Rheometry () generically refers to the experimental techniques used to determine the
rheological
Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an appli ...
properties of materials,
that is the qualitative and quantitative relationships between
stresses and
strain
Strain may refer to:
Science and technology
* Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes
* Strain (chemistry), a chemical stress of a molecule
* Strain (injury), an injury to a mu ...
s and their derivatives. The techniques used are experimental.
Rheometry investigates materials in relatively simple flows like steady shear flow, small amplitude oscillatory shear, and extensional flow.
The choice of the adequate experimental technique depends on the rheological property which has to be determined. This can be the steady shear
viscosity
The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water.
Viscosity quantifies the inte ...
, the linear
viscoelastic
In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly wi ...
properties (complex viscosity respectively
elastic modulus
An elastic modulus (also known as modulus of elasticity) is the unit of measurement of an object's or substance's resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The elastic modulus of an object is ...
), the elongational properties, etc.
For all real materials, the measured property will be a function of the flow conditions during which it is being measured (
shear rate
In physics, shear rate is the rate at which a progressive shearing deformation is applied to some material.
Simple shear
The shear rate for a fluid flowing between two parallel plates, one moving at a constant speed and the other one stationary ...
,
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
, etc.) even if for some materials this dependence is vanishingly low under given conditions (see
Newtonian fluids
A Newtonian fluid is a fluid in which the viscous stresses arising from its flow are at every point linearly correlated to the local strain rate — the rate of change of its deformation over time. Stresses are proportional to the rate of chang ...
).
Rheometry is a specific concern for
smart fluid
A smart fluid is a fluid whose properties (e.g. viscosity) can be changed by applying an electric field or a magnetic field.
The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magn ...
s such as
electrorheological fluid
Electrorheological (ER) fluids are suspensions of extremely fine non-conducting but electrically active particles (up to 50 micrometres diameter) in an electrically insulating fluid. The apparent viscosity of these fluids changes reversibly by an ...
s and
magnetorheological fluids, as it is the primary method to quantify the useful properties of these materials.
Rheometry is considered useful in the fields of
quality control
Quality control (QC) is a process by which entities review the quality of all factors involved in production. ISO 9000 defines quality control as "a part of quality management focused on fulfilling quality requirements".
This approach places ...
,
process control
An industrial process control in continuous production processes is a discipline that uses industrial control systems to achieve a production level of consistency, economy and safety which could not be achieved purely by human manual control. I ...
, and industrial process modelling, among others.
For some, the techniques, particularly the qualitative rheological trends, can yield the classification of materials based on the main interactions between different possible elementary components and how they qualitatively affect the rheological behavior of the materials.
Of non-Newtonian fluids
The viscosity of a non-Newtonian fluid is defined by a power law:
::
where ''η'' is the viscosity after shear is applied, ''η
0'' is the initial viscosity, ''γ'' is the shear rate, and if
*
, the fluid is
shear thinning
In rheology, shear thinning is the non-Newtonian behavior of fluids whose viscosity decreases under shear strain. It is sometimes considered synonymous for pseudo-plastic behaviour, and is usually defined as excluding time-dependent effects, suc ...
,
*
, the fluid is
shear thickening
A dilatant (, ) (also termed shear thickening) material is one in which viscosity increases with the rate of shear strain. Such a ''shear thickening fluid'', also known by the initialism ''STF'', is an example of a non-Newtonian fluid. This beh ...
,
*
, the fluid is Newtonian.
In rheometry, shear forces are applied to
non-Newtonian fluid
A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, i.e., constant viscosity independent of stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid. Ketchup, for exa ...
s in order to investigate their properties.
Shear thinning fluids
Due to the shear thinning properties of blood,
computational fluid dynamics
Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate th ...
(CFD) is used to assess the risk of
aneurysm
An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus (s ...
s. Using High-Resolution solution strategies, the results when using non-Newtonian rheology were found to be negligible.
Shear thickening fluids
A method for testing the behavior of shear thickening fluids is stochastic rotation dynamics-molecular dynamics (SRD-MD).
The
colloidal particles
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...
of a shear thickening fluid are simulated, and shear is applied. These particles create hydroclusters which exert a drag force resisting flow.
See also
*
Continuum mechanics
Continuum mechanics is a branch of mechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as discrete particles. The French mathematician Augustin-Louis Cauchy was the first to formulate such m ...
*
Dynamic shear rheometer
A dynamic shear rheometer, commonly known as DSR, is used for research and development as well as for quality control in the manufacture of a wide range of materials. Dynamic shear rheometers have been used since 1993 when Superpave was used for c ...
*
Electrorheological fluid
Electrorheological (ER) fluids are suspensions of extremely fine non-conducting but electrically active particles (up to 50 micrometres diameter) in an electrically insulating fluid. The apparent viscosity of these fluids changes reversibly by an ...
*
Ferrofluid
Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid (usually an organic solvent or water). Each magnetic particle ...
*
Fluid mechanics
Fluid mechanics is the branch of physics concerned with the mechanics of fluids ( liquids, gases, and plasmas) and the forces on them.
It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical and bio ...
*
Magnetorheological fluid
*
Rheology
Rheology (; ) is the study of the flow of matter, primarily in a fluid ( liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an appl ...
*
Rheometer
A rheometer is a laboratory device used to measure the way in which a dense fluid (a liquid, suspension or slurry) flows in response to applied forces. It is used for those fluids which cannot be defined by a single value of viscosity and t ...
*
Smart fluid
A smart fluid is a fluid whose properties (e.g. viscosity) can be changed by applying an electric field or a magnetic field.
The most developed smart fluids today are fluids whose viscosity increases when a magnetic field is applied. Small magn ...
References
Continuum mechanics
Fluid mechanics
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