Search Results (294)

Hydrogels used for fracture sealing during heavy-oil thermal recovery are repeatedly exposed to high-temperature steam, dehydration, pressure disturbance, and cooling, conditions that often lead to progressive network deterioration and loss of sealing efficiency. To address this limitation, a thermally triggered self-reinforcing covalent–physical double-network nanocomposite hydrogel was developed by combining a sparse MBAA-crosslinked P(NaAMPS-co-NVP-co-AM) covalent scaffold with a reversible Laponite-mediated physical network. The material response was systematically evaluated through cyclic hydrothermal treatment at 180 °C, while fracture-sealing and resealing performance was examined separately under steam-exposure conditions. Artifact-controlled experiments were further introduced to distinguish genuine cycle-induced reinforcement from dehydration, continued post-curing, and conventional thermal aging. The results show that the NaAMPS/NVP/AM molar ratio of 40/20/40 with 1.00 wt% Laponite provided a suitable balance between precursor processability, hydrothermal stability, and mature network stiffness. After five thermal cycles at 180 °C, the storage modulus of the Lap-DN hydrogel increased from 74.4 to 89.1 kPa, while the compressive stress at 50% strain increased from 0.641 to 0.842 MPa, corresponding to reinforcement ratios of 1.198 and 1.314, respectively. Meanwhile, the mean equivalent pore diameter decreased from 6.2 to 4.8 μm, indicating progressive refinement of the load-bearing network. The hydrogel retained 76.3% of its initial water and 81.6% of its initial volume after five cycles in the reference brine and preserved a cycle-5 modulus retention of 101.3% even at 150,000 mg/L salinity. In fracture-sealing tests, Lap-DN sustained a breakthrough pressure of 3.47 MPa and reduced fracture conductivity by 92.4% in a 1.60 mm fracture. More importantly, the same sealing body maintained a breakthrough pressure of 4.55 MPa after five steam impact–recovery cycles in a 1.20 mm fracture, corresponding to 106.1% of the first-cycle value, while 95.0% of the pre-breakthrough pressure resistance was restored within 30 min of cooling. These results are consistent with a cycle-induced reorganization of the Laponite-mediated physical constraints within the permanent covalent scaffold, although the transient dissociation and reassociation of individual polymer–Laponite junctions were not directly observed. Within this evidence-based interpretation, cyclic thermal perturbation is associated with mechanical reinforcement and repeated fracture resealing rather than acting solely as a damaging factor. This work provides a materials-design strategy for hydrogel sealing systems operating under cyclic steam and high-salinity conditions. Full article

Conventional cement concrete has difficulty simultaneously achieving relatively high strength, large deformation capacity, and satisfactory post-cracking damage resistance, which limits its further use in demanding pavement applications. This study comprehensively evaluates the strength development, deformation capacity, post-cracking load-bearing behavior, repeated-impact response, fracture performance, and crack-evolution characteristics of a dense polyacrylate-modified concrete (PMC). Under the material composition and curing conditions adopted in this study, the PMC combines relatively high flexural strength with substantially enhanced deformability: its 28 d flexural strength and ultimate flexural strain are 51.5% and 505.1% higher, respectively, than those of conventional concrete, while exhibiting more stable post-cracking load-bearing and crack-propagation behavior. The repeated-impact and fracture responses further show that the material can sustain higher levels of cumulative nominal impact-energy input and provides greater fracture resistance and damage tolerance. SEM observations reveal film-like polymer connections on the surfaces of hydration products; this local morphology is consistent with the macroscopic toughness and stable crack-propagation characteristics, providing an experimental basis for further optimization of high-strength, high-toughness polymer-modified concrete for demanding service scenarios such as heavy-duty pavements and steel bridge-deck pavements. Full article

