Search Results (755)

Flexible pressure sensors serve as core sensing components for wearable health monitoring systems, electronic skins for soft robots, and flexible human–machine interaction devices. Benefiting from the interfacial electric double-layer polarization effect, iontronic sensing delivers far higher pressure response sensitivity than conventional parallel-plate capacitive sensors, endowing it with distinctive advantages in the detection of weak physiological signals. Nevertheless, current dense ionic thin-film dielectric layers suffer from limited deformation space under compression and poor low-pressure sensing capability. Mainstream high-precision micropillar arrays are fabricated via photolithography, 3D printing, and metal etching molds, which require costly equipment and complicated fabrication procedures, making large-area mass production unfeasible. Random frosted concave-convex microstructures feature disordered dimensions, leading to severe device hysteresis and narrow linear ranges, which fail to achieve ultrahigh sensitivity alongside a wide pressure detection range simultaneously. To address the aforementioned multiple bottlenecks, this paper proposes a low-cost resin template replication process to fabricate TPU-based ionic thin-film dielectric layers with ordered micropillar array microstructures. Combined with inkjet-printed silver conductive PI flexible electrodes, an iontronic flexible pressure sensor with a sandwich layered structure is constructed. Multi-dimensional investigations including microscopic morphology characterization, electromechanical sensing performance calibration, and human wearable application tests are systematically implemented to thoroughly elucidate the synergistic enhancement mechanism of the arrayed micropillars. Test results demonstrate that the effective pressure detection range of the sensor spans 0–1038 kPa, accommodating ultra-low pressures such as pulse signals as well as medium-to-high-pressure loads including joint bending. The sensitivity reaches 23.27 kPa⁻¹ within the low-pressure range of 0–200 kPa and remains stable at 3.52 kPa⁻¹ in the high-pressure range of 200–1038 kPa, with piecewise linear fitting correlation coefficients of 0.93 and 0.96 respectively. Both the response time and recovery time of the device are 40 ms, and the hysteresis error throughout the loading-unloading cycle is merely 2.62%. After 20,000 consecutive cyclic loading-unloading tests, the peak capacitance output only decays by 5.1%, verifying outstanding mechanical fatigue resistance and electrical stability. Validations in multi-scenario applications prove that the sensor can accurately capture human physiological and motion signals including radial artery pulses, laryngeal deformation induced by multi-syllable vocalization, and multi-angle bending of fingers and elbow joints, suitable for home-based health monitoring, quantitative rehabilitation training, flexible tactile interaction and other scenarios. The entire fabrication process eliminates high-precision micro-nano processing equipment such as photolithography systems, plasma etchers and 3D printers; only general chemical raw materials and conventional laboratory instruments are adopted. The reusable templates enable low manufacturing costs and large-area coating forming, offering a novel low-cost technical solution for the engineering implementation and industrialization of high-performance iontronic flexible pressure sensors. Full article

High-frequency induction hardening enhances the surface wear resistance and contact fatigue life of high-speed linear guides, but simultaneously produces an inhomogeneous, layered cross-sectional structure comprising a high-strength, low-ductility outer hardened layer and a low-strength, high-ductility inner core. This structural heterogeneity renders conventional straightening stroke prediction models—predicated on homogeneous material assumptions—fundamentally inadequate. Moreover, the iterative trial-bending operations ubiquitous in industrial practice progressively accumulate plastic strain, causing guide rails to exhibit erratic positive-to-negative deflection reversal during sequential straightening passes. To address these critical challenges, this study proposes a novel two-stage hybrid straightening strategy based on inverse finite element analysis (FEA) and closed-loop experimental feedback. An equivalent hardened layer depth (HD₀) is introduced as a parametric descriptor to construct a layered elastoplastic finite element model, and an inverse simulation strategy is developed to generate a comprehensive three-dimensional stroke–residual deflection prediction dataset encompassing both vertical and lateral straightening conditions across multiple support spans. Displacement-controlled three-point bending experiments validate the layered model and elucidate the mechanism by which cumulative plasticity progressively amplifies cross-sectional plastic sensitivity under repeated loading. Grounded in this physical insight, a hybrid straightening algorithm is formulated, combining dataset-driven initial stroke prediction for rapid large-deformation elimination with an upper-bound constraint and a measurement-feedback-driven sequential reduction compensation scheme for fine-tuning. Comparative experiments demonstrate that the proposed strategy effectively suppresses the oscillatory over-straightening characteristic of conventional empirical trial-and-error approaches, consistently reducing residual deflection below 0.05 mm within two to three loading cycles. This work bridges the gap between theoretical simulation and the complex physical state of actual machining, substantially improving both the efficiency and precision of straightening for guide rails with induction-hardened layers. Full article

