The Rheology Handbook. Thomas Mezger

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СКАЧАТЬ Structural decomposition and regeneration (thixotropic behavior, e. g. of coatings) 12.5 References

      14  13 Shear tests with powders and bulk solids 13.1 Introduction 13.1.1 Classification of bulk solids according to their fluidizability 13.1.2 Influences on the flow behavior of powder 13.2 Shear test of highly compacted, consolidated bulk solids 13.2.1 Pre-compaction of the bulk solid 13.2.2 Pre-shear of the bulk solid 13.2.3 Shear-to-failure of the bulk solid 13.2.4 Further pre-shear and shear-to-failure cycles 13.2.5 The Mohr´s circles 13.2.6 Further tests with shear cells 13.3 Shear test of slightly compacted bulk solids, using the powder cell 13.3.1 Powder cells 13.3.2 Preparations for powder testing 13.3.3 Preliminary tests for fluidization behavior of powders 13.3.4 Powder testing and the determination of the cohesion strength 13.4 References

      15  14 Rheologists and the historical development of rheology 14.1 Development until the 19 century 14.2 Development between 1800 and 1900 14.3 Development between 1900 and 1949 14.4 Development between 1950 and 1979 14.5 Development since 1980 14.6 References

      16  15 Appendix 15.1 Symbols, signs and abbreviations used 15.2 The Greek alphabet 15.3 Conversion table for units 15.4 References

      17  16 Standards 16.1 ISO standards 16.2 ASTM standards 16.3 DIN, DIN EN, DIN EN ISO and EN standards 16.4 Important standards for users of rotational rheometers 16.5 References

      18  Author

      19  Index

1Introduction

       1.1Rheology, rheometry and viscoelasticity

      a) Rheology

      Rheology is the science of deformation and flow. It is a branch of physics and physical chemistry since the most important variables come from the field of mechanics: forces, deflections and velocities. The term rheology originates from the Greek: rhei or rheo meaning to flow [1.1]. Thus, rheology is literally flow science. However, rheological experiments do not merely reveal information about flow behavior of liquids but also about deformation behavior of solids. The connection here is that a large deformation produced by shear forces causes many materials to flow.

      All kinds of shear behavior, which can be described rheologically in a scientific way, can be viewed as being in between two extremes: flow of ideal-viscous liquids on the one hand and deformation of ideal-elastic solids on the other. Illustrative examples coming close to these two extremes of ideal behaviors are a low-viscosity mineral oil and a rigid steel ball. Viscosity and flow behavior of fluids are explained in Chapter 2. Elasticity and deformation behavior of solids are described in Chapter 4.

      Behavior of all real materials is based on the combination of both a viscous and an elastic portion and therefore, it is called viscoelastic. Wallpaper paste is a viscoelastic liquid, for example, and a gum eraser is a viscoelastic solid. Information on viscoelastic behavior can be found in Chapter 5. Complex and extraordinary rheological behavior is presented in Chapter 9 using the example of surfactant systems.

      Table 1.1 shows the most important terms, all of which will be covered in this book. This chart can also be found at the beginning of Chapters 2 to 8, with those terms given in bold print being discussed in the chapter in hand.

Table 1.1: Overview on different kinds of rheological behavior
Liquids		Solids
(ideal-) viscousflow behaviorviscosity law(according to Newton)	viscoelasticflow behaviorMaxwell model	viscoelasticdeformation behaviorKelvin/Voigt model	(ideal-) elasticdeformation behaviorelasticity law(according to Hooke)
flow/viscosity curves	creep tests, relaxation tests, oscillatory tests

      Rheology was first seen as a science in its own, right not before the beginning of the 20th century. However, scientists and practical users have long before been interested in the behavior of liquids and solids, although some of their methods have not always been very scientific. A list of important facts of the historical development in rheology is given in Chapter 14. Of special interest are here the various attempts to classify all kinds of different rheological behavior, such as the classification of Markus Reiner in 1931 and 1960, and of George W. Scott Blair in 1942; see also [1.2]. The aim of the rheologists’ is to measure deformation and flow behavior of a great variety of matters, to present the obtained results clearly and to explain it.

      b) Rheometry

      Rheometry is the measuring technology used to determine rheological data. The emphasis here is on measuring systems, instruments, and methods for testing and analysis. Both liquids and solids, but also powders, can be investigated using rotational and oscillatory rheometers. Rotational tests which are performed to characterize viscous behavior are presented in Chapter 3. In order to evaluate viscoelastic behavior, creep tests (Chapter 6), relaxation tests (Chapter 7) and oscillatory СКАЧАТЬ