The reduction in embodied environmental impacts in residential construction is increasingly important as operational energy performance improves and the relative contribution of materials, replacements, and end-of-life processes grows. This study presents a building-level life cycle assessment of a block of flats in Czechia over a 50-year reference study period. The inventory was derived from the bill of quantities and technical documentation and modelled in LCA for Experts using the integrated Sphera database. The assessed modules comprise A1–A3, A4, B4, B6, C1–C4, and D. Operational energy use in B6 was the largest positive contributor to global warming potential, reaching 16.31 million kg CO₂ eq. (1111 kg CO₂ eq./m²). Product-stage impacts in A1–A3 amounted to 7.15 million kg CO₂ eq. (488 kg CO₂ eq./m²), while replacements in B4 generated 3.32 million kg CO₂ eq. (227 kg CO₂ eq./m²), equivalent to approximately 46% of initial product-stage impacts. Replacement hotspots occurred mainly in non-load-bearing elements, equipment and facilities, façade and roof components, and technical systems. Including B4 changes hotspot prioritisation: products with limited A1–A3 impacts may become significant because of shorter service lives and repeated replacement. Linking building parts, material categories, and individual datasets supports durability, maintainability, and replacement planning in life-cycle GWP reduction. Full article

Seismic pier-top pounding in high-speed railway bridges transfers short-duration girder-restraint contact forces into bridge piers, coupling local contact damage with global vibration and possible base yielding. This critical review evaluates how evidence and modelling strategies can be transferred from local contact mechanics to pier response and, ultimately, to whole-bridge seismic demand. The literature is synthesized across experimental and refined numerical characterization, reduced-order contact–structure modelling, response-equivalent-pulse construction, and nonlinear whole-bridge analysis. A qualitative evidence-confidence grading is introduced to distinguish the strength and transferability of the available evidence based on study independence, evidence type, and configuration similarity. The primary scope is high-speed railway bridges, while the underlying contact–structure modelling principles are transferable to conventional railway and highway bridges with comparable pier-top restraints, subject to bridge-specific calibration. Conventional spring-dashpot models are computationally efficient but sensitive to contact stiffness, damping, restitution, and damage assumptions, whereas refined finite-element models resolve local response at substantially greater computational cost. Static, impulse-equivalent, and prescribed pulse representations can reduce analysis effort, but agreement in force or impulse alone does not ensure equivalence in pier displacement, base moment, plastic rotation, or residual demand. Demand-oriented pulses can reproduce selected component-level responses within a calibrated applicability domain, while response-triggered loading remains a conditional system-level reduction requiring reliable event logic, state updating, and independent benchmark validation. Future research should prioritize realistic restraint tests, identifiable parameter ranges, multi-demand validation, uncertainty quantification and damage-updatable repeated-impact models. These advances can provide a mechanics-based basis for performance-oriented restraint assessment, while practical design application requires consistency with code-based seismic restraint provisions and post-earthquake track-system serviceability criteria. Full article

Conventional concrete pavement materials remain limited in flexural strength, deformability, post-cracking load-carrying capacity, and impact resistance. To address these deficiencies, this study investigates the effects of polymer modification and ultrashort ultrafine steel fiber reinforcement on the static and dynamic mechanical responses and crack evolution of concrete. The results show that polymer modification enhances deformability, while steel fiber incorporation further increases flexural strength and ultimate flexural strain and improves post-cracking load-carrying capacity. Under repeated impact loading, the nominal impact energy input required for initial cracking and final failure increased; in particular, polymer-modified concrete containing 5% steel fibers showed increases of 938.76% in ultimate flexural strain and 8682.63% in the number of impacts to failure relative to ordinary concrete. The matrix and interfacial morphologies observed by scanning electron microscopy (SEM) were consistent with the macroscopic mechanical responses, supporting the interpretation that polymer modification improves matrix and interfacial integrity, while steel fibers contribute to post-cracking load transfer through crack bridging. Overall, the material exhibited high deformability and damage tolerance, indicating its potential for specialized pavement applications. Full article

