Search Results (280)

This study delves into the delamination-driven nonlinear buckling characteristics of metal–composite cylindrical shells with different interfacial strengths. Although surface treatments are known to affect bonding performance, their specific influences on the delamination buckling behavior of metal–composite cylindrical shells remain underexplored. Accordingly, sandblasting and polishing processes were employed to the fabrication of single-lap shear specimens. The topography of the treated surface was then characterized through scanning electron microscopy, optical profilometry, and contact angle measurements. For topography characterization and performance tests, sandblasted and polished metal–composite cylindrical shells were fabricated for hydrostatic tests. A cohesive zone model was used to analyze the influences of interfacial strength on the nonlinear buckling characteristics of metal–composite cylindrical shells, and the modeling results were validated by benchmarking them with experimental results. Subsequently, a detailed parametric study was conducted to investigate the effects of cohesive zone parameters and geometric imperfection on the load-bearing capacity of the shells. The new findings reveal that among the fabricated steel specimens, the specimens subjected to 80-mesh sandblasting exhibited the highest bond strength in single-lap shear tests, with the bond strength being 2.56 times higher than that of polished specimens. Moreover, sandblasted metal–composite cylindrical shells exhibited a 55.0% higher average collapse load than that of polished metal–composite cylindrical shells. Full article

The miniaturization of heat exchangers requires advanced manufacturing methods, as conventional techniques such as milling or casting are insufficient for producing complex microscale geometries. This study investigates the feasibility of using selective laser melting (SLM) with 316L stainless steel powder to fabricate compact heat exchangers with minichannels. The exchanger was designed using Autodesk Inventor 2023.3 software and produced under optimized process parameters. Measurements using a hydrostatic balance demonstrated that the applied process parameters resulted in a relative material density of 99.5%. The average microhardness in the core region of the SLM-fabricated samples was 255 HV, and the chemical composition of the final material differed only slightly from that of the feedstock material (stainless steel powder). Dimensional accuracy, surface quality, and internal structure integrity were assessed using computed tomography, optical microscopy, and contact profilometry. The fabricated component demonstrated high geometric fidelity and channel permeability, with local surface deformations associated with the absence of support structures. The average surface roughness (Ra) of the minichannels was 11.11 ± 1.63 µm. The results confirm that SLM technology enables the production of functionally viable heat exchangers with complex geometries. However, limitations remain regarding dimensional accuracy, powder removal, and surface roughness. These findings highlight the potential of metal additive manufacturing for heat transfer applications while emphasizing the need for further research on performance testing under real operating conditions, especially involving two-phase flow. Full article

Iberian ham is a valuable product worldwide. At present, this product is mostly distributed and packaged in sliced form, which can result in loss of quality and safety. Moreover, non-biodegradable packaging exacerbates environmental problems. In this study, the application of active packaging based on a chitosan gel-like film and rice bran extract was investigated for the preservation of sliced Iberian ham. For this purpose, the packaging effectiveness on its own and in combination with high hydrostatic pressures was tested in comparison with untreated samples in refrigerated storage. The results showed that the active packaging used can maintain the reddish colour of sliced dry-cured Iberian ham, whereas browning took place in the control samples. Similarly, lipid oxidation of the product slowed, whereas protein oxidation was not affected by the packaging. This treatment also significantly reduces the number of microorganisms during storage. Full article

Hydrodynamic slamming loads during water landing are one of the main concerns for the structural design and wave resistance performance of large amphibious aircraft. However, current existing sensors are not used for full-scale hydrodynamic load flight tests on complex models due to their large size, fragility, intrusiveness, limited range, frequency response limitations, accuracy issues, and low sampling frequency. Fibre-optic sensors’ small size, immunity to electromagnetic interference, and reduced susceptibility to environmental disturbances have led to their progressive development in maritime and aeronautic fields. This research proposes a novel hydrodynamic profile encapsulation method using ultra-thin surface-mounted micro-electromechanical system (MEMS) fibre-optic Fabry–Pérot pressure sensors (total thickness of 1 mm). The proposed sensor exhibits an exceptional linear response and low-temperature sensitivity in hydrostatic calibration tests and shows superior response and detection accuracy in water-entry tests of wedge-shaped bodies. This work exhibits significant potential for the in situ monitoring of hydrodynamic loads during water landing, contributing to the research of large amphibious aircraft. Furthermore, this research demonstrates, for the first time, the proposed surface-mounted pressure sensor in conjunction with a high-speed acquisition system for the in situ monitoring of hydrodynamic pressure on the hull of a large amphibious prototype. Following flight tests, the sensors remained intact throughout multiple high-speed hydrodynamic taxiing events and 12 full water landings, successfully acquiring the complete dataset. The flight test results show that this proposed pressure sensor exhibits superior robustness in extreme environments compared to traditional invasive electrical sensors and can be used for full-scale hydrodynamic load flight tests. Full article

