Search Results (333)

The recycling of construction and demolition waste and the reduction of carbon emissions are important issues in sustainable construction. Recycled aggregate concrete (RAC) is promising for structural use, but the weak old mortar and multiple interfacial transition zones in recycled coarse aggregate (RCA) may reduce the load-transfer capacity at the steel–concrete interface. To address this problem, this study developed carbonated recycled aggregate concrete-filled flat steel tube (FST-CRAC) members and investigated their interfacial bond–slip behavior through material strength tests and push-out tests on nine specimens. The effects of RCA replacement ratio, carbonation treatment, section aspect ratio, and width-to-thickness ratio were examined. RCA was carbonated at 0.5 MPa for 24 h. The 28-day compressive strength increased from 32.6 to 44.3 MPa in the uncarbonated P series and from 36.2 to 46.2 MPa in the carbonated T series. However, because the two series were developed through separate preliminary mix-design trials, these differences should be interpreted as being jointly associated with carbonation treatment and mix-proportion adjustments rather than as evidence of an isolated causal effect of carbonation. Push-out failure was governed by interfacial debonding, local crushing near the corners, and post-peak frictional slip, with damage consistently concentrated at the short sides and corners of the flat section. Carbonation treatment increased the peak bond load by 2.85–26.23%, with the largest benefit observed at a moderate replacement ratio, while increasing the RCA replacement ratio from 50% to 100% increased the peak load by 27.90% for uncarbonated specimens but only 4.21% for carbonated specimens, indicating that carbonation reduces the sensitivity of bond capacity to replacement ratio. A moderate increase in section aspect ratio increased the peak load by 22.30–25.86%, and reducing the width-to-thickness ratio increased the peak load by 5.95–40.92%. A four-linear bond–slip constitutive model was proposed to describe the full interfacial response, from initial bonding through peak degradation to residual friction. These findings provide experimental support for the use of carbonated recycled aggregates in steel tube-confined composite members and a basis for subsequent nonlinear analysis. Full article

Interfaces at multiple scales within rocks critically control the mechanical properties of rock masses. However, the mechanisms by which interface roughness characteristics affect non-plastic deformation remain incompletely understood. In this study, particle-flow simulations were used to conduct loading–unloading tests on rough interfaces. The results show that contact surfaces inclined relative to the overall interface provide additional resistance during unloading and recovery, thereby increasing both the magnitude and likelihood of interfacial hysteresis. This mechanism explains why hysteresis can occur under loading normal to the interface. Differences between the static and dynamic friction coefficients, together with dynamic changes in the normal vectors of the contact surfaces, further intensify the hysteretic response. When deformation of the surrounding material is considered, the “lateral compression–expansion effect” caused by asperity extrusion and interlocking under compression, as well as the slip-induced “dilatancy effect,” also contributes substantially to rough-interface hysteresis. In addition, initial stress on crack surfaces can enhance the degree of hysteresis. The grain-based rock model incorporating interface roughness and in situ stress effectively reproduces the non-plastic hysteretic behavior of rocks. Full article

This paper investigates the stress corrosion cracking (SCC) behavior under constant loading conditions and the early-stage grain-scale deformation mechanisms of a friction-stir-welded (FSW) joint of 7A52 aluminum alloy. The results show that when a constant load equivalent to 1.0 times the yield strength (439.43 MPa) of the base metal is applied, the joint fractures after 72 days of immersion in a 3.5 wt% NaCl solution, with the fracture located in the heat-affected zone on the advancing side (AS-HAZ). The fracture surface exhibits a mixed-mode morphology characterized by both brittle and ductile features. Observations suggest that cracks mainly initiate at the bottom of corrosion pits, at grain boundaries, and at the interfaces between precipitates (such as Mg-Si-rich, Al-Fe-rich, or Al-(FeMn)-rich) and the Al matrix. It is suggested that the initiation mechanisms are closely related to galvanic corrosion, interfacial weakening, and mechanical property mismatch. In situ tensile and EBSD results indicate that the AS-HAZ is the first region to undergo deformation. As the load increases from 400 N to 1500 N, the degree of strain localization intensifies, with high-strain regions preferentially concentrated at grain boundaries. Grain boundary damage is likely a key mechanism responsible for the initial failure on the advancing side of the FSW joint. Further in situ SEM observations reveal that during the early stage of tensile deformation, as the load increases from 300 N to 455 N, the grain surface in the AS-HAZ evolves from a flat morphology to a typical orange peel appearance. Meanwhile, grain boundaries change from clearly visible to blurred, slip traces increase, and multiple slip systems are activated within the grains. The continuous pile-up of dislocations at grain boundaries leads to a sharp increase in local stress concentration, ultimately inducing grain boundary instability and crack nucleation. Full article

