Search Results (419)

The cement plug-casing interface is critical for long-term wellbore integrity in well abandonment to prevent fluid channeling. However, traditional cement easily debonds under long-term in situ stress and fluid exposure, causing seal failure and safety risks. To address this issue and overcome the limitations of conventional cement, a three-dimensional finite element model was established based on stress-seepage coupling theory. A systematic comparative analysis of the interface debonding mechanisms for three materials—cement, resin, and alloy—and their different combination sequences was conducted. The entire process of interface damage was quantified. The effects of material combination, formation elastic modulus, and injection rate on sealing performance were analyzed. Results show that the stiffness gradient dominates the failure mode, and the “cement–resin–alloy” configuration best suppresses damage propagation, reducing failure height by about 30%. Additionally, interface integrity is sensitive to formation constraints and operational parameters: the interface failure height decreases as the formation elastic modulus increases, and increases as the injection rate rises. The findings of this study can provide a theoretical basis and engineering reference for the optimal design of composite plugging barriers in demanding operational conditions, such as those encountered in carbon sequestration wells. Full article

This study presents an experimental investigation into a novel hybrid strengthening system for reinforced concrete (RC) beams that combines externally bonded carbon-fiber-reinforced polymer (CFRP) sheets with a spray-applied polyurea coating (Linex XS-350). Seven beams were tested under four-point bending to evaluate the effects of two main parameters, CFRP thickness and single vs. double layers, and polymer coating configurations, i.e., none, thin with 2 mm, thick with 4 mm, and embedded. The coating was intended to act as an elastic confinement layer that mitigates peeling stresses and enhances CFRP concrete bond performance. The results demonstrated significant improvements in strength, ductility, and strain capacity for coated specimens compared with CFRP-only beams. The inclusion of Linex increased the ultimate load by up to 24% in single-layer beams and 20% in double-layer beams, while bottom-fiber strain at failure increased by more than fivefold, indicating enhanced CFRP utilization. The uncoated beams failed prematurely by CFRP peeling, whereas the coated and embedded specimens transitioned to CFRP rupture with more gradual and ductile behavior. The combined use of multiple CFRP layers and polymer coating produced the most effective performance, with the double-layer embedded configuration (B7) achieving the highest load, strain, and energy absorption. The findings confirm that integrating polyurea coatings with CFRP can effectively delay debonding and significantly improve the reliability and toughness of strengthened RC members, offering a practical solution for more resilient structural retrofitting. Full article

Material-extrusion (MEX) printing with automated filament switching enables single-build multi-material laminates, but interfaces between dissimilar polymers may govern failure. Here, monolithic PETG, monolithic PC–ABS, and an alternating PETG/PC–ABS laminate (COMP) with 0.2 mm laminae (4 mm total) were fabricated and benchmarked. Tensile behavior was measured using ISO 527-2 Type 1B specimens at 5 and 50 mm/min, complemented by three-point bending in horizontal/vertical orientations, unnotched Charpy impact (ISO 179), Shore D hardness (ISO 868), and SEM fractography. COMP delivered the highest horizontal flexural strength (159.82 ± 25.42 MPa), exceeding both single-material baselines, indicating improved bending load capacity in the preferred orientation. In Charpy impact, COMP absorbed more energy than PETG in the horizontal condition (0.86 ± 0.14 J vs. 0.57 ± 0.06 J) but remained below PC–ABS. In tension, COMP strength decreased by ~21–23% relative to PETG and by ~5–6% relative to PC–ABS at both speeds, consistent with interface-controlled damage. SEM revealed void-assisted crack initiation and interfacial debonding aligned with raster paths, highlighting interfacial strengthening and porosity reduction as key routes to improve tensile performance while retaining favorable flexural and impact response. Full article

