Characteristics of an elementary fold
Laminated composite structures

A unidirectional ply is made up of long, parallel fibers oriented in a single direction. For example, figure 9 shows a carbon/epoxy UD typical of aeronautical applications. These fibers are resin-bonded. To be able to dimension a structure, it is necessary to characterize this ply in terms of rigidity and strength.

Let's consider a parallelepiped specimen made from this material and define the orthonormal reference frame (l, t, z) such that the l direction is parallel to the fiber direction or longitudinal (hence the notation l), t the transverse direction and z the out-of-plane direction (figure 9). For this material, the three perpendicular planes (l, t), (t, z) and (l, z) are planes of symmetry. The material is said to be orthotropic,...