Search Results (694)

With the rapid development of the hydrogen economy, Type IV composite pressure vessels have emerged as the core components of on-board hydrogen storage systems. However, accurate fatigue life prediction remains a critical bottleneck limiting their design optimization and safe operation. Existing methods often exhibit prediction errors exceeding ±50% due to the inherent scatter, anisotropy, and complex service environments of composites. This study proposes an improved simulation method for fatigue life prediction of Type IV cylinders. Systematic tension–tension fatigue tests were conducted on carbon fiber-reinforced polymer (CFRP) laminates at four ply angles (0°, ±15°, ±30°, ±45°) and PA6 liner at three temperatures (−30 °C, 25 °C, 82 °C) to establish comprehensive S-N curve databases. The results reveal that ply angle is the predominant factor governing CFRP fatigue performance, while temperature significantly influences PA6 behavior, and failure mode transitions from fiber fracture to matrix-dominated damage as ply angle increases. A fatigue analysis model was developed in nCode, incorporating the ply fatigue Algorithm to characterize the anisotropic fatigue behavior of CFRP overwraps. Full-scale validation on Type IV cylinders under cyclic pressure (2–87.5 MPa) confirmed the method’s effectiveness, achieving prediction errors of 11.5% and 35.3% for the two failed specimens, with failure locations well predicted. This study provides a rapid and reliable engineering calculation method and data support for the anti-fatigue design, safety assessment, and life management of Type IV cylinders. Full article

The extracellular matrix (ECM) regulates skeletal muscle development through biochemical signaling and mechanical interactions. While Matrigel supplementation is commonly used to enhance engineered muscle formation, the contribution of specific ECM proteins remain incompletely defined in 3D systems. Here, we evaluated the effects of laminin and fibronectin supplementation on myogenic differentiation in collagen type I hydrogels and assessed their influence on passive tissue compaction and alignment in 3D constructs. Two-dimensional collagen hydrogels supplemented with increasing concentrations (0–100 µg/mL) of laminin or fibronectin were screened to maximize the myoblast fusion index. These concentrations were incorporated into 3D myocyte-seeded hydrogels cultured between flexible posts to quantify passive compaction forces via cantilever mechanics. Fibronectin supplementation (10 µg/mL) resulted in significantly greater early post displacement and sustained passive compaction compared to laminin-supplemented and unsupplemented controls. Constructs cultured under tension between posts exhibited enhanced alignment, with fibronectin further increasing the proportion of fibers oriented within 0–20° of the tension axis. Together, these findings demonstrate that fibronectin enhances early passive compaction dynamics and tension-mediated alignment in collagen-based skeletal muscle constructs. These results provide insight into how specific ECM components influence 3D tissue organization and may inform the design of engineered muscle models for regenerative applications. Full article

This study evaluated the effectiveness of maleic anhydride polypropylene (MAPP) in improving the mechanical performance and interfacial adhesion of lignocellulosic fiber-reinforced polypropylene (PP) composites. Based on Scanning Electron Microscopy (SEM) investigations, the relationship between fiber fraction, MAPP content, mechanical characteristics, and fracture morphology was the main focus. The test results showed that the stiffness and tensile strength of the composites increased with the addition of MAPP. The esterification reaction between the anhydride groups of MAPP and the hydroxyl groups of the fibers strengthened the interphase covalent bond, with the 46:50:4 composition producing the highest elastic modulus of 79.67 MPa and maximum tensile stress of 11.01 MPa. The dense interphase zone, few gaps, and no dominant fiber tension were all confirmed by SEM morphology, and also indicated effective stress transfer from the PP matrix to the fibers. However, the toughness of the material decreased significantly with increasing stiffness. Due to strong plastic deformation in the PP matrix that is not tightly attached to the fibers, the composition without MAPP (30:70:0) shows high impact energy and breaking strain, reaching 25.39 kJ/m² and 121.26%, respectively. The increase in chemical bonding at 4% MAPP content limits the mobility of the polymer chains, making it more brittle. In addition, even though MAPP is still present in the system, increasing the fiber fraction above 60% causes agglomeration, decreased homogeneity, and increased voids due to limited matrix wetting, ultimately deteriorating the mechanical properties. Tensile stress and elastic modulus have a very strong positive correlation (R² = 0.93), while impact energy and strain have a good correlation (R² = 0.89). The results overall showed that the ideal MAPP dosage is in the range of 4% before interface saturation occurs and confirmed that MAPP efficiency is determined by the balance between fiber composition, MAPP quantity, and dispersion homogeneity. Full article

