Search Results (1,504)

Polyether Ether Ketone (PEEK) is a high-performance polymer increasingly utilized in additive manufacturing due to its exceptional thermal, chemical, and mechanical properties. Thus, they are used to produce aerospace brackets, fuel system parts, seals, compressor valve plates, etc. This study investigates the mechanical performance of both neat PEEK and glass fiber-reinforced PEEK (PEEK + GF) composites fabricated via fused deposition modeling (FDM). The effects of print speed, print orientation, and post-heat treatment were systematically evaluated. Among the tested orientations, the 0° print direction with post-heat treatment at 250 °C yielded highest tensile strength of ~80 MPa, outperforming the 45° and 90° orientations. Print speeds ranging from 5 to 20 mm/s and annealing temperatures between 250 °C and 300 °C significantly influenced material properties. For neat PEEK, both tensile strength and microhardness improved with increasing print speed and post-heat treatment, peaking at 20 mm/s and 250 °C. However, annealing at 300 °C led to performance degradation, attributing to gas-induced porosity within the material. The PEEK + GF composites achieved a maximum ultimate tensile strength (UTS) of approximately 83 MPa under the same optimal conditions (20 mm/s print speed and 250 °C post-treatment). This enhancement is attributed to improved fiber alignment along the print path, increased crystallinity, and superior interfacial bonding. Notably, the composites did not exhibit the microstructural damage observed in neat PEEK at the higher annealing temperature. Full article

Polymer nanocomposites offer significant potential for improving the strength-to-weight ratio and dynamic behavior of drone blades. This study examines the vibration characteristics of tapered aramid (Kevlar)/epoxy composite blades reinforced with nanocarbon fillers—graphene (2D), multi-walled carbon nanotubes (MWCNTs, 1D), and fullerene (0D)—to determine the most effective filler for enhancing stiffness and operational stability. The laminated blades (300 mm length, 200 mm width, root thickness 13 mm, tip thickness 8 mm) incorporate ply drop-offs and a central honeycomb core. Modeling was performed using classical laminate plate theory integrated with the finite element method (FEM) in MATLAB (R2016a). Under clamped–free–free–free boundary conditions, the study considered rotational speeds of 750–2250 rpm, setting angles of 30–60°, various fiber orientations, and nanofiller contents of 0–10 wt.%. The results indicate that while the setting angle minimally affects natural frequency, it significantly influences damping in modes (1,2) and (2,1). Increasing nanofiller content improves stiffness, with optimal performance observed near 5 wt.%. At 1500 rpm in mode (1,1), MWCNTs provided the greatest enhancement. Overall, MWCNTs exhibited superior stiffness improvement and rotational stability compared to other fillers. Full article

This paper presents an experimental and numerical study on the effect of steel fiber distribution on the flexural behavior of self-compacting mortars (FRSCMs). Six FRSCM mixtures were modeled in ABAQUS as prismatic specimens (40 × 40 × 160 mm³) subjected to static three-point bending. The methodology involved two steps: (i) preparation of six mortar variants composed of three layers with different hooked steel fiber dosages (20, 30, and 40 kg/m³ for M20, M30, and M40) assembled in various configurations to study fiber distribution effects; (ii) numerical modeling of prismatic specimens in ABAQUS, using structured meshing with C3D8R hexahedral elements. Each layer was meshed separately with aligned nodes to ensure proper assembly. Our results highlight the strong influence of fiber distribution: despite identical fiber content (90 kg/m³ of hooked steel fibers), flexural strength varied across beam configurations. Layered casting led to an increase in flexural strength of up to 71.83% compared to the reference. The numerical predictions closely matched the experimental results, with relative errors ranging from 1% to 8.13% for most variants, demonstrating the reliability of the model. The larger discrepancies observed for specimens M324 and M342 are attributed to the limitation of the study to the elastic domain, as damage and plasticity effects were not included in the simulations. The distribution and orientation of fibers (particularly steel fibers) in a cementitious matrix, namely concrete or cement mortar, has been the subject of several studies aimed at determining the best mechanical performance of fiber-reinforced concrete. The proposed modeling approach of bending mechanical behavior allows us to predict the effects of fiber distribution in fluid mortars and reinforced self-compacting mortars, thereby reducing the need for extensive experimental testing. It also represents a significant improvement over existing approaches reported in the literature. Full article

