查看更多>>摘要：? 2022 Elsevier LtdThe sulfuration corrosion behavior of Inconel 600 alloy in high-temperature flue gas was investigated. The element distribution around corrosion layer, corrosion morphology and the phase composition of the corrosion layer were analyzed by scanning electron microscope (SEM) and X-ray diffractometer (XRD), respectively. The results indicate that the alloy is susceptible to be corroded in high-temperature sulfur-containing atmosphere. The corrosion mechanism is that, on the one hand, sulfur (S) could penetrate the Cr2O3 oxide layer, diffuse into the matrix along the grain boundary, combine with chromium (Cr) to form Cr sulfide and weaken the intergranular bonding strength. On the other hand, sulfur (S) in the flue gas and nickel (Ni) in the alloy matrix form Ni3S2 with low melting point, which is continuously generated and melted during service, and eventually results in the constant occurrence of sulfuration corrosion.
查看更多>>摘要：? 2022 Elsevier LtdMany oil and gas pipelines are parallel with high voltage transmission lines in a long distance. Corrosion failures in such situation have been reported and typical corrosion morphology (stone-hard-soil) have found in these failures. In this paper, AC corrosion behavior and the effects on corrosion process after the formation of typical corrosion morphology are investigated in earth alkaline rich environment through laboratory simulated tests. This study produce a corrosion rate map where high CP AC corrosion and local corrosion are observed. In domain of high CP AC corrosion, local environment, including typical morphology of stone-hard-soil and corrosive electrolyte at interface, are analyzed. After the formation of stone-hard-soil, the electric field and its effects on migration of Cl-, are discussed. These results, combining the changes in instantaneous potential and pH at local regions, provide a guide to understand the occurrence and development of local corrosion under high CP level and AC interference.
查看更多>>摘要：? 2022 Elsevier LtdWe present a case study investigating the failure mode of upper copper electrode weld wheels being used in a mash seam welding process in an industrial production line. The upper electrode wheels had a much shorter lifetime than the lower electrode. Published literature on the degradation mechanisms of electrodes has focused on resistance spot welding. There are far fewer studies of failure modes in mash seam welding failure modes. This study presents the compositional and mechanical analysis of a failed copper upper electrode taken from a mash seam welding production line. Optical and scanning electron microscopy with x-ray compositional results showed the formation of steel-copper mixing regions on the surface of the electrode in contact with the steel, and within the electrode itself. Existence of mixing regions in the electrode are further supported with localized hardness mapping by nanoindentation, which confirms the steel-copper mixed regions exist up to 0.8 – 1.2 mm below the knurled electrode's surface. In addition to the mixed region, there was clear evidence of copper grain fragmentation as the steel was worked into the copper electrode. We conclude that failure occurred because intermittent air gaps between the electrode and steel during rolling caused insufficient cooling of the steel piece, causing a melt pool at the workpiece surface. This molten steel adhered to the copper electrode and was gradually pushed into the copper leading to electrode failure. Solutions to extend the service life were proposed, based on a thorough understanding of electrode degradation mechanism and deliberate electrode design changes.
查看更多>>摘要：? 2022The scatter of casting defects induced by the casting process causes the scatter of mechanical properties of cast alloys. The cylinder head of a high-power density engine is huge and complex, which frequently leads to fatigue behavior due to scattering and uncertainty of casting defects. A statistical approach is used to examine the mechanical properties at multiple places of a cylinder head with a complicated construction, including the top plate, the connecting wall, and the bottom plate, in order to determine the scatter of casting defects. A prediction model is built based on the pore of fatigue crack initiation and predicts the fatigue life well. The findings show that the grain size scatters at different positions of the cylinder head correspond to tensile properties, while porosity scatters at the crack initiation site of fracture specimens from different positions of the cylinder head correspond to fatigue life. As a result, the microstructure of the complicated cylinder head at different sites is a major element influencing the spatial scatter of mechanical characteristics, which can be exploited to promote cylinder head optimization.
查看更多>>摘要：? 2022 Elsevier LtdOne of the challenges that data-based gas path component monitoring systems are facing, is the poor performance in those operational conditions that are not considered in the training process. An approach could be retraining the model repeatedly with a large number of previous and fresh data from the scratch, which would require a lot of time and storage memory. To address this problem, a component fault diagnostic system based on the bank of online sequential extreme learning machines (OSELMs) are applied that can incrementally update with any number of new training samples. This system is adapted for a two-shaft industrial gas turbine that is used for power generation. Besides, an optimal set of measurements are selected as the input of the system using a hybrid approach based on the variable length genetic algorithm and extreme learning machine (VLGA-ELM). The performance of OSELM based diagnostic system is compared with several batch learning algorithms by analyzing the confusion matrix of all systems. The results show that the OSELM based approach reflects a promising compromise between the overall accuracy, false positive rate, F1-score and false negative rate, while having the least training time compared with the other systems.