Composite materials, known for their enhanced mechanical strength through fiber reinforcement, are increasingly used in industrial applications. However, like metals, they suffer strength degradation from cyclic loading, making fatigue failure a critical concern. The fatigue behavior of polymer composites is strongly influenced by factors such as stress amplitude, stress ratio, and loading frequency. Conventional stress-life approaches often treat these factors independently, which limits their predictive accuracy. This study introduces a novel frequency–stress–ratio fatigue index, integrated into a residual-strength degradation approach, to predict fatigue life under constant amplitude, tension-tension loading conditions. To the best of the authors’ knowledge, the majority of models available in the literature require substantial experimental data to calibrate the parameters essential for their application in real-world scenarios. The proposed model requires only two material parameters and assumes failure occurs when the residual strength degrades to the level of the applied maximum stress. The results demonstrate that the proposed formulation provides a unified representation of fatigue behavior influenced by both cycle-dominated and time-dependent mechanisms, offering robust predictive capabilities. This approach not only addresses a critical need for reliable and practical fatigue prediction methods in composite materials but also contributes significantly to the optimization of engineering design processes. Full article

This study investigates the effects of filament winding parameters (tension and mosaic pattern) on the mechanical performance of thin-walled fiber-reinforced polymer composite tubes under internal pressure. The pressure was generated through axial compression of an elastomeric insert, providing a controlled alternative to conventional hydrostatic burst testing. Tubes were manufactured with different combinations of winding tension (10–50 N) in the ±55° and hoop layers. Within the ±55° layer, several mosaic pattern configurations were tested. Structural responses were evaluated using pressure testing, Digital Image Correlation (DIC), and Scanning Electron Microscopy (SEM). 20 N was identified as the most efficient tension level, improving interlaminar integrity and increasing hoop tensile strength by approximately 8–13%. Specimens with a hoop layer failed abruptly by hoop-dominated brittle fracture, characterized by longitudinal splitting and fiber rupture in the circumferential direction. Among the investigated mosaic configurations, the 3/3 pattern demonstrated the most efficient structural response—the mean hoop tensile strength (1088 ± 43 MPa) was approximately 31–40% higher than that of the remaining configurations (722–798 MPa). Overall, the results indicate that both winding tension and mosaic pattern influence the failure pressure, with optimized configurations contributing to improved pressure resistance and structural consistency. Full article

This study experimentally investigates the structural behavior of hexagonal- and square-shaped composite specimens subjected to vertical compression, vertical tension, and diagonal tension loading. The specimens were fabricated using four- and six-layer alkali-resistant (AR) glass textile reinforcements embedded in a modified cementitious mortar via pull, pour, and roll manufacturing techniques. The mechanical performance of polyvinyl alcohol (PVA) fiber-reinforced composite connectors and steel clamp-type elements was also evaluated at the joints of hexagonal specimens under vertical tension and lateral shear loading. The results show that increasing the number of textile layers significantly enhances structural performance. A 50% increase in textile layers improved load-carrying capacity by up to 56% in compression, 104% in tension, and 216% in diagonal tension. Corresponding increases of approximately 20–42% in ductility and up to 266% in energy dissipation capacity were observed. No failure occurred in the connecting elements, confirming their adequate stiffness, strength, and ductility. In addition, validated three-dimensional finite element models were developed to simulate the response of the hexagonal specimens. Overall, the proposed system demonstrates strong potential for applications such as infill walls, cladding, and sandwich panels due to its favorable strength, ductility, and energy absorption capacity. Full article

This review examines recent advances in multifunctional probes that integrate optical and electrochemical channels for in vitro/in vivo studies. Integration of electrodes with optical fibers provides a powerful platform for localized light delivery and simultaneous electrochemical detection of cellular metabolites both within and at the surface of single living cells. These hybrid devices bridge optical stimulation methods, including optogenetics, and electrochemical monitoring of the cellular response within the same experimental preparation. The review systematically categorizes distinct probe architectures: optical nanoendoscopes for intracellular measurements, probes with a shared opto-electrochemical channel, devices where optical and electrochemical channels are physically separated, and probes engineered for neural interfaces and scanning probe microscopy. For each category, fabrication approaches, surface modification strategies, and representative biological applications are discussed. Particular attention is given to the fundamental tension between optical transparency and electrical conductivity in shared-channel designs, to the mechanical requirements imposed by neural tissue on implantable probes, and to the spatial resolution limits of current scanning probe platforms. The review concludes with a critical assessment of current limitations and future directions, including higher spatial resolution, simultaneous multiplexed analyte detection and broader translation of these technologies toward in vivo experimental models. Full article