This study investigates the fatigue behavior of 3D-printed ABS subjected to cyclic torsional loads, with a focus on the effects of infill density and raster angle on torsional fatigue performance. A total of 50 test specimens representing 25 unique combinations of infill density (20%, 40%, 60%, 80%, 100%) and raster angle (25°/−65°, 45°/−45°, 75°/−15°, 0°/90°) were fabricated and tested using the cyclic torsion system. Fatigue failure was defined as a 75% reduction in torsional strength, recorded through cycle-by-cycle torque monitoring. The twist angle was cyclically varied between ±10° at a frequency of 5 Hz until failure occurred. The results indicate that increasing infill density significantly improves fatigue life by reducing internal porosity and enhancing load transfer, with the greatest gains observed at high infill levels (≥80%). Raster angle has a minimal effect at low infill densities but becomes critical at higher densities, where optimized filament orientations substantially extend fatigue life. Intermediate raster angles, particularly 25° and 75°, outperform orthogonal layouts by enabling better stress redistribution and inter-layer load sharing, while a 90° orientation leads to premature failure due to stress concentration and inter-layer debonding. When normalized by mass, specimens with 100% infill and intermediate raster angles achieve the highest fatigue endurance, highlighting the synergistic role of infill density and raster orientation in optimizing the durability and mass efficiency of 3D-printed components under cyclic torsional loading. Full article

The precision of data gathered from Ultra-Weak Fiber Bragg Grating (UWFBG) sensing technology is limited when measuring strain within asphalt pavements. To better understand its measurement mechanism and correct possible errors, this study examines the synergy deformation behavior between UWFBG and asphalt mixtures under loads. Initially, the mesoscopic model of asphalt mixture containing UWFBG was constructed using a discrete element model, followed by the validation of the model. Then, the propagation of microcracks at the interface between the asphalt mixture and UWFBG was analyzed, revealing damage characteristics of this material under various loading stages. Additionally, a quantitative relationship between the crack width and the monitoring strain was identified. The significant effect of introducing the sensor on crack propagation and interface debonding in strain response was also highlighted. The results indicate that when displacement exceeds 1.4 mm during a bending test, the number of both damage and microcracks increases markedly, with cracks progressively developing. Especially at the UWFBG interface subjected to a tensile load, microcrack growth rises sharply, leading to the failure of the interface. The mor-UWFBG interface is not the main damage location, but it is the most vulnerable location to damage and may be the one affecting the monitoring of UWFBG. Without sensors, a consistent linear relationship between monitoring strain and crack width is observed within the asphalt mixture. After introducing the UWFBG sensor, the strain-crack response of the asphalt mixture is divided into three stages: crack initiation, crack propagation, and interface debonding. When the crack width surpasses 0.03 mm, interface debonding significantly influences the strain growth rate, indicating the necessity of correcting the synergy deformation. Full article

The tensile capacity of a connection is predicted through the use of established models, among which the bond behavior between CFRP layers and concrete is always considered. In structures reinforced with CFRP, the prediction of the bond force between concrete and CFRP is essential, as the connection must be designed to withstand the required tensile capacity. An underestimation can lead to inefficient design, while an overestimation risks premature debonding failure, potentially compromising structural safety and serviceability. In recent applications, the bond force between concrete and CFRP has been increased through the use of the Externally Bonded Reinforcement on Groove (EBROG) method. However, due to the structural complexity introduced by the grooved interface, accurate prediction of its bond strength remains challenging, and conventional analytical models may not fully capture the underlying nonlinear interactions. In this technique, CFRP layers are placed into grooves to enhance the interaction among the adhesive, concrete, and CFRP. However, due to the structural complexity of this connection, accurate prediction of its bond force is challenging and requires the application of artificial intelligence methods. This study develops a machine learning (ML) framework to predict the bond strength of the EBROG technique. Four ML models, Support Vector Machine (SVM), Gaussian Process Regression (GPR), Decision Tree, and XGBoost, were implemented, and their hyperparameters were optimized via Bayesian optimization. The models were evaluated using multiple statistical metrics, with the XGBoost algorithm demonstrating superior predictive performance, achieving an R² of 0.987 and an RMSE of 0.522 kN. This represents an improvement of approximately 5.6% in R² and a reduction of over 53% in RMSE compared to the existing analytical model. SHAP analysis provided interpretable, data-driven insights, revealing that fracture energy is the predominant factor governing bond strength and elucidating nonlinear interactions between key design parameters. This ML-fracture mechanics framework not only offers superior prediction but also advances the mechanistic understanding of the EBROG bond behavior. Full article

