Search Results (1,003)

The increasing demand for high-performance and multifunctional polymer materials has driven interest in improving the mechanical properties of polymer components produced through additive manufacturing. This study aims to systematically investigate and comparatively evaluate the effects of low-content nanofiller incorporation on the structural, thermal, and mechanical performance of PLA-based materials produced via fused deposition modeling (FDM), with a focus on identifying filler-dependent behavior under different loading conditions. In this study, polylactic acid (PLA) composites reinforced with 0.5 wt.% graphene (Gr) and 0.5 wt.% silver (Ag) nanoparticles, added separately, were produced using fused deposition modeling (FDM) and comparatively investigated. Each nanofiller was incorporated individually into PLA-based filaments, and standard test specimens were fabricated via 3D printing. Structural, thermal, and mechanical properties were evaluated using tensile, compressive, and three-point bending tests, along with SEM, EDS, XRD, FTIR, DSC, and TGA analyses. The results showed that pure PLA exhibited typical brittle behavior and a single-stage thermal degradation profile. The tensile strength of pure PLA was 41.93 MPa, and the flexural strength was 70.76 MPa. The addition of 0.5 wt.% graphene led to noticeable improvements, particularly in flexural properties, while only a minimal (almost negligible) increase was observed in tensile strength, with tensile strength increasing to 42.24 MPa (+0.74%) and flexural strength increasing to 110.78 MPa (+56.6%). In contrast, 0.5 wt.% Ag exhibited mixed and load-dependent mechanical behavior, with slight improvements in flexural strength but reductions in tensile and compressive properties, where tensile strength decreased to 22.13 MPa (−47.2%) while flexural strength increased to 112.06 MPa (+58.3%). Structural and thermal analyses indicated that both nanofillers did not significantly alter the PLA matrix chemically, while contributing to controlled changes in material properties primarily through physical interactions. The novelty of this work lies in the comparative evaluation of graphene and silver nanoparticle reinforcement at a fixed low loading level within FDM-processed PLA, combined with a comprehensive and correlated analysis of mechanical, structural, and thermal behavior on the same specimen sets, enabling a clearer understanding of filler-dependent performance mechanisms in additively manufactured nanocomposites. Overall, it was concluded that low-rate nanofiller additions, when properly dispersed, may lead to selective improvements in the performance of PLA-based composites depending on filler type and loading mode, and show potential for advanced engineering applications such as lightweight structural components, functional sensors, and additive-manufactured parts requiring tailored mechanical performance and multifunctionality. Full article

The increasing incidence of traffic accidents involving elderly pedestrians has highlighted the necessity for effective strategies to improve visibility in low-light environments. Conventional safety garments based on retroreflective materials or optical fibers exhibit limitations, including passive operation and low luminance. In this study, a textile-based organic light-emitting diode (OLED) safety garment with automatic light-sensing functionality is proposed to overcome these limitations. The OLED devices were fabricated on an ultrathin polyethylene terephthalate (PET) substrate and transferred onto a textile substrate to maintain flexibility and wearability. A light-emitting module incorporating a LilyPad Arduino and ambient light sensor was implemented to enable automatic illumination under low-light conditions. The fabricated textile-based OLED exhibited a luminance of 550 cd/m² at 4.5 V and maintained stable performance after transfer, with a T₅₀ lifetime of 485 h. Thermal analysis showed a minimal temperature increase of 2.9 °C after 5 h of operation, remaining below body temperature. Moreover, mechanical testing confirmed over 95% luminance retention after 2,000 bending cycles. The fabricated OLED-based luminous safety garment exhibited lightweight wearability with a total weight of 140 g and improved visibility at observation distances of up to 50 m under low-light conditions. These results indicate that the proposed OLED-based luminous safety garment can offer a viable solution for enhancing the safety of elderly pedestrians. Full article

