Search Results (33)

The hanging of hard roofs in coal seams poses a significant threat to the safe mining of coal. Hydraulic fracturing is an important method to achieve the pre-weakening of coal seam roofs. Clarifying the scope of hydraulic fracturing in coal seam roofs and its influencing factors is a prerequisite for ensuring the effectiveness of the pre-weakening process. In this paper, we developed a fluid–structure coupling numerical simulation model for hydraulic fracturing based on the element damage theory, and have systematically examined the effects of both engineering parameters and geological factors on the hydraulic fracture propagation behavior of the segmented fracturing of coal seam roofs. Results indicate that increasing the injection rate can significantly enhance fracture propagation length. A larger stress difference directs fractures along the maximum principal stress direction and effectively extends their length. Additionally, increasing the spacing between fracture stages reduces stress interference between clusters, leading to a transition from asymmetric to uniform fracture propagation. To validate the numerical simulation results, we conducted a field test on the hydraulic fracturing of the coal seam roof, and monitored the affected area by using transient electromagnetic and microseismic monitoring techniques. Monitoring results indicated that the effective impact range of field hydraulic fracturing was consistent with the numerical simulation results. Through the systematic monitoring of support resistance and coal body stress, the supporting resistance in the fractured zone decreased by 25.10%, and the coal seam stress in the fractured zone exhibited a 1 MPa reduction. Observations demonstrate the significant effectiveness of hydraulic fracturing in regional control of the coal seam roof. This study combines numerical simulation with engineering practice to investigate hydraulic fracturing performance under varying operational conditions, with the findings providing robust technical support for safe and efficient mining production. Full article

This work develops a unified size-dependent shear deformation theory (SDSDT) to analyze the free vibration behavior of a functionally graded (FG) magneto-electro-elastic (MEE) microplate under fully simply supported conditions, open- or closed-circuit surface conditions, biaxial compression, magnetic and electric potentials, and uniform temperature changes based on consistent couple stress theory (CCST). The FG-MEE microplate is composed of BaTiO₃ (a piezoelectric material) and CoFe₂O₄ (a magnetostrictive material). Various CCST-based SDSDTs, considering couple stress and thickness stretching effects, can be reproduced by employing a generalized shape function that characterizes shear deformation distributions along the thickness direction within the unified SDSDT. These CCST-based SDSDTs encompass the size-dependent classical plate theory (CPT), first-order shear deformation theory (SDT), Reddy’s refined SDT, exponential SDT, sinusoidal SDT, and hyperbolic SDT. The unified SDSDT is validated by comparing its solutions with relevant three-dimensional solutions available in the literature. After validation and comparison studies, we conduct a parametric study, whose results indicate that the effects of thickness stretching, material length-scale parameter, inhomogeneity index, and length-to-thickness ratio, as well as the magnitude of biaxial compressive forces, electric potential, magnetic potential, and uniform temperature changes significantly impact the microplate’s natural frequency. Full article

Addressing the critical technological needs for the real-time monitoring of stress distribution in mining areas, a new method for inverting goaf pressure using distributed optical fiber monitoring data is proposed. By coupling the key stratum fracture mechanics model with the subsidence trajectory function model, a theoretical model is established to accurately describe spatial stress evolution during coal mining. The model quantifies the relationship between goaf pressure changes and key stratum failures through a two-stage analysis of the subsidence process, based on distinct mechanical properties before and after key stratum fracture. Physical model experiments (3 m × 0.2 m × 1.1 m) using Brillouin Optical Time Domain Analysis (BOTDA) technology validated the proposed method, with comprehensive monitoring of key stratum deformations. By coupling the fracture mechanics model of the critical layer and the settlement trajectory function model, the dynamic transformation of the pre-fracture and post-fracture stages is realized, and the stress evolution can be monitored and predicted in real time. The results demonstrate spatial consistency between key stratum fracture locations and goaf peak stress positions. High-precision optical fiber sensing detected an ultimate strain threshold of 4000 με for key stratum failure, with pre-fracture strain measurements consistently below this threshold. The developed stress inversion formula successfully predicted pressure distribution patterns within the goaf, achieving real-time monitoring capabilities. Compared with the BPPS measurements, the deviation in the inverted data is less than 8.88%, the root mean square error (RMSE) is 0.98–1.20 in different propulsion stages, and the coefficient of determination (R²) is between 0.72 and 0.85. These findings provide a crucial theory for predicting peak stress evolution in mining areas, with implications for improving safety monitoring systems and optimizing mining operations. Full article

