Search Results (4,286)

Reinforced Concrete (RC) structures experience progressive degradation over their service life due to mechanical loading and environmental exposure, leading to reduced bearing capacity and compromised structural safety. Incorporating discrete fibers into concrete mitigates crack propagation and enhances ductility, resulting in fiber-reinforced concrete (FRC) with superior fracture energy, durability, and sustainability characteristics. Despite these advantages, research on Structural Health Monitoring (SHM) techniques for FRC elements remains limited. The Electromechanical Impedance (EMI) method, which exploits piezoelectric transducers as both actuators and sensors, offers high sensitivity for detecting early-stage damage by monitoring variations in local mechanical impedance. This study investigates the effectiveness of a deep learning-enabled EMI framework for assessing the structural condition of FRC beams under flexural loading. A one-dimensional convolutional neural network (1D-CNN) is proposed to automatically extract salient features from high-frequency EMI signatures and classify structural health into three predefined states. The model is rigorously evaluated using specimen-invariant validation to ensure generalization across different FRC specimens, addressing a critical limitation of conventional cross-validation approaches in SHM research. Experimental tests on FRC beams instrumented with surface-bonded PZT transducers provide a dataset of 264 EMI responses for training and validation, enabling direct comparison between common and specimen-invariant validation schemes. The results demonstrate the superior robustness of the specimen-invariant approach and confirm the capability of the proposed 1D-CNN to identify flexural damage progression in FRC elements accurately. An ablation study further highlights the contribution of each architectural component to overall model performance. The findings underscore the potential of integrating EMI-based sensing with advanced deep learning models for reliable, automated, and scalable SHM of next-generation resilient concrete infrastructures. Full article

Carbon fiber-reinforced polymer (CFRP) laminates are susceptible to barely visible impact damage (BVID) under low-energy bird-strike-like conditions. However, in previous studies, most damage evaluations for BVID were limited to a single scale. In this work, a multiscale characterization and evaluation method integrating the analytic hierarchy process (AHP) and the CRITIC weighting method was proposed to investigate the damage evolution of CFRP laminates under low-energy impacts (approximately 12–33 J). Delamination area (S_Da), indentation depth (P_D), surface crack aspect ratio (R_A), energy dissipation, and compression-after-impact (CAI) strength were analyzed based on phased-array ultrasonic C-scanning, 3D optical profilometry, and scanning electron microscopy. The results showed that P_D, S_Da, and energy dissipation increased from 108.73 μm to 213.93 μm, from 228.6 mm² to 695.8 mm², and from 5.96 J to 21.40 J, respectively, with increasing impact energy. Meanwhile, CAI strength decreased from 202.2 MPa to 118.9 MPa, with a maximum degradation rate of 41.16%. A critical transition was observed in the medium-to-high energy range, where delamination growth gradually plateaued, while intralaminar cracking and fiber fracture became increasingly dominant. The proposed framework enables quantitative grading of BVID severity and provides a practical basis for assessing residual damage in impacted CFRP laminates. Full article

This study investigates the stress–strain state of rocks subjected to the impact of penetrators with diverse configurations, employing numerical simulations in the ANSYS Workbench Static Structural module. The research focuses on the interaction between roller cone drill bit teeth and rock formations during blast hole drilling. Through finite element modeling using a linear elastic constitutive model, the influence of penetrator geometry, position relative to borehole walls, angle of attack, and distance to open surfaces on rock fracture parameters is analyzed. Key quantitative findings include: the relative breaking force near the borehole wall reaches 2.8 for soft rocks (siltstones) with a 10 mm tooth diameter, and decreases to approximately 1.0 at a distance of 1.5d from the wall; the optimal angle of attack ranges from 60° to 90° depending on rock hardness; and the proximity to a free surface reduces fracture resistance to as low as 0.23 of the baseline value. Six sets of parabolic regression equations (R² > 0.95) are derived for relative breaking forces across three rock hardness groups and two tooth diameters. Optimal parameters for tooth placement, borehole bottom shapes, and operational conditions are proposed. Implementation of the recommended parameters is estimated to increase drilling efficiency by 10–20% and extend tool service life by 15–30%. The findings provide a scientific foundation for designing advanced roller cone drill bits suitable for rocks with Protodyakonov hardness indices ranging from f = 5 to f = 18. Full article

