Search Results (222)

Under out-of-plane loading, composite sandwich wall panels may develop relative slip between the wythes and end slip at the intermediate-layer interface, weakening composite action and flexural stiffness. Previous studies have mainly focused on bearing capacity and connector performance, while the complete slip-development process, parameter effects, and quantitative slip-warning indicators remain insufficiently investigated. To investigate the flexural slip mechanism and design control method, three one-way composite sandwich wall panels with different wythe thicknesses, reinforcements, and stiffness ratios were tested under four-point bending. The load–deflection response, crack development, relative slip, and end slip were recorded. The measured slip values were normalized by the midspan yield deflection to obtain the absolute slip ratio, relative slip ratio, and end slip ratio. The results show that both the relative slip between the inner and outer wythes and the end slip exhibit a three-stage evolution with increasing load: almost no slip before cracking, approximately linear development after cracking, and rapid increase after yielding. The stiffness matching of the inner and outer wythes and the thickness of the intermediate layer are important factors affecting slip development. Based on the test results and comparison with existing experimental data, the yielding stage is recommended as the slip-warning control point, with warning values of 0.03 for the relative slip ratio and 0.06 for the end slip ratio. Finally, a simplified model based on partial composite action theory was established using binary linear regression and the least-squares method. The model achieved a centered $R^2$ of 0.937, while the slip influence coefficient increased from 2.4–8.8% at yielding to 30.3–66.0% at the peak stage, quantitatively supporting yielding-stage warning control. Full article

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

Historical earthquake records are inherently incomplete: many sites that were likely damaged were never documented, leaving spatial gaps in the macroseismic record. This study evaluates whether intensity values at unreported sites can be estimated from the spatial relationships of surrounding reports, framing the task as a spatial data imputation problem. Three spatial imputation methods, Linear regression, K-Nearest Neighbors (KNN), and Kriging, were applied to eight macroseismic datasets, comprising two historical Dead Sea Transform earthquakes (1927 Dead Sea, 1837 South Lebanon) and six instrumental events from major strike-slip fault systems. Model performance was assessed with 5-fold cross-validation under random and spatial-block designs, using Mean Squared Error (MSE) and success rate, defined as the percentage of predictions falling within ±0.5 and ±1.0 intensity units of observed values. Under random cross-validation, simple and locally focused models performed on par with the complex geostatistical approaches. For the geographically concentrated historical data, success rates reached up to 90% within ±1.0 intensity units. San Andreas events yielded the strongest results among instrumental datasets, while Caribbean events showed the weakest performance due to spatial reporting biases. Under spatial-block cross-validation, performance declined across all models, with linear regression and Universal Kriging proving most robust to spatial extrapolation. These findings provide a methodological basis for estimating intensity at undocumented sites. While continuous intensity mapping from sparse data remains inadvisable, point-based imputation offers a practical tool for enriching historical earthquake records, with direct implications for seismic research along poorly documented fault systems. 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

To address low seeding accuracy and poor seed-fertilization coordination caused by wheel slip and vibration in undulating terrains, a model 2BJD-4 precision corn planter featuring an independent electric-drive transmission was developed. The planter integrates furrow opening, fertilization, single-seed precision metering, soil covering, and compaction into a coordinated one-pass operation. Key mechanical assemblies include a servo-motor-driven finger-clamp seed meter, a parallel four-bar terrain-following mechanism, and an external fluted-roller fertilization meter. To capture complex non-linear soil-tool interactions, a predictive surrogate model was established using Support Vector Regression (SVR) and coupled with the Dung Beetle Optimizer (DBO) for global parameter optimization. Comprehensive field trials validated that the SVR-DBO framework outperformed traditional Response Surface Methodology, securing an optimal qualified spacing index of 92.8% and a planting depth qualification rate of 93.0% under experimental conditions. These findings demonstrate the technical feasibility of the proposed design in maintaining seed spacing and depth uniformity under tested topographies, offering a practical reference for the development of precision planters in hilly and plain regions. Full article