This paper investigates cyclic pure shear under biaxial tensile loading and finite strain conditions. To interpret the experimental measurements, a set of stress and strain parameters is defined without assuming any specific constitutive model. In addition, a power-conjugate stress–strain rate pair is introduced within the finite strain framework, whose tensor contraction gives the internal power per unit mass. The test was applied to characterize the cyclic pure shear behavior of a coated woven polyester fabric commonly used in the maritime industry for sailmaking applications. A cruciform specimen geometry, specifically designed for pure shear testing and including three slits in each arm, is proposed and was validated by full-field strain measurements obtained using stereo digital image correlation (SDIC). During the tests, a non-contact CCD camera target-tracking system was used to measure strain evolution. This system enables monitoring of the distortion angle between warp and weft yarns, as well as strain in the warp, weft, and principal strain directions. The results reveal a new ratcheting phenomenon, characterized by progressive strain accumulation in the warp and weft directions during successive shear cycles, leading to a gradual increase in the specimen’s surface area. Full article

Glass fiber–reinforced polymer (GFRP) reinforcement provides an effective alternative to conventional steel in concrete structures due to its corrosion resistance. Nevertheless, the lower elastic modulus of GFRP necessitates careful consideration of serviceability behavior in GFRP-reinforced concrete members. This study presents a numerical sectional analysis model for predicting the flexural response and ultimate capacity of hybrid reinforced concrete beams incorporating embedded GFRP profiles in combination with either mild steel or GFRP reinforcement bars under monotonic static loading. The proposed model employs realistic nonlinear stress–strain relationships for concrete and steel, together with secant moduli of elasticity evaluated at different loading stages. Particular emphasis is placed on detailed stress distribution in flexural sections, including the contribution of tension stiffening in the post-cracking regime. The formulation integrates nonlinear constitutive material behavior with theoretical sectional equilibrium to evaluate the effective flexural secant stiffness. For practical serviceability assessment and to reduce dependence on complex analytical procedures, strain vectors and stiffness matrix components are derived using elasticity coefficients that reflect modulus degradation obtained from numerical analysis. The accuracy of the model is verified through comparison with experimental results, including ultimate flexural capacity and moment–deflection responses. Many crucial parameters were studied, such as the longitudinal reinforcement ratio, type of reinforcement, concrete compressive strength, position of the I-GFRP profile, and rotation of the I-GFRP profile. The results of this study demonstrated that both the longitudinal reinforcement ratio and the rotation of the I-GFRP profile have a significant influence on the ultimate load capacity and deflection behavior. The close agreement between numerical predictions and experimental observations demonstrates the reliability and applicability of the proposed model for structural engineering analysis and design. Full article

Carbon fiber textile-reinforced engineered cementitious composite (CTR-ECC) is widely utilized in structural strengthening applications due to its advantages of low weight and high strength. A comprehensive understanding of its mechanical behavior under off-axis tension is crucial for addressing the prevalent off-axis stress states in engineering practice. This paper presents an experimental investigation on the off-axis tensile properties of CTR-ECC. Specimens were fabricated with four off-axis angles: 0°, 15°, 30°, and 45°. The study revealed three main findings: (1) Under axial (0°) loading, failure is characterized by yarn fracture and interface slip, whereas off-axis tension induces a stable progressive delamination failure in textile-reinforced ECC systems. (2) While CTR-ECC exhibits higher tensile strength than plain ECC at all angles, its strength decreases significantly as the off-axis angle increases (e.g., a 27.1% reduction at 15°). Off-axis layouts, however, substantially improve energy absorption, with strain energy density increasing by up to 368.4% at 30°. (3) A phenomenological constitutive model was developed, which can adequately capture the stress–strain response of CTR-ECC under various off-axis angles, with coefficients of determination (R²) exceeding 0.9 in all cases. These results provide important insights into the failure mechanisms and performance design of CTR-ECC under off-axis tension conditions. Full article

