Search Results (538)

This study develops a numerical model based on a multi-physics coupled finite element method to predict the carbonation depth of hardened alkali-activated slag under accelerated carbonation curing conditions. Drawing on existing literature data, the chemical composition and porosity of alkali-activated slag at different ages were determined under non-carbonation conditions, supported by thermodynamic and kinetic analyses of alkali activation reactions. A differential equation governing CO₂ diffusion—incorporating diffusion rate, diffusion coefficient, carbonation reaction rate, and related parameters—was established using Fick’s second law. The influence of humidity and carbonation degree on the reaction rate was quantified, and a correlation between carbonation degree and porosity was derived through thermodynamic analysis. These equations were solved numerically in a two-dimensional domain to predict carbonation depth over time. The results demonstrate that the proposed model, using only raw material composition and curing conditions, achieves reasonable accuracy in predicting carbonation depth. Full article

Piezoelectric composites have found a wide range of applications in smart structures and devices and effective numerical methods should be developed to simulate not only the macroscopic coupled piezoelectric performances, but also the details of the local distributions of the stress and electric field. In this paper, we proposed a multi-scale asymptotic algorithm based on the Second-Order Two-Scale (SOTS) analysis method for the piezoelectric eigenvalue problem in perforated domain with periodic micro-configurations. The eigenfunctions and eigenvalues are expanded to the second-order terms and the homogenized eigensolutions; the expressions of the first- and second-order correctors are derived successively. The first- and second-order correctors of the eigenvalues are determined according to the integration forms of the correctors of the corresponding eigenfunctions. Explicit expressions of the homogenized material coefficients are derived for the laminated structures and the finite element procedures are proposed to compute the homogenized solutions and the correctors numerically. The error estimations for the approximations of eigenvalues are proved under some regularity assumptions and a typical numerical experiment is carried out for the two-dimensional perforated domain. The computed results show that the SOTS analysis method is efficient in identifying the piezoelectric eigenvalues accurately and reproducing the original eigenfunctions effectively. This approach also provides an efficient computational tool for piezoelectric eigenvalue analysis and can extend to other multi-physics problems with complex microstructures. Full article

As a green-material structure, cross-laminated timber (CLT) has attracted increasing attention and applications in construction. This study presents an analytical model for a CLT plate under the coupling effect of load and moisture content, where the moisture-induced deformation and moisture-dependent properties are both considered. In the analytical model, state-space equations for moisture variables and for stresses and displacements in the CLT plate are established based on moisture diffusion theory and three-dimensional elasticity theory, respectively. Using the transfer matrix method, the relationships of moisture variables, stresses, and displacements between any two layers of the CLT plates are formulated. The analytical solutions are then determined by the load and moisture conditions applied to the top and bottom surfaces. Comparative analysis indicates that the proposed solution surpasses finite element methods in both computational accuracy and efficiency. In addition, the stress and displacement patterns of CLT plates under pure load and pure moisture conditions, as well as their interrelations, are investigated through a decoupled analysis. An applicable modified superposition principle is then proposed. Finally, a detailed parametric study is conducted to examine the effects of moisture distribution and wood species. Full article

Circular concrete-filled steel tube columns prepared with 100% recycled aggregate concrete (RACFST) are of interest for sustainable, carbon-neutral construction. However, recycled aggregates typically have higher water absorption and lower stiffness, raising concerns about seismic performance. This paper investigates the low-cycle cyclic behavior and displacement ductility of circular RACFST columns. Ten short columns were tested under an axial load ratio of ≈0.20, with varying diameters of 165 and 219 mm and concrete strengths of C30, C40, and C50, along with companion natural-aggregate CFST control specimens. A three-dimensional finite element model was developed and calibrated based on the test results, and parametric simulations were conducted to study the effects of geometry and material parameters. Two distinct flexural failure modes with outward bulging at the base were observed. These two distinct flexural failure modes refer to (1) local outward bulging of the steel tube accompanied by buckling near the base (e.g., specimens RACFSTC40-165-1 and RACFSTC30-219-1) and (2) flexural yielding with extensive concrete crushing around the base region (e.g., specimens RACFSTC50-219-2 and FSTC40-219-2). The first mode was characterized by early steel local deformation and shell instability, while the second showed more distributed plasticity with crushing of recycled aggregate concrete. These modes underline the influence of D/t and concrete strength on failure progression. The results indicate that RACFST columns attain a peak strength comparable to conventional CFST, while achieving significantly greater drift ductility and energy dissipation; the equivalent viscous damping ratio was found to increase with drift at ≈0.04–0.08 for low drifts and ≈0.10–0.18 for moderate drifts, suggesting that existing CFST design provisions are applicable, with only a minor ~3–5% reduction in core concrete strength recommended for stability. Full article

