TABLE OF CONTENTS In this chapter, the basic theory needed for the determination of the stresses, strains, and deformations in fiber composite structures is outlined. Attention is concentrated on structures made in the form of laminates because that is the way composite materials are generally used.
From the viewpoint of structural mechanics, the novel features of composites (compared with conventional structural materials such as metals) are their marked anisotropy and, when used as laminates, their macroscopically heterogeneous nature.
There is a close analogy between the steps in developing laminate theory and the steps in fabricating a laminate. The building block both for theory and fabrication is the single ply, also referred to as the lamina. This is a thin layer of the material (typical thickness around 0.125 mm for unidirectional carbon/epoxy "tape" and 0.25 mm for a cross-ply fabric or "cloth") in which all of the fibers are aligned parallel to one another or in an orthogonal mesh. The starting point for the theory is the stress-strain law for the single ply referred to its axes of material symmetry, defined here as the 0 1, 2, 3 material axes. In constructing a laminate, each ply is laid-up so that its fibers make some prescribed angle with a reference axis fixed in the laminate. Here the laminate axes will be defined as the x-, y-, and z-axes.
All later calculations are made using axes fixed in the structure (the structural axes). In a finite element model, the material...
