Search Results (674)

Agricultural steel pipelines are essential components of pressurized irrigation systems, yet localized corrosion-induced pinholes severely compromise their structural integrity by creating critical stress concentrations. To address the lack of performance-based maintenance guidelines, this study experimentally evaluates three repair techniques—a multi-joint hinge clamp, a GFRP composite sleeve, and overlay welding—applied to steel pipes containing simulated pinhole defects representing 6% and 10% circumferential damage. Four-point bending and uniaxial tensile tests were conducted to simulate transverse overburden and longitudinal axial loading encountered in buried pipelines. Results reveal that repair effectiveness strongly depends on both loading mode and damage severity. At 6% damage, all methods effectively restored bending capacity, with the GFRP sleeve achieving near-complete recovery. Under tensile loading, however, external-confinement methods provided limited ductility improvement because they lack a direct axial load-transfer path. In contrast, overlay welding consistently achieved substantial structural restoration by eliminating stress concentrations and shifting fracture to the parent pipe material. Furthermore, a significant transition in repair performance was observed near the 6% damage level, beyond which confinement-based repairs exhibited reduced efficacy. These findings demonstrate that repair performance cannot be reliably assessed from bending behavior alone and highlight the importance of considering both loading conditions and damage severity in rehabilitation design. The study provides a quantitative framework for load-specific pipeline rehabilitation strategies. Full article

This review comparatively analyzed MWCNT-reinforced thermoplastic polyester nanocomposites based on petroleum-derived (PET, PBT) and bio-based (PLA, PBS) matrices, focusing on processing methods, mechanical performance, thermal stability, electrical behavior, and recyclability. Optimal MWCNT loadings typically ranged from 0.3 to 3 wt.%; higher loadings induced nanotube agglomeration and deteriorated properties due to poor dispersion and stress concentration. Melt mixing, solution blending, direct compounding, and in situ polymerization were evaluated, and their influence on dispersion quality, interfacial bonding, and scalable manufacturability was discussed. PET exhibited the largest improvements in mechanical and thermal performance (tensile strength and modulus increases >300% in optimized systems); acid or compatibilizer functionalization of MWCNT improved PET thermal stability by approximately 20–50 °C and promoted heterogeneous nucleation. PBT reached optimal reinforcement at 0.3–1 wt.% MWCNT, yielding tensile strength increases up to ~57% alongside increased crystallinity and faster crystallization kinetics. PLA generally showed reduced tensile strength after MWCNT addition unless compatibilized (e.g., via plasticizers or grafting), whereas PBS consistently gained strength, modulus, and crystallinity but experienced reductions in ductility. Electrical percolation thresholds varied widely (0.25–14 wt.%), demonstrating that dispersion quality, nanotube functionalization, and processing route governed conductivity and percolation behavior more than matrix chemistry. Recyclability and circular economy aspects were assessed: while PET/MWCNT systems showed promise for mechanical recycling and property recovery, data on repeated reprocessing, CNT structural integrity, and long-term electrical performance were scarce; PBT recycling studies were limited, and PBS/PLA recycling with retained conductive networks remained underexplored. Based on the comparative analysis, key limitations, critical research gaps, and practical recommendations for processing, compatibilization, and end-of-life evaluation were identified to guide future work aimed at enhancing both performance and sustainability of polyester/MWCNT nanocomposites. Full article

The present study investigates the combined influence of manufacturing route and material configuration on the mechanical, elastic, viscoelastic, and impact behavior of Kevlar–carbon hybrid laminates. Three eight-ply laminate configurations (V1, V2, and V3) were manufactured through distinct technological routes: fully prepreg-based hot pressing, Kevlar-prepreg/dry-carbon hand lay-up followed by vacuum curing, and multi-stage hybrid consolidation combining repeated hot pressing with subsequent vacuum curing. The experimental characterization included tensile tests according to ASTM D3039, compression tests according to ASTM D695, determination of Young’s modulus from extensometer measurements and Poisson’s ratio using strain-gauge instrumentation, dynamic mechanical analysis (DMA), and low-velocity impact tests under controlled energy conditions. The novelty of this work consists in the integrated process–configuration–property comparison of these Kevlar–carbon hybrid routes within the same experimental framework, rather than in a generic demonstration that manufacturing affects composite laminates. The V1 laminate exhibited the highest strength-related performance, reaching an average tensile strength of 335.88 MPa and a compressive strength of 165.85 MPa, and it also showed the highest DMA storage modulus at 30 °C, E’ = 53.42 GPa. The V2 laminate presented lower tensile performance but the most pronounced damping response, with the highest tanδ peak value. The Young’s modulus determined from the extensometer measurements was 29.26 ± 1.45 GPa for V1, 26.10 ± 0.22 GPa for V2, and 29.52 ± 1.27 GPa for V3, indicating comparable longitudinal stiffness for the V1 and V3 laminates. The results indicate that the measured behavior is governed by the combined effects of reinforcement form, matrix/resin arrangement, consolidation route, and laminate architecture. Direct quantification of laminate compaction, fiber volume fraction, and void content was outside the scope of the present experimental campaign and is identified as a necessary step for future validation. Full article