Transient extrusion defects are a fundamental process control challenge in fused granular fabrication (FGF), arising from the finite melt pressurization time of screw-driven extruders at each start–stop event. This study presents an integrated experimental and analytical framework for the characterization and open-loop feedforward compensation of these transient dynamics, demonstrated on two composite thermoplastic feedstocks: a recycled random polypropylene (RPP1) and a 20 wt% wood-fiber-reinforced polypropylene composite (WFPP). Unlike prior filament- or single-material feedforward strategies, this framework derives and statistically validates material-specific compensation parameters across two rheologically distinct feedstocks. Single-layer road experiments were conducted on a custom instrumented FGF platform across a 2³⁻¹ half-fraction factorial design varying melt temperature, print acceleration, and nozzle diameter, with screw speed stepped among 20, 40, and 80 RPM to excite transient states; deposited road geometry was digitized and spatially registered to the synchronized process signals. Main-effects regression confirmed that nozzle diameter is the dominant predictor of mean road width, while screw velocity exerts a significant negative effect attributable to speed-dependent backflow. Prediction-error minimization on the pooled multi-experiment dataset yielded a parsimonious first-order transfer function, G(s) = 0.990/(1 + 1.909s), whose time constant is physically attributed to melt compressibility in the barrel volume upstream of the nozzle restriction. This model was embedded in a G-code post-processor implementing two sequential corrections: a material-specific steady-state slip gain and a discrete linear-advance term parameterized by the identified time constant. For RPP1 at the nominal gain, the print latency interquartile range decreased from 5–20 mm to 2–8 mm without degrading steady-state dimensional accuracy; the combination of nominal gain with active retraction further reduced latency to near-zero. Analysis of covariance (ANCOVA) confirmed that optimal feedforward gains are statistically material-dependent across all three quality metrics (p < 0.05), providing statistical justification for material-specific compensator parameterization. The results establish a practical, hardware-agnostic route to reduce transient deposition defects in pellet-based additive manufacturing, extensible to additional feedstocks. Full article

Indoor companion, rehabilitation, logistics, laboratory transport, and service robot scenarios require mobile platforms that can follow a human operator safely and flexibly under lighting changes, occlusion, texture-poor corridors, and dynamic pedestrian environments. Vision-, LiDAR-, and UWB-based following systems can provide high perception capability, but their deployment cost, environmental dependence, and sensing complexity remain limiting factors for low-perception-dependence applications. This paper presents a passive following system for a Mecanum-wheel mobile platform based on gimbal posture perception and orthogonal odometry fusion. A rope-tensioned two-axis gimbal is mounted above a 300 mm × 300 mm × 150 mm omnidirectional chassis, and a six-axis inertial sensor installed at the top of the gimbal detects pitch and roll changes induced by user traction. A piecewise posture-to-velocity mapping model with a dead zone, saturation, low-pass filtering, and acceleration limiting converts the user’s traction intention into planar velocity commands in the vehicle coordinate frame. To reduce pose errors caused by Mecanum-wheel slip and discontinuous roller-ground contact, two orthogonal passive odometry wheels and inertial attitude estimation are fused to provide planar position feedback for closed-loop following. A prototype was implemented using an Infineon TRAVEO CYT4BB77 controller, TI DRV8701E motor drivers, six-axis IMUs, magnetic encoders, and an embedded display interface. Experiments evaluated attitude estimation accuracy, planar localization accuracy, passive following performance, gyroscope compensation, and open-loop/closed-loop following. The compensated attitude module achieved a static yaw drift of 0.45 deg/h and a dynamic attitude RMSE below 0.56 deg. Orthogonal odometry fusion produced an average positioning error of 3.8 mm over a 3000 mm linear displacement, reducing error by approximately 84.6% compared with pure Mecanum-wheel drive odometry. In a 5000 mm forward traction task, closed-loop following reduced the average distance error from 38.6 mm to 11.5 mm compared with open-loop attitude mapping. The results indicate that the proposed gimbal-orthogonal odometry architecture provides a compact, intuitive, and environment-robust solution for passive following on omnidirectional mobile platforms. Full article

Literature-based compilation indicates that there have been 165 earthquakes with moment magnitude M_w ≥ 7.0 in the period 1980–2024 for which identifiable source-parameter estimates are available. Despite the relative scarcity of such events globally, this dataset is sufficiently large to perform a robust rupture analysis. Using ordinary least-squares regression, we characterized the relationships between M_w and eight source parameters: rupture length (L), rupture width (W), rupture area (S), maximum slip (D_max), average slip ($\stackrel{- -}{D}$), average rupture velocity (V_r), source-averaged static stress drop (Δσ), and rupture duration (T_R). The logarithms of rupture length, width, area, maximum slip, and average slip generally showed statistically significant linear relationships with M_w. In contrast, average rupture velocity and static stress drop showed weak and mostly statistically insignificant relationships with M_w. Rupture duration was more strongly correlated with M_w for reverse/thrust- and normal-fault earthquakes than for strike-slip earthquakes. Strike-slip earthquakes had a mean length-to-width ratio of 3.97, compared with 2.05 and 2.43 for reverse/thrust- and normal-fault earthquakes, respectively. For the 25 events with both maximum- and average-slip estimates, the ratio D_max/$\stackrel{- -}{D}$ ranged mainly from 1.5 to 3.5, with a mean of 3.18, indicating spatially heterogeneous slip distributions. Because the dataset was compiled from studies using different source models and inversion methods, the resulting equations should be interpreted as dataset-specific empirical relationships. Full article

