Search Results (1,678)

Background: Occlusal splints are exposed to prolonged intraoral conditions, including saliva, temperature fluctuations, and mechanical loading, which may alter their mechanical performance over time. The increasing use of SLA 3D-printed photopolymer resins for splint fabrication has introduced new materials whose aging-related mechanical stability remains insufficiently characterized. Objectives: This in vitro study evaluated the effects of accelerated aging in artificial saliva on the Shore D hardness and flexural properties, including flexural modulus, flexural strength, and strain at failure, of four polymeric materials used for occlusal splint fabrication: a thermoformed PETG material (Duran, C), a milled PMMA (Bilkim Polywax, F), and two SLA-printed photopolymer resins (HARZ Labs Dental Clear, H; NextDent Ortho Rigid, N). Materials and Methods: Eighty rectangular specimens (n = 20/material) were fabricated following ASTM D790 and subjected to accelerated aging in Fusayama artificial saliva at 60 °C for 24, 48, and 72 h. Shore D hardness was assessed first as a non-destructive measurement, followed by three-point bending tests yielding flexural modulus, flexural strength, and strain at failure. Data were analyzed using one-way ANOVA and post hoc multiple comparisons at a significance level of α = 0.05. Results: Aging effects were material-dependent. Duran (C) showed no statistically significant changes in Shore D hardness (p = 0.651) and only non-progressive variations in flexural behavior. Bilkim Polywax (F) exhibited a significant hardness reduction at 48 h (p = 0.004) and selective changes in flexural strength at 72 h. HARZ Labs Dental Clear (H) showed the most severe and progressive deterioration, with significant reductions in all evaluated parameters, including hardness decreases of up to 5.8% and flexural modulus reductions exceeding 49%. NextDent Ortho Rigid (N) demonstrated an initial hardness decrease followed by stabilization, with a significant reduction in flexural modulus at 72 h. Conclusions: Under the accelerated hydrothermal aging conditions employed in this study, the two investigated SLA-printed photopolymer resins (HARZ Labs Dental Clear and NextDent Ortho Rigid) exhibited greater mechanical deterioration than the tested thermoformed PETG and milled PMMA materials. These findings are limited to the investigated materials, standardized rectangular specimens, and the specific accelerated aging protocol used in this study. Among the tested materials, thermoformed PETG demonstrated the greatest mechanical stability. Material-specific evaluation of aging resistance remains advisable before routine clinical application, particularly for digitally fabricated occlusal splints intended for prolonged intraoral service. Full article

To investigate the evolution of acoustic emission (AE) parameters during the flexural failure of reinforced concrete (RC) beams subjected to freeze–thaw and corrosion, four RC beams were fabricated and assigned to four conditioning regimes: no deterioration, freeze–thaw only (75 cycles), corrosion only (4.8% mass loss), and combined. Three-point bending tests were conducted, combining AE and digital image correlation (DIC) techniques. The damage process was divided into four stages: micro-crack initiation, stable crack propagation, unstable crack propagation, and failure. The evolution of AE parameters including ring count, energy, amplitude, peak count, and duration was analyzed. Each parameter is positively correlated with load level and rises as the damage stage advances. The slope of cumulative parameters reflects crack development more reliably than instantaneous values. The effect of corrosion on these parameters is significantly greater than that of freeze–thaw. For corroded beams, AE parameter levels are higher during the micro-crack initiation stage but lower during the stable crack propagation stage. The overall AE activity decreases with increasing deterioration degree. High-amplitude events increase with damage progression, but fewer high-amplitude events are observed at the failure stage of severely deteriorated beams. This study reveals the correspondence between AE parameters and damage stages, providing an experimental basis for damage assessment using AE techniques. Full article