Aim: Preoperative planning and in-office patient education are essential elements of clinical management in patients afflicted with hand injuries. Three-dimensional (3D) printing aims to tackle these challenges by converting feedstock material into solid replicas. The purpose of this study was to review the clinical uses for 3D printing in hand surgery to identify approaches for delivering more personalized treatment strategies. Method: A systematic review was completed following PRISMA guidelines using Medline, Embase, and CINAHL databases, identifying studies published between 2013 and January 2025. A two-stage screening process, involving title, abstract, and full text reviews, was performed independently by two reviewers. Eligible studies included those involving patients with hand or wrist injuries (up to the distal radius) where 3D printing was utilized for diagnosis, surgical intervention, or rehabilitation. Results: The review included 751 patients (mean age: 38 years, range: 5–81 years) across 58 studies. The distal radius was the most commonly studied anatomical region (47%, N = 27), followed by the scaphoid (19%, N = 11). Key applications of 3D printing included preoperative planning (19%, N = 11), patient education (5%, N = 3), medical training (7%, N = 4), intra-operative assistance (38%, N = 22), splinting and casting (19%, N = 11), and prothesis and functional reconstruction (12%, N = 7). Conclusions: Despite its early stage of adoption in hand surgery, 3D printing has shown advantages, especially in enabling more personalized treatment strategies by improving intra-operative assistance, preoperative planning, and patient education. Further research is required to determine whether it positively affects postoperative outcomes, to calculate the cost–benefit ratio, and to compare its usage against standards of care. Full article

A variety of Offshore Floating Photovoltaics (OFPVs) applications rely on the capacity of their floating support structures displacing in the shape of surface waves to reduce extreme wave-induced loads exerted on their floating-mooring system. This wave-adaptive displacement behaviour is typically realized through two principal design approaches, either by employing slender and continuously deformable structures composed of highly elastic materials or by decomposing the structure into multiple floating rigid pontoons interconnected via flexible connectors. The hydrodynamic behaviour of these structures is commonly analyzed in the literature using potential flow theory, to characterize wave loading, whereas in order to deploy such OFPV prototypes in realistic marine environments, a high-fidelity numerical fluid–structure interaction model is required. Thus, a versatile three-dimensional numerical scheme is herein presented that is capable of handling non-linear fluid-flexible structure interactions for Very Flexible Floating Structures (VFFSs): Multibody Dynamics (MBD) for modularized floating structures and floating-mooring line interactions. In the present study, this is achieved by employing the Smoothed Particles Hydrodynamics (SPH) fluid model of DualSPHysics, coupled both with the MBD module of Project Chrono and the MoorDyn+ lumped-mass mooring model. The SPH-MBD coupling enables modelling of large and geometrically non-linear displacements of VFFS within an Applied Element Method (AEM) plate formulation, as well as rigid body dynamics of modularized configurations. Meanwhile, the SPH-MoorDyn+ captures the fully coupled three-dimensional response of floating-mooring and floating-floating dynamics, as it is employed to model both moorings and flexible interconnectors between bodies. The coupled SPH-based numerical scheme is herein validated against physical experiments, capturing the hydroelastic response of VFFS, rigid body hydrodynamics, mooring line dynamics, and flexible connector behaviour under wave loading. The demonstrated numerical methodology represents the first validated Computational Fluid Dynamics (CFD) application of moored VFFS in three-dimensional domains, while its robustness is further confirmed using modular floating systems, enabling OFPV engineers to comparatively assess these two types of wave-adaptive designs in a unified numerical framework. Full article

