Search Results (116)

The existing stability analysis of Coulomb retaining walls is derived on the basis of four assumptions, and there is no clear description of the interaction mechanism among wedge-shaped bodies, retaining walls, and the two. This article proposes a new method for calculating the stability of Coulomb retaining walls. For soil wedges and retaining walls, numerical theoretical solutions for the stress distribution in soil wedges and retaining walls were obtained on the basis of stress balance differential equations, coordination equations, force boundary conditions, and macroscopic equilibrium. The boundary condition between the soil wedge and the retaining wall is that the resultant force and moment between the two are continuous. Assuming that the soil wedge and retaining wall satisfy the Duncan–Zhang model and the linear elastic Hooke constitutive model, respectively, the strain solutions of the soil wedge and retaining wall are obtained. Assuming that both the peak strength criteria for the soil wedges and the concrete retaining walls satisfy the Mohr–Coulomb criterion, the location of the first point of failure for the soil wedges and retaining walls is determined. Taking the garbage transfer station in Lvcongpo Town, Badong County, as an example, the analysis of the force and displacement of the retaining wall and years of operation show that the proposed method for calculating the stress and strain of the retaining wall and the new method for evaluating the stability of the retaining wall based on the point strength criterion are feasible. Full article

Intra-tissue endoscopy, providing real-time images at all scales, from macroscopic to microscopic, from inside living tissue during surgical procedures, has revealed the existence of a body-wide fibrillar architecture that extends from the surface of the skin to the cell. Different types of cells are housed within this fibrillar architecture and gather together to carry out specific functions. This challenges the commonly accepted notion of the organization of living matter that associates separate organs with connective tissue packaging. We are thus confronted with the global nature of the living human body and its vital processes. This paper sets out to describe the architecture of this fibrillar network which could be assimilated with the fascial tissue and which attributes a more constitutive role to connective tissue. It also demonstrates how movements within this fibrillar network can occur with minimal local distortion while maintaining tissue continuity. The authors propose that the gliding of tissues can be explained by the existence of a highly adaptable fibrillar network that enables the gliding of distinct anatomical structures such as tendons and muscles, without any dynamic influence on the surrounding tissues. The authors propose a new model of tissue movement based on the observation of a ubiquitous dynamic polyhedric fibrillar network with an apparently dispersed and complex pattern of organization, that forms fluid-filled microvolumes, and is found everywhere in the human body. Furthermore, this fibrillar network appears to act as a force absorption system, in addition to providing a framework or scaffolding for cells throughout the body. Observation during intra-tissue endoscopy suggests that this fundamental architectural organization extends into the extracellular matrix that is the natural environment of all cells in the living body, regardless of their size, location or specific function. Full article

The development and validation of constitutive models for high-temperature deformation are critical for bridging microstructure evolution with macroscopic mechanical behavior in materials. In this study, we systematically analyzed the hot deformation behavior of Fe-Mn-Cr-based alloys, compared the modeling processes of physical, phenomenological, and data-driven approaches in detail, and optimized their structural and predictive properties. First, the advantages, disadvantages, and applicability of three traditional models, namely the physical Arrhenius model, the phenomenological Johnson–Cook model, and the artificial neural network (ANN) model, are compared for flow stress prediction. Subsequently, traditional mathematical derivations and numerical optimization methods are evaluated. The parameters and architecture of the ANN model are then systematically optimized using optimization algorithms to enhance training efficiency and prediction accuracy. Finally, sensitivity analysis integrated with Bayesian posterior probability density functions enables the calibration of physical model parameters and uncertainty quantification. The results demonstrate that the ANN with optimized parameters and architecture achieves superior prediction accuracy (R² = 0.9985, AARE = 3.01%) compared to traditional methods. Bayesian inference-based quantification of parameter uncertainty significantly enhances the reliability and interpretability of constitutive model parameters. This study not only reveals the strain–temperature coupling effects in the hot deformation behavior of Fe-Mn-Cr-based alloys but also provides systematic methodological support for constitutive modeling of high-performance alloys and a theoretical foundation for material processing technology design. Full article

