## 4.1.1 Modulus, Moduli

Modulus is Latin for stiffness, like in Young’s modulus. The plural is Moduli. A lamina can be approximated very well by a transversely isotropic material, which requires 5 properties to be completely described. Sometimes it is convenient to use 6 properties, although one of the 6 can be computed from the other. The 5 useful properties are: . Longitudinal modulus. Longitudinal means fiber direction, i.e., 1-direction. . Transverse modulus. Transverse means perpendicular to the 1-direction but still in the plane (surface) of the lamina. . In-plane Shear modulus. . In-plane Poisson’s ratio. . Intralaminar Poisson’s ratio.

The following derived properties are necessary if the lamina needs to be modeled as orthotropic [3, Eq. (1.91)], [4, Eq. (1.91)], for example to generate input data for certain finite element analysis software: . Through-the-thickness modulus. . Intralaminar Shear modulus, also called out-of-plane shear modulus. . .

I prefer to report (or seek) rather than because the former is always a value approximately in the range 0.3–0.5, while the later can be anything. So, I can immediately tell if the data I am given is reasonable or not. Since always must be available, you can can easily calculate one from the other using the formula above, which is nothing but Equation 4.2.