A numerical model to simulate the laser thermoforming process (LTF) is proposed. It is developed on the basis of the thermodynamically consistent theory of coupled thermo-viscoplasticity and is suitable for modeling the LTF for thin-walled metal structural elements. In the frame of this model, the problem statement consists of the Cauchy relation, equations of motion, and the energy balance equation, which is reduced to the heat conduction equation, along with mechanical and thermal boundary conditions, as well as initial conditions. To describe the behavior of the material, a generalized model of physically nonlinear temperature-dependent thermo-viscoplasticity is used. Spatial discretization of the axisymmetric problem of laser pulse loading of the disk is performed by the FEM. The unsteady LTF process of the deformed disk configuration is simulated. The final profile of the disk is obtained as a result of a thermally induced residual stress–strain state caused by the rapid heating and subsequent gradual cooling of the material under the laser-irradiated area. Full article

Among various continuum mechanics approaches, size-dependent theories have gained significant attention for their ability to model these effects in micro- and nanostructures. This study presents an exact solution for the flexural analysis of thick microplates based on consistent couple stress theory. Unlike conventional plate theories, such as the Kirchhoff and first-order shear deformation theories, this work employs three-dimensional elasticity theory to accurately model the mechanical response of thick microplates. The governing equations are derived within the framework of couple stress theory, incorporating length-scale effects, and solved under simply supported boundary conditions. The results demonstrate significant reductions in both in-plane and out-of-plane displacements, approximately 24% and 36%, respectively, compared to classical elasticity predictions. These findings highlight the critical role of size effects in accurately predicting the mechanical behavior of microscale structures. The insights gained from this study are particularly relevant to the design and analysis of polymeric and composite microstructures, where small-scale mechanical phenomena influence performance and reliability. Full article

Boundary element methods provide powerful techniques for the analysis of problems involving coupled multi-physical response. This paper presents the integral equation formulation for the size-dependent thermoelastic response of solids under steady-state conditions in three dimensions. The formulation is based upon consistent couple stress theory, which features a skew-symmetric couple-stress pseudo-tensor. For general anisotropic thermoelastic material, there is not only thermal strain deformation, but also thermal mean curvature deformation. Interestingly, in this size-dependent multi-physics model, the thermal governing equation is independent of the deformation. However, the mechanical governing equations depend on the temperature field. First, thermal and mechanical weak forms and reciprocal theorems are developed for this theory. Then, an integral equation formulation for three-dimensional size-dependent thermoelastic isotropic materials is derived, along with the corresponding singular infinite-space fundamental solutions or kernel functions. For isotropic materials, there is no thermal mean curvature deformation, and the thermoelastic effect is solely the result of thermal strain deformation. As a result, the size-dependent behavior is specified entirely by a single characteristic length scale parameter $l$, while the thermal coupling is defined in terms of the thermal expansion coefficient $\alpha$, as in the classical theory of steady-state isotropic thermoelasticity. Full article

Exposure to elevated temperatures leads to the deterioration of the mechanical properties of cementitious materials. However, the inclusion of fibers can mitigate, to some extent, the negative effects of high temperatures on these materials. Specifically, polypropylene (PP) fibers, a synthetic fiber type, have been demonstrated to improve the performance of cement-based composites. Therefore, it is essential to investigate the impact of temperature on the behavior of fiber-reinforced mortar for its broader application in construction. This study explores the effects of varying PP fiber contents (0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1%) and different temperature exposures (25 °C, 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C) on the performance of cement mortar. The experimental results show that elevated temperatures significantly degrade both the mechanical and thermal properties of fiber-reinforced mortar. As the temperature and fiber content increase, both the quality and thermal conductivity of the mortar decrease. Between 25 °C and 200 °C, the incorporation of PP fibers (ranging from 0% to 0.2%) significantly enhances the compressive and flexural strengths of the mortar. However, this improvement becomes less pronounced as the fiber content exceeds 0.2%. At temperatures above 200 °C, further increases in temperature, coupled with higher fiber contents, consistently lead to a reduction in the compressive and flexural strengths. Based on the principles of continuous damage mechanics (which describes the degradation and fracture of materials under loading) and the dual-parameter Weibull distribution theory, a constitutive model is proposed to describe the damage behavior of high-temperature PP-fiber-reinforced mortar under uniaxial compressive stress. Full article

