Carbon-based textile as a smart sensory device for self-monitoring of fiber-reinforced concrete elements

This study investigates the flexural behaviour and microstructure-property relationships of natural silk fabric-reinforced epoxy composites fabricated using a cast moulding route. Three rectangular specimens (100 × 20 × 5mm) were tested under three-point bending in accordance with ASTM D790 with a 60mm support span. The composites were produced at moderate fibre volume fractions (approximately 20-40 vol%), and their density and void content were evaluated using mass-volume measurements and optical image analysis. The measured flexural strength ranged between 100 and 130MPa, with results reported as mean values along with standard deviation. The composites exhibited a pseudo-ductile response characterized by an initial linear elastic region followed by progressive damage and gradual post-peak softening. Although peak stresses were comparable, clear differences in strain-to-failure and post-peak stability were observed, indicating that deformation behaviour is governed primarily by interfacial integrity and microstructural heterogeneity. Multiscale characterization using optical microscopy and scanning electron microscopy (SEM) was carried out to establish structure-property relationships. Optical observations revealed that voids and non-uniform resin impregnation influence crack initiation and propagation. SEM-based fractography identified dominant failure mechanisms including matrix cracking, interfacial debonding, fibre pull-out, and localized fibre fracture. Specimens with improved impregnation showed better interfacial continuity and crack-bridging, whereas defect-rich regions exhibited premature damage initiation and unstable crack growth. The results demonstrate that load transfer and flexural stability are governed by interfacial stress transfer and processing-induced heterogeneity. The study provides a mechanistic interpretation of flexural behaviour and offers a basis for positioning silk-epoxy composites within natural fiber reinforced systems.

Hydro-mechanical loading on shale can cause not only deformation of matrix but also evolution of cracks. As they both have significant impacts on fluid flow and volumetric behaviors of shales in fundamentally different ways, it is important to decouple their respective contributions. This study develops a robust deep learning-based segmentation framework to decouple matrix deformation and crack evolution in shales using X-ray computed tomography (CT). A shale X-ray CT dataset was generated, while varying saturation (i.e., as-received, saturated, and oven-dried) and imaging conditions (i.e., X-ray source voltages of 100 kV, 150 kV, and inside an aluminum ring). Using this dataset, 13 deep learning architectures were benchmarked, taking the widely adopted U-Net as a baseline. Three-fold cross validation results showed that FRRN-A and FRRN-B outperformed U-Net, with mean intersection over union values close to 85%. Moreover, FRRN-B with cross-entropy loss and a crack weight of 100 was found to be the optimal model for crack volume estimation based on their accuracy and robustness. This optimal model demonstrated its capability in visualizing 3D crack networks and decomposing bulk volumetric strains into matrix and crack contributions during wetting and drying. The matrix deformation appeared to be reproducible regardless of the initial crack configuration, while the crack evolution contributed to about 11–19% of the bulk strains and highly variable, highlighting the localized nature of crack opening/closure. By isolating matrix strains, the proposed framework provides an automated and interpretable platform that bridges observations of hydro-mechanical experiments on shale and continuum-scale constitutive modeling. • A deep learning-based segmentation framework for shale CT imageries is developed. • A shale CT dataset under typical hydro-mechanical test conditions was generated. • FRRN achieved high accuracy and robustness in separating fine cracks in shale matrix. • Loss function was optimized to address underrepresentation of the crack phase. • Swelling and shrinkage can be decoupled into matrix deformation and crack evolution.

Auxetic dimensionality governs impact resilience in composite laminates

A unified framework for interface-controlled matrix cracking in ceramic matrix composites

Accurate damage characterization in thermoset Carbon Fiber-Reinforced Polymer (CFRP) composites using Acoustic Emission (AE) requires statistically robust and interpretable models. This study employs multinomial logistic regression with forward selection and Type III analysis to identify the minimal set of AE parameters necessary for classifying damage mechanisms (fiber breaks, delamination, matrix cracks) in quasi-isotropic thermoset CFRP laminates under synchronously recorded load conditions. Starting from 18 conventional time- and frequency-domain descriptors, forward selection yielded seven candidate predictors. However, Type III analysis revealed that only four parameters, Load, Initiation Frequency, Amplitude, and Average Frequency, provide unique, statistically significant contributions (p < 0.05). The remaining predictors became redundant once these four were included. Machine learning and deep learning models trained on this minimal feature set achieved validation accuracies up to 98.7% on external specimens. High-frequency components (>1 MHz), as recorded at the sensor location after propagation and sensor convolution, were associated with fiber break events at elevated loads, while delamination events exhibited higher amplitude and lower-frequency content (<200 kHz) compared to matrix crack events. These observed frequency ranges reflect the combined effects of source mechanisms, guided wave dispersion in the 2.4 mm thick laminate, PWAS sensor response, and HDT-based hit segmentation, and are consistent with established AE damage signatures in literature. The results indicate that this four-parameter set is sufficient to classify the labeled AE waveform classes under monotonic tensile loading of quasi-isotropic [45/90/−45/0]2s laminates, achieving 98.7% agreement with reference labels assigned via waveform morphology and spectral analysis. The proposed approach reduces computational overhead and enhances interpretability for structural health monitoring applications, pending validation across broader material systems and loading scenarios. A limitation of this study is that reference labels were assigned using waveform morphology and spectral analysis, lacking independent physical validation (e.g., microscopy).

