Did you know that the fuselage of the Concorde can expand by up to a metre in supersonic flight?

Why do you think that the cables supporting the Severn Road Bridge are adjustable?

Why do civil engineers always insert gaps between sections of a concrete road or in a concrete wall?

All these things have something to do with the nature of the materials being used.

Testing materials to find out if they can perform as required is a very important part of technology.