Which laminate characteristic introduces coupling between extensional and bending stiffness in Classical Laminated Theory?

Which laminate characteristic introduces coupling between extensional and bending stiffness in Classical Laminated Theory?

• A. Symmetric laminate stacking sequence.
• B. Uniform ply thickness across all plies.
• C. Non-symmetric laminate stacking sequence.
• D. Quasi-isotropic stacking.

Answer: (C)

In Classical Laminated Theory, extensional–bending coupling shows up when the laminate is not symmetric through its thickness. This coupling is represented by the B matrix, which links in-plane strains to bending curvatures and moments to in-plane strains. When the layup is symmetric about the mid-plane, the B matrix becomes zero, so bending and extension responses are independent. If the stacking sequence is not symmetric, the B term is nonzero, and applying in-plane loads can induce bending (and vice versa). So, the laminate characteristic that introduces this coupling is a non-symmetric through-thickness stacking sequence. Symmetric layups eliminate the coupling, uniform ply thickness alone doesn’t create it, and quasi-isotropic stacking is about in-plane isotropy and stiffness rather than through-thickness symmetry—though a symmetric quasi-isotropic layup would still have no coupling.

In Classical Laminated Theory, extensional–bending coupling shows up when the laminate is not symmetric through its thickness. This coupling is represented by the B matrix, which links in-plane strains to bending curvatures and moments to in-plane strains. When the layup is symmetric about the mid-plane, the B matrix becomes zero, so bending and extension responses are independent. If the stacking sequence is not symmetric, the B term is nonzero, and applying in-plane loads can induce bending (and vice versa).

So, the laminate characteristic that introduces this coupling is a non-symmetric through-thickness stacking sequence. Symmetric layups eliminate the coupling, uniform ply thickness alone doesn’t create it, and quasi-isotropic stacking is about in-plane isotropy and stiffness rather than through-thickness symmetry—though a symmetric quasi-isotropic layup would still have no coupling.