Finely dispersed Al–Ca–Ti composite alloys with a set of remarkable properties can be considered as new promising structural materials. For wider use of these alloys, data on their fatigue behavior are needed. In this work the comparative study of the low-cycle fatigue strength of hot-rolled Al–xCa–0.2Ti alloys with different eutectic fractions determined by different calcium contents was conducted. The fatigue tests were carried out according to a single-plane bending scheme using a dynamic mechanical analyzer. A symmetrical loading cycle (asymmetry coefficient R = −1) with a constant stress amplitude was used. The maximum number of cycles was 20,000. It was found that increasing the eutectic fraction from 40% to 80% led to a 75% increase in the fatigue limit—from 80 to 140 MPa—which directly correlated with the alloy’s yield strength. The fatigue crack propagation occurred with the formation of a scaly fracture surface, whereas final static rupture was associated with a ductile dimple fracture. The microstructural mechanisms of alloy fatigue failure were discussed. It was found that increasing the total length of the eutectic particles/aluminum matrix interphase boundaries changed the failure mechanism to a more brittle one. Full article

The whole pavement life cycle is divided into five phases: raw material production, construction, service use, maintenance and rehabilitation, and end-of-life (EOL). Distinct system boundary definitions (cradle to gate, cradle to site, cradle to grave) are clearly distinguished, and two categories of vehicle-related emissions are strictly differentiated: baseline vehicle operation emissions (excluded) and pavement-induced incremental emissions (included only for full cradle-to-grave accounting). According to cited highway pavement inventory data (functional unit: 1 m² full cross-section composite pavement, cradle-to-gate material-only boundary), cement-related materials account for merely 4.7% of total structural material mass yet contribute over 84.5% of material-phase carbon emissions, while asphalt mixture construction emissions generally make up less than 10% of mixing-stage outputs. In the use phase, pavement deformation, rolling resistance elevation and surface texture loss trigger extra vehicle fuel consumption and associated greenhouse gas increments. Maintenance-stage emissions stem from repair material manufacturing, on-site machinery operation and traffic congestion delays during lane closure; milling, transportation and recycling dominate EOL carbon outputs. This review further classifies all emissions into direct engineering emissions and pavement-derived indirect emissions, compares carbon performance and service-life extension effects of eight mainstream maintenance strategies, and thoroughly decomposes milling, stockpiling, haulage and recycling links of waste asphalt, alongside multiple environmental burden allocation methods for reclaimed asphalt pavement (RAP). A full spectrum of green low-carbon technologies is summarized, including biochar bio-materials, RAP, crumb rubber, industrial byproducts, warm-mix asphalt (WMA), cold recycling and CCUS negative-carbon materials. We also balance their emission reduction benefits against potential deterioration risks to rutting resistance, fatigue life and moisture stability. Combined with a life-cycle cost assessment (LCCA), this study analyzes cost-emission trade-offs of all technical routes, and deeply discusses multi-source uncertainty, sensitive input parameters and universal methodological limitations of pavement LCA. Core takeaways indicate that raw material production and long-term service use are the two dominant carbon emission stages; a medium RAP-WMA combination and cold in-place recycling represent the most economically and environmentally balanced mitigation solutions. Major research gaps and targeted future research directions are proposed, providing standardized theoretical support and dual environmental–economic decision references for low-carbon asphalt pavement design and full-life carbon accounting. Full article

