Stress-Strain Metal and Plastic

An explanation is reviewed regarding a particular distinction between the mechanical behaviors of metals and unreinforced reinforced plastics (URPs). The typical stress/strain curve for metal exhibits a linear elastic region followed by yield at the yield stress, plastic flow, and ultimately failure at the failure stress [reinforced thermosets (RTSs) have similar behavior]. Yield and failure occur at corresponding strains. Thus, yield and feilure can be called the critical strains. However, it is easier in many products to restrict factor to a stress analysis alone. 

By comparison, it may appear unjustified to state that plastic failure criteria are usually defined in terms of critical strain (rather than stress), and, by comparison with metal, going from strain to stress may appear to be a limited analysis. This apparent error depends on recognition of the fact that stresses and strains are not as intimately related for URPs as they are for metals. This action is demonstrated by reviewing stress/ strain curves for typical URPs material. 

For RTSs with short fibers, such as bulk molding compounds (BMCs), there may be only a low level of viscoelasticity, anisotropy, and inhomogeneity (Chapter 4). However, these RPs with the TS resin 

The mechanical behavior of metals in service can often be assumed to be that of a linear, isotropic, and elastic solid. Thus, design analysis can be based on classical strength of materials theory extensively reviewed in textbooks and literature. Practically, results may be used in the form of standard formulae, or design charts for a selected class of applications. Such uses are most appropriate to components of simple geometric shapes for which standard solutions exist, or for more shapes that are complex where they can possibly be used for initial approximate design calculations. 

For the more complex, and shapes that do not exist, the solution of the applicable elasticity equations may require some form of numerical procedure, such as finite element analysis (FEA) or finite difference analysis (FDA). If design analysis involves frequent consideration of similar problems, then the burden on the designer can be reduced by generating a set of solutions presented as a set of design charts. An alternative is to 

---