Search Results (5,309)

Q345 steel is usually used on structures working under high temperature where creep deformation could endanger their structural integrity. In order to support the application of steel structures made of Q345 under high temperature, a fracture analysis on defective Q345 steel in the process of small-scale creep crack propagation has been performed. Three-dimensional finite element models with a semi-elliptical surface crack have been established, and the crack propagation process of Q345 steel has been simulated at 400 °C. The constraint effect near the crack tip in the process of creep crack propagation has been analyzed using the J-A₂ two-parameter method in which the influence of the crack aspect ratio, loading level, and biaxial loading ratio was studied. The previously developed constraint-based R6 procedure was adopted to assess the structural integrity of the cracked structure under small-scale creep conditions. The results showed that small-scale creep crack propagation behavior exhibits great influence on both crack tip fields and a constraint effect near the crack tip. The increase in the biaxial loading ratio, loading level, and aspect ratio of the crack could lead to an increase in the J integral, an enhancement of the constraint effect, and a decrease in the safe area in the failure assessment diagram for the cracked structure in the process of small-scale creep crack propagation. Full article

The present study focuses on the mechanical performances of basalt fiber-reinforced composites based on the more environmentally friendly Recyclamine^® resin (BR) and conventional and widely used room-cured epoxy systems (BE). Specifically, the study probes the tensile and compressive responses of the composites fabricated by vacuum-assisted resin transfer molding. Experimental results revealed that the tensile strength of basalt–Recyclamine was higher than its counterpart (464 MPa compared to 390.9 MPa). At the same time, the BR performed only marginally better under compression, with a strength of 237.7 MPa compared to 233.9 MPa for BE. However, the BR demonstrated significantly enhanced ductility reflected by its greater compressive strain capacity (3.9% compared to only 1.1%). Different microscopic analyses unveiled distinct failure mechanisms, with more progressive failure patterns observed in BR compared with the brittle fracture characteristics of the BE composite. The performance of several micromechanical models was also investigated, with their results corroborating with the experimental results with varying degrees of accuracy. The statistical analysis showed great consistency in the results, with the CoV value below 10%. Experimental results indicated that the basalt–Recyclamine composites can be considered a promising sustainable alternative to traditional polymeric resin-based systems due to their balanced mechanical performance and environmental advantages. Full article

In order to systematically study the drying characteristics, microstructure, and mechanical properties of potato in an electrohydrodynamic (EHD) system, this paper uses different discharge voltages for drying experiments. The results show that the discharge produces reactive nitrogen–oxygen particles, the intensity of which increases with increasing voltage. Under 0–30 kV, the higher the electric field, the faster the drying speed of the samples. The 30 kV group dried 40.5% faster than the control group. The EHD drying group had better color, shrinkage, rehydration capacity, and effective water diffusion coefficient. Rehydration capacity was positively correlated with electric field strength. EHD-treated potato flakes form a porous network structure and expose starch granules, as shown by scanning electron microscopy and infrared spectroscopy. Higher voltage results in a greater proportion of ordered protein structure. EHD drying retains more water than the control, with the best results at 30 kV, as shown by low-field nuclear magnetic resonance (NMR). Texture analysis showed that adhesion peaked in the 25 kV group, and the 15 kV group had the best Young’s modulus and the lowest fracture rate. This study provides a theoretical basis and experimental foundation for the application of EHD drying technology in potato drying and deep processing. Full article