Background: Epidemiological patterns vary across populations and treatment centres worldwide, with obesity consistently reported as the main risk factor. The primary aim of this study was to characterise age- and sex-adjusted body mass index (BMI) z-scores in children with slipped capital femoral epiphysis (SCFE) treated in Bern, as well as to investigate their association with clinical characteristics. A secondary aim was to compare the observed characteristics with those reported internationally. Methods: This is a single-centre, retrospective cohort study conducted at the Department of Pediatric Surgery, University Children’s Hospital, Inselspital, University of Bern, and included patients under the age of 18 who were treated for SCFE between 2005 and 2025. Demographic, clinical, and anthropometric data were collected for all patients, including sex, age at the time of surgery, slip severity using the Southwick angle, intraoperative slip stability, symptom duration, as classified by Fahey/O’Brien, affected side of the hip, as well as height and weight at the time of surgery. The primary outcome was the age- and sex-adjusted BMI z-score at the time of surgery. Analyses stratified by sex, age, and slip severity were prespecified as secondary analyses. All other subgroup analyses were exploratory and hypothesis-generating. Results: The final cohort included 90 males (69.23%) and 40 females (30.77%). BMI data were available for 114 of the 130 patients. Two-thirds of the patients (62.3%) were overweight or obese. The median BMI z-score was 1.43 (interquartile range 0.72–2.19; mean 1.31 ± 1.11) and was significantly higher than the expected reference value of 0 (p < 0.001). There was no statistically significant difference in BMI z-scores between females and males (p = 0.288). A statistically significant association was observed between age at surgery and BMI z-score. Higher age at surgery was associated with lower BMI z-scores (p = 0.007). There was a trend towards lower BMI z-scores with increasing slip severity. However, this difference did not reach statistical significance (p = 0.158). In an exploratory, hypothesis-generating analysis, patients with stable slips had significantly higher BMI z-scores than those with unstable slips (p = 0.008). This association persisted after adjustment for age and after correction for multiple testing (p_adj = 0.032). A further exploratory, hypothesis-generating analysis showed that BMI z-scores also differed significantly across symptom duration, as classified by Fahey/O’Brien (p = 0.026). The lowest values were observed in the acute-on-chronic group. However, these differences just missed the threshold for statistical significance after adjustment for age and after correction for multiple testing (p_adj = 0.052). Conclusions: In Switzerland, children diagnosed with SCFE had a significantly higher BMI compared to the reference population. Our study revealed that two-thirds of the children were classified as overweight or obese, with obesity being approximately ten times more prevalent among this group compared to the overall Swiss paediatric population. A higher relative body weight was found to be independently associated with a younger age at surgery, consistent with obesity accelerating skeletal maturation and advancing the manifestation of SCFE. We identified a trend towards lower BMI z-scores with increasing slip severity; however, this finding did not reach statistical significance. Consequently, elevated body weight should be regarded as a marker of predisposition and earlier disease onset rather than of slip severity. Childhood obesity prevention may be relevant to SCFE prevention in Switzerland. Full article

This study proposes a novel friction-based beam-to-column shear connection designed to behave as a nominally pinned joint while avoiding any perforation of the connected members. The connection relies on frictional resistance to transfer shear forces, enabling full reversibility and preserving the integrity of the structural elements for future reuse. A comprehensive design methodology is first introduced, addressing key parameters such as clamping force, friction coefficient, and slip resistance. Subsequently, an extensive numerical investigation is carried out using refined finite-element models, i.e., considering multiple geometric configurations and loading conditions. The local behaviour of the connection is hence assessed in terms of stiffness, strength, and slip capacity. Results show that—with proper sizing—plastic deformation localises in the beam while the joint remains elastic and slip is limited, confirming the conservativeness of the approach. The joints behave as nominally pinned in terms of resistance while showing moderate stiffness. Derived findings highlight the feasibility of adopting friction-based, non-invasive connections as a viable alternative for circular steel construction, contributing to the ongoing transition toward more sustainable structural systems. Full article