Geometric discontinuities in aero-engine turbine blades generate multiple stress concentrations along the airfoil, rendering life prediction exceptionally challenging. While conventional skeletal point method (SPM) offers reasonable accuracy in predicting creep-fatigue-interaction (CFI) life for simple structural specimens, they prove inadequate for geometries with poor symmetry. This study introduces a novel two-dimensional skeletal point method (2D SPM) to analyze stress evolution characteristics, identify representative stresses, and predict CFI life in complex structures. Leveraging the film-cooling hole (FCH) features of a representative turbine blade, three perforated plate specimens were designed, manufactured, and subjected to CFI testing. Failure analysis confirmed crack initiation at hole-edge stress concentration zones, followed by inward propagation. Specimen fracture surfaces exhibited predominantly ductile dimpling features, with multi-origin fatigue characteristics observed only near hole-edges, collectively indicating creep-damage-dominated failure mechanisms. Five life prediction methodologies were comparatively evaluated. The results demonstrate that the 2D-SPM achieved the highest accuracy (all predictions within twofold scatter bands), followed by the conventional SPM (also within twofold scatter bands). The nominal stress method showed moderate accuracy (within fivefold scatter bands), while both hot point method and TCD methods proved unsuitable for creep-fatigue scenarios with significant stress evolution. Full article

Objectives: To evaluate the influence of two surface finishing procedures—mechanical polishing and glaze firing—on the color stability and wear behavior of lithium aluminium disilicate (LAD) hybrid abutment crowns over a three-year clinical observation period. Methods: Twenty-four patients requiring 34 implant-supported single crowns were included in this prospective clinical study. LAD abutment crowns were fabricated using n!ce ceramic and a CAD/CAM workflow and finished either by mechanical polishing (P, n = 17) or glaze firing (G, n = 17). After insertion as well as after one and three years (P: n = 9, G: n = 9) of clinical use color measurements were performed using spectrophotometry, and color differences (ΔE00) were calculated. Wear was assessed by digital surface comparison of baseline and the two follow-up scans using three-dimensional analysis software. Reference teeth (R) were defined and evaluated comparable to the P and F groups. Biological and technical complications were recorded throughout the observation period. Results: Color deviations increased over time in all groups (P, G, R). After three years, G showed lower mean color differences (ΔE00 ≈ 2.77) compared with F (ΔE00 ≈ 5.40), although the difference was not statistically significant. No significant differences in vertical height loss were observed between P and G. One adhesive fracture occurred both in the P and G group, five crowns (P: n = 3, G: n = 2) developed periimplantitis. Conclusions: Both polishing and glazing resulted in comparable clinical outcomes regarding color stability, wear behavior, and complication rates. Clinical Significance: Both finishing protocols might be a reliable option for LAD hybrid abutment crowns. Full article

Models are described for calculating the crack initiation times for Alloy 600 and Type 304 SS in PWR and BWR primary coolant circuits, respectively. In PWRs, initiation is defined in terms of the grain boundary oxidation concept of Scott and Le Calvar, whereas in BWRs, cracks are envisioned to nucleate from corrosion pits. In contrast, in BWRs, we envision cracks to nucleate from corrosion pits, with the difference in the two systems being primarily due to electrochemical factors. Thus, in BWR primary coolant and the absence of hydrogen water chemistry (HWC), the oxidizing conditions due to the radiolytic production of H₂O₂ cause the ECP to be significantly more positive than the critical pitting potential. Accordingly, the nucleation and growth of pits due to passivity breakdown and the establishment of differential aeration between the pit nucleus’s internal and external environments, which results in growth of pits to the critical size necessary to satisfy the Kondo criteria for transition of a pit into a crack, is judged to be a realistic scenario. Contrariwise, in PWR primary coolant, the ECP is so negative [≈−1.0 V_she] due to the large amount of pressurizing H₂ present in the circuit [20–60 cm³(STP)/kg H₂O] that the nucleation and growth of pits is not possible. However, Totsuka and Smialowska found that MA Alloy 600 suffers hydrogen-induced cracking (HIC) at an ECP < −0.85 V_she, demonstrating that, in service with a high hydrogen concentration, brittle fractures will occur. The initiation sites were not identified. The crack initiation models for Alloy 600 in PWRs and Type 304 SS in BWRs reproduce the effects of the following independent variables: applied stress, temperature, cold work, grain boundary segregations, water chemistry, pH, and electrochemical potential. The origins of the observed scatter in experimentally measured crack initiation times are discussed, and the challenges of developing a more general crack initiation model (GCIM) are identified. From a mathematical viewpoint, the most significant challenge arises from the nested distributions involving the many parameters and expressions within the GCIM that are either distributed because of an imprecise definition or because some experimentally determined input parameters are experimentally scattered. Additionally, the evolution of semi-elliptical surface cracks resulting from the electrochemical crack length (ECL) being shorter than the classical mechanical crack length (MCL) must be incorporated if the GCIM is to find utility in the water-cooled nuclear power industry where semi-elliptical surface cracks are normally observed. Full article

