This study investigates methods to suppress consolidation deformation in gap and overlap regions between prepreg tows generated during Automated Fiber Placement (AFP). Inspired by the shape self-repair behavior during composite consolidation observed in the authors' previous research, deformation suppression is explored through control of fiber/resin flow. Specifically, flow is promoted by modifying pressurization and heating cycles during autoclave curing, while an inverse approach is examined by suppressing flow through insertion of thin resin sheets into gap regions. The effectiveness of the proposed concepts is examined by cross-sectional thickness measurements after curing and by in-situ deformation monitoring using an embedded optical fiber shape sensor during consolidation. The influence of pressurization timing, heating profile, and material addition in gap regions on deformation behavior is discussed. These results suggest that controlling fiber/resin flow during consolidation can be an effective strategy for suppressing gap/overlap deformation and may offer practical pathways for improving AFP-manufactured composite quality.
Accurate characterization of the out-of-plane shear properties of laminated composites is essential for understanding their structural integrity under complex loading. While in-plane shear moduli are well-studied, out-of-plane properties are often challenging to measure, especially in natural fiber-based laminates. This study proposes an experimental method, based on the Mindlin-Reissner plate theory, to determine out-of-plane shear moduli of woven kenaf laminates using a torsional test setup enhanced by three-dimensional digital image correlation (3D-DIC). Rectangular specimens of two lengths (50 mm and 90 mm) were clamped and subjected to quasi-static torsion. The torque was recorded using a load cell, and full-field strain was captured via 3D-DIC. The average in-plane shear modulus (G(12)) was found to be 1589.5 MPa, while the out-of-plane shear modulus (G(13)) was 693.85 MPa. A specimen geometry sensitivity analysis revealed that a width-to-thickness ratio below 3 leads to significant overestimation or underestimation of the respective shear moduli. The proposed method is non-destructive, adaptable to relatively thin laminates, and well-suited for characterizing sustainable composites, making it a promising tool for design and performance assessment in bio-based structural applications.
Thermal barrier coatings (TBCs) are applied to mitigate the thermal degradation of substrate materials in high-temperature environments and have seen limited application in polymer matrix composites (PMCs) due to the latter's poor thermal stability. This study presents a novel TBC design for carbon fiber reinforced polymer (CFRP) composites using a physics-informed neural network (PINN). A PINN framework is developed to simulate transient heat conduction in both unprotected and TBC-protected CFRP composites, with validated with experimental data. The effects of TBC layering and interfacial thermal resistance on its overall thermal resistance performance are also analyzed. The proposed PINN model accurately predicts temperature distributions in CFRP and TBC-protected CFRP composites. It estimates CFRP backside equilibrium temperatures of predicts CFRP backside equilibrium temperatures of 239.9 degrees C for the uncoated laminate and 216-230.5 degrees C for TBC/CFRP systems, depending on coating architecture and interfacial resistance. Excellent agreement (within similar to 1%) with experimental observations is achieved when temperatures are evaluated over the representative averaging domain, while larger deviations for other averaging domains reflect spatially non-uniform heating and experimental uncertainties. This work provides the foundation for designing TBCs with superior thermal barrier performance. The PINN-based TBC design presents a potentially useful approach for thermal management in aerospace composite applications under extreme conditions.
The Ethylene propylene diene monomer (EPDM) and raw materials, containing refractory materials (such as Montmorillonite clay), traditional flame retardants (ammonium polyphosphate, named as APP, and Pentaerythritol, named as PER), and chopped carbon fibers (named as CCF), were melt-masticated in various formulations at low temperature, followed via curing process at high temperature at next step. These nanocomposites were evaluated as potential ablative materials. Thermal stability was characterized by thermogravimetric analysis (TGA), while ablative performance was assessed using an oxyacetylene torch test. Key findings revealed that clay platelet sintering formed a dense, stacked silicate network that effectively functioned as a thermal and oxygen diffusion barrier. PER served dual roles as both a combustion modifier and coupling agent, significantly enhancing char formation and ablative performance. Furthermore, the synergistic interaction between APP and PER substantially improved thermal protection. Within the EPDM matrix, CCF formed a reinforcing skeletal structure that enhanced char layer integrity. However, at elevated CCF loading (13 weight present, wt.%), the development of an interconnected conductive network adversely increased back-face temperatures, consequently reducing ablation efficiency. Optimum performance was demonstrated by the Clay-20 formulation (20wt.% clay, 7wt.% CCF), which exhibited outstanding residual mass (83.41%) and maintained the lowest recorded back-face temperature (60 degrees C) among all tested compositions.