To address the issue of size effects in axisymmetric deformation of small-scale solids, this work proposes a 4-node 12-DOF element for axisymmetric problems based on the consistent couple stress theory (CCST), following the framework of the unsymmetric finite element method. With the use of the penalty function method, an independently assumed rotational field is introduced into the virtual work principle to approximate the physical rotation, ensuring the satisfaction of the C¹ continuity requirement of the CCST in a weak form. As a benefit, the enriched C⁰ isoparametric-based interpolation is employed to construct the test functions for displacement and rotation. Furthermore, the force-stress field that satisfies the equilibrium equations related to axisymmetric deformation is employed as the element’s force-stress trial function. In order to circumvent locking issues, reduced integration is employed in the penalty stiffness integration process. The numerical results demonstrate that the new element exhibits high computational accuracy and convergence rate in both static and modal analysis problems, effectively capturing size-dependent phenomena. Full article

This research paper presents an experimental, theoretical, and numerical study of the thermomechanical behavior of single-crystal and polycrystal copper under uniaxial stress compression loading at varying rates of deformation. The thermomechanical theory is based on a thermodynamically consistent framework for single-crystal face-centered cubic metals, and assumes that all plastic power is partitioned between stored energy due to dislocation structure evolution (configurational) and thermal (kinetic vibrational) energy. An expression for the Taylor–Quinney factor is proposed, which is a simple function of effective temperature and is allowed by second-law restrictions. This single-crystal model is used for the study of single- and polycrystal copper. New polycrystal thermomechanical experimental results are presented at varying strain rates. The temperature evolution on the surface of the polycrystal samples is measured using mounted thermocouples. Thermomechanical numerical single- and polycrystal simulations were performed for all experimental conditions ranging between ${10}^{-3}$ and 5 × ${10}^3$ ${\mathrm{s}}^{-1}$. A Taylor homogenization model is used to represent polycrystal behavior. The numerical simulations of all conditions compare reasonable well with experimental results for both stress and temperature evolution. Given our lack of understanding of the mechanisms responsible for the coupling of dislocation glide and atomic vibration, this implies that the proposed theory is a reasonably accurate approximation of the single-crystal thermomechanics. Full article

The functionally graded (FG) flexoelectric material is a potential material to determine the structural morphing of aircrafts. This work proposes the penalty 20-node element based on the consistent couple stress theory for analyzing the FG flexoelectric plate and shell structures with complex geometric shapes and loading conditions. Several numerical examples are examined and prove that the new element can predict the size-dependent behaviors of FG flexoelectric plate and shell structures effectively, showing good convergence and robustness. Moreover, the numerical results reveal that FG flexoelectric material exhibits better bending performance and higher flexoelectric effect compared to homogeneous materials. Moreover, the increase in the material length scale parameter leads to a gradual increase in the natural frequencies of the out-of-plane modes of FG flexoelectric plate/shell, while the natural frequencies of the in-plane modes change minimally, resulting in the occurrence of mode-switching phenomena. Full article

A frequency up-conversion piezoelectric energy harvester (FUC-PEH) consists of a force amplifier, a piezoelectric stack, a low-frequency oscillator (LFO), and a stop limiter. The force amplifier generates the amplification of stress on the piezoelectric stack. The LFO, comprising a spring and a mass block, impacts the stop limiter during vibration to induce high-frequency oscillations within the piezoelectric stack. In this paper, we represent and simplify the FUC-PEH as a lumped-parameter model based on piezoelectric material constitutive equations and structural dynamic theories. Using the electromechanical analogy, we developed an equivalent circuit model (ECM) of the FUC-PEH. A parametric study was performed to investigate the impact of system parameters, such as spring stiffness and concentrated mass, on the FUC-PEH performance. The collision-induced amplitude truncation (AT) effect enlarges the operation bandwidth. ECM simulations show that low-frequency input excitation is converted into a high-frequency output response, enhancing the energy conversion efficiency. Furthermore, we aimed to improve the FUC-PEH’s performance using a synchronous electric charge extraction (SECE) circuit. Using the ECM approach, we established a system-level model that considers the electromechanical coupling behavior. The simulation results provide insights into the performance of FUC harvesters with SECE circuits and offer valuable design guidance. Full article

