Search Results (195)

The shift toward lightweight powertrain architectures necessitates a detailed characterization of polymer gears to verify their efficiency and durability. This study investigated the effectiveness of non-contact structured-light 3D scanning for evaluating the surface topography and dimensional tolerance quality of polymer gears produced via distinct manufacturing technologies. A structured-light 3D scanner was used to capture dense point clouds (exceeding 6 million points) of gears produced by three methods: conventional hobbing (POM-C), Material Extrusion (MEX) with carbon fiber reinforcement, and Selective Laser Sintering (SLS). The manufactured parts were compared against the nominal Computer Aided Design (CAD) models to evaluate their geometrical deviations in accordance with DIN 3961 and surface roughness parameters per ISO 25178. The experimental results revealed a consistent ranking of manufacturing quality. The conventionally hobbed POM-C gear exhibited superior precision, achieving DIN quality grades of Q9–Q10 and the smoothest surface finish (S_a = 5.0 µm). Among additive manufacturing techniques, SLS-printed PA 12 showed intermediate quality (Q11, S_a = 12 µm), whereas MEX-printed PPS-CF exhibited significant deviations (exceeding Q12) and the highest surface irregularity (S_a = 25 µm) due to stair-stepping effects. These findings indicate that while additive manufacturing offers geometric flexibility, conventional hobbing retains a decisive advantage in dimensional precision. The optical scanning methodology demonstrated here constitutes an efficient metrological framework for gear quality control, with potential applications extending to the quality assurance of additively manufactured adaptive fixtures and assembly tooling, including automotive assembly operations. Full article

The increasing availability of multi-material fused filament fabrication (FFF) systems has intensified the need for a systematic understanding of interfacial adhesion between model and support polymers. In this study, the adhesion behavior of commonly used engineering thermoplastics and dedicated support materials was investigated in the context of multimaterial FFF. A comprehensive experimental methodology was developed, including a custom tensile test specimen and fixture specifically designed to quantify interfacial adhesion under controlled conditions. Material combinations based on ABS, ASA, PETG, and carbon-fiber-reinforced PA (PAHT-CF), together with manufacturer-recommended and alternative support materials, were evaluated using uniaxial tensile testing and fracture surface analysis. The results demonstrate that interfacial adhesion strongly depends on material compatibility and processing conditions, and that dedicated support materials generally provide lower adhesion than model–model combinations. However, significant deviations were observed: SUPP PA exhibited unexpectedly high adhesion when paired with PAHT-CF, while SUPP ABS proved to be a more versatile support across multiple model materials, offering a favorable balance between sufficient adhesion during printing and ease of removal. Several material pairs showed negligible adhesion, leading to separation during manufacturing and limiting their practical applicability. Microscopic analysis revealed the coexistence of diffusion-driven bonding, mechanical interlocking, and weak boundary layer effects. The findings highlight that optimal support performance requires neither minimal nor excessive adhesion, and provide experimentally validated guidance for selecting material combinations and process windows in multimaterial FFF. Full article

To address the engineering problems of high cement content, high brittleness, and weak frost resistance of cement-improved loess in the seasonal frozen soil area of Northwest China, F1 ion curing agent (F1) and cement composite improved loess (FCIL) were used in this paper. Through unconfined compressive (UC) strength tests, consolidated undrained (CU) triaxial shear tests, and microscopic pore characteristics analysis, the mechanical properties, freeze–thaw cycle deterioration law, and microscopic pore structure of FCIL were studied. The effects of cement content (C_c), F1 dosage (C_F), number of freeze–thaw cycles (N_F-T), and confining pressure (σ₃) on the strength, deformation behavior, and pore characteristics of FCIL were analyzed. The synergistic improvement mechanism of FCIL, as well as the freeze–thaw damage mechanism, was elucidated. The results show that C_c is the primary factor controlling the strength of improved loess. The incorporation of F1 can further increase UCS and markedly enhance the failure strain (ε_f), thereby achieving simultaneous improvements in strength and ductility. An appropriate mix proportion was identified as C_F = 0.2 L/m³ and C_c = 6%. After 7 d curing, FCIL exhibited a UCS of 1.35 MPa, a cohesion (c) of 205 kPa, an internal friction angle (φ) of 36.2°, and ε_f 1.8 times that of loess improved with C_c = 6% cement alone. CU triaxial shear tests indicate that, under all tested conditions, the stress–strain responses of FCIL exhibit σ3-sensitive strain-softening behavior. As C_c and σ₃ increase, triaxial peak strength (q_max) and secant modulus (E₅₀) increase significantly. Compared with natural loess (NL), FCIL shows a markedly lower porosity (n), a substantial increase in the proportion of micropores, and reductions in medium and small pores. After multiple freeze–thaw cycles, the evolution of the pore structure is effectively restrained. This indicates that the combined use of F1 and cement promotes the formation of a dense layered stacking structure, significantly improves the microscopic pore-size distribution, and enhances the mechanical performance of loess under freeze–thaw environments. Full article

