancelled or revoked, thus costing you your professional position.
The obvious consequence of defaulting on federal student loans is that the lender will pursue you, perhaps passing your account to a debt collection agency to chase, thus increasing the balance of the debt as collection costs are levied. As the loan is a federal one then federal tax or state taxes in the form of refunds due to you can be taken by the IRS to use towards the outstanding balance of your debt.
State benefits such as social security retirement benefits and social security disability benefits can be intercepted and used towards the debt. Administrative wage garnishments can be enforced with your employer having to send 15% of your disposable wages towards the loan, thus causing professional embarrassment.
If you allow your loans to fall into default then the consequences are your responsibility. There is no need to go into a default situation if you are open with your lender and seek advice if you experience problems coping with the repayments. There are various options open to the borrower long before default is reached and these should actively be pursued rather than simply allowing the debt to default. Federal student loan default will follow you for a long time and is an expensive route to go down.