Search Results (562)

This paper introduces a temperature-based design method for determining the tensile concrete cone capacity of anchors subjected to fire exposure. Current prescriptive approaches, most notably Eurocode 2, rely solely on embedment depth and fire duration for fire exposure from one or more directions on one concrete face with and without edge effects. The purpose of this work is to develop a temperature-based design method for predicting tensile concrete cone failure of anchors under fire conditions. Through an experimental program, this study demonstrates that anchor capacity can be conservatively described by temperature associated with embedment depth. A parametric analysis on the influence of concrete strength, anchor group effect, edge effect, concrete cracking, anchor type and heating orientation on different concrete faces defines the scope of application of the design method. The proposed method incorporates measured temperature profiles, offering a more precise alternative to the existing design method in Eurocode 2 and enabling flexible design for different structural configurations and fire scenarios. Optimized design is enabled in comparison to the existing prescriptive method (EN 1992-4) exclusively based on embedment depth and fire duration. Research findings demonstrate that anchor capacity correlates strongly with the temperature at the effective embedment depth under varying conditions. Full article

Welding is widely used to join steel components in energy storage systems, wind power generation systems, and transportation infrastructure. During service, surface defects in steel welds can promote rapid crack propagation and sudden fracture. To address this issue, this study presents an induction thermography framework for post-weld quality inspection of surface-breaking defects in welded steel structures. First, a yoke excitation structure was optimized and evaluated through numerical simulation and experimental validation, and its performance was compared with those of a straight coil and a three-loop coil. The results show that the yoke configuration maintains sufficient heating intensity in the weld region while improving the spatial uniformity of the thermal response. Furthermore, a speed-based reconstruction method was developed to reduce the effects of specimen motion and coil occlusion. By aligning thermal responses from the same physical locations in sequential thermograms, the method reconstructs a continuous temperature field over an extended inspection area. Consequently, the reconstructed images retain clear crack-related thermal features and provide stable inputs for automated analysis. In addition, DeepLabv3+, DSCA-UNet, and feature pyramid network (FPN) were used as representative segmentation models to evaluate the suitability of the reconstructed thermograms for automated defect extraction. On the current laboratory dataset, the three models achieved precision values of 90.4%, 88.6%, and 92.6%, respectively. These results indicate the potential of the proposed framework, while further validation with larger datasets and natural weld defects is still required. Full article

Ground penetrating radar (GPR) is widely used for non−destructive evaluation of pavement structures, yet the automatic detection of internal cracks remains challenging due to variations in crack geometry, infilling materials, and antenna configurations that significantly alter signal responses. Most existing machine learning approaches focus on improving detection accuracy but pay limited attention to the inherent symmetries and invariances present in GPR data. This study proposes a symmetry−informed learning framework for robust pavement crack detection across different antenna orientations and material conditions. Laboratory concrete slabs containing cracks with varying widths (2–30 mm) and depths (10–110 mm) were constructed and tested under five representative crack states: air−filled, dry sand, fresh water, saturated sand, and bitumen−filled. GPR data were collected using a 2.3 GHz system under perpendicular and parallel broadside antenna orientations to capture rotational variability. A deep learning model was developed with symmetry−aware training strategies that exploit rotational consistency and material−invariant feature learning. Comparative experiments were conducted to evaluate detection performance and cross−condition generalization. Results demonstrate that incorporating symmetry improves model robustness and generalization across unseen orientations and filling conditions. The proposed framework highlights the importance of symmetry−informed learning for reliable AI−driven GPR inspection of pavement infrastructure. Full article

