This study investigates Mode I fatigue delamination in carbon fiber reinforced polymer composites under two-level block variable amplitude (VA) loading, with particular emphasis on correlating delamination behavior with microstructural damage evolution. Double cantilever beam (DCB) specimens were subjected to controlled variations in peak load, load ratio, and loading transition rate, using constant amplitude (CA) loading as a baseline reference. A piecewise fitting methodology was developed for compliance-cycle curves to accurately determine delamination onset life (N onset), yielding more conservative estimates than standard methods. Experimental results identify peak load, load ratio, and loading transition rate as decisive factors governing fatigue damage accumulation. Fractographic analysis reveals two competing failure mechanisms with distinct delamination behaviors: fiber/matrix interfacial debonding, dominant at higher load levels and faster transition rates, produces relatively clear crack paths and accelerated damage growth; whereas mixed failure mode, combining interfacial debonding with matrix shearing damage and prevailing at lower load levels and slower transition rates, generates tortuous crack paths that significantly retard delamination progression. The transition between these mechanisms is governed by the synergistic effects of load level and loading transition rate, with higher transition rates promoting earlier transitions to interfacial-dominated failure. Hackle length measurements provide quantitative evidence of this transition, exhibiting distinct characteristics under different failure mechanisms. These findings establish comprehensive relationships between VA loading parameters and damage mechanisms, providing critical insights for developing microstructure-informed fatigue life prediction models.

Carbon fiber-reinforced polymer (CFRP) composites are widely used in the aerospace industry owing to their high specific strength and modulus. To further expand their utility, structure-function integration is increasingly pursued by incorporating high-loading functional fillers into their interlaminar resin-rich regions. However, the interlaminar behavior of such highly filled composites is complex, and their Mode I interlaminar fracture characteristics and crack propagation mechanism remain poorly understood. To fill this gap, specimens with varying high particle mass fractions were fabricated via a multi-layer resin film infusion (MLRFI) process, to systematically investigate the effects of highly filled particles on their Mode I interlaminar fracture behavior and crack propagation mechanism. Results show that 33.3 vol% filler loading only induced local crack deflection with limited toughening effect. At 50 vol% filler loading, the crack propagation mode shifted from interlaminar-dominated to synergistic interlaminar-intralaminar propagation, fully activating energy dissipation mechanisms and increasing Mode I fracture toughness by 70.5%. Conversely, excessive 60 vol% filler loading introduced numerous weak interfaces, leading to an interlaminar-dominated crack path and reduced fracture resistance. Furthermore, a high-fidelity embedded finite element model (EFEM) was established, which reveals how interleaved high-loading particles mediates composite damage evolution, providing a reliable reference for interlaminar cracking prediction in such composites.

Fiber hybridization offers a useful way to achieve an optimal combination of stiffness and toughness via developing pseudo-ductile behavior. As for intralayer hybrid composites, the dispersion of carbon fiber bundle is crucial to their mechanical properties and damage modes. In this work, intralayer hybrid composites with different fiber bundle dispersion were designed and manufactured. Then, the tensile behaviors of these hybrids were tested experimentally and simulated via FEM. The results indicated that the carbon fiber bundles were more prone to fragmentation with higher dispersion ratio, which could be increased via reducing the fiber bundle size or altering the fiber bundle shape. As a result, the intralayer hybrid composite with dispersed carbon fiber bundles tended to exhibit pseudo-ductility. With the carbon fiber bundle dispersion ratio increasing, the carbon fiber bundle volume fraction (VCFB), at which the pseudo-ductile behavior was demonstrated, could be improved from 10 % to 18.3 %. Furthermore, the tensile strength was increased by 15.5 % for the dispersed hybrid composite with VCFB=10 % and 6.1 % for that with VCFB=13.3 % compared to their counterparts with centralized carbon fiber bundles.