To meet the stringent requirements for the synergy of ultra-high strength and exceptional toughness in drilling equipment for ultra-deep wells, this study employs molecular dynamics (MD) simulations to systematically investigate the intrinsic effects of spatial configurations (Cluster vs. Dispersion) of five transition metal elements (Co, Mo, Ni, Ti, and W) in an iron matrix on micro-defect evolution and mechanical performance. The simulation systems, each containing approximately 54,000 atoms, were initially relaxed under an isothermal-isobaric (NPT) ensemble at 300 K for 50 ps to ensure thermodynamic equilibrium, and were subsequently deformed under uniaxial tensile loading at a strain rate of 5 × 10⁹ s⁻¹. The results demonstrate that the distribution pattern of solute atoms influences the mechanical response. The cluster configuration generally weakens the matrix strength, a behavior indicative of stress localization and dislocation pile-up at the interfaces; in contrast, the dispersed configuration is associated with a more thermodynamically stable state and enhanced ultimate load-bearing capacity. Specifically, the Fe-Mo dispersed system reaches an ultimate tensile strength (UTS) of 28.32 GPa under the studied conditions, which exceeds the pure Fe benchmark of 24.90 GPa—an enhancement that points toward the formation of denser local atomic ordering and extensive dislocation network hardening. Meanwhile, the Fe-W dispersed system exhibits sustained dislocation activity up to large strains, suggesting that enhanced cross-slip contributing to its relatively high ultimate tensile strain and toughness. Based on these atomistic insights, a “Mo-W composite dispersed” micro-configuration design strategy is proposed as a conceptual direction for further exploration. 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

Additive manufacturing has opened an extraordinary design space for polymer metamaterials, enabling microstructures whose macroscopic mechanical behavior is governed largely by geometry rather than by chemical composition. A principled design framework must solve two coupled problems: a forward problem (given a microstructure, predict effective properties) and an inverse problem (given target properties, generate a microstructure). Convolutional neural networks (CNNs) solve the forward problem accurately, but the inverse problem remains more challenging for three reasons reported in the literature: (i) many surrogates predict only a scalar proxy rather than the full second-order elastic tensor; (ii) fixed or randomly initialized inverse decoders create a distribution-shift gap between surrogate predictions and physical re-evaluation; and (iii) dataset bias toward near-solid configurations limits exploration of low-density and anisotropic designs. We present a unified framework, the Operator-Physics-Enhanced Reverse Architecture (OPERA), that addresses all three issues. First, the forward surrogate predicts the complete $3\times 3$ plane-stress stiffness tensor $C^{\mathrm{eff}}$ in Voigt notation, with an analytical layer enforcing $C_{ij}=C_{ji}$ and positive definiteness by construction, achieving $R^2>0.99$ on the directional moduli and density and $R^2>0.88$ on the off-diagonal coupling term $C_{16}$ and the effective Poisson ratio. Second, a normalizing-flow decoder ${\mathcal{F}}_{\varphi }$, jointly trained with the forward surrogate, keeps inverse design on the training manifold and reduces the surrogate–PDE re-evaluation gap from more than 30% to below 6% on held-out targets. Third, a five-family dataset with uniform coverage of $\rho \in [0.10,0.95]$ is augmented through an expected-improvement active-learning loop. We embed minimum-feature-size, connectivity, and print-direction constraints into the optimization through differentiable regularization and report agreement of $R^2=0.987$ between predictions and tensile measurements on ten FDM-printed specimens. The framework is demonstrated on five problems (auxetic, extreme anisotropy, isotropic low-density, chiral, and hierarchical), with an average target error of 6.8%. The results are framed relative to a reproduced scalar-proxy baseline; we provide an explicit statistical uncertainty analysis, a baseline-reproduction protocol, and a discussion of the method’s assumptions and numerical enforcement. Full article