This study evaluates the optical properties and mechanical durability of adhesive restorations fabricated using different techniques for the treatment of single-tooth loss in the posterior region after an aging process. Sixty extracted human teeth (thirty molars and thirty premolars) were restored using three different fabrication methods: 3D-printed resin restorations, fiber mesh-reinforced direct composite restorations, and indirect composite restorations. Color stability was assessed using a spectrophotometer, and fracture resistance was measured using a universal testing machine. Finite element stress analysis (FEA) was conducted to validate mechanical test results under simulated intraoral conditions. The fiber-reinforced composite group exhibited the highest fracture resistance (1057.91 MPa), while 3D-printed restorations showed the lowest (p < 0.05). Regarding color stability, the fiber-reinforced group demonstrated the highest ΔE⁰⁰ values (ΔE⁰⁰ = 1.71), differing significantly from the other groups, while the 3D-printed and indirect composite restorations showed no significant difference. Mechanical test results were consistent with FEA findings. These results indicate that fiber reinforcement enhances mechanical durability in high-load-bearing areas, while 3D-printed restorations may not yet be suitable for posterior regions. However, their potential use in anterior restorations, where occlusal forces are lower, warrants further investigation to improve material properties. Full article

Compared with traditional gas reservoirs, ultra-deep and ultra-high-pressure tight sandstone gas reservoirs are characterized by well-developed faults and fractures, strong heterogeneity and stress sensitivity, and complex in situ stress distribution. Traditional three-dimensional geological models and numerical models ignore the variation characteristics of reservoir in situ stress during the production process, it affects the accuracy of the subsequent fracturing modification design and development plan formulation. Therefore, based on the integrated method of geological engineering, this article first carried out high-temperature and high-pressure stress sensitivity tests on reservoir rock samples and fitted the stress-sensitive mathematical model to clarify the influence of high temperature and high pressure on permeability. Then, aiming at the problem of four-dimensional in situ stress variation caused by the coupling of the seepage field and stress field during the exploitation of tight sandstone gas reservoirs, combined with the results of well logging interpretation, rock physical property analysis, and mechanical experiments, based on the three-dimensional geological model and geomechanical model of the gas reservoir and coupled with the stress-sensitive characteristics of the reservoir, a four-dimensional in situ stress model for the reservoir of tight sandstone gas reservoirs was established. The prediction of the variation law of four-dimensional in situ stress during the production process was carried out. Finally, the influence of considering stress sensitivity on reservoir production was simulated. The results show the following: ① The production process has a significant impact on the magnitude and distribution of four-dimensional in situ stress. With the decrease in pore pressure, both the maximum horizontal principal stress and the minimum horizontal principal stress decrease. ② In the area near the production well, the direction of in situ stress will significantly deflect over time. ③ In an ultra-deep and ultra-high-pressure environment, the gas reservoir is affected by the stress-sensitive effect. The stable production time of the gas well is reduced by two years, and the cumulative gas production decreases by 5.01 × 10⁸ m³. The research results provide the temporal stress field distribution results for the simulation and prediction of the secondary fracturing of old wells and the commissioning fracturing of new wells in the target well area. Full article

Hybrid additive manufacturing (AM) provides a unique way of fabricating complex geometries with onboard machining capabilities, combining both additive and traditional subtractive techniques and resulting in reduced material waste and efficient high-tolerance components. In this work, a hybrid AM technology was used to create 316L stainless steel (316L SS) components using laser-wire-directed energy deposition (LW-DED) coupled with a CNC machining center on a single platform. Fully reversed fatigue tests were completed to investigate the as-manufactured life span of the additively manufactured structures for three different deposition rates of 6.33 g/min, 7.12 g/min, and 7.91 g/min. High-cycle fatigue test results showed that the fatigue performance of the tested specimens is not dependent on the deposition rates for the investigated parameters, with specimens with a 7.12 g/min deposition rate showing comparatively superior behavior to that of the other deposition rates at higher stress amplitudes. Fractography analysis was used to investigate the fractured surfaces, showing that the crack initiation sites were predominantly near the edges and not affected by the volumetric defects generated during manufacturing. X-ray-computed tomography (X-ray CT) analysis quantified the effect of the as-manufactured porosity on fatigue behavior, showing that the amount of porosity for the build rates used was insufficient to have a substantial impact on the fatigue behavior, even as it increased with the deposition rate. Full article

