Search Results (16,661)

Placing empty holes between charging holes is widely used in blasting engineering to achieve directional fracture blasting. Studies have shown that the presence of a notch along the empty hole wall enhances stress concentration and supports improved control over crack propagation. The notch angle and length are the two main parameters influencing the impact of notch holes. Therefore, in this study, we used numerical simulations to investigate how varying notch angles and lengths influence the directional fracture blasting effect. The findings suggest that, among the different types of holes used in directional fracture rock blasting, notched empty holes have the most significant guiding effect, followed by empty holes, while the absence of empty holes yields the least effective results. In the directional fracture blasting of a notched empty hole, stress concentration occurs at the notch tip following the explosion. This alters the stress field distribution around the empty hole, which shifts from a compressive to a tangential tensile state. Additionally, this concentration of stress causes the explosion energy to be focused on that location, resulting in a directional fracture blasting effect. In blasting construction, selecting the appropriate notch hole parameters is necessary to achieve optimal effects and reduce damage to surrounding rocks. Based on the notch parameters assessed in this study, the optimal effect of directional fracture blasting is achieved when the notch angle is 30°. Full article

This study examines the crack resistance of basalt-fiber-reinforced concrete (BFRC) materials subjected to freeze–thaw cycles (FTCs). We utilized a φ50 mm Split Hopkinson Pressure Bar (SHPB) apparatus alongside numerical simulations to carry out impact compression tests at a velocity of 5 m/s on BFRC specimens that experienced 0, 10, 20, and 30 FTCs. Additionally, we investigated the effects of basalt fiber (BF) orientation position and length on stress intensity factors. The results reveal that with an increasing number of FTCs, the dynamic crack propagation speed of BFRC with a prefabricated crack inclined at 0° rises from 311.84 m/s to 449.92 m/s, while its pure I fracture toughness decreases from 0.6266 MPa·m^0.5 to 0.4902 MPa·m^0.5. For BFRC specimens with a prefabricated crack inclination of 15°, the dynamic crack propagation speed increases from 305.81 m/s to 490.02 m/s, accompanied by a reduction in mode I fracture toughness from 0.3901 MPa·m^0.5 to 0.2867 MPa·m^0.5 and mode II fracture toughness from 0.6266 MPa·m^0.5 to 0.4902 MPa·m^0.5. In the case of a prefabricated crack inclination of 28.89°, the dynamic crack propagation speed rises from 436.10 m/s to 494.28 m/s, while its pure mode II fracture toughness decreases from 1.1427 MPa·m^0.5 to 0.7797 MPa·m^0.5. Numerical simulations indicate that fibers positioned ahead of the crack tip—especially those that are longer, located closer to the crack tip, and oriented more perpendicularly—significantly reduce the mode I stress intensity factor. However, these fibers have a minimal impact on reducing the mode II stress intensity factor. The study qualitatively and quantitatively analyzes the crack resistance of basalt-fiber-reinforced concrete in relation to freeze–thaw cycles and the fibers ahead of the crack tip, offering insights into the fiber reinforcement effects within the concrete matrix. Full article

The application of nanocomposites based on polyacrylamide hydrogels as well as silica nanoparticles in various tasks related to the petroleum industry has been rapidly developing in the last 10–15 years. Analysis of the literature has shown that the introduction of nanoparticles into hydrogels significantly increases their structural and mechanical characteristics and improves their thermal stability. Nanocomposites based on hydrogels are used in different technological processes of oil production: for conformance control, water shutoff in production wells, and well killing with loss circulation control. In all these processes, hydrogels crosslinked with different crosslinkers are used, with the addition of different amounts of nanoparticles. The highest nanoparticle content, from 5 to 9 wt%, was observed in hydrogels for well killing. This is explained by the fact that the volumes of injection of block packs are counted only in tens of cubic meters, and for the sake of trouble-free workover, it is very important to preserve the structural and mechanical properties of block packs during the entire repair of the well. For water shutoff, the volumes of nanocomposite injection, depending on the well design, are from 50 to 150 m³. For conformance control, it is required to inject from one to several thousand cubic meters of hydrogel with nanoparticles. Naturally, for such operations, service companies try to select compositions with the minimum required nanoparticle content, which would ensure injection efficiency but at the same time would not lose economic attractiveness. The aim of the present work is to develop formulations of nanocomposites with increased structural and mechanical characteristics based on hydrogels made of partially hydrolyzed polyacrylamide crosslinked with resorcinol and paraform, with the addition of commercially available nanosilica, as well as to study their thermal degradation, which is necessary to predict the lifetime of gel shields in reservoir conditions. Hydrogels with additives of pyrogenic (HCSIL200, HCSIL300, RX380) and hydrated (white carbon black grades: ‘BS-50’, ‘BS-120 NU’, ‘BS-120 U’) nanosilica have been studied. The best samples in terms of their structural and mechanical properties have been established: nanocomposites with HCSIL200, HCSIL300, and BS-120 NU. The addition of hydrophilic nanosilica HCSIL200 in the amount of 0.4 wt% to a hydrogel consisting of partially hydrolyzed polyacrylamide (1%), resorcinol (0.04%), and paraform (0.09%) increased its elastic modulus by almost two times and its USS by almost three times. The thermal degradation of hydrogels was studied at 140 °C, and the experimental time was converted to the exposure time at 80 °C using Van’t Hoff’s rule. It was found that the nanocomposite with HCSIL200 retains its properties at a satisfactory level for 19 months. Filtration studies on water-saturated fractured reservoir models showed that the residual resistance factor and selectivity of the effect of nanocomposites with HCSIL200 on fractures are very high (226.4 and 91.6 for fracture with an opening of 0.05 cm and 11.0 for porous medium with a permeability of 332.3 mD). The selectivity of the isolating action on fractured intervals of the porous formation was noted. Full article

