查看更多>>摘要：? 2022 Elsevier LtdThis paper proposed a fatigue test load spectrum compilation method for key pantograph components to study the reduction of the pantograph development cycle and optimization of its structural design to ensure the service reliability of pantographs. This paper established a pantograph-catenary coupling dynamics model to obtain the stochastic load-time histories with the upper frame of a modern high-speed pantograph as the research object. The stress load spectrum of the pantograph upper frame was obtained using finite element simulations with polynomial fittings. This paper proposed an extrapolation method for the rainflow count matrix of the stress load spectrum based on the two-dimensional kernel density estimation theory. This paper applied the equivalent damage criterion, gave the load back-propagation method, and further obtain the accelerated load spectrum, and verified the load spectrum by designing the bench test for fatigue test. The results showed that the accelerated load spectrum obtained by back-propagation can retain the complete load characteristics of the original spectrum and accurately simulate the combined load effect under the actual use of the pantograph. This method improves the accuracy and efficiency of accelerated life testing of pantograph components and provides a reference basis for the subsequent development of reliability design, accelerated life testing, and life prediction of key pantograph components.
查看更多>>摘要：? 2022 Elsevier LtdLocal fault failures could greatly affect the vibrations of cylindrical roller bearings (CRBs). However, most previous works defined the fault surface as the smooth ones, whose actual roughness features were ignored. To overcome this problem, this study presents a time-varying stiffness excitation model for a CRB including a local fault with the roughness surface based on Greenwood and Williamson's method. A dynamic model with the time-varying stiffness excitation model is developed to analyze the effects of the roughness and local fault on the contact features and vibrations of CRB. The changes of time-domain contact features and vibrations for defective CRB with and without the roughness surface are analyzed. Note that the roughness surface can greatly affect the contact stiffness, contact deformation, and vibrations for CRB under a small force. But its effect will decrease with the increment of radial load, which will close the value of smooth CRB. This paper can show some guidance for CRBs including the local faults with the roughness surface.
查看更多>>摘要：? 2022 Elsevier LtdThe aim of the study was to analyze the damage occurring in vitrified clay sewers operated for a period of 130–142 years based on the results of their CCTV testing. In view of the fact that there are very large differences in the assessment of the forecast lifetime of sewer pipes, as reported by the different institutions, and significant differences in the survival functions developed for these pipes, particular attention has been paid to identification of the causes of this situation. One of the most important results of the research and analyses conducted is demonstration that models predicting the durability of vitrified clay pipes and the survival functions created for them should be developed separately for sewers laid in dry soils and water-saturated soils. The research has also shown that various so-called primary damages were observed in sewers, which occurred during transport, storage, and installation of pipes. Failure to take into account the possibility of these damages in the durability models being developed and in the related survival functions makes it impossible to predict the actual durability of these pipes. An analysis of the results also confirmed the thesis formulated on the basis of studies of vitrified clay pipes in Canada that the deterioration of vitrified clay pipes is not age-dependent when the pipes are properly designed and installed, with no damage during installation.
查看更多>>摘要：? 2022 Elsevier LtdRailways play a pivotal role in transportation systems worldwide. Effective maintenance policies are crucial to guarantee the reliability and availability of such systems inserted in a challenging and competitive environment. In this scenario, condition-based and predictive maintenance strategies emerge as key components of the European rail traffic system, where common advanced monitoring solutions of railway assets serve as performance metrics for the development of maintenance rules. However, the effectiveness of a good maintenance policy is intrinsically dependent on a clear assessment of the system on target, including not only aspects related to its complexity and financial importance, but fundamentally the physical characteristics and the environmental and operational conditions to which the system is subject to. In this sense, simulation models are useful as they can mimic the behaviour of systems, especially those too complex to solve analytically, incorporating the characteristics and the inherent stochastic behaviour associated with them, including their correlation structure. This study focuses on the locomotive bogie, which is a complex subsystem of the train onto which the wheels of the vehicle are fixed. The main components of the bogie are described as well as the stochastic behaviour associated with the occurrence of failure. A Discrete Event Simulation (DES) model is proposed to study the impact on the system, in terms of reliability and availability, under different scenarios with varying assumptions on the underlying failure modes, repairs, and on the failures’ correlation structure. The results point out that the model is suitable for representing the main characteristics of this train subsystem, and it identifies the parameters and components that are more critical in terms of reliability and availability fluctuations when contrasted with the variations imposed on the model by considering different scenarios. Overall, the DES model allows the robust assessment of where the focus should be put according to the uncertainty embedded in the correlations of failures and/or in the maintenance durations.
查看更多>>摘要：? 2022 Elsevier LtdAs the vulnerable component of diesel engine, cylinder head is subjected to the thermo-mechanical coupling loads more and more heavily. For establishing a simple and effective technology to evaluate the damage degree, a prediction method based on simulated component is developed in the present work. By the comparison of temperature and stress at measured points, it shows that the simulation and testing results have a good agreement, verifying the effectiveness of simulated component. Applying Sehitoglu theory and loading spectrums, the failure locations are predicted successfully. Then damage characteristics of thermo-mechanical fatigue are analyzed at failure locations. It indicates that mechanical damage takes a leading role compared with oxidative damage and creep damage, and thermal load is more sensitive to mechanical damage in three damage types. This study may provide an effective way to estimate the service life of cylinder head.