This systematic review aimed to evaluate whether cross-sectional geometry is associated with cyclic fatigue resistance of nickel–titanium (NiTi) endodontic instruments and to identify the geometric and materials-related features most frequently associated with improved fatigue performance. The protocol was prospectively registered on the Open Science Framework (OSF). PubMed, Scopus, Embase, Web of Science, and WorldCat were searched in April 2026 in accordance with PRISMA 2020. Eligible studies were comparative in vitro investigations that explicitly evaluated cross-sectional geometry or a related geometric parameter as a prespecified study factor and reported quantitative cyclic fatigue outcomes. Of 107 screened records, 66 full-text reports were assessed and 23 studies were included in the qualitative synthesis. Twenty-two studies had a medium risk of bias and one had a low risk of bias according to the Quality Assessment Tool for In Vitro Studies (QUIN). Cyclic fatigue resistance was most often reported as time to fracture or number of cycles to failure. Instruments with reduced metal mass, smaller core volume, lower cross-sectional area, and greater flexibility tended to demonstrate higher fatigue resistance in curved canals. S-shaped and double-S-shaped cross-sections were most consistently associated with favorable outcomes; however, this association is more plausibly related to reduced bending stiffness and canal-wall contact forces than to increased intrinsic material fatigue strength. Flat-side designs did not show a consistent advantage. The evidence was limited by heterogeneous testing protocols and residual confounding by alloy, heat treatment, taper, manufacturing, surface condition, and kinematics. No meta-analysis or quantitative dimensional correlation was feasible because testing conditions and detailed geometric parameters were inconsistently reported. Full article

Metals are widely used in various types of structural applications such as the automotive, aerospace and construction industries. However, their service life is limited due to the various loads they experience during operation. Specifically, cyclic loading can lead to the early fatigue failure of these structures. Therefore, early detection of fatigue deformation is essential to prevent catastrophic failures. In this study, an automated electrical resistance data acquisition system was developed using LabVIEW to obtain measurements from a Keithley 6221 current source for fatigue damage detection. The results showed an increase in electrical resistivity after the application of cyclic loading. It was observed that electrical resistivity increased after each set of loading cycles, with an average increase of 7.38%, a stress level of 260 MPa (high-cycle fatigue), and a 6.5% increase after the application of 25,000 cycles at 165 MPa (low-cycle fatigue). Scanning Transmission Electron Microscopy (S/TEM) was used for microstructural investigation as a proof of concept for the high-cycle fatigue sample interrupted after 25,000 cycles to analyse the modification in dislocation structures as well as a qualitative increment in the dislocation density with respect to the initial microstructural state of the as-machined sample. Such a modification in dislocation structures as well as an increment in dislocation density corroborates the findings proposed by electrical resistivity measurement. The results demonstrated that electrical resistivity measurement provides a promising non-destructive approach for the early detection of fatigue damage in metallic materials. Full article

