Search Results (97)

The mesoscopic-scale discrete element method (DEM) modeling approach demonstrated high compatibility with macroporous recycled concrete (MRC). However, existing DEM models failed to adequately balance modeling accuracy and computational efficiency for recycled aggregate (RA), replicate the three distinct interfacial transition zone (ITZ) types and pore structure of MRC, or establish a systematic calibration methodology. In this study, PFC 3D was employed to establish a randomly polyhedral RA composite model and an MRC model. A systematic methodology for parameter testing and calibration was proposed, and compressive test simulations were conducted on the MRC model. The model incorporated all components of MRC, including three types of ITZs, achieving an aggregate volume fraction of 57.7%. Errors in simulating compressive strength and elastic modulus were 3.8% and 18.2%, respectively. Compared to conventional concrete, MRC exhibits larger strain and a steeper post-peak descending portion in stress–strain curves. At peak stress, stress is concentrated in the central region and the surrounding arc-shaped zones. After peak stress, significant localized residual stress persists within specimens; both toughness and toughness retention capacity increase with rising porosity and declining compressive strength. Failure of MRC is dominated by tension rather than shear, with critical bonds determining strength accounting for only 1.4% of the total. The influence ranking of components on compressive strength is as follows: ITZ (new paste–old paste) > ITZ (new paste–natural aggregates) > new paste > old paste > ITZ (old paste–natural aggregates). The Poisson’s ratio of MRC (0.12–0.17) demonstrates a negative correlation with porosity. Predictive formulas for peak strain and elastic modulus of MRC were established, with errors of 2.6% and 3.9%, respectively. Full article

Low-frequency vibration isolation metamaterials (LFVIMs) remain challenging in generating ultra-low-frequency bandgaps around 10 Hz and below. For this issue, a novel LFVIM composed of a square steel auxetic core perforated with orthogonally aligned peanut-shaped holes and a silicone rubber coating is proposed, leveraging the auxetic core’s unique resonance behavior. The superiority in bandgap creation of the peanut-shaped perforations is illustrated by comparing them to elliptical and rectangular perforations. Furthermore, a filled auxetic core is explored as well, to enhance its wave attenuation potential. The wave propagation mechanisms of both the unfilled and filled LFVIMs are comparatively studied by finite element simulation validated against an existing LFVIM design and scaled-down vibration testing. Compared to the unfilled LFVIM, the filled case merges smaller bandgaps into three wider full bandgaps, increasing the relative bandgap width (RBW) from 44.25% (unfilled) to 58.93% (filled). Subsequently, the role of each design parameter is identified by parametric analysis for bandgap tuning. The coating material shows a significant influence on the RBW. Particularly, optimizing the coating’s Poisson’s ratio to 0.2 yields a maximum RBW of 93.95%. These findings present a successful strategy for broadening LFVIM applications in the regulation of ultra-low-frequency Lamb waves. Full article

The implementation of lean drilling and completion design techniques is a pivotal strategy for the petroleum and natural gas industry to achieve green, low-carbon, and intelligent transformation and innovation. These techniques significantly enhance oil and gas recovery rates. In shale gas development, the shale brittleness index plays a crucial role in evaluating fracturing ability during hydraulic fracturing. Indoor experiments on Gulong shale oil were conducted under a confining pressure of 30 MPa. Based on Rickman’s brittleness evaluation method, this study performed numerical simulations of triaxial compression tests on shale using the finite discrete element method. The fractal dimensions of the fractures formed during shale fragmentation were calculated using the box-counting method. Utilizing the obtained data, a multiple linear regression equation was established with elastic modulus and Poisson’s ratio as the primary variables, and the coefficients were normalized to propose a new brittleness evaluation method. The research findings indicate that the finite discrete element method can effectively simulate the rock fragmentation process, and the established multiple linear regression equation demonstrates high reliability. The weights reassigned for brittleness evaluation based on Rickman’s method are as follows: the coefficient for elastic modulus is 0.43, and the coefficient for Poisson’s ratio is 0.57. Furthermore, the new brittleness evaluation method exhibits a stronger correlation with the brittleness mineral index. The fractal characteristics of crack networks and the relationship between symmetry response and mechanical parameters offer a new theoretical foundation for brittle weight distribution. Additionally, the scale symmetry characteristics inherent in fractal dimensions can serve as a significant indicator for assessing complex crack morphology. Full article

