Search Results (1,272)

The effects of different surface pretreatments on the microtensile bond strength (µTBS) between a bulk-fill resin-based composite cavity base material (Bulk Base HARD II) and 4-META/MMA-TBB resin (Super-Bond EX), which is often used as a luting agent for indirect dental restorations, were investigated. Six experimental treatments were established: 10% citric acid/3% ferric chloride conditioner (10-3), self-etching primer (Teeth Primer; TP), silane coupling agent (M&C Primer; MC), 10-3+MC, TP+MC, and a control group with no treatment. The µTBS was measured after 1 week (immediate group) and 6 months (aged group) of water storage. There were no significant differences in µTBS among the immediate subgroups. However, the aged 10-3+MC group exhibited the highest bond strength, significantly outperforming the control group. On the other hand, the µTBS of the aged TP group was significantly lower than those of both aged 10-3 and 10-3+MC. MC alone did not enhance bond strength, and its application after TP led to a nonuniform surface morphology, raising concerns about adhesive stability. Failure mode analysis indicated that cohesive failure within the luting cement was predominant, with mixed failures being more frequent in the aged TP group. Overall, MC may not be necessary, and 10-3 conditioning does not adversely affect bond strength. Based on the results of this in vitro study, the most effective clinical practice entails pretreatment of the prepared cavity employing a citric acid/ferric chloride conditioner. Full article

To address the technical challenges associated with complex connection configurations and excessively long lap zones in the industrialized and prefabricated construction of reinforcements, this study proposes a novel parallel-lap splice that incorporates a third overlapping reinforcement. This innovative design offers several advantages, including neat ends, ease of construction, and enhanced economic efficiency. An experimental investigation was conducted to evaluate the effects of this new splice on the flexural behavior of reinforced concrete (RC) beams, with lap length (l_l) as the key variable (l_l = 64d, 40d, and 25d). A total of nine simply supported RC beams (three groups of three specimens each), all incorporating parallel-lap splices, were tested under four-point bending. The key mechanical properties were analyzed, including the mechanical characteristics, failure modes, flexural capacity, bending stiffness, and maximum flexural crack width. The experimental and analytical results reveal that RC beams with the new parallel-lap splice exhibit a distinctive “one primary + two secondary” crack pattern, characterized by a dominant flexural crack at midspan and secondary cracks at the ends of the lap zone. At the ultimate limit state, specimens with l_l = 64d experienced concrete crushing at the top surface of the midspan while those with l_l = 40d and l_l = 25d did not. Additionally, the l_l = 64d and l_l = 40d beams showed slight strength hardening, whereas the l_l = 25d beams exhibited rapid strength degradation. In terms of load-bearing capacity, both the l_l = 64d and l_l = 40d beams met the requirements specified in current design codes, while the l_l = 25d specimens showed a reduction in capacity exceeding 20%. Under serviceability limit states, midspan deflections and maximum crack widths for the l_l = 64d, l_l = 40d, and l_l = 25d specimens were found to fully comply with, marginally satisfy, and fail to meet the requirements of the design code, respectively. Based on these findings, as well as regression analysis of the relationship between peak load and lap length, it is recommended that a reasonable lap length for the proposed parallel-lap splice be taken as 60d, with a lap length correction factor of 1.5. Full article

The operation of medical cyclotrons for PET radiopharmaceutical production presents significant radiological and environmental challenges that require systematic risk assessment and evidence-based mitigation strategies. In this study, an integrated framework combining Failure Mode and Effects Analysis (FMEA) with a quantitative Defense Effectiveness Factor (DEF) approach to evaluate and reduce residual risk in a real urban cyclotron facility. High-criticality failure modes (Risk Priority Number $\ge 120$) affecting HVAC systems, stack exhaust, and power supply were identified and validated through a Delphi expert consensus process. These modes were addressed with multi-layered defense-in-depth strategies: redundant systems (occurrence reduction, 60–80% effectiveness), real-time monitoring (detection reduction, 40–50% effectiveness), and design robustness (severity reduction, 70–85% effectiveness). The combined DEF yielded a 96–97% risk reduction. One-way sensitivity analysis confirmed the robustness of these results, with residual annual effective dose to the representative person remaining between 50–88 $\mathsf{\mu }$Sv/year (well below the IAEA 1 mSv/year public dose constraint) even under pessimistic scenarios. Primary exposure pathways were inhalation and cloud gamma from ${}^{18}$F and ${}^{41}$Ar during the early-morning production window, while secondary pathways were negligible due to the short half-lives of the radionuclides. These findings demonstrate that the integration of FMEA with DEF-based defense-in-depth and Gaussian plume modeling provides a transparent, robust, and regulatory-compliant framework for managing radioactive atmospheric emissions in urban medical cyclotron facilities. Full article

