Shear flow thickening

Attempting to flow past thin sections to fill wider sections is difficult or may be impossible, because the flow thickens enroute acts like plaque forming along walls of a human artery. Even if both of these ills are avoided, the final result may still contain areas of high shear stresses invisible to the eye but waiting in ambush to cause failure later under extreme conditions previously thought to be well within the material s specifications. 

Table 3.3 Summary of the relations for Newtonian and shear thinning/shear thickening fluids in the case of a simple fully-developed shear flow (Couette flow, isothermal) [6], [14]...

Shear thickening in polymers with multiple stickers is thought to be caused by a shear-induced change in the balance between intramolecular and intermolecular associations (Witten and Cohen 1985). According to this idea, at low shear rates, many of the associations are intramolecular and therefore contribute little or nothing to the viscosity. Shearing flow stretches the molecules, and thus it makes intermolecular associations more probable. The result is an increase in viscosity. The increase in viscosity causes the chain to stretch even more, and this promotes even more interchain associations. The result can be a runaway increase in the viscosity, or shear-induced gel formation. 

Kumar, P., C.L. Martin, and S. Brown, Shear Rate Thickening Flow Behavior of Semisolid Slurries, Metallurgical Trans. A 24(A) 1107-1116 (1993). 

There are three types of melt behavior in a simple shear flow dilatant (D) (shear thickening) Newtonian (N), and pseudoplastic (P) (shear thinning). Similarly, in an extensional flow, the liquids may be stress hardening (SH), Troutonian (T), or stress softening (SS). By definition, the response considered here is taken at sufficiently... 

We next examine the stationary stresses of the tension-dissociation coupling model. Typical numerical results for the affine tfansient networks are presented in Figure 9.8 for the thinning case (a) g = 1, and the thickening case (b) g=0.01 under shear flow [36]. The sfresses and the shear rate are presented in the units of vk T and Po. The shear viscosity shows thinning in (a) and thickening in (b). 

LCP s often display a range of phenomena not often seen, if at all, with Isotropic polymers. These Include the existence of negative first normal stress difference, regions of shear thickening viscosity, and secondary maxima In transient shear flow [2,19]. 

Although in a shear flow the viscosity of a polymeric fluid usually decreases with increasing deformation rate, in an extensional flow the viscosity frequently increases with increasing extension rate that is, the fluid is extensional thickening (recall Figure 2.1.3). Figure 4.2.5 shows the time-dependent uniaxial extensional viscosity... 

However Bhattacharjee etal. [43] and Wapperom etal. [44] showed that the DCS-CS model anomalously predicts shear thickening in steady shear flows. This defect has recently been corrected by Marrucci and lanniruberto [ 31,32 ], by using a tensor A that includes both chain orientation and stretch, and obeys the following dynamical equation ... 

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