Analyze of Materials Due to Their Flow Behaviours

In: Science

Analyze of Materials Due to Their Flow Behaviours

ANALYZE OF MATERIALS DUE TO THEIR FLOW BEHAVIORS

ABSTRACT
In this article, four different samples’ flow behaviors are analyzed; either they are Newtonian or Non-Newtonian materials.   Parallel plate rheometer is preferred to adjust the shear stress and shear rate relationship of the specimens at 25°C and 70°C   and test results are evaluated with the plotted flow and viscosity curves. Then, samples are categorized due to their time dependence or shear stress dependence.

  1. INTRODUCTION
A Newtonian fluid is a fluid whose stress versus rate of strain curve is linear and passes through the origin. The constant of proportionality is known as the viscosity.
A simple equation to describe Newtonian fluid behavior is
(1)
Where;
τ is the shear stress exerted by the fluid [Pa]
μ is the fluid viscosity - a constant of proportionality [Pa·s]
  is the velocity gradient perpendicular to the direction of shear   [s−1]
For a Newtonian fluid, the viscosity depends only on temperature and pressure (and also the chemical composition of the fluid if the fluid is not a pure substance), not on the forces acting upon it. Water is a typical Newtonian fluid.
In a Non-Newtonian fluid, the relation between the shear stress and the strain rate is nonlinear. Therefore a constant coefficient of viscosity cannot be defined and they can even be shear –stress dependent or time-dependent.
Shear stress dependent materials are divided into two groups. In shear thickening materials, the viscosity increases with increased shear rate. These materials are categorized as dilatant materials such as sand in water. In shear thinning materials, the viscosity decreases with increased shear rate. These materials are called pseudo plastic materials such as latex, paint, syrup...  
Time dependent materials are also divided into two groups. Apparent viscosity increases with duration of stress in rheopectic materials such as some lubricants where as the apparent viscosity decreases...

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