Fiber-hybridization is an effective strategy to overcome the catastrophic fracture of fiber-reinforced polymer composites via achieving pseudo-ductility. However, the demonstration of pseudo-ductile behavior is limited by low carbon fiber volume fraction, i.e. low stiffness and strength, for traditional carbon/glass hybrid composites with all carbon layers centralized in the middle. In this work, a new layup concept based on layer dispersion was introduced to improve the carbon fiber volume fraction of hybrid composites while maintaining pseudo-ductile behavior. Different hybrid configurations with dispersed layups were tested experimentally and validated numerically. The results have shown that by splitting the centralized carbon layers into different dispersion units, the damage mechanisms of the hybrids can be significantly differed. Firstly, the interaction between two dispersed carbon layers was reduced with the increasing of the distance between them, which promoted more carbon layer fractures and was therefore beneficial for pseudo-ductility. Secondly, the hybrid composites tended to fail in a premature way, when the thickness of a single dispersion unit was increased to 80 mu m. Compared to traditional pseudo-ductile hybrid composites, the maximum carbon layer volume fraction of pseudo-ductile hybrids with dispersed layups was up to 25.0 %, which was a 76 % improvement. As a result, the tensile modulus was increased by 16.70 % and the pseudo-yield stress was improved by 24.64 % in comparison with those of the hybrids with all carbon layers in the middle.

With the increasing demand for the construction of large‐scale space structures and on‐orbit maintenance of spacecraft, there is an urgent need for materials and processes tailored for on‐orbit manufacturing. This review highlights challenges in on‐orbit manufacturing using polymer‐based 3D printing, i.e., Fused Deposition Modeling (FDM) and Direct Ink Writing (DIW) technologies. Though FDM has been validated in on‐orbit manufacturing to some extent, its reliance on thermoplastics faces limitations in energy efficiency, thermal stability, and scalability for large space structures. A novel direct ink writing coupled with frontal polymerization (FP‐DIW) approach is proposed, which synergizes frontal polymerization's energy‐efficient in‐situ curing with DIW's equipment simplicity and structural flexibility. This method enables unsupported fabrication of complex geometries and fiber‐reinforced composites with superior mechanical performance, space‐environment resistance, and functional integration. Based on FP‐DIW, a full‐lifecycle framework, including self‐healing, FP‐DIW repair, and FP‐DIW remanufacturing, is proposed for future on‐orbit manufacturing. This paper aims to shed light on the material as well as process selection for on‐orbit manufacturing, hence to promote the development of on‐orbit manufacturing technology.

To investigate the effect of interlaminar properties on the tensile properties of fiber hybrid composites,two kinds of epoxy resins with different toughness,7901 and 9A16,were used as the matrix.Interlayer carbon/glass hybrid composites with different numbers of carbon fiber layers were designed and manufactured.The effects of mode Ⅱ interlaminar fracture toughness(GⅡC)on the failure mode and mechanical properties of carbon/glass hybrid composites were investigated through both theoretical and experimental investigation.The results show that,the higher mode Ⅱ interlaminar fracture toughness is,the more the carbon layer tends to fail in fragmentation,achieving a higher critical thickness for fragmentation,which is beneficial for achieving pseudo-ductility.In addition,the GⅡC on the modulus and strength of hybrid composites is marginal,as the variation is within 5％.However,the GⅡC demonstrates a significant impact on the pseudo-ductility strain,which is decreased by 40.7％when the GⅡC is increased from 1.75 N/mm to 2.08 N/mm.

The interfacial bonding is of essential importance for the mechanical properties of high-temperature resistant carbon fiber/phthalonitrile composite materials. To promote the interfacial adhesion of carbon fiber/phthalonitrile composites, three surface modification methods, namely HP302 sizing, diazotization modification, and oxidation-diazotization modification, were applied and compared. The results showed that the de-sizing treatment barely affected the mechanical properties of the composites. Both re-sizing with HP302 agent and diazotization modification improved the mechanical properties, while the mechanical properties were drastically decreased via the oxidation-diazotization modification. Among these surface modification methods, the diazotization treatment derived the best mechanical properties of carbon fiber/phthalonitrile composites both at room and high temperature. Specifically, the flexural strengths were 345 MPa (RT), 525 MPa (300 degrees C), and 442 MPa (400 degrees C), which were 47%, 302%, and 281% higher than those of the pristine composites. The interlaminar shear strengths were 33 MPa (RT), 26 MPa (300 degrees C), and 27 MPa (400 degrees C), which were all over twofold than those of the original counterparts.{Graphical abstract}