Deep learning-based road crack segmentation can achieve high benchmark performance on public datasets, but its reliability in UAV-acquired field imagery remains uncertain because real road scenes contain various crack-like non-crack features. This study assessed the field transferability of a public-dataset-trained crack segmentation model using UAV-acquired road images. Nine semantic segmentation model configurations were trained and compared using integrated public crack datasets, and U-Net++ with a ResNet50 backbone was selected for UAV field application. After confidence-based data refinement and training data augmentation, the final model achieved precision, recall, Dice, and IoU values of 0.802, 0.787, 0.794, and 0.659, respectively, on the public validation dataset. Field evaluation was conducted on 148 UAV images and manually corrected UAV ground-truth patches generated from non-overlapping 8 × 8 image grids. The total UAV field evaluation produced precision, recall, Dice, and IoU values of 0.856, 0.806, 0.830, and 0.710, respectively. Major errors were associated with crack-like non-crack factors, including lane markings, manholes, repaired boundaries, shadows, surface contamination, and reflections. Threshold sensitivity analysis indicated that approximately 0.4–0.5 was a practical operating range under the tested UAV conditions. These results show that idealized public-dataset evaluation can overestimate real-world UAV performance and that field transferability evaluation is essential for reliable UAV-based pavement inspection. Full article

This study investigates the flexural behavior, load-carrying capacity, and crack propagation of concrete beams reinforced with hybrid glass-fiber-reinforced polymer (GFRP) and steel bars. To evaluate the structural performance, concrete beam specimens with cross-sectional dimensions of 150 mm × 300 mm and a total length of 2050 mm were fabricated using a design concrete compressive strength of 35 MPa and tested under flexural loading. Each tested specimen featured a distinct hybrid reinforcement configuration to investigate the influence of bar arrangement on the mechanical behavior. Flexural cracks were systematically monitored using a crack-width comparator gauge at specific loading stages, accounting for key milestones such as ultimate load capacity and sudden load drops. The experimental findings were complemented by an analytical model to validate the performance parameters and predict the ultimate capacity. The results demonstrate that the specific configuration and arrangement of hybrid reinforcement significantly influence the post-cracking stiffness and crack growth. Specifically, the hybrid configuration effectively balances the ductile response of steel with the brittle behavior of GFRP, achieving significant control over serviceability crack widths and an enhanced ultimate load-carrying capacity. Experimental results indicated that for elements exhibiting identical axial stiffness, the reinforcement layering configuration provided a 66% improvement in the deformability factor alongside a 10% enhancement in the load-carrying capacity. It is recommended that the steel tension reinforcement be positioned in the inner layer at a spacing of about two times the GFRP bar diameter to mitigate corrosion risks. Additionally, it was established that the theoretical load capacity accounted for 70% to 86% of the experimental load capacity. Full article

The fundamental issue in designing encapsulation-based self-healing concrete structures is the design of microcapsules. However there are few studies in the literature on this topic; not only is the fracture of microcapsules crucial for releasing the healing agent to heal fractures in the concrete matrix, but also the amount of the healing agent and expected crack widths. Therefore, in this paper, a novel design method of dimensioning microcapsules for encapsulation-based self-healing concrete (SHC) with consideration for a sufficient volume of healing agent to heal a specific crack width is developed. It is based on the configuration of the representative volume element (RVE) and the unit cell (UC), and associates them with the volume fraction (V_f) and the crack width as variables with applied periodic boundary conditions (PBCs). It is also validated through numerical fracture modeling using the eXtended Finite Element Method (XFEM), and cohesive surface (CS) technique. Effects of interfacial cohesive properties, the microcapsule size, and volume fraction on the load carrying capacity and the crack pattern are investigated numerically. The obtained results are in good agreement with the literature. The developed design method can serve as a valuable tool for obtaining a preliminary design of microcapsules for SHC. Full article