Wildfires significantly affect wood properties and usability, yet their impact on hardwood species remains insufficiently understood. This study presents an exploratory characterization of moderately fire-affected pedunculate oak (Quercus robur L.) wood, combining physical, mechanical, chemical, and thermal analyses to evaluate depth-related changes within outer stem zones. Samples were collected from bark and from wood originating approximately 1 cm and 1–2 cm beneath the cambial region to evaluate radial variation associated with moderate surface fire exposure. The oven-dry density of fire-affected wood reached 720 kg·m⁻³, corresponding to values marginally below the literature reference ranges reported for unaffected oak wood. Bending strength decreased to 85.56 MPa, while compressive strength remained within or marginally above the literature reference (71.16 MPa), and Brinell hardness (42.75 MPa) stayed within the typical range for oak. Chemical and elemental analyses revealed degradation of polysaccharides and carbon enrichment in surface layers. FTIR and DSC analyses suggested partial hemicellulose degradation, structural modification of cellulose, and reduced thermal reactivity in outer stem regions. Despite these changes, the higher heating value (19.09–19.56 MJ·kg⁻¹) remained within the literature reference ranges reported for oak wood. The results suggest that under moderate surface fire conditions, fire-induced changes were primarily concentrated in outer stem layers, while inner wood retained properties comparable to the literature reference values for unaffected oak wood. These findings indicate that moderately fire-affected oak wood may remain suitable for selected material or energy-related applications following appropriate quality assessment and removal of thermally altered surface zones. Full article

Thermal modification (TM) enhances wood properties, but a gap exists in validating non-destructive testing (NDT) methods for thermally modified woods, as chemical and structural alterations may influence wave propagation. This study validated NDT wave propagation methods to estimate static MOE in Eucalyptus sp., Pinus sp., and Cedrela sp. woods subjected to TM (140 °C to 240 °C). Impulse excitation (longitudinal and flexural modes) and ultrasonic waves (90 kHz and 500 kHz) were used to obtain dynamic MOE, which was compared with static MOE obtained from three-point bending tests. Results showed high coefficients of determination (R² > 90%) across all species and treatments. Longitudinal excitation presented the highest accuracy (R² up to 97.96%); for ultrasound, 500 kHz was superior to 90 kHz. Control conditions and 240 °C resulted in the highest R² values, indicating greater predictability. As a novel contribution, robust quantitative correlations between NDT methods and static MOE were established specifically for thermally modified tropical woods. Validated methods provide reliable tools for industrial quality control and process optimization, enabling rapid non-destructive assessment without material sacrifice. Full article

This study reports the physicochemical characterization and structure–property relationships of rigid sheep wool/phenolic novolac panels developed as bio-based thermal insulation for building envelopes. Mixed Polish sheep wool was washed, mechanically opened, and formed into nonwoven mats, then impregnated with either neat or flame-retardant novolac resin to obtain lightweight boards with a fiber content of about 50 wt%. Elemental analysis, ICP-OES, FTIR spectroscopy, and laser and electron microscopy were used to evaluate the fiber composition, keratin structure, morphology, and fiber–matrix interfaces. Mechanical performance under three-point bending and shear, differential scanning calorimetry, thermogravimetric analysis, and transient hot-probe thermal-conductivity measurements were applied to link microstructure with functional behavior. Novolac impregnation transformed the compliant wool mat into self-supporting panels, increasing the flexural modulus to the 0.8–1.4 GPa range and flexural strength to approximately 48–52 MPa, while the shear modulus and work to failure rose by more than an order of magnitude relative to the loose wool reference. Thermal conductivity remained in a typical range for natural-fiber insulations (λ = 0.061 W·m⁻¹·K⁻¹ for the wool mat and 0.071–0.074 W·m⁻¹·K⁻¹ for the composites), although higher than that of expanded polystyrene. DSC and TGA confirmed that wool fibers remain thermally stable up to about 200–220 °C, that the novolac resin cures around 140 °C, with typical phenolic reaction enthalpies, and that both formulations generate high char residues of roughly 60–80 wt% at 600 °C under nitrogen, evidencing a strong charring propensity rather than directly quantifying fire resistance. Overall, the results position sheep wool/novolac panels between conventional bio-based insulation and structural composites and highlight their potential as sustainable, circular insulation materials for energy-efficient building envelopes. Full article

Metamaterials with tailored structural architectures enable negative thermal expansion through geometric mechanisms that counteract constituent-level positive expansion. This study evaluates the thermomechanical performance and structural limits of polymer and hybrid NTE lattices. We systematically classify the dominant kinematic mechanisms, including bimetallic bending, rotational squares, and re-entrant honeycombs, and quantify the inherent trade-offs between effective thermal contraction, structural stiffness, and mass efficiency. The analysis demonstrates that reliance on idealized linear–elastic and rigid-lever models leads to significant predictive discrepancies when evaluating the physical response of polymeric and hybrid prototypes. We establish that these deviations are fundamentally governed by localized stress singularities at multi-material interfaces and the profound thermoviscoelastic softening of polymers as they approach the glass transition temperature ($T_g$). We conclude that accurate prediction of the cyclic lifespan and dimensional stability of these systems requires a transition to coupled multiphysics frameworks. Specifically, integrating temperature-dependent cohesive zone modeling and time–temperature superposition principles is essential for capturing interfacial delamination and thermal ratcheting in high-performance polymeric NTE metamaterials. Full article