The development of durable road sealing materials capable of maintaining performance under combined mechanical and climatic loads remains a critical challenge for modern infrastructure. Conventional bitumen-based sealants exhibit limited resistance to high-temperature deformation, cracking, and adhesion degradation, leading to reduced service life. This study proposes a rheology-oriented approach to the design of polymer-reinforced bituminous sealants based on penetration-grade bitumen 50/70 and 70/100 modified with styrene–butadiene–styrene (SBS) copolymers up to 9 wt.% and reinforced with cellulose fibers. The rheological behavior of the developed composites was investigated using dynamic shear rheometry to determine the complex shear modulus (G*), phase angle (δ), and temperature–frequency dependencies in the range from −20 to +90 °C, while infrared spectroscopy was employed to assess intermolecular interactions. Adhesion performance was evaluated at different temperature. The modified systems demonstrated a 5–10-fold increase in G*/sinδ enhanced high-temperature stability, and improved adhesion and crack resistance compared to base bitumen. Based on the obtained rheological and performance indicators, the developed composition was approved for subsequent pilot-scale testing and field validation as a promising road sealing material. Full article

The increasing demand for sustainable materials has accelerated the development of environmentally friendly filaments for fused deposition modeling (FDM). In this study, the surface roughness and thermal degradation behavior of sustainable PLA-based filaments, including PLA, recycled PLA (Re–PLA), and wood-filled PLA (Wood–PLA), were systematically investigated under different FDM printing conditions. A full factorial experimental design was employed to identify the dominant processing parameters and optimize surface quality. Surface roughness was evaluated using values Ra, Rz, and Rq parameters measured on three different surface orientations (top surface at 0°, top surface at 45°, and side surface). Scanning electron microscopy (SEM) was used to examine the relationship between roughness measurements and surface morphology, while thermogravimetric analysis (TGA) was performed to evaluate the thermal degradation behavior of the filaments in relation to printing temperature. The results have shown that filament material is the most important parameter affecting surface roughness. While Wood–PLA exhibited the highest roughness due to fiber-induced surface heterogeneity, recycled Re–PLA showed moderate surface irregularities resulting from degradation compared to pure PLA. Despite a rougher filament surface prior to production, recycled PLA exhibited a surface morphology similar to that of pure PLA after printing, influenced by the processing parameters. Furthermore, SEM findings indicated that the Ra parameter predominantly reflects macro-scale surface topography, while local microstructural heterogeneity can be better characterized by complementary roughness parameters such as Rz. These findings support optimizing printing conditions to improve surface quality and more widespread use of sustainable FDM filaments in applications where surface roughness is critical. Full article

The research gap addressed in this study is the lack of a transparent and quantitative evaluation of the governing parameters influencing deflection behavior in reinforced concrete (RC) beams reinforced with glass fiber-reinforced polymer (GFRP) bars. The objective of this study is to identify and quantify the relative importance of the key parameters controlling deflection in GFRP-reinforced RC beams, which exhibit fundamentally different behavior compared to steel-reinforced beams due to the linear-elastic response of GFRP bars until rupture. To achieve this objective, the method integrates explainable artificial intelligence (XAI) techniques, including SHapley Additive exPlanations (SHAP), Pearson correlation heatmap, scatter plot analysis, and sensitivity analysis—with experimental structural data obtained from beams with three different concrete strength classes. The main contribution of this study is the quantitative ranking and interpretation of the governing parameters affecting deflection behavior through a transparent and data-driven framework. Key parameters—including elastic modulus (Ec), compressive strength (fck), creep coefficient (φ), failure moment (Mexp), effective moment of inertia (Ieff), and applied load (P)—were evaluated. The results consistently indicate that stiffness- and capacity-related parameters dominate the deflection response. Sensitivity analysis reveals that the failure moment (Mexp) is the most influential parameter, contributing approximately 23% of the total relative influence on deflection, followed by compressive strength (fck) and cracking-related parameters. Pearson correlation heatmap and scatter plot analyses further confirm strong relationships between deflection and Ec, fck, φ, and Ieff. The proposed framework improves the interpretability of deflection prediction in GFRP-reinforced RC beams and provides a transparent basis for serviceability-based structural design and performance-oriented assessment. Full article