The study of the compression characteristics of loess in seasonal regions involves analyzing the mechanical properties and mesoscale damage evolution of intact loess subjected to dry–wet freeze–thaw cycles. This study meticulously examines the evolution of the stress–strain curve at the macroscale and the pore structure at the mesoscale of loess by consolidation and drainage triaxial shear tests, as well as nuclear magnetic resonance (NMR), under varying numbers of dry–wet freeze–thaw cycles. Then, utilizing the Duncan–Chang model (D-C), the damage model for intact loess is derived based on the principles of equivalent strain and Weibull distribution, with testing to verify its applicability. The results indicate that the stress–strain curve of undisturbed loess exhibits significant strain softening during the initial stage of the freeze–thaw dry–wet cycle. As the number of cycles increases, the degree of strain softening weakens and gradually exhibits a strain-hardening morphology; the volume strain also changes from dilatancy to shear contraction. According to the internal pore test data analysis, the undisturbed loess contributes two components to shear strength: cementation and friction during the shear process. The cementation component of the aggregate is destroyed after stress application, resulting in a gradual enlargement of the pore area, evidenced by the change from tiny pores into larger- and medium-sized pores. After 10 cycles, the internal pore area of the sample expands by nearly 35%, indicating that the localized damage caused by the dry–wet freeze–thaw cycle controls the macroscopic mechanical properties. Finally, a damage constitutive model is developed based on the experimental phenomena and mechanism analysis, and the model’s validity is verified by comparing the experimental data with theoretical predictions. Full article

This study introduces a novel discrete element method (DEM) model for compacted loess, incorporating a bond rate parameter within a linear contact bond model to simulate constitutive damage behavior. This enhancement significantly improves the characterization of structural damage from repeated wet–dry cycles, offering a quantitative method for predicting damage progression. Unlike existing DEM models, our model directly uses a bond rate parameter to quantitatively describe inter-particle bond deterioration, reflecting reduced bonding strength due to pore structure development and the weakening effect of water. Rigorous calibration and validation were performed using comparative experiments. A key innovation is the systematic analysis of microscopic parameters (contact stiffness, friction coefficient, contact strength, and bond rate) and their impact on macroscopic mechanical behavior. Our findings show that decreasing the bond rate significantly reduces the macroscopic mechanical properties, providing valuable insights into the micro–macro relationship. We comprehensively evaluated prediction sensitivity to these parameters. This methodology offers a new perspective on using DEM for predicting crucial civil engineering material properties, providing a valuable reference for incorporating bond rate parameters into future modeling, particularly for long-term geotechnical material behavior under environmental degradation. The model’s accurate representation of wet–dry cycle effects on loess strength improves earth structure design and safety. Full article

For the purpose of precisely depicting the failure and deformation of mudstone at varying burial depths under engineering activities, a statistical meso-damage constitutive model of mudstone was established on the basis of continuum damage mechanics, with the adoption of the compound power function and the Mohr–Coulomb yield criterion. Through triaxial compression tests under diverse confining pressures, the validity of this constitutive model was verified, and the macroscopic effects of mudstone damage evolution induced by internal defects and alterations in meso-structures were analyzed. The results reveal that an increase in confining pressure can remarkably enhance both the peak strength and the residual strength of mudstone. The constitutive model demonstrates relatively high accuracy in predicting the stress–strain responses, as well as the residual strength of mudstone. Moreover, parameter ε0 is capable of reflecting the macroscopic deformation strength of mudstone. Specifically, the larger the value of parameter ε0 is, the greater the peak deviatoric stress of mudstone will be, accompanied by a stronger bearing capacity. Parameter m, on the other hand, governs the brittle-to-ductile transition characteristics under failure. It also demonstrates that the macroscopic brittle failure characteristics of mudstone will become more noticeable as the value of parameter m increases. Full article

