Are engine casings expected to contain turbofan blade fragments? On Southwest 1380, initial indications are that a fragment of the engine blade pierced the engine casing, which then hit the airplane window (or perhaps a part of the casing did). According to the BBC, 


  Mr Sumwalt also said a casing on the engine was meant to contain any parts that come loose but, due to the speed at impact, the metal was able to penetrate the shell. 


Is this an reasonably expected containment failure?  Or is the failure to contain surprising to industry experts?
We don't yet know how or why the engine casing failed to contain the fan blade on Southwest 1380.

But yes: Not only are the engines designed to contain blade failures at fan red-line speeds, but they are also required by 14 CFR 33.94 to confirm they do, typically via destructive "blade-off testing."
(There are a number of good videos of this testing online: Search "turbine blade fail test" or "blade-out engine test.")

As noted here "fan blade-out" failures in the real world are virtually unseen.  (Turbine blade failures are relatively common and can even go unnoticed until major service teardowns.)