Hysteresis structural breakdown

Thixotropy is the time-dependent analogue of shear-thinning and plastic behaviour, and arises from somewhat similar causes. If a thixotropic system is allowed to stand and is then sheared at a constant rate, the apparent viscosity decreases with time until a balance between structural breakdown and structure re-formation is reached. If the sheared system is then allowed to stand, it eventually regains its original structure. A thixotropic hysteresis loop (Figure... 

Tattersall (T43) found that pastes of w/c ratio 0.28-0.32 and age 4.5 min followed the Bingham model at low rates of shear, but that at higher rates the structure broke down irreversibly. Several other investigators have obtained similar results, but negative hysteresis has also been observed (e.g. Ref. R30), probably due to the use of hysteresis cycles of long duration, in which the structural breakdown due to shear is outweighed by the effects of... 

Structure Breakdown. When a linearly elastic material is deformed and then allowed to relax, the stress-strain curve is fully reversible, as illustrated in Figure 17.5, frame (a). For a larger deformation, the curve is generally not linear, and perceptible hysteresis tends to occur, as depicted in frame (b). Nevertheless, the deformation is fully reversible. This means that deformation/relaxation has left the structure unaltered repeating the test on the same specimen leads to an identical result. The hysteresis is due to energy dissipation, caused by flow of solvent through the gel network if it concerns a gel, as mentioned in Section 5.1.3. 

Structural breakdown is a time-dependent process resulting in a decrease in the viscosity of a product. The classical approach to characterizing structural breakdown is the measurement of the hysteresis loop, first reported by Green and Weltmann (1943). A sample is sheared at a continuously increasing, then continuously decreasing, shear rate, and a shear stress-shear rate flow curve is plotted. If structural breakdown occurs, the two curves do not coincide, creating a hysteresis loop. The area enclosed by the loop indicates the degree of breakdown. 

Influence of Solvents. The stress-strain curves of untreated and ether-extracted corneum in water show marked differences (81). Untreated corneum, extended 5% and relaxed, shows hysteresis similar to that observed for other keratinaceous structures (Figure 35). The deformation mechanism is completely reversible, and hydrogen-bond breakdown and slow reformation may be the major factors determining the stress-strain relationships. With ether-extracted samples, complete recovery is observed from 5% extension but with little or no hysteresis. The more rapid swelling and lack of hysteresis of ether-extracted corneum in water may be related to the breakdown of hydrogen bonds normally shielded from the eflFects of water by the lipid-like materials removed by ether. 

Bias-induced reverse piezoelectric response Broadband dielectric spectroscopy (BDS) Dielectric permittivity spectrum Dielectric resonance spectroscopy Elastic modulus Ferroelectrets Electrical breakdown Acoustic method Characterization Dynamic coefficient Interferometric method Pressure and frequency dependence of piezoelectric coefficient Profilometer Quasistatic piezoelectric coefficient Stress-strain curves Thermal stability of piezoelectricity Ferroelectric hysteresis Impedance spectroscopy Laser-induced pressure pulse Layer-structure model of ferroelectret Low-field dielectric spectroscopy Nonlinear dielectric spectroscopy Piezoelectrically generated pressure step technique (PPS) Pyroelectric current spectrum Pyroelectric microscopy Pyroelectricity Quasistatic method Scale transform method Scanning pyroelectric microscopy (SPEM) Thermal step teehnique Thermal wave technique Thermal-pulse method Weibull distribution... 

There is considerable evidence that all the hysteresis effects observed in these materials and most of the viscoelastic behavior can be caused by the time dependent failure of the polymer on a molecular basis and are not due to internal viscosity [1,2]. At near equilibrium rates and small strains filled polymers exhibit the same type of hysteresis that many lowly filled, highly cross-linked rubbers demonstrate at large strains [1-8]. This phenomenon is called the "Mullins Effect" and has been attributed to micro-structural failure. Mullins postulated that a breakdown of particle-particle association and possibly also particle-polymer breakdown could account for the effect [3-5]. Later Bueche [7,8] proposed a molecular model for the Mullins Effect based on the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the composite. Such deformations would cause a highly non-uniform strain and stress gradient in the polymer... 

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