Ultra-large underground metal mines often have complex surrounding rock structures, making traditional assessment methods inadequate for warning against the sudden failure of highly brittle rock masses. To accurately identify high-risk rock layers, this study combines Brazilian splitting tests with acoustic emission (AE) monitoring on four typical surrounding rocks. A normalized damage–stress brittleness coefficient (NDBC) is proposed, and Gaussian mixture model (GMM) clustering is employed to analyze crack evolution mechanisms. Different from conventional brittleness indexes merely based on mechanical parameters, the proposed NDBC characterizes rock brittleness from the perspective of progressive damage evolution driven by acoustic emission microfracture information, providing a dynamic evaluation basis for sudden instability in highly brittle rock masses. The GMM clustering automatically identifies crack features and accurately quantifies the transition from tensile peak to increasing shear during the failure process. The research shows that: (1) AE characteristics during the failure stage are manifested as medium- to high-frequency signals caused by small-scale cracks. (2) Siliceous limestone exhibits extremely high brittleness (NDBC of 0.07) and sudden failure due to the difficulty of microcrack propagation, posing a greater risk of instability and potential overall collapse during mining; in contrast, granite (NDBC of 0.23) is more ductile, showing progressive damage accumulation. (3) Initial rock splitting failure is primarily tensile cracking, with shear cracking increasing as failure approaches, transitioning the failure mechanism to a tensile–shear composite mode. Therefore, establishing a differentiated monitoring and prevention system based on AE main frequency identification and GMM analysis, designating siliceous limestone surrounding rock areas as key prevention zones, can effectively reduce the risk of sudden instability and ensure safe mining operations. Full article

To investigate the bonding performance between Northeast larch (Larix gmelinii) and carbon fiber-reinforced polymer (CFRP) as well as basalt fiber-reinforced polymer (BFRP), this paper systematically analyzes the effects of fiber-reinforced polymer (FRP) type, bonding length, and bonding width on the mechanical behavior of the interface through single shear pull-out tests. A total of 20 FRP-timber specimens were designed for the tests, and their ultimate bearing capacity, failure mode, strain distribution, and load-slip relationship were measured. The results indicate that BFRP exhibits greater ductility, averaging 35.04% higher than CFRP, while CFRP demonstrates significantly higher tensile strength, exceeding BFRP by 83.41%. The failure mode of CFRP specimens primarily involves debonding at the timber-adhesive interface, whereas BFRP specimens mainly exhibit debonding at the FRP-adhesive interface. An increase in bonding width leads to a larger bonding area, resulting in a higher ultimate load capacity. However, due to the limitations of effective bonding length, the ultimate load increases rapidly when bonding length is raised from 50 mm to 100 mm, but further increases in length yield diminish returns in load capacity. Strain distribution analysis reveals that the strain in FRP decreases linearly along the bonding length, with peak strain increasing as bonding width decreases. Based on the experimental data, a predictive model for interfacial debonding load capacity was developed, demonstrating good robustness with an average coefficient of determination (R²) of 0.65. This model provides a reliable theoretical reference for evaluating the ultimate load capacity of FRP-reinforced Northeast larch structures, while also offering essential experimental evidence and theoretical support for FRP reinforcement design in Northeast larch wood structures. Full article

