Stress Development at the Onset of Steady Shearing Flow

Stress Development at the Onset of Steady Shearing Flow (355-35 ) 

At sufficiently low shear rates the viscosity is constant. If a constant shear rate in this range is imposed, the shear stress should grow monotonically to its steady state value c(oo) according to the equation from linear viscoelasticity  

At higher shear rates the steady-state viscosity o(cc)/y begins to depend on y. If a constant shear rate in this range is imposed, the shear stress rises beyond its steady state value, passes through a maximum before eventually approaching the steady state, (t(oo) = rj(y)y. The stress at the maximum o-(tm) grows in relation to ff(oo) as y increases. The time to reach the maximum tm is found to be inversely proportional to shear rate  

The total shear at the stress maximum ym is ytm, so for a given polymer ym is independent of y, and has a value which is typically in the range of 2.0 3.0 shear units. The normal stress displays a similar overshoot behavior, although ym and the time to reach steady state appear to be greater for pu 22 than for r. 

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