In this paper, the effects of 4 wt.% of silicon on the microstructure and mechanical properties of AM50 magnesium alloys fabricated by the casting method are presented. New AM50/Si material and the base AM50 alloy were gravity cast into a metal mould under the same conditions for comparison. Analyses of the alloys’ microstructures were carried out by light microscopy (with differential interface contrast), scanning electron microscopy (with an energy dispersive X-ray spectrometer), as well as X-ray diffraction (XRD). In as-cast conditions, both materials were composed of α-Mg solid solution, α + γ eutectic (where γ is Al₁₂Mg₁₇), Al₈Mn₅ intermetallic phases and discontinuous γ precipitates. The AM50/Si material also consisted of the Mg₂Si phase. This structural constituent appeared in the form of primary crystals with regular polygonal morphology and an α + Mg₂Si eutectic in the form of “Chinese script”. In the microstructure of the AM50/Si material, the Mn₃SiAl₉ ternary phase was also identified. The detailed analyses presented in this paper revealed that the new ternary Mn₃SiAl₉ structural compound caused a reduction in the volume fraction of the Al₈Mn₅ phase but did not completely replace it. These two phases formed competitively. The fabricated material exhibited higher tensile and compression strength as well as yield strength in comparison with the AM50 alloy. Additionally, analyses of the fracture surfaces of the AM50/Si material carried out using scanning electron microscopy (SEM) were presented. Full article

Metal Digital light processing (MDLP) offers high resolution and excellent surface quality, but the final properties of printed parts are highly dependent on post-processing. In this study, the effects of debinding, decarburization, and sintering on the shape fidelity, microstructure, and mechanical properties of MDLP-fabricated 316L stainless steel were systematically investigated. The optimal post-processing route consisted of debinding in an inert atmosphere, decarburization in air within 400–600 °C, and sintering at 1370 °C for 4 h under flowing nitrogen. Under these conditions, the sintered parts achieved a relative density of 98.03 ± 0.23%, hardness of 380.63 ± 9.15 HV, elastic modulus of 213.47 ± 5.5 GPa, tensile strength of 519.7 ± 22 MPa, and elongation at fracture of 76.8 ± 9.3%. Microstructural analysis showed that increasing the sintering temperature reduced porosity and smoothed the morphology of Cr-rich oxygen-containing second phase regions, thereby alleviating stress concentration and improving mechanical properties. This study provides an effective post-processing strategy for MDLP-fabricated 316L stainless steel and examines the microstructural origins of the observed property evolution. Full article

Numerical simulation of sequential fracturing in horizontal wells for shale gas and oil extraction requires careful consideration of mechanical interactions between proppant and fracture surfaces—a challenge that remains largely unresolved. This study proposes a novel phase-field model featuring a strain-based formulation and a width-dependent proppant reaction force. Unlike previous studies, we integrate an empirical propped force solution, adapted from established work to account for rock properties and proppant support, to capture nonlinear fracture closure. Results show that reaction stress models significantly dictate propped geometry. The model’s fracture length, width, and closure predictions are validated against theoretical solutions. We conducted a sensitivity analysis to evaluate how fracture deflection angles and widths vary with dimensionless fracture spacing, in situ stress contrast, and proppant strength. Numerical results show that proppants induce pronounced morphological asymmetry and distinct geometric discrepancies. Specifically, the heterogeneous support provided by proppants and the resulting stress redistribution alter fracture propagation paths, leading to an 8% reduction in fracture length and a marked difference in fracture orientation of approximately 80° between supported and unsupported fractures, highlighting the important role of proppants in governing fracture geometry. Both dimensionless fracture spacing and in situ stress contrast strongly influence fracture deflection, with proppant strength also contributing. The propped-force formulation is further extended to nonplanar fractures, enabling application to sequential fracturing with multiple fractures. These results highlight fracture propagation mechanisms and demonstrate the robustness of the proposed phase-field model. Full article

