Materials science nonlinear behavior

Fang, D. and Li, C., 1999, Nonlinear electric mechanical behavior of a soft PZT 51 ferroelectric ceramic. Journal of Materials Science 34 4001 4010. 

On a material science level, thermoplastics also have different behaviors than many other materials. For starters, most thermoplastics are anisotropic that is, they have different properties when measured in different directions. They also have different behavior in compression than they do in tension. And their mechanical behavior is nonlinear, in that their behavior does not follow the traditional linear stress-strain relationship seen in metals. This means the classic engineering equations for structural calculations are not always accurate. 

Polymer science is a specialized field of materials science that focuses on the study of polymers. In addition to the unique characteristics of thermoplastics described earlier (anisotropic behavior, nonlinear elastic response, etc.), polymer science also has a unique language (Figure 3.6). Just like the word plastic has many meanings, many of the words used in polymer science have many meanings. In this section, we will review some of the more important terms, in order to provide a platform for subsequent discussion. 

A number of fluids mentioned throughout the text that are of importance in physicochemical hydrodynamics do not behave in the Newtonian fashion outlined in Section 2.2. That is, the stress tensor is not a linear function of the rate of strain tensor. Such nonlinear fluids are termed non-Newtonian and the study of their behavior falls under the science of rheology, which deals with the study of the deformation and flow of matter. The materials encompassed by this broad subject cover a spectrum from Newtonian fluids at one end to elastic materials at the other with such fluids as tars, liquid crystals, and silly putty in between. Among the fluids we have discussed in the text that do not exhibit a Newtonian behavior are some polymeric liquids, some protein solutions, and suspensions. 

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