Search Results (1,743)

Additive manufacturing (AM) has evolved from a rapid prototyping technique into a versatile platform for fabricating advanced functional materials and complex engineering components. While polymers remain the dominant material class due to their processability and tunable properties, recent developments have expanded AM to include high-performance composites, nanocomposites, and metallic materials. This review provides an overview of functional materials for additive manufacturing, emphasizing the relationships between material design, processing conditions, microstructure evolution, and resulting properties. Key functional polymer systems are discussed, including conductive, stimuli-responsive, elastomeric, high-performance, bio-based, and nanocomposite materials reinforced with nanoparticles, carbon nanomaterials, MXenes, and fibers. This review also examines processing–structure–property relationships common to polymer- and metal-based AM, highlighting the roles of anisotropy, defect formation, residual stresses, and post-processing in determining component performance. Finally, current challenges and emerging trends—including multi-material and 4D printing, machine learning-assisted optimization, and digital materials design—are discussed. Overall, the review highlights how advances in materials science and intelligent manufacturing are expanding the capabilities of additive manufacturing for multifunctional engineering and biomedical applications. Full article

Natural fiber-reinforced polymer composites are attractive for lightweight and sustainable engineering applications; however, property scatter remains a major barrier to reliable design. Mean tensile properties alone are insufficient when material selection depends on repeatability and lower-tail performance. This study presents a statistical variability and lower-tail reliability assessment of flax, jute, and carbon fiber composite laminates using 590 open-access tensile test records from a published natural-fiber composite dataset. Flax and jute were selected as representative bast-fiber systems covering a range of woven, unidirectional, and short-fiber architectures; carbon fiber was included as a synthetic-fiber reference system. Three mechanically important properties were analyzed: the recalculated tensile modulus, tensile strength, and axial failure strain. Normal, lognormal, and two-parameter Weibull distributions were screened for each material–property combination using the Akaike information criterion (AIC); empirical fifth percentiles (P5) and bootstrap 95% confidence intervals (CI) were computed as lower-tail descriptors. The results show that Carbon-0 has the highest lower-tail modulus and strength, with empirical fifth percentiles of 104.95 GPa and 989.64 MPa, respectively. Among the natural fiber systems, Flax-0 and Flax-VE-0 provided the highest lower-tail strengths, whereas Flax-Twill and Flax-CP showed the highest lower-tail failure strains. The lowest tensile strength coefficient of variation was observed for Flax-90 (2.41%), followed by Flax-Twill (3.43%), Flax-0 (4.50%), Jute-Satin (4.83%), and Jute-Plain (4.92%). A balanced reliability ranking that combined lower-tail property ranks and coefficient of variation ranks identified Flax-0, Flax-VE-0, Flax-Twill, Flax-CP, and Jute-Satin as the most favorable natural-fiber systems. The lower coefficient of variation values observed in aligned and satin-weave architectures relative to short-fiber and plain-weave systems reflect the role of fiber orientation uniformity in moderating property scatter at the laminate scale. This study provides a reproducible statistical framework based on lower-tail performance descriptors for comparative screening purposes, not on formal design allowables for distinguishing high mean performance from reliable minimum-level performance in natural fiber composite laminates. Full article

Externally bonded reinforcement (EBR) using fiber reinforced polymer (FRP) is one of the most widely used techniques for strengthening reinforced concrete (RC) structures. However, early debonding of the concrete surface layer in the EBR method limits its structural performance. Recently, the externally bonded reinforcement on grooves (EBROG) method has emerged as a promising alternative. This study experimentally investigates the bond behavior between CFRP plates and concrete strengthened using the EBROG method. A total of 78 specimens were fabricated and evaluated using single-lap shear tests. The investigated parameters include groove dimensions, number of grooves, and concrete compressive strength. A digital image correlation (DIC) system was used to measure displacement. Unlike the EBR method, no debonding of the concrete surface layer occurred in the EBROG specimens, and the bond strength improved by 49.56–154.48% without additional surface treatment. Increased groove dimensions and a greater number of grooves significantly enhanced the bond performance. Higher concrete compressive strength and larger groove dimensions also delayed the onset of debonding. Based on the experimental results, a new effective strain model was proposed, and flexural capacity predictions using this model showed higher accuracy than those obtained from existing models. Full article