Heat pumps are core equipment for efficient low-grade thermal energy utilization and low-carbon transformation of the energy structure, offering significant energy-saving potential in building heating and industrial waste heat recovery. This paper reviews the research progress and technical challenges of compression, absorption, and adsorption heat pumps as well as nanofluid-enhanced heat transfer technology and elastocaloric heat pump systems. Air source heat pumps can delay frosting through variable frequency, heat storage, and waste heat recovery. However, accurate prediction models for performance degradation under extreme cold conditions are lacking. Although ground source and water source heat pumps exhibit significant energy efficiency advantages, ground source systems may suffer from performance degradation due to underground thermal imbalance. The application of water source systems is strictly constrained by water resource conditions. Driven by low-grade waste heat, absorption heat pumps employing traditional working pairs suffer from crystallization, corrosion, or high rectification energy consumption. The COP of a single-effect cycle under 80~100 °C waste heat is only 1.2~1.9, while hybrid cycles can reach approximately 3.2 at 120~150 °C. Although adsorption heat pumps achieve significantly improved performance under continuous heat recovery cycles, the full-scale power density of novel adsorbents such as metal–organic frameworks is inferior to the power density of traditional silica gel. Moreover, under off-design conditions, the performance drops by 23~48% compared to theoretical values. Nanofluids can enhance heat transfer, but the long-term effects of particle agglomeration at high temperatures on pump power consumption and system compatibility remain to be systematically evaluated. Elastocaloric heat pump systems can achieve refrigerant-free cooling, but current prototypes still cannot compete with traditional vapor compression systems in long-cycle fatigue reliability and power density. Current heat pump technologies generally face challenges such as insufficient adaptability to extreme conditions, bottlenecks in working fluids and materials, and a lack of long-term validation. Future research must construct a multi-source coupling optimization system, address common problems in working fluids and materials, promote long-term validation and kilowatt-level prototype demonstrations, and drive the large-scale deployment and engineering application of heat pump technology toward high efficiency, intelligence, and high reliability. Full article

Aluminium alloys are increasingly adopted in structural engineering due to their favourable strength-to-weight ratio, durability against corrosion, and sustainability benefits. This paper examines the cyclic response of hollow section beams manufactured from 6082-T6 aluminium alloy through a combined numerical–experimental approach. Based on experimental results available in the literature concerning aluminium beams subjected to incremental cyclic bending, an efficient computational model is developed within the OpenSees framework to reproduce cyclic hardening and low-cycle fatigue. The modelling strategy integrates the Giuffrè–Menegotto–Pinto constitutive law with a fatigue material formulation. Model parameters are calibrated against experimental force–displacement responses and cumulative dissipated energy to ensure an accurate representation of observed behaviour. The numerical results show good agreement with experimental data, successfully reproducing both the global cyclic response and material degradation phenomena. Full article

Background: Energy dissipation reflects the viscoelastic behavior of biological tissues and plays a key role in arterial elastic recoil and diastolic flow support. In the native aorta, efficient storage and release of mechanical energy are essential for maintaining ventriculo–aortic coupling. The energy dissipation ratio (EDR) quantifies the proportion of mechanical energy lost during a loading–unloading cycle and may provide insight into the biomechanical performance of aortic substitutes. Bovine pericardial patches (BPPs) are widely used in cardiovascular surgery for arterial reconstruction, patch angioplasty, and tubular replacement. Today, EDR has not been systematically investigated in BPPs. Methods: Forty glutaraldehyde-treated BPPs from four commercial manufacturers (n = 10 per supplier) were subjected to low-cycle fatigue testing using a uniaxial tensile system under controlled physiological conditions (37 °C). Standardized bone-shaped specimens were tested at progressive strain percentage levels. Thickness, EDR, and the percentage of specimens failing to reach progressively higher strain levels were evaluated from stress–strain hysteresis loops. Results: BPPs thickness ranged from 0.253 to 0.608 mm, with no significant differences among most groups. For the 10% strain, all BPPs reached the target deformation and demonstrated comparable EDR values. In detail, the mean EDR was 21.40 ± 7.02% for Edwards Lifesciences, 24.95 ± 6.80% for Supple Peri-Guard (Baxter), 24.99 ± 6.04% for Xenosure (LeMaitre), and 23.37 ± 6.12% for Invengenx–Tisgenx, with no statistically significant intergroup differences (p > 0.05). For the 20% strain, only 18.75% of specimens remained structurally intact, and variability increased. At 30% strain, structural failure occurred in nearly all samples. No significant orientation-dependent differences were observed. Conclusions: Commercially available BPPs exhibit similar biomechanical behavior under moderate deformation. However, tolerance to higher strain is limited. EDR analysis provides a clinically relevant parameter to assess elastic performance and may contribute to optimizing aortic substitute selection. Full article

