Rheology studies the principles that indicate how fluids move.
Rheology is the specialty of physics focused on the analysis of the principles that determine how fluids move . The concept was proposed by the American scientist Eugene Cook Bingham ( 1878 – 1945 ) in the first half of the 20th century .
What rheology does is study the link between the force exerted on a material and the deformation it experiences when it flows. Through constitutive equations , it is possible to establish a model about the way these substances behave.
In this context, deformation is a change that occurs in the shape or size of a body due to the production of internal forces that arise as a result of the application of one or more forces, or thermal expansion . To carry out the measurement of the deformation, the magnitude called unitary or axial deformation is used, which engineering defines as the modification of the length of a body for each unit.
Rheology and mechanics of continuous media
The branch of physics in which the concept of rheology is studied is the mechanics of continuous media , also known as physics of continuous media , which is based on a single model to treat fluids, rigid solids and deformable solids. Fluids can be classified as gases or liquids.
On the other hand, the notion of internal force refers to a set of forces and moments that are applied to a section of a structural element and that present a relationship of static equivalence with respect to the distribution of internal stresses, that is, they give as result is a force and its moments are equal.
The properties that rheology is responsible for studying are analyzed with an instrument known as a rheometer , which makes it possible to carry out deformations under control, measuring the efforts. In this way, the viscosity and normal stress coefficient of each substance can be determined, among other properties.
Eugene Cook Bingham was the one who proposed the concept of rheology.
Viscosity
The concept of viscosity should be understood as the resistance that a given fluid offers before deforming when subjected to stress. It is important to note that all fluids discovered by humans are viscous to some degree; Therefore, when you want to simulate zero viscosity, you must use the ideal fluid assumption.
Another point to keep in mind regarding viscosity is that it is only appreciated when the liquid is in motion ; In fact, a definition of viscosity proposes it as the relationship that exists between the shear stress (explained in the following paragraph) and the velocity gradient.
The name normal stress , on the other hand, is known as that which occurs as a result of tensions normal (in other words, perpendicular) to the surface for which the magnitude of stress is intended to be determined. The effort that arises from the shear stresses (that is, tangential ) to the plane in question is called shear .
Usefulness of rheology
Thanks to rheology, we can know precisely how fluids and solids react to stress. In the case of ideal fluids , their deformation is irreversible: the energy takes the form of heat and is dissipated in the material, without being able to be recovered despite the end of the effort. In ideal solids , however, the energy that drives elastic deformation is recovered when the stress is removed.
Rheology provides information, for example, about the process that food undergoes when it is chewed and swallowed. This matter , through chewing and the action of saliva, is deformed and transformed into a paste that flows into the body.