Search Results (902)

Natural fiber-reinforced thermoplastic composites have gained increasing attention due to the abundant availability of natural fibers, their ability to effectively reinforce polymer matrices, and the resulting partial biodegradability of the final material. This study presents numerical modeling strategies for investigating the manufacture of spherical caps made from polypropylene composites reinforced with woven flax fabrics. The investigation considers both cold incremental forming and stretch-forming processes, performed either with or without the support of a partial counter die. Building on the findings of a previous experimental study conducted by the authors on compression-molded laminates manufactured using untreated woven flax fabrics and without coupling agents and formed without localized heating, numerical predictions are compared with experimental results in terms of final geometry, forming forces, and failure mechanisms. The findings highlight the need for a thorough understanding of material behavior to fully exploit finite element analysis as a reliable predictive tool in the forming of these innovative lightweight composite structures. Full article

Hybrid composites combining natural and synthetic fibers have emerged as promising materials for lightweight ballistic protection systems due to their ability to balance mechanical performance, energy absorption, and sustainability. This study investigates the influence of stacking sequence on the ballistic response of epoxy hybrid composites reinforced with raffia and carbon woven fabrics subjected to 9 mm projectile impact. Four stacking-sequence configurations were investigated: alternating laminates (R₂C₂)₃ and (C₂R₂)₃, and block laminates R₆C₆ and C₆R₆, all containing identical reinforcement contents. Ballistic response was evaluated through impact and residual velocities, velocity reduction, absorbed energy, energy absorption efficiency, momentum reduction, and Doppler radar velocity profiles. All laminates were completely perforated but maintained their structural integrity after impact, without catastrophic fragmentation. The results showed that architectures with carbon fiber layers positioned at the impact face, namely (C₂R₂)₃ and C₆R₆, exhibited the lowest residual velocities and the highest absorbed energies, reaching 136.8 J and 135.4 J, respectively. Energy absorption efficiencies ranged from 16.6% to 19.1%, indicating similar ballistic responses among all configurations. Statistical analysis revealed no significant differences among the investigated architectures (p > 0.05). Overall, the results indicate that the impact-face reinforcement exerts a secondary influence on ballistic response, whereas the total reinforcement content governs energy dissipation during projectile penetration. Full article

The extreme temperature cycling (−196 °C to 125 °C) and intense ultraviolet radiation on the lunar surface pose significant degradation risks to polymeric materials and their fibrous reinforcements. This work presents a comparative durability assessment between basalt fiber fabric and basalt rock powder after accelerated cyclic thermal shock treatments and UV exposure, aiming to establish a fundamental durability database for basalt fibers as candidate reinforcements for future polymer-matrix composites in lunar exploration. Multiscale characterizations reveal that regardless of the number of treatment cycles, the fiber surface morphology remains intact without cracking or etching. X-ray diffraction and Fourier-transform infrared spectroscopy confirm that the amorphous silicate network of the basalt fibers is well preserved, with no thermally induced recrystallization or compositional alteration. Thermogravimetric analysis further demonstrates that the treated fabrics retain the inherent thermal stability of pristine basalt, indirectly evidencing structural integrity. Importantly, the tensile strength of basalt yarns does not exhibit a cycle-dependent degradation trend, and the K/S colorimetric values remain stable even under combined thermal and UV exposure. Collectively, these findings confirm that basalt fiber fabric possesses exceptional resistance to lunar-mimetic aggressive environments, and its durability is comparable to that of natural basalt rock. Full article

Okra (Abelmoschus esculentus) stems represent an abundant lignocellulosic resource with considerable potential for sustainable textile and bio-composite applications. This study investigated the effects of biological, alkaline (1–7.5 wt.% NaOH), and combined extraction methods on the physicochemical, structural, and mechanical properties of okra fibers. FTIR and XRD analyses confirmed the progressive removal of hemicellulose and lignin, resulting in increased cellulose crystallinity after alkaline treatment. Optical microscopy revealed enhanced fiber individualization and cleaner surface morphology. Increasing the NaOH concentration improved fiber density, reduced hygroscopicity, and enhanced mechanical performance. The highest cellulose content (76.52%), tensile strength (148.57 MPa), and Young’s modulus (6.62 GPa) were achieved with 7.5 wt.% NaOH treatment. However, excessive treatment severity induced partial cellulose degradation. Overall, alkali-treated okra fibers exhibited improved structural organization, reduced moisture sensitivity, and enhanced mechanical properties, highlighting their potential as lightweight and sustainable reinforcements for technical textile and bio-composite applications. Full article