The force conditions experienced by spacecraft and astronauts in space are vastly different from those in Earth’s gravitational environment, hence it is necessary to conduct adequate micro-low-gravity environment simulation tests on the ground before launch. In this paper, an overview is provided of the current status of micro-low-gravity simulation test technology for spacecraft based on hydrostatic air-bearing. The paper systematically organizes the application of hydrostatic air-bearing technology in micro-low-gravity simulation tests, such as the deployment of space mechanisms, spacecraft GNC (Guidance, Navigation, and Control), on-orbit operations of space manipulators, and astronaut training. It summarizes the principles of air-flotation micro-low-gravity simulation technology in different scenarios and distills suitable solutions for various requirements. Finally, the paper looks forward to the development trends of air-flotation micro-low-gravity simulation test technology and proposes key technical challenges that need to be overcome in aerostatic bearing. Full article

This study proposes a novel unified constitutive model that systematically integrates the microstructure evolution and macroscopic stress–strain response during the hot deformation of a Ni-based superalloy. The proposed model incorporates a suite of microstructural variables, including damage fraction, recrystallization fraction, δ phase content, average grain size, and dislocation density. Furthermore, the model explicitly considers critical macroscopic stress state parameters, specifically the magnitude and orientation of maximum principal stress, hydrostatic stress component, and Mises equivalent stress. A comparative analysis of rheological curves derived from uniaxial tension and compression experiments reveals that the prediction errors of the proposed model are less than 3%. The model is subsequently implemented to investigate the evolution characteristics of the damage accumulation fraction and δ phase content under varying stress directions and initial δ phase contents. An advanced computational framework integrating the finite element method with the proposed constitutive model is established through customized subroutines. The framework exhibits exceptional predictive accuracy across critical regions of disk forging, as evidenced by a close agreement between computational and experimental results. Specifically, the relative errors for predicting recrystallization fraction and average grain size remain consistently below 8% under varying stress–strain conditions. Testing results from four representative regions demonstrate a good alignment of high-temperature tensile properties with the macroscopic stress–strain distributions and microstructure characteristics, thereby confirming the model’s reliability in simulating and optimizing the forging process. Full article

Composite pressure vessels offer significant advantages over traditional metal-lined designs due to their high strength-to-weight ratio, corrosion resistance, and design flexibility. This study investigates the structural design, winding process, finite element analysis, and experimental validation of a glass fiber-reinforced composite low-pressure vessel. A high-density polyethylene (HDPE) liner was designed with a nominal thickness of 1.5 mm and manufactured via blow molding. The optimal blow-up ratio was determined as 2:1, yielding a wall thickness distribution between 1.39 mm and 2.00 mm under a forming pressure of 6 bar. The filament winding process was simulated using CADWIND software (version 10.2), resulting in a three-layer winding scheme consisting of two helical layers (19.38° winding angle) and one hoop layer (89.14°). The calculated thickness of the composite winding layer was 0.375 mm, and the coverage rate reached 107%. Finite element analysis, conducted using Abaqus, revealed that stress concentrations occurred at the knuckle region connecting the dome and the cylindrical body. The vessel was predicted to fail at an internal pressure of 5.00 MPa, primarily due to fiber breakage initiated at the polar transition. Experimental hydrostatic burst tests validated the simulation, with the vessel exhibiting failure at an average pressure of 5.06 MPa, resulting in an error margin of only 1.2%. Comparative tests on vessels without adhesive sealing at the head showed early failure at 2.46 MPa, highlighting the importance of head sealing on vessel integrity. Scanning electron microscopy (SEM) analysis confirmed strong fiber–matrix adhesion and ductile fracture characteristics. The close agreement between the simulation and experimental results demonstrates the reliability of the proposed design methodology and validates the use of CADWIND and FEA in predicting the structural performance of composite pressure vessels. Full article