The precursor infiltration and pyrolysis (PIP) route is widely adopted to fabricate carbon fiber-reinforced silicon carbide (C_f/SiC) composites; however, the atomic-scale restructuring of the pyrolytic carbon/silicon carbide (PyC/SiC) interface during ceramization—and its impact on mechanical integrity—remains elusive. Here, reactive molecular dynamics (ReaxFF MD) simulations elucidate the coupled thermochemical–mechanical evolution of polycarbosilane (PCS) precursors on PyC substrates with orientation angles (OAs) of 0°, 25°, 55°, and 85°. Dynamic pyrolysis triggers a pivotal transition from sp² to sp³ hybridization at the interface. High-OA substrates (55° and 85°) present a dense population of reactive edge sites, fostering extensive cross-interfacial covalent bonding. Subsequent shear loading reveals that these pyrolysis-induced chemical bridges govern failure modes, shifting from interlayer sliding dominated by weak non-bonded interactions (0°) to ductile fracture featuring uniform plasticity and crack deflection. The OA = 55° interface attains a theoretical peak shear strength of 15 GPa and exhibits the most favorable combination of high strength and ductile failure under tensile loading, owing to an optimal balance between reactive site availability and interlayer steric openness. In contrast, the OA = 85° interface, despite comparable peak stress, fails via brittle crack penetration into the SiC matrix. By correlating atomistic structure with macroscopic performance, this study provides a bottom-up framework for engineering C_f/SiC composites via interfacial texturing and optimized pyrolysis protocols. Full article

This study discusses the thermal behavior of glass fiber-reinforced SiO₂-filled polymers in dry milling. Focus is put on the effects of the addition of SiO₂ particles on cutting-generated heat and the fresh-surface integrity of the composite. Cutting trials were developed using a Spinner U-620 5-axis CNC machine. Real-time temperature histories owing to the dry milling of both Glass/Epoxy and Glass/Polyester composites were recorded using thermocouples preinstalled within the composite specimen. SEM inspections were conducted to elucidate the prevailing failure mechanisms during the material removal process. The results showed that fiber orientation significantly dominated thermal responses. Cutting perpendicular to the fiber orientation results in a critical temperature, while the addition of SiO₂ particles effectively reduces the temperature overlaps and peak values, causing the temperature to drop. The addition of SiO₂ serves to keep the temperature sufficiently lower than the glass transition point of the matrix. However, increasing the feed rate from 50 mm/min to 150 mm/min reduced the overall temperature during cutting. Under similar cutting conditions, Glass/Polyester composites exhibited lower peak temperatures and heat quantities than Glass/Epoxy regardless of the feed rate and fiber orientation. Observations revealed that fiber orientation and matrix type strongly influence the intensity of the thermal and mechanical damages induced. These findings suggest that the addition of silicon dioxide can adjust the thermal balance in dry cutting and may improve the composite’s structural integrity significantly. Such a composite design promotes the heat control of sensitive parts in advanced engineering applications. Full article

Reinforcement congestion in reinforced concrete (RC) beam–column joints creates constructability difficulties and may compromise seismic performance due to inadequate consolidation and confinement. Although fiber-reinforced concrete (FRC) has been widely investigated as an alternative to dense transverse reinforcement, current seismic codes (e.g., ACI 318-19, TBEC-2018) do not provide explicit provisions to quantify the interaction between steel fiber dosage and joint shear demand. This study examines the feasibility of partial stirrup replacement through a hybrid confinement strategy that preserves minimum transverse reinforcement for bar stability while using steel fibers to compensate for joint shear demand. Two large-scale exterior beam–column assemblies were tested under quasi-static reversed cyclic loading: a code-compliant reference specimen and a hybrid specimen incorporating minimum stirrups with 0.5% hooked-end steel fibers. The hybrid specimen exhibited improved stiffness retention and energy dissipation without brittle joint shear failure. A validated nonlinear finite element model (VecTor2) was used to conduct a parametric investigation covering beam reinforcement ratios of 1.3–1.5% and fiber volume fractions of 0.5–1.2%. Results demonstrate a consistent non-linear interaction between beam-induced joint shear demand and fiber contribution. This interaction is formulated through a demand-based exponential relationship that links required steel fiber dosage to joint shear demand while preserving minimum transverse reinforcement for longitudinal bar stability. The proposed model provides a design-compatible framework for hybrid fiber-stirrup confinement in seismic design practice. Full article

