A rheological perspective

The study of fluid changes! Material forms a flow, and the dynamics are called changes. Usually the research object is a system that has a quasi-equilibrium and relatively slow change due to viscosity. In the theoretical system, most of them are the ideas of viscous fluid mechanics~~~ ~~~:) Personal understanding, not published

　Rheology is a new branch of mechanics. It mainly studies the deformation and flow laws of physical materials related to time factors under conditions such as stress, strain, temperature, humidity, and radiation. 　　The "SEE technology and its industrial application and derivative product technology" invented by Zhang Xini is a practical example of successfully developing "practical technology" and "lighting products" and "new green lighting source - smart lamp" by applying the "electron rheology" theory. 　　Therefore, rheology, its rheology and rheology technology will increasingly play an important role in the depth and breadth of physical applications. 　　A brief history of the development of rheology Rheology appeared in the 1920s. Academics are studying industrial materials such as rubber, plastics, paint, glass, concrete, and metals ； Rocks, soil, petroleum, minerals and other geological materials ； In the process of studying the properties of biological materials such as blood, muscles and bones, it was discovered that the use of classical elasticity theory, plasticity theory and Newtonian fluid theory could no longer explain the complex characteristics of these materials, so the idea of ​​rheology was born. British physicists Maxwell and Kelvin had long recognized that there is a time effect that is closely related to changes in materials and time. 　　Maxwell discovered in 1869 that materials can be elastic or viscous. For viscous materials, the stress does not remain constant but decreases to zero at a rate that depends on the value of the starting stress applied and the properties of the material. This phenomenon is called stress relaxation. Many scholars have also discovered that although the stress remains unchanged, the material rod can continue to deform over time. This property is creep or flow. 　　After long-term exploration, people finally learned that all materials have time effects, so rheology emerged and flourished after the 1930s. In 1929, the United States founded the Rheology Society on the initiative of Professor Bingham. ； In 1939, the Royal Netherlands Academy of Sciences established a rheology group headed by Professor Berges. ； In 1940, the Society of Rheologists appeared in the UK. At that time, Dutch work was at the forefront, and the 1948 International Rheology Conference was held in the Netherlands. France, Japan, Sweden, Australia, Austria, Czechoslovakia, Italy, Belgium and other countries have also established rheology societies. 　　The development of rheology is closely related to world economic development and industrialization process. Modern industry requires high-quality metals, alloys, ceramics and high-strength polymers that are resistant to creep and high temperature. Therefore, rheology related to solid creep, viscoelasticity and creep rupture has developed rapidly. The development of nuclear reactors and particle accelerators in the nuclear industry has opened new areas for the study of deformations caused by radiation. 　　In the earth sciences, the important factor of time processes has long been known. Rheology provides physical-mathematical tools for the study of extremely interesting geophysical phenomena in the earth's crust, such as postglacial ascent, folding of layered rocks, orogenesis, the origin of earthquakes, and mineralization. Earth's internal processes, such as magma activity and mantle thermal convection, can now be simulated using high-temperature and high-pressure rock rheology experiments, thus developing geodynamics. 　　In civil engineering, deformation of a building's soil foundation can last for decades. Creep fractures can still occur in underground tunnels decades after they are completed. Therefore, the research on soil rheological properties and rock rheological properties has received increasing attention. 　　It has a wide range of applications in the fields of force, heat, sound, light and electricity. For example, in the "Zhang Xini Smart Light Laboratory", a series of new electric light stories happened. It once again proves the assertion that "all modern civilization begins with electric lights." Electric light, like a centenarian, has entered the three centuries of "19th", "20th" and "21st". Nowadays, there are three main types of electric lights that are common in our lives, one is called "incandescent light", the other is called "fluorescent light", and the other is called "smart light". “"Incandescent light bulb" was invented by Edison in 1879 and was the starting point of electric light. ； “"Fluorescent lamp" was invented by Philips in 1938. It is the hero of electric light. ； “"Smart Lamp" was invented by Sydney Zhang in 2003. It is the new favorite of electric lights. These are examples of the widespread application of rheological theory in the fields of rheology and rheological technology. 　　The research content of rheology The research content of rheology is the creep and stress relaxation phenomena of various materials, the yield value, and the rheological model and constitutive equation of materials. 　　The rheological properties of materials are mainly manifested in two aspects: creep and stress relaxation. Creep refers to the process in which the deformation of a material increases over time under the action of a constant load. Creep is caused by the readjustment of the molecular and atomic structure of the material, a process that can be characterized by lag time. When the load is removed, the deformation of the material partially or completely returns to the original state, which is another phenomenon of structural readjustment. 　　When a material is under constant strain, the stress decreases to a certain finite value over time, a process called stress relaxation. This is another phenomenon where the structure of the material is readjusted. 　　Creep and stress relaxation are the external manifestations of changes in the internal structure of matter. This observable physical property depends on the statistical properties of the material's molecular (or atomic) structure. Therefore, within a certain stress range, although the position of a single molecule (or atom) will change, the statistical characteristics of the material structure may not change. 　　When the shear stress acting on the material is less than a certain value, the material only produces elastic deformation. ； When the shear stress is greater than this value, the material will undergo partial or complete permanent deformation. Then this value is the yield value of this material. The yield value marks the limit value where the material has complete elasticity and enters the flow phenomenon, so it is also called the elastic limit, yield limit or flow limit. The same material may have several different yield values, such as creep limit, fracture limit, etc. In the study of materials, various yield values ​​of materials are generally studied first. 　　