Fracture healing remains a major challenge in orthopedic practice, and natural bioactive products have attracted increasing interest as supportive agents for bone regeneration. Apilarnil (drone larvae homogenate), a bee-derived natural product with antioxidant and anti-inflammatory properties, has not previously been investigated in fracture healing. This study evaluated the effects of oral apilarnil on experimental femoral fracture healing in rats. Forty-two male Wistar Albino rats underwent standardized closed femoral fracture fixation with intramedullary Kirschner wire stabilization and were randomly assigned to either a control group or an apilarnil-treated group receiving 400 mg/kg/day orally. Animals were sacrificed on postoperative days 15, 30, and 45. Fracture healing was assessed radiologically using the Lane and Sandhu scoring system, histopathologically using the Huo scoring system, and biomechanically by a three-point bending test. Histopathological scores were significantly higher in the apilarnil group on postoperative day 15 (p = 0.042), whereas no significant differences were observed at later time points. Biomechanical testing demonstrated significantly greater fracture strength in the apilarnil-treated group on postoperative days 30 (p = 0.001) and 45 (p = 0.004), while radiological scores did not differ significantly between groups throughout the study. These findings suggest that apilarnil may support fracture healing by enhancing early tissue repair and improving the biomechanical properties of healing bone, warranting further experimental and clinical investigation. Full article

Recycled tire polymeric fiber (RTPF) is a type of nylon fiber recovered from end-of-life tires. Depending on the processing stages, RTPF exists in two forms, fibrils (FS) and fiber bundles (FB). Although fiber reinforcement has been widely investigated for cement-stabilized soils, the fracture behavior and reinforcing mechanisms of RTPF remain insufficiently understood. Three-point bending tests using DIC, CT, and SEM analyses were conducted. The results indicate that RTPF delays crack initiation, increasing both the time interval from initiation to fracture and the ultimate crack width. Flexural strength increases with RTPF content and exhibits a power-law relationship. Both FS and FB significantly improve unstable fracture toughness, increasing it from 0.19 MPa·m^1/2 in the control specimen to 0.37 MPa·m^1/2 and 0.78 MPa·m^1/2, respectively. Fracture energy increases by 49% and 228%, respectively. The peak reinforcing efficiency was achieved at the RTPF content of 0.2–0.4% for FS and 1–2% for FB. The higher distribution coefficients and lower orientation reflect an isotropic fiber distribution, which is beneficial for inhibiting multi-directional crack propagation. A calculation method was developed to estimate fracture toughness from the fiber reinforcing parameter, with the findings showing good agreement with experimental results. These findings demonstrate the feasibility of utilizing RTPF as a sustainable reinforcement material for improving the fracture resistance of cement-stabilized soils in geotechnical engineering applications. Full article

We report on an evaluation of cutting edge ultra-thin glass processed by a novel ultrashort pulsed-laser robot system. The system consists of a six-axis articulated industrial robot with an ultrashort pulsed laser integrated on the link after the robot’s elbow. Mirrors are used for beam aligning and guiding, and a 2D galvanometer scanner and an F-Theta lens mounted on the last robot axis are used for material processing. Ultra-thin glass AF 32 eco is cut using robot motion only and combined scanner–robot motion, with additional axis rotations about the laser beam focusing in two directions. Hybrid cutting is compatible with a wide range of rotation angles, achieving cutting-edge angles from 88.9° to 119.7°. The influence of cutting-edge angles and cutting methods is further evaluated using residual stress measurements and three-point bending tests, revealing that the cutting method has a dominant impact on cutting-edge quality. To demonstrate the large-scale cutting with defining cutting-edge angles, a trapezoid is cut using the hybrid method with extra robot axis rotation, which achieves an average cutting-edge angle of 91.9°. Full article

