## 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.

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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.