This paper investigates the interlaminar delamination behavior of 3D needled nonwoven preforms. Predicting this behavior is challenging due to the complex fiber architecture of the needled preform. To address this, a novel hybrid finite element modeling approach is proposed. In this approach, the nonwoven fabric plies are modeled using shell elements and the z-directional needling fiber bundles are modeled using truss elements. The model is rigorously grounded in experimental characterization: geometric parameters and distributions are derived from Micro-CT scans, while the constitutive laws for fabric bending and bundle pull-out are calibrated via dedicated picture frame and fiber bundle pull-out tests, respectively. The key innovation lies in this efficient multicomponent representation, which captures the essential delamination mechanisms without prohibitive computational cost. The load-displacement curves predicted by the model demonstrate close agreement with experimental results. Furthermore, applying this model reveals a significant new finding: the average delamination load exhibits an approximately linear relationship with needling density. This work provides a reliable numerical framework for analyzing and optimizing the interlaminar performance of 3D needled preforms.

To characterize the nonlinear, anisotropic, and large-deformation behavior of three-dimensional angle-interlock preforms during forming over complex surfaces, a multi-mode decoupled hyperelastic constitutive model is established. Based on structural tensors and physical invariants associated with different deformation modes, strain energy density functions are formulated for warp/weft tension, thickness compression, in-plane shear, and out-of-plane shear, and the corresponding material parameters are identified through mechanical characterization tests. The model is implemented in ABAQUS via a VUMAT user material subroutine, and its predictive capability for complex-surface forming is validated by hemispherical forming experiments. The results show that the established model can reasonably predict the load–displacement response, the in-plane shear angle distribution on the convex side, and the boundary draw-in behavior during forming. The relative errors in the peak load and the peak shear angle along the 45° path on the convex side are 15.2% and 6.3%, respectively. During forming, in-plane shear is the dominant deformation mode, with a maximum shear angle of 37.4°, mainly located in the curvature transition region between the hemispherical punch-contact region and the flange region on the concave side. The sectional out-of-plane shear angle remains relatively low overall, with elevated values mainly concentrated in the bending transition zones of the sections. Different initial yarn orientations primarily alter the spatial distribution of high-shear regions and the boundary contour evolution, while exerting limited influence on the maximum shear angle. These results provide a reference for the forming simulation and process optimization of three-dimensional woven preforms over complex surfaces.

In this study, A novel wear-resistant slippery liquid-infused porous surface (SLIPS) is wrapped around the Si₃N₄ fiber to mitigate the wear damage induced by the high-frequency weaving process. The SLIPS were fabricated by infusing soybean oil (SO) and epoxidized soybean oil (ESO) into porous substrates with a controllable pore size distribution, which was achieved through the hydroxyl acrylic resin (HAR) cross-linking process. The morphological structure, mechanical properties, and tribological performance of the SLIPS, as well as their protective effectiveness for Si3N4 fiber, were systematically investigated. The results indicate that SLIPS formed with the porous substrate featuring an optimized pore size distribution of 823 nm achieve remarkable surface flatness and enhanced mechanical properties. Meanwhile, the ESO-infused SLIPS exhibit a low and stable COF (0.019) and superior wear resistance (604 cycles). Notably, the Si3N4 fiber protected by this system retained over 90% of its residual breaking strength even after 800 friction cycles. The superior protective capability of SLIPS is governed by a dynamic "release-and-reabsorb" tribological mechanism, efficiently driven by the synergistic pore regulation and chemical anchoring effect. This work provides a scalable interfacial engineering approach for the weaving protection of advanced ceramic fibers.

The interfacial properties of carbon fiber/epoxy composites are inherently influenced by their heterogeneous microstructure. However, quantitatively linking specific heterogeneity parameters to interfacial behavior has been difficult using experimental approaches. To address this, we present a data-driven framework that combines Latin hypercube sampling (LHS), molecular dynamics (MD) simulations, and machine learning. Fifty atomistic interface models with systematically varied heterogeneity were built using LHS. From MD simulations, five interfacial features were extracted. These results show that mechanical properties and interfacial density respond noticeably to heterogeneity, with coefficients of variation (CV) exceeding 10%. In contrast, the interfacial contact area remained relatively stable, showing only a 2% CV. Principal component analysis condensed the five features into two main dimensions: interfacial contact density and interfacial fracture resistance, together explaining 86.78% of the total variance. A generalized additive model was then developed, successfully mapping heterogeneity parameters to these two dimensions with good predictive accuracy (validation R2 > 0.8). The model indicates that interfacial contact density depends mainly on carbon fiber vacancy site density, following an almost linear negative trend. Interfacial fracture resistance, however, is nonlinearly and positively influenced by epoxy cross-linking density. Using this model, dense sampling across the heterogeneity parameter space revealed a complete topography of interfacial state space. Cluster analysis identified four typical states, each with distinct atomic packing densities and failure mechanisms. This study offers a new perspective and a theoretical basis for designing high-performance composite interfaces.