In the aviation industry the so-called ballistic impact of small accidental or human-made sources on aircraft elements during their service life encompasses several scenarios of practical interest. The experimental assessment of ballistic impact requires dedicated infrastructures (such as the light-gas gun system utilized in this study) and exhibits intrinsic difficulties, mainly concerning the proper acceleration of a projectile and the accurate measurement by a high-speed camera of its (inlet and outlet) velocity. As a first objective, this study aimed at characterizing the dynamic response of fiber metal laminates, manufactured ad hoc by the authors with two different stacking sequences currently not available in commerce. The layups included aluminum 2024 T3 and aramid fiber-reinforced prepregs, leading through specific treatments to excellent specific properties. The collision of the laminate with a 25 g, 9 mm radius steel sphere, traveling at speeds ranging from 90 to 145 m/s, caused a variety of scenarios: partial or complete penetration, with the projectile passing through and continuing its trajectory, remaining stuck in the sample (embedment) or even being bounced back (ricochet). The experimental information led to the estimation, for each typology of sample, of a conventional ballistic limit according to the Lambert-Jonas approximation, as a second objective, these data were utilized to validate an accurate heterogeneous model of the samples developed in the ABAQUS^® platform, discretized by finite elements in explicit dynamics and including geometric nonlinearity and contact. We describe plasticity and damage of the metal layers by the Johnson–Cook phenomenological model, progressive failure in the fiber-reinforced plies through a 2D Hashin criterion with damage evolution, and interlaminar debonding at multiple cohesive interfaces governed by the Benzeggagh–Kenane criterion. The outlet speed of the bullet measured during the experiments was retrieved correctly by this model, and a satisfactory agreement of the finite element predictions was found with the deformation patterns and the damage mechanisms identified by post mortem visual inspection. Finally, several discussion points are raised, concerning the robustness of the numerical analyses, the reliability of the constitutive modeling and the identification of the governing parameters. Full article

Conventional Fiber-Reinforced Polymer (FRP) materials may exhibit certain performance uncertainties in harsh environments, limiting their reliability for structural strengthening. To address this, Basalt Fiber-Reinforced Polymer (BFRP) plates fabricated with silicate-modified epoxy resin are proposed for the flexural strengthening of reinforced concrete (RC) beams. The research aims to evaluate their short-term strengthening performance and establish a reliable calculation method for flexural capacity. Four-point bending tests were conducted to investigate the effects of BFRP plate thickness and end anchorage configuration on failure modes, flexural capacity, and ductility. Finite element simulations incorporating interfacial bond–slip behavior reproduced typical debonding failures, followed by a comprehensive parametric analysis. Based on the experimental and numerical results, a modified BFRP plate strain formula at debonding was proposed to establish a calculation method for the flexural capacity of BFRP-strengthened beams governed by debonding failure. The results indicate that beams without end anchorage were prone to interfacial debonding, where increasing the plate thickness from 0.5 mm to 2 mm raised the flexural capacity gain from 4.5% to 15% but intensified the ductility reduction from 42.9% to 64.9%. Conversely, applying mechanical anchorage improved the ductility index by over 20% compared to unanchored counterparts. The adopted FRP–concrete bond–slip constitutive model accurately characterizes interfacial debonding behavior, and the proposed flexural capacity model demonstrates high accuracy with overall deviations within 5%. It can be concluded that the novel BFRP plates exhibit strengthening behavior comparable to existing FRP systems. Effective end anchorage further enhances flexural capacity and prevents brittle failure. The proposed debonding strain formula for the novel BFRP system offers a reliable basis for capturing the critical onset of interfacial failure. Building upon this, the developed flexural capacity model provides a reliable theoretical basis for the design and assessment of RC beams strengthened with the novel BFRP plates. Full article

