Perhaps you should try some spelling variations:
acoustical materials » acoustic materials, acoustic material, optical materials
elastic materials » plastic materials, viscoelastic materials, ceramic materials
optic materials » optical materials, basic materials, ionic materials

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: %((optic materials) OR (((acoustical materials) OR (elastic materials))))%22.
• Adding a wildcard symbol may retrieve word variants: %((optic materials) or (((acoustical materials) or (elastic materials))))%22*.