Search Results (123)

Cracks in planetary gearbox casings generate additional vibration responses, which may be used for monitoring structural degradations. This paper provides a signal processing framework to effectively track casing crack-related features in planetary gearboxes using the carrier synchronous signal average (C-SSA). The proposed algorithm is based on processing the hunting-tooth synchronous signal average (H-SSA) to extract the C-SSA which contains the cyclic interaction between the gear loadings and the corresponding casing response. The root mean square (RMS) of the C-SSA signal can then serve as a health condition indicator (CI) to track crack propagation. Further enhancement can be achieved by applying the Hilbert transform (HT) on the C-SSA using the full bandwidth to derive squared envelope signal, which enhances the trending capability. To remove cyclic temperature influences observed in the trends, singular spectrum analysis technique (SSAT) has been used to ensure that the trend reflects the changes purely due to the damage progression. Experiments using three casing-mounted sensors show good capability to track crack progression. Tests under 100%, 125%, and 150% load levels show consistent performance across these operating conditions, with better results seen at higher loads. The results demonstrate that C-SSA and its squared envelope signal effectively enhance the sensitivity and reliability of vibration-based casing crack detection, providing a practical tool for long-term structural health monitoring of planetary gearboxes. Full article

Accurate fault diagnosis of gear transmission systems is crucial for ensuring mechanical reliability and preventing catastrophic failures. However, existing research predominantly focuses on single-gear crack faults, often overlooking the complex coupling effects when cracks occur simultaneously on meshing gears in practical engineering scenarios. To address this research gap, a multi-degree-of-freedom dynamic model incorporating time-varying mesh stiffness under normal, single-crack, and coupled-crack conditions is established. Experimental validation is conducted based on an FZG closed test rig for power flow. The results indicate that the mesh stiffness under coupled-crack conditions is generally lower than that under single-crack conditions. In the time-domain vibration response, the periodic impact amplitudes induced by coupled cracks are significantly amplified, with the impact period jointly influenced by the rotational speeds of both the driving and driven gears. According to frequency-domain analysis, coupled cracks result in a notable increase in harmonic peaks of the mesh frequency, enhanced sideband amplitudes, and a modulation period that is between the rotational frequencies of the driving and driven gears. The simulation results from the dynamic model show high consistency with the experimental signals in terms of time-frequency characteristic trends and time-domain indicators such as the crest factor, thereby validating the effectiveness of the dynamic model. This study elucidates the unique influence mechanism of coupled cracks on the dynamic behavior of gear systems and can provide theoretical guidance for the accurate diagnosis and condition assessment of multi-tooth faults in subsequent research. Full article

This study compared the mechanical and thermal properties of new and retrieved multizone rhodium-coated superelastic nickel-titanium (NiTi) archwires across anterior and posterior segments. Using three-point bending tests, Scanning Electron Microscopy with Energy-Dispersive Spectroscopy analysis, and multiple linear regression, it was found that the posterior segments of new wires generated forces 0.50–0.80 N higher than those of anterior or retrieved specimens. While anterior segments exhibited higher austenite start and finish temperatures (by 6.15 °C and 5.21 °C, respectively) compared to posterior segments, these temperatures remained below average intraoral levels, and clinical retrieval did not significantly alter transformation temperatures. However, retrieved wires produced lower overall forces, likely due to surface cracking identified through microscopy. Ultimately, while posterior segments consistently generate higher forces than anterior segments, the observed reduction in force over time and the risk of surface degradation led to the conclusion that these archwires are not recommended for tooth movements exceeding 2 mm. Full article

Conventional glass ionomer cement (GIC) is a reaction product formulated from glass powders and polycarboxylic acid aqueous solution. This material has garnered significant attention in restorative dentistry due to its favorable properties, including chemical adhesion to tooth structure, biocompatibility, and sustained fluoride release, coupled with its minimal pulp irritation. However, its low mechanical strength, high brittleness, and susceptibility to cracking limit its use in stress-bearing areas of teeth. To expand the clinical application scope of GIC and develop an “ideal” dental restorative material, enhancing traditional GIC is necessary. This narrative review summarizes the main strategies for enhancing GIC, covering modifications to both the powder and liquid components. The key findings indicate that incorporating reinforcing fillers into the powder or modifying the polyacid chemistry can significantly improve mechanical properties such as compressive, tensile, and flexural strength. Additionally, some modifications help maintain or enhance fluoride release. However, the translation of many laboratory-based improvements to clinical practice requires further validation. In conclusion, while numerous promising enhancement routes exist, future development should focus on synergistic approaches and rigorous clinical evaluation to advance towards high-performance, durable restorative materials. Full article