Lock-in thermography is a widely used nondestructive testing technique for detecting subsurface defects in solid materials. In this study, one-dimensional analytical modeling and three-dimensional finite element simulations were combined to elucidate how lateral heat conduction influences quantitative depth estimation in titanium alloy material using two inversion strategies: the blind frequency method and the phase difference method. Parametric analyses were conducted for defect radius-to-depth ratios ranging from 0.5 to 8 under various excitation frequencies. Results show that the blind frequency method can significantly underestimate defect depth with errors of up to 20.7% when the radius-to-depth ratio is as small as 0.5. To mitigate this bias, an exponential correction model was developed to compensate for lateral conduction effects, reducing the error to within ±5%. The accuracy of the phase difference method is found to depend jointly on defect depth, excitation frequency, and the ratio of defect radius to thermal diffusion length; estimation errors become negligible when this ratio exceeds 3. The novelty of this work lies in identifying lateral conduction as a key bias source and establishing a quantitative correction framework for the depth inversion based on the blind frequency method. The proposed approach is expected to enhance the accuracy of quantitative thermography for engineering applications. Full article

The underground interchange structure is a crucial component of urban underground construction facilities. Its seismic performance in soft ground under the influence of traveling-wave effects has not yet been studied. If not addressed in a timely manner, it will pose serious construction safety risks. This study develops a two-dimensional finite element model of a representative underground interchange, employing the multi-linear kinematic–dynamic interaction model to capture nonlinear material behavior. Incremental dynamic analysis is integrated with probabilistic fragility assessment to examine damage evolution, deformation, internal forces, and stress responses under both uniform and non-uniform seismic inputs. Results indicate that the overall seismic performance is satisfactory, with a low probability of exceeding moderate damage. Plastic damage is concentrated in the central frame and the base of the right-hand wall. Compared with traveling-wave excitations, uniform inputs generally produce larger displacements, particularly in the lower structure. Although axial and shear forces show limited sensitivity to wave type or propagation velocity, they increase significantly under non-uniform input, with axial forces reaching up to 16.9 times those under uniform excitation. Non-uniform input also doubles stress extremes and intensifies stress concentrations at frame nodes. These findings underscore the need to incorporate traveling-wave effects into seismic evaluation and offer methodological insights for the design and reinforcement of underground interchanges in weak soils. Full article

It is crucial to control and comprehend the interaction between elemental adsorbates and two-dimensional materials to drive future generations of electronic, sensing, and energy applications. One such material, particularly interesting from the perspective of tunability, is silicene—the silicon-based cousin of graphene. In this work, we investigate nearly 2000 atomic adsorption models on silicene via a combination of density functional theory (DFT) and machine learning (ML). Different systems with varied adsorption geometries, element identities, and surface coverages were optimized using spin-polarized DFT, and the most stable configurations were selected based on adsorption energy. This information was used to train various ML models, including tree-based models and artificial neural networks, to predict adsorption geometry (classification) and adsorption energy (regression). The current hybrid DFT + ML approach provides a transferable framework for high-throughput screening of element-functionalized silicene and other 2D surfaces, which is of immense importance in directing surface modification strategies in electronic and catalytic device engineering. Full article