Railway turnouts are subject to disproportionately high maintenance costs, partly driven by ballast void formation under asymmetrically loaded sleepers. Existing turnout models rely on detailed three-dimensional finite element track representations and do not readily support iterative long-term settlement analyses across the complete turnout geometry. This paper presents a computationally efficient physics-based vehicle–track interaction (VTI) framework extended to railway turnouts, incorporating a dual track model with equivalent foundation stiffnesses, a rail pad layer, and a crossing nose impact model. A modular sleeper dynamics model, formulated as an Euler–Bernoulli beam on a tensionless Winkler foundation, is coupled with the VTI framework to compute spatially resolved dynamic ballast pressure distributions along individual sleepers. A local pressure-based settlement model then allows the study of sleeper–ballast void formation over repeated axle passes. The framework is applied as a proof of concept to two in-service railway turnouts, one with and one without under sleeper pads, and complemented by a parametric study varying train speed, vehicle type, and rail pad stiffness. Void formation concentrates in the crossing nose region, consistent with laboratory measurements and particle-scale simulations. Under sleeper pads reduce peak ballast pressure by 38 to 44% and substantially reduce void formation across the crossing panel, thereby lowering overall track settlement and supporting the maintenance of track geometry in the turnout during operation. Vehicle type is the dominant influencing factor, with the locomotive producing up to 83% higher peak pressure than the passenger car model. The proposed framework provides an efficient tool for comparative turnout design, offering insight into the force transfer and settlement mechanisms of railway turnouts. Full article

The coal–roof/floor combination system is a special geological structure consisting of both coal and roof/floor materials, which often leads to the occurrence of impact failure. The instability and failure of the coal seam are not caused by a single disturbance, but often occur under repeated loading and unloading processes under the action of mining stress. Thus, research on the impact failure, especially the energy evaluation of coal–rock combination materials under cyclic loading and unloading, is of great significance for understanding the rock burst mechanisms of deep coal mines. This paper focuses on the combination material formed by coal seam and roof and floor rock. Taking the #9 coal seam and roof and floor sandstone from the Zhangshuanglou Coal Mine as the test subjects, conventional triaxial compression and cyclic loading and unloading tests were conducted on sandstone, coal, and coal–rock combination material, respectively. Based on the strain energy evolution characteristics, the failure behavior of the coal–rock combination materials throughout the entire process of energy accumulation, dissipation, and release during cyclic loading and unloading are discussed. The research finds that the macroscopic failure behavior of the tested coal–rock combination specimens is dominated by the weaker coal component, and there are marked differences between the tested sandstone and coal components in their respective energy storage capacities, release characteristics, and dissipation behavior. On the basis of these measured differences and of CT-confirmed failure localization within the coal layer, it is inferred—as a mechanistic working hypothesis rather than a directly demonstrated result—that the main driving energy for the impact failure of the coal component may originate from the elastic strain energy stored in the roof/floor sandstone components, released preferentially toward the coal through their interfaces. For mining and excavation at high-in-situ-stress mining areas, the essence of the impact failure of surrounding rock is the non-coordination of energy storage and release between the roof and floor rock materials and the coal seam. The key to preventing impact failure is to eliminate the differences in energy storage and release between different rock materials in the coal seam. Full article

Airport pavement damage is mostly caused by the cumulative effect of subgrade settlement, but existing calculations for subgrade cumulative settlement seldom consider the dynamic variation characteristics of the degree of compaction of subgrade soil under repeated loading. Accordingly, based on the proposed modified bounding-surface model for silt, numerical simulations of runway cumulative settlement under cyclic impact aircraft loading are performed. The study first reveals the quantitative influences of pavement structural parameters on runway cumulative settlement under conventional layered compaction of subgrade. Then, under different structural parameters, the differences in runway settlement between overall and layered compaction of subgrade are compared quantitatively. The following conclusions are drawn: First, as pavement parameters increase, the influence of parameters of the surface layer and the thickness of the base course increases greatly, whereas the influence of the elastic modulus of the base course decreases. Second, the maximum increments of cumulative settlement and its change rate induced by the layered compaction form are 63% and 88%, respectively. As the thickness of the surface layer exceeds 0.36 m, the influence of compaction form can be neglected. Therefore, appropriate ranges of pavement parameters can effectively decrease the effect of compaction form. Third, as the thicknesses of the surface layer and the base course are less than 0.31 m and 0.28 m, respectively, and the elastic modulus of the base course is greater than 1.6 GPa, the sensitivity of settlement to changes in pavement parameters is less affected by different compaction forms, and the influence of the compaction form can be ignored in optimization of the elastic modulus of the surface layer. Full article

