Search Results (248)

Carbon fiber-reinforced polymer (CFRP) composites are increasingly used in aerospace, rail transportation, and energy engineering owing to their high specific strength and corrosion resistance. However, their complex and interacting damage mechanisms, including delamination and matrix cracking, present significant challenges for reliable structural health monitoring. Fiber Bragg grating (FBG) sensors offer distinct advantages for monitoring composite structures because of their compact size, immunity to electromagnetic interference, embeddability, and capability for distributed strain measurement. Nevertheless, the effectiveness of an FBG sensing network depends strongly on the spatial distribution of the sensing points. This study proposes a finite-element-assisted framework for evaluating and improving FBG sensor layouts for strain-field reconstruction and structural feature characterization of composite plates. The framework first reconstructs the spatial strain field from limited sensing data using interpolation and least-squares fitting methods, and then evaluates the performance of existing and candidate sensor layouts based on reconstruction errors and spatial coverage of structurally important regions. A strain-gradient-informed heuristic strategy is subsequently developed to improve sensor placement by combining high-gradient region identification, spatially uniform coverage, minimum-distance constraints, and predefined support-region monitoring requirements. The Fourier least-squares fitting method provides the lowest reconstruction error among the investigated approaches and is therefore adopted for subsequent layout evaluation and improvement. Finite-element simulations and experimental measurements are used to assess the reconstruction performance and identify the advantages and limitations of different sensor layouts under static and dynamic loading conditions. The results demonstrate that the proposed framework can effectively evaluate existing FBG layouts and provide a systematic basis for their improvement, while also revealing the trade-off between local strain-gradient resolution and global spatial coverage. The proposed framework provides practical guidance for the performance-oriented design and improvement of FBG sensor networks for structural health monitoring of composite structures. Full article

Production of short-fiber-reinforced carbon/carbon composites (SF-C/C composites) is typically based on the pyrolysis of short-fiber-reinforced plastics (CFRPs) produced by compression molding. The production of C/C composites is generally a highly time- and energy-intensive process, particularly for complex geometries. Injection molding can offer an attractive alternative due to its high level of automation, cost efficiency, and ability to produce complex geometries. However, in contrast to compression molding, the shorter fiber lengths resulting from the compounding process and the parameter/geometry-dependent cavity-filling behavior in injection molding lead to a complex three-dimensional fiber orientation distribution. This can profoundly affect both the pyrolysis behavior of the CFRPs and the properties of the resulting SF-C/C composites. In this study, CFRP plates (150 × 150 × 4 mm³) were injection-molded at varying injection rates and mold temperatures. The influence of these parameters on the properties of the resulting SF-C/C composites was systematically investigated. Characterization included shrinkage and warpage behavior, porosity, microstructure via light microscopy and X-ray computed tomography, and flexural properties. The results show that the homogeneity of fiber orientation within the component is critical for controlling warpage during pyrolysis. In particular, asymmetric flow-line formation leads to non-uniform shrinkage across the thickness and promotes warpage. Therefore, achieving a homogeneous and/or symmetric distribution of the fiber orientation is essential for producing warpage-free SF-C/C composites by injection molding. Full article

Carbon-fiber-reinforced silicon carbide (C/SiC) ceramic matrix composites (CMCs) exhibit substantial application potential in the field of advanced industrial manufacturing, attributed to their inherent superiorities such as high specific strength, excellent high-temperature resistance, and prominent corrosion resistance. Nevertheless, hole-exit delamination is a critical defect in C/SiC composite drilling, which impairs the structural integrity and service reliability of components, restricting their engineering implementation. To address this issue, this study proposes and systematically investigates a compressive stress-assisted drilling method for delamination suppression via applying external compressive stress. Using the delamination factor for quantitative evaluation, comparative experiments were conducted under unassisted drilling, graphite-plate-assisted drilling without preload, and graphite-plate-assisted drilling with varying preload torques. The results indicate that compressive stress significantly mitigates delamination, with a maximum delamination factor reduction rate of 18.29%. Mechanistically, the compressive stress effectively controls delamination by suppressing Mode I crack propagation at the crack tip and elevating the critical strain energy release rate. Furthermore, this work elucidates that the essential role of the graphite plate is to provide a controllable in-plane pre-compressive stress field for the workpiece drilling zone. Full article