Aramid nanofibers (ANFs) inherit the exceptional properties of the bulk counterparts, while introducing a large specific surface area and excellent processability. However, the strong inter-fibrillar interactions and tendency to agglomerate hinder their high-content incorporation into polymer matrices. Here, we report a one-pot reprotonation–compounding strategy for fabricating aramid nanofiber-reinforced poly(vinyl alcohol) (ANF–PVA) composite films, where the ANF dispersion was mixed with polymers during the protonation process to form a continuous 3D network in the ANF-PVA film. The optimized film with a loading of 20 wt% ANFs exhibited a tensile strength of 122.2 MPa and a toughness of 28.36 J m⁻³. Furthermore, the high ANF loading enabled versatile applications. A robust ANF-PVA hydrogel, prepared via salt-induced gelation, delivered 132% enhancement in tear strength and 38.2% increase in cyclic compressive strength compared with the PVA hydrogel. Moreover, inspired by the “brick-and-mortar” architecture of natural nacre, the fully organic ANF-PVA film was incorporated into carbon fiber/epoxy laminates, with a configuration of one nacre-inspired film per five prepreg plies, achieving a 36.5% improvement in impact toughness and minimal loss in flexural strength. This scalable reprotonation–compounding approach provides a general route for producing high-loading ANF-based composites, paving the way for the broader utilization in advanced materials. Full article

Bamboo is a natural fiber-reinforced composite whose macroscopic mechanical properties depend on the microscale synergistic deformation of fibers and parenchyma. However, existing in situ SEM testing techniques are mainly designed for metallic tensile testing and are unsuitable for analyzing bamboo’s meso-scale behavior. To address this, we developed an in situ SEM three-point bending instrument specifically for natural fiber materials. The instrument keeps the region of interest (ROI) stably centered in the SEM field of view through a stationary central indenter and symmetrically moving supports. It offers a 0–450 N load range, 0.5N force resolution, 1 μm displacement resolution, and is compatible with a Tescan Vega 4 SEM chamber. Using this instrument, in situ bending tests were performed on Moso bamboo (Phyllostachys edulis) with fiber volume fractions of 23%–42%, combined with digital image correlation for full-field strain measurement. Results show that flexural modulus, strength, and fracture work all increase significantly with fiber content. A microstructural failure classification framework was established based on in situ SEM observations, categorizing the observed failure modes according to the local arrangement of fibers and parenchyma. The proportions of these failure modes were found to be closely associated with the gradient distribution of strength and toughness across the culm wall. Three extrinsic toughening mechanisms were identified: fiber-induced crack deflection, parenchyma cell collapse densification, and fiber–parenchyma interfacial debonding. The developed instrument and analysis method offer a promising experimental platform for multi-scale mechanical characterization of natural composites. Full article

Polyhydroxybutyrate (PHB) composites represent a promising sustainable solution to address the environmental challenges posed by conventional polymers across multiple sectors. This comprehensive review synthesizes current knowledge on PHB-based composites, examining their development, performance, and biodegradation characteristics in diverse applications such as packaging, biomedical devices, agriculture, aerospace, and environmental remediation. Various composite fabrication methods, including melt blending, solution casting, electrospinning, and in situ polymerization, are evaluated for their impact on functional properties. Natural fiber- and nanomaterial-reinforced PHB composites are critically analyzed for their mechanical integrity, thermal stability, surface chemistry, biodegradability, and environmental compatibility. Practical challenges, including manufacturing scalability, cost-effectiveness, and long-term stability in complex environments, are discussed within circular economy and regulatory frameworks to situate PHB composites for realistic industrial and environmental deployment. This review provides timely insights for researchers and practitioners aiming to develop environmentally compatible, scalable biopolymer-based solutions across multiple domains. Full article