In the field of long-distance partial discharge (PD) detection for submarine cables, there is an urgent need for a remote demodulation distributed detection technology deployable at multiple critical locations to overcome the limitations of single-point measurement. Factory joints of high-voltage submarine cables are high-risk components for PD, and long-distance fiber optic acoustic sensing technology holds the greatest potential for online monitoring. However, due to the viscoelasticity of the joint’s polymer insulation structure, sound propagation distance is severely limited, and non-multi-point measurement cannot achieve effective coverage of the measurement area. This paper proposes a quasi-distributed remote demodulation sensing system, in which both the fiber optic interferometer and the distributed feedback fiber laser (DFB-FL) serve as sensors, enabling highly sensitive quasi-distributed PD detection. The DFB-FL itself is highly sensitive to strain, and the multiple fiber coils formed by the interferometer arms are also highly sensitive to strain. Both can be modulated by the micro-strain induced by the acoustic field generated from PD in the polymer solid, producing phase shifts of the optical waves, which are then intrinsically demodulated by the interferometer system to extract the vibration signals caused by the discharge. Theoretical analysis shows that the sensitivity increases with the length of the unbalanced arm, with the upper limit constrained by laser coherence and optical attenuation; for the PD frequency band, the optimal unbalanced length is below 200 m—this design rule is applicable to on-chip interferometric sensors. The interferometer coils employ bend-insensitive fibers to suppress optical loss and improve fringe visibility. Meanwhile, three fiber coil configuration schemes are constructed to enhance the detection sensitivity to acoustic signals. Simulation results generate frequency response contour maps based on Young’s modulus, indicating that the solid-wound coil achieves the highest amplitude and the broadest bandwidth, with an optimal response frequency of approximately 50 kHz. Experimental results demonstrate that among the three structure types, the solid-wound coil also achieves the largest response ratio. Finally, in tests performed on a 220 kV submarine cable intermediate joint (with the system installed inside the metallic sheath), the minimum detectable discharge level in the DFB-FL region reached 6.75 pC, while that for the fiber coil reached 12.66 pC; when installed outside the metallic sheath, the minimum detectable discharge levels were 53.2 pC for the grating region and 89.6 pC for the fiber coil. Full article

This work presents an experimental and numerical investigation on the cyclic behaviour of square hollow section (SHS) beams made of 6060-T6 aluminium alloy subjected to non-uniform cyclic bending. Eight specimens with width-to-thickness ratios ranging from 18 to 48 were tested under a three-point cyclic bending protocol. The work provides relevant experimental findings, including moment-chord rotation curves, the number of cycles to local buckling onset, failure modes, and energy dissipation capacity. Additionally, a numerical model was created implementing a damage model to predict the progressive degradation and failure mechanism of the beams. Finally, the reliability of the Finite Element model was assessed by direct comparison of the results with the experimental data. Full article

Fracture in concrete is inherently a multi-stage process, yet traditional three-stage frameworks do not explicitly distinguish between micro-crack development and macro-crack propagation, particularly under varying ligament length conditions. The influence of ligament length (notch-to-depth ratios of 0.0, 0.2, 0.3, 0.4, and 0.5) on the crack propagation characteristics in notched concrete beams under three-point bending is investigated. Three-dimensional digital image correlation (3D DIC) was employed to monitor full-field displacement and strain, enabling the evaluation of key fracture parameters including horizontal displacement, crack mouth opening displacement (CMOD), horizontal strain, fracture process zone (FPZ) length, macro-crack length, and total fracture zone length. A high-magnification industrial camera (100×) was simultaneously used for real-time observation of the notch tip. Based on the evolution of these parameters, the fracture process was divided into four distinct stages: linear elastic stage, micro-crack initiation and propagation stage, macro-crack initiation and propagation stage, and complete failure stage. The industrial camera observations confirmed macro-crack initiation at approximately 60% of the post-peak load, validating the proposed four-stage division. Quantitative results show that increasing the notch depth ratio from 0.0 to 0.5 reduces the peak load by approximately 30–40% and decreases the nominal stress proportionally. The FPZ was found to be fully developed at the 60% post-peak load threshold, after which it diminished as macro-crack propagation dominated. Aggregate bridging, crack deflection, and crack branching were consistently identified as the primary toughening mechanisms governing the ligament effect. The crack propagation mechanisms in the four stages are controlled by the combined effects of front free boundary effect, stress concentration effect, ligament effect, and back free boundary effect. These findings provide a refined understanding of concrete fracture that can inform the safety assessment and design of concrete bending members in infrastructure construction. Full article