Rainfall-induced landslide mitigation remains a critical research focus in geotechnical engineering, particularly for safeguarding buildings and infrastructure in unstable terrain. This study investigates the stabilizing performance of slopes reinforced with negative Poisson’s ratio (NPR) anchor cables under rainfall conditions through physical model tests. A scaled geological model of a heavily weathered rock slope is constructed using similarity-based materials, building a comprehensive experimental setup that integrates an artificial rainfall simulation system, a model-scale NPR anchor cable reinforcement system, and a multi-parameter data monitoring system. Real-time measurements of NPR anchor cable axial forces and slope internal stresses were obtained during simulated rainfall events. The experimental results reveal distinct response times and force distributions between upper and lower NPR anchor cables in reaction to rainfall-induced slope deformation, reflecting the temporal and spatial evolution of the slope’s internal sliding surface—including its generation, expansion, and full penetration. Monitoring data on volumetric water content, earth pressure, and pore water pressure within the slope further elucidate the evolution of effective stress in the rock–soil mass under saturation. Comparative analysis of NPR cable forces and effective stress trends demonstrates that NPR anchor cables provide adaptive stress compensation, dynamically counteracting internal stress redistribution in the slope. In addition, the structural characteristics of NPR anchor cables can effectively absorb the energy released by landslides, mitigating large deformations that could endanger adjacent buildings. These findings highlight the potential of NPR anchor cables as an innovative reinforcement strategy for rainfall-triggered landslide prevention, offering practical solutions for slope stabilization near buildings and enhancing the resilience of building-related infrastructure. Full article

Due to compatibility issues between traditional reinforcing materials and the substrate of museum wooden artifacts, interface failure occurs after crack reinforcement, particularly under dry and wet cycling conditions. This significantly compromises the durability of reinforcement. To resolve this issue, dealkalized lignin was grafted onto epoxy acrylate (LEA) to synthesize a novel consolidant with both humidity responsiveness and mechanical compatibility. The resulting LEA exhibited excellent multilayer adsorption capability and demonstrated synchronous and uniform hygroscopic expansion behavior, closely matching that of archeological wood. DMA revealed that LEA2 has an elastic modulus of 261.58 MPa and a Poisson’s ratio of 0.35, comparable to artificially degraded wood, effectively mitigating interface stress caused by rigidity differences. Furthermore, LEA effictively reinforced micron-scale cracks while maintaining the original microstructure of the wooden artifact. This material provides a promising solution to the compatibility challenges of traditional consolidants under humidity fluctuations and offers a new approach for the stable preservation of museum wooden artifacts. Full article

The strength of soft rock masses progressively deteriorates under dissolution effects, leading to extensive pore development and structural loosening within the rock matrix. This process induces water and sand inrush phenomena at excavation faces, posing substantial challenges to construction safety. This study systematically investigates the strength degradation mechanisms and engineering disaster evolution of soft rock subjected to water–rock interactions. Utilizing representative water-rich soft rock specimens from a tunnel in central Yunnan, a multi-scale analytical framework incorporating X-ray diffraction mineral analysis systems, triaxial mechanical testing systems for rocks, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) was implemented. This integrated methodology comprehensively elucidates the macro–meso damage evolution mechanisms of soft rock under water–rock coupling interactions. The results indicate that as the dolomite content decreases and the impurity content increases, the softening grade of the rock rises, leading to more extensive pore development. Uniaxial compression tests revealed that the Poisson’s ratio of soft rock is significantly higher than that of typical rock. Triaxial compression tests demonstrated that confining pressure has a substantial impact on soft rock, particularly affecting Poisson’s ratio. Increased water content was found to significantly reduce the strength of the soft rock. Compared to loose soft rock, the radial strain of denser soft rock was markedly greater than the axial strain, and the soaking damage effect was more pronounced. This study provides a valuable insight into the mechanical and permeability behavior of soft rock under different conditions, and provides valuable insights into the solutions for soft rock in geological engineering such as tunnel excavations. Full article