Under different physical conditions (such as temperature, pressure, humidity, radiation, electromagnetic field, etc.), the equation that uses the physical variables of stress, strain and time to quantitatively describe the state of the material is called the rheological equation of state or the constitutive equation. The rheological properties of materials can generally be simulated by two methods, namely mechanical models and physical models.: 　　In simple cases (uniaxial compression or tension, single shear or pure shear), the stress-strain characteristics can be described by a mechanical rheological model. When evaluating creep or stress relaxation test results, the use of mechanical rheology models can be helpful in understanding the rheological properties of materials. Such models have been used for decades. They are relatively simple and can be used to predict material deformation under arbitrary stress histories and temperature changes. 　　The rheological model of the mechanical model does not consider the internal physical properties of the material, such as molecular motion, dislocation motion, crack expansion, etc. At present, the requirements for the quality of materials are getting higher and higher, such as high-strength and super-tough metals, high-strength and high-temperature-resistant ceramics, high-strength polymers, etc. Their study must consider the internal physical properties of the material, so the high-temperature creep theory was developed. This theory expresses the physical constants of the internal structure of the material by considering the impact of defects within the solid crystal and at the boundaries of the grains on the rheological properties of the material, that is, the physical rheological model of the material. 　　Research methods of rheology Rheology has been developed as an experimental basic subject from the beginning, so experiment is one of the main methods of studying rheology. It acquires physical concepts and develops new macroscopic theories through macroscopic experiments. For example, the tension, compression, and shear tests of material specimens are used to explore the relationship between stress, strain and time, and to study the yield law and the long-term strength of the material. Through microscopic experiments, we can understand the microstructural properties of materials, such as defects in polycrystalline material particles, the properties of particle boundaries, and basic properties such as dislocation states, and explore the rheology mechanism of materials. 　　Fluid materials are generally tested with a viscometer. For example, the falling ball viscometer method is used to calculate Newton's viscosity coefficient by calculating the time it takes for a sphere to sink due to its own weight in a fluid. ； By studying the pressure difference at both ends of the tube and the flow rate of the fluid when the fluid flows in the tube viscometer, the tube viscometer method can be used to obtain the Newtonian viscosity coefficient and the Bingham fluid yield value. ； The rotating cylinder method uses a coaxial double-layer cylindrical cylinder to rotate the outer cylinder at a certain speed, and uses an instrument to measure the rotation angle of the inner cylinder to obtain the relationship between the Newtonian viscosity coefficient of the fluid between the two cylinders and the rotation angle. 　　The experimental methods for elastic and viscoelastic materials are divided into three types: creep test, stress relaxation test and dynamic test.: 　　Creep experiments on materials generally involve applying a constant tensile force to the material specimen to study the tensile creep properties of the material. ； Apply a constant shear force to the material in a specialized shear instrument to study the material's shear creep properties ； Use a triaxial instrument to apply axial stress and hydrostatic pressure to the material specimen to study the one-way or three-way compression creep properties of the material. ； Use a torsional rheometer to apply a constant torque to the material specimen to study the torsional creep properties of the material. ； As well as the bending method that applies a constant bending moment to the beam-shaped specimen to study the deflection and creep properties of the material. 　　The stress relaxation experiment is to place the material specimen on the stress relaxation tester, causing the specimen to produce a constant deformation, measuring the attenuation of the stress on the specimen with time, studying the rheological properties of the material, and also calculating the spectrum of the material's relaxation time. This test can also be performed on a bending rheometer, a torsional rheometer, and a compression rheometer. This method is suitable for polymer materials and metal materials. 　　In addition to static tests such as creep and stress relaxation, dynamic tests can also be performed, that is, sinusoidal vibrations within a certain spectrum range are applied to the material specimen to study the dynamic effects of the material. This method is particularly suitable for polymer linear viscoelastic materials. Through this experiment, two physical quantities can be obtained: The elastic energy accumulated inside the material due to deformation of the material ； Energy dissipated per vibration cycle. The dynamic test can measure the relationship between energy dissipation and frequency. Through this rule, it can be compared and analyzed with the creep test and a model can be established. 　　In the above-mentioned various experimental work, various modern measurement principles and methods must be studied and applied. The emergence of large-scale electronic computers has had a profound impact on research in the field of rheology. For example, complex topics such as large strains and large displacements of nonlinear materials have been studied using the finite element method or the finite difference method. 　　With the development of economy and industrialization, rheology will have a broad field of development, and has gradually penetrated into many disciplines to form corresponding branches, such as polymer material rheology, fracture rheology, soil rheology, rock rheology, applied rheology, etc. In theoretical research, it has gone beyond the concept of uniform continuous media and begun to explore the rheological characteristics of discrete media, inhomogeneous media and incompatible elastic media. The research on experimental principles and testing techniques as well as the application of electronic computers will play an important role and play a huge role in the development of rheology.

Rheology: It is the science that studies the flow and deformation of materials. Polymer Rheology: It is a branch of rheology that focuses on the rheology of polymer melts. It is a very young science that has only received attention in recent decades. Due to practical difficulties, even qualitative laws have not been agreed upon. And now learn * There are still some basic rules for the rheology of polymers. Although they are not perfect, they play a great role in guiding the processing and molding of polymers.

Rheology is a science that studies the flow and deformation of materials when subjected to external forces. Rheology control processes in coating technology include stirring, mixing, pigment dispersion, filling, pumping, coating application, coating, sagging, leveling, penetration of porous substrates and pigment deposition, etc. Rheology is mainly divided into three categories: experimental rheology, structural rheology and theoretical rheology.

Are there any textbooks on rheology? ? ? Where can I find it? ? ? Looking for a bachelor's degree * Constitutive relations of non-Newtonian fluids

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