GH4099 is a nickel-based, high-temperature, precipitation-strengthened alloy with excellent mechanical properties and corrosion resistance, widely used in aerospace components. The performance of parts produced by additive manufacturing depends significantly on alloy powder quality and heat treatment. In this study, GH4099 alloy powder was prepared using the EIGA method, and its morphology, particle size distribution, and flowability were analyzed. The mechanical properties and microstructure of parts before and after solution-aging treatment were compared. Results showed that the powder had good sphericity and flowability, with a median diameter D50 of 28.88 μm. The formed parts underwent solution treatment at 1140 °C for 2 h followed by aging at 850 °C for 8 h. After heat treatment, the transverse tensile strength increased to 1122.11 MPa (+15.1%) and the yield strength to 866.56 MPa (+22.3%), while the longitudinal tensile strength reached 1116.81 MPa (+29.4%) and the yield strength 831.61 MPa (+35.2%). This improvement is attributed to the precipitation of γ′ phase. Fractographic analysis revealed a mixed fracture mode characterized by ductile dimples and cleavage facets, indicating that the alloy exhibits favorable toughness-related features under mechanical loading. These findings demonstrate the excellent microstructure and mechanical performance of GH4099 alloy in AM applications, providing a basis for its further use in high-performance aerospace components. Full article

Nowadays, reverse osmosis (RO) desalination has become a highly effective and economical solution to address water scarcity worldwide. The membranes used in this type of separation are influenced by both pre-treatment operations and feed water quality, leading to fouling, a complex phenomenon responsible for reducing treatment performance and shortening membrane lifespan. In this study, an autopsy of a RO membrane from the Boujdour plant was performed, and a fouling prediction tool based on transmembrane pressure (TMP) was developed using MATLAB/Simulink (R2015a) with an artificial neural network (ANN) model. The impact of membrane fouling on treatment performance was also examined through one year of monitoring. A detailed analysis of the fouled membrane was conducted using SEM/EDS techniques to characterize the fouling on the membrane’s surface and cross-section. The results revealed significant fractures on the membrane surface, with fouling predominantly consisting of organic deposits (characterized by a high oxygen concentration of 39.69%) and inorganic fouling, including Si (7.99%), Al (2.79%), Mg (1.56%), Fe (1.27%), and smaller quantities of K (0.87%), S (0.36%), and Ca (0.12%). The ANN model for predicting transmembrane pressure was successfully developed, achieving a high R² value of 92.077% and a low mean square error (MSE) of 0.005657. This predictive model demonstrates the ability to forecast future TMP cycles based on historical data. The research provides a detailed understanding of the types of fouling affecting RO membranes and contributes to the development of preventive strategies to mitigate membrane fouling. Full article

A study was conducted on the mechanical behavi or of the completion string in a 10,000 m ultra-deep well from western China’s oilfields to identify the causes of plastic failure in the string. This article analyzes the interaction between fluid and tubing in high-pressure and high-production gas wells by establishing a fluid structure coupling four-equation model. Through fatigue tests, it was found that P110 tubing material has a stress amplitude related ratchet effect, revealing the softening characteristics of tubing material. Through case analysis, the fatigue of the entire wellbore was analyzed, and it was shown that the fatigue hotspot is concentrated near the neutralization point, and stress concentration under high-production and low-production conditions leads to the degradation of tubing material performance under fatigue load. After continuous service for 30 days under high-production and low-production conditions, the entire wellbore section exhibited a softening phenomenon, and the yield strength began to decrease below 4349 m and 4324 m well depths, respectively. The safety factor of the entire wellbore section decreased. Within 284 days of production, the fatigue damage of the entire wellbore section was less than 5%, and the remaining yield change and material softening of the tubing string were negligible. However, there was an impact load during the lifecycle, which caused severe fluctuations in the wellbore safety factor and was the main cause of tubing string fracture. Subsequent research should integrate diverse well cases exhibiting varying production parameters to establish a statistically robust predictive framework for safety factor variations. Full article

