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Author index ►Bin Yu, Yuanjing Chen, Qinghua Liu

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Experimental study on the influence of coarse particle on the yield stress of debris flows

Appl. Rheol.26:4 (2016) 42997 (13 pages) ►

Former studies show that the coarse particle plays a very important role in the determination of the yield stress of fluid-solid mixtures such as debris flows. The characteristics of the coarse particle in these mixtures include particle size, gradation, shape, and type of material. To assess the influence of these coarse particles on the yield stress the concept of equivalent volumetric solid concentration C is introduced. The equivalent concentration can be derived from the volumetric solid concentration by considering the particle size, gradation, shape, and type of material. Laboratory experiments to determine the yield stress of various mixtures were conducted to calibrate the coefficients of these coarse particle characteristics. A yield stress phenomenological expression is proposed using the refined volumetric solid concentration (equivalent concentration), which could be calibrated by the experiments in this study. The validation of this phenomenological expression with data from literature shows good agreements, especially for higher volumetric concentrations of the sediments.► Cite this publication as follows:

Yu B, Chen Y, Liu Q: Experimental study on the influence of coarse particle on the yield stress of debris flows, Appl. Rheol. 26 (2016) 42997.

Suspensions of SiO_{2}microspheres in glycerine exhibit drastic shear-thickening behavior under steady shear and dynamic oscillatory shear test. The rheological behavior of suspensions agrees with the modified Cox-Merz rules as the dynamic oscillatory rheological behavior at low frequency could be reasonably interpreted in terms of the steady shear behavior. As new insight, the effect of shear history and the relaxation on the rheological behavior was investigated in detail. The result showed that under continuous shear, the viscosity decreases after a 'pulse': The degree of decrease is directly proportional to the shear rate. Similar phenomenon is also found under the continuous stress and dynamic oscillatory shear rate sweep. The shear history shows a non-negligent effect on the rheological behavior, the suspensions with higher viscosity show a lower viscosity under the same shear rate. Moreover, the relaxation time of suspensions shows the direct dependency on the initial viscosity, while the volume fraction of suspensions also affect the relaxation time. For more enlapsed times, also longer relaxation times are needed for the suspensions with lower volume fraction and higher initial viscosity.► Cite this publication as follows:

Chen Y, Li X, Zeng G, Liu W: The influence of continuous shear, shear history and relaxation on the rheological behavior of SiO2/glycerine suspensions, Appl. Rheol. 25 (2015) 44806.

For developing a new composite material owning shear-thickening characteristic, the rheological behaviors of nano-sized precipitated calcium carbonate (PCC) particles with irregular sharp in glycerine were investigated systematically by means of steady and dynamic rheometry. The results showed that the concentrated PCC suspensions exhibit a strong shear-thickening behavior under both steady and dynamic oscillatory shear when the volume fraction of PCC above the threshold (about 41 %). In steady shear tests, the critical shear rate decreases and the maximum viscosity in shear thickening region increases dynamically with the increase of volume fraction. While, for suspensions with different volume fractions, the similar critical stress for the onset of shear thickening is found. In dynamic strain sweep at different fixed frequencies, with the increase of fixed frequency, the complex viscosity of suspensions decreases slightly, while the critical strain for shear-thickening shifts to lower value. The dynamic oscillatory rheological behavior of suspensions at low frequency (w < 100 rad/s) could be reasonably interpreted in terms of the steady shear behavior. For the suspensions with same volume fraction, it was interestingly found that the critical dynamic shear rate equaled to the product of critical strain and frequency could agree well with the critical shear rate in steady shear. Moreover, the rheological behavior of PCC suspensions shows excellent reversibility and reproducibility.► Cite this publication as follows:

Chen Y, Xu W, Xiong Y, Peng Y, Peng C, Ou Z: Shear-Thickening Behavior of Precipitated Calcium Carbonate Particles Suspensions in Glycerine, Appl. Rheol. 25 (2015) 12466.

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