Bridge-arm reactors subjected to long-term AC–DC composite currents with multiple harmonics may develop non-uniform winding temperature rise and thermal-expansion mismatch, leading to localized thermal stress concentrations and potential insulation cracking. Unlike previous studies focused mainly on purely AC conditions, this study investigates a ±800 kV dry-type air-core bridge-arm reactor and develops a thermo-mechanical model incorporating AC–DC composite currents and harmonic losses. To mitigate thermal stress concentration, an axially segmented configuration is proposed to relieve the restraint associated with cumulative axial thermal expansion. The results show that a 65% axial segmentation ratio provides the best stress-regulation performance among the investigated cases. Under AC–DC composite conditions containing second- and fifth-order harmonics, the maximum Von Mises stress and maximum first-principal stress decrease by 33.42% and 38.11%, respectively, while the stress distribution becomes more uniform. The analysis is based on a two-dimensional axisymmetric model with one-way thermo-mechanical coupling and excludes long-term cyclic thermal aging and interfacial slip between winding and insulation layers. These findings provide theoretical support for the stress-oriented structural design and reliability assessment of high-capacity bridge-arm reactors. Full article

Reinforced concrete (RC) structures are susceptible to crack initiation and propagation during service, making accurate numerical simulation of crack behavior essential for assessing structural durability and safety. Current numerical approaches for simulating concrete cracking include smeared/continuum approaches, extended finite element method (XFEM), phase-field methods, and meso-mechanical models. In particular, smeared/continuum approaches (e.g., smeared crack and plastic-damage models such as CDP) indirectly reflect cracking through diffusive damage fields without providing explicit geometric information on crack locations and propagation paths. The XFEM module in commercial software is further restricted to first-order elements and encounters difficulties in simulating multi-crack propagation. These limitations indicate that further development of complementary crack-simulation frameworks is warranted. To this end, this paper presents a cracking simulation framework for RC members within the theoretical framework of the Specified Stress Method, adopting an adaptive degree-of-freedom strategy to balance computational accuracy and efficiency. The method introduces inelastic strain as an additional unknown and establishes a variational principle and the corresponding virtual work equation. Concrete cracking is described by specifying the stress on the crack plane to zero, so that the crack-surface stress remains zero after cracking, thereby avoiding the issue of damage reversibility and improving computational convergence. The method requires neither a predefined crack path nor remeshing after cracking. Unlike smeared/continuum approaches that rely on diffusive damage fields, the crack propagation paths, distribution characteristics, and evolution of multiple cracks are characterized through the spatial distribution of cracked integration points within the finite element mesh. In the present implementation, crack initiation is governed by the maximum tensile stress criterion, and a linear elastic constitutive model is adopted for concrete as a deliberate simplification to establish and verify the core computational mechanism of the framework. The proposed method was examined through three numerical examples. First, comparison with theoretical solutions confirmed the algorithm’s correctness in simulating cracking in heterogeneous RC tension members. Second, comparison with experimental results demonstrated qualitatively consistent crack propagation trends and load–displacement responses for RC beams under mixed-mode cracking; the calculated ultimate load of the plain concrete beam is lower than the experimental value, which is attributable to the use of the maximum tensile stress criterion without fracture energy considerations, and certain crack morphology deviations are observed due to the neglect of reinforcement–concrete bond-slip. Third, a multi-crack simulation of an under-reinforced RC beam showed that, whereas the XFEM module in ABAQUS captures only a single dominant crack near the mid-span, the proposed algorithm predicts multiple distributed cracking zones on both sides of the mid-span, qualitatively consistent with the typical flexural cracking behavior of under-reinforced RC beams; the algorithm also supports second-order elements (e.g., C3D20R) unavailable in the ABAQUS XFEM implementation. While the method is still in an exploratory stage, these results confirm the feasibility and potential of the Specified Stress Method as a complementary framework for RC cracking simulation, providing a basis for further development. Full article

The path-tracking and motion control of autonomous tractor–trailer systems (TTSs) in unstructured off-road environments have become important research topics of intelligent equipment. Traditional control architectures face challenges due to multiple physical constraints such as time-varying soil rheology, time-varying wheel slip, multi-body nonlinear coupling, and vehicle stability constraints. This review provides an overview of advanced control technologies for autonomous TTSs in off-road environments. First, this review analyzes multi-source sensors and joint state estimation frameworks for time-varying terrain classification, all-wheel slip ratio estimation, and articulation angle. Secondly, nonholonomic kinematic, multi-body three-dimensional spatial dynamic, and tire–soil interaction mechanic models are deconstructed for on-axle and off-axle hitching configurations. On this basis, adaptive kinematic control, model predictive control (MPC), robust disturbance rejection, and distributed electric-drive control strategies are compared horizontally, and the application of active trailer steering, torque vectoring, and implemented chassis cooperative control in active safety is elaborated. Finally, emerging research directions, including online tire–soil interaction learning, embodied AI foundation models, and V2X-enabled multi-vehicle cooperative platooning, are discussed to provide insights into the development of next-generation fully autonomous off-road tractor–trailer systems. Full article