Interest in applying hybrid retrofitting approaches to existing buildings is steadily increasing. In this study, an attempt was made to seismically retrofit an RC (reinforced concrete) building using CFRP (carbon fiber-reinforced polymer) and dampers. For this purpose, nonlinear time history analysis was performed. The placement of dampers in the RC frame required the use of panels. Panels do not interact with columns; however, the interaction between the panels and the beams was considered. First, the behavior of a single-story RC frame with panels was numerically analyzed using Abaqus 2017. Then, a typical old RC building was modeled in SAP2000 v26 under three configurations: its existing condition with hollow brick infill walls, a CFRP-retrofitted condition, and a condition retrofitted with a hybrid CFRP–damper system, in which lightweight concrete panels replaced the hollow brick infill walls. When the results were compared, the hybrid retrofitting approach with CFRP and Idrizi dampers reduced story displacement by 41.13–42.70% in the X direction and by 32.74–46.89% in the Y direction, on average. Base shear forces were reduced by approximately 31–33% in the X direction and 6–9% in the Y direction. Improvements were also observed in beam plastic hinge conditions. Thus, the hybrid approach was found effective for seismic retrofitting. Full article

Carbon fibers, whose origins are closely intertwined with precursor chemistry and processing conditions, have become indispensable structural lightweight materials due to their exceptional combination of low density, high tensile strength, and high stiffness. This review aims to provide a combined overview of the mechanical properties of carbon fibers by tracing their development from the historically dominant polyacrylonitrile (PAN) and mesophase pitch systems to emerging polyethylene (PE)-based alternatives. Based on decades of fundamental and applied research, this review outlines how precursor molecular structure, stabilization pathways, and carbonization conditions direct microstructural growth and thereby mechanical performance. Established structure/property relationships in PAN and mesophase pitch fibers are discussed alongside recent insights into the sulfonation, crosslinking, and carbonization behavior of PE-based precursor systems. Additionally, this review presents current knowledge on production costs, market dynamics, and the environmental impact of carbon fiber manufacturing, highlighting how energy-intensive processing remains a key barrier to broader industrial adoption. Combined, the findings presented in this review provide an integrated basis describing how precursor selection, processing strategy, and resulting morphology shape mechanical behavior and clarify the position of PE-based carbon fibers within the broader landscape of cost, performance, and sustainability. Full article

Multi-material structures such as carbon fiber reinforced polymer (CFRP) and epoxy resin are increasingly used in modern power equipment. However, significant differences in their thermophysical properties result in distinct defect thermal responses, which can reduce the reliability of infrared thermography inspections. To address this issue, this study investigates the thermal response mechanisms and quantitative analysis of defects in multi-material power equipment through finite element simulation and experimental validation. Three-dimensional transient heat transfer models containing air voids and heterogeneous insert defects were established using COMSOL Multiphysics for both carbon fiber reinforced polymer and epoxy resin matrices. Pulsed infrared thermography experiments were subsequently conducted to verify the simulation results. The effects of material properties, defect geometry, and cover-layer thickness on thermal response characteristics were systematically analyzed. The results show that thermal diffusivity is the key factor governing defect signal evolution. Carbon fiber reinforced polymer exhibits rapid thermal propagation and early transient responses, whereas epoxy resin produces delayed and slowly increasing thermal signals. Greater defect depth weakens thermal contrast and delays peak response time, while larger defect diameters enhance defect detectability. Increasing cover-layer thickness significantly attenuates defect signals and reduces imaging contrast. Experimental results are in good agreement with simulation predictions, confirming the validity of the proposed models. This work provides a quantitative analysis of defect thermal behavior in multi-material systems and offers a theoretical basis for adaptive infrared thermography inspection and condition assessment of power equipment. It should be noted that this study focuses on mechanistic understanding and parametric analysis rather than on proposing a dedicated quantitative defect-sizing or inversion method. Full article

Carbon fiber-reinforced polymer (CFRP) composites are widely used in the aerospace industry. The residual stresses generated during the curing process significantly affect their mechanical properties. In this study, a multi-field coupled simulation of curing and subsequent uniaxial tension is performed on CFRP laminates with different curing parameters. First, the curing process is simulated to obtain the residual stress distribution in the composite. Then, the residual stresses are introduced as initial stresses for the subsequent loading step. The influence of curing parameters on the mechanical properties of composite laminates under uniaxial tension is analyzed. The results show that the temperature of the first holding stage has a significant effect on the residual stresses. When the temperature is set to 383 K, 403 K, or 413 K, the curing residual compressive stress exceeds the critical value of −50.424 MPa, and the ultimate tensile strength of the laminates decreases by approximately 20.7%. However, the large residual compressive strain also delays the initiation of matrix tensile damage, postponing the initial failure displacement from 1.025 mm to about 1.111 mm. When the holding time of the second stage varies between 80 min and 160 min, the residual stress after curing and the tensile strength of the laminates remain almost unchanged. This study provides a basis for selecting curing parameters of composite materials and offers new insights into improving their mechanical properties. Full article