The increasing integration of carbon fiber prepreg composites into aerospace and marine structures necessitates the development of lightweight joints with superior mechanical performance. This study presents an experimental investigation of the failure behavior of co-molded metallic inserts embedded in carbon fiber prepreg laminates under pull-out and shear loading conditions. Inserts manufactured from 17-4PH stainless steel and Ti-6Al-4V (grade 5) titanium alloy were integrated into laminates composed of T700 unidirectional fibers and SE 84LV epoxy resin. Specimens (101.3 × 101.3 mm2) were fabricated using a controlled co-curing process to ensure consistent interfacial bonding. The effects of insert material and geometry on load transfer mechanisms, failure modes, and ultimate load capacity were systematically analyzed. Results indicate that insert geometry governs stress distribution and interfacial load transfer efficiency, directly influencing the initiation of damage. Distinct failure mechanisms, including interfacial debonding, progressive matrix cracking, fiber breakage, and localized delamination, were identified. Titanium inserts demonstrated improved specific performance, whereas stainless steel inserts provided higher absolute load capacity under certain configurations. The findings underline the critical interplay between material selection and geometric design, offering new insights into optimizing co-molded joint configurations for enhanced structural efficiency, damage tolerance, and reliability in advanced composite applications.

Attaining optimal reusable energy absorption after multiple high-strain-rate impacts while preserving a lightweight design continues to be a significant challenge in thin-walled structural engineering. The study involved the development and thorough investigation of a negative-stiffness (NS) spring-type mechanical metamaterial under quasi-static compression. A regression-based multi-response optimization method was utilized to determine the ideal strut thickness (t = 2.6 mm) and loading conditions (F = 300 N), incorporating factors such as stiffness, strain energy, negative Poisson’s ratio (NPR), and total strain. The metamaterial was fabricated utilizing carbon fiber reinforced polymer (CFRP) using the Vacuum Infusion Process, producing a gradually stiffer (GS) composite microstructure. Quasi-static compression experiments were conducted and correlated with numerical models. Experimental findings exhibited auxetic properties, characterized by a Poisson’s ratio of −0.34, energy absorption of 226.54 mJ, and stiffness of 1092 N/mm. The results demonstrated significant consistency with simulations (Poisson’s ratio −0.36, energy absorption 214.30 mJ, stiffness 1398 N/mm), validating the accuracy of the prediction model. High-resolution scanning electron microscopy showed progressive failure processes, such as fiber pull-out, interlaminar delamination, and matrix cracking, signifying effective energy dissipation and structural robustness. These mechanisms become progressively cohesive under increased stress, emphasizing the resilience of the CFRP-based metamaterial.

A strain-insensitive method for matrix crack density detection in FRP composites using embedded FBG sensors

A novel IR-SRGAN assisted super-resolution evaluation of photothermal coherence tomography for impact damage in toughened thermoplastic CFRP laminates under room and low temperature

AI-driven detection of failure modes in thermoplastic composites using acoustic emission techniques

To clarify the effects of fiber orientation (FO) and resin content (RC) on the mechanical properties of basalt fiber reinforced polymer (BFRP) composites, a full factorial experimental design was employed. Fiber orientations of 0°, ±45°, and 0/90°, together with resin contents of 40 wt.%, 50 wt.%, and 60 wt.%, were selected as the main variables. Nine groups of BFRP laminates were fabricated via hand layup, followed by tensile, flexural, interlaminar shear, and impact tests. The contribution degrees of each factor were analyzed using the two-factor analysis of variance method. The results demonstrate that fiber orientation determines the load transfer efficiency and anisotropy of composites. Proper alignment along the loading direction significantly improves mechanical properties. Tensile strength is primarily dominated by fiber orientation. At a resin content of 50 wt.%, the tensile strengths of 0°, ±45°, and 0/90° laminates are 151 MPa, 119 MPa, and 286 MPa, respectively. Resin content dominates interfacial bonding and internal defects. An optimal resin volume fraction ensures sufficient wetting and strong interfacial adhesion, leading to the best mechanical performance. Resin content significantly affects flexural strength, interlaminar shear strength (ILSS), and impact performance. The tensile, bending and impact properties are influenced by the coupling effect of fiber orientation and resin content. Microstructural observations reveal that the dominant damage mechanisms include interfacial debonding, fiber pull out, and matrix cracking. At the same time, a regression model was established to conduct a thoroughness test on the experimental results. The fitting effect is excellent.

