查看更多>>摘要：? 2022 Elsevier LtdIt is required that the hydraulic pipe in the landing gear cabin must withstand the impact of a strong blast wave to maintain airworthiness. The article presents the results of analyzing the dynamic behaviors of hydraulic pipes subjected to the blast pressure of aircraft tire blowout. Considering various inflation pressures and blast modes, the distributions of equivalent stresses and deformations in space and time domains under transient jet were discussed using the finite element method. This paper also compared the variations of normal displacements along the axis direction of a hydraulic pipe with two blast modes, and the differences between them were discussed. Moreover, the equivalent static pressure was applied to the pipe model for numerical analysis. Relevant research results showed that it was not sufficient to use equivalent static pressure for safety assessment. Numerical analysis in the present study indicates that the hydraulic pipe will bear extremely severe impact by high-speed jet released in a tire blowout. Both inflation pressure and blast mode are the key factors that can significantly influence the dynamic responses of hydraulic pipes. According to the analysis results, it was found that the failure of the hydraulic pipe will probably appear in the areas near the two ends of the pipe. The conclusions acquired can provide important references for the future design of a hydraulic pipe in the landing gear cabin.
查看更多>>摘要：? 2022 The Author(s)Following a shaft failure or loss of load in a gas turbine engine, the turbine overspeeds due to the continuing expansion through the stage(s). The overspeed may result in hazardous conditions which have to be prevented. Several mitigation methods include the control system's response by shutting the fuel flow, mechanical friction to reduce turbine acceleration, and blade release at a predetermined rotational speed. The release of the blades not only terminates the gas torque which accelerates the disk, but also increases the disk burst speed at reduced centrifugal load. In this manuscript, a design space exploration is presented to avoid disk burst by blade-off in a civil large turbofan engine through a parametric design of blade firtree and disk post system. The firtree design parameters used in the study are the contact angle between the blade firtree and the disk post, firtree bottom flank angle, firtree flank length and firtree thickness with respect to the disk post. The LS-DYNA finite element software was used in the simulations to generate possible failure scenarios. These were ‘disk burst’ and ‘blade-off’. Blade-off conditions manifested in two ways as a function of design parameters. The first type was blade release from serrations without disk post failure, and the second type was blade escape with disk post failure. Following the design space exploration, the effect of several design and material parameters on the design space was investigated. These parameters are; the contact friction coefficient between the blade firtree and disk post, firtree serration number, and the strain hardening behavior of the material.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, a three-stage model of the corrosion-fatigue life prediction of reinforced concrete square piles in marine environments is established. First, a two-dimensional diffusion equation of chloride ions is presented. A simplified corrosion pit model is given to estimate the pit nucleation time. Second, according to the principle of competition between the growth rate of corrosion pits and the growth rate of cracks, a rate competition model is proposed. Third, a crack growth model is established based on the Paris-Erdogan equation. Finally, an example is illustrated to verify the validity of the model, and a parametric analysis of the main influencing factors is conducted. The analysis results show that the corrosion-fatigue life decreases with increasing surface chloride concentration, chloride diffusion coefficient, concrete compressive strength, reinforcement stress range, reinforcement diameter and cyclic load frequency. The corrosion-fatigue life increases as the critical chloride concentration and concrete protective layer thickness increase.
查看更多>>摘要：? 2022Cartridge brass, because of its high ductility and formability, is used for the development of different ammunition components, plumbing accessories, fasteners, radiator cones etc. A series of cupping, annealing, deep-drawing, tapering and washing operations on the as-received brass disc are generally required for fabrication of different ammunition components. A 130 mm shell made up of cartridge brass was reported to crack during firing. These cracks led to shell expansion, which was stuck in the cannon and caused clogging. Failure analysis of brass shell was carried out. Overall composition of the brass shell was in accordance with 70/30 brass. Microstructural and mechanical characterization of the failed brass shell revealed presence of elongated grains, mechanical twins, relatively higher strength and lower ductility, which pointed out towards the possibility of insufficient annealing times. On the other hand, discoloration of the crack surface, porous and zinc depleted microstructure near cracks and transgranular mode of failure without multiple branching revealed that the brass shell suffered from plug type dezincification. Reduced strength of the studied brass shell due to dezincification helped in crack initiation whereas reduced ductility due to insufficient annealing time facilitated crack propagation. Use of alloys which are more resistant to dezincification as a starting material and optimization of annealing times to obtain desired levels of ductility, were recommended as corrective measures.
查看更多>>摘要：? 2022 Elsevier LtdThis paper investigates fatigue failure transition boundary of Load-carrying Cruciform Weld Joint (LCWJ) with different yield strength mismatch ratios and geometrical sizes of welded joints under cyclic loading conditions using a semi-empirical analytical method, which is based on the obtained fatigue test data and finite element analysis. To examine the fatigue failure mode transition relationship in CLWJs, different mismatch ratios and local geometries (plate thickness, weld size, and penetration ratio) were designed and fabricated to evaluate potential fatigue initiations (weld toe or weld root). The numerical simulations of cyclic responses at weld toe and weld root were conducted by material cyclic plastic properties from fatigue data of standard coupon specimens. A uniform effective notch energy indicator in the previous investigation was utilized to characterize the low and high cycle fatigue life by extending the SED method on the combination of generalized Neuber concept of Fictitious Notch Rounding (FNR). The related analytical formulations for potential failure points were used to predict the fatigue assessment indicator of LCWJ, considering the effects of plasticity and mechanical heterogeneity and geometry configurations. The effective notch energy relationship between the weld toe and weld root in LCWJ was determined by the established analytical solutions, verified by the fatigue data. The strategy is expected to provide some insights into assessing fatigue life for various types of weld joints for different potential failure locations.