查看更多>>摘要：? 2022 Elsevier LtdWheels are important components for the general vehicle reliability. Their design validation is usually based on fatigue tests conducted in laboratory under constant amplitude load conditions, according to industrial standards. In the off-highway industry, the variety of applications and machines often makes it difficult to complete standard tests, due to the high load capacity requirements or to lack of information about specific applications. Therefore, strain data acquisition during field test on real machines can be a useful tool to understand actual load conditions. In this paper, a fatigue life assessment based on field test is applied to a multipiece wheel that experienced an unexpected crack development in a critical section. The local strain approach is used, together with rainflow counting method and Palmgren-Miner rule for the total damage evaluation. Mean stress influence is considered through the Smith-Watson-Topper method. The fatigue life estimation is completed for structural steel S355J2. The influence of extremely hard working conditions is also investigated and assessed to be the root cause of the failure. Finally, a possible design improvement regarding the use of a higher base material grade S690 is evaluated and proposed.
查看更多>>摘要：? 2022 Elsevier LtdFull-scale fatigue tests and numerical damage simulation were performed to evaluate the effectiveness and durability of two cold reinforcement methods (bonding steel angle, hybrid bonding and bolting steel angle), under the action of fatigue loads and environmental effects. Fatigue test results after reinforcement and the further long-term durability test results including both internal and exterior girders under different environmental effects indicate that two cold reinforcement techniques are highly effective and durable to arrest distortion-induced fatigue cracking and decrease out-of-plane distortion. Numerical fracture evaluation considering both durability and fatigue damage of cold reinforcement joints shows stress intensity factor (SIF) at fatigue crack tips reduced below threshold, demonstrating that cracks would not propagate, consistent with test results. The innovative hybrid cold bonding and bolting steel angles reinforcement method is recommended, because it can not only avoid traffic disruption and angle falling, but also arrest fatigue crack growth effectively without drilling hole damage at girder flanges.
Dini Hariyanto S.Hozaifa Hasan W.Adi Himarosa R.Akhsin Muflikhun M....
15页
查看更多>>摘要：? 2022 Elsevier LtdFailure analysis of the platen superheater tube, water wall tube, and sealpot plate were investigated in the present study. To examine the causes of failure, various techniques, including visual examination, chemical composition test using Optical Emission Spectrometry (OES), fracture surface examination using Scanning Electron Microscope (SEM), tensile test, hardness test, and metallography test were carried out. Samples average thickness were 6.46 mm, 6.23 mm, and 9.29 mm, respectively. The chemical composition of the platen superheater tube, water wall tube, and sealpot plate material samples was not conforming to the standard material. The eroded tube surface contributed to the failure mechanism that caused by escaping steam in high velocity which leading to another leakage. This escaping steam also damages the adjacent surface by 'steam cutting' mode and erosion in both platen superheater tube and water wall tube.
查看更多>>摘要：? 2022In order to reveal the impact of environmental vicissitudes on weathering failure of stacked wall and sandwich wall, the capillary water rise mechanism and its spatial distribution in these two types of walls are studied based on SF (Sharp Front) theory in this paper. The result shows that the horizontal bonded mortar and the vertical interlayer soil can block and promote the capillary rise process respectively. In the freeze–thaw experiment, 6 groups of walls with different freeze–thaw cycles are used to simulate stacked wall and sandwich wall with different weathering degrees. Then moisture meter and strength meter are used to extract data and further analyze the distribution and evolution of weathering performance of these walls. The result shows that with increasing freeze–thaw cycles, the moisture content of both the stacked and sandwich walls is increasing while the strength is decreasing. The moisture content curve, strength increment curve, and crack density curve of the stacked walls all shows a “concave” form, with maximum values in the lowest two layers and then drops sharply with increasing height. However, these curves of sandwich walls are all viewed as a “straight” form, with all values decreasing nearly linearly as height increases. There is an obvious linear relationship between the moisture content and the strength increment, and the corresponding slopes are-5.556 for stacked walls and-8.8891 for sandwich walls, indicating that the strength attenuation problem faced by sandwich wall is more serious. Furthermore, compressive tests revealed that after 20 freeze–thaw cycles, the sandwich wall's strength decreased by an additional 11.7 percent as compared to the stacked wall.
查看更多>>摘要：? 2022 Elsevier LtdSpring-energized polytetrafluoroethylene (PTFE) seals are typically utilized to meet requirements of long service life due to their excellent temperature and chemical resistance. After high-cycle operations, the contact pressure between the seal lip and the associated counterpart possibly decrease because of the wear on the contact surface and this eventually leads to loss of the sealing capability. Evaluations of the wear and resulting sealing performance of the seal are rather essential, however, the corresponding experiments are generally time consuming and costly. Simulation procedures for the seal based on the finite element analysis were therefore developed in the current study. Experimental and numerical investigations of mechanical behaviors of the canted coil spring and PTFE materials were first performed. A wear analysis model for the spring-energized PTFE seal used in a glue dispenser with reciprocating motions for semiconductor equipment was subsequently constructed. The modified Archard model was implemented into a self-coded user subroutine of commercial finite element software to assess the amount of wear on the seal. Simulation results revealed that the geometry dimensions of the worn seal are in fair agreement with those of the corresponding samples. Contact pressure distributions of the seal lip were also examined during the operations. Peak of the contact pressure was found to gradually decrease along with the increase of cycles due to the wear, and potential fluid leakage was then assessed via the Reynolds equation. Numerical calculations showed that no leakage would occur after ultra-high cycle operations which was consistent with practical observations.
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