Complex sentence: Its use has broadened to the automotive and sport equipment sectors as well as aircraft, although its use there is now partly being taken over by carbon fiber which weighs less per given volume and is stronger both by volume and by weight.
Split into simpler sentences: Its use has broadened to the automotive and sport equipment sectors. In aviation, fiberglass is now partly being taken over by carbon fiber which weighs less per given volume and is stronger both by volume and by weight.