In deep-buried tunnels, the loads acting on supporting structures continuously increase due to the rheological behavior of surrounding rock, while the performance of the secondary lining gradually degrades under environmental effects. These delayed features have significant implications for tunnel safety but are rarely incorporated into the reliability evaluation of tunnels. In this study, the surrounding rock is modeled using the Burgers model, and an analytical solution is developed by incorporating the degradation and damage of the secondary lining. Parametric analysis is conducted to identify the key factors governing tunnel response. Subsequently, limit state functions are established, and a time-dependent system reliability analysis is performed. Results indicate that tunnel response and reliability are highly sensitive to rheological parameters. Among the rheological parameters, the elastic shear modulus of the Maxwell elements G_e has the most pronounced influence on deformation, whereas the elastic shear modulus of the Kelvin elements G_k governs the stress response of the secondary lining. The time-dependent failure probability increases rapidly in the early stage and gradually stabilizes thereafter. Insufficient initial support strength is identified as the dominant failure mode of system failure. Furthermore, G_e and G_k are the key parameters affecting tunnel reliability, and increasing G_k improves the reliability index by more than 1500%. Meanwhile, the variation in system reliability is mainly affected by the failure mode of insufficient initial support strength. These findings provide quantitative guidance for the design, construction, and long-term maintenance of deep-buried tunnels in rheological rock. Full article

The depletion of natural river sand resources in the construction industry and the pollution caused by iron tailings storage in the steel industry are the two major challenges currently faced. The use of iron tailings in construction materials is widely regarded as one of the most sustainable and cost-effective approaches. Based on C30 concrete, 12 steel tube iron tailings sand (IOT) concrete columns with different IOT substitution rates were designed and fabricated in this paper, and axial compression test research was conducted on them; finite element simulations were conducted for comparison with the experimental results, focusing on the influences of IOT substitution rate (0–100%), steel pipe wall thickness (1–4 mm), and steel strength (Q235, Q355, Q390, Q420, Q460) on the bearing capacity of concreted steel tube columns were parametrically analyzed. By comparing the calculation methods of the bearing capacity of concrete-filled steel tube columns in five relevant standards, the calculation formula for the bearing capacity of IOT columns was corrected and obtained. The results show that the failure mode of the IOT column is similar to that of the ordinary column, and the steel tube wall has all undergone circumferential band shear buckling. As the replacement ratio of IOT increases, the load-bearing capacity of columns initially improves and then declines. The finite element analysis results show that the bearing capacity of the IOT column is directly proportional to the wall thickness of the steel pipe, and increasing the wall thickness of the steel pipe can effectively improve the bearing capacity of IOT columns. The discrepancy between the predicted and experimental bearing capacities of IOT columns obtained based on the revision of the “Technical Code for Concrete-filled Steel Tube Structures” (GB 50936-2014) is within 10%, which can effectively predict the load-bearing capacity of IOT columns within a certain range. Full article

Vision-based navigation systems (VINS) are increasingly utilised as an alternative to GNSS for UAVs operating in urban environments, but they suffer from performance degradation under visual fault conditions like illumination variation, rapid motion, texture-less environments, and weather effects. While hybrid architecture incorporating Kalman filters and machine learning (ML) improves performance, they often lack evidence of providing contingency for non-Gaussian error distributions, limiting operational safety. To address these shortcomings, an enhanced hybrid VINS architecture is proposed, featuring a Bayesian GRU-based error correction network (B-GRU) to provide a contingency while compensating model errors. To the best of the authors’ knowledge, this is the first attempt to estimate uncertainty using a B-GRU compensator while addressing data uncertainty for VINS applications. The system architecture integrates an Error-State Kalman Filter (ESKF) and the B-GRU, compensating for position errors with uncertainty prediction. The proposed approach is validated using datasets from MATLAB incorporated in an Unreal Engine simulated environment, replicating the complex fault conditions. The ML model is trained on various visual failure modes to adapt the variability in the signal patterns during flights with simulated datasets and tested across varied flight paths and lighting scenarios. The results demonstrate that the fusion strategy effectively corrects erroneous measurements arising from corrupted sensor data and imperfect models and achieves an improvement of 78.06% compared to SOTA hybrid VIO on the horizontal axis while capturing complex flight dynamics in an unseen environment. A comparative analysis demonstrates the effectiveness of B-GRU in mitigating failure modes with a predictive error boundary, achieving a 72% improvement in performance compared to the architecture that integrates GRU-based error compensation. This approach shows a step forward in enhancing positioning accuracy and contingency in challenging urban environments. Full article

