In continuous and aligned composites, are mechanical properties highly isotropic or anisotropic?

• A. False
• B. True
• C. Only the longitudinal orientation is anisotropic
• D. Only the transverse orientation is anisotropic

Answer: (B)

Direction-dependent behavior in the material is what's being tested. In continuous, aligned fiber composites, the fibers run in one direction and carry most of the load along their length, giving a high stiffness and strength in that longitudinal direction. Perpendicular to the fibers, the load is mainly carried by the softer matrix, so the stiffness and strength are much lower. Because the mechanical response changes with direction, the material is anisotropic rather than isotropic. It's not correct to say only the longitudinal direction is anisotropic, and it's not isotropic overall.