Stress Relaxation after Cessation of Steady-State Non-Newtonian Flow

Stress Relaxation after Cessation of Steady-State Non-Newtonian Flow 

The alternative type of stress relaxation experiment portrayed in Fig. 1 -5, which 

Apparent shear relaxation modulus a(t)ly plotted logarithmically against time for a 20% solution of polystyrene, Mw = 1.80 X 10 in chlorinated diphenyl at 33.5 C. Values of strain y as follows open circles without pip, 0.41 pip up, 1.87 pip with successive 45 rotations clockwise, 3.34,5.52,6.68,10.0,13.4,18.7, and 25.4. (Einaga and collaborators. ) Reproduced, by permis.sion, from Polymer Journal. 

The normal stresses present during the steady-state flow also relax after its cessation, and the course of the primary normal stress difference, (oi j — T22) (f). where the superscript ss again refers to this particular type of experiment, is also shown in Fig. 2-13. Here, also, the relaxation is the more rapid, the higher the shear rate which precedes it. However, the normal stress difference relaxes more slowly than the shear stress. 

Relaxation of shear stress and primary normal stress difference after cessation of steady state flow, for a 4% solution of polystyrene with molecular weight 1.8 X 10 in chlorinated diphenyl as described in the text. Numbers refer to the shear rate preceding cessation of flow. 

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