Heavy industrial vehicles operating in aluminum smelters are exposed to severe thermal, mechanical, and environmental stresses, which increase the likelihood of failure and unplanned downtime. This study proposes an Economic Risk Priority Number (ERPN) framework to address the limitations of the conventional Risk Priority Number (RPN) used in Failure Mode and Effects Analysis (FMEA). A five-year maintenance dataset (2019–2024), comprising 2303 corrective work orders from 58 heavy equipment units, was analyzed. The classical RPN approach prioritized failure modes mainly according to occurrence and detectability, identifying the wheel and hydraulic subsystems as the most critical. In contrast, the proposed ERPN framework integrates economic impact through maintenance cost, manpower cost, and production loss, resulting in the engine subsystem being ranked as the most critical. The most severe engine failure caused an estimated financial loss of approximately USD 1.92 million due to extended downtime and repair costs. Root cause analysis identified coolant loss, low oil pressure, and excessive vibration as the main contributors to catastrophic engine failure, supported by diagnostic evidence and repeated alarm patterns. Statistical validation performed using the Kruskal–Wallis test confirmed significant differences among subsystem risk distributions for both RPN (χ² = 846.07, df = 4, p < 0.0001) and ERPN (χ² = 131.69, df = 4, p < 0.0001). The findings demonstrate that ERPN provides a more economically meaningful framework for maintenance prioritization and offers a practical decision-support tool for reducing operational risk in aluminum smelter fleets. Full article

Gravel particles are widely developed and randomly distributed in deep reservoirs of the Tarim Oilfield, western China. The mechanical behavior of conglomerate, the main component of the gravel layer, under varying confining pressure and different gravel content, remains poorly understood, especially in terms of the microscopic aspect, which limits the analysis of the variation patterns of underground engineering parameters. This study conducts triaxial compression tests on outcrop specimens from various stress levels to analyze the effects of stress state and stress differences on the mechanical parameters and failure modes. After that, a kind of numerical modeling method based on the discrete element method (DEM) is proposed, which considers the random distribution of gravel particles, to study the microscopic observation of mechanical characteristics and crack propagation of conglomerate under different stress state conditions. The experimental and numerical simulation results indicate that the horizontal strain before failure remains nearly constant in the axial direction while increasing linearly for the horizontal stress. And, it was observed that the volumetric failure was accompanied by gravel fragmentation, sliding, and falling. Numerical simulations reveal that cementation strength and gravel content significantly influence mechanical properties and failure modes, which are the main factors. This study provides some useful references for further understanding of the mechanical behavior and failure mechanisms of rocks in the gravel layer, in particular, the numerical modeling method for heterogeneous materials. Full article

To reveal the progressive collapse mechanism of reinforced concrete spatial beam–slab structures with unequal spans and improve their collapse-resistant design level, this study investigates the progressive collapse resistance of reinforced concrete spatial beam–slab structures with unequal span arrangements. A finite element model of the spatial frame structure was developed in ABAQUS under inner column failure conditions, and pushdown analysis was employed for numerical simulation of the test samples. The effects of the inner column failure position, beam–slab parameters, floor slab damage performance, and beam-end internal forces on the collapse capacity of reinforced concrete spatial beam–slab structures were analyzed. The results indicate that, under inner column failure, the floor slab contributes 40–50% of the structure’s bearing capacity; under side column failure, it contributes 20–30%; and under corner column failure, it contributes 15–25%. A larger beam span reduces the structure’s bearing capacity after column failure. Additionally, equal-span designs exhibit a “lag” in force compared with unequal-span designs, and lateral constraints of the floor slab have minimal influence on the bearing capacity of slabless structures. The beam and slab design parameters significantly affect the bearing capacity and ductility of a structure. The damage performance of the floor slab under small deformations reflects its yield mode, enabling inference of the crack distribution. These findings provide scientific insight into the progressive collapse mechanism of unequal-span reinforced concrete spatial beam–slab structures. On the practical side for engineering design, a bearing capacity formula incorporating the influence of the floor slab in unequal span arrangements is proposed. The innovation of this paper lies in systematically analyzing the differences in progressive collapse between equal-span and unequal-span structures, as well as the influence of the floor slab on the progressive collapse of unequal-span structures, thereby providing a theoretical basis for research on the progressive collapse of unequal-span structures such as the Xuankou Middle School in Wenchuan. Full article