查看更多>>摘要：? 2022 Elsevier LtdCorrosion is a significant cause of degradation of silicon photovoltaic modules. In this study, the corrosion of multicrystalline passivated emitter and rear cells (PERC) was investigated using both experimental and numerical approaches to identify high-corrosion locations and their effect on cell parameters. Corrosion environments were simulated by immersing the device in acetic acid solution at various dwell times. The impact of the acetic acid concentration and relative humidity was examined. Thermodynamic and kinetic analyses of corrosion were performed using a Pourbaix diagram and finite element analysis, respectively. The results indicate that the device power reduces slowly in pure water but is faster in acidic environments at dwell times below 96 h. The power loss was over 60% in all environments at a dwell time of 144 h. In particular, a rapid power loss over 40% was observed at a high acetic acid concentration of 20 wt% after a dwell time of merely 48 h. The power loss in the water environment can essentially occur due to the formation of a surficial metal oxide layer, while in an acidic environment, it may be due to corrosion and/or metal electrode dissolution. The simulation and experimental results demonstrate that the rear aluminum around the silver contact suffers crucially from corrosion; thus, it is the main cause of device power losses. A polymer (EPDM) efficiently prevents water penetration into the electrode areas, thus minimizing power loss due to corrosion, and effectively solves the problem without impacting the production cost.
查看更多>>摘要：? 2022 Elsevier LtdThe electrical connector of the traction motor is an important device to ensure the stable operation of the electronic system of the EMU. Damage to the crown spring inside the connector will cause the traction motor to lose power supply. In this work, the damage morphology, composition and damage depth of the crown spring damage area were systematically analyzed using macroscopic and microscopic analysis equipment. Results show that the coating of the slightly damaged reeds was oxidized. Moderately damaged reeds have severe mechanical wear that caused the coating to disappear. Severely damaged reeds are caused by the combined action of mechanical wear, electrical wear and oxidative wear. At this stage, the connector joint heats up rapidly, which causes the crown spring to melt. The results show that the failure of the crown spring is the result of the combined effect of mechanical wear, electrical wear, and oxidative wear.
查看更多>>摘要：? 2022 Elsevier LtdWith the increase in energy demand and in mining intensity, the phenomenon of multiple coal seam mining has appeared in major coal mining countries. While the downward mining method is generally adopted and under the damage of the upper coal seam, the structure and stress environment of the coal roof are very different from those of a single coal seam in remining. The rock layer between the two coal seams is affected by repeated mining and is prone to rotation instability, which makes it more difficult to reserve gob-side entries along the gob in the lower coal seams. This article mainly targets the case of the gob in the Panel #11426 of Xieqiao Mine, and studies the failure mechanism and control technology of the gob-side entry retaining in short-distance coal seam. First, the floor stress distribution law after mining in the upper coal seam is calculated according to the elastic theory, and verified by FLAC3D numerical simulation; secondly, the floor failure depth after the upper coal seam is calculated according to the elastic–plastic theory. Based on the “block-dispersions” structure, the failure process of the roof of the roadway under close gob is analyzed. Further, it is proposed during the roadway excavation, to adopt support methods such as erecting U-steel retractable supports and back-wall filling; during the mining and before the gob-side entry retaining, the installation of roof bolts (cables), the reinforcement of the roof of the area to be filled and the in-wall filling techniques etc. to control the surrounding rock of gob-side entry. The engineering test was carried out along the track at the Panel #11426 of Xieqiao Mine. The onsite monitoring showed that: the maximum subsidence of the reserved gob-side entry roof along the gob was 180 mm, and the maximum approaching distance of the two banks was 328 mm, which met the engineering requirements. The research results can provide guidance for the design gob-side entry retaining along gobs under similar mining geological conditions.
查看更多>>摘要：? 2022 Elsevier LtdTo enhance the understanding of the corrosion mechanism on rapid perforation failure, the corrosion behavior of L245N with the synergistic effect of O2-Cl? and different Cl? contents in CO2-O2-Cl? environment were studied by weight-loss test and characterization analysis. It showed that the O2 was the dominant factor inducing localized corrosion and the synergistic effect of O2-Cl? in CO2-O2-Cl? environment mainly accounted for the growth of the corrosion, because porous Fe oxides generated by O2 promoted the mass transfer and catalysis of Cl? and Cl? in turn promoted the expansion of localized corrosion pits. The increase of the Cl? under low content enhanced the synergistic effect with O2, while high content of Cl? (3000–5000 mg/L) could reduce the solubility of CO2/O2 and replace the adsorption of corrosive medium and ions on the substrate surface, inhibiting the cathodic process of corrosion reaction.
查看更多>>摘要：? 2022 Elsevier LtdIn this work, the cavitation erosion-corrosion performances of X65 pipeline steel at different locations of Venturi pipe is studied. Results show that the collapse of bubbles at throat downstream would induce pitting damage, thus accelerating the localized corrosion. The cavitation erosion is totally induced by the corrosion enhanced erosion at the employed flow rate. The local hardness degradation and crack initiation at the anodic sites are the two basic requirements for the occurrence of erosion. Along with the formation of deep pits, the fracture of steel substrate at pit boundary becomes the main contributor of erosion, which is induced by the repeated bubble collapse and the assistant of corrosion. The synergy of corrosion and cavitation erosion is the main lead of steel failure in Venturi pipe.
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