The first test article of a SpaceX Crew Dragon undergoes structural load testing to demonstrate the spacecraft’s ability to withstand the tremendous forces it’s exposed to during space flight.
The backbone of Crew Dagon is a metallic welded pressure vessel. SpaceX has completed manufacturing of the first two pressure vessels to be used for ground testing, and is currently manufacturing two Crew Dragon flight articles.

KSC-20160621-PH_SPX01-0001 Photo credit: SpaceX Larger image