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Inspired by the multilayer structure of the shellfish, a novel two-dimensional (2D) composite structure consisting of graphene oxide, MoS2 and graphene oxide (G/M/G) was integrated to the flexible pressure sensing. The composite structure was prepared by the vacuum suction filtration in order to imitate the high toughness of shellfish. Based on the strategy of strain engineering, a comprehensive experimental bench capable of meeting different strain conditions was connected to a push–pull meter and an LCR digital bridge, and then a computer was used to record the changes in transducer capacitance when an external load was applied to the meter. Graphene oxide (GO) and G/M/G supercells were constructed, and density functional theory (DFT) simulations of the initial energy band structure under strain-free conditions were carried out to determine the relationship between the band gap, conductivity, capacitance, and sensitivity of the G/M/G structure based on band gap theory, and to easily understand the mechanism of the shellfish heterostructure leading to enhanced sensitivity of the sensors. Using two-point bending and axial tensile tests, a flexible pressure sensing device was designed to realize positive strains in the ranges of 0%–5 % and 5%–50 %. The results show that the sensitivity of both GO and G/M/G capacitive pressure sensors decreased with increased strain, and the sensitivity of the G/M/G sensors was significantly improved by 75%–102 % compared to the GO sensors at the same strain. The parallel-plate capacitor model and crack growth theory well explain the experimental results at small and large strains. Our results provide new concepts for the design of novel flexible sonar with high sensitivity and large strain operating range by a simple vacuum filtration method, which can be extended to the design of other high-performance 2D flexible electronic devices. Inspired by the multilayer structures of shellfish in nature, we constructed a GO/MoS2/GO heterojunction pressure sensor. The working range under strain and the pressure sensitivity of this new bio-inspired sensor were respectively improved by 25% and 102% compared to the traditional GO sensor structure. [ABSTRACT FROM AUTHOR]

Channel fracturing technology is designed to form fractures supported by non-uniform pillar proppants. Non-cured adhesive resin-coated proppant gradually becomes viscous after immersion and agglomerates during transportation. The pillars are stable after the fracture is closed. They not only maintain a certain compressive strength but also maintain long-term conductivity. Currently, there are few evaluations of coated proppant migration. Based on CFD-DEM method, a two-phase flow coupling model considering the adhesive contact force of coated proppant particles is established to study the cementation characteristics of coated proppant during transportation. The transportation mechanism of coated proppant are revealed by numerical calculation analysis. The results show that different from the conventional proppant, the migration process of the coated proppant is divided into four stages (1) the softening of the proppant contact; (2) the paving of the proppant agglomeration; (3) proppant pillars growth along fracture height; and (4) proppant pillars growth along fracture length. We have completed a preliminary geometric characteristics evaluation of sand bank formed by coated proppant by evaluating the pore volume ratio (the ratio of void volume between pillars to the sand bank volume) under various parameters. This evaluation offers some theoretical guidance for the optimization of channel fracturing proppant injection parameters. [ABSTRACT FROM AUTHOR]

Vertical drains have been widely used in soil improvement projects to accelerate consolidation and improve the strength of soft soil. Previous consolidation models are mainly based on instantaneous loading, which cannot reflect the actual time-variable loading condition. This paper presents a set of analytical solutions for consolidation with vertical drains under depth and time-dependent loading, involving one-step loading, multi-step loading, and cyclic loading. A four-element model, which is a combination of the Merchant model and Maxwell model, is introduced to consider the rheological characteristics of the soil. By simulating the results of a consolidation test, it is found that the four-element model is more accurate than the Merchant model in predicting the changes in pore pressure and settlement during the clay consolidation process. Based on the solutions obtained, several factors affecting consolidation behavior are investigated. It has been shown that the rheological behavior becomes more and more obvious at the later stage of consolidation with the decrease both in the modulus of the spring in the Kelvin body and the viscosity coefficient of the independent dashpot. With the increase in the viscosity coefficient of the dashpot in the Kelvin body, the rate of consolidation becomes faster at an initial stage but slower at a later stage. For cyclic loading, the consolidation degree in each cycle reaches a maximum at the end of unloading and reaches a minimum at the beginning of the loading. [ABSTRACT FROM AUTHOR]