Burrs generated during the drilling of carbon fiber-reinforced plastics (CFRPs) would seriously reduce the service life of the components, potentially leading to assembly errors and part rejection. To solve this issue, this paper proposed a finite element (FE) model with multiscale modeling to investigate the formation and distribution of burrs at various processing conditions. The FE model comprised the microscopic fiber and resin phases to predict the formation process of burrs, while part of the CFRP layers was defined to be macroscopic equivalent homogeneous material (EHM) to improve the computational efficiency. A progressive damage constitutive model was proposed to simulate the different failure modes and damage propagation of fibers. The impact of strain rate on the mechanical properties of the resin and CFRP layers was considered during the formulation of their constitutive models. With this numerical model, the formation process of the burrs and the drilling thrust force were accurately predicted compared to the experimental measurements. Then, the burr distributions were analyzed, and the influences of the drill bit structures and drilling parameters on burrs were assessed. It was concluded that the burrs were easily generated in the zones with 0° to 90° fiber cutting angles at the drilling exit. The sawtooth structure could exert an upward cutting effect on burrs during the downward feed of the tool; thus, it is helpful for the inhibition of burrs. More burrs were produced with higher feed rates and reduced spindle speeds. Full article

This paper presents an innovative procedure for the stability assessment of masonry domes, aiming at simplifying the modelling and the computational stages of structural analysis. It exploits a macroscopic approach to discretise masonry, specifically using elastic bodies linked by nonlinear interfaces. The latter are made by axial and, when needed, tangential trusses—in turn characterised by an elastic perfectly plastic/brittle behaviour—which constitute the joints connecting homogenised elastic macroblocks. The objective is—by employing low-cost commercial Finite Element software—to predict the behaviour of a masonry curved structure up to failure, maintaining the computational complexity low and the approach accessible to a common user. The process enables not only the quantification of damage at failure but also the tracking of its evolution within the structure, by examining axial forces found in the trusses at each load step. The method allows the modelling of the response of any kind of masonry structure under imposed loads or displacements. Its efficacy is proven on a paradigmatic dome (Global Vipassana Pagoda, Mumbai, India) by comparing the results with limit analysis precedent studies. Finally, the major reliability of a 3D approach is demonstrated. Full article

A comprehensive understanding of the mechanical behavior of backfill under compression is crucial for optimizing its design, improving stope stability and enhancing resource recovery. Laboratory testing and numerical simulation were conducted to study the mechanical properties and damage mechanism of cemented tailings backfill (CTB) with different cement-to-tailings (c/t) ratios under uniaxial compression. Laboratory testing was used to investigate the strength and deformation characteristics, macroscopic failure modes, and energy evolution patterns of CTB, while simulation with Particle Flow Code (PFC) was employed to explore the distribution of microcracks and mesoscopic damage mechanisms. A constitutive model accounting for the initial compaction stage was proposed, validated, and applied to practical engineering. The results show that as the c/t ratio decreases, the failure mode of CTB transforms from shear failure to combined tensile–shear failure, and tensile failure. Mesoscopically, a higher c/t ratio leads to more bond contacts, which increases the bearing capacity and consequently causes more cracks to damage CTB. From an energy standpoint, the damage mechanism of CTB is further analyzed and the development of energy is characterized by four stages. Moreover, to explore the failure mechanism of CTB, an innovative constitutive model was proposed and verified through experiments. The matching coefficients, based on the novel constitutive model, indicate that CTB with a c/t ratio of 1:6 is qualified for all current mining depths, and a c/t ratio of 1:10 is sufficient to depths below 300 m. Full article