Background and Objectives: Open-angle glaucoma subtypes share a structural phenotype but differ in pathophysiology: pseudoexfoliative glaucoma (PXG) involves vascular endothelial dysfunction associated with deposition of exfoliative material, whereas normal-tension glaucoma (NTG) reflects primary vascular dysregulation in the absence of elevated intraocular pressure. We characterized subtype-specific OCT angiography (OCTA) profiles obtained from a 3 × 3 mm macular scan and evaluated their discriminatory power for pairwise subtype classification. Materials and Methods: This was a single-center, cross-sectional study of 304 eyes: 198 glaucomatous eyes—primary open-angle glaucoma (POAG, glaucoma simplex in our clinical nomenclature), n = 102; PXG (glaucoma capsulare), n = 68; NTG (glaucoma sine tensio), n = 28—and 106 healthy controls. The Cirrus HD-OCT 5000 AngioPlex 3 × 3 mm OCTA protocol was used to assess vessel density (VD), perfusion density, foveal avascular zone (FAZ) morphology, ganglion cell complex (GCC), and retinal nerve fiber layer (RNFL) thickness. Analyses included Kruskal–Wallis tests with Bonferroni post hoc correction, ROC analysis with DeLong comparison of combined versus structural-only models, multivariate regression, and an exploratory XGBoost classifier with SHAP-based interpretation. Results: VD Inner and Perfusion Inner were lower in PXG (16.37 ± 3.33%; 0.31 ± 0.05) than in POAG (18.73 ± 3.41%; 0.34 ± 0.05; both p < 0.001); Perfusion Inner was also lower than in NTG (p < 0.05). FAZ Area was largest in NTG (0.27 ± 0.11 mm²) and greater than in PXG (0.19 ± 0.08; p < 0.01); FAZ Circularity differed across subtypes (p < 0.001). Combined OCTA–structural models outperformed structural-only models for POAG vs. PXG (DeLong p = 0.002) and for PXG vs. NTG (AUC = 0.770; p = 0.010). Sector-resolved Spearman analysis revealed subtype-specific coupling: in NTG, VD Inner and Perfusion Inner correlated with the inferior RNFL (r = 0.53 and r = 0.52; both p < 0.01); in PXG, coupling shifted nasally (r = 0.41 and r = 0.46; both p < 0.001). The exploratory XGBoost classifier separated glaucoma from controls with an internal cross-validated AUC of 0.975 ± 0.008 (5-fold CV; not externally validated); FAZ Circularity (mean |SHAP| = 0.418) and FAZ Area (0.411) were the top inter-subtype features, supported by case-level SHAP. RNFL avg and average GCC independently predicted MD across subtypes; in PXG, Perfusion Inner also predicted MD (β = −32.78; p = 0.032). Conclusions: In this single-center, cross-sectional cohort, OCTA revealed subtype-associated macular microvascular profiles that are complementary to structural OCT. Reduced vessel and perfusion density characterized PXG, whereas FAZ enlargement and reduced circularity distinguished NTG and PXG. Vascular–structural coupling was nasal-predominant in PXG and inferior-predominant in NTG. Combined multimodal models outperformed structural-only approaches. Macular perfusion additionally predicted MD in PXG. The XGBoost/SHAP analysis is exploratory; prospective and externally validated studies are required before clinical deployment. Full article

Three-dimensional braided carbon-fiber-reinforced polymer (CFRP) composites are promising for lightweight aircraft propeller blades. Aircraft composite structures may approach temperatures of 80–90 °C under the combined effects of solar radiation, infrared heating, and ground reflection. Yet the thermo-mechanical failure mechanisms of low-braiding-angle architecture remain insufficiently understood. This study comparatively investigates the tensile behavior and damage evolution of low-angle four-directional (3D4A-20°) and five-directional (3D5A-20°) braided CFRP composites under axial tension at both room temperature and 90 °C. A multi-scale approach integrating in situ X-ray computed tomography, digital image correlation, digital volume correlation, and scanning electron microscopy was used to characterize strain localization, internal cracking, and fracture morphology. At room temperature, 3D5A-20° shows higher stiffness and strength than 3D4A-20° because additional axial yarns improve load-transfer and three-dimensional constraint. At 90 °C, matrix softening and interfacial degradation accelerate crack initiation, strain localization, and damage propagation in both architectures. Nevertheless, 3D5A-20° maintains more stable and progressive damage evolution, whereas 3D4A-20° exhibits earlier crack coalescence and greater mechanical degradation. Overall, elevated temperature accelerates damage evolution through matrix softening and interfacial degradation, whereas braided architecture determines load transfer and crack connectivity. These findings provide guidance for the design of low-angle braided composites for thermally exposed aircraft propeller blades. Full article

