Oscillation is damped - why?

Hey there!

I've got a model that is pretty similar to a goal in soccer. My material is steel. Now, if I put an impulse on it (pressure for a few milliseconds in Abaqus/Explicit) on one beam of the goal, the goal begins to oscillate. This oscillation is nearly completely damped within a second. Why is that? My material is just elastic, so it should oscillate forever!?

I would be happy about an answer!
Thanks in advance,

Max