In a symmetric cross-ply $[0/90]_s$ laminate, which of the following terms in the classical laminate $[A][B][D]$ stiffness matrices is strictly EQUAL TO ZERO?

(A) All coupling stiffness terms $B_{ij} = 0$, and in-plane shear coupling terms $A_{16} = A_{26} = 0$

(B) The extensional modulus term $A_{11}$

(C) The bending stiffness term $D_{22}$

(D) The transverse shear term $A_{44}$

Answer Key:

A

### Solution: Symmetry eliminates $[B]$ entirely ($B_{ij} = 0$). Cross-ply ($0^\circ$ and $90^\circ$ only) eliminates shear-extension coupling ($A_{16} = A_{26} = 0$) and bend-twist coupling ($D_{16} = D_{26} = 0$). Correct: A.

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