Lattice structures, with their unique design, offer properties like a programmable elastic modulus, an adjustable Poisson’s ratio, high specific strength, and a large specific surface area, making them the key to achieving structural lightweighting, improving impact resistance, vibration suppression, and maintaining high thermal efficiency in the aerospace field. However, functional prediction and inverse design remain challenging due to cross-scale effects, extensive spatial freedom, and high computational costs. Recent advancements in AI have driven progress in predicting lattice structure functionality. This paper begins with an introduction to the lattice types, their properties, and applications. Then the development process for the performance-prediction methods of lattice structures is summarized. The current applications of performance-prediction methods, which are data-driven and related to material properties, structural properties, and performance under conditions of coupled multi-physical fields, are analyzed, and this analysis further extends to the data-driven methods in relation to their prediction of lattice structure functionality. This paper summarizes the application of data-driven methods in the prediction of the mechanical, energy absorption, acoustic, and thermal properties of lattice structures; elaborates on the application of these methods in the optimization design of lattice structures in the aerospace field; and details the relevant theory and references for the field of lattice structure performance analysis. Finally, the progress and problems in the functional prediction of lattice structures under the current research is demonstrated, and the future development direction of this field is envisioned. Full article

Wellbore instability is a major constraint in large-scale shale oil extraction. This study focuses on the shale–sandstone interbedded shale oil reservoirs in the Chang 7 area, delving into the evolutionary principles governing wellbore stability in horizontal drilling operations within these formations. A geological feature analysis of shale–sandstone reservoir characteristics coupled with rigorous mechanical experimentation was undertaken to investigate the micro-mechanisms underpinning wellbore instability. The Mohr–Coulomb failure criterion applicable to sandstone and the multi-weakness planes failure criterion of shale were integrated to analyze the stress distribution of surrounding rocks within horizontal wells, facilitating the computation of collapse pressure and fracture pressure. A finite element model of wellbore stability in shale–sandstone horizontal drilling was established, and then we conducted a comprehensive analysis of the impacts of varying elastic moduli, Poisson’s ratio, and in-situ stress on wellbore stability. The findings reveal that under varying confining pressures, the predominant failure mode observed in most sandstone samples is characterized by inclined shear failure, coupled with a reduced incidence of crack formation. The strength of shale escalates proportionally with increasing confining pressure, resulting in a reduced susceptibility to failure along its inherent weak planes. This transition is characterized by a gradual shift from the prevalent mode of longitudinal splitting towards inclined shear failure. As the elastic modulus of shale rises, the discrepancy between circumferential and radial stresses decreases. In contrast, with the increasing elastic modulus of sandstone, the gap between circumferential and radial stresses widens, potentially inducing potential instabilities in the wellbore. An increase in sandstone’s Poisson’s ratio corresponds to a proportional increase in the difference between circumferential and radial stresses. Under reverse fault stress regimes, wellbore collapse and instability are predisposed to occur. Calculations of collapse pressure and fracture pressure reveal that the safety density window is minimized at the interface between shale and sandstone, rendering it susceptible to wellbore instability. These research findings offer significant insights for the investigation of wellbore stability in interbedded shale–sandstone reservoirs contributing to the academic discourse in this field. Full article

