Thin Laminate Theory Thin laminates of unidirectional material, utilized in many composite structures, simplify the analysis. In general a thin laminate is considered one where the skin thickness is less than 0.3 of an inch thick. This does not include the thickness of a core if it is used. Here the only mechanical properties that must be determined are These are typically determined experimentally using standard mechanical testing procedures. Typical material properties for some common composite materials are indicated below.
Example ply engineering constants.
Stiffness and Compliance Just as the Young's Modulus represents the stiffness of an isotropic material, composite materials have a stiffness matrix. Here E-1 is the compliance of the material. Lamina compliance is important because the engineering constants in table 1 are easily placed into the compliance matrix but not into the stiffness matrix. The previous matrix represented the on-axis ply properties where the fiber direction is oriented 0 degrees in reference to the material axis. The resulting matrix is called the transformed reduced stiffness matrix.