The application of cyanate esters has been greatly limited by their high curing temperatures, which induce residual thermal stress and subsequently degrade their mechanical properties. In this study, hydroxybenzonitrile homologs (HBNx) were developed to reduce curing temperature of bisphenol E cyanate ester (BECE) while improving their mechanical properties. It was found that the position of hydroxy (-OH) substituent in HBNx had a significant impact on the curing temperature of BECE. Among the homologs, ortho-hydroxybenzonitrile (HBN2) demonstrated the highest reactivity, as indicated by quantum chemical calculations and confirmed by differential scanning calorimetry analysis. As a result, the curing temperature of BECE was effectively reduced from 250 degrees C to 140 degrees C with the addition of 15 wt% HBN2. Additionally, the addition of HBNx improved the mechanical properties of cyanate ester resins and their composites reinforced by quartz fibers (GF). Specifically, the mechanical properties of HBNx/BECE castings remained at high levels, with impact strength, tensile strength, and flexural strength measured at 38.6 kJ/m2, 94.5, and 100.0 MPa, respectively. Furthermore, the mechanical properties of GF/HBNx/BECE composites exhibited an overall improvement, with the maximum enhancements in short-beam shear strength, tensile strength, and flexural strength reaching 78.0%, 27.3%, and 45.1%, respectively. Nevertheless, the hydroxy substituent position in HBNx had a relatively minor impact on these mechanical properties. This study presents a promising strategy for synergistically enhancing both the processability and mechanical properties of CE resins and their composites in a cost-effective manner.

The aviation industry has a substantial demand for bismaleimide (BMI) resins that possess high toughness, excellent thermal stability, and low dielectric constant, which are critical for wave-transparent materials. This study presents the synthesis of a novel fluorinated polyetherimide (F-PEI) and its integration with BMI resin using an in situ pre-polymerization method. Upon blending 4 wt% F-PEI with bismaleimide resin, the resulting blending resin (BDP-4) demonstrated a significant enhancement in both impact strength (59.6 % increase) and flexural strength (13.9 % increase) compared to the unmodified BMI. Additionally, the glass transition temperature of BDP-4 was enhanced to 299.3 degrees C, representing a 5 degrees C increase, and the corresponding dielectric constant (k) and dielectric loss (tan delta) at 15.2 GHz were decreased from 3.02 to 2.96 and from 0.010 to 0.009, respectively. These improvements are attributed to the phase separation induced by the F-PEI content, which engendered a synergistic toughening mechanism beneficial for both thermal and dielectric attributes. Notably, the flexural strength (630.1 MPa), flexural modulus (26.5 GPa), and interlaminar shear strength (67.1 MPa) of quartz fiber reinforced F-PEI/BMI composites (QF/BDP-4) exceeded those of pure BMI composites. The findings indicate that F-PEI modification is an effective strategy for advancing BMI resin performance, with potential applications in high-performance industries such as aerospace and electronics.

The high curing temperature and long curing cycle severely reduce the processability of cyanate ester (CE) resins and increase production costs. To lower the curing temperature and save costs, prevalent catalysts are normally used, but they frequently result in detrimental effects on the mechanical, dielectric, and thermal properties of the resin. In this study, aminobenzonitrile homologues (ABN(x)) were developed to facilitate the curing of bisphenol E cyanate ester (BECE). The amino group within ABN(x) functioned as a catalyst to accelerate the curing reaction, while the cyano group within ABN(x) engaged in copolymerization with BECE. Therefore, the curing temperature of BECE could be tailored by varying the type and quantity of introduced ABN(x). Among the homologues, meta-aminobenzonitrile (ABN(3)) demonstrated the highest reactivity based on the quantum chemical calculation. As a result, the largest reduction of curing temperature of BECE is 100 degrees C (from 250 degrees C to 150 degrees C). Meanwhile, the excellent mechanical properties of BECE were maintained and even improved. The addition of ABN(x) up to 15 wt% did not compromise the viscosity of BECE (<= 203 mPa s at 30 degrees C), maintaining it at an optimal level for liquid moulding. Furthermore, the short-beam shear strength and the flexural strength of the quartz fiber reinforced BECE composites were improved by 71% and 37% after incorporating 7 wt% ABN(x), respectively. The current study offers a promising strategy for synergistically enhancing both the processability and mechanical properties of CE resins and their composites in a cost-effective manner.

