查看更多>>摘要：The unusual premature failure of a heavy-duty truck engine crankshaft has been the subject of a rigorous study, and this manuscript describes it in detail. The failure was happened to begin with the growth of the crack from the surface defects, in the form of the clusters of non-metallic inclusions, in the lubrication hole zone of the first main journal, which was the stress concentration zone. A series of experiments including chemical composition, microstructure, mechanical properties, hardness, toughness, and fractography were performed on the failed crankshaft. In addition, the stress analysis was performed on the crankshaft. Careful fractographic study with scanning electron microscopy equipped with energy dispersive spectroscopy revealed that failure with cluster inclusions MnS (r = S/Mn = 0.024 > 0.01) was more than the standard amount. Besides, stress analysis showed that the stress field in stress concentration zones with the lubricating hole is much less than the web-crankpin fillet but the presence of cluster impurities, low hardness (>600 HV0.1 proposed standard), downshifting has caused the growth of primary cracks. It is recommended to first increase the hardness by about 43% and then, decrease the size of non-metallic inclusions so that primary crack growth does not initiate from the worst clusters of inclusions.
查看更多>>摘要：To explore the fatigue failure laws of dropper structures, this study performs impact fatigue tests and local simulation analyses on two newly proposed dropper structures. The failure modes of droppers having two different structures are examined, and the reasons for the differences between them discussed. During the crimping process, the large deformation of the tooth-shaped crimping dropper caused significant initial damage to the copper wire surface, significantly reducing the load-bearing capacity of the dropper. For the elliptical crimping dropper, the reduced size of the heart-shaped retaining ring resulted in a relatively high tensile stress along the edge of the dropper, resulting in crack initiation and structural fracture failure. Under the double logarithmic coordinates, linear relationships were observed between the impact load and life of both structural types of droppers. By performing fitting, the relationships between the impact load and life of the two types of droppers are determined.
查看更多>>摘要：To study the typical rail corrugation in braking sections at large slope downhills of Chinese highspeed railways, finite element models of wheelset-rail-brake systems of various high-speed trains are established in the present paper. Then, the complex eigenvalue analysis method is used to study friction self-excited vibration characteristics of wheelset-rail-brake systems in braking sections at large slope downhills. Finally, the influences of friction coefficient of the braking subsystem and vertical fastener stiffness of the wheelset-rail subsystem are analyzed. Results show that the friction self-excited vibration of the entire system induced by the stick-slip friction coupling effect of the wheelset-rail subsystem and the rolling-slip friction coupling effect of the braking subsystem is the dominant cause of rail corrugation. Then, the brake combination of the wheel disc and axle disc is more likely to cause the friction self-excited vibration of the wheelsetrail-brake system than the single braking mode. Parametric analyses show that with the increase of the friction coefficient of the braking subsystem, the self-excited vibration of the entire system increases, which means that the possibility of rail corrugation increases. Furthermore, with the increase of the vertical fastener stiffness of the wheelset-rail subsystem, the self-exicted vibration of the entire system first decreases and then gradually increases. When the vertical fastener stiffness is 30 MN/m, rail corrugations can be suppressed to a certain extent.
查看更多>>摘要：In gas-turbine engines, temporary variation of the temperature field in the turbine inlet causes thermal stress on the turbine components. In military engines, the afterburner is a source of additional stress to turbines, especially when it is activated. The aim of the study is failure analysis of the turbine components of the RD-33 turbofan, operated by the Polish Air Force. The results of visual inspection illustrate the critical condition of turbine blades and guide vanes. The sources of thermal and dynamic stress are analyzed. It is shown that the specific design of the afterburner activation system is a significant contributor to accelerated degradation of the turbine components and premature grounding of engines. After activating the afterburner, during the ignition and propagation of the flame, local overheating of the turbine components occurs and initiates their damage. To reduce the operating costs of the engine, actions limiting the negative impact of the afterburner on the turbine durability are proposed.
查看更多>>摘要：To lay the foundation for monitoring the mine vertical shaft deformation and mitigating its influence on the guide rail, this paper studies the deformation law of the guide rail and its interaction mechanism with the shaft under non-mining action. Firstly, the correction coefficient is introduced into the settlement equation, and its compression modulus is inverted by the particle swarm optimization (PSO). Secondly, the relationship between the elastoplastic interface of the vertical additional force (VAF) and the bottom aquifer (BA) water head is deduced, and then its distribution law varied with water head is obtained. Finally, a finite element model using spring elements to simplify the interaction between the shaft and surrounding rock-soil body is established to analyze the shaft deformation law, its interaction mechanism with the guide rail, and the guide rail deformation rule in different connection states. It can be obtained from the analysis results that using the improved settlement equation as the PSO objective function weakens the influence of compressive modulus with the change of soil settlement, and enhances the calculation precision on the BA settlement, so that the deduced relationship between the bottom aquifer water head and the elastoplastic interface of the VAF is consistent with the actual soil settlement and deformation laws. The spring element can effectively simulate the interaction between the shaft and rock-soil body, which makes the action mechanism between them to consistent with the actual situation. Owing to the vertical compression deformation of the shaft, the force direction on the guide rail subjected to the shaft varies with the position, which bears the vertical upward force in the upper section, the vertical downward force in the middle section and the vertical upward force in the lower section. There are obvious differences in the deformation laws of the guide rail corresponding to different connection states, disconnected positions and non-mining shaft deformation, which exist a certain regularity corresponding their respective states. The guide rail mainly produces the fluctuating deformation along the bunton direction, and its amplitude and range increase with the non-mining shaft deformation. All in all, the guide rail deformation can reflect the state of itself, the shaft and the connection between them, which can provide reference and guidance for the monitoring of the shaft deformation and the safety of the mine hoisting system.