Electrical slip rings are key components for power and signal transmission in rotating equipment, and degradation of sliding electrical contact is a major factor limiting their reliability. To analyze the sliding electrical contact behavior of slip rings, an elastoplastic contact framework incorporating thermal–mechanical–electrical coupling is developed. The semi-analytical method combined with discrete convolution-fast Fourier transform is employed to efficiently solve the coupled contact problem, while J₂ flow theory and radial return algorithm are adopted to determine plastic deformation. Based on the proposed model, the elastoplastic sliding electrical contact behaviors of smooth and sinusoidal surfaces are systematically investigated. The results show that plastic deformation increases the contact area, thereby reducing the electrical contact resistance, current density at the contact edge, and maximum temperature rise, although it may induce the residual stress. Reducing the asperity height of sinusoidal surfaces while maintaining multiple discrete micro contact spots can effectively lower the electrical contact resistance and interfacial temperature rise. The proposed model provides a useful theoretical tool for evaluating the thermal–mechanical–electrical performance of sliding electrical contact in slip rings. Full article

Existing spillway piers constructed more than 60 years ago in Japan are usually reinforced with round rebars and have very low rebar ratios; consequently, their seismic response may be strongly influenced by post-cracking bond–slip. However, the applicability of nonlinear analytical models to such piers has not yet been systematically clarified. In this study, practical modeling strategies for existing spillway piers were investigated by performing Incremental Dynamic Analysis (IDA) using both a beam model based on nonlinear moment–curvature (M-φ) relationships and a 3D finite element analysis that explicitly accounts for bond–slip between concrete and rebar. An actual spillway pier was analyzed at multiple seismic intensity levels, and the effects of bar diameter, rebar ratio, and bond condition were examined via 3D finite element analysis. The results showed that the beam model is useful for global screening but may misclassify the damage mode because it cannot explicitly represent bond–slip. By contrast, the 3D finite element analysis reproduced flexure-dominant damage patterns and quantified the influence of bond–slip on maximum displacement, residual displacement, rebar strain, tensile damage distribution, and compression damage distribution. These differences became more pronounced under stronger ground motions and for larger bar diameters and lower rebar ratios. The findings support a staged strategy for seismic performance evaluation that combines beam models for global screening with 3D finite element analysis for detailed member-level assessment. Full article

By systematically conducting seismic damage investigations of tunnels crossing active faults, this study summarizes the failure characteristics of typical damage cases and performs model tests at a similarity ratio of 1:50 to examine the dislocation-induced failure mechanisms of tunnel structures subjected to reverse strike-slip faulting, reverse faulting, and strike-slip faulting, respectively. In view of the lack of systematic theoretical calculations in existing articulated anti-dislocation fortification methods, a displacement-pattern-based calculation method for the articulated fortification width is proposed. The main conclusions are as follows: The failure of tunnels crossing active faults results from the coupling of fault dislocation, strong-motion inertial forces, and surrounding rock restraint, and is jointly controlled by multiple factors including fault type, movement mode, geometric relationship, structural stiffness, and surrounding rock properties. Under reverse strike-slip faulting, the tunnel failure is dominated by a combination of oblique shear and compression, exhibiting an overall spatial “S”-shaped deformation; under strike-slip faulting, the tunnel experiences combined shear and bending failure with an overall planar “S”-shaped deformation; under reverse faulting, shear failure prevails, locally accompanied by tensile failure. The proposed calculation method for the articulated fortification width not only fills the gaps in previous studies but also broadens its scope of application. It is applicable not only to the displacement patterns addressed in this paper but also to other displacement patterns that conform to tunnel dislocation. Full article

Quantum algorithms for flow simulation are advancing rapidly, but reproducible wall-bounded benchmarks with classical reference data are still needed to evaluate future quantum and hybrid quantum-classical solvers. This work presents a forced D3Q19 multiple-relaxation-time (MRT) lattice-Boltzmann method (LBM) benchmark for body-force-driven Poiseuille flow in a three-dimensional channel. The solver combines periodic streamwise and spanwise boundaries, halfway bounce-back walls, moment-space relaxation, and body-force forcing with the half-force velocity correction. The solution is verified against the analytical parabolic profile using relative $L_2$ and maximum profile errors, mass conservation, extrapolated wall slip, and wall-normal leakage. A verification study over grid resolution, relaxation time, forcing strength, and initialization demonstrates second-order grid convergence and robust conservation behavior. The verified timestep is then decomposed into quantum-relevant primitives, including streaming, wall reflection, moment transformation, MRT relaxation, equilibrium evaluation, forcing, macroscopic recovery, and measurement. The resulting benchmark connects flow-solver accuracy metrics with operator-level requirements for quantum implementation, providing a compact reference problem for future quantum processing unit (QPU)-assisted, hybrid quantum-classical, and quantum-linear-solver-based computational fluid dynamics (CFD) studies. Performance gains over classical LBM execution are not assessed here. Full article