This study focuses on addressing the challenges of poor integrity and insufficient mechanical properties in carbon fiber honeycomb composites, which arise from weak interlaminar node connections and unequal free/bonded wall thicknesses. These issues are particularly critical in the field of satellite antennas, which require lightweight and high-load-bearing structures. To achieve continuous fibers and superior cell integrity in honeycomb materials, a honeycomb core structure with equal thicknesses for free walls and bonded walls was developed via 2.5D interlayer interlocking weaving technology. Honeycomb sandwich structure specimens with honeycomb cell side lengths of 5, 9, and 15 mm and equal-wall-thickness were fabricated. Additionally, comparison specimens with unequal wall thickness and 15 mm cell side length were prepared. Out-of-plane compression tests were conducted, combined with damage characterization using SEM, 3D profilometer, and high-definition video capture. A mesoscale-macroscale damage model was established, demonstrating good agreement between simulation and experimental mechanical responses. Analysis indicates that the small-cell-size equal-wall-thickness structure exhibits excellent out-of-plane compression performance, with a 296.88% strength increase compared to the large-cell-size equal-wall-thickness specimen. Notably, the equal-wall-thickness structure demonstrates a 63.6% strength improvement over the unequal-wall-thickness specimen under identical side wall length conditions. Simulation and experimental results reveal that the damage in honeycombs with equal wall thickness originates from microcracks in the matrix, progresses through fiber fracture and cell wall buckling, and ultimately leads to the progressive collapse of the honeycomb cells. This study provides an important theoretical and experimental basis for the design and optimization of high-performance honeycomb structures.

Jute fiber composites have weak interfacial bonding and poor hygrothermal stability. This paper proposes a new method for engineering a tough organic interfacial layer on jute fiber surfaces using Reactive Black 5 (RB5) dye. RB5 molecules formed stable covalent ether bonds with jute fibers through Michael addition reaction, improving the thermal stability of the fibers (with a slightly lower onset degradation temperature but enhanced main-stage resistance) and making them exhibit "low polarity, high dispersion" characteristics (polar component 1.8mN/m, dispersion component 30.2mN/m). Unidirectional (0 degrees) and cross-ply (90 degrees) structure composites were prepared with epoxy resin matrix, generating strong van der Waals forces and potential pi - pi interactions. The results show that the CP (90 degrees) RB5 composite presents a uniform black color. The constructed tough interfacial phase substantially improved the thermal stability and load transfer efficiency of the composite. The initial decomposition temperature (T5%) increased by 26.39 degrees C while the main degradation (T20% and Tmax) shifted to a slightly lower temperature. The interfacial shear strength (ILSS) increased by 39.98%, tensile strength increased by 40.31%, flexural strength increased by 123.89%, showing a "fiber-resin aggregate" ductile failure mode with no acetaldehyde release. After hygrothermal aging, the performance of the CP (90 degrees) RB5 composite was stable. Although the hue shifted, it still maintained a uniform black color. Compared with the untreated sample, T5% increased by 12.31 degrees C while the main degradation temperature (T20% and Tmax) also decreased slightly, the tensile strength retention rate was as high as 105.26%, the flexural strength retention rate was 56.65%, and the VOC emission was the lowest, with no formaldehyde or acetaldehyde release. It exhibits significant potential for applications in automotive interiors and rail transit interiors, where stringent mechanical performance and resistance to hygrothermal aging are required.

ABSTRACT In this study, by varying the proportions of four sets of yarns (binder, weft, warp insertion and weft insertion), four concave 3D angle‐interlock woven composites (3DAWCs), named S1(1:1:0:0), S2 (0.5:1:0.5:0), S3 (1:0.5:0:0.5), S4 (0.5:0.5:0.5:0.5), were designed and fabricated. Compression after multi‐angle (90°, 75°, and 60°) impact (CAI) tests on four concave 3DAWCs were conducted. The surface crack propagation and the internal yarn failure patterns were characterized by using 3D profilometer and CT scanning. A concave 3DAWC CAI model at microscale was established for finite element (FE) analysis. The results indicated that the ultimate strength and compressive stiffness of the four 3DAWCs increased as the impact angle decreased. The analysis of surface compression damage shown that the greater the impact angle, the more prone 3DWACs were to crack propagation. The study further revealed that the incorporation of weft insertions into the reinforcement of 3DAWCs were highly effective in enhancing CAI strength. And introducing warp insertions in 3DAWCs could reduce crack propagation. The results of the FE calculation and the CT characterization are highly consistent, which verifies the reliability of the model. The simulation results shown that a reduction in the impact angle leads to an increase in the stress transfer efficiency of the yarn during compression, and the significant deformation of the weft is the main cause of crack propagation.