Carbon fiber-reinforced composites are widely used in the aerospace industry due to their exceptional mechanical properties. However, the dome region of composite pressure vessels is prone to stress concentrations under internal pressure, often resulting in premature failure and reduced burst strength. This study developed a finite element model of a reinforced dome structure, which showed excellent agreement with hydrostatic test results, with less than 5.9% deviation in strain measurements. To optimize key reinforcement parameters, a high-accuracy surrogate model based on a backpropagation neural network was integrated with a multi-objective genetic algorithm. The results indicate that compared to the unreinforced dome, the optimized structure reduced the maximum fiber-aligned stress in the dome region by 6.8%; moreover, it achieved a 9.3% reduction in overall mass compared to the unoptimized reinforced configuration. These findings contribute to the structural optimization of composite pressure vessel domes. Full article

Slope failures in overconsolidated hard clays present significant geotechnical challenges, particularly in stratified formations prone to pre-existing discontinuities. Despite extensive research on residual shear strength and fissuring in stiff clays, the role of undetected tension cracks and their interaction with hydrogeological conditions in temporary excavations remains underexplored. This study addresses this research gap through a detailed case study of a slope failure during an unsupported residential excavation on Corfu Island, Greece. The investigation aimed to identify the failure mechanism, assess the influence of geological discontinuities and groundwater conditions, and evaluate the contribution of residual shear strength to slope stability. The methodology combined field observations, laboratory testing (including unconfined compression and ring shear tests), and numerical modelling using both finite element (FEM) and limit equilibrium (LEM) approaches. The results revealed that a nearly vertical, pre-existing fissure—acting as a tension crack—and water infiltration along the clay–sandstone interface significantly reduced the factor of safety, triggering a planar slide. Both FEM and LEM analyses indicated that critical conditions for failure were reached with a residual friction angle of 19°, inclined sandstone layers at 15–17°, and hydrostatic pressure from groundwater accumulation. This study demonstrates the compounded destabilizing effects of undetected discontinuities and water pressures in stratified hard clays and underscores the necessity of comprehensive geotechnical assessments for temporary excavations, even in seemingly stable formations. Full article

This paper investigates a polymer composite and carbon fiber impregnated with epoxy resin for the fabrication of a lightweight and high-strength composite casing for rocket propulsion systems. It describes the winding technology which uses a removable mandrel and angular winding at ±55° and ±20° to expand the stress distribution, as well as alternating angles of ±45° and 80° to improve resistance to tensile and torsional loads. A fixture has been developed that ensures ease of disassembly and good strength of the final products. Hydrostatic tests showed the operational stability of the casings under internal pressure up to 10 MPa for a 1.5 mm-thick casing and 18 MPa for a 3 mm-thick casing, which confirms the effectiveness of the proposed technology. The research results demonstrate the high reliability and potential exploitation of composite materials. Full article

Environmentally friendly biopolymer nanofibrous composite membranes with enhanced mechanical properties and thermal stability were fabricated via electrospinning with different compositions of polylactic acid (PLA) and cellulose acetate (CA). Firstly, PLA and CA composite membranes were prepared and optimized. Then, the optimized membranes were annealed at temperatures ranging from 80 °C to 140 °C, for annealing times between 30 and 90 min. The developed membranes were characterized by FE-SEM, XRD, FR-IT, TGA, DSC, tensile testing, water contact angle, and resistance to hydrostatic pressure. PLA 95-CA 5 was the optimum composite, with a tensile strength 9.3 MPa, an average fiber diameter of 432 nm, a water contact angle of 135.7°, and resistance to a hydrostatic pressure of 16.5 KPa. Annealing resulted in further improvements in different properties. The annealed membranes had thermally stable microporous structures, without shrinkage or deterioration in nanofiber structure, even at an annealing time of 90 min and an annealing temperature of 140 °C. By increasing either the annealing time or temperature, the crystallinity and rigidity of the nanofiber composite membranes were increased. The annealed membrane demonstrated a tensile strength of 12.3 MPa, a water contact angle of 139.2°, and resistance to a hydrostatic pressure of 36 KPa. Electrospinning of PLA-CA composite membranes with enhanced mechanical properties and thermal stability will pave the way for employing PLA-based membranes in various applications. Full article