This study investigates the Chinese market’s physicochemical properties and sensory attributes of 14 original-cut potato chip brands. Color characteristics, compositional analysis, sugar content, acrylamide levels, and textural properties were examined alongside sensory evaluations. Significant variations were observed across all the parameters. Color analysis revealed diverse L*, a*, and b* values, with total color difference (ΔE) strongly correlating with sensory scores (r = 0.73, p < 0.01). A compositional analysis showed substantial differences in protein (5.19–8.51%), fat (27.91–40.16%), and moisture (0.67–3.78%) contents. Acrylamide levels varied widely (166.7–1101.78 mg/kg), positively correlating with the sucrose content (r = 0.57, p < 0.05). A textural analysis demonstrated significant variations in hardness (379.38–1103.6 gf) and fracturability (167.5–857.77 gf), with fracturability negatively correlating with sensory scores (r = −0.75, p < 0.01). A sensory evaluation revealed distinct brand preferences, with the total scores ranging from 65 to 85. This comprehensive analysis provides valuable insights into the complex interplay between the physicochemical properties and consumer perception of potato chips in the Chinese market and offers potential directions for product optimization and quality control in the snack food industry, inspiring hope and innovation among industry professionals. Full article

Coal pillars are loaded and unloaded repeatedly when mining, which lead to fractures in the coal close, open, generate and expand. As a result, the permeability of coal is changed. The high permeability fractures in coal and rock between the upper gobs and the lower working faces are the main channels for fresh air entering the upper gob, which could induce spontaneous combustion of coal in gob. To identifying the air leakage channels, multiple mining of closely coal seams was numerically conducted with three working face layouts. The failure and permeability characteristic of coal pillar in closely coal seams gob under multiple mining were obtained and analyzed. When the working faces are mined, the vertical stress and horizontal stress of the upper coal pillar in gob load and unload synchronously in all three working face layouts. The laterally directed horizontal stress could unload to zero due to no confine on the lateral side of coal pillar. The stress in the middle of upper coal pillar loads continuously until the lower working face is mined. When the lower coal seam working face is mined, the coal and rock between the upper and lower coal seams damage in shear and tension. When the lower coal seam working face is staggered from the upper coal seam working face, the permeability of the coal and rock pillar increases more than 22000 times due to tension damage of the coal and rock pillar. As a result, the coal and rock pillar is the main channel for fresh air flowing into the upper gob. The high permeability coal pillar provides favorable conditions for spontaneous combustion of coal in gob. Full article

Among 3D printing technologies, fused filament fabrication (FFF) is a fast, simple, and low-cost technology that is being explored in a variety of industries. FFF produces composites using thermoplastic filaments, limiting the applicability of welding. Therefore, mechanical fastening is required to join FFF composites with metals or dissimilar materials. The strength characteristics of fastened joints vary with fiber orientation, necessitating further research. Additionally, in the case of FFF, the strength trends may differ from those of traditional composites due to the voids and curved surfaces formed during the process. In this study, 3D-printed composite specimens with seven different fiber orientations were fabricated using the Markforged X7™ printer. The bearing strength and failure modes were analyzed as a function of fiber orientation. Unlike traditional composites, specimens with a ±15° fiber orientation exhibited a 7.56% higher bearing strength compared to those with a 0° orientation. However, the fracture energy of the ±15° specimens was 39.56% lower. Specimens with fiber orientations between 0° and ±45° primarily showed bearing failure modes, while those with orientations from ±60° to 90° exhibited net-tension failure modes. These results confirm that when using manufacturing methods like FFF, the strength trends vary with fiber orientation compared to traditional composites. Further research is necessary to optimize fiber orientation and improve structural performance. Full article