3D textile structure resin matrix composites (3DTSRMCs) are increasingly employed in aerospace applications owing to their significant advantages, including excellent mechanical properties, flexible structural design, and superior near-net-shape capabilities. However, these materials are commonly subjected to prolonged cyclic loading during service, which can diminish their damage tolerance and reduce their service life. Addressing this challenge has become a central focus of research in recent years. In light of this, this paper provides a comprehensive overview of recent advances in the experimental characterization and theoretical analysis for 3DTSRMCs' fatigue behavior, and the content covers several critical topics. First, a detailed classification of 3DTSRMCs is provided according to the preform forming technologies, and basic principles and key parameters of fatigue are introduced; on this basis, the experimental testing method and advanced damage detection technology are summarized, followed by a detailed discussion on some factors affecting the fatigue behavior of 3DTSRMCs; furthermore, the research status of fatigue theory analysis methods of 3DTSRMCs is reviewed; finally, the review identifies current technical challenges and emerging research trends. This work aims to provide valuable theoretical insights and technical references to support further investigations into the fatigue performance of 3DTSRMCs.

The Mode I interlaminar fracture toughness (GIc) of seawater-aged carbon fiber reinforced polymer (CFRP) composites depends on a delicate balance between opposing hygrothermal aging mechanisms, further influenced by salt-induced effects. This complexity creates a gap in predictive models for post-aging interlaminar properties, hindering the marine application of CFRP composites. To address this challenge, we propose a phenomenological model for quantitatively predicting the GIc of CFRP subjected to seawater aging at different concentrations, based on seawater aging and delamination failure mechanisms. Our model predicts GIc directly from fundamental material properties, such as equilibrium moisture content and glass transition temperature, and estimates GIc scatter bands under different seawater concentrations using Monte Carlo simulations. Validation with computational and experimental data reveals a maximum mean absolute percentage error (MAPE) of 7.59

Fine-woven needled C/C composites typically served in thermal structural components under high-load impact, where their service environment involved complex dynamic loads. In this study, the effects of strain rate and loading mode on impact performance and damage evolution mechanisms were investigated by combining experimental and finite element methods. Results showed that the impact performance of the composites demonstrated significant strain rate dependence and anisotropy. The X-impact strength and modulus increased moderately with strain rate, which was attributed to the dense in-plane yarn. In contrast, the Z-impact exhibited a more prominent strain rate strengthening effect: at low strain rates, its performance was limited by interfacial microcracks; while at high strain rates, the straight Z-yarns enabled rapid stress transmission, leading to Z-impact performance surpassing that of the X-impact. Strain rate and loading direction jointly influenced the damage evolution. For X-impact, damage initiated at in-plane yarn intersections and accelerated with increasing strain rate. For Z-impact, interfacial microcracks were dominant at low strain rates, whereas Z-yarn failure and shear damage became the main modes at high strain rates. The revealed strain rate dependence and anisotropy of impact performance, and the proposed finite element method provided theoretical guidance for the service application of C/C composites.

Gradient structural design has emerged as an effective approach for improving the impact resistance and damage tolerance of composites. This work investigates the low-velocity impact behavior and damage evolution of two typical gradient-structured three-dimensional (3D) braided composites (4D-F5D and F5D-4D). Drop-weight impact tests combined with high-speed photography were employed to characterize the impact response and progressive damage process. The results reveal that the 4D-F5D composite exhibits a 15.63% higher peak load and superior initial flexural stiffness compared with the F5D-4D composite. X-ray computed tomography (CT) results demonstrate that the F5D-4D composite presents more severe internal damage, with an 8.53% higher crack volume fraction and a wider matrix damage region. Although axial yarns on the impact surface effectively suppress through-thickness crack propagation and prevent complete penetration failure, the total absorbed energy of the two composites remains nearly identical (59.02 J vs. 59.58 J). This study demonstrates that concentrating axial yarns on the non-impact surface (4D-F5D) enhances load-bearing capacity and structural stability under low-velocity impact. The results provide key experimental evidence and theoretical support for optimizing the structural design of 3D braided composites.

