ABSTRACT
When a chemist or a chemical engineer looks at a polymer, he or she sees a molecular structure with atoms, C-C bonds, chains, branches, crosslinks, and crystals. However, a design engineer who looks at a polymer sees a mechanism with springs, dashpots, and sliding blocks. For example, if we were to draw a box around an element of material, we can imagine that within the box is a spring, as in Figure 3.1a, or a dashpot (viscous damper), as in Figure 3.1b. These two models represent a linear elastic solid and a linear viscous fluid, respectively. For the first, the linear elastic solid, the σ (ε) relationship is linear
(3.1)
For the linear elastic fluid, the σ(ε) relationship is linear
(3.2)
where η is the viscosity and . The linear-solid behavior may be expected for small strains and for temperature T < Tg (the glass-transition temperature). The linear fluid behavior may be expected at T ≈ Tm (the melting temperature).