Triply periodic minimal surface (TPMS) gyroid lattices are promising lightweight and energy-absorbing polymer structures, but their manufacturability by material extrusion (MEX) depends strongly on cell size, grading direction, and relative density. This study investigates PLA gyroid lattices with uniform and graded cell-size configurations using initial and final cell sizes of 1, 1.5, and 2 mm and target relative densities of 10, 20, and 30%. A full-factorial design was used to construct a printability map, followed by quasi-static compression testing, areal surface-roughness characterization, and SEM observation of representative specimens. The printability results showed that low-density fine-cell configurations were most prone to incomplete wall formation and collapse, whereas the 30% relative-density group was printable for all investigated cell-size combinations. Under compression, the 30% relative-density uniform 1 mm gyroid showed the highest maximum stress among the tested configurations, while graded structures terminating in smaller cells also provided favorable load bearing and energy-absorption behavior. The plateau stability index, calculated from stress fluctuations between collapse and densification, helped distinguish stable progressive collapse from more oscillatory deformation. Surface roughness and SEM observations further indicated that smoother, more continuous wall surfaces were associated with more uniform deformation, whereas rougher and defect-rich surfaces promoted localized buckling, cracking, and brittle collapse. Overall, the results identify experimentally supported relationships between gyroid cell-size configuration, printability, surface integrity, and compressive response within the investigated PLA MEX design space. Full article

Purpose—The flexspline of a harmonic drive constitutes a thin-walled structure with discontinuous gear rim and cylinder configuration, where cyclic stresses induce stress concentration, followed by crack initiation, propagation, and ultimately fatigue failure. This paper reviews advancements in understanding its mechanical properties and fatigue failure mechanisms, aiming to establish a foundation for enhancing operational longevity and guiding future research. Design/Methodology/Approach—The study integrates meshing theory, tooth shape parameters, cylinder stress influencers, and assembly/meshing stress considerations. Theoretical analysis, finite element simulations, and experimental methods are employed to examine stress patterns and fatigue dynamics. Structural parameters and tooth profiles are systematically analyzed for their impact on stress distribution and fatigue life. Findings—Flexspline fatigue failure arises from tooth root stress concentration and cylinder bending stress accumulation. The double-circular-arc tooth profile boosts load capacity by 35% relative to the involute profile, yet demands high-precision machining to preserve meshing performance. Increasing cylinder length mitigates stress concentration but reduces torsional stiffness, while optimized root fillet radii can lower the stress concentration coefficient by 28%. Assembly interference and meshing contact stress accelerate crack initiation, as validated by transient dynamics simulations. Surface strengthening processes (e.g., shot peening) enhance fatigue life by up to 66% through residual compressive stress regulation. Originality/Value—This paper synthesizes multi-scale research on flexspline design, structural optimization, and fatigue mechanisms, proposing novel approaches such as “manufacturability-oriented optimization” and digital twin-driven monitoring. By linking dynamic loads, material properties, and geometric parameters, it bridges theoretical gaps and provides actionable insights for high-precision harmonic drives in robotics and aerospace, advancing reliability in precision transmission systems. Full article

The welded bead bending test (WBBT) serves as a pivotal procedure for evaluating the crack-arrest capacity of structural steels used for construction of safety-critical infrastructure according to ZTV-ING Part 4 or Deutsche Bahn Standard 918 002-02. Previous research has established that light optical microscopy images (LOMs) of specimens that do not pass the WBBT are frequently characterised by a high prevalence of Widmanstätten ferrite within the base material. While convolutional neural networks (CNNs) have successfully classified WBBT outcomes based on LOMs, the implemented approaches did not enable simultaneous pixel-wise delineation required for accurate quantification of Widmanstätten ferrite. However, the tonal similarity between Widmanstätten ferrite and polygonal ferrite renders conventional intensity-based thresholding ineffective for differentiation, necessitating a morphology-based segmentation approach. The present study proposes an automated semantic segmentation framework for the precise delineation of three microstructural phases present within the WBBT LOMs: polygonal ferrite, pearlite, and Widmanstätten ferrite. Utilising a dataset of 20 LOMs and corresponding manually annotated masks, five UNet encoder backbones were evaluated: ResNet-152, Xception, SE-ResNet-50, DenseNet-169, and EfficientNet-B5. To identify the optimal configuration for this microstructural segmentation task, each architecture was assessed using three distinct weight initialisation strategies: (A) ImageNet, (B) MicroNet, and (C) a combined approach. For Widmanstätten ferrite segmentation at patch level, DenseNet-169 pretrained on ImageNet achieves the best performance (Dice: 50.75% ± 3.38%, IoU: 38.45% ± 3.01%). Following inference-based aggregation, Xception pretrained on ImageNet yields improved results (Dice: 68.74% ± 1.12%, IoU: 52.52% ± 1.28%), with an MAE of 4.55% ± 0.80%. Full article