The packaging process of fiber Bragg gratings (FBGs) directly determines the strain transfer efficiency, chirp occurrence, and sensing performance of the sensors. At present, relevant theoretical and experimental studies on the surface roughness of packaging substrates remain scarce. In this paper, combined with the theoretical model of interfacial debonding driving force and the sensing mechanism of FBGs, the FBG sensing performance under different substrate surface roughness conditions was investigated. Experimental results show that an excessively high substrate surface roughness will induce FBG chirp when the external strain reaches 1.143 × 10⁻³, leading to the failure of strain transfer. In contrast, an excessively low surface roughness will weaken the interfacial coupling, thus reducing the strain response capability and cyclic stability of the sensor. The substrate surface treated by sandblasting with 150# abrasive exhibits the optimal comprehensive performance: The strain response capability of the FBG reaches 6.99994 × 10⁻⁶ pm/ε with a linear fitting coefficient of 0.99994, presenting excellent linear response and cyclic stability. This study clarifies the optimal range of substrate surface roughness for FBG packaging and can provide theoretical and technical references for the packaging design and optimization of high-performance FBG sensors. Full article

This study investigates the influence of fiber bridging on the interlaminar strength of carbon fiber-reinforced polymer (CFRP) made from recycled carbon staple fiber yarn (rCF), compared to CFRP made from new fibers (vCF). Double-cantilever beam (DCB) tests measure the resistance of both materials against crack formation and the corresponding energy release rate (ERR). Several microscopic tools (SEM, CT) were then used to analyze the fracture surfaces and characterize the underlying failure mechanisms of the fiber bridges. The resulting ERR of rCFRP is four times (2140 J/m² compared to 587 J/m²) higher than that of vCFRP. SEM images of the fracture surface reveal that the fracture mechanism is fiber debonding followed by fiber pull-out with constant friction. This finding is confirmed by calculating the fiber bridging stress using the mathematical formulation of this effect resulting in a fiber bridge tension of approximately 70 N/mm². The main reason for the increased ERR of rCFRP compared to vCFRP is the extensive occurrence of fiber bridges in rCFRP due to the inhomogeneity of the rCF roving. This results in a pronounced nesting effect between adjacent rCF layers. The influence of the nesting effect on the ERR was investigated by testing samples with an increased layer orientation difference of 3° and 5°. This results in an ERR decrease of 26% in rCF and 30% in vCF. The nesting effect can be eliminated in vCFRP, but in rCFRP higher layer orientation, nesting is still visible. This finding suggests that the coarse, inhomogeneous structure of the rCFRP roving causes nesting regardless of the layer orientation and leads to a pronounced tendency to form fiber bridges. Full article

To investigate the effects of freeze–thaw cycles on the fatigue performance of reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) grid-polymer modified cement mortar (PCM) composites, this study conducted experimental research under combined freeze–thaw and fatigue loading on beams with two reinforcement ratios (0.84% and 1.31%). The evolution of failure modes, variations in fatigue life, accumulation of residual deformation, and the development of strains in various materials were analyzed. Experimental results show that CFRP grid–PCM strengthening can significantly improve the fatigue performance of beams. The fatigue life of beams with a low reinforcement ratio increased by approximately 275% after strengthening; even after undergoing freeze–thaw cycles, beams with a high reinforcement ratio could withstand over 3 million fatigue load cycles, demonstrating excellent long-term fatigue resistance. Under combined freeze–thaw and fatigue loading, the crack development in strengthened beams exhibited a typical three-stage characteristic, and the failure mode transitioned from fatigue fracture of steel reinforcement to a composite form involving fiber pull-out of the CFRP grid or interfacial debonding. Based on experimental data, a cumulative evolution model considering the synergistic damage of concrete, CFRP grid, and interfacial bonding was established, which effectively describes the stiffness degradation and damage accumulation process under combined freeze–thaw and fatigue action. The research findings provide a theoretical basis for the fatigue performance evaluation and life prediction of CFRP grid-strengthened RC structures in cold regions. Full article