This study statistically examines how fused deposition modeling (FDM) parameters influence the mechanical behavior of FDM-printed lattice structures. Diamond triply periodic minimal surface (D-TPMS) lattice structures were 3D-printed using carbon fiber-reinforced polylactic acid (PLA/CFs) composites. The effects of FDM parameters, including extruder temperature (ET), printing speed (PS), and layer thickness (LT), on the mechanical behavior of D-TPMS structures were investigated using response surface methodology (RSM). Uniaxial compression testing was performed to evaluate the mechanical properties of the 3D-printed samples, including compressive modulus (E), peak strength (σ_peak), and specific energy absorption (SEA). The optimal FDM parameter settings for maximizing E, σ_peak, and SEA were determined using multi-objective optimization via the desirability function. A deformation analysis was further conducted. The as-built D-TPMS samples generally matched the design relative density (44%), with absolute errors of 0.3–4.5%, while the largest deviation (~4.5% below the design value) occurred at low-ET and high-LT combinations. The results showed that LT was the dominant factor affecting E and σ_peak, accounting for 77.45% and 89.25% of the total variation, respectively, whereas ET had the most significant influence on SEA, accounting for 55.76% of its total variation. In addition, increasing ET improved interfacial bonding and shifted the failure mode from early wall and layer fracturing to predominantly wall yielding, thereby enhancing structural integrity during compression. Higher LT deteriorated the mechanical properties (E, σ_peak, and SEA) and promoted a progressive failure mode characterized by gradual interlayer separation. The findings revealed that the optimal settings (60 mm/s PS, 232 °C ET, and 0.2 mm LT) simultaneously maximized E (0.567 GPa), σ_peak (15.937 MPa), and SEA (15.510 J/g), with high predictive accuracy (maximum % error ~±1.41%). Correlation analysis further revealed significant relationships between as-built relative density and the compression responses E, σ_peak and SEA, with correlation coefficients exceeding 0.8. Overall, this study advances the understanding of how FDM printing parameters govern the mechanical behavior of PLA/CFs D-TPMS lattice structures and highlights the potential for predicting their mechanical performance. Full article

Carbon fiber-reinforced polymer (CFRP) repair is widely used to rehabilitate corroded steel pipelines; however, the relative influence of CFRP repair geometry on stress reduction remains insufficiently quantified. This study investigated the effects of CFRP thickness and repair length on the hoop stress response of steel pipelines containing circumferentially uniform longitudinal corrosion defects under internal pressure. An axisymmetric finite element model was developed in ABAQUS and verified against an analytical multilayer cylinder solution based on the Lamé thick-cylinder theory. The model was based on an idealized circumferentially uniform corrosion defect, linear elastic material behavior, and perfect bonding between the steel pipe, epoxy filler, and CFRP repair layer. A parametric study was performed by varying the defect depth, defect length, CFRP thickness, and repair length. The results showed that CFRP thickness was the dominant parameter controlling the repair effectiveness. For the deepest defect case, increasing the CFRP thickness ratio from 0.25 to 0.75 increased the hoop stress reduction from approximately 40% to more than 58% for the shorter defect and from approximately 40% to more than 62% for the longer defect case. In contrast, increasing the repair length beyond full defect coverage produced only marginal additional stress reduction. Based on a 10% stress-tolerance criterion relative to the intact pipe response, the required CFRP thickness-to-defect-depth ratio increased with defect severity. These findings support the preliminary CFRP repair sizing by prioritizing repair thickness over excessive repair length. Full article

Lattice structures are widely utilized in lightweight engineering due to their design flexibility and tailorable mechanical properties. However, polymer lattices often exhibit limited load-bearing capacity and moderate crashworthiness under compression. This study proposes a hybrid reinforcement strategy based on the integration of carbon fiber-reinforced polymer (CFRP) rods into polymeric Kelvin-cell lattices. The specimens were manufactured via masked stereolithography, and the effects of rod placement pattern, the number of rods, and rod-length configuration were systematically investigated under quasi-static compression. Crashworthiness was evaluated in terms of force–displacement response, deformation mode, and crashworthiness metrics. Compared with the empty Kelvin-cell lattice, the best-performing hybrid configuration increased energy absorption, specific energy absorption, and mean crushing force by approximately 356%, 307%, and 356%, respectively. Mechanistically, distributed rod placement promoted more uniform load sharing, while the effect of increasing rod number depended strongly on the rod-length configuration. In addition, delayed or sequential reinforcement strategies provided superior performance and an enhanced balance between energy absorption and force efficiency. Regression models and ANOVA consistently identified rod-length configuration as the dominant design variable. These findings demonstrate that CFRP rod reinforcement can effectively enhance the crashworthiness of polymeric Kelvin-cell lattices, provided that the rod placement pattern, rod number, and rod-length configuration are designed jointly. Full article