Fiber-reinforced aerogel composites are attractive for thermal protection applications because porous polymer networks can suppress heat transfer while maintaining structural stability. In this study, carbon fiber felt was integrated with a polyimide aerogel via a freeze-drying-assisted multicycle impregnation process to achieve controlled formation of interconnected aerogel networks within the fibrous scaffold. With increasing impregnation cycles, the composites exhibited progressive microstructural densification and improved structural stability. Although bulk density increased, thermal protection performance under prolonged butane-torch exposure was significantly enhanced, showing delayed backside temperature rise and improved resistance to structural degradation compared with bare carbon felt. Post-ablation analyses revealed the formation of a micro-/nanoporous polymer-derived char layer and a multilayer thermal-resistance structure, which contributed to suppressed heat transfer during flame exposure. These results indicate that effective thermal protection in CF/PA composites is governed by dynamic microstructural evolution and char-layer formation rather than intrinsic room-temperature thermal conductivity alone. The proposed multicycle impregnation strategy provides a scalable approach for designing lightweight polymer-based thermal protection materials operating in high-temperature environments. Full article

This research investigated the feasibility of 3D-printed external fixator (EF) rings made from carbon fiber reinforced polyamide 6 (PA6-CF) as an alternative to the conventional metallic counterpart. The study integrated tensile testing with digital image correlation (DIC) in as-printed and cold plasma-sterilized conditions, finite-element analysis (FEA) under wire loading, topology optimization for material and energy reduction, and evaluation of printability limits for large PA6-CF rings. The average Young’s modulus was 4.76 GPa and the maximum tensile strength was 60.5 MPa for as-printed samples, decreasing by 6.4% and 10.4% after sterilization, respectively. Using these properties as model inputs, FEA predicted safety factors larger than 1.42 for all configurations under 1000 N wire pretension, while topology optimization targeted up to 50% mass reduction without compromising ring stiffness. The study also revealed challenges in the printability of PA6-CF for large and thin components, including dimensional contraction, significant warping and moisture-induced defects, requiring an experienced 3D printer operator. Full article

This study presents a detailed experimental investigation of the mechanical, fatigue, and dynamic properties of a 3D-printed PA12 CF15 composite at different temperatures. The mechanical properties determined in the temperature range from 23 °C to 120 °C were later implemented in numerical simulations to evaluate the suitability of the material for thermo-mechanical loading conditions. Quasi-static tensile test results revealed a decrease in elastic modulus, yield strength, and ultimate tensile strength with increasing temperature. Fatigue testing demonstrated that increasing load levels lead to reduced durability and a lower maximum number of cycles to failure. Furthermore, elevated testing temperatures caused the composite to exhibit more pronounced plastic behavior, resulting in temperature-dependent fatigue performance. SEM analysis indicated that higher temperatures increase the plasticity of the composite, thereby reducing the reinforcing effect of carbon fibers. The mechanical characteristics obtained experimentally were incorporated into a finite element model, allowing a preliminary assessment of the feasibility of manufacturing an intake manifold from PA12 CF15 using additive manufacturing technology. The results of this study provide valuable data for the design and analysis of dynamically and thermally loaded engineering components produced from PA12 CF15 composites. Full article

