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Rheological Principles
Published in B. R. Gupta, Rheology Applied in Polymer Processing, 2023
The rheopectic behaviour is demonstrated by some clay suspensions in water, specific gypsum paste, printer ink etc. In the body the synovial fluid (a viscous transparent lubricating fluid, occurring typically within the tendon sheaths and the capsular ligaments surrounding movable joints) exhibit the property of rheopexy[3a].
The Science and Practice of Ceramic Suspensions
Published in Navid Hosseinabadi, Hossein Ali Dehghanian, Suspension Plasma Spray Coating of Advanced Ceramics, 2022
Navid Hosseinabadi, Hossein Ali Dehghanian
When the stress is released, the strain will, in principle, recoil to zero as long as the applied stress is lower than the yield stress. After the applied stress exceeds a critical value, the material will ultimately flow. The strain will then increase at a constant rate that depends on the applied stress. A transitional stress region exists between “flow” and “no-flow,” where flow is delayed. The delay time decreases with increasing stress. This behavior can be understood on the basis of slow, stress-driven rearrangements in microstructure that weaken the structure and ultimately lead to yielding and flow. The term rheopexy typically refers to the increase in viscosity with time of some thixotropic materials held at constant low shear rate (or stress). This results in the reversible shear thickening in stable colloidal dispersions, although in practice shear thickening may also be associated with irreversible particle aggregation and dilatancy. The importance of this phenomenon is, shear thickening in colloidal dispersions often seriously limits formulations for coating and spraying operations, as well as flow rates for pumping concentrated dispersions.
Flows, Gradients, and Transport Properties
Published in Joel L. Plawsky, Transport Phenomena Fundamentals, 2020
In a flow where the shear rate changes with time, we can have different phenomena. A thixotropic fluid has a viscosity that decreases with time under a sudden applied stress. One can imagine a process of bond breakage occurring where, as time increases, more bonds are broken and so the viscosity decreases. A rheopectic fluid has a viscosity that increases with time under the applied stress. Here we can envision generating entanglements within the fluid making it difficult to move.
Time-dependent rheological behaviour of cemented backfill mixture
Published in International Journal of Mining, Reclamation and Environment, 2018
X. J. Deng, B. Klein, J. X. Zhang, D. Hallbom, B. de Wit
Due to instrument limitations, the sample with a 3600 s curing time could not be tested. Figure 9(a) shows the time-dependent rheological behaviour of CBM with various curing times. As described, the shear stress and apparent viscosity decrease at first until it reaches a minimum and then increase with shearing time; both thixotropic and rheopectic behaviours were found. The sample with 600 s curing time showed a ‘relatively steady state’ shear stress over a shear period from 1400 to 1800 s. In this period, the shear stress of the sample nearly achieves a constant level, before beginning to increase. This ‘relatively steady state’ period observed is likely due to the dynamic balance between the microstructure rebuilding and shear-induced breakdown in this shearing period [49]. After this period, the microstructure rebuilding rate is higher than the shear-induced breakdown rate, resulting in the shear stress rising again.