The disposal of waste rock wool insulation materials has become an increasing environmental concern, while their reuse in cementitious composites remains insufficiently explored, particularly under elevated-temperature conditions. Moreover, limited information is available regarding the influence of fiber pretreatment on the residual mechanical performance of cementitious mortars after fire exposure. Therefore, this study investigates the effect of untreated rock wool fibers (URWFs) and hydrothermally treated rock wool fibers (TRWFs) on the mechanical and thermal performance of cementitious mortar. The waste fibers were hydrothermally treated by immersing 40 g of fibers in 1 L of water, stirring for 10 min, followed by filtration and oven drying at 105 °C for 24 h. Mortar specimens incorporating eight fiber dosages (2.5%, 5.0%, 7.5%, 10.0%, 12.5%, 15.0%, 17.5%, and 20.0% by weight of cement) were tested for compressive strength after 28 days of curing and after exposure to elevated temperatures of 400, 500, and 600 °C for 2 h, followed by natural air cooling. The results demonstrated that hydrothermal treatment significantly enhanced the residual compressive strength of fiber-reinforced mortars compared with untreated fibers, with the greatest improvement observed after exposure to high temperatures. The optimum fiber content (2.5–5.0%) provided the highest retained strength ratio, improving residual compressive strength by 25.1% compared with the corresponding URWF, while exhibiting a retained strength ratio of 54.8%, slightly exceeding the control mixture 54.5%. TRWF mortars also exhibited lower water absorption of up to 18% reduction, and lower densities of up to 60% reduction compared to URWF mortars, indicating improved matrix densification, fiber–matrix bonding, and thermal stability. These findings demonstrate that hydrothermal treatment is an effective and sustainable approach for upgrading waste rock wool fibers into value-added reinforcement for lightweight, low-permeability cementitious mortars with improved fire resistance. The study is limited to compressive strength evaluation, and future work should investigate tensile and flexural behavior, ductility, energy absorption, crack propagation, and long-term durability. Full article

Natural fiber-reinforced polymer composites are attractive for lightweight and sustainable engineering applications; however, property scatter remains a major barrier to reliable design. Mean tensile properties alone are insufficient when material selection depends on repeatability and lower-tail performance. This study presents a statistical variability and lower-tail reliability assessment of flax, jute, and carbon fiber composite laminates using 590 open-access tensile test records from a published natural-fiber composite dataset. Flax and jute were selected as representative bast-fiber systems covering a range of woven, unidirectional, and short-fiber architectures; carbon fiber was included as a synthetic-fiber reference system. Three mechanically important properties were analyzed: the recalculated tensile modulus, tensile strength, and axial failure strain. Normal, lognormal, and two-parameter Weibull distributions were screened for each material–property combination using the Akaike information criterion (AIC); empirical fifth percentiles (P5) and bootstrap 95% confidence intervals (CI) were computed as lower-tail descriptors. The results show that Carbon-0 has the highest lower-tail modulus and strength, with empirical fifth percentiles of 104.95 GPa and 989.64 MPa, respectively. Among the natural fiber systems, Flax-0 and Flax-VE-0 provided the highest lower-tail strengths, whereas Flax-Twill and Flax-CP showed the highest lower-tail failure strains. The lowest tensile strength coefficient of variation was observed for Flax-90 (2.41%), followed by Flax-Twill (3.43%), Flax-0 (4.50%), Jute-Satin (4.83%), and Jute-Plain (4.92%). A balanced reliability ranking that combined lower-tail property ranks and coefficient of variation ranks identified Flax-0, Flax-VE-0, Flax-Twill, Flax-CP, and Jute-Satin as the most favorable natural-fiber systems. The lower coefficient of variation values observed in aligned and satin-weave architectures relative to short-fiber and plain-weave systems reflect the role of fiber orientation uniformity in moderating property scatter at the laminate scale. This study provides a reproducible statistical framework based on lower-tail performance descriptors for comparative screening purposes, not on formal design allowables for distinguishing high mean performance from reliable minimum-level performance in natural fiber composite laminates. Full article