This article provides a comprehensive, step-by-step framework that bridges the gap between the theory and engineering practical applications of Powder Bed Fusion (PBF) technology for producing high-quality metal parts suitable for end users. This proposed framework integrates multiple aspects into a coherent methodology on how to evaluate the PBF parameters and processing conditions, in order to establish a reliability scale for the PBF process on the Realizer 250 SLM machine. Experimental research, conducted over the past 10 years, reveals that the PBF process often encounters challenges related to process stability and part consistency. To address these issues, this paper introduces a novel method for evaluating the manufacturing process by considering the obtained physico-mechanical characteristics. The determined properties of PBF samples were ultimate tensile strength, Young’s modulus, the Poisson ratio, maximum elongation, hardness, and surface roughness. Test specimens were fabricated and tested without applying a stress relief heat treatment. Four bio-metal materials were studied as follows: pure Titanium, Ti6Al7Nb, CoCr, and CoCrWMo. Optimal processing parameters were established for each material focused on laser power, scanning speed, and hatch distance. To have a high chance of successfully printing, each material has its own set of PBF parameters. The results showed that the mechanical resistance can be up to 441 MPa for pure Ti (parameters 120 W, 500 mm/s, 0.12 mm) and 1159 MPa for CoCrWMo alloys (parameters 85 W, 500 mm/s, 0.10 mm). The mechanical properties of these materials are presented, offering valuable data for finite element analysis (FEA) necessary for designing medical implants. This paper provides practical guidelines beneficial for both medical application designers and manufacturers using PBF technology, contributing to enhanced reliability and efficiency in PBF-based metal part production. Full article

Metamaterials represent artificially structured materials that exhibit unusual properties, such as a negative refractive index, negative permeability and permittivity, negative cloaking by Poisson ratios and optical effects, etc., which are inaccessible in natural materials. According to recent developments, novel devices and tools based on metamaterials are attracting great interest as they offer improved performance, functionality, sensitivity, biocompatibility, complex structures, and design freedom. Leveraging numerical design approaches, such as finite element analysis and finite difference time domain methods, researchers have tailored metamaterials to meet specific requirements in various areas through a range of manufacturing techniques. These materials can be broadly classified into optical, mechanical, thermal, electromagnetic, and acoustic categories based on their properties and intended use. The choice of fabrication method depends heavily on the specific application, the desired scale, and the complexity of the metamaterial design. These manufacturing methods can be broadly divided into top-down and bottom-up approaches, while each of them has advantages and limitations and offers valuable pathways for the development of the final product. This review offers a basic overview of metamaterials, covering their fundamental principles, fabrication and characterization techniques, and current design methodologies. It also explores their diverse applications, including specific case studies in medicine, while addressing existing limitations and challenges. Finally, this review highlights future perspectives, emphasizing the need for continued innovation in fabrication and characterization to unlock the full potential of metamaterials. Full article

Mechanical properties are one of the most important characteristics of biomaterials for many different applications, including biomedicine. Soft biomaterials, such as hydrogels, are difficult to characterize by conventional mechanical testing, because their mechanical properties are much lower than required by conventional testing machines. In this work, we aimed to systematically study the mechanical behavior of a model soft material, polyacrylamide hydrogels, under different loading modes: tension, torsion, compression, and indentation. This allowed us to develop a comprehensive approach to the mechanical testing of soft materials. To overcome excessive compression and slippage of the hydrogel samples when fixed in the grips during tension, additional 3D-printed grips were designed. Digital image correlation was used to determine the Poisson’s ratio of the hydrogels. The Young’s modulus values obtained from all types of mechanical tests analyzed were highly correlated. However, for hydrogels with a low crosslinker concentration, 1–2%, tension–compression asymmetry was observed. Moreover, the results of the mechanical tests were verified in indentation tests, including analytical estimation, and full-scale and numerical experiments. We also discuss the limits of using a two-parameter Mooney–Rivlin model for fitting hydrogel uniaxial tension deformation curves, which was unstable for the hydrogels with 4 and 9% crosslinker concentration. The implemented approach provided a comprehensive analysis of the mechanical behavior of biomaterials. The elastic moduli for all hydrogels studied were in the range from 20 to 160 kPa, which corresponds well to human soft tissues, making them a promising material for application as tissue-mimicking phantoms. Full article