To clarify the nonlinear degradation of volumetric performance caused by piston–cylinder wear in axial piston pumps under multiple operating conditions, this study develops an integrated framework linking local wear-induced leakage to whole-pump output characteristics. A mathematical model incorporating piston kinematics, eccentric-clearance leakage, chamber-pressure dynamics, and whole-pump flow was established and implemented in Amesim. A four-factor mixed-level orthogonal design and analysis of variance were then employed to quantify the effects of wear clearance, eccentricity, load pressure, and shaft rotational speed. The results show that their contributions to volumetric efficiency follow the order: motor rotational speed > load pressure > wear clearance > eccentricity, whereas load pressure is the dominant factor affecting pressure ripple. A wear clearance of approximately 0.1 mm marks the onset of pronounced leakage-induced performance degradation. At this clearance and a load pressure of 20 MPa, increasing the rotational speed from 500 to 3000 r/min improves the volumetric efficiency from 67.48% to 94.44%, with an average increase of 5.39 percentage points per 500 r/min. Comparative experiments on normal and artificially worn pumps were conducted to validate the model. The measured motor-speed slip under high-load conditions was incorporated to correct the theoretical displacement and distinguish speed-induced flow reduction from internal leakage. After correction, the maximum relative error between the simulated and experimental results was below 3.7%. The proposed framework integrates mechanism-based leakage modeling, multi-factor contribution analysis, and speed-corrected experimental validation, providing a theoretical basis for the wear assessment, piston–cylinder clearance design, and flow compensation of axial piston pumps under variable operating conditions. Full article

Fluid injection in deep reservoirs can induce fault reactivation and seismicity, posing challenges for geothermal and subsurface energy development. This study investigates the mechanical interaction between two adjacent non-intersecting faults under fluid injection using a pseudo-three-dimensional thermo-hydro-mechanical (THM)-coupled numerical model. The results show that injection first triggers slip on F2, which then redistributes stress onto F1. The response of F1 is strongly heterogeneous: some segments are stabilized due to a decrease in Coulomb failure stress, whereas other segments are destabilized due to an increase in Coulomb failure stress. Stress-path analysis indicates that the immediate response of F1 to F2 slip is mainly governed by changes in effective normal stress and shear stress, rather than abrupt pore pressure changes on F1. These findings demonstrate that fault slip can act as a mechanical stress source that either promotes or inhibits adjacent fault reactivation. Therefore, slip-induced stress transfer should be explicitly considered when assessing fault stability in reservoirs containing multiple closely spaced faults. Full article

Understanding how methane moves through nanoporous media is key to predicting performance in unconventional gas reservoirs. At these extremely small scales, pore sizes approach the molecular level, where classical flow assumptions begin to fail and multiple transport mechanisms can occur at the same time. In this work, a unified framework is developed to characterize methane flow regimes using a real-gas corrected Knudsen number. By combining pore size, pressure, and temperature within a single formulation, the approach captures how flow behavior evolves across realistic reservoir conditions. A unified flow regime map is used to characterize the gradual shift in transport behavior—from adsorption-dominated and diffusion-like mechanisms in ultra-tight pores, to transition and slip flow, and eventually to continuum (Darcy) flow in larger pores. The results show that pore size plays the dominant role in determining flow behavior, while pressure introduces a dynamic effect, particularly during reservoir depletion. Sensitivity analysis also highlights that flow regime classification depends not only on thermodynamic conditions but also on molecular-scale parameters such as methane diameter. Comparison with established models and experimental observations shows that the framework captures the expected increase in rarefaction effects at low pressures and small pore sizes. Overall, the results emphasize that gas transport in nanoporous systems is not governed by a single mechanism but evolves over time and across scales. The proposed framework offers a simple, physically grounded tool for identifying dominant transport mechanisms and supporting model selection, while also providing a foundation for more advanced descriptions of gas flow in unconventional reservoirs. Full article