Background: Normobaric hypoxia is increasingly used as an additional environmental stimulus in training programs; however, its practical role in improving anaerobic performance remains unclear. This study analyzed how a four-week high-intensity interval training (HIIT) program performed under different hypoxic exposure models affected selected anaerobic performance indices in young men. Methods: Forty-five healthy, non-elite physically active men completed the study. Participants were assigned to one of four groups: control, normoxic training, live low–train high group, and live high–train low group. The training intervention consisted of 12 HIIT sessions performed over four weeks. Anaerobic performance was assessed before and after the intervention using a 20-s maximal cycling sprint test. Results: No significant group × time interactions were found for any variables obtained from the 20-s maximal cycling sprint test, including peak power (PP; p = 0.109, ηp² = 0.136), relative peak power (rel_PP; p = 0.641, ηp² = 0.040), relative mean power (rel_MP; p = 0.438, ηp² = 0.063), relative total work (rel_TW; p = 0.515, ηp² = 0.054), fatigue index (FI; p = 0.231, ηp² = 0.099), and time to peak power (tPP; p = 0.673, ηp² = 0.036). Conclusions: The findings suggest that, under the applied conditions, normobaric hypoxia does not provide a sufficient additional stimulus to enhance anaerobic performance adaptations. From an applied exercise physiology perspective, the specificity and structure of the training stimulus are critical when designing short-term HIIT interventions. They may be more important than hypoxic exposure itself for improving short-duration maximal cycling sprint performance. Full article

The cyclic material properties are crucial for accurate assessment of structural response; however, conventional numerical methods often fail to replicate the mechanical degradation caused by ultra-low cycle fatigue (ULCF) damage accumulation. This paper focuses on a novel constitutive model characterizing the continuous degradation in yield stress and stiffness under large-strain tension–compression cyclic loads. A series of 32 cyclic tests on circular notched specimens covering a range of stress triaxialities are first revisited to systematically identify the cyclic softening behavior. The corresponding limitations of the widely applied classical Chaboche theory are examined, and an enhanced elastoplastic constitutive framework is proposed accordingly. On this basis, the stress-weighted ductile fracture model (SWDFM), which is developed from micro-damage mechanics, is then employed as the internal damage criterion of the proposed constitutive model. Explicit functional relationships linking the evolved yield stress and Young’s modulus to the imposed damage index are established and calibrated against the test data. Based on these findings, a new cyclic ductile constitutive model is developed, which is programmed into the UMAT subroutine compatible with ABAQUS/Standard. Numerical validations against the experimental cyclic responses exhibit good agreement, as indicated by the considerably low average errors of 5% for both strength and stiffness, demonstrating its validity in terms of the hysteretic behavior simulation for metals subjected to progressive ULCF damage. Full article

Interfacial bond failure is a common form of distress in rigid–flexible composite pavements, especially in tunnel environments with harsh service conditions. Epoxy-emulsified asphalt (EEA) is widely used as a high-performance interlayer bond coat, but its dynamic damage evolution under coupled thermomechanical loading remains insufficiently characterised. In this work, 45° static oblique shear tests and stress-controlled dynamic shear fatigue tests were performed on a C40 concrete-EEA-asphalt mixture composite system. Tests covered a temperature range of −10 °C to 45 °C, loading frequencies of 1 to 15 Hz, and three stress levels (0.3, 0.4, 0.5). An optimised geometric tangent method (GTM) was adopted to objectively locate the fatigue failure inflexion point, reducing the empirical bias inherent in traditional stiffness degradation analysis. Test results showed that an EEA application rate of 0.8 kg/m² yielded the best overall interface performance, balancing mechanical interlocking and cohesive strength. At this application rate, the interfacial peak shear strength reached 1.72 MPa, with improved interfacial deformation compatibility and energy dissipation capacity. Fatigue damage followed a distinct three-stage stiffness degradation pattern. High temperatures and low loading frequencies accelerated rheological behaviour of the asphalt phase, shortened the stable damage propagation phase, and promoted premature interlayer slippage. Based on the experimental data, a phenomenological fatigue life prediction model was established, incorporating temperature, loading frequency and stress level. The model supports quantitative assessment of progressive interfacial damage and provides practical reference for structural durability design and life-cycle maintenance of composite tunnel pavements. Full article