In response to the increasing needs for environmentally friendly products, lignocellulosic natural fibers have been of interest as potential replacements for synthetic reinforcement materials in textiles, composites, and related applications. Among these resources, bast fibers derived from plant stems (flax, hemp, nettle, jute, hop), which contain a high cellulose content, have good mechanical properties, low density, and are renewable, are highly promising. Steam explosion has emerged as a green fiber extraction, defibrillation, and surface modification pretreatment technology. Despite the growing number of studies on steam-exploded natural fibers, a comprehensive understanding of the relationships between processing conditions, fiber modifications, mechanisms, and end-use performance remains limited. This review investigates the structural, chemical, and morphological influences of steam explosion on bast fibers. Specifically, it focuses on the mechanism of steam explosion including the solubilization of hemicellulose, partial lignin redistribution or removal, fiber individualization, and cellulose enrichment. The literature indicates that steam explosion can improve fiber separation, fineness, surface morphology, and interfacial adhesion of the composite materials and reduce the use of hazardous chemicals compared with conventional extraction methods. Nonetheless, conflicting results have also been documented, where the same steam explosion conditions can yield distinct fiber characteristics according to biomass type, composition of biomass, moisture concentration, and the amount of processing involved. Excessive treatment severity may lead to fiber shortening, cellulose degradation, and deterioration of fiber quality, particularly for textile applications requiring long fibers. This review highlights current knowledge gaps regarding the optimization of processing conditions, the understanding of steam explosion mechanisms, and the scale-up of the technology for industrial applications. Full article

This study examines the effect of small ply angle deviations on the structural response of carbon fiber-reinforced polymer laminates representative of structures used in unmanned aerial vehicles (UAVs). A combined experimental and numerical approach was applied, including cantilever bending tests and experimental modal analysis, supported by finite element simulations. Laminates with nominal ply orientations of 0°, 5°, and 10° were manufactured using a manual hand lay-up process to reflect typical production variability. The results show that the numerical model accurately captures the observed trends in both bending deformation and natural frequencies, with discrepancies up to 12.5%. A consistent tendency to slightly overestimate stiffness was observed, leading to lower predicted deflections and higher natural frequencies compared to experimental data. The findings confirm that finite element modeling can reliably detect and predict the structural effects of small fiber misalignment, supporting its use in the assessment and design of lightweight composite structures used in UAV applications. Full article

Fused Deposition Modeling (FDM) has emerged as one of the most widely adopted additive manufacturing (AM) technologies, valued for its simplicity, cost-effectiveness, and versatility in fabricating complex geometries. The geometry of the extrusion nozzle plays a critical role in determining melt flow behavior, extrusion stability, and final print quality of thermoplastic materials. When utilizing natural fiber-reinforced thermoplastic composites (NFRCs), understanding and optimizing nozzle geometry becomes increasingly important due to the complex rheological behavior of fiber-filled melts, including challenges such as increased viscosity, shear-thinning effects, and susceptibility to nozzle clogging. The reviewed literature shows that optimized nozzle geometry, supported by computational and statistical tools, can improve the printability and mechanical performance of natural fiber composites, although further advancements are needed to address material variability and complex fiber–matrix interactions. This review paper presents a comprehensive overview of the effects of nozzle geometry on melt flow behavior in FDM, covering computational modeling approaches, experimental characterization studies, and optimization methodologies for enhancing the performance of natural fiber-reinforced composites in additive manufacturing applications. The integration of sustainable materials into FDM processes represents a significant advancement toward environmentally responsible manufacturing while maintaining mechanical performance requirements. Full article