This study examines factors affecting the thermal expansion behavior of continuous welded rails (CWRs) in urban rail systems and investigates conditions that lead to rail weld fractures. Parameters affecting CWR fractures near ventilation shafts in urban rail systems are identified through field investigations and machine learning analysis. Further, a computational fluid dynamics analysis is employed to evaluate the range of temperature variation around tunnel ventilation shafts that affects the CWR fractures. Load conditions, including temperature changes, were analyzed using a validated numerical model to determine the axial stress in the CWR, which resulted in a 23% reduction in the axial stress in the weld joint. The results confirm that increased localized temperature fluctuations around tunnel ventilation shafts lead to a higher frequency of CWR fractures. Full article

Low-cycle fatigue damage accumulation exhibits inherent nonlinear characteristics, particularly under variable-amplitude loading conditions, where loading sequence exerts significant influence on damage evolution. This investigation conducted strain-controlled variable loading fatigue tests on nickel-based superalloy specimens at 650 °C. Comparative microstructural analysis through scanning electron microscopy revealed distinct fracture features between variable-amplitude and constant-amplitude loaded specimens. A novel fatigue damage accumulation model was developed through three critical advancements: mathematical formulation of strain amplitude as an exponential function based on the damage equivalence principle, explicit integration of loading sequence effects, and systematic calibration using experimental data. Comparative analysis with existing fatigue damage models revealed that the proposed methodology demonstrates notable advantages in both prediction accuracy and implementation simplicity. Full article

Background: This institutional, register-based analysis aimed to evaluate the feasibility of using CT-based sacral Hounsfield units (HUs) for assessing bone density in pelvic fragility fractures and to explore their potential correlation with DEXA measurements and osteological laboratory diagnostics. Methods: Patients aged > 80 years, admitted between 2003 and 2019 with pelvic ring fractures, were analyzed in this retrospective single-center study. CT scans were evaluated according to the classification of fragility fractures of the pelvis (FFPs), which guided treatment decisions (conservative or surgical). The diagnosis of a fragility fracture was based on both fracture morphology and patient history, including the presence of low-energy trauma. Bone health was assessed using standardized laboratory diagnostics including serum calcium, phosphate, alkaline phosphatase, and 25(OH)-vitamin D, in addition to DEXA scans and CT-derived Hounsfield units. Vitamin D levels and bone density evaluations were analyzed to identify possible correlations among these factors and with fracture patterns. Results: A total of 456 patients (mean age 87.3 years, 79.6% female) were included. The CT-based FFP classification identified Type II as the most common fracture type (66.7%). Conservative treatment was the predominant approach (84.9%). Serum 25(OH)-vitamin D deficiency was observed in 62.7% of the patients, while osteopenia and osteoporosis were found in 34.3% and 46.5% of cases, respectively. HU values at S1 showed significant correlation with femoral neck T-scores, highlighting the utility of CT scans for bone density assessment. Conclusions: This study emphasizes the complementary roles of CT-derived HU values and DEXA T-scores in evaluating bone quality and fracture severity in geriatric patients with FFP. While DEXA remains the gold standard, CT imaging offers valuable early insights, supporting the timely initiation of osteoporosis therapy. Given the high prevalence of fragility fractures in this age group, early CT-based screening may facilitate earlier initiation of osteoporosis-specific therapy, including anabolic agents where indicated. Further research is needed to explore the relationships between vitamin D levels, bone density assessments, and fracture types. Full article