To ensure the reliability of carbon-fiber-reinforced polymer (CFRPs) structures, robust structural health monitoring (SHM) is required for timely damage diagnosis. Over the decades, Lamb-wave-based techniques have been widely used to inspect composite structures owing to their high sensitivity to internal defects. Damage-sensitive features from nonstationary Lamb-wave signals can be captured in the frequency and time domains using the continuous wavelet transform (CWT). However, extracting localized damage features from these images is highly challenging. Accordingly, this study proposes a multipatch deep feature learning method for damage detection and severity classification in CFRP plates using Lamb-wave CWT images. The images are partitioned into multiple local patches for patch-wise deep feature extraction using a convolutional neural network (CNN). The proposed model is evaluated on CFRP composite plates with three simulated damage severity levels (D1, D2, and D3) produced using mass blocks of different weights. Among the evaluated patch configurations, the proposed physics-inspired patching achieves the highest classification accuracy of 98.2%, outperforming conventional uniform multipatch baselines. For damage detection, the proposed method achieves high classification performance, with precision, recall, and F1-scores of 100% for both healthy and damaged samples, outperforming comparison models, including a custom CNN, VGG19, and ResNet50. For damage severity classification, the proposed model achieves F1-scores of 0.98, 0.97, and 0.98 for D1, D2, and D3, respectively, consistently outperforming the baseline models across various evaluation metrics. Under Gaussian noise, the proposed method maintains a robust classification accuracy of 96.1% at 20 dB signal-to-noise ratio, corresponding to a performance reduction of 1.7% compared with noiseless data, suggesting its reliability for realistic SHM environments. Full article

To address the increasing demand for energy-efficient buildings, this study experimentally characterizes the effective (λ_eff) and apparent (λ_app) thermal conductivity of 3D-printed polymer plates. While 3D printing offers significant design flexibility, a lack of comprehensive comparative data between printable polymers and conventional building materials limits their integration into large-scale facade systems. This research investigates four distinct materials: standard polylactic acid (PLA Basic), foamable poly-L-lactic acid (PLA Aero), amorphous polyethylene terephthalate glycol (PETG), and carbon fiber-reinforced polyethylene terephthalate (PET-CF). Utilizing the guarded hot plate (GHP) method (ASTM C177, EN 12667, EN 12939), steady-state heat flux and temperature gradients were measured. The methodology incorporates a rigorous uncertainty analysis (k = 2) addressing the inherent inhomogeneity of additively manufactured components. Results demonstrate significant variations: PLA Aero achieved a 57.3% reduction in thermal conductivity (0.114 ± 0.005 W/(m·K)) compared to PLA Basic (0.267 ± 0.011 W/(m·K)), while PET-CF showed increased conductivity (0.533 ± 0.021 W/(m·K)) due to carbon fiber bridging. Notably, multi-layered PLA Aero assemblies outperformed conventional double-glazed units, reaching a minimum λ_app of 0.051 W/(m·K). These findings validate the GHP method for 3D-printed polymers and provide a technical foundation for material selection in next-generation, energy-efficient smart facades. Full article

The enhancement of reinforced concrete (RC) beams using externally bonded carbon fiber-reinforced polymer (CFRP) systems and shape memory alloy (SMA) systems has been growing in recent years, but its comparison is not generalizable unless it is based on an equal basis of stiffness. In this paper, an equivalent axial stiffness approach is applied to study the effect of CFRP and SMA plates on RC beams. The following four beam configurations were considered: Unstrengthened control beam, beam strengthened with a 5 mm SMA plate, beam strengthened with a 5 mm CFRP plate, and beam strengthened with an 18.96 mm SMA plate, which was chosen to provide similar axial stiffness as the 5 mm CFRP plate. The finite element model was created using ANSYS and compared with experimental results from the literature, and was further validated with a mesh sensitivity study. The test results indicated that all strengthening systems had a better flexural response than the control beam, but with varying degrees of improvement depending heavily on the amount of stiffness provided by the strengthening material. The control beam showed the first signs of cracking and had the lowest resistance. The moderate improvement was seen in the 5 mm SMA plate, which increased the load corresponding to the first crack to 50.2 kN from 41.7 kN. The 5 mm CFRP beam and the stiffness-equivalent SMA 18.96 mm beam, on the other hand, were able to significantly improve the first-crack load to 77.6 kN and 82.97 kN, respectively. In terms of flexural strengthening performance, stiffness equivalence takes into account the first-crack load of the performance of the SMA beam, which shows that SMA can provide flexural strengthening performance comparable to, and even higher than, that of the CFRP system in terms of crack-initiation resistance. The overall performance of the strengthened beams was also found to be better than the control beam in terms of the post-cracking stiffness and moment—curvature relationships. These results indicate that a stiffness-equivalent framework is more rational than comparing the two strengthening systems directly in terms of thickness, and in this way, the ability to compare the advantages and disadvantages of the two systems. The conclusions, however, should be understood based on the assumptions of the numerical model, such as the perfect bond assumption at the interface and the use of a simplified monotonic material model used for SMA. Additional studies should be conducted that incorporate debonding, cyclic loading, temperature, and field size verification. Full article