Background/Objectives: Early studies have suggested that the SARS-CoV-2 virus has a deleterious effect on bone mineral density and may increase the risk of pathological fractures. This study characterized vertebral compression fractures in patients with and without a prior diagnosis of COVID-19. Methods: Using a nationwide claims database, this retrospective study used ICD-10 billing codes to identify patients with a diagnosis of vertebral compression fracture from January 2020 to April 2022. Two cohorts were created based on whether the patients had a concurrent diagnosis of COVID-19. Patient demographics, comorbidities, and outcome measures were characterized by descriptive analysis. Results: In total, 413,425 patients met the inclusion criteria. Among them, a total of 23,148 patients (5.60%) had a diagnosis of COVID-19 at the time of their compression fracture. Among the COVID-19 patients, the incidences of vertebral compression fracture were 0.42% in 2020 and 0.33% in 2021, in comparison to the historical average yearly incidence of 0.17% across all patients. The patients with COVID-19 at the time of compression fracture diagnosis had a higher rate of vitamin D deficiency (OR: 1.25) and a lower rate of routine healing (OR: 0.61). The patients without COVID-19 were more likely to be osteoporotic (OR: 0.88), experience additional compression fractures (OR: 0.38), and have kyphoplasty or vertebroplasty (OR: 0.73). Conclusions: Despite lower rates of osteoporosis, patients with a concomitant COVID-19 diagnosis exhibited a higher incidence of compression fractures. Although more research is needed, these results support increasing bone health surveillance in patients with a history of COVID-19 infection. Full article

Background/Objectives: Malnutrition has been associated with increased morbidity and mortality in elderly patients diagnosed with heart failure (HF). However, nutritional problems are underdiagnosed in these patients. This study aimed to analyse malnutrition prevalence in elderly HF patients and its impact on survival. Methods: We conducted a retrospective observational study including patients aged ≥85 years diagnosed with HF followed up by a specific HF unit between 2015 and 2023. All patients underwent a nutritional assessment at the start of follow-up. Demographic characteristics, comorbidities, functional, cognitive and frailty status, heart disease characteristics and laboratory data, as well as admissions, emergency department visits and survival, were collected. The sample was categorised according to nutritional status into normonutrition and impaired nutritional status, and differences were evaluated. Results: Of a total of 413 patients, 52.8% were female, and the mean age was 88.4 ± 2.9 years. A total of 25.4% were at risk of malnutrition and 2.2% malnourished. Dementia [OR = 3.99, 95%CI (2.32–6.86); p < 0.001], hip fracture [OR = 3.54, 95%CI (1.75–7.16); p < 0.001)], worse Barthel index score [OR = 5.44, 95%CI (3.15–9.38); p < 0.001), worse Pfeiffer test [OR = 5.45; 95%CI (3.29–9.04); p < 0.001), worse Frail index [OR = 6.19; 95%CI (2.45–15.61); p < 0.001] and higher Charlson index [OR = 1.95; 95%CI (1.21–3.15); p = 0.006] were associated with worse nutritional status. In addition, patients with poor nutritional status lived 16.69 months less (p < 0.001) than normonutrited patients. Conclusions: At least one in four elderly patients with HF under outpatient follow-up has an impaired nutritional status. This is associated with hip fracture and greater functional and cognitive decline. Patients who are malnourished or at risk of malnutrition survive less than those who are not malnourished. Full article

The assessment of fatigue cracks is an elementary part of the design process of lightweight structures subject to operational loads. Although angled sheets are standard components in forming technology, fatigue crack growth in geometries like C- and L-sections has been little-studied and is mostly limited to crack growth before the transition through the corner. In this study, fatigue crack propagation is simulated to explore the influence of sheet thickness, corner angle and corner radius on the fatigue life in an L-section. The stress intensity factor (SIF) is derived as the driving force of crack growth over the full crack path. Special attention is paid to the evolution of the SIF in the radius sub-section and its implications on the fatigue life. The results show that the SIF in an angled sheet for given loading conditions and crack lengths cannot be readily approximated by the SIF in an equivalent straightened sheet. The bending angle and radius lead to crack growth retardation or acceleration effects. These findings are important for the design and optimization of forming geometries with regard to fatigue crack growth. Full article