The rapid growth of electric vehicles (EVs) has increased tire-tread wear because higher load and instantaneous torque generate elevated vertical and tangential stresses. Rubber friction consists of two physically distinct mechanisms - adhesion, governed by real contact area, and hysteresis, governed by viscoelastic energy dissipation - each responding differently to slip velocity, temperature, and multiscale roughness. However, previous studies could not quantitatively separate these contributions because the required viscoelastic, roughness, friction, and wear data were not acquired under matched conditions and were rarely integrated within a unified physics-based framework, leading to reliance on total friction coefficients. Although theoretical models such as Kl & uuml;ppel - Heinrich and Persson establish the basis for adhesion and hysteresis friction, experimental studies have rarely extended these frameworks to mechanism-specific energy-to-wear correlations. This study extends the Kl & uuml;ppel - Heinrich (KH) friction model to compute adhesion- and hysteresis-related frictional-energy rates and correlates them with LAT-100 abrasion results. Adhesion energy exhibited a stronger correlation with wear, supporting a physics-based framework for EV-specific tread-wear prediction within the investigated compound - surface configuration.
This paper presents an automated, wide-range fiber orientation evaluation method for recycled carbon fiber nonwoven fabrics using a Gabor filter-based spatial frequency analysis, specifically designed for implementation in continuous manufacturing. The validity of the method was investigated by comparing the orientation probability distributions with manual datasets, which demonstrated good agreement. This method was applied to wide-area images acquired using a line- scan camera, which continuously simulates quality assurance. The findings revealed that specular reflections from carbon fibers aligning in the transport direction resulted in a significant overestimation of the predicted stiffness. A comparison between images obtained under specular and diffuse-reflection conditions using a line-scan camera showed that diffuse-reflection images captured under diffuse-reflection conditions at lighting angles of 100 degrees-120 degrees were the most effective for accurate analysis. These findings enable real-time stiffness prediction and reliable quality assurance in continuous manufacturing processes.
In this study, the bending fatigue properties and failure mechanisms of thick quasi-isotropic carbon-fiber-reinforced plastic laminates were investigated. The span-to-thickness ratio L/h was varied to examine the failure modes. Static tests revealed that specimens with lower L/h ratios exhibited shear failure and higher apparent interlaminar shear strength. The DIC measurements indicated an almost constant shear strain for specimens with different L/h values. During fatigue tests for specimens with L/h = 4, an increase in shear strain and a 10% decrease in stiffness were confirmed until shear failure occurred, although surface cracks were not observed. Acoustic emission analysis revealed matrix cracks and delamination happened throughout the test, and X-ray computed tomography revealed void volumes ranging from 1% to 3%. These findings suggest that internal voids cause matrix cracks and delamination, followed by shear failure after cyclic loading.
Adhesive joints in carbon fiber reinforced plastic (CFRP) structures may contain weak bonds that are difficult to detect and can trigger mixed-mode crack propagation, leading to the use of redundant mechanical fasteners. To realize boltless aircraft adhesive structures, this study investigates crack arresters based on interlocking fiber features for suppressing mixed-mode crack propagation in weakly bonded joints. After establishing a reproducible weak bond preparation method, three interlocking fiber features were examined: Straight Interlocking Fiber Feature (SIFF), Mechanically Hooked Interlocking Fiber Feature (MHIFF), and Diagonally Interlocking Fiber Feature (DIFF). Crack lap shear static and fatigue tests were conducted to evaluate crack arresting performance. All interlocking fiber features arrested interfacial debonding at the fiber cross-link and enhanced static strength, with DIFF achieving the highest strength, up to 2.6 times that of a normally bonded joint without crack arresters. In fatigue tests, SIFF did not suppress mixed-mode crack propagation, whereas MHIFF and DIFF suppressed fatigue crack growth beyond the fiber cross-link up to 100,000 cycles. Among the three interlocking fiber features, DIFF exhibited the most favorable balance of mixed-mode fatigue crack suppression and structural simplicity, indicating high potential for practical applications. (188 words)
Titanium dioxide (TiO2) is known for its excellent UV-shielding capability, but its inherent photocatalytic activity poses a problem by degrading the polymer matrix and compromising durability. To address this issue, this study involved creating a physical barrier by forming a silica (SiO2) shell on the TiO2 surface via a sol-gel process, followed by surface functionalization with (3-aminopropyl)triethoxysilane (APTES) to maximize interfacial bonding with the epoxy. XPS and TEM analyses confirmed the intended core-shell structure and the introduction of amine groups, while photocatalytic experiments demonstrated that the SiO2 shell effectively suppressed the photoactivity of TiO2. In mechanical property evaluations, the addition of pristine TiO2 resulted in a 15.8% improvement in flexural strength, whereas TiO2@SiO2 showed a slightly lower improvement of 13.2%. However, the composite with TiO2@SiO2@APTES exhibited a maximum flexural strength improvement of 26.1% and retained over 52% higher strength than pure epoxy even after 15 days of UV accelerated aging. This clearly demonstrates that amine functionalization not only protects the epoxy matrix from UV degradation but also provides superior mechanical reinforcement through strong interfacial bonding. Therefore, this study presents an effective strategy for designing highly durable composite materials for extreme environments, such as aerospace applications.