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Wave-absorbing honeycomb sandwich structure (HSS) is widely used in aviation equipment, playing an important role in the integration of load-bearing and stealth shielding. The high-intensity service of aviation equipment beyond design condition accelerates damage and complicates failure triggers. In this work, a decentralized construction strategy with multiple resonant absorption peaks is proposed to enhance the electrical performance damage tolerance (EDT) of wave-absorbing HSS in 4-18 GHz frequency band. The designed multi resonant absorption peaks for 30 mm thick wave-absorbing honeycomb with 1 mm thick SiO2 fiber reinforced epoxy resin (SiO2f/ER) composites as top and bottom panels occur in the vicinity of 5 GHz, 9 GHz, 13 GHz, and 17 GHz, respectively. When the panel damage area accounts for 72 % or the penetrating damage area accounts for 18 %, the effective absorption bandwidth (EAB) of proposed HSS covers 4-18 GHz, indicating excellent EDT. By analyzing the normalized impedance, Smith chart, as well as power loss density, the excellent EDT is attributed to the pinning effect at each resonant frequency point, which benefits both impedance matching and electromagnetic wave (EMW) attenuation.

The impinging stream reactor is an efficient equipment for fluid mixing that strengthens the mass and heat transfer in two fluids mixing processes, with potential for many chemical engineering and industrial applications. In this paper, the flow characteristics and concentration distribution of baffle-type impinging stream reactor are analyzed by numerical simulation to optimize the reactor. The influence of different baffle spacing W and baffle aspect ratio ? on the velocity, turbulent kinetic energy and mixing effect of the reactor are explored. It is indicated that the flow regime changed with the inserted baffle in reactor. With the decrease of the baffle spacing and the baffle aspect ratio, the velocity, turbulent kinetic energy and the fluid mixing intensity firstly increase and then decrease. The mixing intensity of the flow field with different baffle spacing is compared, it is found that W = 40mm>W = 60mm>W = 30mm>W = 80 mm. The mixing intensity with different baffle aspect ratios are found that ?=1>?=1.5>?=0.75. The baffle-type impinging stream reactors with W = 40 mm and ?=1 have the best mixing effect.

Efficient toughening of the interlaminar fracture toughness for CFRP composites without sacrificing in-plane mechanical performance remained an unresolved challenge. Here, we present a synergistic toughening strategy by construction of hierarchical architecture, within which carbon nanotubes (CNTs) in-depth stitched into the nano-channel between neighboring carbon fibers at the interlaminar region. Mode I fracture test revealed that, even at low concentration of CNTs (0.3 wt%), a considerable improvement (50%) on mode I fracture energy GIc of composites can be realized, from 1098.6 to 1647.8 J/m2 which is nearly two times greater than that of most aerospace CFRP laminates (∼500 J/m2). The excellent fracture toughness is predominantly attributed to the desired hierarchical architecture, which simultaneously triggered the intrinsic toughening by CNTs nano-bridging and extrinsic toughening mechanisms due to carbon fiber bridging, as was demonstrated by SEM images of fracture surfaces and further verified by finite element simulations. These findings offer significant guidelines for designing CFRP composites with high fracture toughness by application of low content CNTs using cost-effective resin mixing process.

Superhydrophobic property is highly demanded for fiber reinforced polymer composites (FRPC) to deal with the accumulation of ice and stains. However, the traditional superhydrophobic coating prepared by nanoparticles & adhesive strategy cannot avoid the unreliable interfaces. Herein, the flexible interface-free superhydrophobic films were fabricated by infusing the paper template with PTFE and subsequent sintering treatment. The adjustable self-growing hierarchal structure could be achieved by crystallization of PTFE tuned by cooling rate. By pressure-assisted integrated molding, the optimized textured film obtained at a cooling rate of 2 degrees C/min was employed to FRPC with reliable interfacial bonding. The prepared superhydrophobic FRPC (SH-FRPC) could withstand at least 800 cycles' tape peeling, 200 cycles' sandpaper friction and 24.8 m/s water impact (We = 16908) with unchanged superhydrophobicity. Besides, the worn surface by extreme effect recovered its super -hydrophobicity by specific sandpaper friction in <10 s or reheat treatment at 380 C. What's more, the prepared SH-FRPC shown excellent self-cleaning and anti-icing capacities compared with the original FRPC. With outstanding operational feasibility and retention of mechanical properties, the multi-functional FRPC is attrac-tive for applications in rainy or dusty environments.