Aircraft landing gear systems are essential to safe and efficient flight operations, as they operate under demanding conditions during takeoff, landing, and ground maneuvers. Because they are exposed to high loads and repeated stress, their reliability has a direct impact on safety, maintenance planning, and overall operational performance. This study explores the use of three decision-support approaches, namely the Analytic Network Process (ANP), the Decision-Making Trial and Evaluation Laboratory (DEMATEL), and an adapted Fuzzy Cognitive Map (FCM), to examine a critical landing gear subsystem. The analysis identifies the most influential engineering management factors affecting subsystem reliability and compares how the three methods capture factor importance and interdependencies. The results show that maintenance planning efficiency, failure mode criticality, cost of downtime, and workforce coordination consistently emerge as key reliability-related dimensions. The adapted FCM provides a broader uncertainty-aware representation of indirect causal propagation, while ANP supports prioritization through network-based weighting and DEMATEL highlights cause–effect structures among the factors. Overall, the findings demonstrate that combining these complementary methods can strengthen reliability-oriented decision-making by clarifying which factors should receive priority in maintenance, operational planning, and management strategies. Full article

The performance of ultra-high-performance fiber-reinforced concrete (UHPFRC) under repeated low-velocity impacts, particularly in the context of nominally fixed boundaries relevant to protective structures, remains underexplored. In practice, protective components made of UHPFRC, such as falling object barriers and vehicle parapet systems, are exposed to foreseeable repeated low-velocity impacts; however, no standardized design provisions or residual capacity assessment methods exist for such members, particularly under nominally fixed boundary conditions. This study presents an integrated experimental and numerical investigation into the progressive damage and failure mechanisms of a 50 mm thick UHPFRC plate with nominally fixed (bolted clamping) boundaries subjected to sequential low-velocity impacts. A custom drop-weight test setup was used for impact loading, while high-speed 3D digital image correlation (3D-DIC) captured the quarter-field transient kinematics, which were reconstructed back to the full field based on verified test symmetry and complemented by traditional accelerometer and strain gauge measurements. The results demonstrate a distinct progression of damage. Initial low-energy impacts (196 J/drop) caused negligible damage, highlighting the material’s tolerance. Subsequent higher-energy impacts induced a transition from flexural cracking to a combined flexural–punching shear failure mode. The model-assisted nominal secant stiffness indicator decreased by 5.3% over the repeated 0.5 m drops and fell by 50.8% after the 2.0 m drop, quantifying the transition in structural behavior. A finite element (FE) model, incorporating the concrete damaged plasticity (CDP) model with an energy-based degradation law, was developed and evaluated against the experimental data. This model replicated both the quantitative dynamic responses (with model-to-test ratios of peak acceleration, strain, and displacement between 0.86 and 1.30 across three energy levels) and the qualitative damage evolution. The model thus evaluated enabled a model-derived reconstruction of the critical impact force–time history, revealing the evolution of structural degradation toward the exhaustion of the plate’s global flexural resistance and the transition to a punching shear mechanism. Full article