Spent coffee grounds (SCGs) and lignin-derived binders, such as ammonium lignosulfonate (ALS), are increasingly being explored as renewable resources to reduce reliance on conventional formaldehyde-based resins in wood-fiber biocomposites. Although prior work has shown that SCG–ALS adhesive systems can achieve promising mechanical performance, two practical aspects essential for industrial applications and circular design remain insufficiently explored: a predictable and reproducible visual appearance and credible end-of-life options. In this study, sustainable wood-fiber biocomposites bonded with SCG and ALS were assessed from an aesthetic performance and end-of-life perspective. Color was quantified in the CIE L*a*b* (CIELAB) space and expressed as total color difference (ΔE*) relative to a reference panel. Increasing total SCG + ALS content from 40 to 75 wt.% based on oven-dry fibers produced pronounced darkening, with lightness decreasing from L* = 47.1 to 34.3 and ΔE* increasing from 18.38 to 32.51. Short-term composting behavior was explored by embedding fragments from formulations with 40–60 wt.% total SCG + ALS (based on oven-dry fibers; equal SCG/ALS shares) into a mixed organic substrate adjusted to an initial C/N ≈ 30 and monitored for 30 days in pots and trays. The process remained predominantly mesophilic (≈14–22 °C); nevertheless, visible microbial colonization and progressive surface degradation were observed, indicating susceptibility to biological activity under moist, nutrient-rich conditions. Overall, the results show that SCG–ALS content strongly governs the visual identity of the biocomposites and suggest composting-oriented routes as a potential end-of-life direction at an exploratory level, while highlighting the need for standardized compostability assessment and longer-term monitoring to substantiate circularity claims. Full article

The increasing demand for sustainable and environmentally friendly construction materials has spurred interest in biopolymer composites reinforced with agricultural waste. Rice husk (RH), a byproduct of rice milling, is abundant and rich in lignocellulosic fibers and silica, making it excellent for use in fiber-reinforced biopolymers. The novelty of this study lies in its integrated and construction-oriented evaluation of rice husk (RH)-reinforced biopolymers, combining mechanical, thermal, environmental, and economic perspectives within a single framework. The study introduces a novel comparative approach by benchmarking multiple polymer matrices-including PP, recycled HDPE, epoxy, PLA, and bio-binders-under unified quantitative performance criteria. Another key novelty is the identification of the dual functional role of silica-rich RH in simultaneously enhancing structural strength and flame retardancy while contributing to carbon emission reduction. With a high silica content (15–20%) and lignocellulosic structure, RH serves as a natural filler that enhances the performance of polymer matrices such as polypropylene (PP), epoxy, polylactic acid (PLA), and recycled polyethylene. Mechanically, RH-reinforced composites demonstrate significant improvements in tensile, flexural, and impact strength. For example, PP composites with NaOH-treated RH and coffee husks achieved tensile strengths between 27.4 MPa and 37.4 MPa, with corresponding Young’s modulus values ranging from 1656 MPa to 2247.8 MPa. Recycled HDPE-RH blends reached tensile strengths up to 74 MPa and flexural values of 39 MPa, validating their structural applicability. Epoxy matrices embedded with 0.45 wt.% RH nanofibers showed degradation thresholds of 411 °C and 678 °C, reflecting substantial thermal resistance. Flame retardancy is further improved by the presence of RH biochar, which leads to reduced peak heat release rate (PHRR) and enhanced char formation. In building insulation applications, RH-based composites exhibit low thermal conductivity values between 0.08 and 0.14 W/m·K, contributing to energy efficiency. Economically, RH reduces material costs by 30–40%, while environmentally, its integration lowers carbon emissions in PP composites by up to 10%, and promotes biodegradability. Despite challenges such as moisture absorption and interfacial adhesion, these can be mitigated through alkali treatment, compatibilizers (e.g., MAPP), or hybrid reinforcement strategies. Full article

This study examines the combined effects of styrene–butadiene rubber (SBR) latex and fiber reinforcement on the mechanical and electrical properties of a high-performance fiber-reinforced composite (HPFRC). Mixtures incorporating steel fibers (SF, 0–4.5%), carbon fibers (CF, 0–1%), and hybrid SF/CF systems were evaluated, with 10–20% of the mixing water replaced by SBR. Electrical resistivity, rheological behavior, mechanical properties, and durability-related parameters were assessed and compared with plain and fiber-reinforced mixtures. Results showed that SBR significantly improved rheological behavior, flexural performance, durability, and interfacial bonding, while moderately enhancing compressive strength. The incorporation of fibers led to reduced electrical resistivity, with CF being more effective than SF, and the lowest resistivity of 4 Ω·m was achieved using a hybrid system of 0.25% CF and 1.5% SF. The addition of SF up to 1.5% increased compressive strength by up to 21%, whereas CF at 0.5% yielded the highest strength of 120 MPa. Durability indicators, including water absorption, sorptivity, and ultrasonic pulse velocity, were significantly improved at low SBR and fiber dosages. Interfacial treatment with SBR enhanced slant shear and pull-off strengths by up to 75% and 121%, respectively, confirming the effectiveness of polymer modification for multifunctional and repair-oriented HPFRC applications. Full article