Fractured coal in the residual-strength stage is a primary medium for gas migration and drainage in deep mining areas. To investigate the hydro–mechanical seepage response of post-peak fractured coal under constant-pressure-difference conditions, triaxial CO₂ seepage tests were conducted on coal specimens collected from the Xinyuan Coal Mine. A Weibull-based damage constitutive model was established to characterize the confining-pressure-induced hysteresis in the damage-evolution path. The flow-rate evolution and Reynolds number analysis indicated that gas flow remained within the linear Darcy regime. A controlled-variable analysis was used to examine the competing effects governing permeability evolution. Mechanical compaction induced an exponential decrease in permeability, whereas the decrease in permeability with increasing pore pressure was interpreted, within the proposed model framework, as the combined effect of possible adsorption-induced matrix swelling and weakened gas slippage. To address the limitations of conventional constant-slip-factor models, a pressure-dependent slip modulation coefficient was introduced into a composite permeability equation incorporating effective stress, adsorption-related deformation, and dynamic gas slippage. Global nonlinear fitting yielded R² = 0.97 and an RMSE of 0.1909, with the residuals generally distributed around zero, supporting the fitting reliability of the model within the investigated stress–pressure range. Response-surface analysis identified mechanical compaction as the dominant controlling mechanism, while adsorption-related deformation and gas slippage acted as secondary correction mechanisms. The proposed framework provides a quantitative basis for distinguishing the mechanical and fluid-related effects governing permeability evolution in post-peak fractured coal. Full article

Underground fluid injection is regarded as one of the important factors inducing seismic activity. This study therefore proposes a method to predict the maximum damage area and seismic magnitude induced by fluid injection, in order to quantify the relationship between stress disturbances in faults and induced seismic activity during fluid injection. This method involves analysing a three-dimensional geological model of fault permeability evolution in order to define the seismic rupture zone of faults during fluid injection projects. It also involves calculating the maximum damage area and seismic magnitude induced by injection and verifying the method’s effectiveness using field data. The results show that, during deep injection, continuous injection of fluid reduces the effective stress on the fault and increases the fracture area. Following the sudden cessation of injection, the rupture area and maximum seismic magnitude reach their peak values. During the initial stage of injection, seismic magnitude increases rapidly with the rupture radius of the fault, while the growth rate of seismic magnitude decreases during the stable injection stage. Once injection has ceased, the rupture range and seismic magnitude will gradually stabilise throughout the entire geological self-balancing stage. Periodic injection results in the largest fault rupture area, whereas linear growth injection induces the highest seismicity. Strike-slip faults exhibit the most significant increase in rupture area, whereas normal faults demonstrate more intense seismicity evolution. Low permeability, proximity to injection wells and direct well closure exacerbate instability, whereas linear slow closure is the safest option. These research results can inform seismic risk management in fluid injection engineering. Full article

In shale reservoirs, where stress heterogeneity and fracture systems commonly coexist, elastic anisotropy is jointly controlled by in situ stress and fractures, resulting in pronounced azimuthal dependence in wide-azimuth AVO/AVAZ responses. This behavior directly affects fracture characterization and hydraulic fracturing design. However, existing studies commonly attribute anisotropy to either fractures or uniaxial stress perturbations in isolation, and a systematic equivalent-medium formulation that unifies stress-driven stiffness evolution with fracture-weakness effects remains insufficient. To address this gap, we derive an acoustoelastic expression under the weak-stress perturbation assumption, combining background stiffness with third-order stress effects. By incorporating linear-slip fracture weakness, we construct a coupled stress–fracture equivalent stiffness matrix. Using Christoffel eigenanalysis and a welded-interface operator, we then compute anisotropic parameters and AVAZ responses under different stress paths. Numerical simulations show that the principal stress difference dominates both the splitting of reflection curves and azimuthal fluctuations, with an approximately linear sensitivity within the weak-stress regime. Unlike conventional descriptions of fracture-induced anisotropy, in which fracture parameters are commonly prescribed, the proposed framework constructs a physically traceable modeling chain from triaxial stress perturbations to stress-dependent fracture weakness, equivalent orthorhombic stiffness, Christoffel-equation-based wave propagation, and AVAZ responses. This provides a forward-modeling foundation for interpreting coupled stress–fracture anisotropy and for designing future inversion constraints under weak-perturbation conditions. Full article