This article presents the results of a study focused on enhancing the permeability resistance of roadways using polyformaldehyde fiber-reinforced concrete. The uniqueness of this study is its interest in polyformaldehyde fiber, which has not been widely studied in underground mining roadways, especially in relation to its impact on permeability resistance. The permeability resistance of polyformaldehyde fiber-reinforced concrete with different lengths (30 mm, 36 mm, 42 mm) and dosages (5 kg/m³, 7 kg/m³, 9 kg/m³) was tested by the step pressure method and seepage height method. The hydrostatic pressure and seepage height of polyformaldehyde fiber-reinforced concrete were analyzed, and the best polyformaldehyde fiber-reinforced concrete with the best permeability resistance was selected to carry out numerical simulation based on a phosphate mine in Yunnan Province. The changes in the pore water pressure, maximum principal stress, and displacement of the roadway’s surrounding rock under the influence of groundwater seepage were analyzed. The results show that the addition of polyformaldehyde fiber can effectively improve the impermeability of concrete. With the increase in length and dosage, the impermeability of the polyformaldehyde fiber concrete increases first and then decreases. Under ordinary support conditions, the surrounding rock of the roadway is affected by the seepage of groundwater over time, which leads to the roadway strength’s decline and creep deformation, necessitating the strengthening of the roadway’s anti-drainage measures. Under conditions of reinforcement with polyformaldehyde fiber concrete, the displacement of the top of the roadway obviously reduces, which can effectively improve the permeability resistance and stability of the roadway. Full article

Geometric and mechanical analyses were performed on 82 selenium-rich eggs, which underwent hydrostatic testing as 2 raw eggs, 60 steamed eggs, and 20 emptied eggshells. By analyzing the geometric and mechanical properties of the egg, we can draw inspiration from its structural design to create a pressure shell capable of effectively withstanding the immense water pressure in deep-sea environments. The major axis, minor axis, egg-shape coefficient, weight, thickness, volume, superficial area, and ultimate compressive strength were measured, and their correlations were analyzed. The thickness, egg-shape coefficient, and ultimate compressive strength were normally distributed, and many parameters were strongly correlated. Moreover, finite element analysis was conducted to evaluate the compressive resistance of egg-like pressure shells made from different materials, including metal, ceramic, resin, and selenium-enriched eggshell materials. The performance ratio of the ceramic shells was 2.6 times higher than that of eggshells, and eggshells outperformed metal and resin shells by factors of 2.14 and 4.49, respectively. The eggshells had excellent compression resistance. These findings offer novel insights into the design and optimization of egg-like pressure shells. Full article

By monitoring the solidification of droplets of plant latices with a fast quartz crystal microbalance with dissipation monitoring (QCM-D), droplets from Campanula glomerata were found to solidify much faster than droplets from Euphorbia characias and also faster than droplets from all technical latices tested. A similar conclusion was drawn from optical videos, where the plants were injured and the milky fluid was stretched (sometimes forming fibers) after the cut. Rapid solidification cannot be explained with physical drying because physical drying is transport-limited and therefore is inherently slow. It can, however, be explained with coagulation being triggered by a sudden decrease in hydrostatic pressure. A mechanism based on a pressure drop is corroborated by optical videos of both plants being injured under water. While the liquid exuded by E. characias keeps streaming away, the liquid exuded by C. glomerata quickly forms a plug even under water. Presumably, the pressure drop causes an influx of serum into the laticifers. The serum, in turn, triggers a transition from a liquid–liquid phase separated state (an LLPS state) of a resin and hardener to a single-phase state. QCM measurements, optical videos, and cryo-SEM images suggest that LLPS plays a role in the solidification of C. glomerata. Full article

Reinforced concrete (RC) tanks are essential for storing liquids and bulk materials across various industries. However, simplified analytical methods fall short in providing an accurate analysis, while traditional methods, such as finite element modeling, can be computationally intensive and time-consuming, especially when dealing with nonlinear material properties and complex geometries, like conical and cylindrical shapes. This highlights the need for a more efficient and simplified analysis approach. Accordingly, the present paper introduces a machine learning (ML) framework as an effective predictive tool for RC conical and cylindrical tanks under hydrostatic pressure. Data from 320 RC conical and cylindrical water tanks, previously analyzed using finite element modeling, were used to train and test various ML models, considering geometrical and material nonlinearities. Four machine learning models—decision trees, random forests, gradient boosting, and extreme gradient boosting—were utilized to predict critical internal forces, including the maximum ring tension force, maximum meridional moment, and maximum meridional axial force. The accuracy of each model was evaluated using different statistical measures. To improve model interpretability and identify key predictors, feature importance techniques were employed to rank the significance of each input variable to the predictions. Furthermore, Accumulated Local Effects (ALE) plots were utilized to visualize the relationships between model inputs and outputs, providing a clearer understanding of the inner workings of the ML models. The combined use of feature importance and ALE plots enhances model transparency by illustrating how specific features contribute to the predictions, thereby supporting the informed application of ML in the structural design and analysis of RC tanks. Ultimately, the framework presented in this study aims to promote the practical application of machine learning in structural engineering, contributing to simpler, more efficient, and accurate analysis and design processes for RC water tanks. Full article