Clamp band separation mechanisms are widely used in spacecraft interfaces, and the clamp band preload is a key factor governing both connection reliability and separation performance. The conventional torque-control method is susceptible to friction-induced preload non-uniformity in clamp band separation mechanisms. To overcome this limitation, thermal preloading has been proposed as an alternative installation method. In this paper, a thermo-mechanical analytical model is established for clamp band separation mechanisms during thermal preloading based on curved-beam and thin-shell theories. Theoretical analysis shows that the preload distribution can be divided into three characteristic zones: a stick zone, a slip zone, and a separation zone. In the stick zone, the preload remains constant and is mainly governed by thermal stress and structural relative stiffness. In the slip zone, friction dominates the load transfer, leading to a non-uniform preload distribution. In the separation zone, local disengagement occurs near the clamp band joint end due to the eccentricity-induced bending moment. The proposed model is validated by finite element simulations, and parametric studies are conducted to reveal the effects of friction coefficient and structural geometric parameters on preload distribution. Based on the theoretical model, a zoned-heating method is proposed to improve preload uniformity, providing a useful reference for optimizing the thermal preloading method. Full article

New partially bio-based, waste-derived composites are manufactured from date palm surface fibers (DPSF), waste coffee filters (CFP), and disposable medical isolation gowns (MIG). These three disposable raw materials fill landfills and create an environmental problem. Therefore, the objective of this current study is to use such materials in creating promised thermal insulation and sound absorption boards. Six hybrid composites with different compositions were made using Polyvinyl acetate (PVA) wood adhesive as a binder. Three of them were made of DPSF and MIG, and the other three were composed of DPSF and the CFP. Different tests were performed on the developed composites, such as thermal conductivity measurements, sound absorption and noise reduction determination, surface morphology image analysis, thermogravimetric analysis, and three-point bending tests. The results showed that the thermal conductivity coefficients for the hybrids DPSF + MIG and DPSF + CFP are in the ranges 0.0493–0.0613 W/(m·K) and 0.052–0.065 W/(m·K), respectively, over the temperature range 24–82 °C. The sound absorption coefficient (SAC) is greater than 0.4 for all composites at frequency bands greater than 500 Hz. The noise reduction coefficient (NRC) is ≥0.45 for all composites. Surface morphology images of the composites were also reported. The results also show that the composites are thermally stable at temperatures up to 258.3 °C. The flexural modulus ranges between 5.0 and 8.46 MPa for the medical isolation gown composites and 2.49 and 5.57 MPa for the coffee filter paper composites. The hybrid composites have a lower moisture content of 0.51% to 2.5%. These promising results support the use of these composites for thermal insulation and sound absorption in building construction as alternatives to conventional thermal insulations derived from crude fuels. Full article

There is a growing demand for extreme miniaturization and enhanced sensitivity in next-generation sensing systems, including wearable devices and bioelectronics. Such advanced platforms require highly conductive, biocompatible, and mechanically robust architectures capable of conforming to dynamic surfaces. Conventional metallic thin-film fabrication techniques have reached their fundamental physicochemical limits, often suffering from suboptimal mechanical strength, complex multi-step processing, and high costs. In contrast, additive manufacturing methodologies offer streamlined microfabrication, yet traditional printing methods frequently struggle with low-viscosity constraints, insufficient metal loading, and significant material losses. This paper covers the morphological fidelity, mechanical resilience, and electrical performance of rheologically tailored, high-concentration (above 90%) gold nanoparticle paste deposited via Ultra-Precise Dispensing (UPD) technology. The capability of the UPD system to print complex, high-density fractal geometries with linewidths down to 5 μm is evaluated on both rigid and flexible substrates, glass and polyimide, respectively. The mechanical structural integrity of these conductive traces is characterized under initial 360-degree bending tests. Finally, the electrical stability and thermal response of a printed proof-of-concept temperature sensor are evaluated. The printed fractal microstructures exhibit good resolution and the fabricated sensor demonstrates good stability, displaying a linear thermal response with a temperature coefficient of resistance of 1.98·10⁻³ °C⁻¹, validating this combined material-deposition approach for microelectronics. Full article