Extreme orbital thermal cycling and temperature-dependent clearance nonlinearity make it difficult to predict contact–impact, stick–slip, and bifurcation responses of flexible deployable space structures with sufficient stability, accuracy, and computational efficiency. An Adaptive Dissipation–Precision Coordinated Multi-Scale Implicit Integration Algorithm (ADPC-MSIIA) is proposed. First, an absolute nodal coordinate formulation (ANCF)-based thermo-mechanical clearance-joint model with thermal-viscosity-modified contact and frictional/impact heat feedback is established; second, a dual-time-scale implicit integration scheme with dual-$\alpha$ stability–dissipation control and third-order compensation is developed; finally, numerical validation is performed using a linear single-degree-of-freedom (SDOF) benchmark, a temperature-dependent clearance impact oscillator, finite-element and published benchmark comparisons, and a deployable annular truss antenna case. Simulation results show that ADPC-MSIIA achieves a high-frequency spectral radius of $0.867$, an effective convergence order of $2.98$, a maximum contact force error of $3.1\%$, and a $51.7\%$ reduction in the global cumulative error compared with the generalized-$\alpha$ method. This study contributes to knowledge by linking temperature-driven clearance evolution, frictional heat feedback, and adaptive numerical dissipation within a unified framework for predicting non-smooth thermo-mechanical deployment dynamics of large flexible space structures with clearance joints. Full article

This study examines non-Newtonian electromagnetohydrodynamic (EMHD) blood flow via a diseased curved artery with minor stenosis and an aneurysm, adding a no-slip boundary condition, using targeted medication delivery of nanoparticles. The non-Newtonian behavior of blood flow is accounted for by the Casson fluid model. Using Corcione’s model, we have calculated the effective viscosity and thermal conductivity of nanofluids. The interaction of the nanofluid with physical phenomena such as viscous dissipation, electro-osmosis, radially applied uniform magnetic field and Joule heating can change the hemodynamic parameters of the fluid. The Crank–Nicolson approach has been used to calculate the velocity, temperature, and concentration patterns within the Debye–Huckel linearization approximation. Streamlines are delineated to analyze flow patterns across distinct physical factors. This study supports the design of magnetically guided $F{e}_3{O}_4$ nanoparticle–based targeted drug delivery systems for treating vascular diseases such as stenosis and aneurysm, improving site-specific therapeutic efficiency. The numerical insights into thermal effects and arterial geometry help to optimize nanoparticle transport, enhancing treatment precision while minimizing systemic side effects. Full article

This study presents a probabilistic seismic fragility assessment of a jointed rock slope by integrating field characterization, incremental dynamic analysis (IDA), and numerical modeling. Dominant joint sets are identified through field mapping, and key discontinuity parameters are estimated for the Barton–Bandis non-linear shear strength criterion. Dynamic simulations are performed using the distinct element method with the continuously yielding (C-Y) joint model to capture progressive shear degradation. Twenty real earthquake ground-motion records are scaled incrementally to perform IDA, with critical block displacement and cumulative joint slip adopted as engineering demand parameters (EDPs). A probabilistic seismic demand model (PSDM) is developed to correlate peak ground acceleration (PGA) with EDPs. Kinematic analysis indicates that planar failure along joint set 1 is the most likely failure mechanism (90% probability), followed by wedge failure along the intersection of joint sets 1 and 2 (52%). Fragility curves are derived for three displacement-based damage states: minor (1 cm), moderate (5 cm), and severe (15 cm). The results demonstrate that seismic deformation is strongly controlled by discontinuity geometry and progressive joint slip, with the slope exceeding the severe damage state at PGA levels as low as 0.4 g, indicating high seismic vulnerability. This highlights the importance of integrating field characterization with dynamic numerical modeling for reliable seismic stability assessment of such discontinuous rock mass. Future work should incorporate larger datasets, in situ testing, and 3D modeling to enhance assessment reliability. Full article

Given the great burial depth, ancient depositional age, and multi-phase tectonic evolution of deep formations, drilling operations are highly susceptible to wellbore instability. The design and deployment of directional wells further exacerbate this risk, underscoring the need for quantitative risk assessments for directional drilling operations. Based on linear poroelasticity theory, a mechanical model for directional wellbore stability is established to enable wellbore stability evaluation and trajectory optimization design. Furthermore, an intelligent prediction method for collapse pressure is proposed using the XGBoost algorithm. The results indicate that the prediction accuracy of collapse pressure reaches 93%. Under strike-slip in situ stress regimes, wellbore stability is most critical for vertical wells, whereas horizontal and directional wells exhibit lower collapse pressure. The optimal wellbore trajectory is determined to be a horizontal well with an azimuth approximately 36° deviated from the maximum horizontal principal stress direction. The intelligent prediction results show a 98% goodness-of-fit with theoretical calculations, reducing the calculation time from hours to seconds. This study provides a novel approach for wellbore stability analysis and offers a practical tool for the rapid risk assessment of wellbore collapse during directional drilling operations. Full article