Proximal femoral fractures associated with osteoporosis are an important clinical problem, yet how bone quality independently influences stress distribution remains insufficiently understood. This study aimed to quantitatively compare surface stress distribution between normal and osteoporotic proximal femoral models using thermoelastic stress analysis (TSA). Fourth-generation composite femurs with identical external geometries were subjected to cyclic compressive loading at a 9° adduction angle, with different maximum loads applied to avoid structural failure (normal: 1900 N; osteoporotic: 1000 N). TSA was performed using an infrared lock-in system to obtain surface stress maps, and stress values were evaluated across key proximal regions and along the medial and lateral cortices. The osteoporotic group showed higher maximum stress values in the medial neck (−37.79 vs. −11.52 MPa), lateral neck (24.70 vs. 8.75 MPa), and intertrochanteric crest (−17.98 vs. −6.05 MPa), corresponding to approximately 1.8–3.5-fold increases compared with the normal model values normalized to 1000 N. Mean stress values were also higher by approximately 1.9–2.4-fold across regions. These results suggest that reduced bone quality is associated with increased proximal stress concentration. They may also help guide implant and fixation strategies, including stem selection and fixation configuration, by identifying regions susceptible to stress concentration under different bone quality conditions. Full article

Bone tissue plays a vital role in the human body and possesses intrinsic self-repair mechanisms; however, large defects or pathological fractures may exceed its natural healing capacity. Bone tissue engineering provides promising strategies to restore bone integrity through the use of scaffolds, growth factors, and stem cells. While calcium phosphate (CaP)-based ceramics, such as hydroxyapatite (HAp) and tricalcium phosphate (TCP), represent the current benchmark, their limitations, including slow degradation (HAp) and limited osteoinductivity (TCP), have driven the development of alternative biomaterials. In this context, magnesium phosphate (MgP)-based materials have gained increasing attention due to their tunable resorption rate, improved biodegradability, and ability to stimulate osteogenesis and angiogenesis through the release of magnesium (Mg²⁺) ions. This study reports on composite scaffolds based on electrospun poly(ε-caprolactone) (PCL) fibres coated with MgP layers doped with lithium (Li) and zinc (Zn), designed to mimic the nanofibrous architecture of the extracellular matrix. Lithium and zinc were selected due to their known ability to modulate cellular response, with lithium promoting osteogenic activity and zinc contributing to improved cell proliferation and antibacterial potential. The phosphate phases obtained by coprecipitation were deposited onto the PCL fibres using Matrix-Assisted Pulsed Laser Evaporation (MAPLE), enabling controlled surface functionalization. Following thermal treatment, the formation of the crystalline magnesium pyrophosphate (Mg₂P₂O₇) phase was confirmed by chemical and structural characterization. The combination of a slowly degrading PCL matrix, providing sustained structural support, and a bioactive MgP coating, enabling rapid and controlled ion release, results in improved scaffold performance in terms of biocompatibility, biodegradability, and bioactivity. While the slow degradation rate of PCL ensures mechanical stability over an extended period, the surface-deposited MgP phase allows immediate interaction with the biological environment, facilitating faster ion release and enhancing cell–material interactions. These findings highlight the potential of the developed composites as promising candidates for trabecular bone regeneration and as viable alternatives to conventional CaP-based scaffolds in regenerative medicine. Full article

Fused deposition modeling (FDM)-based three-dimensional (3D) fabrication offers a viable approach to manufacturing highly customized carbon fiber-reinforced polyether ether ketone (CFR-PEEK) components with complex geometries. However, the mechanical properties and surface roughness of FDM-fabricated parts are strongly influenced by processing parameters, particularly layer thickness. This study investigates the influence of layer thickness (0.1 mm and 0.2 mm) on the surface roughness, crystallinity, mechanical properties, and morphological characteristics of FDM-printed 10% CFR-PEEK specimens. The specimens were characterized using mechanical testing, differential scanning calorimetry (DSC), confocal laser microscopy, X-ray micro-computed tomography (µCT), and scanning electron microscopy (SEM). The results show that specimens printed with a 0.2 mm layer thickness exhibit higher crystallinity and ball indentation hardness while also showing increased surface roughness and porosity, with µCT analysis revealing larger and more spatially clustered voids near the sub-perimeter regions. In contrast, specimens printed with a 0.1 mm layer thickness demonstrate higher tensile strength, elastic modulus, elongation at break, and compressive stress. SEM fractography further indicates improved interlayer bonding and a relatively cohesive fracture surface in specimens printed with a 0.1 mm layer thickness. These findings demonstrate clear layer-thickness-dependent processing–structure–property relationships in FDM-printed CFR-PEEK composites and provide guidance for optimizing printing parameters to achieve improved mechanical performance. Full article