This work develops a three-dimensional (3D) weak formulation, based on the consistent couple stress theory (CCST), for analyzing the size-dependent dynamic instability behavior of simply-supported, functionally graded (FG) cylindrical microshells that are subjected to combinations of periodic axial compression and external pressure. In our formulation, the microshells are artificially divided into n_l layers. The displacement components of each individual layer are selected as the primary variables, which are expanded as a double Fourier series in the in-plane domain and are interpolated with Hermitian C² polynomials in the thickness direction. Incorporating the layer-wise displacement models into our weak formulation, we develop a Hermitian C² finite layer method (FLM) for addressing the current issue. The accuracy and the convergence rate of our Hermitian C² FLM are validated by comparing the solutions it produces with the accurate two-dimensional solutions of critical loads and critical pressures of FG cylindrical macroshells and single-walled carbon nanotubes, which were reported in the literature. The numerical results show the effects of the material length-scale parameter, the inhomogeneity index, the radius-to-thickness and length-to-radius ratios, the load magnitude ratio, and the static and dynamic load factors on the first principal and first secondary instability regions of parametric resonance of simply-supported FG cylindrical microshells are significant. Full article

Nearshore waves and currents induced by breaking of obliquely incident waves are important dynamic factors that significantly affect pollutants movement at offshore zones. A combined numerical model in orthogonal curvilinear coordinates is developed to simulate pollutants movement in surf zones, including a wave transformation model based on the parabolic mild slope equation, a wave-induced current model, and a pollutant transport model driven by waves and currents. This combined model has been applied to pollutants movement laboratory cases, and comparison of the simulations with experimental measurements shows good agreement. The model has also been applied to simulation of the Gourlay experiment and it shows consistent results with the distribution of waves and offshore currents. This coupled numerical model has preliminarily improved the situation of rare numerical research on the nearshore pollutant transport in coastal wave and wave-induced current based on wave radiation stress theory in orthogonal curvilinear coordinates. Full article

A model of consolidation for a single-drain well under vacuum preloading, based on Biot’s axisymmetric theory and considering the “real strain” hypothesis, was established using the finite element method. Degenerating the consolidation equation of real strain yielded the Barron’s classical free strain and equal strain equations. The free strain and equal strain finite element models were derived by imposing boundary and constraint conditions on the real strain FEM model. The validation of the simulation process confirmed that the numerical model achieved consistent outcomes, with the theoretical values postulating its effectiveness. The real strain model revealed the Mandel–Cryer effect of soil near the vertical drain during the initial vacuum preloading consolidation process, causing the effective stress to increase more than the effective stress generated by the vacuum pressure and leading to a greater reduction in the void ratio. This phenomenon is one of the reasons for clogging during the vacuum preloading process. However, the free strain and equal strain models cannot produce this effect because they cannot describe the coupling between soil deformation and fluid flow. The parameter analysis of the real strain model showed that as Poisson’s ratio for soil decreased, the consolidation rate of soil also decreased, while the Mandel–Cryer effect of soil increased. Full article

In order to effectively prevent and control the problem of water inrush from the through-type fault floor, based on the analysis of the case data of water inrush from the fault structure in the Fengfeng mining area, the types of karst water inrush from the floor are divided into 3 categories, 6 subcategories, and 17 fine categories. Four water inrush modes are summarized: composite structure water inrush, through-type fault water inrush, roof crack expansion water inrush, and floor vertical crack expansion water inrush. Based on the grey correlation theory and combined with the Analytic Hierarchy Process (AHP), this paper evaluates the water inrush risk of the F_55-1 through-type fault zone from a micro individual perspective, taking the Xin’an Mine as the engineering background. Based on the water–rock coupling theory, the FLAC^3D numerical simulation software is applied to study the disaster mechanism of the water inrush mode of the through-type fault. Through analyzing the changes of primary fracture stress and displacement of the intact floor strata and the aquifuge, and the pressure changes of confined water in fault zones, the collaborative water inrush mechanism of the damage and fracture of the bottom plate rock layer, the expansion and connection of the original fracture, and the seepage and progressive intrusion of the pressure water during the advancing process of the working face is analyzed. The research results indicate that the evaluation result of the water inrush risk of the F_55-1 through-type fault in Xin’an Mine is Level I, belonging to the high risk and consistent with the actual situation model, verifying the rationality of the evaluation model. The process of water inrush in the numerical model is summarized as follows: a rock pressure failure zone is caused by the rupture and instability of floor aquifuge; a progressive intrusion zone develops—water inrush is connected between rock pressure failure zone and progressive intrusion zone; floor lagging flood occurs. Under the combined action of mine pressure and confined water pressure, the progressive intrusion height of confined water is significantly increased. The research results have important reference basis for future coal mining planning. This provides engineering reference and practical experience for the prevention and control of water damage in structured bottom plates under similar conditions. Full article