The reliable evaluation of the interfacial bonding quality of steel structures strengthened with carbon fiber-reinforced polymer (CFRP) is crucial to ensuring the long-term service safety of the structures. Focusing on the active and passive detection methods based on piezoelectric sensing, this paper takes numerical simulation as the core research method to provide theoretical verification and mechanism explanation for subsequent key experiments, thus supporting the accurate detection of interfacial damage in CFRP–steel plate joints. A 3D piezoelectric–structural coupling finite element model and a 2D ultrasonic guided wave propagation finite element model were established via COMSOL Multiphysics 6.2 to systematically simulate the electromechanical response characteristics of three piezoelectric sensors (PMN-PT, PZT and PVDF). The research focused on analyzing the potential output and voltage–load response of the three sensors, and simultaneously explored the propagation laws and energy evolution mechanisms of ultrasonic waves in the presence of different debonding damages and groove defects in CFRP plates. The simulation results show that the PMN-PT sensor exhibits the optimal detection performance, with its peak potential output reaching 2.66 times that of the PZT sensor and 4.69 times that of the PVDF sensor, with a load sensitivity of 484.3 mV/kN. In the ultrasonic active detection of interfacial debonding damage, the first-wave amplitude has a significant positive correlation with the debonding length, and this characteristic is attributed to the strong reflection effect and energy accumulation caused by the acoustic impedance mismatch at the CFRP–air interface. For the internal groove defects in CFRP plates, the simulation clarifies that the increase in groove length leads to energy trapping in the plate, while the increase in groove depth intensifies ultrasonic wave energy reflection. The numerical simulation results were compared and verified with data from companion experiments conducted by the authors’ team, showing a high degree of consistency, which confirms the accuracy and reliability of the established finite element models. Meanwhile, the physical essence of damage detection is elucidated from the perspective of wave theory, providing a solid numerical analysis foundation and theoretical support for the intelligent monitoring of interfacial damage in CFRP–steel structures. Full article

Bone fractures are often treated using invasive methods involving osteosynthesis plates. These plates are typically made of metallic materials such as titanium or steel. However, their high stiffness relative to bone tissue can contribute to the undesirable stress shielding effect. Therefore, there is a growing interest in developing new, more friendly biocompatible materials with improved mechanical properties. A promising candidate is a polymer composite made of high-strength PEEK reinforced with carbon fibers, which was the subject of this study. The aim of this work was a numerical analysis of osteosynthesis plates made from conventional materials and from PEEK-CF composite. The study also included geometric modification of the composite plate using topology optimization methods to reduce the stress shielding effect. The obtained results confirmed that the use of a geometrically optimized composite osteosynthesis plate can reduce bone unloading and ensure an appropriate stress distribution in the implant–bone system. Full article

Composite materials are extensively used in the aeronautical and aerospace industries for their high strength-to-weight ratios but are vulnerable to barely visible impact damage (BVID), which can severely compromise structural integrity. Digital shearography (DS) provides a non-contact, full-field solution for subsurface inspection; however, low signal-to-noise ratios in raw phase maps often hinder precise damage identification. This study explores a post-processing methodology utilizing a band-pass filtering algorithm and temporal summation to isolate damage-related spatial frequencies. An in-house digital shearography system was used to inspect a carbon-fiber-reinforced polymer (CFRP) plate subjected to 13.5 J and 26.2 J impacts. Twelve phase maps, acquired during the thermal cooling stage, were processed using a multi-pass filters to systematically analyze different frequency ranges. Results demonstrate that summing multiple filtered phase maps significantly enhances the contrast of damage signatures compared to single phase maps or traditional unwrapping techniques. Furthermore, quantitative assessment using image quality metrics, such as the generalized contrast-to-noise ratio (gCNR), confirmed that optimal frequency selection is essential for an accurate damage delineation. This approach provides a robust framework for improving the reliability and sensitivity of non-destructive testing in composite structures. Full article