Ti alloys are widely used in aerospace and biomedical fields due to their high mechanical properties under severe loading. Interest in additively manufactured Ti6Al4V has increased, but further research is needed to fully characterize their properties. This work compares the effects of surface properties, internal defects, microstructure, hardness, and Hot Isostatic Pressing (HIP) or Vacuum Heat Treatment (VHT) on the fatigue behavior of Ti6Al4V produced by Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Printing parameters and post-processing were optimized to achieve high density and minimal porosity, providing a solid basis for realistic fatigue comparisons. Samples were characterized in terms of microstructure (optical microscopy and SEM), mechanical properties (hardness mapping), surface texture (confocal microscopy), and internal defects (image-based analysis). Uniaxial fatigue limits were determined by a Dixon-Mood staircase method, and failed specimens were analyzed for fracture surfaces and defect areas. Applied load on flaws was evaluated to identify root causes of fatigue failure. Results showed that fatigue of as-printed samples is governed by surface roughness, while machined specimens are controlled by internal defect size. Machining increased the fatigue limit roughly threefold, and HIP further improved it by 10–20% by reducing internal porosity. In conclusion, with properly optimized melting parameters, both EBM and SLM produce similar mechanical performance at comparable roughness, supporting their use for structural components. Full article

Objective: CAD-CAM technology enables biomimetic dentistry by producing highly accurate, minimally invasive restorations that replicate the biomechanical behavior of intact teeth. This study evaluated the fracture resistance of overlays with margins at different supragingival levels, including a flat occlusal design and compared them with conventional full crowns. All restorations were fabricated from chairside CAD/CAM resin-matrix ceramic for maxillary premolars. Methods and Materials: Sixty-four CAD/CAM resin-matrix ceramic restorations were fabricated and randomly assigned to four groups (n = 16): (1) overlay with a margin 2 mm above the gingiva (Ov2m); (2) overlay with a 4 mm supragingival margin (Ov4m); (3) overlay with a 4 mm margin and flat occlusal surface (OvF4m); and (4) full-coverage crown with a gingival-level margin (FCC). Preparations were standardized by one operator. Restorations were adhesively cemented to resin dies, thermocycled 10,000 times (5–55 °C), and loaded to failure in a universal testing machine (1 mm/min). Data were analyzed using one-way ANOVA and post hoc tests (α = 0.001). Results: Among overlays, Ov2m showed the highest fracture resistance (1605 ± 88 N), followed by Ov4m (1403 ± 63 N). OvF4m recorded the lowest value (1257 ± 73 N). FCC exhibited the greatest overall resistance (1838 ± 106 N), significantly higher than that of any overlay group. Conclusions: Overlays with margins 2 mm above the gingiva had higher fracture resistance than those with more coronal margins or flat occlusal designs. Full-coverage crowns showed the greatest strength, highlighting the impact of margin position and preparation design on restoration performance. Full article

The combined arch theory provides an effective means for designing support parameters in roadways within loose and fractured surrounding rock. A clear understanding of the internal stress evolution during the load-bearing process of the combined arch is of guiding significance for optimizing roadway support. Taking the 11308 return airway of a mine in Inner Mongolia as the engineering background, this study adopts a combined research approach of theoretical calculation, numerical simulation and laboratory testing. It systematically investigates the internal stress evolution of the anchored combined arch load-bearing structure in roadways with loose and fractured surrounding rock. The load-bearing capacity and failure characteristics of the anchored combined arch under different roof support schemes are explored and analyzed. An optimized support scheme for the loose and fractured roof is proposed and applied in the field, and the monitoring results verify its effectiveness. The results indicate that bolt density is a key factor affecting the load-bearing performance of the combined arch. As bolt spacing decreases, the vertical stress concentration in the anchored structure increases, and its deformation resistance is enhanced. During the stage from load-bearing to failure of the combined arch, the changes in vertical and horizontal stresses within the arch become more stable, and the load-bearing capacity is significantly improved. Comparison between the model test results and theoretical calculations shows good agreement, verifying the rationality of the theoretical calculations. Pressure sensors were pre-installed in the laboratory model to monitor the vertical stress changes in the anchored structure throughout the loading process, and numerical simulations confirmed the stress concentration effect of the combined arch. It was also found that the instability of the anchored structure is controlled by the shear plane at the arch feet. Finally, the bolt spacing in the 11308 return airway of the Inner Mongolia mine was optimized to 0.7 m, and field monitoring was introduced. The maximum roof surface settlement displacement was 15 mm, and the maximum roof separation was 3 mm, confirming that these parameters can meet the roadway stability requirements. Full article