Some Common Solid Engineering Materials

In Chapter 17, we vnll look more dosely at materials that commonly are used in various engineering applications. We will also discuss some of the basic physical characteristics of materials that are considered in design. We will examine the application and properties of common solid materials such as metals and their alloys, plastics, glass, and wood and those that solidify over time such as concrete. We will also investigate in more detail basic fluids such as air andvrater. 

Another critical physical property of polymers is elasticity. The ability of many polymeric materials to be stressed and deformed but return to their original shape is a characteristic that is often valuable to engineers. Fibers, in particular, must be elastic. Polymers that are particularly flexible and elastic are sometimes referred to as elastomers. Looking at the molecular structure of elastomers, we find that they tend to share some common traits. In particular, the geometry of the carbon backbone is often such that the elastomer forms an amorphous solid rather than a crystalline one. The forces between polymer molecules in an amorphous solid are not as strong as those in a more crystalline system, so they can be deformed and restored with less force. 

Geologic materials like oil shale are commonly treated as elastic/plastic solids. Fracture under intense loading is then modeled as an extension of plasticity or is treated with a separate fracture model. In applications like rock blasting, the latter approach is preferable, since fracture of rock is qualitatively different from plastic flow. Even so, continuum damage models have been used to model blasting for engineering applications. Some calculations with such a model will be presented below. 

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