In this paper, an ultra-thin and wear-resistant protective membrane is employed to reduce wear damage to Si3N4 fiber during the weaving process. Specifically, the polyurethane/polyvinylidene fluoride (PU/ PVDF) nanofiber membrane with a three-dimensional structure was first wrapped on Si3N4 fiber using the electrostatic spinning method, followed by improving the interfacial bonding between the nanofibers to form a wear-resistant layer by the cross-linking method. The results show that the electrospinning technique can be used to uniformly and continuously wrap the PU/PVDF nanofiber membrane on Si3N4 fiber, and the hydroxy acrylic resin (HAR) can form a cross-linking structure between the PU/PVDF nanofiber membrane to improve its mechanical properties. The protective membrane with a different cross-linking degree could be reasonably controlled to ensure that it provides excellent protection for the Si3N4 fiber during friction. When the cross-linking time was 6s, the protective membrane wrapped on the Si3N4 fiber had the lowest friction COF (0.022) and excellent wear-resistant capability (578 friction cycles), with a 2.1

ABSTRACT A data‐driven framework integrating micro‐CT characterization with stochastic modeling is developed to generate statistically equivalent 3D virtual fiber architectures for carbon fiber nonwoven preforms. Key microstructural descriptors, including fiber length, orientation, curvature, and bundle width, are extracted from micro‐CT data to serve as inputs for the stochastic fiber growth algorithm. Multi‐scale calibration and validation confirm the statistical equivalence between the virtual preform and the physical specimen. The calibrated model parameters include fiber length distribution (lognormal, μ = 1.9, σ = 0.633), orientation distributions (polar angle: normal at 90° with σ θ = 1.1°; azimuthal: bimodal at 15°/155° with σ φ = 45°), and curvature autocorrelation coefficients ( R Δθ = 0.7, R Δφ = 0.5). The spatial hashing strategy reduces computational cost, enabling efficient generation of large‐scale preforms. This modeling framework allows the geometric reconstruction of fibrous materials with different fiber volume fractions and provides a sound geometric basis for evaluating permeability and mechanical properties of the composites.

3D layer-to-layer interlock woven composites (3D LTLIWCs) are inevitably subjected to the severe cyclic vibration fatigue environment in the application of aero-engine structures and their durability should be proven. In this paper, three 3D LTLIWCs with different preform structure types are prepared by adjusting warp interlacing frequency. First-order cantilever bending resonance tests are conducted at four stress levels to evaluate dynamic response. The characterization capabilities of two fatigue life models are compared. The interrupted fatigue tests incorporating with optical microscopy and micro-computed tomography are employed to illustrate damage evolution. The results show that the fatigue life of 3D LTLIWCs decreases gradually with increasing stress levels. However, due to its lowest warp interlacing frequency, the SS structure effectively dissipates and transfers fatigue stress, resulting in the longest fatigue life among all structures. The frequency degradation occurs in three phases: stable, linear, and accelerating. Compared to the Basquin model, the Weibull model demonstrates superior fitting capability and predictive accuracy, and is used to was used to estimate the stress limit values of PS, TS, and SS that can withstand 107 cycles without failure, which are 125 MPa, 134 MPa, and 173 MPa respectively. The damage undergoes an evolution process involving matrix cracking, interfacial debonding, fiber bundle splitting, and yarn fracture. Besides, the interfacial debonding length of SS is longer than that of PS and TS, but its warps is not prone to catastrophic shear fracture and the overall damage degree is low.

Variable-thickness 3D woven composites (VT-3DWCs) have been increasingly applied in the aerospace field, and their performance characteristics and failure behavior are closely related to the yarn-reduction position distribution. Based on the same preform weaving pattern, two types of VT-3DWCs with different yarn-reduction position distributions are prepared by reducing the number of outer-layer yarns: novel gradual yarn reduction 3D woven composites (GYR-3DWCs) and conventional abrupt yarn reduction 3D woven composites (AYR-3DWCs). Their thickness transition regions are divided into four equidistant parts (P1-P4), and one layer of yarns is alternately removed from the front and back surfaces of each part. Axial tensile tests are conducted using a combination of 3D profilometer, scanning electron microscope (SEM) and digital image correlation (DIC) to acquire mechanical response curves, multi-scale damage morphologies and full-field strain distributions. A macro-meso coupled finite element model is developed based on X‐ray micro-computed tomography (Micro-CT) slice images, and a progressive damage theory model is incorporated to predict tensile properties and analyze damage evolution. Results show that the maximum relative error between predicted and tested values of tensile modulus and strength is only 5%, which proves that the effectiveness and reliability of the proposed model. Compared with AYR-3DWCs, the average tensile modulus and strength of GYR-3DWCs are increased by 13.2% and 23.8%, respectively. This indicates that the uniform yarn-reduction distribution significantly improves the tensile properties of VT-3DWCs. Moreover, the major failure modes of the specimens are binder/warp yarn fracture and matrix cracking, with damage concentrated in P4 of the thickness transition region.