In the present study, an Engineering Critical Assessment (ECA) is conducted for an International Maritime Organisation (IMO) Type C liquefied CO₂ (LCO₂) cargo tank to evaluate the effect of finite element configuration on structural integrity in the presence of potential flaws. With the increasing demand for LCO₂ carriers to support carbon capture, utilisation, and storage (CCUS), conventional stress-based design approaches outlined in the International Gas Carrier (IGC) Code have limitations because they neglect imperfections resulting from fabrication and material. To assess these flaws, the fracture mechanics-based ECA methodology, as prescribed by the BS 7910 standard, is applied to a bilobe IMO type C tank designed for cryogenic and pressurised conditions. The assessment integrates fracture toughness, stress intensity factor, and applied loads. Both the two-dimensional shell element model and the three-dimensional solid element model are developed and compared in terms of stress distribution, safety factor for fracture, and fatigue crack growth predictions. Results show that while shell models offer computational efficiency, solid models capture bending stresses and stress concentrations at geometric discontinuities more accurately, resulting in higher reliability in ECA outcomes. The comparative analysis highlights that the web and butt weld near the centre bulkhead are the most vulnerable regions, and fatigue crack growth is highly sensitive to input data, such as stress intensity factor range and fatigue crack growth laws. These findings provide practical guidance for applying ECA in bilobe LCO₂ tank design and safety assessment. Full article

The presence of fling step and forward directivity, as distinctive features of near-fault ground motions, can lead to substantial alterations in the seismic performance of reinforced concrete bridges. This study examines the seismic performance of reinforced concrete bridges with various deck slabs subjected to two distinct sets of earthquake events. One set is of forward-directivity records, and the other set is of fling-step records. Three-dimensional finite element models for the analyzed reinforced concrete bridges are constructed using the CSI-BRIDGE v26 software package, incorporating appropriate material and geometric nonlinearities. The developed bridge models are of three spans and have different deck slab systems, namely, box girder, RC girder, and hollow core slab bridges. Extensive nonlinear response time-history analyses of various configurations representing the examined RC bridges are performed to elucidate the impact of seismic loads, including forward-directivity and fling-step records, on the seismic response of supporting columns and deck slabs in the longitudinal direction. The numerical simulations indicate that ground vibrations with fling step significantly amplify the seismic response demands in both substructure and superstructure elements. Moreover, bridge type substantially influences the induced seismic responses, particularly supporting columns and deck slabs. Full article

Gas pipelines are a critical means of transportation in industrial production. To detect gas pipeline leaks, ultrasonic transducers with specific center frequencies and high sensitivity are required. This paper proposes a novel air-coupled ultrasonic transducer design based on a horn-type matching layer and a bending-mode type of piezoelectric material, specifically tailored for gas leak detection scenarios. The transducer design is optimized by the finite element method, focusing on the basic components of the piezoelectric bimorph, the horn and the supporting tube. First, the influence of various dimensional parameters of the piezoelectric bimorph on the bending vibration mode was analyzed. Then, the effects of the other two components, the horn and the supporting tube, on the piezoelectric bimorph vibration mode were investigated. A parametric scan on the dimensions of these components was conducted to optimize the transducer’s output. Finally, ultrasonic transducers using PMN-PT and PZT were fabricated and tested. The results show that the sensitivity of those transducers surpasses that of similar commercial transducers, especially the PMN-PT one with a center frequency of 40 kHz and a peak receiving sensitivity of −51.1 dB. This transducer, benefiting from the high-performance piezoelectric material and the bending vibration mode, proves to be a promising candidate for high-precision leak detection in gas pipelines. Full article