Zirconia is widely used in full-arch restorations due to its strength and aesthetics, but failures can still affect its performance in clinical practice. In this report, a full-arch tooth-supported zirconia bridge fractured prematurely (eleven months), encouraging an investigation into its design and failure mechanisms. STL files obtained from the dental laboratory revealed regions of reduced framework thickness, falling below the manufacturer’s recommendations. Fractographic analysis of the fractured pieces indicated a multifactorial failure pattern. Notable features included a thick cement layer, surface damage likely caused by the CAM bur during milling, and occlusal wear affecting the glazed surface. Crack propagation was observed in an occlusal-to-cervical direction. While no single factor could be definitively identified as the primary cause, the failure is attributed to the combined effect of insufficient design, surface damage, and biomechanical overload. Importantly, most such factors are not visible before failure, raising questions about the proper evaluation of zirconia-based restorations prior to their cementation. Full article

Joint roughness coefficient (JRC) and inclination exert a decisive influence on the stability and safety of rock mass engineering. Simulations of uniaxial compression were conducted on saw-tooth-shaped joint specimens using a calibrated particle flow (PFC2D) model. The specimens contained five JRC values (0, 5, 10, 15, 20) and five joint inclinations (0°, 30°, 45°, 60°, 90°). The results indicate that at joint inclinations of 0° and 90°, JRC has a marginal influence on peak stress and elastic modulus. In contrast, as the inclination increases, the peak stress, peak strain, and elastic modulus collectively exhibit an approximate V-shaped trend. The dominant failure mode observed was a mixed splitting-shear mechanism. The number of cracks at final failure increases with higher JRC values under the same joint inclination. As the joint inclination varied, the distributions of global, tensile, and shear cracks all exhibited similar V-shaped trends. Concurrently, the proportions of different microcrack types demonstrated relative stability throughout the failure process, with tensile and shear failures constituting the dominant microscopic mechanisms. Full article

This paper presents a hybrid knowledge-based expert system (KBES) designed to predict crack incubation and fatigue life in gear design, serving as both a research tool and an educational resource. While crack growth and initiation are well understood, crack incubation remains a challenging area. The presented expert system (KBES) integrates a novel mathematical model for crack incubation based on analogy and defect analysis principles with an optimization algorithm for gear design. The system uses genetic algorithms to optimize gear parameters, demonstrating a 5–10% deviation from experimental values in a specific gear design problem case study. Based on this KBES and a hybrid approach, we developed a learning environment based on an intelligent tutoring system (ITS) which serves older students (MSc and PhD) as a learning environment for the acquisition of knowledge and, above all, for the development of an in-depth understanding of the phenomena that occur both during incubation and initialization and during the further propagation of cracks in the root of the gear tooth, which is the basis for determining the lifespan of gear transmissions. Full article

Drilling methods have been increasingly employed for shaft excavation in coal mines in western China. However, the rock fragmentation performance of milled-tooth roller cutters remains inadequate under Jurassic strata conditions. To address this issue, a numerical orthogonal simulation study based on the Finite-Discrete Element Method (FDEM) was conducted. Cutter tooth edge geometry, cutter diameter, cone angle, and penetration depth were considered as four factors at three levels. The effects of these factors on average force, specific energy, damage factor, and proportion of shear cracks were investigated. The efficiency coefficient method was then applied to identify the optimal cutter, and the 8^# roller cutter was determined to be the most effective. The results indicated that cutter tooth edge geometry had the most significant influence on average force and specific energy, whereas penetration depth primarily affected the damage factor and proportion of shear cracks. Compared with the prototype cutter, the 8^# cutter, characterized by a 370 mm large cone-end diameter, a 3° cone angle, and V-edged teeth, exhibited superior rock fragmentation efficiency, achieving a maximum improvement of 31%. These results provide a theoretical basis for the structural optimization of cutters used in shaft drilling in coal mines in western China. Full article