In this study, an active vibration control (AVC) strategy is effectively used on a system made of a honeycomb polymer–paper core and carbon fiber-reinforced polymer (CFRP) plates. A cost-effective and practical solution based on an AVC system has been developed and tested using a microcontroller unit (MCU) from Texas Instruments. The control system is studied by applying out-of-plane disturbances to the composite panel via an electrodynamic shaker, by exciting the identified mode shapes obtained through experimental modal analysis, i.e., impact tests. The actuator chosen for the AVC system is a Macro Fiber Composite (MFC) patch. Multiple analog signal processing circuits were developed to scale and shift the signal at the input and output of the MCU. The proposed control algorithm is based on a positive position feedback (PPF) technique. Modal analysis was performed to identify the natural frequencies and mode shapes of the structure, which are essential for the design and tuning of the modal-based PPF controller. This analysis also enabled optimal sensor and actuator placement, ensuring effective targeting and control of the dominant vibration modes. Then, a series of tests were performed using pure sine excitations at frequencies of interest, close to the 2nd and 8th mode at 25.13 Hz and 129 Hz, respectively. The results of the experiments revealed a velocity attenuation of 55.8% to 76.9% and a Power Spectral Density (PSD) attenuation of 5.8 dB to 12.8 dB, depending on the mode under study. Owing to the size and mass properties of the Macro Fiber Composite (MFC) patches, the control system is very much suitable for automobile and aerospace applications. Full article

To address the problem of insufficient shear bearing capacity of highway reinforced concrete (RC) T-beams, this paper systematically conducts a comparative study on the shear performance of RC T-beams strengthened with UHPC-CFP toughened composite plates of different configurations, and proposes a shear strengthening method using UHPC-CFP toughened composite plates. Comparative tests on different strengthening configurations are carried out. Meanwhile, a finite element numerical model is established to compare with the experimental results, analyze the influences of different strengthening schemes on the shear bearing capacity and mechanical properties of the beams, reveal the shear strengthening mechanism, and put forward a recommended formula for calculating the shear bearing capacity. The results show that after the diagonal cracks appeared in Beam T-0, they propagated rapidly from the support to the loading point. Beam T-1 had more diagonal cracks in the concrete between the UHPC-CFP toughened composite strips, while Beam T-2 had fewer. Fine cracks occurred in the UHPC-CFP toughened composite strips of Beams T-1 and T-2, whereas no cracking was observed in the UHPC composite rectangular plate of Beam T-3. The shear capacity of all strengthened beams was improved, with increases of 27.0%, 40.5%, and 43.2% for Beams T-1, T-2, and T-3, respectively. Beam T-3 exhibited the maximum deflection, and the strengthening configuration of Beam T-2 was determined to be the optimal. The carbon fiber strips embedded in UHPC effectively delayed the propagation of cracks in the UHPC plate and played the role of “reinforcement”. The truss–arch model theory is also applicable to the shear mechanism of concrete T-beams strengthened with UHPC-CFP toughened composite plates. Verification of Beams T-2 and T-3 using the proposed formula for shear design of strengthened beams showed that the average ratio of the calculated shear capacity to the experimental value was 0.87, indicating the reliability of the calculation results. Full article

Polymer nanocomposites offer significant potential for improving the strength-to-weight ratio and dynamic behavior of drone blades. This study examines the vibration characteristics of tapered aramid (Kevlar)/epoxy composite blades reinforced with nanocarbon fillers—graphene (2D), multi-walled carbon nanotubes (MWCNTs, 1D), and fullerene (0D)—to determine the most effective filler for enhancing stiffness and operational stability. The laminated blades (300 mm length, 200 mm width, root thickness 13 mm, tip thickness 8 mm) incorporate ply drop-offs and a central honeycomb core. Modeling was performed using classical laminate plate theory integrated with the finite element method (FEM) in MATLAB (R2016a). Under clamped–free–free–free boundary conditions, the study considered rotational speeds of 750–2250 rpm, setting angles of 30–60°, various fiber orientations, and nanofiller contents of 0–10 wt.%. The results indicate that while the setting angle minimally affects natural frequency, it significantly influences damping in modes (1,2) and (2,1). Increasing nanofiller content improves stiffness, with optimal performance observed near 5 wt.%. At 1500 rpm in mode (1,1), MWCNTs provided the greatest enhancement. Overall, MWCNTs exhibited superior stiffness improvement and rotational stability compared to other fillers. Full article