Carbon nanotube (CNT)- and graphene flake (GF)-modified polyester (PET) nonwoven composites were prepared using a one-sided impregnation process with waterborne polyurethane (PU) as the binder. The objective of this work was to clarify how the geometry and loading of one-dimensional CNTs and two-dimensional GFs regulate conductive network formation, anisotropic mechanical behavior, and thermal response in PU/PET nonwoven composites. The novelty of the study lies in the direct comparison of CNT and GF fillers in the same nonwoven/PU matrix and in correlating filler morphology with mechanical reinforcement, electrical conductivity, and textile-related thermal management performance. The sample codes C5 and C6 represent CNT contents of 5 and 6 wt.%, respectively, while G4 and G6 represent GF contents of 4 and 6 wt.%, respectively. Scanning electron microscopy (SEM) showed that GF tended to form sheet-like coatings on fiber surfaces and to fill inter-fiber pores, whereas CNTs showed more local aggregation because of their high surface energy. The composites exhibited anisotropic tensile behavior, with higher tensile strength in the longitudinal direction than in the transverse direction. In the longitudinal tensile test, G4 reached a tensile strength of 13.01 MPa, while C5 reached 11.35 MPa. With increasing carbon material content, both the electrical and thermal conductivities of the composites increased. The electrical conductivity reached 0.02100 S/cm for C6 and 0.05893 S/cm for G6. The thermal conductivity of the CNT/PU/PET composites increased from 0.1163 to 0.1923 W/(m·K), whereas that of the GF/PU/PET composites increased from 0.1793 to 0.2537 W/(m·K). Infrared thermal imaging further indicated that carbon material addition produced faster heating and slower heat dissipation than the unmodified PU/PET sample. These results provide a useful reference for developing multifunctional nonwoven composites for smart textiles, special protective clothing, wearable thermal management layers, and flexible electronic textile substrates. Full article

Hydrogen embrittlement (HE) is a critical issue that constrains the service reliability of structural alloys in hydrogen-rich environments. For the CoCrNi medium-entropy alloy (MEA), the interplay between deformation twins (DTs) and HE remains controversial, and the mechanism by which pre-strain-induced twin boundaries (TBs) influence hydrogen migration pathways and fracture behavior still requires further elucidation. To address this, the present study employed multiple complementary techniques, including slow strain rate tensile (SSRT) testing, electron backscatter diffraction (EBSD) analysis, direct hydrogen visualization via hydrogen microprinting (HMP), and microhardness measurements, to comparatively investigate the hydrogen-induced cracking behavior of the alloy subjected to pre-strain levels of 0%, 30%, and 50%. Experimental results reveal that dense nanoscale TBs can serve as both effective hydrogen trapping sites and diffusion barriers, substantially modifying the hydrogen distribution pattern and preventing substantial hydrogen enrichment at grain boundaries (GBs). This twin-dominated regulatory mechanism significantly suppresses hydrogen-induced intergranular fracture, endowing the material with outstanding HE resistance. These findings elucidate the intrinsic anti-HE mechanism governed by twin structures and provide a microstructural design basis for the development of high-performance hydrogen-resistant multi-principal element alloys (MPEAs). Full article

To investigate the synergistic regulatory mechanism of vein structure and temperature on crack propagation behavior in plant leaves, this study conducted systematic tensile tests to determine the fracture behavior of leaves with different numbers of veins (0, 1, and 2) at various pretreatment temperatures (35–55 °C). A fractal-corrected fracture energy model was subsequently developed. The results show that both the crack fractal dimension and fracture energy first increase and then decrease with rising temperature, peaking at 45 °C. Fracture energy decreases as the number of veins increases: by approximately 60% for a single vein, and nonlinearly for two veins (synergy factor ranging from 0.59 to 0.71), indicating diminishing toughening returns. When the angle between the crack propagation direction and the vein is less than 90°, veins do not provide a toughening effect but instead act as preferential failure pathways, although they prolong the overall crack propagation duration. Crack propagation velocity exhibits intermittent fluctuations. In the temperature range of 50–55 °C, toughness increases and velocity fluctuations diminish. For double-vein leaves, velocity fluctuations are mild in the early stage, but a pronounced peak occurs later upon interface breakthrough. This model provides a reference for the quantitative analysis of fracture behavior in plant leaves. Full article