Background/Objectives: Measuring the physical functioning of older hip fracture patients using wearables is desirable, with physical activity monitoring offering a promising approach. However, it is first important to assess physical activity in healthy older adults. This study quantifies physical functioning with physical activity parameters and assesses those parameters in community-dwelling older adults. The results are compared with the results from one case participant 2 months post-hip fracture surgery. Methods: Twenty-four community-dwelling older adults (aged ≥ 80) participated. The acts of moving around the house, toileting, getting in/out of bed, and preparing meals was quantified by total time, time spent sitting, standing, and walking, number of transfers, and intensity of physical activity. MOX and APDM sensors measured the intensity of physical activity, with the tasks performed in a living lab while video-recorded. The case participant’s total time and intensity of physical activity were measured for walking to a door and getting in/out of bed. Results: Preparing meals showed the longest total time and time spent standing/walking, while moving around the house and getting in/out of bed had the highest intensity of physical activity. Only getting in/out of bed required sitting. The physical activity parameters varied among participants, with very active participants completing tasks faster. The case participant had longer total times and lower intensities of physical activity two months post-surgery compared to before the fracture. Conclusions: This study provides initial insights into the physical activity levels of community-dwelling older adults. It represents the beginning of more efficient and continuous monitoring of physical functioning. Full article

Carbon-fiber-reinforced carbon and silicon carbide (C/C-SiC) composites were prepared using chemical vapor infiltration (CVI) combined with reactive melt infiltration (RMI). The microstructure and flexural properties of C/C-SiC composites after oxidation in different temperature water vapor environments were studied. The results indicate that the difficulty of oxidation in water vapor can be ranked from easy to difficult in the following order: carbon fiber (CF), pyrolytic carbon (PyC), and ceramic phase. The surface CFs become cone-shaped under corrosion. PyC has a slower oxidation rate and lower degree of oxidation compared to CF. The SiO₂ layer formed by the oxidation of SiC and residual Si was insufficient to fully cover the surface of CFs and PyC. As the temperature increased, the oxide film thickened, but the corrosion degree of CF and PyC intensified, and the flexural performance continuously deteriorated. The flexural strength of C/C-SiC composites was 271.86 MPa at room temperature. Their strength retention rates were all higher than 92.19% after water vapor corrosion at 1000 °C, still maintaining the “pseudoplastic” fracture characteristics. After water vapor corrosion at 1200 °C, the CFs inside the composites sustained more severe damage, with a strength retention rate as low as 48.75%. The fracture mode was also more inclined towards brittle fracture. Full article

The present study focuses on advancing one of the most popular AM techniques, namely, laser powder bed fusion (LPBF) technology, which has the ability to produce complex geometry parts with minimum material waste but continues to face challenges in minimizing the surface roughness. For this purpose, a novel hybrid manufacturing technology, which applies in a single setup (in-envelope) both LPBF technology and high-speed machining, was examined in this research for the fabrication of tensile specimens with three different surface finish conditions: as-built, hybrid (in-envelope machining) and post-machining (out-of-envelope) on Inconel^® alloy 718, hereafter referred to as IN718. As the application of the IN718 alloy in service is typically specified in the precipitation-hardened condition, three different heat treatments were applied to the tensile specimens based on the most promising thermal cycles identified previously for room-temperature tensile properties by the authors. The as-built (AB) specimens had the highest average surface roughness (R_a) of 5.1 μm ± 1.6 μm, which was a significant improvement (five-fold) on the hybrid (1.0 μm ± 0.2 μm) and post-machined (0.8 μm ± 0.5 μm) surfaces. The influence of this surface roughness on the mechanical properties was studied both at ambient temperature and at 650 °C, which is close to the maximum service temperature of this alloy. Regardless of the surface conditions, the room-temperature mechanical properties of the as-fabricated IN718 specimens were within the range of properties reported for standard wrought IN718 in the annealed condition. Nonetheless, detailed examination of the strain localization behavior during tensile testing using digital image correlation showed that the IN718 specimens with AB surfaces exhibited lower ductility (global and local) relative to the hybrid and post-machined ones, most likely due to the higher surface roughness and near-surface porosity in the former. At 650 °C, even though the mechanical properties of all the heat-treated IN718 specimens surpassed the minimum specifications for the wrought precipitation-hardened IN718, the AB surface condition showed up to 4% lower strength and 33–50% lower ductility compared with the hybrid and PM surface conditions. Microfocus X-ray computed tomography (µXCT) of the fractured specimens revealed the presence of numerous open cracks on the AB surface and a predisposition for the near-surface pores to accelerate rupture, leading to premature failure at lower strains. Full article

