查看更多>>摘要：? 2022The river water has a high sand content and the characteristics of mixed distribution of sand particles with different diameters. The effect of sand particles on the dynamic characteristics and wear of centrifugal pumps is an important issue when handling particulate slurry. The objective of this work is to establish the effect of flow rate and sand volume concentration variation on pump energy performance, outlet pressure pulsation, pump body vibration, and pump impeller wear. Experiments were conducted in a pilot plant test rig with five flow rates and three particle concentrations based on multi-size particulate slurry. It was observed that the head and efficiency of the centrifugal pump decrease with the increase of sand concentration, whereas the effect of small sand concentration on the energy performance of the pump is weak. The larger the flow rate of centrifugal pump, the lower the pressure pulsation and vibration intensity of pump body, but the more serious the impeller wear. When the sediment concentration increases, the pressure pulsation at the pump outlet and the vibration intensity of the pump body increase, and the impeller wear is more serious. In addition, with the increase of pump operation time, the outlet of blade pressure surface, the middle area of blade suction surface and the outlet area of impeller back shroud passage are seriously worn, and the outlet of blade pressure surface is the most serious.
查看更多>>摘要：? 2022 Elsevier LtdTunnels are unavoidably constructed in layered rock masses, and tunnel collapses are often associated with such layering. Two violent collapses at the Yangshan tunnel were analysed in this study to investigate the mechanism of tunnel collapse in a soft-hard interbedded surrounding rock mass. The in situ stress field was obtained by combining hydraulic fracturing tests and multiple regression analysis. The first collapse occurred in the area where extremely high in situ stress and high in situ stress transformed. The extremely high in situ stress state during construction had not received timely attention, and the support measure under the condition of a high-grade surrounding rock mass was still used. Insufficient support strength was the primary cause of the first collapse. The excavation process of the Yangshan tunnel was simulated by a numerical method. The surrounding rock mass of the second collapse, interbedded with soft mudstone and hard sandstone, was dominated by tensile stress. The soft mudstone could not resist the large tensile stress, and the displacement of the tunnel vault increased sharply. Microseismic monitoring was used to highlight the dangerous areas and the types of rock mass failure during the excavation. The microseismic monitoring results were consistent with the numerical simulation results, which were used to describe the mechanism of the second collapse of the Yangshan tunnel. The excavation of a soft-hard interbedded rock mass would lead to tensile stress in the tunnel vault. If the soft rock layer was located in the tunnel vault, tensile failure of the rock mass would occur due to its lower strength.
查看更多>>摘要：? 2022This research investigates the aging resistance of a silicone product exposed to highly alkaline conditions. A silicone membrane was immersed in a pH 13.5 solution and aged up to 30 days at four temperatures between 40 °C and 70 °C. The effects of alkaline aging on morphology, mechanical properties, thermal properties and surface chemistry of the alkaline-exposed silicone membranes were scrutinized by various techniques. On alkaline solution aging, both surface and bulk morphology and chemical structure were found to evolve as the silicone membrane experienced toughness deterioration. After failure criteria were established based on practical considerations, the service life of the silicone product was estimated using the Dakin-Arrhenius model, which provided for a cross-linking activation energy of 60 kJ/mol. The calculated service life of over one year for silicone membranes revealed alkaline immersion provides significant aging acceleration, although prediction of silicone performance in contact with concrete in field situations requires further investigation.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, the seismic vulnerability appraisement, together with repairing and consolidation operations, of a masonry building with cultural and artistic value located in a small city near Naples are reported and discussed. After a brief digression about the condition of historical and cultural Italian heritage damaged by seismic events and usually in poor condition due to a lack of maintenance, the case study is presented and described, providing not only historical news but also information about as-built status, spaces, functions and structural issues. Once the principal failure modes affecting the building are identified, the estimation of seismic vulnerability is performed through three different evaluation levels given by the Italian Guidelines on Cultural Heritage. The analysis results, compared to each other, have shown the problems and the high vulnerability degree of the building. Finally, according to the Italian Guidelines, the consolidation and upgrading interventions are proposed and described to ensure a safety use of the Masseria under seismic actions.
查看更多>>摘要：? 2022 Elsevier LtdThe role of pouch battery configurations in structural integrity under bending loads was investigated using finite elements and compared with experiments. Three-point bending tests were firstly conducted for different pouch battery configurations to obtain force–displacement curves. A finite element model of the pouch battery under the three-point bending was then simulated employing a homogenization technique to reduce the simulation cost and time consumption significantly. Force-displacement curves from the simulation results were extracted and validated by the curve obtained from the bending tests. The validation allowed detailed analysis of stress distribution and deformation inside the pouch battery model. Regions in which short circuits might occur were then identified. The role of folded configuration and pouch casing to resist flexural damage was confirmed by structural strength improvement of 14 and 30 times, respectively. These results may be used for design consideration on safer pouch batteries.