Generative artificial intelligence (AI) is increasingly used to support decision-making in manufacturing quality assurance (QA), but its adoption raises concerns regarding governance, traceability, and auditability. This paper proposes a proactive framework that integrates generative AI into quality management and auditing while preserving standards alignment and human oversight. The framework structures quality activities across supplier, in-process, and post-market domains and across three hierarchical levels—product, process, and operation—to link quality outcomes with documentary evidence requirements. A proof-of-concept (PoC) study in electronics manufacturing focused on New Product Introduction (NPI) planning and compared two parallel workflows: an expert QA team and a generative AI-assisted chatbot workflow. Within a fixed time window, both workflows produced an aligned Process Failure Mode and Effects Analysis (PFMEA), Control Plan, supplier Production Part Approval Process (PPAP) request package, and internal audit evidence pack. Three independent experts evaluated the integrated deliverable package using five indices covering documentation quality and audit readiness, detection and containment logic, process capability and stability, governance and provenance safeguards, and execution (time) efficiency. Compared with the expert package, the generative AI–assisted workflow produced more traceable, governance-rich documentation (ownership, versioning, clause-to-evidence links) and reduced manual audit-evidence consolidation, supporting quality planning and change-control readiness. Full article

This study investigates the undrained bearing capacity of strip foundations subjected to inclined loading on two-layer cohesive slopes using finite element limit analysis (FELA). Both lower bound (LB) and upper bound (UB) theorems with adaptive mesh refinement are employed to conduct comprehensive parametric analyses examining the influence of key geotechnical and geometric factors on the bearing capacity factor N_ci and associated failure mechanisms. The parameters investigated include the interlayer shear strength ratio c_u1/c_u2, load inclination angle α, upper layer thickness ratio D/B, setback distance b/B, normalized undrained shear strength of the upper layer c_u1/γB, and slope angle β. The results demonstrate that load inclination and interlayer strength contrast have a pronounced effect on the bearing capacity, while the failure mode transitions between foundation failure and overall slope failure depending on the geometric configuration. The numerical results are validated against existing published data, showing excellent agreement with a maximum relative error of 1.19%. Comprehensive design charts are provided to facilitate the bearing capacity estimation and failure pattern identification under various geometric and loading configurations, offering practical guidance for geotechnical engineers dealing with foundations on stratified slopes. Full article

The structural safety of polar ships is critically dependent on local ice loads acting in the ship–ice interaction area. Ice conditions and ship speeds play dominant roles in influencing local ice loads. Field measurement serves as a crucial approach for accurately assessing and scientifically understanding local ice loads and ice conditions. The instrumentation for the field measurement on RV Xuelong-2 is discussed in this study. In the 12th Chinese National Arctic Research Expedition, digital processing technologies are employed for image recognition and statistical analysis of ice concentrations and thicknesses. The influence coefficient matrix method is validated by a physical experiment and applied to identify local ice loads from ice-induced strains. Subsequently, the relationship between local ice loads, ice conditions, and ship speeds is statistically analyzed and mechanistically explained. The results show that the coupling effect between ship speeds and ice parameters, along with the competition between ice failure modes, may cause ice load peaks to transition from increasing to decreasing at a specific ship speed and ice thickness. A prolonged ice load duration under high ice concentrations is an important factor contributing to the positive correlation between ice load peaks and ice concentrations. Full article

In order to protect the high-sensitivity optical lens of the “magnetic field and velocity field imager” in extreme deep space environments, this paper proposes a new type of dual redundant planetary differential lens cover drive mechanism. In view of the critical vulnerability that traditional single-motor direct drive is prone to sudden mechanical jamming and catastrophic single-point failure (SPF) in severe tasks such as Jupiter exploration, this study constructs a “dual input single output (DISO)” rigid decoupling architecture from the perspective of physical topology. Through theoretical analysis and kinematic modeling, the adaptive decoupling mechanism of the two-degree-of-freedom (2-DOF) system under unilateral mechanical stalling is revealed. Dynamic analysis shows that in the nominal dual-motor synergy mode, the system shows a significant “kinematic load-sharing effect”, thus greatly reducing the sliding friction and gear wear rate. In addition, under the severe dynamic fault injection scenario (maximum gravity deviation and sudden jam superposition of a single motor), the cold standby motor is activated and the dynamic takeover is quickly performed. The high-fidelity transient simulation based on ADAMS verifies that although the fault will produce transient global torque spikes and pulsed internal gear contact forces at the moment, all extreme dynamic loads remain well within the structural safety margin. The output successfully achieved a smooth transition, which is characterized by a non-zero-crossing velocity recovery. This research provides an innovative theoretical basis and a practical engineering paradigm for the design of high-reliability fault-tolerant mechanisms in deep space exploration. Full article