This study examines the effect of small ply angle deviations on the structural response of carbon fiber-reinforced polymer laminates representative of structures used in unmanned aerial vehicles (UAVs). A combined experimental and numerical approach was applied, including cantilever bending tests and experimental modal analysis, supported by finite element simulations. Laminates with nominal ply orientations of 0°, 5°, and 10° were manufactured using a manual hand lay-up process to reflect typical production variability. The results show that the numerical model accurately captures the observed trends in both bending deformation and natural frequencies, with discrepancies up to 12.5%. A consistent tendency to slightly overestimate stiffness was observed, leading to lower predicted deflections and higher natural frequencies compared to experimental data. The findings confirm that finite element modeling can reliably detect and predict the structural effects of small fiber misalignment, supporting its use in the assessment and design of lightweight composite structures used in UAV applications. Full article

The performance of steel structures can decrease over time due to several factors and therefore requires serious consideration to avoid any risks to users. Currently, strengthening of structures using fiber-reinforced polymer (FRP) materials is gaining in popularity. This paper presents a finite element (FE) analysis to investigate the flexural performance of steel I-beams strengthened with unbonded carbon FRP (CFRP). A total of 38 beam models is developed with four influential parameters considered, namely CFRP thickness, CFRP elastic modulus, type of steel beam cross-section, and strengthening length. The results of the investigation confirm that unbonded CFRP strengthening improves the performance of steel I-beams. Initial stiffness and moment capacity of the beams increase as the thickness of CFRP, CFRP elastic modulus, and strengthening length increase. The increase in the initial stiffness of beams tends to be linear as the length of strengthening increases. Meanwhile, the linear trend occurs only up to CFRP lengths of 700 mm or 800 mm for the increase in beam moment capacity. Unbonded CFRP strengthening contributes higher to steel beams with a lower moment of inertia. Full article

Battery housings are critical structural and safety components in electric vehicles, fulfilling multiple functions related to mechanical protection, crashworthiness, thermal management, fire resistance, electromagnetic shielding, and integration of battery modules into the vehicle body. While metallic housings, particularly aluminum and steel, remain dominant in industrial applications, increasing attention is being given to composite materials as lightweight alternatives capable of improving energy efficiency and extending driving range. However, the growing use of composites in battery enclosures raises important questions regarding recyclability, end-of-life management, and compatibility with circular economy principles. This review critically examines the current state of the art in composite materials used for electric vehicle battery housings, with particular emphasis on glass- and carbon-fiber-reinforced thermoplastics, thermoset composites, sandwich structures, and hybrid multi-material systems. The paper discusses the functional requirements imposed on battery housings and analyzes how these requirements influence material selection and design strategies. Particular attention is devoted to recycling pathways applicable to composite battery enclosures, including mechanical recycling, thermal treatment, chemical recycling, and reuse-oriented approaches, as well as to the limitations associated with mixed-material assemblies, adhesives, coatings, and integrated functions. The review also addresses circular design strategies for battery housings, including design for disassembly, material traceability, modularity, and the incorporation of recycled polymers and secondary reinforcements into new housing systems. Current research gaps are identified in the integration of structural performance, fire safety, manufacturability, and recyclability within a single design framework. The analysis shows that thermoplastic composites currently offer the most promising route toward circular battery enclosures, while thermoset-based systems still face significant challenges in high-value recycling. The paper concludes by outlining future research directions required for the development of lightweight, safe and recyclable composite battery housings aligned with sustainable mobility and circular economy goals. 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

In-plane curved steel beams with circular hollow sections (CHSs) are widely gaining appeal in bridges. Strengthening such elements for increased demand or decreased strength due to environmental effects or fatigue, without affecting the usage of structure, is a timely need. Carbon fiber-reinforced polymer (CFRP) materials have been a promising solution for such situations. This paper investigates the flexural behavior of CFRP-strengthened vertically curved steel beams with CHSs. Sixteen such beams, each with a span of 1200 mm and having four different radii of curvature, i.e., 0 m, 2000 mm, 4000 mm, and 6000 mm, and retrofitted with a range of CFRP bond lengths, are considered. Numerical models of these beams are developed and validated using the results of tests performed by the authors, and the validated models were used to simulate bond characteristics and structural performance. Optimum performance was noted in the specimens strengthened with CFRP fibers attached in the axial direction of the members, irrespective of their curvature. On average, strength enhancements of 21% and 14% were obtained in CFRP-strengthened straight and curved beams, respectively. Detailed bond characteristics presented in this paper under transverse loads yield important data for researchers, designers and material developers to strengthen in-plane curved steel members. Full article