Abstract
Yield stress materials have a wide range of commercial applications. Yet, the suitable way of determining the yield stress values of a given material has been the subject of many studies and debates. Yield stresses are dependent on the material (shear) history and composition, which implies that robust protocols should be developed to study the yield stress dependence on a given parameter. In this study, three natural mud samples from a port having different densities were chosen for analysis. Four different geometries including concentric cylinders (Couette), cone and plate, parallel plates, and vane geometries were used. Our aim was to find the geometry and measurement protocol that best adapted to natural mud samples: the measurement should be reasonably fast and the major changes in sample structure (two-step yielding) should be recorded within the same measurement. Various rheological experiments such as stress sweep, oscillatory amplitude sweep, creep and stress growth tests were tested. Two-step yielding behavior was observed for the mud samples in stress sweep and amplitude sweep tests. The first yield point was linked with the breakage of interconnected network of aggregates/flocs while the second one was attributed to the collapse of aggregates into the smaller flocs or individual particles. Stress sweep tests proved to be practical, time efficient, and reliable tests for measuring yield stress values. Our study showed that Couette and parallel plate geometries are the most suitable geometries for analyzing the two yield stresses of the samples. Vane geometry is appropriate to study consolidated (solid-like) systems as for these samples a Couette geometry cannot be used because the bob could get stuck during the experiment.
Highlights
Composite materials can exhibit either solid-like or liquid-like properties when submitted to an applied stress
Two-step yielding behavior was observed for the mud samples in stress sweep and amplitude sweep tests
Ref. (Van Kessel and Blom, 1998) (Fass and Wartel, 2006) (Huang and Aode, 2009) (Yang, Yu, Tan, and Wang, 2014b) (Yang, Yu, Tan, and Wang, 2014b) (Yang, Yu, Tan, and Wang, 2014b) (Xu and Huhe, 2016) (Fonseca, Marroig, Carneiro, Gallo, and Vinzón, 2019) (Fonseca, Marroig, Carneiro, Gallo, and Vinzón, 2019) (Fonseca, Marroig, Carneiro, Gallo, and Vinzón, 2019) (Fonseca, Marroig, Carneiro, Gallo, and Vinzón, 2019) (Nie, Jiang, Cui, and Zhang, 2020) (Shakeel et al, 2020) This study comparatively lower (i.e., 5.8–7.1 Pa) for the Couette geometry while the fluidic yield stress values were smaller (i.e., 20.5–22.5 Pa) for the vane geometry. This result shows that the Couette geometry is more effective in breaking the network of flocs/aggregates while for the breakdown of flocs into individual particles, vane geometry is better
Summary
Composite materials can exhibit either solid-like or liquid-like properties when submitted to an applied stress. These materials behave like an elastic solid at small stresses whereas they tend to flow above a critical value of stress, called yield stress. Yield stress determination is very important for industrial processes. Our overall goals are to study the yield stresses of mud sediments and to propose an appropriate geometry and rheological method for these systems. Yield stress has been found to be an important parameter to define navigable fluid mud layers for ports and waterways (Kirichek et al, 2018; Møller, Mewis, and Bonn, 2006; Nguyen and Boger, 1992). Our present study is imbedded in a larger scale project which aims at correctly assessing the so-called nautical bottom within navigable channels
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