Chapter 4 - Mechanics of a Composite Layer

Abstract

The aim of this chapter is to describe mechanics of composite layer. A characteristic composite laminate is comprised of individual layers which are composed of unidirectional plies with the same or regularly alternating orientation. A layer can also be made from metal, thermosetting or thermoplastic polymer or fabric or can have a spatial three-dimensionally reinforced structure. In contrast to a ply, a layer is generally referred to the global coordinate frame x, y, and z of the structural element rather than to coordinates 1, 2, and 3 associated with the ply orientation. Usually, a layer is much thicker than a ply and has a more complicated structure, but this structure does not alter through its thickness, or this change is ignored. Thus, a layer can be defined as a three-dimensional structural element that is uniform in the transverse, normal to the layer plane, direction. Isotropic layer is the simplest layer that can be observed in composite laminates is an isotropic layer of metal or thermoplastic polymer that is used to protect the composite material and to provide tightness. A composite layer with the simplest structure consists of unidirectional plies whose material coordinates, 1, 2, and 3, coincide with coordinates of the layer, x, y, and z. The principal material axes of an outer circumferential unidirectional layer of a pressure vessel coincide with global coordinates of the vessel. Textile pre-forming plays an important role in composite technology providing glass, aramid, carbon, and hybrid fabrics that are widely used as reinforcing materials. The main advantages of woven composites are their cost efficiency and high processability, particularly, in lay-up manufacturing of large-scale structures.