Targeting the concern that nearby inflexible buildings may be at risk for safety issues due to the surface deformation caused by foundation pit excavation disruptions, this paper took the large-scale foundation pit in the Hongshaquan second mine stope in Xinjiang as the research backdrop. To examine the deformation mechanism, generic numerical simulation models were built with varying excavation depths. The unloading effect of foundation pit excavation was addressed using the Fourier integral approach, which is based on elastic theory. An elastic theoretical analytical approach for the surrounding deformation during disturbances due to the excavation of foundation pits was derived by superimposing the unloading impact of the surrounding soil and including pertinent boundary conditions. By contrasting the outcomes of the numerical simulation with the theoretical analysis and the real on-site monitoring data, the accuracy of this approach was confirmed. The findings indicated that the deformation of the surrounding ground surface rises as the excavation depth grows during the foundation pit excavation process in open-pit mines. The deformation decreases with increasing distance from the slope crest to the monitoring location. The deformation of the surrounding ground surface reduces as the rock and soil mass’s elastic modulus and Poisson’s ratio rise. However, the deformation of the surrounding ground surface increases as the excavation depth and slope angle rise. This study offers fresh ideas and approaches for examining how the surrounding ground surface deforms while a foundation hole is excavated. Full article

In this paper, specimens that contain cavities are tested and the critical force for crack initiation is compared to predictions made by the Coupled Criterion (CC). First, the material parameters Young’s modulus, Poisson’s ratio, fracture toughness, and critical stress are calibrated with tensile tests of three specimen shapes. Then, the critical force and crack initiation position are predicted for three other specimen shapes, called validation specimens. The predictions made by CC use stresses and incremental energy release rates that are computed by the Finite Element Method (FEM) and the Scaling Law based Meta Model (SLMM+AC). The predictions are validated against the tensile test results of the validation specimens. A Monte Carlo approach is used to compute prediction intervals for the critical force to make a statement about the quality of the predictions. The position of the crack initiation was predicted accurately, but the predicted critical loads deviated from the measured load up to 25%. Full article

Gate dielectrics are essential components in nanoscale field-effect transistors (FETs), but they often face significant instabilities when exposed to harsh environments, such as radioactive conditions, leading to unreliable device performance. In this paper, we evaluate the performance of ultrascaled transition metal dichalcogenide (TMD) FETs equipped with vacuum gate dielectric (VGD) as a means to circumvent oxide-related instabilities. The nanodevice is computationally assessed using a quantum simulation approach based on the self-consistent solutions of the Poisson equation and the quantum transport equation under the ballistic transport regime. The performance evaluation includes analysis of the transfer characteristics, subthreshold swing, on-state and off-state currents, current ratio, and scaling limits. Simulation results demonstrate that the investigated VGD TMD FET, featuring a gate-all-around (GAA) configuration, a TMD-based channel, and a thin vacuum gate dielectric, collectively compensates for the low dielectric constant of the VGD, enabling exceptional electrostatic control. This combination ensures superior switching performance in the ultrascaled regime, achieving a high current ratio and steep subthreshold characteristics. These findings position the GAA-VGD TMD FET as a promising candidate for advanced radiation-hardened nanoelectronics. Full article

Hydrogen storage in intermetallic compounds, known as solid-state storage, relies on a phase change by the metal alloy. This phenomenon causes a violent change in volume at the crystalline scale, inducing a change of volume for the millimetric particles and, with time, important stresses on the tanks. It is thus necessary to know the mechanical behavior of the material to report these phenomena and improve the tanks’ reliability. The present study deals with the mechanical characterization of Ti_0.5Fe_0.45Mn_0.05 alloy at different scales. First, the elastic modulus was measured by compression tests of cylindrical samples. The estimated macroscopic elastic modulus was about 198 GPa, with high variability, from 163 to 229 GPa. Secondly, ultrasonic elastic characterization together with instrumented indentation allowed an estimation of both Young’s modulus and Poisson’s ratio at 269 GPa and 0.29, respectively. Finally, the nanoindentation results, combined with SEM imaging and EDS analyses, revealed that several metallurgical phases coexist below the particle scale. Four distinct domains in terms of elasticity were clearly identified. The coherence of all these estimations is discussed and interpreted considering the true microstructure of the material and the defects present in the different samples. Full article