Three-dimensional layer-to-layer interlock woven (3D LTL) preforms are ideal reinforcement materials for complex curved components like engine blades due to their exceptional integral formability. However, during forming processes, the inevitable macro-scale deformation of the preform leads to mesoscale variations within internal yarns, such as misalignment, slippage, and compaction. Developing simulation models capable of efficiently predicting these variations as well as the global forming behavior for complex geometries is a prerequisite for achieving precise preform design. Therefore, we propose a new yarn-scale preform deformation simulation model to describe the deformation behavior of 3D LTL preforms during the hemispherical forming process. The effects of mesh density and coefficient of friction on the model's computational efficiency and accuracy were examined. Based on this, the model predicted the mechanical response, shear deformation, and in-plane indent area during preform forming. Quantitative comparison with experimental results validated the developed approach. The model accurately predicts the forming behavior of 3D LTL preforms, demonstrating good agreement in terms of both global deformation behavior and local structural variations.

The core layer of 3D woven spacer fabric reinforced polymer composites (WSFC) is relatively weak, leading to limited mechanical properties. In this work, improvements in the mechanical properties of 3D WSFC were achieved by modifying the core layer structures, including foam filling, double-layer stacking, and misaligned stacking. The results show that the flexural strength of 3D WSFC foam sandwich panels in the weft direction is significantly greater than that in the warp direction. Filling the core layer with epoxy microsphere foam and polyurethane foam enhances the warp direction flexural strength by 51.8% and 124.3%, respectively. Moreover, variations in core layer structure significantly influence the flexural behavior and damage modes of the 3D WSFC foam sandwich panels. The double-layer structured 3D WSFC foam sandwich panels exhibit less damage than the single-layer panels. When the core structure is misaligned, both types of 3D WSFC foam core sandwich panels show similar mechanical properties, significantly reducing the performance differences across directions. To further understand the mechanical response, macro/meso-scale models of 3D WSFC foam sandwich panels with various core configurations were developed, enabling in-depth analysis of stress distribution and damage mechanisms.

Parametric full-scale finite element models were established based on actual yarn structure to predict the three-point bending properties and progressive failure process of 3D angle-interlock woven composites(3DAWCs) under different yarn densities. The simulation results are in good agreement with experimental data, verifying the validity of models. The results show that yarn density has a strong correlation with the bending behavior of 3DAWCs. The bending performance is positively correlated with warp yarn density, but first positive then negative with weft density. During the bending process, the warp yarns are the main load-bearing components. Damage first occurs on the outer warp yarns, and propagates towards the interior of material along the thickness direction. The weft yarns and the matrix bear part of the load, and and failed due to shear and compressive effects respectively. Appropriately increasing the yarn density is beneficial for making the stress distribution more uniform, while an excessively high weft yarn density will lead to stress concentration, thus causing a decline in the bending performance of 3DAWCs.

Realistic geometric models of fiber structures are essential for numerical analysis of textile reinforced composites. Micro-structures of textiles are however often complex due to the contact interactions of the fibers and yarns. Textiles are prone to deform during the forming process for their flexible property, which further increases the difficulty of fiber structure modeling. High fidelity and efficiency modeling of the textiles still remains some challenges. Commonly used geometric modeling methods stay at the research on the meso-scale, or yarn level. The fiber-scale modeling method has been developed rapidly in recent years, which is able to generate geometric models very close to the actual textiles. Problems of forming and deformation simulations are also solved by fiber-scale modeling method. This paper gives an overview of the literatures dedicated to the fiber-scale modeling of textiles. Formulations of fiber-scale strategy are introduced, based on which these models are divided into two categories: the digital element approach and the virtual fiber method. Applications of fiber-scale models are summarized, advantage and disadvantage of the existing modeling methods are discussed. Latest developments of fiber-scale modeling technology for improving the modeling accuracy and efficiency are presented.