In many composites, E2 is much lower than E1.

In many composites, E2 is much lower than E1.

• A. E2 is higher than E1
• B. E2 is the same as E1
• C. E2 is much lower than E1
• D. E2 is unrelated to E1

Answer: (C)

Stiffness in fiber-reinforced composites is highly directional: the modulus along the fiber direction (E1) is built up mainly by the stiff fibers, while the modulus across the fibers (E2) is governed by the softer matrix and the fiber–matrix interface. Because fibers are much stiffer than the surrounding material, loading along their length yields a large E1. Perpendicular to the fibers, the load has to deform the matrix and weakly bonded interfaces, so the material stretches more and E2 remains small. This is why, in many composites, E2 is much lower than E1. If E2 were higher than E1 or equal to E1, that would imply isotropy or unusual stiffness in the transverse direction, which isn’t typical for standard fiber-reinforced laminates.

Stiffness in fiber-reinforced composites is highly directional: the modulus along the fiber direction (E1) is built up mainly by the stiff fibers, while the modulus across the fibers (E2) is governed by the softer matrix and the fiber–matrix interface. Because fibers are much stiffer than the surrounding material, loading along their length yields a large E1. Perpendicular to the fibers, the load has to deform the matrix and weakly bonded interfaces, so the material stretches more and E2 remains small. This is why, in many composites, E2 is much lower than E1. If E2 were higher than E1 or equal to E1, that would imply isotropy or unusual stiffness in the transverse direction, which isn’t typical for standard fiber-reinforced laminates.