The laminate stiffness matrix is an 8 x 8 matrix that contains the ABD matrix (6 x 6) as well as the shear matrix C (2 x 2).
 | (5–128) |
The ABD matrix of the laminate is the stiffness matrix of the laminate. A is the in-plane stiffness matrix, B describes the coupling between in-plane forces and bending moments and D is the flexural stiffness matrix. The B matrix becomes 0 in the case of a symmetrically balanced laminate.
In addition to the ABD terms the shear matrix C is evaluated as well. The shear matrix has form
and 
represent the 
and 
stiffness, respectively.
The compliance matrix is an 8 x 8 matrix that contains the inverse of the ABD matrix and the inverse of the C matrix. The inverse of the ABD is also called the abd matrix (ABD -1).