Current understanding of carbon fiber-reinforced PETG (PETG-CF) honeycomb structures remains limited, with their mechanical properties and failure mechanisms insufficiently characterized across a wide operational temperature range from −20°C to 65°C. This study addresses this knowledge gap by systematically investigating the quasi-static compressive response of regular hexagonal PETG-CF honeycombs. A combined approach of experimental testing and thermo-mechanically coupled numerical simulations was employed. Experimental characterization, complemented by fracture surface analysis using scanning electron microscopy (SEM), revealed pronounced temperature-dependent effects on compressive modulus, specific energy absorption (SEA), and failure modes. The results indicate a clear trend, the compressive modulus decreases from 47.76 MPa at −20°C to 39.84 MPa at 65°C, while the SEA declines by 52.4%, from 1.03 MJ/m 3 to 0.49 MJ/m 3 . Failure modes exhibit strong temperature dependence. Brittle fracture, characterized by matrix cracking and fiber breakage, dominates at low temperatures (−20°C, −10°C, 0°C). At 25°C, a brittle-to-ductile transition occurs, whereas plastic buckling and interfacial debonding become the primary failure mechanisms at higher temperatures (45°C and 65°C). Finite element analysis further elucidates the role of geometric stress concentration zones as consistent initiation sites for failure. Importantly, the evolution of failure is governed by the temperature-dependent plastic deformation capability of the PETG-CF matrix. This work establishes a fundamental link between temperature and the progression from microscopic damage to macroscopic failure, providing a theoretical foundation for the design of lightweight structures operating across broad temperature ranges.

The present study systematically evaluates and compares the mechanical performance of CARALL_5 fiber metal laminates (FMLs) and GLARE_5 FMLs with two distinct stacking sequences. The mechanical performance was assessed considering the tensile strength, flexural strength, and impact strength of the two FMLs. Under tensile loading conditions, type-2 CARALL_5 FML exhibited a tensile strength of 776 ± 73 MPa, against a tensile strength of 466 ± 39 MPa exhibited by GLARE_5 FML. In comparison, type-1 CARALL FML, with aluminum as the outermost layers exhibited a comparatively lower tensile strength of 610 ± 53 MPa, while exhibiting a stepped failure pattern during tensile loading, indicating gradual progression of damage, and enhanced damage tolerance. The FMLs displayed failure modes such plastic deformation, fiber breakage, matrix cracking, and delamination under tensile loading conditions. The maximum values of flexural strength of around 1092 ± 85 MPa was observed in type-2 CARALL_5 FML, where the carbon fiber layers were on the outermost layers. In comparison, type-2 GLARE_5 FML displayed a 48% flexural strength, due to the lower elastic modulus and stiffness displayed by the glass fibers. Furthermore, type-1 CARALL_5 FML showed an impact energy of 14.2 ± 0.59 J, which was 98% greater than the impact energy of type-1 GLARE_5 FML. The observed failure modes were plastic deformation, fiber–matrix debonding, matrix cracking, and delamination. Based on these findings, type-1 CARALL_5 FMLs are ideal for applications involving tensile and impact loads, where it is crucial to retain load-bearing capacity even after sustaining damage. In contrast, type-2 CARALL_5 FML is more appropriate where the ability to endure bi-axial loading is essential.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-026-50170-5.

Abstract To investigate the mechanical behaviour of T300/EM119 composite laminates, [±45°] and [0°/90°] layups were subjected to quasi-static tensile and tension-tension fatigue testing, and a residual-strength model was constructed from the measured data. Fatigue fracture morphologies were characterized by scanning electron microscopy (SEM), and a finite-element model was employed to simulate fatigue life and the progression of failure. The results indicate that the average ultimate strength of the [0°/90°] laminate was 599.2 MPa, which was substantially greater than the 219.6 MPa measured for the [±45°] laminate (an increase of approximately 173%). Fatigue failure was shown to result from a combination of fibre fracture, matrix cracking, interface debonding and delamination. Delamination damage and fibre breakage were found to be particularly pronounced in the [±45°] layup, which was attributed to the higher shear stresses sustained by that configuration. Predictions of fatigue life and dominant failure modes obtained from the finite-element simulations were in good agreement with experimental observations.