Background: Numerical simulation is a technique that utilizes electronic computers to combine concepts of the discrete element method (DEM), finite element method (FEM), computational fluid dynamics (CFD), etc., and express simulated behaviors utilizing numerical computations and images. Compaction is the main process of tablet manufacturing; most of the current studies have focused on macroscopic compaction and tablet characterization, while the internal stress state and microstructure changes as a result of the compaction process are not well understood. Therefore, an in-depth understanding of the flow and compaction behavior of pharmaceutical powders is essential for the analysis and control of the compaction process. Methods: Current research shows that compaction is shifting from macroscopic behavior toward internal microscopic behavior using numerical simulation technology. Results: This review focuses on the application of various numerical simulation technologies during compaction and the contact model, or the constitutive equation commonly used in numerical simulation. In addition, the difficulties of numerical simulation technology in calibrating powder parameters and the limitations of the current research are also discussed. Conclusions: Numerical simulation research in medicine and other fields will continue to flourish as numerical simulation technology advances, attracting more and more researchers using it effectively. Full article

In this paper, a reliable model of the viscosity in liquids in the dual model of liquids (DML) framework is developed. The analytical expression arrived at exhibits the correct T–dependence Arrhenius-like exponential decreasing trend, which is typical of Newtonian simple fluids. The model is supported by the successful comparison with both the experimental values of the viscosity of water, and with those related to the mechano-thermal effect in liquids under low-frequency shear, discovered a few years ago, for which the first-ever theoretical interpretation is given by the DML. Moreover, the approach is even supported by the results of numerical models recently developed, that have shown that dual liquid models, such as the DML, provides very good agreement with experimental data. The expression of viscosity contains terms belonging to both the subsystems constituting the liquid, and shows an explicit dependence upon the sound velocity and the collective vibratory degrees of freedom (DoF) excited at a given temperature. At the same time, the terms involved depend upon the Boltzmann and Planck constants. Finally, the physical model is coherent with the Onsager postulate of microscopic time reversibility as well as with time’s arrow for macroscopic dissipative mechanisms. Full article

The mechanical characterization of carbonate rock is crucial for the development of a hydrocarbon reservoir and underground gas storage. As a kind of natural composite material, the mechanical properties of carbonate rock exhibit multiscale characteristics. The macroscopic mechanical properties of carbonate rock are determined by the mineral composition and structure at the micro scale. To achieve a mechanical investigation at the micro scale, this study designed a scheme for micromechanical characterization of carbonate rock. First, scanning electron microscope observation and energy dispersive spectroscopy analysis were combined to select the appropriate micromechanical test areas and to identify the mineral types in each area. Second, the selected test area was positioned in the nanoindentation instrument through the comparison of different-type microscopic images. Finally, quasi-static nanoindentation was carried out on the surface of different minerals in the selected test area to obtain quantitative mechanical evaluation results. A typical carbonate rock sample from the Huangcaoxia gas storage was investigated in this study. The experimental results indicated apparent micromechanical heterogeneity in the carbonate rock. The Young’s modulus of pyrite was over 200 GPa, while that of clay minerals was only approximately 50 GPa. In addition, the proposed micromechanical characterization scheme was discussed based on experimental results. For minerals with an unknown Poisson’s ratio, the maximum error introduced by the 0.25 assumption was lower than 15%. To discuss the effectiveness of the nanoindentation results, the characterization abilities constituted by lateral spatial resolution and elastic response depth were analyzed. The analysis results revealed that the nanoindentation measurement of clay was more susceptible to influence by the surrounding environment as compared to other kinds of minerals with the experimental setup in this study. The micromechanical characterization scheme for clay minerals can be optimized in future research. The mechanical data obtained at the micro scale can be used for the interpretation of the macroscopic mechanical features of carbonate rock for the parameter input and validation of mineral-related simulation and for the construction of a mechanical upscaling model. Full article