Deep drilling equipment operates under high-load, strong-vibration, intermittent-impact, and variable environmental conditions, which motivate sensing systems that provide low-noise acquisition, synchronized triaxial measurements, local data integrity, and quantitative measurement-chain characterization. This paper presents a Zynq UltraScale+ MPSoC-based triaxial vibration sensing station for deep drilling equipment applications. The modular station integrates conditioned-voltage triaxial accelerometer interfaces, analog signal conditioning, 24-bit simultaneous analog-to-digital conversion, electrical isolation, local solid-state-drive storage, Ethernet/wireless communication, and GPS-disciplined oven-controlled crystal oscillator (OCXO) timing. The programmable logic performs deterministic acquisition, GPS pulse processing, oscillator calibration, and DMA transfer, while the processing system facilitates storage, network communication, device-state management, and host computer interaction. The sensing electronics are evaluated through zero-input noise, an experiment-specific input-amplitude-to-noise ratio, gain linearity, thermal stability, repeatability, and station-to-station local-PPS timing tests. The characterized electronics achieve a mean equivalent input noise of 0.31 microvolts, a test-derived ratio of 135.08 dB, and a mean station-to-station local-PPS falling-edge difference of 0.34 microseconds. A lightweight post-acquisition interpretation workflow using learnable multichannel weighted fusion, a convolutional autoencoder, a training-distribution-based quantile threshold, and an auxiliary classification branch achieves 0.9705 accuracy and 0.9704 F1-score on a public triaxial bearing dataset under the reported protocol. A crane-based experiment evaluates deployment feasibility and the sensing–analysis workflow using controlled operating events and a removable stationary mass disturbance. The results provide an engineering sensing basis for distributed monitoring studies on deep drilling equipment. Full article

Aligned recycled carbon fiber (rCF)/polyetherimide (PEI) tapes are a promising material for lightweight aerospace thermoplastic composite structures with reduced environmental impact, provided that their directional properties can be translated into robust components. To assess the viability of rCF/PEI for aircraft interior applications, this study tracks the development of the “Eco Bracket” across four key stages: sustainability screening, coupon characterization, microstructural interpretation, and application-level structural assessment. A project-level life-cycle assessment compared an Additive Fusion Technology (AFT) rCF/PEI bracket with cast and milled aluminum routes and yielded a short-term climate impact of 0.678 kg CO₂-eq for rCF/PEI, representing a significant reduction compared to 5.1 kg CO₂-eq for cast aluminum and 20.9 kg CO₂-eq for milled aluminum. Coupon testing characterized the anisotropic mechanical response of the rCF/PEI tape, including the elastic moduli and strengths under axial and transverse tension, in-plane shear, and axial and transverse compression. Scanning electron microscopy of a representative fracture surface showed a rough, fiber-dominated morphology with exposed fiber bundles, pull-out, and local variations in matrix coverage, supporting the interpretation that consolidation and local wet-out quality govern the transfer from coupon capability to component performance. At the application level, the manufactured rCF/PEI bracket achieved a peak load of 3517.6 N, corresponding to 93% of the strength of an industry-standard polyetherketoneketone (PEKK) reference bracket, and failed in the fastener-hole region predicted as critical by the finite element model. The combined results indicate that aligned rCF/PEI tapes can deliver mechanical properties consistent with the design requirements of aircraft interior brackets, while process robustness, fiber-path fidelity, and local consolidation quality remain the key barriers to repeatable component performance. Full article