Polyethylene Terephthalate Glycol (PETG) is a thermoplastic material used in Fused Deposition Modelling for prosthetic applications, where mechanical properties are strongly dependent on process parameters. This study investigated the effects of carbon fibre (CF) content, print orientation (PO), and print temperature (PT) on the mechanical performance of PETG, fabricated using a Bambu Lab A1 printer. Tensile, three-point bending and impact testing were conducted to characterise the mechanical response of printed specimens. A Taguchi L9 array was employed to evaluate parameter effects while minimising experimental runs, and factor effects were quantified using per-response general linear models. Findings indicated that PO and PT significantly affected tensile behaviour, while CF content dominated flexural stiffness and impact response, with the strongest tensile response at 240 °C attributed to improved interlayer bonding. CF reinforcement increased stiffness and flexural strength but had limited effect on tensile strength and a reduced impact resistance at higher loadings, indicating increased brittleness. PO was identified as the most influential factor, with upright specimens exhibiting superior tensile performance, consistent with more favourable alignment of filament deposition with the loading direction. These findings demonstrate that the mechanical behaviour of CF-PETG is strongly process-dependent, informing its future application within prosthetic limb design. Full article

The manufacturing of drug-loaded filaments aimed for fused deposition modeling (FDM) three-dimensional printing (3DP) is still an important challenge because the filament mechanical profile and printing performance depend on both formulation and process-related factors. This study investigated the impact of extrusion technology on the mechanical properties and printability of paracetamol-loaded polyvinyl alcohol filaments with variable compositions. Filaments with compositions according to a full-factorial design were processed by single-screw extrusion (SSE) and twin-screw extrusion (TSE). Mechanical properties were assessed using the 3-point bending test and stiffness test. The thermal behavior of the components was evaluated through differential scanning calorimetry (DSC), while printability was evaluated through feeding and printing tests. Both formulation factors affected mechanical performance. High paracetamol content generally reduces stiffness and flexural resistance while increasing deformation capacity, suggesting a secondary plasticizing effect in the studied concentration range. Mannitol exhibited limited plasticizing efficiency, with flexibility decreasing at high ratios. DSC indicated partial crystallinity after extrusion, with TSE showing lower residual melting enthalpies than SSE. TSE filaments provided higher model reproducibility, broader mechanical ranges, and higher printability scores. This study shows that formulation effects depended strongly on extrusion technology and highlights TSE as a more robust platform for producing printable pharmaceutical filaments. Full article

Bamboo is a natural fiber-reinforced composite whose macroscopic mechanical properties depend on the microscale synergistic deformation of fibers and parenchyma. However, existing in situ SEM testing techniques are mainly designed for metallic tensile testing and are unsuitable for analyzing bamboo’s meso-scale behavior. To address this, we developed an in situ SEM three-point bending instrument specifically for natural fiber materials. The instrument keeps the region of interest (ROI) stably centered in the SEM field of view through a stationary central indenter and symmetrically moving supports. It offers a 0–450 N load range, 0.5N force resolution, 1 μm displacement resolution, and is compatible with a Tescan Vega 4 SEM chamber. Using this instrument, in situ bending tests were performed on Moso bamboo (Phyllostachys edulis) with fiber volume fractions of 23%–42%, combined with digital image correlation for full-field strain measurement. Results show that flexural modulus, strength, and fracture work all increase significantly with fiber content. A microstructural failure classification framework was established based on in situ SEM observations, categorizing the observed failure modes according to the local arrangement of fibers and parenchyma. The proportions of these failure modes were found to be closely associated with the gradient distribution of strength and toughness across the culm wall. Three extrinsic toughening mechanisms were identified: fiber-induced crack deflection, parenchyma cell collapse densification, and fiber–parenchyma interfacial debonding. The developed instrument and analysis method offer a promising experimental platform for multi-scale mechanical characterization of natural composites. Full article

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 study investigates machine learning-based optimization of the mechanical properties of environmentally friendly biopolymer nanocomposites produced by incorporating lignin nanoparticles (NLPs) and maleic anhydride (MA) into a polylactic acid (PLA) matrix. Lignin was extracted from black pine using a deep eutectic solvent method and melt-compounded with PLA via twin-screw extrusion, followed by injection molding. Mechanical performance was evaluated using tensile and three-point bending tests, while fracture morphology was examined by scanning electron microscopy (SEM). Random Forest (RF) and Extreme Gradient Boosting (XGBoost) models were applied to predict and optimize mechanical properties using lignin and MA contents as input variables, with an 80/20 training–testing data split. Experimental results showed that neat PLA exhibited the highest tensile strength (61 MPa) and modulus (5.2 GPa). The addition of low lignin contents with MA slightly reduced tensile properties but significantly enhanced flexural strength (≈58 MPa) and modulus (≈3.9 GPa). SEM observations revealed uniform nanoparticle dispersion and crack-free fracture surfaces at low lignin loadings, whereas higher lignin contents resulted in agglomeration and brittle behavior. Both machine learning models demonstrated high predictive accuracy, with RF outperforming XGBoost. The results confirm that MA improves interfacial adhesion and that data-driven approaches effectively support optimization of biopolymer nanocomposite compositions. Full article