This paper presents a numerical comparative study on the ignition characteristics of straight-channel and U-bend micro catalytic combustors, with particular focus on the role of inlet velocity. A two-dimensional computational fluid dynamics model with coupled gas-phase and surface catalytic reaction kinetics for propane combustion is developed using a fluid simulation program ANSYS Fluent. The catalyst coating (Pt/Al₂O₃) is modeled as a zero-thickness reaction surface, and the U-bend design features an uncoated recirculating channel to ensure identical catalyst loading between the two configurations. Simulations are conducted over an inlet velocity range of 0.25–8 m/s. Key ignition and combustion metrics including ignition temperature, ignition time, maximum combustion temperature, heterogeneous reaction contribution, and thermal/species field distributions are systematically compared. Results reveal a crossover in relative performance depending on flow regime. At low velocities (≤2 m/s), the straight-channel combustor exhibits lower ignition temperatures; at high velocities (≥4 m/s), the U-bend design achieves superior ignition performance with lower ignition temperatures (e.g., 526 K vs. 555 K at 8 m/s) and higher combustion temperatures (1726 K vs. 1474 K at 8 m/s). However, the straight-channel combustor consistently yields shorter ignition times across all velocities (25.9–108.6 s) compared to the U-bend (52.6–145.2 s). The heterogeneous reaction contribution decreases with increasing inlet velocity for both designs, with the straight-channel maintaining higher values than the U-bend. The U-bend achieves higher maximum temperatures due to enhanced heat recirculation, particularly at high flow rates. The findings suggest that the U-bend configuration is advantageous for high-flow-rate applications requiring low ignition temperatures and high combustion temperatures, whereas the straight-channel design is preferable for rapid cold-start scenarios. Full article

An analytical model is developed to investigate the bending performance of composite I-beams with corrugated steel web (CSW) under thermo-mechanical coupling. The CSW is idealized as an equivalent orthotropic plate according to the principle of stiffness equivalence and heat conservation. The steady-state temperature field of the composite I-beam cross-section is obtained using the finite difference method. Based on thermoelastic theory, analytical solutions for the stresses and displacements of the composite beam subjected to thermo-mechanical loads are derived by the eigenvalue method and transfer matrix method. The results obtained in this study are compared with available experimental results from a steel–concrete composite bridge deck, ABAQUS (version: 2023) finite element simulations, and the temperature distributions specified by JTG D60-2015, AASHTO 2017 and DIN 101. In addition, the superposition principle for thermo-mechanical conditions is verified by the analytical forms of stress and displacement solutions. And the research results show that increasing interfacial stiffness restrains the relative thermal deformation between the concrete slab and the steel I-beam, thereby increasing temperature-induced stresses and deformations. Finally, a partial thermal insulation method is proposed to mitigate temperature gradients, thermal stresses and upward thermal deformation, thereby improving the service performance of the composite beam under thermal actions. Full article

This paper investigates the thermal buckling behavior of a four-edge simply supported bimodular functionally graded rectangular thin plate subjected to thermal loads. Unlike existing studies, this work introduces the bimodular effect into the thermal buckling analysis of functionally graded thin plates for the first time, accounting for the influence of tension–compression modulus on the critical temperature difference. The problem is challenging due to the complexity of materials and the nonlinearity of structural thermal buckling. For the theoretical analysis, we propose a simplified mechanical model which contains the four important assumptions: there exists a neutral plane in bending; the influence of shear stresses may be neglected; the membrane effect and bending effect are considered separately; and there are two different buckling regimes: a compression-dominated pre-buckling state and a bending-dominated post-buckling state. Three types of thermal loading cases are considered, including uniform temperature rise, linear temperature gradient through the thickness, and nonlinear temperature distribution satisfying Fourier’s law of heat conduction. Within the framework of the simplified mechanical model, the pre-buckling membrane forces, equilibrium equations, and stability equations are derived, thus obtaining a closed-form analytical expression for the critical buckling temperature difference under three different temperature rise modes. The reliability of the present analytical model is validated through comparison with finite element results. Furthermore, a detailed parametric study is conducted to reveal the influences of aspect ratio, width-to-thickness ratio of plate, bimodular indices, and gradient parameters of materials on the critical temperature difference. The results provide a theoretical basis for the thermal stability design of bimodular functionally graded plates operating in high-temperature environments. Full article