Thermoplastic carbon fiber-reinforced polymer (CFRP) composites possess the intrinsic capability to heal delamination and matrix cracks via thermal re-melting. However, under impact loading, they are prone to severe fiber fracture, which significantly compromises their repairability. To address this, this study introduced polytetrafluoroethylene (PTFE) films as pre-set interlaminar defects within continuous carbon fiber-reinforced polyamide 6 (CF/PA6) thermoplastic cross-ply laminates. Low-velocity impact tests were conducted at varying energy levels to comparatively investigate the impact response and damage mechanisms of the CFRPs with and without embedded defects. Experimental results indicate that the embedded interlaminar defects triggered a transition in the failure mode of the CFRP from brittle fracture to progressive damage behavior. Compared to the baseline laminates, the specimens with embedded defects maintained higher flexural stiffness under low-energy impact. Furthermore, they effectively reduced the extent of fiber breakage by dissipating impact kinetic energy through extensive delamination, interlaminar frictional sliding, and plastic micro-deformation. These findings verify the feasibility of achieving macroscopic pseudo-ductility through interlaminar microstructural tailoring. This research provides an experimental basis and methodological support for the pseudo-ductile design of thermoplastic composites. Full article

At present, conventional cold storage facilities in China are poorly suited to on-farm storage demands for agricultural produce, mainly due to their large spatial requirements, complex and labor-intensive installation procedures, limited portability, and insufficient coverage in rural areas. These limitations significantly contribute to post-harvest losses of perishable crops such as cherry tomatoes. To address this challenge, the present study proposes a compact and temporary cold storage system—gas-inflated membrane cold storage (GIMCS)—which exploits the inherent safety, cost-effectiveness, ease of deployment, and adaptability of inflatable membrane structures. A series of mechanical performance tests, including tensile strength, pressure resistance, and burst tests, were conducted on PA/PE (Polyamide/Polyethylene) composite membranes. The optimal configuration was identified as a membrane thickness of 70 μm, a gas column width of 2 cm, and a PA/PE composition ratio of 35%/65%. Thermal performance evaluations further revealed that filling the inflatable structure with 100% CO₂ yielded the most effective insulation. Through structural optimization, a cotton-filled gas-inflated membrane cold storage system (CF-GIMCS) incorporating a dual insulation strategy—combining intra-membrane and extra-membrane insulation—was developed. This multilayer configuration significantly reduced conductive and convective heat transfer, resulting in enhanced thermal performance. A comparative evaluation between GIMCS and a conventional cold storage system of equivalent capacity was conducted over a 15-day storage period, considering construction cost, temperature uniformity, and fruit preservation quality. The results showed that the construction cost of GIMCS was only 38% of that of conventional cold storage. The internal temperature distribution of GIMCS was highly uniform, with a maximum horizontal temperature difference of 1.4 °C, demonstrating thermal stability comparable to conventional systems. No statistically significant differences were observed between the two systems in key post-harvest quality indicators, including weight loss and respiration rate. Notably, GIMCS exhibited superior performance in maintaining fruit firmness, with a hardness of 1.30 kg·cm⁻² compared to 1.26 kg·cm⁻² in conventional storage, indicating a potential advantage in shelf-life extension. Overall, these findings demonstrate that GIMCS represents an affordable, technically robust, and portable cold storage solution capable of delivering preservation performance comparable to—or exceeding—that of conventional cold storage. Its modularity, mobility, and ease of relocation make it particularly well suited to the operational and economic constraints of smallholder farming systems, offering a practical and scalable pathway for improving on-farm cold chain infrastructure. Full article

Physical activity often remains low after hospitalisation for acute exacerbation of Chronic Obstructive Pulmonary Disease (AECOPD). Although post-hospitalisation rehabilitation has shown to support recovery, its impact on daily activity levels in the early post-exacerbation phase is unclear. This study describes the changes in physical activity (PA) and clinical outcomes during an 8-week rehabilitation following hospitalisation for AECOPD. This prospective observational cohort study included patients recently discharged after AECOPD from Aalborg University Hospital, Denmark. Participants received municipality-delivered post-hospitalisation rehabilitation consisting of tailored physiotherapy and occupational therapy of individually determined frequency. PA was assessed using thigh-worn triaxial accelerometers measuring 24 h/day over 8 weeks. Clinical outcomes included lung function (FEV1% predicted), dyspnoea scores, health-related quality of life (EuroQol 5-dimension, 5-level (EQ-5D-5L); EuroQol visual analogue scale (EQ-VAS)), frailty (Clinical Frailty Scale (CFS)), functional status (Short Physical Performance Battery (SPPB)), and symptom burden (COPD Assessment Test (CAT); St. George’s Respiratory Questionnaire (SGRQ)). Changes from baseline to 8 weeks were analysed using linear mixed-effects models and bootstrap resampling. Forty-three participants with a mean age 73.4 years, 67.4% female, and moderate frailty (CFS 5.4 ± 1.3) were included. Physical activity remained largely unchanged. Gait speed and total SPPB declined, whereas self-perceived health improved (EQ-VAS Δ +7.8, p = 0.008). Lung function, dyspnoea, and health related quality of life scores showed no significant change. In this frail, recently admitted COPD population, physical activity did not increase during the rehabilitation period, and some functional parameters declined. The improvement in self-perceived health suggests a divergence between subjective and objective outcomes. These findings highlight the need for long-term, tailored, and flexible approaches to support recovery after AECOPD. Full article