查看更多>>摘要：? 2022 Elsevier LtdShale gas produced from wells contains free water, solid particles, and other corrosive substances, so shale gas production lines are at high risk of failure. The bending pipe of gas production in Shunan Gas Mine failed during service. In order to find out the causes of the failure of the bends and to provide technical support for the safe transmission of shale gas, Tensile testing machine, Vickers hardness tester, Charpy notch impact testing machine and metallographic microscope were used to test the mechanical properties and metallographic structure of the pipe sample material. The corrosion by- products were analyzed by scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer. Finally, the Computational Fluid Dynamics (CFD) is used to simulate the erosion behavior of the curved pipe under different working conditions. The results show that the chemical composition, tensile strength, yield strength, hardness, impact performance and grain size grading of the gas bending pipe meet the relevant requirements. The corrosion by-product was identified as FeCO3 by the microstructure characterization analysis, energy spectrum analysis and XRD. The corrosion by CO2 was the main cause for perforation and pitting pits. CFD simulation results show that sand gas has obvious erosion phenomenon on the pipe wall, and with the increase of flow rate, the erosion rate of sand and gravel on the pipe sample increases, and the larger the particle size, the higher the erosion rate of sand and gravel on pipe sample. Combined with the erosion and corrosion results, it is concluded that the erosion of sand-bearing gas makes the inner wall material of the elbow fall off, accelerates the corrosion of CO2 on the pipe wall, and finally leads to the failure of the gas production elbow.
查看更多>>摘要：? 2022 Elsevier LtdFatigue testing has been conducted on welds of AA2024 (Al4.5Cu1.4 Mg0.5Mn) alloy to Ti6Al4V alloy made using friction stir lap welding (FSLW). During FSLW, pin bottom aimed for touching the Ti6Al4V plate (dPin≈0), although it could readily penetrate (dPin > 0). It has been found that fatigue limit of the AA2024/Ti6Al4V welds was slightly higher than the fatigue limits of the FSL Al-to-Al alloy welds reported in literature. Examination has demonstrated that forming a very thin interface layer during FSLW was the major mechanism responsible for the good fatigue strength. The diffusion weld distance outside the pin width in dPin > 0 welds was significantly larger than that in dPin≈0 welds. Thus, the fatigue limit of dPin > 0 welds was comparable to the fatigue limit of dPin≈0 welds despite of the mix stir zone (MSZ) in dPin > 0 welds being a brittle one. The different thermomechanical conditions for the different diffusion-weld widths will be illustrated.
查看更多>>摘要：? 2022 Elsevier LtdThe shipping industry is becoming equipped with the innovative devices day by day. It is important to monitor all the devices on the ship and to store this data. It is foreseen that IoT technology will be widely used in the near future in ships that are considered to be a factory. In this study, the ship of 4310 Gross Tonnage, Oil/Chemical Tanker's 5435 HP diesel engine was investigated. The thermal, vibration and current data of the 7.5 kW 3-phase induction motor in the cooling pump used for the cooling system of this ship's main engine were analysed. These data were received with IoT sensors and transferred to the web interface. Monitoring of these data is provided by Node-RED, which is cost-effective and can easily process the information received from IoT devices. The system in this study consists of an architecture that receives instantaneous data from sensors, transfers them to the internet via electronic circuit, and transfers them to users via the dashboard and stores these data on MySQL. A system that observes errors of the cooling pump of ship's main engine by analysing these real time data and gives warning before failure occurs is designed.
查看更多>>摘要：? 2022 Elsevier LtdHigh-speed railway axle is the critical safety component of modern ground vehicles, which experiences extremely complex environments. In this paper, the effect of corrosion on the fatigue behavior of EA4T axle steel was investigated in an artificial rainwater environment. Combining scanning electron microscopy (SEM) and synchrotron radiation X-ray micro computed microtomography (SR-μCT) with theoretical analysis, damage measurement enabled a full evolution characterization of the corrosion process for exploring the corrosion mechanism and its influence on the fatigue life. It is found that the corrosive environment significantly reduced fatigue strength and facilitated multiple crack initiation, while showed relatively little effect on the long fatigue crack growth. The fitness of the 3-P Weibull distribution was slightly higher than that of the Gumbel distribution in terms of crack population. The life prediction model incorporating the pit growth, short crack, and long crack stages showed a good agreement within the 95% and 5% probabilistic S-N curve.
查看更多>>摘要：? 2022 Elsevier LtdMultiple cases of failure in the primary suspension system of LHB coaches were reported in specific light-weight passenger coaches recently. Frequent failure in suspension systems led to increased downtime and maintenance costs. Failure was associated to fatigue in primary helical springs and was found to be preceded by failure of hydraulic dampers. We present a study on analysis of these failures and suggest design modifications for enhancing fatigue life. A flexible finite element model of the bogie, with suspension system involving flexible helical springs, is developed and simulated for typical load and vehicle speed parameters. Conditions of damper failure are incorporated and the exact location of failure and the observed fatigue life of spring are validated. Loading on the bogie involves tare weight and rail-wheel contact forces. Rail-wheel contact forces are computed through multibody dynamic model for typical track irregularity data. Linear static analysis is done to obtain stresses under steady loads. This is followed by pre-stressed modal analysis and harmonic response simulation of the flexible model of the bogie. Fatigue life computation under combined static and alternating load conditions is done by employing the Modified Goodman diagram. Iterative modifications in design of the primary suspension springs are carried out. Minimal changes, which do not require change in the designs of associated components or change in the manufacturing set-up, are suggested. Modifications are validated through comparative fatigue life estimation.
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