The cyclic performance of welded aluminum joints is crucial for the load-bearing capacity and durability of lightweight structural applications, particularly under low-cycle fatigue (LCF) conditions. Reliably assessing such behavior is essential to applying and further developing design standards, such as EN 1999-1-3. This paper presents the results of an experimental study of welded EN AW-7020 aluminum joints that were subjected to constant-amplitude loading with varying stress ratios. Fatigue tests were conducted on butt welds and cruciform joints with stress ratios ranging from R = −0.25 to R = 0.5. The resulting S–N curves were evaluated and compared with the corresponding detail categories according to EN 1999-1-3. The results demonstrate a clear dependence of fatigue strength on the applied stress ratio; increasing mean stress reduces the allowable stress range. For all configurations investigated, the experimental fatigue strength exceeds the standardized design curves, indicating a generally conservative assessment within the current design framework. However, the influence of the stress ratio is not adequately captured; significant scatter is observed due to local effects in the welded region, especially in the heat-affected zone. The derived fatigue parameters were integrated into the Aluminum Fatigue Database (Alfabet), which was expanded in this study by combining new experimental results with existing literature data. These findings highlight the limitations of the nominal stress concept in the LCF regime and contribute to developing more accurate, material-specific fatigue design approaches. Full article

Aluminum alloys are widely used in the automotive and aerospace industries due to their low density and very high specific strength, and high-pressure die casting (HPDC) allows us to mass-produce complex components despite porosity and microstructural heterogeneity. In this study, we examine the individual and combined effect of grain refinement (AlTi5B1), chemical modification (AlSr15), and T6 heat treatment on the microstructure, mechanical properties, and corrosion of ENAC 46000 alloy produced in cold-chamber HPDC. The material characteristics were assessed through hardness, tensile, fatigue, and corrosion testing as well as optical microscopy, SEM, and EDS measurements. The microstructural characteristics were found to be fine α-Al grains, and Sr modification transformed eutectic Si into a fibrous structure. T6 treatment dissolved coarse Al₂Cu phases into fine coherent precipitates. T6 heat treatment was the primary strengthening process and produced an increase in hardness of 59% (to 143 HB) compared to non-T6 conditions, while the fatigue resistance was still excellent in the as-cast state (1.16 × 10⁶ cycles). Moreover, the modified and T6-treated condition exhibited the lowest corrosion rate (15.3 × 10⁻³ mm/year). Therefore, because no single processing route is the best way to maximize all performance characteristics (as well as process efficiency), a multi-property evaluation should be performed to tailor treatment to the engineering service requirements. Full article

Underwater concrete infrastructure is gradually damaged by water scouring, chloride ingress, freeze–thaw cycles, and fatigue loading, so reliable in situ repair materials are increasingly needed. Conventional cement-based repair materials are often unsuitable for underwater use because they disperse in water, bond weakly to wet substrates, and show limited durability. Polymer-modified cementitious materials can reduce these problems by combining cement compatibility with polymer film formation and interfacial strengthening. Water-soluble polymers mainly improve fresh-state cohesion and anti-washout performance through adsorption, bridging, and flocculation regulation. In comparison, polymer emulsions and latexes are more effective after hardening, improving bonding, crack resistance, and durability through polymer films and organic–inorganic networks. For self-leveling underwater repair, the flow spread should reach at least 130 mm. For vertical repair with a 20 mm layer, a yield stress of about 360 Pa is needed to prevent sagging. Therefore, performance should not be judged by strength alone, but by constructability, interfacial water films, and pore connectivity. Future studies should consider responsive polymers, multi-component modification, standardized tests, and low-carbon binders. Full article