The actuator is a critical component of the micromanipulator. By utilizing the properties of expansion and contraction, the piezoelectric actuator enables the manipulator to handle and grasp miniature objects during micromanipulation. However, in piezoelectric ceramic disc actuators with conventional surface electrode configurations, the actuating force generated in the radial direction is relatively limited. When used as the actuation element of the manipulator, achieving regulation over a wide range of operating strokes becomes challenging. Therefore, altering the electrode structure is necessary to generate a greater radial force, thus enhancing the positioning and grasping capabilities of the operating arm. This paper investigates a piezoelectric actuator with interdigitated spiral electrodes, featuring a constant pitch between adjacent electrodes. The radial force was tested under mechanical clamping conditions, and the influence of the electrical signal was examined. The characteristics of the electrode structure were described, and the working principles of the piezoelectric actuators were analyzed. Theoretical equations were derived for the macroscopic characterization of the radial clamping force of the actuator, based on the piezoelectric constitutive equation, geometric principles, and Bond matrix transformation relationships. A finite element model was developed, reflecting the features of the electrode structure, and finite element simulations were employed to verify the theoretical equations for radial force. To prepare the samples, encircled interdigitated spiral electrode lines were printed on the PZT-52 piezoelectric ceramic disc using a screen printing method. The clamping force experimental platform was established, and experiments on the clamping radial force were conducted with electrical signals of varying waveforms, frequencies, and voltages. The experimental results show that the piezoelectric ceramic disc actuator with an interdigitated spiral electrode line structure, when excited by a stable sine wave operating at 200 V and 0.2 Hz, generated a peak force of 0.37 N. It was 1.76 times greater than that produced by a previously utilized piezoelectric disc with conventional electrode structures. Full article

This paper presents an innovative numerical approach to simulating the progressive caving of rock mass in the overburden and floor during longwall mining. A modified caving algorithm is incorporated into FLAC3D 9.0, augmented with the IMASS constitutive model, to accurately replicate the fracturing response of various strata. This study aimed to analyze the longwall caving performance, overburden fracturing response, and shield support characteristics to optimize the mining process and enhance safety. The numerical analysis revealed a progressive stress release at the longwall face, attributed to damage in the form of spalling, which was accompanied by a high level of displacement. The fracture process zone above the shield canopy was not significant, indicating the effective performance of the shield in controlling the roof. However, the floor heave highlights the need for the implementation of effective risk and safety measures. Goaf is predicted to form with a longwall advance rate of 25.0–30.0 m, resulting from progressive macroscopic fracturing caused by the development of cracks initiated by bedding plane and rock mass failures. Above the caved zone, an active fracture zone is observed to evolve due to the continuous longwall mining and caving process. Full article

To elucidate the degradation mechanism of expansive soil–rubber fiber (ESR) under freeze–thaw cycles, freeze–thaw cycle tests and consolidated undrained tests were conducted on the saturated ESR. The study quantified the elastic modulus and damage variables of ESR under different numbers of freeze–thaw cycles and confining pressure, and proposed a damage constitutive model for ESR. The primary findings indicate that: (1) The effective stress paths of ESR exhibit similarity across different numbers of freeze–thaw cycles, the critical stress ratio slightly decreased by 8.8%, while the normalized elastic modulus experienced a significant reduction, dropping to 42.1%. (2) When considering the damage threshold, the shear process of ESR can be divided into three stages: weak damage, damage development, and failure. As strain increases, the microdefects of ESR gradually develop, penetrating macroscopic cracks and converging to form the main rupture surface. Eventually, the damage value reaches 1. (3) Due to the effect of freeze–thaw cycles, initial damage exists for ESR, which is positively correlated with the number of freeze–thaw cycles. The rubber fibers act as tensile elements, and the ESR damage evolution curves intersect one after another, showing obvious plastic characteristics in the late stage of shear. (4) Confining pressure plays a role in limiting the development of ESR microcracks. The damage deterioration of ESR decreases with an increase in confining pressure, leading to an increase in ESR strength. (5) Through a comparison of the test curve and the theoretical curve, this study validates the rationality of the damage constitutive model of ESR under established freeze–thaw cycles. Furthermore, it accurately describes the nonlinear impact of freeze–thaw cycles and confining pressure on the ESR total damage. Full article