查看更多>>摘要：In this study, the analysis method combining multi-body dynamics (MBD) and finite element analysis (FEA) is used to study the transmission failure of the Zero-Backlash High Precision Roller Enveloping Reducer (ZHPRER). A dynamic model of the reducer is first constructed using the MBD method, and the correctness of the model is verified through experiment. The model is then applied to calculate the change in the contact force of the reducer during the meshing period under different speeds and loads. Finally, the maximum value of contact force in the meshing period of different working conditions is used as a boundary condition, and the weak position in the transmission process is analyzed by the FEA. At the same time, the validity of the FEA model is verified by an overload test. The results show that, within the rated load, the failure mode of the transmission is the fracture of the inner ring assembly shaft caused by fatigue damage or the fatigue deformation or cracking of the worm gear assembly hole. The change in speed and load significantly impacts its fatigue life. When the rated load is exceeded, the failure mode of the transmission is manifested by crushing of the outer ring, rolling bodies, and cracking of the worm gear assembly hole.
查看更多>>摘要：The vibration phenomena which occur in rotary machines, such as power plants, can result in catastrophic consequences. Any failure in any power plant section can result in extended downtime and high repair expenses. Vibration is one of the most common causes of power plant failure. The above-mentioned issues can be avoided using high-accuracy vibration detection and prediction technologies. Therefore, further research into the primary causes of vibration on Combined Cycle Power Plants (CCPPs) can help improve the present vibration evaluation methodologies for power plants. This paper aims to survey some of the most commonly reported factors that can induce vibration in the gas turbine of CCPP. Therefore, this paper aims at reviewing the unbalancing and misalignment, contact among rotating and stationary components (rubbing), steam flow fluctuations, the rotor critical speed, and shorted-turns, which are some of the most common destructive vibrations in this industry. Furthermore, some of the most used well-known technologies for vibration monitoring and evaluation in the gas turbine of CCPPs are described, such as proximity probes, laser Doppler vibrometer, eddy current sensor, and accelerometer, which can be used to create a maintenance time schedule for the gas turbine of CCPPs and also, it helps to reduce maintenance time and power generation costs.
查看更多>>摘要：The failure mechanism of suction valve in high pressure and large flow water hydraulic plunger pump used in coal mine is studied. Previous studies believe that in traditional plunger pump with low pressure and small flow, the impact caused by the dynamic contact between the valve plate and the valve seat is the main reason for the performance deterioration of suction valve. However, in the practical use of high-pressure and large-flow hydraulic plunger pump, it is found that there are signs of rotating wear and material loss on the sealing surface of the suction valve plate. In order to explain the premature failure of the valve, the mathematical model of the force and movement of the valve plate during the suction process of the high-pressure and large-flow hydraulic plunger pump is established. Three-dimensional computational fluid dynamics (CFD) method and nonlinear finite element method are used to numerically analyze the operation process and dangerous conditions of the valve plate. The results show that under the action of the uneven flow field, the combination effects of low speed rotation and heavy load during closing process is the key factor causing material loss. According to the microstructure and elemental composition of the worn surface, the specific wear failure mechanism is determined, and the effectiveness of the numerical method is verified. Finally, the improved valve plate materials are proposed. The field test of high pressure and large flow pump proves that the wear of the valve plate is significantly reduced after the improvement.
Kolblinger, A. P.Tavares, S. S. M.Della Rovere, C. A.Pimenta, A. R....
12页
查看更多>>摘要：The failure of a flange for seawater service in the top side of an oil platform was investigated in this work. The flange was made of superduplex stainless steel UNS S32760, and the chemical composition and the microstructure were found to be adequate, according to ASTM A-182 standard. Deleterious phases such as sigma and chi phases were not found by optical and scanning electron microscopy. The material's mechanical properties and corrosion resistance were also typical of superduplex steel without intermetallic phases. However, the flange has undergone severe crevice corrosion in the gasket region. In the microstructural scale, the ferrite phase was preferentially attacked. EDS analyzes revealed elements typically found in corrosion processes caused by microbiological bacteria. The work shows that the superduplex steel is susceptible to crevice microbiological induced corrosion (MIC), even when the microstructure and fabrication process used are correct.
Dawood, ThikraElwakil, EmadMayol Novoa, HectorGarate Delgado, Jose Fernando...
11页
查看更多>>摘要：The aging and degradation of water supply systems are deemed serious problems that cause pipeline failure and breakages. The risk of watermains failure assessment is one of the key strategies that can pinpoint pipes at risk and maintain their sustainability. This research paper showcases a novel method for deterioration modeling in conjunction with quantifying the water network's failure index (FI). The methodology builds on various algorithms, computational intelligence, and interactions between numerous factors. It involves developing two intelligent models; the first is the Monte Carlo Simulation Model (MCSM) that is designed to estimate the deterioration indices (DIs) of watermains through intricate iterative simulations. The produced indices are then streamlined and channeled to the fuzzy engine to develop the second model, namely, the fuzzy inference system model (FISM). After designing the model's configuration, the DIs are mapped to 84 fuzzy-if-then-rules that are in turn mapped to output values; finally, the fuzzy consolidator generates one crisp number that represents the watermain's FI. The developed method is implemented on the water system of the City of El Pedregal in Peru. The results indicate a moderate risk of failure status, which corresponds to 62.3 FI. Moreover, the efficacy of this method is verified against the multiple linear regression (MLR) method and proved to be sound. This research provides insights for infrastructure managers in the aspects of when to intervene, what to maintain, replace, or rehabilitate, and how to focus their constrained funding on the most deserving assets.
NSTL
Elsevier