To increase printing speed and quality, a route consisting of using two sequential coextruders to form impregnated fiber immediately before feeding it to the printer. Such an approach, aimed at allowing the use of the most common industrial 12K carbon fibers for additive manufacturing, prevents damage to composite fibers during transportation, storage, and loading. An elaborate system was used to prepare carbon fibers impregnated with polypropylene, ethylene vinyl acetate, and their blends. The used scheme allows the production of composite fibers containing from 60 to 80 wt. % of carbon fibers. It was found that the elastic modulus of the composite fibers is close to those for raw carbon fibers and does not depend on the used polymer. It shows that the used carbon fiber path in the polymer melt and two sequential calibrating nozzles result in a high degree of orientation of the elementary filaments in the fiber at impregnation and maintain the elastic properties of the carbon fiber in the resulting composite. The tensile strength of the composite fibers depends on the polymer content in the composite fiber; the highest tensile strength was observed for fibers impregnated with ethylene vinyl acetate when increasing the coextrusion temperature up to 220 °C, which results in a composite fiber with a polymer content of 30 wt. %. A decrease in the polymer content in composite fibers results in a decrease in strength. Full article

Recycled cellulosic fiber (RCF) composites offer significant potential to reduce environmental burdens associated with virgin fiber production; however, their broader adoption remains limited by feedstock variability, recycling-induced degradation, and uncertainty regarding long-term performance. This review critically synthesizes recent advances in RCF composites using a structure–processing–performance–sustainability framework, treating recycled fibers as secondary materials with distinct morphological, chemical, and mechanical characteristics rather than direct substitutes for virgin reinforcements. Emphasis is placed on the effects of fiber shortening, surface damage, moisture sensitivity, and altered surface chemistry on interfacial adhesion, load transfer efficiency, durability, and failure mechanisms. The analysis reveals that many reported performance discrepancies arise from poorly defined structure–property relationships and the absence of standardized characterization, grading, and durability testing protocols for recycled fibers. Addressing these gaps enables more reliable predictive modeling and application-specific material design. Beyond mechanical behavior, the review evaluates various critical factors for integration into higher-value applications such as durability under realistic service conditions, including environmental aging, fire performance, and long-term stability. Emerging strategies such as hybrid reinforcement, environmentally benign surface functionalization, smart functionalities, and recyclable or bio-based matrices are assessed for their potential to enhance multifunctionality and circularity. Overall, the findings indicate that RCF composites can meaningfully contribute to circular material systems if materials design, performance validation, and life-cycle assessment are integrated systematically. Advancing standardized evaluation and aligning materials innovation with circular economy principles are essential to transition RCF composites from downcycled applications to reliable, performance-oriented components in sustainable engineering systems. Full article

Bamboo shoots are a valuable source of dietary fiber and antioxidants; however, their high levels of soluble oxalates and uric acid require reduction prior to consumption. This study evaluated the effects of washing, soaking, and boiling on soluble oxalate content, uric acid content, antioxidant activity, and the phenolic and flavonoid profiles of bamboo shoots. Washing resulted in only slight reductions in soluble oxalates and uric acid. Prolonged soaking (7–10 h) produced more pronounced decreases, while extended boiling (60 min) was the most effective treatment, reducing uric acid and soluble oxalate levels by 86% and 89%, respectively. Processing also led to significant reductions in total phenolic content, antioxidant activity, and individual phenolic and flavonoid compounds, primarily due to leaching and thermal degradation. FTIR analysis indicated that processing mainly affected soluble components, whereas the core polysaccharide structure remained relatively stable. After selecting the optimal pretreatment, the resulting dried powders exhibited markedly reduced antinutritional factors while maintaining desirable nutritional, physicochemical, and functional properties. These findings demonstrate that processed bamboo shoot powder can be safely incorporated into food products and has strong potential as a functional ingredient for health-oriented applications. Full article