Dental composites are commonly used for the restoration of hard tooth tissues, but their low fracture toughness may limit their lifespan. In this study, the effect of liquid rubber modification on the mechanical properties and fracture mechanisms of two types of dental composites, flow and classic, was evaluated. The study used experimental composites containing a mixture of dimethacrylate resins: BisGMA (20% by weight), BisEMA (30% by weight), UDMA (30% by weight), and TEGDMA (20% by weight). Composites were reinforced with Al-Ba-B-Si glass, Ba-Al-B-F-Si glass with particle sizes of 0.7 and 2 μm respectively, as well as pyrogenic silica (20 nm). The inorganic phase was introduced in an amount of 50% vol. for flow material and 80% vol. for classic composite. As a modifier, Hypro 2000X168LC VTB liquid rubber (Huntsman International LLC, USA) was used in an amount of 5% by weight relative to the matrix. The flexural strength, Young’s modulus, and fracture toughness were evaluated. Numerical FEM analysis allowed for the evaluation of stress distribution in the filling area. The results confirmed that the modification of composites with liquid rubber contributes to an increase in fracture toughness. For the flow-type material, the fracture toughness increased from 1.04 to 1.13 MPa·m^1/2. At the same time, a decrease in flexural strength from 71.90 MPa to 61.48 MPa and in Young’s modulus from 2.98 GPa to 2.53 GPa. In the case of the classical composite, the modification with liquid rubber also improved the resistance to fracture, increasing it from 1.97 to 2.18 MPa·m^1/2 while the flexural strength decreased from 102.30 MPa to 90.96 MPa, and the modulus dropped from 7.33 GPa to 6.16 GPa. FEA analysis confirmed that modified composites exhibit a more favorable stress distribution with lower tensile stress levels (approximately 20 MPa in contrast to 25 MPa for the classic composite). Mechanisms of fracture and strengthening were also identified. The main fracture mechanism was intermolecular cracking with crack deflections. Modification with liquid rubber resulted in the formation of elastic bridges and plastic shear zones at the front of the crack. Full article

The joint represents a critical component in precast concrete segmental bridges (PCSBs), playing an essential role in transferring shear stress. The efficacy of steel shear keys in comparison to conventional concrete tooth keys has been proven in terms of their shear transfer capability. In this study, a novel design using ultra-high-performance concrete (UHPC) to replace conventional concrete around the steel shear keys was proposed. A 30 m span precast concrete segmental T-girder with epoxy steel shear-keyed joints was fabricated to evaluate the effectiveness of the joint system. Experimental measurements included crack development, load–deflection response, and strain distribution. Furthermore, a finite element (FE) model was developed and validated with the experimental results. The results indicate that the epoxy steel shear-keyed joints effectively transmitted shear stress between segments, with the girder achieving an ultimate load of 1750 kN and a ductile flexural failure mode. The validated FE model accurately captured the critical characteristics of the structure. Finally, an effective calculation method was introduced to predict the ultimate load. Full article

As a key component of pure electric vehicles, the reducer plays a vital role in power transmission and overall drive system performance. This study investigates the nonlinear dynamic characteristics of helical gears with tooth root crack faults in high-speed reducers. A coupled bending–torsional–shaft dynamic model is developed, in which the time-varying mesh stiffness of cracked helical gears is calculated using an improved potential energy method. The system’s nonlinear dynamic responses under varying mesh error excitation, gear backlash, and damping ratio are numerically obtained via the variable-step Runge–Kutta method. The results reveal that under high input speed conditions, the motion of the faulted system evolves from single-period to quasi-periodic motion as bifurcation parameters change. In the stable state, fault characteristic signals are apparent, whereas under strong nonlinear vibrations and chaotic motion, they become difficult to distinguish in traditional time- and frequency-domain analyses. To address this limitation, the DBSCAN clustering algorithm is introduced, which applies machine learning to cluster the Poincaré cross-sections of the system under different motion states. This approach enables the effective classification and identification of crack-induced and fault-related noise, thereby improving the accuracy of fault detection in nonlinear dynamic gear systems. Full article

Dental enamel exhibits a unique combination of high hardness and high toughness. This outstanding mechanical property is closely tied to its multi-scale hierarchical structure. In this study, rat tooth enamel was selected as the research object, the different structural layers and mechanical properties of tooth enamel were investigated and characterized experimentally. The multi-scale mechanical models with different structural layers were developed and analyzed using numerical simulations. The research results indicate that, regarding the load-bearing mechanism, the outer layer of tooth enamel consists of hydroxyapatite crystal bundles arranged in parallel and inclined orientations, and this structural feature enables it to exhibit excellent elastic modulus and resistance to deformation, while the inner layer with cross-arranged crystal bundles shows different mechanical response characteristics. In terms of crack propagation behavior, the outer layer is more prone to crack initiation due to the consistency of crystal orientation, and the cracks tend to extend in a straight line, while the unique cross arrangement of crystals in the inner layer can effectively inhibit crack propagation by inducing crack deflection and branching mechanisms, thus demonstrating more excellent fracture toughness. This “outer hard and inner flexible” gradient structure design elucidates the synergistic mechanism between crystal orientation and crack propagation behavior in tooth enamel, offering significant design insights for biomimetic composite materials. Full article