To reveal the mesoscopic fracture mechanism of fissured concrete, this study employed the discrete element method (DEM) and adopted the parallel bond model (PBM) within the two-dimensional particle flow code (PFC2D) to construct a mesoscopic model of concrete semi-circular bending (SCB) specimens with prefabricated fissures. Three sets of schemes were designed by varying prefabricated fissure angles (0–45°), aggregate contents (30–45%), and porosities (3–6%), and numerical simulations of three-point bending loads were conducted to explore the effects of each parameter on the crack propagation law and load-bearing performance of the specimens. Validation was performed by comparing the simulated load–displacement curves with the typical quasi-brittle mechanical characteristics of concrete (exhibiting “linear elastic rise–pre-peak stress fluctuation–nonlinear decline”) and verifying that the DEM could accurately capture the entire process from microcrack initiation at the aggregate–mortar interface, crack deflection/bifurcation induced by pores, to macroscopic fracture penetration—consistent with the known mesoscopic damage evolution law of concrete. The results indicate that the crack propagation mode evolves from straight extension to tortuous branching as parameters change. Moreover, the peak strength first increases and then decreases with the increase in each parameter: when the fissure angle is 15°, the aggregate content is 35%, and the porosity is 4%, the specimens achieve an optimal balance between crack propagation resistance and energy dissipation, resulting in the best load-bearing performance. Specifically, the prefabricated fissure angle dominates the stress type (tension–shear transition); aggregates regulate crack resistance through a “blocking–diverting” effect; and pores, acting as defects, influence stress concentration. This study verifies the reliability of DEM in simulating concrete fracture behavior, enriches the mesoscopic fracture theory of concrete, and provides reliable references for the optimization of concrete material proportioning (e.g., aggregate–porosity ratio adjustment) and anti-cracking design of infrastructure (e.g., pavement, tunnel linings) in engineering practices. Full article

Urban subways, as critical strategic spaces, require underground structures with sufficient blast-resistant capabilities. To evaluate the blast resistance performance of underground station structures under ground-level nuclear explosion air shock waves, a three-dimensional finite element model of an underground station was developed using LS-DYNA. The blast mitigation effects of phononic crystals are primarily analyzed and the influence of parameters such as spatial arrangement, buried depth, and material properties of phononic crystals on the blast resistance of underground station structures is systematically examined. The results indicate that a denser configuration of phononic crystals enhances the blast mitigation effect, while the maximum displacement of the structure is increased. Considering the structure’s maximum response and economic feasibility, a spacing of 2 m between phononic crystals is recommended. Additionally, the blast mitigation effect stabilizes when the number of phononic crystal layers exceeds a certain threshold, with two layers being optimal. The buried depth of the phononic crystals has a limited effect on blast mitigation; therefore, positioning them midway between the ground surface and the structure at a depth of 2 m is advised. The material properties of the phononic crystals also have a significant impact on the blast protection. Rubber was found to yield the lowest dynamic response of the station structure, providing the best protective effect. These findings offer insights for designing phononic crystal-based blast protection in underground station structures. Full article

Background and Objectives: This study aimed to evaluate the biomechanical behavior of three-unit implant-supported prostheses with different bridge configurations (mesial cantilever, distal cantilever, and pontic) and two types of retention in the atrophic posterior maxilla, through three-dimensional finite element analysis (3D FEA). The focus was on stress distribution in short implants used in pontic and mesial cantilever designs. Materials and Methods: Six 3D finite element models were developed to represent various prosthetic designs and retention mechanisms in a maxillary segment including the first premolar, second premolar, and first molar regions. Type III bone with 8 mm vertical height simulated an atrophic maxilla. Standard implants were placed in premolar areas and short implants in molar regions. A 100 N oblique load at 45° was applied to each unit to simulate masticatory function. Stress distribution was assessed using von Mises and principal stress criteria. Results: The highest implant and crown stress occurred in the cement-retained distal cantilever (100.14 MPa and 329.95 MPa, respectively), while the lowest values were found in the screw-retained pontic model (44.74 MPa and 81.23 MPa). Mesial cantilevers showed intermediate stress levels. Screw-retained designs generally generated lower stresses within implants than cement-retained ones. In cortical bone, stress ranged from 10.25 MPa in the cement-retained distal cantilever to 4.22 MPa in the screw-retained pontic, while trabecular bone showed maximum stress of 1.69 MPa and 0.82 MPa, respectively. Conclusions: Prosthetic design and retention type significantly influenced biomechanical performance. Screw-retained pontic prostheses with short implants in the molar region provided the most favorable stress distribution. When cantilevers are required, mesial extensions are biomechanically more advantageous than distal ones. Short implants can thus be safely used in the posterior maxilla when accompanied by proper prosthetic design and retention type. Full article