This study investigates the mechanical performance of three temperature-resistant 3D-printable polymer composites for turbine impellers used in district heating networks for pressure reduction. Using fused deposition modeling (FDM), tensile strength and deformation of ASA-X CF10, PA6-GF30, and ePAHT-CF15 were evaluated at temperatures representative of real operating conditions (60–130 °C). These polymer composites were systematically tested, with particular emphasis on annealed ePAHT-CF15. Results demonstrated that annealing significantly improved mechanical performance, yielding higher tensile strength, Young’s modulus, and reduced deformation. Structural analyses confirmed that ePAHT-CF15, particularly when annealed at 200 °C, exhibited superior thermal stability and rigidity, making it the optimal material choice for high-temperature turbine impeller applications. These findings support the design of 3D-printed composite impellers for pump-as-turbine applications in district heating systems, where high stiffness and heat resistance are required. Full article

We demonstrate high-performance MOSFETs on β-Ga₂O₃ films grown by plasma-assisted molecular beam epitaxy (PA-MBE). The high crystalline quality of the β-Ga₂O₃ epilayer was confirmed by X-ray diffraction and atomic force microscopy. An optimized CF₄-plasma treatment was employed to introduce fluorine (F) into the near-surface region, effectively suppressing donor-like states. The resulting devices exhibit an ultralow off-state current of 1 × 10⁻⁹ mA/mm and a stable on/off ratio of 10⁵. A controllable positive threshold voltage shift up to +12.4 V was achieved by adjusting the plasma duration. X-ray photoelectron spectroscopy indicates that incorporated F atoms form F–Ga-related bonds and compensate oxygen-related donor defects. Sentaurus TCAD simulations reveal reduced near-surface charge and a widened depletion region, providing a physical explanation for the experimentally observed increase in breakdown voltage from 453 V to 859 V. These results clarify the role of fluorine in modulating surface defect states in PA-MBE β-Ga₂O₃ and demonstrate an effective route for threshold-voltage engineering and leakage suppression in Ga₂O₃ power devices. Full article

Cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulators have been reported to improve lung function and reduce CF exacerbations. We aimed to investigate the efficacy of CFTR-modulators in CF-associated liver disease (CFLD) during long-term treatment. Longitudinal data were collected from genetically confirmed adult CF patients receiving CFTR-modulators. CFLD was diagnosed using conventional criteria combined with liver stiffness measurement (LSM). A total of 57 patients [56.1% male; median age at baseline (T0), 26 years (interquartile range [IQR], 23–35)] were included. Patients received lumacaftor/ivacaftor and/or elexacaftor/tezacaftor/ivacaftor for a median of 43 months (range, 15–123) until last assessment (T2). The prevalence of CFLD decreased from 15 (26.3%) at T0 to 8 (14.0%) at T2 (p = 0.016), and no new cases of CFLD were observed. Median LSM decreased from 6.2 (IQR 4.9–8.0) to 5.0 kPa (IQR 4.1–6.2) in the overall cohort (p < 0.001) and from 10.2 (IQR 6.8–13) to 6.2 kPa (IQR 5.0–12.4) in the CFLD subgroup (p = 0.025). Mild, transient fluctuations in liver enzymes occurred in 26.3% of patients. In conclusion, adults with CF receiving long-term CFTR modulators, showed improvement of liver disease assessed by ultrasonography and transient elastography. At the last assessment, half of the patients no longer met the criteria for CFLD. Full article