Background/Objectives: Positive end-expiratory pressure (PEEP) increases end-expiratory lung volume through the addition of PEEP-induced lung volume (PEEPVol), potentially affecting respiratory mechanics and energy load. However, its physiological impact in patients without lung injury remains poorly characterized. We hypothesized that PEEPVol would be closely associated with respiratory system loading beyond conventional respiratory mechanics variables. Methods: We conducted a secondary analysis of a prospective physiological study including 16 deeply sedated, mechanically ventilated adults without lung disease. A standardized incremental PEEP titration (0–16 cmH₂O, steps of 4 cmH₂O) was performed under volume-controlled ventilation. At each step, respiratory mechanics were assessed, including static compliance (Cstat), driving pressure, plateau pressure, and mechanical power. PEEPVol was estimated as PEEP × Cstat, and strain indices were derived relative to predicted functional residual capacity. Linear mixed-effects models evaluated changes across PEEP levels, and associations were initially explored using Spearman correlation and linear regression. To account for repeated measurements within subjects, confirmatory linear mixed-effects regression models were subsequently performed using patients as a random intercept. Results: Incremental PEEP significantly increased PEEPVol, plateau pressure, mechanical power, and both static and global strain (all p < 0.001), while changes in compliance and driving pressure were minimal and not clinically meaningful. PEEPVol showed moderate-to-strong correlations with plateau pressure (ρ = 0.68) and mechanical power (ρ = 0.76) and explained 43% and 56% of their variance, respectively (all p < 0.001);these associations remained significant in additional linear mixed-effects regression analyses accounting for within-subject correlation. PEEPVol also correlated strongly with static strain (ρ = 0.93) and global strain (ρ = 0.83); however, because static strain is calculated as PEEPVol/FRCt, this association is mathematically expected rather than an independent physiological finding and is reported here only for completeness. Notably, 11.1% of measurements exceeded Pplat > 30 cmH₂O and 61.9% exceeded MP ≥ 17 J/min, even at moderate PEEP levels. Conclusions: In patients without lung injury, PEEP-induced increases in lung volume are strongly associated with higher mechanical load and strain, despite minimal changes in compliance or driving pressure. PEEPVol may represent a promising physiological surrogate of static lung deformation and energy transfer, whose potential to improve bedside detection of occult overdistension warrants validation against direct imaging or physiological measurements in larger prospective studies. Full article

Wave-in-deck slamming generates highly transient impact loads on coastal and offshore deck structures, while the hydrodynamic processes involving air entrapment and its effect on slamming pressures are not fully understood. In this study, regular-wave impacts on a rigid horizontal deck are experimentally investigated using complementary Particle Image Velocimetry (PIV) and Bubble Image Velocimetry (BIV) measurements to systematically examine the evolution of pressure response, flow dynamics (including velocity, vorticity, and turbulence intensity), and entrapped air-cavity dynamics throughout the impact, oscillation, and suction stages. The results show that during the impact stage, the primary pressure peak is generated by rapid upward momentum transfer beneath the deck, while its magnitude and spatial distribution are strongly influenced by the incident wave height and wave period. During the oscillation stage, repeated compression and expansion of the entrapped air cavity influence the post-impact pressure oscillations through continuous redistribution of the surrounding flow. During the suction stage, gravity-driven water withdrawal and progressive flow separation beneath the deck generate a sustained negative-pressure response. The combined pressure, PIV, and BIV measurements provide an experimental framework for characterizing the relationship between flow evolution, cavity dynamics, and pressure response during aerated wave-in-deck slamming. Full article

The present study is situated within the broader research context of optimizing the use of C60 steel in industrial applications, with a particular emphasis on enhancing durability and fatigue resistance, two critical factors in the field. C60 steel is renowned for its exceptional combination of strength and hardness. However, a critical evaluation is necessary to ascertain the impact of thermal and thermochemical treatments on its performance under fatigue conditions. An investigation was conducted into the crack formation process and the early stages of fatigue in C60 steel. The effects of heat treatment (hardening and tempering) were compared with those of thermochemical treatments (oxidation) on the steel’s microstructure. Furthermore, the performance of C60 steel under fatigue conditions was evaluated based on the applied treatments. The insights gained from this research can optimize the use of this steel in industries requiring high resistance and durability. The study’s methodology encompassed the execution of fatigue tests on a four-point bending machine, a procedure that was meticulously employed to ascertain the onset of microcracking. The C60 steel samples were processed in accordance with SR ISO 1099:2017, entitled “Fatigue testing. Axial load method”. To ensure consistency and comparability of results, the samples were fabricated from the same material charge and machined under identical conditions. A total of 26 samples were utilized, with 13 samples allocated to each treatment type: heat treatment by hardening, tempering, and thermochemical treatment by oxidation. To ensure comparability and scientific interpretability of the results, an identical applied force level was utilized for both treatment conditions. The frequency changes were monitored to evaluate the behavior of the materials under repeated stresses. Finally, the frequency changes were correlated with the number of cycles to identify when microcracks appeared and their evolution. The primary findings of this study indicate substantial disparities between the longevity of thermally and thermochemically modified specimens and the onset of microcrack formation in the material. Full article