Non-linear Mechanical Behavior

The observations, notions and model calculations discussed in the previous two chapters concerned the range of linear responses only. In fact, when working with polymers under realistic conditions one is frequently reaching the limits of these treatments since non-linear effects appear and have to be properly accounted for. We shall deal in this chapter with two cases of special importance  

Qualitative understanding of the origin of the normal stress phenomenon is not difficult. We learned in the previous chapters that a polymer melt resembles a transient network of entangled polymers. High shear rates, as they are encountered in a capillary, result in a deformation of the chains and, therefore, also of the formed network. As a consequence, a tension builds up along the lines of flow and draws the extrudate back when the confinement 

We begin with a discussion of the physical basis of rubber elasticity. 

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Wilhelm M, Reinheimer P, Ortseiferer M, Neidhofer T, Spiess HW (2000) The crossover between linear and non-linear mechanical behavior in polymer solutions as detected by fouriertransform rheology. Rheol Acta 39 241—246... 

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