This study investigates the mechanical behavior and anisotropy of cellular structures fabricated using PolyJet Matrix (PJM) technology from RGD 720 photopolymer resin. Standard ISO 527 specimens were produced at build orientations of 0°, 45°, and 90° to evaluate the influence of printing direction on tensile properties. Based on these results, the optimal 0° orientation was selected for further analysis of cellular structures, including hexagonal, spiral, and quasi-self-similar geometries, manufactured in both unfilled and silicone-filled configurations. Static tensile tests were performed to determine load–displacement characteristics, maximum load, and deformation behavior. The results reveal a strong dependence of mechanical properties on build orientation, with the highest strength observed at 0° and the lowest at 90°, confirming significant material anisotropy. This behavior was further quantified using first- and second-order anisotropy coefficients derived from experimental data. The introduction of silicone filling improved load-bearing capacity, reduced variability, and promoted a more ductile failure mechanism. Among the analyzed geometries, quasi-self-similar structures exhibited the best mechanical performance, while unfilled structures showed lower strength and higher deformation. The findings demonstrate that both build orientation and structural design are critical factors in optimizing the mechanical properties of additively manufactured components and provide a basis for designing tailored cellular structures for engineering applications. Full article

Cu–Fe alloys combine the high electrical conductivity of Cu with the strengthening and magnetic contributions of Fe, making them promising high-strength, electrically conductive functional materials. However, for high-Fe Cu–Fe alloys with Fe contents exceeding 10 wt.%, the microstructural response, texture evolution, and two-phase deformation partitioning during warm rolling remain insufficiently understood. In this study, Cu–10Fe, Cu–15Fe, and Cu–20Fe alloys were investigated to clarify the effect of Fe content on microstructure evolution, texture characteristics, deformation behavior, and property balance after single-pass warm rolling at 500 °C with a 50% reduction. The results show that, as the Fe content increased from 10% to 20%, the Fe-rich phase became progressively denser after warm rolling and gradually transformed from discrete spherical/spindle-like particles into fibrous structures distributed along the rolling direction, while the average grain size of the alloy decreased. EBSD analysis indicates that increasing Fe content weakened the preferred orientation of the Cu matrix. The maximum texture intensity of the Cu matrix decreased from 5.08 to 4.21, and texture showed a weakening trend. The mechanical properties show that, with increasing Fe content, the ultimate tensile strength increased from 434 MPa to 514 MPa, whereas the elongation decreased from 10.7% to 5.1%. This indicates that the increased amount of Fe-rich phase enhanced strength but reduced plasticity; nevertheless, dynamic recovery and local recrystallization induced by warm rolling helped maintain a certain degree of ductility. The electrical conductivity decreased from 19.43% IACS to 16.71% IACS with increasing Fe content, corresponding to a decrease of only approximately 2.7% IACS, suggesting that warm rolling partially mitigated the negative effect of increasing Fe content on electrical conductivity. Based on the combined microstructural, texture, and KAM/GND analyses, the deformation behavior of the alloys with increasing Fe content exhibited a transition from heterogeneous deformation dominated by the Cu matrix/interface to cooperative deformation involving the Fe-rich phase. Full article

Despite the advantages of powder bed fusion–laser beam (PBF-LB), Ti6Al4V components often exhibit high yield strength but limited ductility, which restricts their use in critical structural applications. This study aims to identify the most effective heat treatment to optimize the strength–ductility balance in Ti6Al4V parts produced by PBF-LB and to establish direct correlations between microstructural states, mechanical properties and corrosion behavior. Two distinct post-processing heat treatments were applied, specifically, the first at 500 °C for 5 h and the second at 800 °C for 2 h, both followed by air cooling. The microstructure was characterized using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Mechanical behavior was assessed through Vickers microhardness testing and tensile testing, while corrosion resistance was evaluated via electrochemical measurements. Residual stress profiles were determined using the hole-drilling strain gauge method, in both as-built and heat-treated conditions. The as-built samples displayed a fully martensitic α′ structure with columnar grains aligned parallel to the laser scanning direction, resulting from rapid solidification. Heat treatment at 500 °C caused only partial decomposition of acicular martensite into substructures without altering its acicular morphology, leading to a strengthening effect alongside a reduction in ductility. Conversely, heat treatment at 800 °C offered the most balanced combination of strength and ductility among the conditions studied, albeit with a moderate reduction in corrosion resistance. Full article