In order to promote the sustainable development of road engineering, this study used waste tire rubber powder (RP) and surface organic layered double hydroxide (SOM-LDHs) to modify 70# matrix asphalt. The Box–Behnken design response surface method with three factors (rubber powder content, surface organic layered double hydroxide content, shear temperature) and three responses (penetration, ductility, softening point) was used to optimize the preparation parameters. The optimum formula was determined to be 21.7% rubber powder content, 4.8% surface organic layered double hydroxide content, and 160 °C shear temperature. The effect of the modifier on the surface morphology was analyzed using a rotating film oven test and ultraviolet aging test. The high and low temperature rheological properties of asphalt were evaluated by dynamic shear rheometer (DSR), bending beam rheometer (BBR), and the multi-stress creep recovery test (MSCR). The microstructure was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The aging mechanism was investigated by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The results show that after aging, the complex shear modulus of rubber powder/surface organic layered double hydroxide composite modified asphalt is the highest, which is 27.35% higher than that of matrix asphalt. The rutting factor reaches 79.86 kPa at 46 °C, the phase angle decreases by 11.83% after UV aging, and the high temperature plastic deformation resistance is the best. In the low temperature range of −18 °C to −24 °C, the creep stiffness of the composite modified asphalt is about 30% lower than that of the matrix asphalt, while the m value is increased by about 15%, and the low temperature stress relaxation performance is significantly improved. The strain recovery rate of composite modified asphalt under 3.2 kPa stress reaches 78.5%, and the unrecoverable creep compliance is as low as 0.18 kPa⁻¹, which is better than that of matrix asphalt and single rubber powder modified asphalt. Full article

Crack detection in composite structures remains a central challenge in structural health monitoring, particularly when sensing must rely on a small number of embedded multiplexed fiber Bragg gratings (FBGs). Here, we present a physics-guided convolutional neural network (CNN) framework for crack-associated event detection from multiplexed FBG interrogator signals acquired during the three-point bending of glass-fiber-reinforced polymer (GFRP) beams. The dataset was constructed from raw interrogator recordings and synchronized force–displacement metadata while preserving the cracked and non-cracked loading stages present in the experiments. Each candidate response was encoded by 13 synchronized optical, loading, and mechanics-guided descriptors, including Euler–Bernoulli expected strain and residual terms, where the residual denotes the difference between the measured response and the elastic response predicted by beam theory. A compact one-dimensional CNN operating on 30-response sequences was evaluated on 64 experimental runs under strict leave-one-run-out validation. At the selected operating point, the model reached window-level precision of 0.900, recall of 0.910, F1 score of 0.905, and balanced accuracy of 0.942, while the corresponding run-level decision reached a precision of 0.833, a recall of 1.000, an F1 score of 0.909, and a balanced accuracy of 0.969. Bootstrap resampling over runs yielded 95% confidence intervals of 0.787–0.978 for window-level F1 and 0.769–1.000 for run-level F1. To probe generalization beyond the initial fabrication batch, the final frozen pipeline was also tested once on seven later-batch runs from two newly manufactured specimens, where it reached a window-level precision of 0.908, a recall of 1.000, an F1 score of 0.952, a balanced accuracy of 0.969, an ROC-AUC of 0.979, a PR-AUC of 0.955, and perfect run-level classification. These results show that a compact sequence CNN, enriched with mechanics-guided strain interpretation, can extract robust crack-event signatures from multiplexed FBG measurements while preserving a simple and reproducible modeling pipeline. Full article