There are significant lithological and stress differences between continental shale layers, posing challenges for hydraulic fractures (HFs) to propagate through the formations, leading to weak fracture effects. To address this, this article adopts the finite element and cohesive force element methods to formulate a three-dimensional numerical model for hydraulic fracture (HF) propagation through layers, considering interlayer lithology and stress variations. The accuracy of the model was verified by physical experiments, and the one-factor analysis method was used to creatively reveal the complex mechanism of the effect of geological and engineering variables on the diffusion of HFs in continental shale reservoirs. The results show that high interlayer stress difference, high interlayer tensile strength difference, low interlayer Young’s modulus difference and large interlayer thickness are not conducive to the penetration of HFs, but increasing the injection rate and the viscosity of fracturing fluid can effectively improve the penetration of HFs. The influence ranking of each factor was determined using the grey relational degree analysis method: interlayer stress difference > interlayer Young’s modulus difference > interlayer tensile strength difference > interlayer thickness > injection rate > fracturing fluid viscosity. Full article

Rubber is widely used in situations involving cyclic loads, and the influence of temperature on rubber properties is particularly pronounced under cyclic loading. In this study, mechanical property tests and crack propagation tests of carbon black-filled hydrogenated nitrile butadiene rubber were conducted at four different operating temperatures. Based on the results of the crack propagation tests, the temperature-dependent characteristics of the Paris–Erdogan parameters and strain energy density were clarified. The Paris–Erdogan parameters were successfully expressed as a function of temperature. The strain energy density, on the other hand, exhibited the property of being strongly influenced by factors of strain, loading frequency, and others, while the temperature dependence was weak. On this basis, the unified fatigue crack growth kinetic model was constructed at multiple temperatures. The model results can match the experimental data well, particularly at temperatures of 60 °C and 80 °C. Finally, the fatigue life prediction model at different temperatures was constructed by combining the fatigue life test results. The results indicate a correlation between crack propagation characteristics and fatigue life predictions across different operating temperatures, with the predictions agreeing well with the measured life. The models can be used to analyze early fracture behavior or fatigue life prediction of rubber at different operating temperatures and minimize the need for extensive product testing prior to the manufacture of rubber products. Full article

Background/Objectives: Acute isolated distal radioulnar joint (DRUJ) dislocations are rare and often misdiagnosed during initial evaluation due to subtle clinical presentation, low index of suspicion, and imaging barriers. Prompt diagnosis and treatment are critical to avoid chronic instability, limited wrist mobility, and osteoarthritis. This systematic review evaluates the functional outcomes of conservative and surgical treatment protocols for acute isolated DRUJ dislocations. Methods: A systematic search of PubMed, Scopus, and Mendeley databases (2000–2024) was conducted following PRISMA guidelines. Inclusion criteria involved adult patients with isolated DRUJ dislocations diagnosed and managed within one week of injury. Studies reporting on underage patients, associated fractures, delayed management, and open injuries were excluded. Data on demographics, injury mechanism, diagnostic methods, treatment protocols, and functional outcomes were extracted and analyzed. Results: In total, 22 cases across 20 studies were included. The majority (90.9%) were males, with a mean age of 37.9 years (range: 20–70 years). Falls and sports injuries were the major causes, with volar dislocations predominating (18/22). The misdiagnosis rate was equal to 18%. Most cases were treated conservatively with closed reduction and immobilization for an average of 4.9 weeks. Operative treatment was performed in 6 cases, mainly following failed closed reductions. Functional outcomes were generally favorable, although the same parameters were not consistently studied in all patients. Overall, 82% (14 of 17 patients) achieved a full range of motion; 88% (14 of 16 patients) reported no pain, and all assessed cases had stable DRUJs at follow-up. Conclusions: This review highlights the rarity and diagnostic challenges of this injury. The functional outcomes of both conservative and operative treatment are generally satisfactory. Conservative treatment should be the first-line approach, with surgery reserved for irreducible or unstable cases. Future research using standardized outcome measures is needed to provide guidance for clinicians. Full article