Ensuring thermal stability is a major concern in lithium-ion battery systems. Although phase change materials (PCMs) provide a passive approach for temperature regulation, they are limited by poor heat conduction and potential leakage during phase transitions. This study develops a novel composite PCM (CPCM) using paraffin (PA) as the matrix, copper foam (CF) as a conductive skeleton (10–30 pores per inch, PPI), and a low-melting-point alloy (LMA) as an encapsulant to prevent leakage. The effects of CF pore size on thermal conductivity, impregnation ratio, and leakage resistance were systematically investigated. Results show that CPCM with 10 PPI CF achieved the highest thermal conductivity (4.42 W·m⁻¹·K⁻¹), while LMA encapsulation effectively eliminated leakage. The thermal management performance was evaluated on both a single 18,650 LIB cell and a 2S2P module during rate discharging at 1C, 2C, and 3C. For the module at 3C, the 10 PPI CPCM significantly lowered the maximum temperature from 75.9 °C to 44.6 °C and critically reduced the maximum temperature difference between cells from 10.2 °C to a safe level of 1.2 °C, significantly improving temperature uniformity. This work provides a high-conductivity and leakage-proof CPCM solution based on LMA-encapsulated CF/PA for enhanced thermal safety and uniformity in LIB modules. Full article

Short carbon fiber-reinforced bio-based polyamide 11 (PA11) composites were developed in filament form for Additive Fusion Technology (AFT) 3D printing and benchmarked against injection-molded samples. Composites containing 15 and 25 weight percent (wt%) recycled carbon fibers (rCFs) were successfully extruded into 1.75 mm diameter filaments, whereas higher fiber contents (35 wt%) led to brittle filament failure. AFT printing with subsequent consolidation produced short fiber composites with highly aligned fibers, while injection molding generated more randomly oriented microstructures. Mechanical testing revealed that AFT-printed composites in the fiber direction achieved significantly higher stiffness and comparable tensile strength to injection-molded counterparts. At 25 wt% fiber content, AFT 0° specimens reached an axial tensile modulus of 14.5 GPa, about 32% higher than injection-molded samples (11.0 GPa), with similar axial tensile strength (~123 vs. 126 MPa). However, AFT specimens displayed pronounced anisotropy: transverse (90°) properties dropped to ~2.3 GPa for transverse modulus and ~46–50 MPa transverse tensile strength, near matrix-dominated levels. Impact testing showed orientation-dependent toughness, with AFT 90° samples at 15% fiber content achieving the highest impact energy (76 kJ·m⁻²), while AFT 0° samples were ~30% lower than injection-molded equivalents. Dynamic mechanical analysis confirmed that AFT 0° composites maintained higher stiffness up to ~80 °C. Overall, these results demonstrate that aligned short fiber filaments enable high stiffness and strength performance comparable to injection molding, with the trade-off of anisotropy that must be carefully considered in design. This study is the first to demonstrate the feasibility of combining bio-based PA11 with recycled short carbon fibers in AFT printing, thereby extending additive manufacturing to sustainable and high-stiffness short fiber composites. Full article

Coal-based solid wastes are used for carbon fixation, which can achieve the dual purpose of resource utilization of coal-based solid wastes and CO₂ storage, but carbon fixation has a negative impact on the rheological properties of filling slurry. This paper explores the effect of carbon fixation time on the carbon fixation performance and rheological properties of coal gangue (CG)–fly ash (FA) composite filling materials (CFS) through rheometer, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and other testing methods. The results show that, with an increase in the carbon fixation time, the carbon fixation amount of the CFS shows a trend of increasing first and then stabilizing. Considering the carbon fixation amount and rheological properties of the CFS together, the optimal carbon fixation time is 2 h. At this time, the carbon fixation amount of the CFS is 1.18%, and the yield stress and plastic viscosity are 155.93 Pa and 0.17 Pa·s, respectively. However, with a further increase in the carbon fixation time, the carbon fixation amount basically tends to be stable, mainly because the calcium ions in the CFS are gradually consumed by the reaction as the carbon fixation time increases. The research results are of great significance for improving the utilization of coal-based solid waste and CO₂ storage. Full article