The transient heat-transfer behavior of hybrid natural-fiber-reinforced epoxy composites containing 0–5 wt% conch shell filler and 20–35 wt% combined banana–bagasse fiber reinforcement was evaluated using active infrared thermography. A standardized protocol comprising 30 s of convective heating with 100 °C hot air followed by 60 s of natural cooling was applied to seven composite configurations tested in triplicate. The transient response was analyzed in three phases: active heating (0–30 s), thermal lag (30–57 s), and natural cooling (57–90 s). Maximum temperature ($T_{max}$), heating rate ($R_h$), cooling rate ($R_c$), and a thermal retention ratio ($TR$) were extracted and statistically validated by one-way ANOVA with Bonferroni correction. For specimens exhibiting zero within-group variance at the camera display resolution, significance was confirmed using exact permutation tests. Filler incorporation (3–5 wt%) was the dominant factor governing peak-temperature reduction; F5B15S10 (5 wt% filler, 25 wt% total fiber) achieved the lowest $T_{max}$ (33.80 °C, 4.57 °C below neat epoxy). Cooling efficiency was primarily governed by fiber content; F3B15S20 (3 wt% filler, 35 wt% total fiber) demonstrated the most efficient heat dissipation ($TR=0.721$). These findings demonstrate that heating resistance and cooling efficiency are governed by partially independent mechanisms, enabling tailored material design. This study indicates that the proposed transient thermographic protocol provides a valuable reference to thermal management design of hybrid biocomposites in automotive interior and building envelope applications. Full article

Ultra-high-performance concrete (UHPC) is known for its exceptional compressive strength and durability; however, its brittle nature requires fiber reinforcement to improve toughness and tensile performance. This study investigates the synergistic effects of triple fiber reinforcement, including desized and sized carbon fibers (0.2–1.0 vol%), steel fibers (1.0 vol%), and polypropylene fibers (0.2 vol%) on the fresh, mechanical, durability, microstructure, and fire resistance properties of UHPC. The experimental program included workability, compressive and flexural strength, load-deflection behavior, electrical resistivity, dynamic modulus of elasticity, SEM analysis, and fire resistance at elevated temperatures (425 and 900 °C). The results showed that desized carbon fibers performed better than sized fibers by improving workability, fiber dispersion, flexural behavior, and fiber–matrix bonding. The optimal triple-fiber composition, DC1.0P0.2S1.0, achieved the highest flexural strength of 24 MPa while maintaining compressive strength above 141 MPa. The triple-fiber system provided effective multi-scale crack control, where PP fibers prevented explosive spalling, carbon fibers bridged meso-crack control, and steel fibers enhanced macro-crack load transfer and ductility. SEM analysis further confirmed better dispersion and stronger interfacial bonding of desized carbon fibers. Overall, the optimized triple-fiber system significantly improved flexural performance, toughness, workability, and fire resistance without notably reducing compressive strength, demonstrating strong potential for advanced structural applications. Full article

Short-fiber-reinforced composites (SFRCs) are widely used for their high strength-to-weight ratio. In the Additive Manufacturing (AM) field, Material Extrusion (MEX) processes inherently induce anisotropy, primarily due to fiber alignment along the deposition path, making printing direction and layer orientation critical for mechanical performance. In this study, specimens made of Onyx^®, a carbon short-fiber-reinforced polyamide, were fabricated by varying their orientation on the build platform, thereby producing different infill deposition directions. Each replica contained 25 layers. Two deposition strategies were investigated: a conventional alternating ±45° raster pattern and a 0°/90° configuration. Owing to the odd number of deposited layers, the latter resulted in two distinct stacking configurations, namely 0°/90° and 90°/0°, depending on the orientation of the first deposited layer. With such a strategy, it was possible to obtain configurations with a predominance of fibers either aligned with or transverse to the loading direction, depending on the orientation of the first-deposited layer. Mechanical test results were systematically compared to evaluate the influence of deposition strategy and fiber orientation on tensile performances. The effect of extrusion on fiber alignment was evaluated using Scanning Electron Microscopy (SEM). Mechanical behavior was evaluated using replicated tensile testing (five specimens per condition) and SEM-based fiber-orientation analysis. The investigation confirms the anisotropic nature of MEX-produced SFRCs. In particular, the 0°/90° configuration showed reductions of approximately 24% in tensile strength and 58% in elongation at break compared with the ±45° configuration. These results demonstrate that both extrusion-induced fiber orientation and layer-wise deposition strategy play a crucial role in defining the mechanical response of the material. Full article