TABLE OF CONTENTS 
In Chapter 13 we explored hybrids of four types: composites, sandwiches, lattices, and segmented structures. Each is associated with a set of property-models that allow its properties to be estimated. In this chapter we illustrate their use to design hybrids to fill specified needs needs that cannot be filled by single material choices.
The most common state of loading in structures is that of bending. One measure of excellence in designing materials to carry bending moments at minimum weight is the index E 1/2/ ?, where E is Young's modulus and ? the density. Alloys of aluminum and of magnesium rank highly by this criterion; titanium alloys and steels are less good. How could the performance of magnesium (the best of the lot) be enhanced further? Table 14.1 summarizes the challenge.
| Function | Light stiff beam |
| Constraints | Magnesium matrix |
| Objective | Maximize stiffness to weight in bending (index E 1/2/ ?) |
| Configuration | Fiber composite |
| Free variables | Choice of reinforcement and volume fraction |
The configuration-function matrix of Figure 13.4 suggests that two configurations are able to offer high flexural stiffness at low weight: composites and sandwiches. The choice of shape for a sandwich is limited, so we choose composites. Figure 14.1 is a chart of E and ? for metals and fibers. The criterion of excellence is shown as a set of diagonal contours, increasing...
