ABSTRACT
This chapter focuses on rheology (stress–strain relationships). It determines the suitability of materials to serve specific applications and it helps to relate the results to polymer structure and form. Understanding structure–property relationships allows a better understanding of the observed results on a molecular level, resulting in a more knowledgeable approach to the design of materials. The study of rheology includes two vastly different branches of mechanics called fluid and solid mechanics. The polymer scientist is usually concerned with viscoelastic materials that act as both solids and liquids. Most physical tests involve nondestructive evaluations. Generally, tests are taken using about two-thirds of the static parameter value. There is some limiting stress level below which fatigue does not occur. This value is called the fatigue or endurance limit. The fatigue strength is defined as the stress at which failure will occur for some specified number of cycles. Fatigue life is the number of cycles that are needed to cause failure.
