What is a Z-ply and its purpose in through-thickness reinforcement?

• A. A ply oriented at 45 degrees to the laminate plane to improve in-plane shear
• B. A ply oriented strictly in the laminate plane to increase in-plane stiffness
• C. A ply oriented out of the primary laminate plane to improve through-thickness stiffness and delamination resistance
• D. A ply made of zinc-coated fibers for corrosion resistance

Answer: (C)

A Z-ply is a reinforcement layer whose fibers run perpendicular to the main laminate plane. This through-thickness orientation directly boosts stiffness in the thickness direction and helps resist delamination by bridging cracks that propagate between layers. It’s not about orienting fibers in the plane to increase in-plane stiffness or shear, and it isn’t a coating or material specification for corrosion resistance. By placing a Z-ply, the laminate gains better resistance to interlaminar cracking and improved overall through-thickness stiffness, which is exactly what the option describes.