The clarification of the fracture behavior of CFRP under multiaxial loading has become a research focus; therefore, understanding of the properties of carbon fiber is essential. This study experimentally and analytically clarifies the effect of torsional loading on the tensile strength of PAN-based carbon fiber. Combined tensile-torsional tests were performed under proportional-loading. The results showed that tensile strength decreased as torsional stress increased. Weibull analysis, treating principal stress as a stochastic variable, confirmed that strength variation decreases as the torsional-to-tensile stress ratio increases. To investigate the cause, a defect size distribution analysis was conducted. The findings indicated that the critical defect size increases as the principal stress plane angle increases, whereas its variation decreases. Considering the anisotropy of fiber strength, a new concept of normalized principal stress was introduced. This revealed that fracture behavior conforms to the maximum principal stress theory. Accordingly, a new fracture criterion was formulated using uniaxial tensile strength, X and pure torsional strength, S as: $\sigma = X\left\{ {1 - {{\left({ au/S} ight)}<^>2}} ight\}$sigma=X1-tau/S2.
The elastic moduli of recycled carbon fiber nonwoven reinforced polymer (rCFRP) plates are studied using statistical methods to account for the curved, aligned, and entangled fibers. The effect of these fibers on elastic properties is quantified by introducing a joint expected fiber length cumulative distribution function (JELCDF) per unit area with respect to an orientation angle and curvature. The curvatures and orientation angles of the fibers are measured at the crossing point with the reference line. The explicit polynomial functions of the JELCDF are determined from experimental results using the least-squares method. The joint expected fiber length density function is used to estimate the orthotropic elastic moduli of the rCFRP plate, based on a self-consistent scheme where the curvature effect is neglected. The estimated results show good agreement with the experimental results and the present probabilistic method can be an effective method to estimate the performance of the rCFRP laminates.
This work presents an experimental investigation of the bending behavior and dynamic characteristics of SS316L - IN625 functionally graded (FGM) beam specimens fabricated by powder-blown laser-directed energy deposition (L-DED), with numerical analysis performed to validate the experimental results. The beam specimens, composed of stainless steel (SS316L) and Inconel (IN625), were produced with multiple compositionally varying layers to approximate a smooth gradient through the thickness. The compositional transition was confirmed using energy-dispersive X-ray spectroscopy (EDS). Experimental three-point bending and modal tests were conducted to measure the central displacement and natural frequencies of the fabricated specimens. A corresponding layered numerical analysis was performed using a MATLAB implementation based on an established higher-order formulation and the rule of mixtures with power-law distribution, which has been validated in previous studies. Excellent correlation between numerical predictions and experimental results was achieved, thereby confirming the validity of the experimental results. Based on experimentally supported responses, the fabricated SS316L - IN625 beam specimens are shown to exhibit systematic stiffness-mass redistribution associated with the graded architecture, which governs their flexural response and natural frequencies.
Ultrasonic fatigue testing provides an accelerated method for evaluating very-high-cycle fatigue (VHCF); however, its high test frequency induces self-heating in carbon fiber-reinforced plastic (CFRP) composites. To investigate the effect of self-heating, we conducted hydraulic fatigue tests at multiple temperatures and ultrasonic fatigue tests on quasi-isotropic CFRP laminates. In the S-N diagram, the fitting curves of the hydraulic fatigue test at each temperature intersected at approximately 109 cycles, suggesting that self-heating below 80 degrees C has only a minor influence on final failure in the VHCF regime. However, the quantitative evaluation of cracks per layer revealed different accumulation behaviors, indicating the influence of thermal residual stress and temperature-dependent properties of the epoxy. These results show that although ultrasonic testing is effective for evaluating the fatigue life in VHCF, interpreting the damage mechanisms requires careful consideration of the thermal effects caused by self-heating.
