Rheology : Rheology What is rheology
*Types of Rheology physical and chemical
*what is elasticity and what is newtonian fluid
*when different kinds of polymers flows- crystaline and amorphous
Newtonian and Non_newtownian fluid : Newtonian and Non_newtownian fluid simple equation to describe Newtonian fluid behaviour is
where
t is the shear stress exerted by the fluid ("drag") [Pa] µ is the fluid viscosity - a constant of proportionality [Pa·s] is the velocity gradient perpendicular to the direction of shear [s-1] In common terms, this means the fluid continues to flow, regardless of the forces acting on it. For example, water is Newtonian, because it continues to exemplify fluid properties no matter how fast it is stirred or mixed. Contrast this with a non-Newtonian fluid, in which stirring can leave a "hole" behind (that gradually fills up over time - this behaviour is seen in materials such as pudding, starch in water (oobleck), or, to a less rigorous extent, sand), or cause the fluid to become thinner, the drop in viscosity causing it to flow more (this is seen in non-drip paints, which brush on easily but become more viscous when on walls).
For a Newtonian fluid, the viscosity, by definition, 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.
Deformation : Deformation What is deformation?
What is shear rate?
Describe a sample of polymer under shear stress
What is viscosity
viscosity : viscosity Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional stress. In everyday terms (and for fluids only), viscosity is "thickness." Thus, water is "thin," having a lower viscosity, while honey is "thick," having a higher viscosity. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Put simply, the less viscous something is, the greater its ease of movement (fluidity). [1] All real fluids have some resistance to stress,. The study of viscosity is known as rheology.
Non Newtonian fluid : Non Newtonian fluid A non-Newtonian fluid is a fluid whose flow properties are not described by a single constant value of viscosity. Many polymer solutions and molten polymers are non-Newtonian fluids. In a non-Newtonian fluid, the relation between the shear stress and the strain rate is nonlinear, and can even be time-dependent. Therefore a constant coefficient of viscosity cannot be defined. A ratio between shear stress and rate of strain (or shear-dependent viscosity) can be defined, this concept being more useful for fluids without time-dependent behavior.
Although the concept of viscosity is commonly used to characterize a material, it can be inadequate to describe the mechanical behavior of a substance, particularly non-Newtonian fluids. They are best studied through several other rheological properties which relate the relations between the stress and strain rate tensors under many different flow conditions, such as oscillatory shear, or extensional flow which are measured using different devices or rheometers
Strain Rates : Strain Rates Strain rate, with regards to materials science, is the change in strain over the change in time and is denoted as ?.
? = de/dtstrain rate is rate of deformation
We have
? = de/dt where is the original length and v is the speed of deformation.[1]
In a Newtonian fluid, the relation between the shear stress and the rate of strain is linear, the constant of proportionality being the coefficient of viscosity.