Ultrathin titanium alloy foils are attractive for engineering components requiring flexural compliance and mechanical support, yet their recoverable deformation behavior at the foil scale remains insufficiently characterized. This study evaluates 30 μm Ti–24Nb–4Zr–8Sn (wt.%, Ti2448) foils in the as-rolled and solution-treated states and compares their tensile loading–unloading response with same-thickness CP Ti and Ti–6Al–4V reference foils. The Ti2448 foils exhibit a larger recoverable-deformation window and a lower apparent loading modulus than the reference foils under the same testing protocol. The highest recoverable strain is obtained in the solution-treated longitudinal condition, indicating that the recoverable deformation is sensitive to both processing state and loading direction. These results suggest Ti2448 foils as potential candidates for flexure-related applications requiring large recoverable deformation. Full article

Oil shale often exhibits well-developed internal bedding planes, microcracks and organic-rich weak interfaces, while a mixed failure mode of tensile fracture and shear slip along weak bedding planes can be observed under bending loads. In this study, three-point bending tests were performed on the oil shale, and with the combination of acoustic emission (AE) monitoring to analyze the crack propagation paths, the crack path selection and mixed-mode I-II fracture behavior controlled by bedding were symmetrically investigated. The experimental results demonstrate that crack propagation does not always steadily proceed along the initial direction of pre-existing crack, and instead, the occurrence of pronounced deflection can be observed near the weak bedding planes, indicating a trend of transition from tensile crack to shear slip along bedding, while the obvious mixed-mode I-II fracture characteristics are presented. Meanwhile, this process is also accompanied by the enhanced AE activity and the occurrence of a localized high-energy event. Furthermore, based on theoretical fracture mechanics analysis, it is interpreted that the localized driving force conditions at the crack tip can be altered by the mechanical differences between the bedding weak planes and the matrix, which provides a theoretical explanation for why the crack deflection along the structural weak planes is promoted. These research findings correlate the crack propagation path evolution, AE response and mixed-mode fracture characteristics, which can provide the experimental evidence for understanding the controlling role of crack path selection in brittle shale under bending conditions. Full article

To investigate the stress evolution, deformation behavior, and failure characteristics of composite-reinforced prestressed concrete hollow square piles (PHSC piles) under bending, a four-point bending test was conducted on a full-scale PHSC500 (340) hollow square pile specimen with a length of 7000 mm, a square section of 500 mm × 500 mm, and a hollow core diameter of 340 mm. The test was used to obtain load–deflection curves, crack propagation patterns, deformation responses, sectional strain distributions, and failure modes. In addition, an ABAQUS finite element model was established to compare the bearing capacity, stiffness degradation, and ductility of different pile types with varying prestressed and non-prestressed reinforcement ratios. The results show that vertical cracks changed their propagation direction at the edge of the tensile zone in the flexural–shear region of the PHSC piles and developed into a critical diagonal crack with a width of 1.7 mm. The specimen ultimately exhibited a shear–compression failure mode. During the failure stage, the midspan deflection increased rapidly as the load rose from 710 to 740 kN, with the deflection increasing from 24.88 to 32.00 mm. The load–midspan deflection curve obtained from the finite element analysis was generally consistent with the experimental results. Moreover, the predicted damage concentration zones corresponded well to the experimentally observed crack locations, indicating that the model can be used to analyze relative variations under different parameter conditions. The combination of prestressed and non-prestressed reinforcement improved the flexural capacity and ductility of the PHSC piles. However, ductility did not increase monotonically with the prestressed reinforcement ratio. These findings provide a reference for evaluating the flexural performance of PHSC hollow square piles and optimizing their reinforcement parameters. Full article