The gear transmission system is a safety-critical component in rail transit, typically designed for a service life exceeding 20 years. Failure analysis of such systems remains a key focus for railway engineers. This study systematically investigates four representative cases of premature gear failure in high-speed trains using a standardized analytical procedure that includes visual inspection, chemical analysis, metallographic examination, scanning electron microscopy, and hardness testing. The results identify four primary root causes: subsurface slag inclusions in raw materials, inadequate heat treatment leading to a non-martensitic layer (∼60 μm) at the tooth root, grinding-induced temper burns (crescent-shaped "black spots") accompanied by a hardness drop of ∼100–150 HV, and insufficient lubrication. The interdependencies between these factors and failure mechanisms, e.g., fatigue cracking, spalling, and thermal scuffing, are analyzed. This work provides an evidence-based framework for improving gear reliability and proposes targeted countermeasures, such as ultrasonic inclusion screening and real-time grinding temperature control, to extend operational lifespans. Full article

Bamboo fiber is a prime green fiber due to its renewability, biodegradability, and high specific strength. Bamboo-fiber-reinforced epoxy (BFRE) composites have seen extensive use and shown great promise for natural biofiber-reinforced friction materials. Inspired by the decussated fiber alignment of bovine enamel, this study investigated how fiber orientation influences the tribological properties of BFRE composites. Specifically, the proportion of fibers oriented vertically to the surface was varied at seven levels: 0%, 25%, 33%, 50%, 67%, 75%, and 100%. The tribological performance was assessed through wear reciprocating testing and microscopic morphological characterization techniques. Results indicate that the bio-inspired fiber decussation can reduce the wear loss of the BFRE composites. Among all bio-inspired BFRE composites, BFRE composites with 67% vertical fibers achieve the best wear resistance. The vertical fibers in the BFRE composites can withstand pressure to provide a “compression–rebound” effect, while the parallel fibers can resist shear stress. The decussated structure inhibits crack initiation and propagation during wear and promotes transfer film formation, reducing wear loss. The findings expand understanding of the correlation between the bovine-tooth-like decussated structure and its tribological mechanisms, thereby offering essential guidance for the biomimetic design of high-performance BFRE composites for friction material application. Full article

Objectives: The aim of this study was to evaluate the performance of GPT-4o in identifying nine common dental conditions on panoramic radiographs, both overall and at specific tooth sites, and to assess whether the use of different tooth numbering systems (FDI and Universal) in prompts would affect its diagnostic accuracy. Methods: Fifty panoramic radiographs exhibiting various common dental conditions including missing teeth, impacted teeth, caries, endodontically treated teeth, teeth with restorations, periapical lesions, periodontal bone loss, tooth fractures, cracks, retained roots, dental implants, osteolytic lesions, and osteosclerosis were included. Each image was evaluated twice by GPT-4o in May 2025, using structured prompts based on either the FDI or Universal tooth numbering system, to identify the presence of these conditions at specific tooth sites or regions. GPT-4o responses were compared to a consensus reference standard established by an oral-maxillofacial radiology team. GPT-4o’s performance was evaluated using balanced accuracy, sensitivity, specificity, and F1 score both at the patient and tooth levels. Results: A total of 100 GPT-4o responses were generated. At the patient level, balanced accuracy ranged from 46.25% to 98.83% (FDI) and 49.75% to 92.86% (Universal), with the highest accuracies for dental implants (92.86–98.83%). F1-scores and sensitivities were highest for implants, missing, and impacted teeth, but zero for caries, periapical lesions, and fractures. Specificity was generally high across conditions. Notable discrepancies were observed between patient- and tooth-level performance, especially for implants and restorations. GPT-4o’s performance was similar between using the two numbering systems. Conclusions: GPT-4o demonstrated superior performance in detecting dental implants and treated or restored teeth but inferior performance for caries, periapical lesions, and fractures. Diagnostic accuracy was higher at the patient level than at the tooth level, with similar performances for both numbering systems. Future studies with larger, more diverse datasets and multiple models are needed. Full article