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The curing reaction of cyanate ester (CE) resin is characterized by high temperature and long time, which makes its preparation process complicated, time-consuming, and energy-consuming. To reduce their curing temperature and time, a nonmetallic catalyst, 4-(4-aminophenoxy) phthalonitrile (PN-NH2), was applied to accelerate the curing of bisphenol E cyanate ester (BECE). The effects of PN-NH2 contents on the curing behavior, thermal, mechanical, and dielectric properties of PN-NH2/BECE were investigated. The characteristic curing temperatures of PN-NH2/BECE, compared to that of pure BECE, were significantly decreased by the incorporation of PN-NH2 and so was the activation energy. For instance, when the content of PN-NH2 = 7 wt %, the mixtures would gel at room temperature and the activation energy was decreased by 42.4% for Ozawa-Flynn-Wall method and 45.2% for Kissiger-AkahiraSunose method; compared with pure BECE, the maximum reduction of onset, peak, and endset temperatures for catalyzed resins are decreased by 198.6, 93.5, and 61.9 degrees C, respectively. In addition, unlike the traditional catalysts, PN-NH2 was chemically bounded to the cross-linked network of CE, thus avoiding stress concentration, migration, precipitation, and plasticizing effects of residual catalysts in the cured resins. Consequently, the superior properties of BECE, such as mechanical (flexural strength > 163 MPa and tensile strength > 107 MPa) and dielectric properties (dielectric constant of 2.94 to 3.17), were retained whilst the curing temperatures were greatly reduced. The improved processability could broaden the application of cyanate esters.

The dynamic regulation of infrared signals has received widespread attention. For the typical multilayer adaptive infrared camouflage structure, many efforts have been made to explore a variety of materials; metals, carbon nanomaterials and polymers can all be used in this field. However, little attention has been given to the mechanism of mass transfer within the structure, which could play a decisive role in the infrared camouflage performance. In this paper, the influence of cation and anion enrichment on the band structure and density of states of multiwalled carbon nanotubes (MWCNTs) is discussed through density functional theory (DFT), and the results show that ion migration plays an important role in the regulation of the emissivity. On the basis of theoretical research, a novel waterborne polyurethane (WPU)/ionic liquid (IL) gel is further prepared to realize control of the ionic transport capability, and a MWCNT film-based sandwich structure is fabricated to achieve adaptive infrared camouflage. The maximum emissivity regulation coefficient reaches 0.85, which is the highest to the best of our knowledge. The optimization scheme proposed in this work can provide a good reference for other similar problems.

CFRP composites are widely used in aerospace due to their excellent mechanical properties, however, due to the anisotropy of the individual plies, the electro magnetic interference(EMI) shielding efficiency(SE) for vertically polarized waves of the unidirectional fiber laminates is poor. In order to protect electronics within these equipments from increasingly severe electromagnetic interference, it is particularly important to enhance the electromagnetic shielding efficiency of the CFRP. In this paper, Al particles were introduced and a conductive network was constructed in the CFRP interlaminar region by condensing the Al particles on the prepreg surface. The effects of different Al particle contents on EMI SE and mechanical properties of composites were studied. With the increase of Al particle contents, the electrical conductivity and the EMI SE of CFRP composites increase. When the Al mass fraction in the resin is 33.3%, the in-plane conductivity of the composites increases by 3 orders of magnitude, the EMI SE of the Al particle sandwich CFRP composites is improved by more than 10 dB in the frequency range of 3-17 GHz. With the increase of Al particle contents, the interlaminar shear strength and bending strength of the composites increase first and then decrease. When the Al mass fraction in the resin is 33.3%, the interlaminar shear strength (ILSS) of the composites increases by 5.2% to 80.5 MPa, and when the Al mass fraction in the resin is 50%, the bending strength of the composites increases by 20% to 1441.0 MPa and the bending modulus increases by 10.2% to 101.83 GPa. It can be seen that the mechanical properties and electromagnetic shielding effectiveness of the Al particles sandwich CFRP composite can be improved simutaneously. It is a kind of structure electromagnetic shielding integrated composite with broad application prospects.

Ionogels have attracted tremendous interest for flexible electronics due to their excellent deformability, conductivity, and environmental stability. However, most ionogels suffer from low strength and poor toughness, which limit their practical applications. This article presents a strategy for fabricating ionogels with high toughness by constructing high-density hydrogen bonds within their microstructure. The ionogels exhibit a maximum fracture strength of 11.44 MPa, and can sustain a fracture strain of 506%. They also demonstrate a fracture energy of 27.29 MJ m-3 and offer a wide range of mechanical property adjustments (fracture stress from 0.3 to 11.44 MPa, fracture strain from 506% to 1050%). Strain sensors assembled with ionogels demonstrate exceptional sensing performance and enable motion detection of human joints. This study provides a new approach for achieving strong and tough ionogel design used for high-performance flexible electronic applications.