The Ply Mechanics chapter contains most, if not all, of the formulas in Chapter *Ply Mechanics* of the textbook. These are mostly coordinate transformations to handle the various orientations of the laminas in the laminates. Laminates are dealt with in chapter Macromechanics.

If you expand *Ply Mechanics* (by clicking the
sign) you get something like this:

As you can see, *Ply Mechanics* lets you calculate stiffness matrices (*Q*, and *C*) and compliance matrices (*S*) in 2D (plane stress) and 3D. Also, you can do strain and stress transformations from one coordinate system (say lamina c.s., which is *1,2* axes) to laminate c.s. (which is *x,y* axes).

All of this is quite involved, so you have to read chapter 5 in the textbook to take full advantage of this. Here we show you only the nomenclature, as follows:

*S*is the plane stress compliance matrix in lamina c.s. This 3x3 matrix contains in-plane values only. The 9 values are taken directly from the 6x6 matrix with the same name, in 3D. This is explained in the textbook.*S**is the intralaminar, also called out-of-plane compliance matrix in lamina c.s. This a 2x2 matrix, which is useful in finite element analysis (FEA) when using Reissner-Mindlin plate elements, also called First Order Shear Deformations (FSDT) elements [3, 4].*Q*is the plane stress stiffness matrix in lamina c.s. This 3x3 contains in-plane values only.*Q**is the intralaminar, also called out-of-plane stiffness matrix in lamina c.s. This a 2x2 matrix, which is useful in finite element analysis (FEA) when using Reissner-Mindlin plate elements, also called First Order Shear Deformations (FSDT) elements.*C*is the 3D stiffness matrix in lamina c.s. This 6x6 matrix contains in-plane values only.