Material discontinuities and defects can profoundly impact the structural integrity and overall product quality. In a multitude of industries, ranging from aerospace and automotive to the nuclear sector and manufacturing, even surface discontinuities can pose significant risks to component reliability. This paper presents a planar microwave sensor for non-destructive testing (NDT) to quantify the electromagnetic response to controlled crack-like discontinuities in polylactic acid (PLA) materials. The sensor comprises a host coplanar waveguide (CPW) positioned at the base of an RO3210 substrate and a multiple split-ring resonator (MSRR) on the surface, creating a compact device measuring 30 mm × 50 mm × 1.27 mm. When a discontinuity-free PLA sample-under-test (SUT) is placed above the sensor, the transmission coefficient exhibits a resonance at 1.780 GHz. As the width of the groove-based discontinuity increases, a systematic blue shift in the resonant frequency is observed. The relationship between resonant frequency shift and discontinuity width is established through empirical calibration for both surface and subsurface configurations. The results demonstrate the feasibility of the proposed sensor for calibrated detection and sensitivity-based discrimination of millimeter-scale crack-like discontinuities in PLA within the tested dimensional range. Full article

Composites are widely used in the building sector for high-rise building load-bearing components, bridge decks, prefabricated structural panels, and seismic-resistant members, where excellent mechanical performance and structural durability are critical. As specialized advanced composites, variable stiffness composites (VSCs) have gained increasing engineering applications due to their excellent overall performance. Nevertheless, exploring the fracture characteristics of composite materials, especially VSCs, remains a significant challenge. In particular, cracks in composite components can adversely affect structural integrity and durability. In this study, a dynamic fracture phase-field model for VSCs is developed within the framework of elastic dynamics to investigate crack propagation behavior of VSCs under dynamic loads. The proposed model is first validated by experimental results of fracture behavior of single-edge cracked FRC laminae. Then, the proposed model is employed to systematically study the effects of three fiber orientation design variables and internal defects on the fracture behavior of VSCs. Additionally, fiber trajectories are optimized for different pore distribution configurations. The results demonstrate that the model effectively captures the fracture behavior of VSCs and that optimizing these three design parameters enables the fabrication of high-performance VSCs with enhanced crack propagation resistance. This work provides fundamental insights for the design of curvilinearly fiber-reinforced composites and lays a solid theoretical foundation for the practical application of VSCs in building engineering. 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

This study investigates the use of magnetoelastic sensing for vibration-based structural health monitoring (SHM) of cementitious beam specimens under intact and damaged conditions. Prismatic mortar beams with dimensions of 160 × 40 × 40 mm³ were fabricated following standardized preparation procedures and equipped with annealed amorphous ferromagnetic ribbons, Metglas 2826MB3, for nondestructive magnetoelastic vibration sensing. The specimens were tested under free-vibration conditions in a simply supported configuration, and their vibration response was measured using a detection coil and subsequently analyzed using MATLAB software. The undamaged specimen exhibited a dominant resonance frequency at 6531 Hz, which closely corresponded to the fourth bending mode predicted by Euler–Bernoulli beam theory. Controlled notch-shaped cracks with varying locations and depths were subsequently introduced to evaluate the sensitivity of the sensing system to structural damage. Experimental results showed that the frequency shift is strongly influenced by the location of damage relative to the modal nodes, with maximum sensitivity observed between nodal regions and minimal variation near the nodes. Furthermore, increasing notch-shaped crack depth produced progressively larger frequency shifts, revealing a monotonic and non-linear relationship between damage severity and dynamic response. Polynomial fitting and 3D surface analysis further highlighted the combined influence of crack location and depth on the measured frequency variation. The findings confirm that the magnetoelastic sensor is capable of accurately detecting and magnetically transmitting the vibration state and damage-induced changes in cementitious structures, demonstrating high sensitivity and strong potential for application in vibration-based structural health monitoring systems, particularly in materials characterized by strong vibration damping. Full article

