Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural components with flexoelectricity has been considered by many researchers because of the developments of nanotechnology and the applicability of piezoelectric composite nanobeam structures in Micro/Nano-Electro-Mechanical Systems (MEMS/NEMS). Therefore, the work investigates the size-dependent electromechanical bending of piezoelectrically layered perforated nanobeams resting on elastic foundations including the flexoelectric effect. Within the framework of the modified nonlocal strain gradient elasticity theory, both the microstructure and nonlocality effects are captured. The governing equilibrium equations including piezoelectric and flexoelectric effects are derived using Hamilton’s principle. Closed forms for the non-classical electromechanical bending profiles are derived. The accuracy of the proposed methodology is verified by comparing the obtained results with the available corresponding results in the literature within a 0.3% maximum deviation. Parametric studies are conducted to explore effects of perforation parameters, elastic foundation parameters, geometric dimensions, nonclassical parameters, flexoelectric parameters, as well as the piezoelectric parameters on the bending behavior of piezoelectrically layered perforated nanobeams. The obtained results demonstrate that incorporation of the nondimensional elastic foundation parameters, K_p = 2 and K_w = 20, results in a reduction in the relative percentage reduction in the maximum nondimensional mechanical transverse deflection due to increasing the perforation filling ratio from 0.2 to 1 from 199.86% to 91.83% for a point load and 89.39% for a uniformly distributed load. On the other hand, with K_p = 5 and K_w = 50, the relative percentage difference of the electromechanical bending deflection due to increasing the piezoelectric coefficient, e₃₁₁, reaches about 8.7% for a point load and 8.5% for a uniformly distributed load at a beam aspect ratio of 50. Thus, the electromechanical as well as mechanical behaviors could be improved by controlling these parameters. The proposed methodology and the obtained results are supportive in many industrial and engineering applications, i.e., MEMS/NEMS.

Understanding the rheology behavior of non-Newtonian mine paste backfill is critical to ensure its flowability in the pipeline distribution system. Several rheology measurements methods for paste backfill have been proposed in the literature to quantify the rheology properties. However, there is no definite conclusion on the best measurement method to correctly predict pressure loss in the paste backfill pipeline system with a high solid concentration. This study addresses the issue by comparing several rheology measurements techniques, i.e., coaxial rheometer with various configurations, vane viscometer, and slump and pipe loop tests, with regard to Bingham yield stress, Bingham plastic viscosity, and pressure loss using statistical analysis. The paste backfill samples are prepared from two different mine tailings: finer and coarser particles. The pressure loss from the pipe loop test along with Buckingham-Reiner transformation using the Darcy-Weisbach equation are used as reference properties. The results suggest that a simple slump test can accurately predict the Bingham yield stress for coarser tailing. At the same time, a coaxial rheometer with MVDIN cup is found to predict the Bingham paste properties accurately for finer tailing.

The effect of high temperatures on rock’s thermophysical and mechanical properties is critical to the design of underground geotechnical applications. The current work investigates the impact of temperature on rhyolitic turf rock’s physical and mechanical properties. Intact cylindrical core rock samples were heated to different temperatures (200, 400, 600, and 800 °C). The uniaxial compressive strength (UCS) and elastic modulus of unheated and heated samples were determined as important mechanical properties. In addition, the effect of temperature on the physical properties of rhyolite rock (density, color, and absorption) was investigated in conjunction with its microstructural properties. The hardening of the rhyolitic rock samples was observed below 600 °C, at which point the UCS and elastic modulus decreased to 78.0% and 75.9%, respectively, at 800 °C. The results also show that heating does not significantly affect the density and volume of permeable pore space, but a color change can be observed at 400 °C and above. A microscopic analysis shows the change in microstructural properties of rhyolite rock after heating to 600 °C. Furthermore, the SEM observations of heated materials show structural particle displacements and microcracking, leading to apparent surface cracks.

Coated functionally graded materials (FGMs) are used in several industrial structures such as turbine blades, cutting tools, and aircraft engines. Given the need for analytical and numerical analysis of these complex structures, a mathematical model of tricoated FG structures is presented for the first time in this paper. The objective of this work was to analyze analytically the buckling problem of unidirectional (1D), bidirectional (2D), and tridirectional (3D) coated FG spherical nanoshells resting on an orthotropic elastic foundation subjected to biaxial loads. Based on the generalized field of displacement, a 2D higher-order shear deformation theory was proposed by reducing the number of displacement variables from five to four variables for specific geometry cases. The nonlocal strain gradient theory was employed to capture the size-dependent and microstructure effects. The equilibrium equations were performed by applying the principle of the virtual work, and the obtained differential equations were solved by applying the Galerkin technique to cover all possible boundary conditions. The proposed elastic foundation was defined based on three parameters: one spring constant and two shear parameters referring to the orthotropy directions. A detailed parametric analysis was carried out to highlight the impact of various schemes of coated FGMs, gradient material distribution, length scale parameter (nonlocal), material scale parameter (gradient), geometry of the nanoshell, and variation in the orthotropic elastic foundation on the critical buckling loads.

With the increasing engineering applications of geothermal borehole heat exchangers (BHEs), accurate and reliable mathematical models can help advance their thermal design and operations. In this study, an analytical model with a time-dependent heat flux boundary condition on the borehole wall is developed, capable of predicting the thermal performance of single, double, and multiple closed-loop BHEs, with an emphasis on solar- and waste-heat-assisted geothermal borehole systems (S-GBS and W-GBS) for energy storage. This analytical framework begins with a one-dimensional transient heat conduction problem subjected to a time-dependent heat flux for a single borehole. The single borehole scenario is then extended to multiple boreholes by exploiting lines of symmetry (or thermal superposition). A final expression of the temperature distribution along the center line is attained for single, double, and multiple boreholes, which is verified with a two-dimensional finite-element numerical model (less than 0.7% mean absolute deviation) and uses much lesser computational power and time. The analytical solution is also validated against a field-scale experiment from the literature regarding the borehole and ground temperatures at different time frames, with an absolute error below 6.3%. Further, the thermal performance of S-GBS and W-GBS is compared for a 3-by-3 borehole configuration using the analytical model to ensure its versatility in thermal energy storage. It is concluded that our proposed analytical framework can rapidly evaluate closed-loop geothermal BHEs, regardless of the numbers of boreholes and the type of the heat flux on the borehole wall.