Carbon fiber-reinforced polymer (CFRP) composites are widely employed in the aerospace industry due to their excellent properties such as high specific strength and corrosion resistance. However, the delamination and tearing of composites are prone to occur in the machining of CFRP, which significantly affect its performance. The existing laser-assisted cutting model generally simplifies the machining process into high-temperature conventional cutting, and only reflects the thermal effect by modifying the material parameters. The core selective ablation characteristics of laser–CFRP interaction are completely ignored, and the unique mechanical behavior of bare fiber under a large cutting angle is not modeled, and the quantitative correlation between cutting force evolution and machining damage is lacking. In this study, an innovative method of partially exposing fibers is proposed to simulate laser-assisted machining. A micromechanical model is developed to analyze the removal mechanisms of different phases during CFRP processing, and a cutting force prediction model from the micro to macro scale is also established. At the micro-scale, a micromechanical model for fiber cutting in orthogonal machining of CFRP is constructed based on the elastic foundation beam theory. The results show that the proposed cutting force prediction model has high reliability, and the relative error between the predicted value and the experimental measured value is only 7.81%~8.99%. All experiments were repeated three times. Statistical analysis showed that the repeatability of the results was excellent. Compared with conventional cutting, laser-assisted cutting fundamentally changed the failure mode of the fiber from matrix-constrained crushing fracture to controllable free-end large-deflection bending fracture. This transformation leads to a smoother and more regular fiber fracture surface, which effectively inhibits fiber breakage, matrix tearing, and fiber–matrix interface debonding. Quantitative analysis confirms that under laser-assisted processing conditions, the matrix tearing length is positively linearly correlated with the cutting depth, cutting speed, and bare fiber length. Full article

Iron-based shape memory alloy (Fe–SMA) rebars can generate internal prestress in cement-based members after restrained thermal activation; however, the temperature actually reached by embedded rebars in cracked UHPFRC is difficult to infer from exposed bar segments. This study investigates electrical resistance activation of 4% prestrained Fe–SMA rebars embedded in pre-cracked UHPFRC beams and clarifies the activation-control problem by combining thermocouple measurements with a calibrated two-dimensional electro-thermal simulator. Twelve beams (150 × 150 × 600 mm) containing either Dramix 3D or Dramix 4D hooked steel fibers were first loaded in three-point bending to a mid-span displacement of 4 mm. The 4D series reached a 9.47% higher average pre-cracking load, confirming that fiber geometry modified the cracked state before heating. During activation, the exposed rebar segment reached 200 °C after approximately 77 s, whereas the embedded working segment reached the same target only after approximately 213 s; at that moment, the exposed segment was already close to 350 °C. The calibrated simulator reproduced the target activation time with an error of approximately 3 s and visualized the localized heat transfer from Fe–SMA to UHPFRC. The results demonstrate that activation control based only on exposed-bar temperature may cause under-activation of the embedded reinforcement, and that direct internal temperature monitoring is required for reliable Fe–SMA activation in cracked UHPFRC members. Full article

Wood–polymer composites (WPCs) produced through monomer impregnation have attracted increasing interest as a strategy to improve the durability and performance of wood materials. However, the limited permeability of certain wood species often restricts the effectiveness of impregnation treatments. This study investigates the use of microwave (MW) pretreatment as a drying and microstructural modification step to enhance methyl methacrylate (MMA) impregnation and in situ polymerization in maritime pine (Pinus pinaster) heartwood specimens. Wood specimens were subjected to MW treatment of 700 W and 5 min cycles prior to vacuum-pressure impregnation with MMA and subsequent thermal polymerization. Scanning electron microscopy and treatability parameters confirmed that MW pretreatment increased wood impregnability by generating microcracks and improving monomer penetration, thereby resulting in higher polymer retention and a higher weight percentage gain. As a result, the combined MW+MMA treatment produced a more homogeneous distribution of polymethyl methacrylate within the wood structure. The modified specimens showed a substantial reduction in water absorption and the highest water repellence efficiency among the studied groups, while dimensional stability improved to a lesser extent. In addition, the combined treatment significantly increased bending strength and stiffness, indicating an effective reinforcement of the wood structure through polymer loading. These results demonstrate that MW pretreatment is an efficient strategy to improve the treatability of maritime pine heartwood and to enhance the performance of MMA-based WPCs. Full article