ABSTRACT The characterisation of composite damage at cryogenic temperature (CT) can be evaluated using the acoustic emission (AE) technique if the sensor can withstand CT and the correlation between the AE signal and composite micro-damage can be clarified. In this study, a new cantilevered phase-shifted fibre Bragg grating was used to detect AE signals from carbon fibre reinforced plastic laminates subjected to a three-point-bending test at CT. The sensor captured all low-energy and high-frequency AE hits at CT. The energy and peak frequency of the signals were statistically analysed and were correlated to the deflection – load curves and microscopic observations. The AE hits at CT had higher energies and covered a wider peak frequency range than those at room temperature. The first AE hit appeared earlier at a small deflection at CT than at RT. In addition, the signals at RT caused by the matrix cracks were concentrated in one cluster and those at CT were separated into two clusters, corresponding to matrix cracks and delamination. These phenomena are caused by the greater brittleness and modulus of the resin at CT and the mismatch of thermal expansion between the carbon fibre and resin and between the two adjacent cross-ply laminae.

The crack resistance of unidirectional fiberglass-reinforced plastics based on an epoxy matrix modified with polysulfone (PSU) and furfuryl glycidyl ether (FGE) was investigated. The combined addition of PSU/FGE modifiers to the epoxy matrix increases the crack resistance of glass-fiber-reinforced plastics (GFRPs). The effect of increasing the crack resistance of GFRPs varies depending on the modifier ratio. The greatest increase in crack resistance is achieved with a modifier ratio of 1/0.5. For this ratio, the value of GIRCM is 1.18 kJ/m2 (for unmodified GFRP, GIRCM = 0.72 kJ/m2). With an increase in the FGE concentration in the polysulfone-modified epoxy matrix, the crack resistance of GFRP decreases to a level of ~0.8 kJ/m2. The change in the crack resistance of GFRP is associated with the structure of the epoxy matrix containing different PSU/FGE ratios. A study of the fracture surfaces of GFRPs showed that the greatest increase in the crack resistance of composites is achieved with the formation of extended phases enriched with polysulfone in the epoxy matrix. The size of the dispersed phase is about 3 μm. A correlation has been established between the crack resistance of hybrid matrices and GFRPs. With an increase in the matrix crack resistance by 3.1 times (from 0.37 to 1.15 kJ/m2), the fracture toughness value of GFRP increased by 1.6 times (from 0.72 to 1.18 kJ/m2).

ABSTRACT With the wide application of fiber reinforced composites in cold‐region civil engineering, it is necessary to investigate the influence of freeze–thaw (F–T) cycles on mechanical properties of composites. In this paper, basalt fiber‐reinforced polymer (BFRP) composite was manufactured by vacuum‐assisted resin infusion and exposed to 50, 100, and 200 F–T cycles in water. Flexural and creep properties of F–T exposure were evaluated. Additionally, microstructural and chemical changes were characterized by scanning electron microscopy and Fourier‐transform infrared spectroscopy at the fiber and matrix scales. The results show progressive degradation in flexural and creep behavior with increased F–T cycles. The flexural strength decreased by 24% after 200 F–T cycles, while the flexural modulus increased after 50 F–T cycles and then decreased. The F–T exposure accelerated the creep strain, leading to an earlier onset of tertiary creep. The modified Findley model incorporating F–T influence functions was modified to predict the creep compliance after different F–T cycles. The observed mechanical degradation was primarily due to matrix cracking, interfacial deterioration, and the accumulation of microstructural damage. This paper quantifies the influence of F–T cycles on the flexural and creep behavior and provides valuable guidance for the rational design of FRP composites.

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.

This study investigates the acoustic emission (AE) response and damage mode characteristics of ±45° glass fiber-reinforced polymer (GFRP) composites used in wind turbine blade shear webs under quasi-static tensile loading. It aims to establish the relationship between AE features and three typical damage mechanisms-matrix cracking, interfacial debonding, and fiber fracture-to support damage assessment and structural health monitoring. Quasi-static uniaxial tensile tests with synchronous AE monitoring are conducted on specimens with three orientations (0°, 45°, and 90°). AE features are selected using correlation analysis and principal component analysis, and the HAC-initialized K-means clustering method is employed for damage mode identification. The optimal number of clusters is determined to be three, according to the Davies-Bouldin index (DBI) and the Silhouette index (SI). The resulting low-, mid-, and high-frequency clusters are associated with matrix cracking, interfacial debonding, and fiber fracture, respectively. These interpretations are further supported by wavelet-based time-frequency analysis and microscopic fracture surface observations.