Low-velocity impacts can cause barely visible impact damage (BVID) in carbon-fiber-reinforced polymer (CFRP) laminates, leading to significant reductions in residual compressive strength. Compression-after-impact (CAI) tests are therefore essential for damage-tolerance design, but existing fixtures often allow global buckling or edge crushing, which can compromise test accuracy. This study experimentally investigates the CAI response of two symmetric angle-ply CFRP laminates with reversed stacking sequences, [0/−45/45/90]s and [90/45/−45/0]s, using a modified CAI fixture. Compared to standard CAI rigs, the modified fixture combines the lateral guidance with anti-buckling plates that clamp the upper and lower specimen edges using a bolt–nut assembly, thereby reducing the active gauge length and stabilizing the panel during compression. Rectangular plate specimens were first impacted at low velocity with a hemispherical projectile; the BVID threshold was defined by a permanent indentation depth of 0.8 mm for [0/−45/45/90]s and 0.7 mm for [90/45/−45/0]s, measured 24 h after impact. Subsequent CAI tests showed about a 22% reduction in maximum compressive load at the BVID level for both layups, while the post-impact compressive stiffness decreased by 17% for [0/−45/45/90]s and 6% for [90/45/−45/0]s. These results demonstrate that reversing the symmetric layup significantly affects stiffness degradation and that the proposed CAI setup suppresses global buckling and edge-dominated failures in all testson the investigated thin CFRP laminates, enabling repeatable residual-strength and stiffness measurements. Full article

Carbon Fiber Reinforced Polymer (CFRP)-strengthened steel plate systems demonstrate remarkable advantages in civil engineering structural rehabilitation, with their overall performance critically reliant on the interfacial bond behavior between CFRP and steel plates. This paper systematically reviews the typical failure modes, key factors influencing interfacial bond performance, and corresponding testing methodologies. Research indicates that interfacial shear stress dominates the failure process. Enhanced strengthening efficacy can be achieved by employing CFRP plates with optimized adhesive layer thickness (recommended 0.5–1.5 mm) and double-sided bonding configurations. Concurrently, substrate surface treatment and environmental factors (temperature–humidity, corrosion, etc.) significantly affect interfacial bond performance. Current research primarily focuses on the single-factor and strength failure performance of standard specimens, lacking a systematic understanding of the long-term durability and failure mechanisms of complex structures under multi-field coupling effects. This review further summarizes the distinctive features and application scenarios of innovative strengthening systems—including prestressed, unbonded, and shape memory alloy composite systems—to provide guidance for engineering selection and standardized design. Full article

The durability of the carbon fiber-reinforced polymer (CFRP)–concrete interface is a critical indicator for assessing the service life of composite structures in cold regions. This study systematically investigates the normal bond behavior under coupled deicing salt and freeze–thaw cycles through single-sided salt-frost tests on 126 specimens. The influence of surface roughness, number of freeze–thaw cycles, concrete strength grade, and CFRP material type was systematically evaluated. The results demonstrate that bond behavior is positively correlated with surface roughness, with the f₂ interface exhibiting optimal performance and increasing the ultimate capacity by up to 76.61% compared to the smooth interface. CFRP cloth showed superior bond retention compared to CFRP plates, which experienced a bond strength loss rate up to 26.90% higher than cloth specimens after six cycles. A critical performance threshold was identified between six and eight cycles, where the failure mode transitioned from cohesive adhesive failure to brittle interfacial debonding. Concrete matrix strength had a negligible effect compared to the dominant environmental damage. A two-parameter prediction model based on cycle count and roughness was established with high accuracy. SEM analysis confirmed that epoxy resin cracking, fiber–matrix debonding, and microcrack propagation in the concrete surface layer were the fundamental causes of macroscopic mechanical degradation. These findings provide a theoretical foundation for optimizing interface treatment and predicting the structural integrity of CFRP-strengthened systems in salt-frost regions. Full article