### 5.1.1. Introduction

Layered composite structures are typically formed by placing reinforced plies against a mold surface in desired orientations. In the case of flat and singly curved surfaces, the orientation of the ply stays practically unchanged over the whole application area. When it comes to doubly curved surfaces, a ply can follow the surface only by deforming. In particular, dry and pre-impregnated woven fabrics can adapt to the shape of a doubly curved surface without use of excessive force. Deformation occurs with in-plane shear and up to a certain deformation level the shear stiffness of a fabric is insignificantly small ([ 2 ]).

When a ply deforms by shearing to follow the surface, the fiber orientation changes. Different approaches have been developed for the simulation of the draping process [ 3 ]. The need for draping simulation is twofold. First, the manufacturability of the composite product can be assessed. Areas where the reinforcement cannot follow the surface are indicated and hence measures can be taken in design to avoid this. Second, the draping simulation gives the actual fiber orientations at any location in the model. This information is needed for accurate finite element analysis of the structure.

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