Anisotropy of the elastic properties of cross-ply fiber-reinforced composite materials

A theoretical and experimental study of the anisotropy of the elastic properties of cross-ply fiber-reinforced composite is used. These materials are manufactured by stacking elementary layers made of a random transverse distribution of graphite fibers embedded in epoxy resin. Two laminated and periodic cross-ply composites, exhibiting a fourfold and an eightfold axis of rotation in the long wavelength limit, respectively, are studied. They are obtained from helical stackings of respective helicities of π/2 and π/4. The elastic properties of such materials can be described using elastic constant tensors of various crystalline systems depending on the desired stacking sequence. A long wavelength expansion of ultrasonic waves is used in order to describe the composites as homogeneous. Closed-form analytical expressions are calculated for the entire average elastic constants of the media in terms of the geometric and elastic properties of the elementary layer. Static and ultrasonic measurements of the complete set of the elastic constants of the composites are also performed and compared