The optimized design of key components in harvesting equipment is significantly impeded by the significant grain loss from the header and high energy consumption during stalk cutting that result from the lack of physical and mechanical parameters regarding the plant-flower head system during the mechanized harvesting of edible sunflowers. To furnish the design of mechanized harvesting equipment for palatable sunflowers with theoretical support and foundational data, physical parameters measured included geometrical properties, critical bending angle, coefficient of static friction, moisture content, and head seed collision loss rate. Mechanical parameters—radial elastic modulus, shear modulus, and shear strength—were obtained from stalk compression and shear tests using a universal testing machine. Stem-head detachment force was quantified with a universal testing machine fitted with bespoke fixtures, and orthogonal experiments were conducted with tensile speed, head-picking plate spacing, and tensile angle as factors to establish the significance hierarchy and optimal configuration. Considerable heterogeneity was observed: mean plant height, head diameter, and head thickness were (1733 ± 153) mm, (275 ± 28) mm, and (93 ± 19) mm, respectively. The critical bending angle decreased with height, whereas stalk moisture content increased from base to apex. Mean stalk and head moisture contents were 65% and 61.4%. The coefficient of static friction varied from 0.24 to 0.63 depending on contact material. A critical impact velocity of 2–3 m/s induced mechanical damage and seed cracking. The stalk radial elastic modulus was (1.12 ± 0.27) MPa; shear modulus and shear strength increased with decreasing sampling height, with basal stalks exhibiting a mean shear modulus of 2.47 MPa and shear strength of 1.87 MPa. Sampling position significantly influenced shear modulus (p < 0.05). The factor significance for stem-head detachment force was head-picking plate spacing > tensile angle > tensile speed. The optimal combination (tensile speed 500 mm/min, head-picking plate spacing 50 mm, tensile angle 10°) yielded a detachment force of (202.3 ± 9.5) N, with a relative error below 5% compared to prior detachment force measurements, confirming the reliability of the optimised results. These data provide essential foundations for developing stalk cutting, head inserting, and combine harvesting equipment. Full article

The Ediacaran Dengying Formation 2nd Member (hereafter 2nd Member) in the Sichuan Basin is influenced by major tectonic events including the Caledonian, Indosinian, and Himalayan orogenies and this strata has experienced a complex hydrocarbon accumulation history, resulting in inconsistent gas–water contacts. To elucidate this complex history, this study investigates the diagenetic mineral filling sequence within the Dengying 2nd Member in the Penglai area. We integrated data from analytical techniques such as cathodoluminescence (CL), in situ trace element analysis, U–Pb geochronology, and fluid-inclusion microthermometry. Based on these analyses, this study established the paragenetic sequence, incorporating both diagenesis and hydrocarbon accumulation, for the Dengying 2nd Member. This sequence comprises eight distinct phases of mineral precipitation and hydrocarbon emplacement: fibrous dolomite, granular dolomite, fine crystalline dolomite, first-phase bitumen, medium crystalline dolomite, saddle dolomite, second-phase bitumen, and quartz. From this sequence, we propose a four-stage hydrocarbon accumulation model for the Dengying Formation: (1) primary migration and accumulation during the Indosinian period; (2) oil cracking to gas during the Yanshanian period; and (3) and (4) two distinct stages of gas pool adjustment during the Himalayan period. Corresponding to these stages, this study developed distinct accumulation models and simulated migration and accumulation processes during key stages. The results indicate that the distribution of paleo-oil pools exerts significant control over the location of present-day gas accumulations. Initial oil charge was controlled by the distribution of carrier beds and hydrocarbon charging pathways, with water zones observed more frequently in the lower intervals of the Dengying 2nd Member. Subsequently, gas generated from oil-cracking filled these carrier beds, with areas of gas enrichment correlating with zones of high paleo-oil saturation. Finally, during the later adjustment stages, fault activity induced gas remigration and leakage, significantly impacting the final trapping configuration and preservation of gas accumulations. Full article