The integral welded panel represents a highly promising aircraft structural component, owing to its lightweight design and reduced connector requirements. However, the complexity of its welded structure results in the formation of cross-welded joints. This study systematically investigated the mechanical properties of the cross-welded joints through tensile tests across different welded regions, which were complemented by fracture morphology examination via scanning electron microscopy (SEM). The residual stress distribution was characterized using X-ray diffraction, while electron backscatter diffraction (EBSD) analysis was used to elucidate the relationship between residual stress and microstructure. Key findings revealed that the cross-welded zone exhibited lower yield strength and ductility than the single-welded zone, and the advancing heat-affected zone demonstrated superior tensile properties relative to the retreating side. Residual stress analysis showed that the cross-welded joint lacked the “double peak” profile characteristic and displayed lower maximum residual stress than the single-welded joint. EBSD analysis indicated significant grain elongation in the cross-welded zone due to mechanical forces during the welding process, resulting in higher dislocation density and deformation, corresponding with elevated residual stress levels. Full article

Calcite in hydrocarbon reservoirs records abundant information about diagenetic fluids and environments. Understanding the formation mechanisms of calcite is crucial for predicting reservoir characteristics and hydrocarbon migration. This study identifies the types of authigenic calcite present in the Lower Paleozoic carbonate reservoirs of the Bohai Bay Basin through petrographic analysis, cathodoluminescence, and other experimental methods. By integrating electron probe microanalysis, in situ isotopic analysis, and fluid inclusion studies, we further constrain the source of the diagenetic fluids responsible for the authigenic calcite. The results show that there are at least three types of authigenic calcite in the Lower Paleozoic carbonate reservoirs of the Bohai Sea. Calcite cemented in the syn-depositional-to-early-diagenetic stage displays very weak cathodoluminescence, with δ¹³C and δ¹⁸O and paleo-salinity distributions similar to those of micritic calcite. These features suggest that the calcite was formed during burial heating by sedimentary fluids. Calcite filling fractures shows heterogeneous cathodoluminescence intensity, ranging from weak to strong, indicating multiple stages of cementation. The broad elemental variation and multiple cementation events suggest that the diagenetic fluid sources were diverse. Isotopic data show that samples with carbon isotope values greater than −2.9‰ likely formed through water–rock interaction with fluids retained within the strata, whereas samples exhibiting more negative δ¹³C were formed from a mixed-source supply of strata and mantle-derived fluids. Calcite that fills karst collapse pores exhibits alternating bright and dark cathodoluminescence, strong negative δ¹⁸O shifts, and variability in trace elements such as Mn, Fe, and Co. These characteristics indicate a mixed origin of diagenetic fluids derived from both meteoric freshwater and carbonate-dissolving fluids. Full article

Background and Objectives: Musculoskeletal disorders (MSDs) are a leading cause of absenteeism among healthcare workers (HCWs), impacting healthcare delivery. Pediatric HCWs face specific physical demands such as lifting and awkward postures. While absenteeism rose during the COVID-19 pandemic, its effects on pediatric MSD-related leave remain unclear. This study examined MSD-related absenteeism trends among pediatric HCWs in a Romanian hospital across the pre-pandemic (2017–2019), pandemic (2020–2021), and post-pandemic (2022–2023) periods. Materials and Methods: We conducted a retrospective observational study using records from the hospital’s occupational health database. We included all HCWs who took MSD-related leave during 2017–2023. Diagnoses included arthropathies, dorsopathies, other osteoarticular/connective tissue disorders, and acute trauma or fractures. We used chi-square tests, ANOVA, and regression models to identify trends and predictors. Results: A total of 3388 cases were analyzed. Post-pandemic absenteeism increased significantly (40.1%), especially among women (86.8%), nurses (46.7%), and workers aged ≥46 (62.7%). A seasonal shift was observed, with spring peaks (March 9.7% and May 9.9%) replacing the pre-pandemic autumn peaks (October 11.9% and November 12.8%). The regression models identified age, occupation, and diagnosis type as significant predictors of leave duration. Conclusions: MSD-related absenteeism rose post-pandemic and showed altered seasonal patterns. Occupational and demographic predictors identified through a multivariate analysis highlight the need for anticipatory, evidence-based strategies to support pediatric HCWs, enhance workforce resilience, and sustain healthcare performance. Full article