(1) Background/Objectives: Gap formation contributes to the clinical failure of partial crowns. Therefore, it was analyzed at the interfaces between restoration, luting material, and tooth in partial crowns made of lithium disilicate ceramic (LS2) and nanohybrid composite (RBC) after thermomechanical loading (TCML) using optical coherence tomography (OCT). (2) Materials and Methods: Sixteen human mandibular molars were restored with CAD/CAM partial crowns made of LS2 (IPS e.max^® CAD) or RBC (Tetric^® CAD) using adhesive cementation (Variolink^® Esthetic DC). The restorations were imaged by OCT (1550 nm, 28 kHz) at t0 = 24 h, t1 = 90 days of water, t2 = after TCML with 480,000 loading cycles, and t3 = TCML with 1,200,000 loading cycles. Gap lengths (%) at interface 1 (partial crown-luting material) and interface 2 (luting material–enamel/dentin) were quantified. Groupwise and pairwise comparison of OCT parameters was conducted using the Mann–Whitney U, Friedman, and Conover–Iman tests with Bonferroni correction (α = 0.05). (3) Results: At interface 1, LS2 showed a larger median gap length than RBC (ceramic = 48.4%; composite = 5.2%, p < 0.01). At interface 2, the largest median gap length for LS2 was measured at the dentin (ceramic = 59.7%; composite = 52.5%), while for RBC, the enamel was more affected (ceramic = 26.2%; composite = 36.9%). (4) Conclusions: OCT enables reliable gap detection in partial crowns under functional loading and is therefore suitable for monitoring adhesive interface integrity. Under in vitro conditions, both materials demonstrated stable adhesive performance without debonding, while material-dependent differences in gap formation and distribution were observed. Full article

This in vitro study evaluated the shear bond strength (SBS) and adhesive remnant index (ARI) of orthodontic molar tubes bonded using conventional, hydrophilic, and self-etch adhesives under dry and saliva-contaminated conditions, while also assessing the impact of shear force direction. Extracted molars were bonded with Transbond XT™ (T), Transbond MIP™ (M), or Scotchbond Universal™ (S) under dry or saliva-contaminated conditions. Debonding was performed at 90° or 45°, introducing a clinically relevant but underexplored variable in orthodontic bond-strength testing. ARI scores were assessed via stereomicroscopy and visual inspection. Statistical tests (Kruskal–Wallis and Mann–Whitney) showed no significant SBS differences among adhesives under identical conditions (p > 0.05). However, all adhesives exhibited significantly reduced SBS under saliva contamination (p < 0.001; T: 5.4 vs. 4.1 MPa; M: 5.7 vs. 3.6 MPa; S: 5.5 vs. 4.5 MPa). In dry conditions, SBS was significantly higher with 45° debonding (p < 0.05). Under contamination, SBS varied by ARI score (p = 0.05), with ARI 0 specimens showing higher SBS than ARI 3. These findings confirm that moisture reduces bond strength across adhesive types, while 45° force application enhances SBS under dry conditions. ARI score variability under contamination may reflect complex failure modes. Full article

High-speed permanent magnet machines frequently employ axially constrained solid rotors. These rotors undergo complex failure due to the combined action of centrifugal loading and interference-fit contact pressure. Existing analytical models often overlook this interaction, which can lead to overestimated reliability. To address this limitation, a three-dimensional axisymmetric elastic–static model is developed. This model quantifies how rotational speed and interference fit jointly govern failure behaviour. A systematic computational framework is established to evaluate three primary failure modes: interface debonding, permanent magnet fracture, and retaining sleeve yielding. The framework explicitly accounts for axial constraint effects. Finite element simulations and prototype testing on a 3 kW, 200,000 r/min motor validate the model, confirming its accuracy in predicting failure limits. The stress distributions and dynamic responses under axial constraint are systematically analysed and compared with numerical and experimental results. Consequently, the proposed approach provides a reliable foundation for designing high-speed rotors under axial constraints. Full article

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