The use of Lamb waves (LW) for non-destructive testing of C-FRP components has become established in the aerospace sector due to their advantageous propagation characteristics in plate-like structures. However, the propagation of LW modes is very complex with multifarious factors such as utilised ultrasonic signal, the mechanical behaviour of the materials involved as well as type and location of the defect to be found influencing the developing wave field - just to name a few aspects. In addition, the geometry of the component to be inspected plays a vital role when LW are used to find anomalies as it alters many of the boundary conditions mentioned above. Although different C-FRP components have already been studied in literature, there is a lack of a comprehensive study that clearly and concisely illustrates geometric parameters on Lamb wave propagation in these lightweight components. The target of the present study was thus to identify and discuss similarities and differences for a congruent and geometrically consistent testing program involving various C-FRP components of increasing geometric complexity and affected with different types of damages. To achieve this goal, five numerical models were developed, ranging from comparatively simple monolithic laminates with different thicknesses to more complex shapes such as sandwich components with doublers attached to the facesheets. First, the numerical results were validated using an ultrasonic inspection system that allows for reuse of the tested components by combining a temporarily adhesively bonded actuator with an air-coupled ultrasonic receiver for the ultrasonic measurement. The validated numerical models were then used to highlight technical relationships as well as possibilities and challenges of LW-testing for C-FRP components - important aspects that were finally brought into an overarching context.
Diamond/Cu composites can be used to achieve the efficient heat dissipation of high-power devices. Particularly, the low coefficient of thermal expansion, smooth surface, and relatively low cost of fine-grained diamond/Cu composites make them promising candidates for further research. However, high interfacial thermal resistance is difficult to be mitigated for diamond/Cu composites with a high volume fraction of fine-grained diamond particles, which severely limits their thermal conductivity. In this study, a high-temperature high-pressure infiltration process was employed to construct a three-dimensional (3D) continuous diamond network within the diamond/Cu-B composite, where the fine-grained diamond particles were interconnected by direct bonding. Microstructural characterization provided direct evidence of diamond-diamond bonding that form a primary pathway for efficient phonon transport. This continuous network shifts the heat transfer mechanism from 'metal-matrix-dominated' to 'diamond-network-dominated', thereby overcoming the thermal resistance bottleneck imposed by the high content of fine-grained diamond particles (>= 80%). The composite achieved a thermal conductivity of similar to 399 W/(m.K) while maintaining excellent surface flatness (Ra approximate to 1.3 mu m). The strategy of constructing a continuous diamond network to optimize thermal transport pathways provides a new paradigm for developing next-generation composites with ultra-high thermal conductivity.
Gastric cancer (GC) remains a major global health burden with limited therapeutic options for advanced disease. Dexmedetomidine (DEX), a clinically approved alpha(2)-adrenergic receptor agonist, has shown emerging antitumor potential against GC but suffers from poor tumor accumulation and rapid systemic clearance. In this work, a DEX-loaded hyaluronic acid (HA) nanocarrier (1-HA-2@DEX) was developed to enhance DEX delivery while enabling Cu2+ -responsive fluorescence sensing. The nanocarrier exhibited well-defined structural integrity and optical stability, as confirmed by FT-IR, XRD, and photoluminescence analyses. DEX was efficiently encapsulated with a drug loading content of 7.3 wt% and an encapsulation efficiency of 73%. The fluorescence signal of 1-HA-2@DEX showed sensitive and concentration-dependent quenching toward Cu2+ over 0-200 mu M, with a quenching efficiency of similar to 85.7% at 100 mu M and a Stern - Volmer constant of 5.316 x 10(4) M-1 (R-2 = 0.9908), together with good selectivity and recyclability. In vitro studies using SGC-7901 gastric cancer cells demonstrated that the DEX-loaded HA nanocarrier significantly enhanced anticancer efficacy, achieving 58.6% proliferation inhibition at 48 h and effectively suppressing cell invasion, while the blank carrier showed negligible cytotoxicity. Overall, this study presents a DEX-loaded HA nanocarrier that integrates improved therapeutic efficacy with quantitative Cu-2 sensing, offering a promising strategy for GC treatment and monitoring.
