Design

In the preceding chapters, we have discussed various aspects of fiber-reinforced

polymers, including the constituent materials, mechanics, performance, and

manufacturing methods. A number of unique characteristics of fiber-reinforced

polymers that have emerged in these chapters are listed in Table 6.1. Many of

these characteristics are due to the orthotropic nature of fiber-reinforced com-

posites, which has also necessitated the development of new design approaches

that are different from the design approaches traditionally used for isotropic

materials, such as steel or aluminum alloys. This chapter describes some of the

design methods and practices currently used for fiber-reinforced polymers

including the failure prediction methods, the laminate design procedures, and

the joint design considerations. A number of design examples are also included.

Design analysis of a structure or a component is performed by comparing

stresses (or strains) due to applied loads with the allowable strength (or strain

capacity) of the material. In the case of biaxial or multiaxial stress fields, a

suitable failure theory is used for this comparison. For an isotropic material

that exhibits yielding, such as a mild steel or an aluminum alloy, either the

maximum shear stress theory or the distortional energy theory (von Mises yield

criterion) is commonly used for designing against yielding. Fiber-reinforced

polymers are not isotropic, nor do they exhibit gross yielding. Thus, failure

theories developed for metals or other isotropic materials are not applicable to

composite materials. Instead, many new failure theories have been proposed for

fiber-reinforced composites, some of which are discussed in this section.