Hybrid composite laminates combining pseudo-woven meso-architectured composite (MAC) and unidirectional (UD) sub-laminates manufactured via automated fiber (AFP) placement are attractive as they combine the increased toughness of MAC and higher stiffness of UD while also reducing the manufacturing time. MACs are manufactured via a modified AFP process involving tow skips to create a woven-like architecture using unidirectional tows and introduce shallow crimp angles and complex fiber angle distributions in the architecture. Previous studies on hybrid MAC laminates have shown increased impact damage resistance/tolerance under high- and low-velocity impacts. This work presents an experimental study on the open-hole tension (OHT) and open-hole compression (OHC) response of T800-SC-24k carbon/epoxy laminates of nominal thickness 4.55 mm manufactured via AFP manufacturing. Two hybrid laminate configurations consisting of a UD core and pseudo-woven MAC sub-laminates on the outer surfaces are compared against a traditional UD quasi-isotropic control laminate. One of the hybrid laminate configurations has a plain-woven-like architecture while the other has a complex 3D woven type architecture. The hybrid laminates exhibited a marginal 7% increase in OHT strength and up to a 16% reduction in normal loading direction strains around the hole relative to the control. All three configurations showed comparable OHC strengths. Despite the complex meso-architecture of the MAC sub-laminates, failure in both OHT and OHC is found to be governed primarily by the UD core, which dominates load-carrying capability and failure mechanisms. The results demonstrate that the hybrid laminates maintained or improved in-plane OHT/OHC performance while previously demonstrating better damage resistance and tolerance under impact. Full article

Despite extensive advancements in Engineered Cementitious Composites (ECCs), mixture design remains predominantly empirical, due to the absence of a quantitative parameter directly linking fiber–matrix interfacial mechanics to strain-hardening performance. This study identifies fiber–matrix interfacial friction as a quantifiable parameter and establishes a micromechanics-guided interfacial regulation framework to enhance the toughness of ECC by regulating fiber failure modes. First, a critical fiber–matrix interfacial frictional stress, (τ₀)_crit, corresponding to the transition between fiber pull-out and fracture, was theoretically derived based on energy dissipation maximization during crack propagation. A back-calculation approach was further developed to determine interfacial frictional stress (τ₀) directly from tensile stress–crack opening responses under single-crack tension, eliminating reliance on single-fiber pull-out testing. Then, τ₀ was tuned toward (τ₀)_crit through interfacial regulation using fly ash. Experimental results demonstrate that the toughness of ECC is maximized when τ₀ approaches (τ₀)_crit, confirming the validity of the proposed toughness enhancement mechanism. The study establishes an explicit mechanistic linkage between interfacial micromechanics and macroscopic strain-hardening performance, providing a predictive and quantitative design pathway that transcends empirical mixture adjustment. Full article

In engineered cementitious composites (ECCs), the use of fine quartz sand is associated with high cost and is unfavorable for reducing ECC shrinkage. Moreover, the mining and processing of fine quartz sand impose negative environmental impacts. At the same time, the polyethylene (PE) or polyvinyl alcohol (PVA) fibers added to ensure ECC ductility are expensive, which limits the widespread application of ECCs. With the aim of waste utilization and cost reduction while improving efficiency, this study employs geopolymer aggregate (GPA) as an alternative to fine quartz sand and partially replaces PE fibers with steel fibers to develop an economical and environmentally friendly geopolymer aggregate ECC. Six groups of ECC specimens with different mix proportions were designed and tested under uniaxial compression, flexural loading, and uniaxial tension. Different aggregate types (fine quartz sand and geopolymer aggregate) and volume fraction ratios of PE fibers to steel fibers (0:2.0, 0.5:1.5, 1.0:1.0, 1.5:0.5, and 2.0:0) were adopted to investigate their effects on mechanical properties, microstructural characteristics, and material sustainability. The experimental results reveal the failure process and deformation characteristics of the ECCs at different loading stages. The results indicate that geopolymer aggregate, owing to its lower stiffness and fracture energy, can promote multiple cracking behavior in ECCs. Although the complete replacement of quartz sand with porous GPA initially causes a slight reduction in the compressive and flexural strengths of the matrix, the hybridization strategy—partially replacing PE fibers with steel fibers—effectively compensates for this strength loss while maintaining excellent ductility. By comparing sustainability indicators with those of conventional ECCs, the results demonstrate that hybrid fiber geopolymer aggregate ECCs can effectively reduce material costs and carbon dioxide emissions. These findings verify the sustainability of producing green ECCs using industrial solid waste as an aggregate and provide guidance for the application of environmentally friendly geopolymer aggregate ECCs. Full article