查看更多>>摘要：? 2022 Elsevier LtdRail spalling is a typical form of wheel-rail rolling contact fatigue (RCF), and is a difficult problem that has always existed in railways. Once the wheel rolls across the spalling failure area, there will be a violent dynamic wheel-rail interaction. This paper presents an explicit high-speed 3D wheel-rail rolling contact transient explicit finite element model that considers local rail spalling failure. The dynamic wheel-rail interaction under the condition of different spalling lengths and contact stress states, as well as plastic strain of the rail when the wheel rolls across the rail spalling, are calculated using the theory of transient wheel-rail dynamics. In addition, the time–frequency analysis is carried out to obtain the distribution characteristics of dynamic response signals such as axle box acceleration, rail vibration acceleration and dynamic vertical wheel-rail force in time domain and frequency domain. Furthermore, when the vehicle travels at a high speed, the speed and radius of the wheel have little influence on the dynamic vertical wheel-rail force, or on the wavelet energy peak and frequency. The effect of the mutual dynamic correlation is small. But the dynamic vertical wheel-rail force, along with wavelet energy peak and frequency, increase in an approximately linear fashion with the impact acceleration of wheelset and the length of spalling failure. These results can be used to guide the dynamic detection of local defects on rails.
查看更多>>摘要：? 2022 Elsevier LtdThe microstructure of the flow lips formed at the lower corner of gauge face in the longitudinal section of worn high rails serving in curved tracks has been investigated. The radii of the curved tracks are 1500 m (S1, sharper curve) and 4000 m (S2, milder curve). Sharper curves result in a higher angle of attack (AOA) between rail-wheel thus leading to higher lateral contact forces as well as tangential frictional forces thus facilitating plastic flow. Such conditions favour formation of flow lips where rail material flows from the rail upper gauge face to the lower corner of the gauge face. A combination of optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and nano-indentation hardness measurements have been used for the characterization of the flow lip. It is observed that the outermost region of the flow lip consists of a uniformly present white etching layer (WEL) followed by an intermittently present brown etching layer (BEL) where the WEL and BEL thickness is less for milder curves. The WEL has the highest hardness and consists of fine grains of ferrite and particles/fine fragments of cementite. The BEL is relatively softer than WEL and has a similar appearance to WEL, but patches of lamellar structure appear with increasing depth from the outer edge. Beyond the BEL region, layers of deformed pearlitic structure are observed, and a more intact pearlitic structure is observed at a much lower depth for the milder curve than the sharper curve. For both the curvatures at a given depth, the hardness of pearlite bears a Hall-Petch type of relationship to the pearlitic interlamellar spacing. However, the alignment of the deformed microstructure is heavily dependent on the curvature. It has been found to align almost parallel (4°–10°) to the rail longitudinal axis for the milder curvature and at around 21°–35° for the sharper curvature. Cracks originate from the brittle WEL region due to contact fatigue whereas crack propagation is driven by bending stresses. Cracks have been found to move parallel to the alignment of the deformed pearlite along longitudinal direction for the milder curvature. Alignment of pearlite also motivates the crack propagation trajectory for the sharper curvature and hence the crack moves at an angle between 21° and 35° with the longitudinal direction but becomes almost perpendicular after a distance. Shallow cracks travelling parallel to the rail outer edge in S2 can result in spalling of the rail material leading to wear, whereas for sharper curves, cracks run deeper into the railhead. Thus, the tendency for rail failure through 'Reverse Transverse Fracture' – which involves crack initiation at the lower gauge corner and propagation into the railhead – increases with the sharpness of the rail curvature.
查看更多>>摘要：? 2022 Elsevier LtdHigh-pressure injection molding is an important industrial process, which requires a precise cooling stage. In this work, we analyzed the reasons for the corrosion failure of the cooling circuit of molds in the molding plant. The cooling circuit was inspected visually and collected samples were further analyzed in a laboratory using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The main problems were an improper selection of the antibacterial agent and materials of the cooling circuit. Based on the performed analyses, a possible mechanism of the corrosion attack was proposed and recommendations to decrease the number of corrosion-related failures and services were formulated.
查看更多>>摘要：? 2022 Elsevier LtdDeveloping electric-driven seismic vibrator is a promising way to realize green exploration. To ensure the service life of the power supporting frame under long-term operation, a method of predicting fatigue life under random load is proposed. First, stress history of the maximum stress node is obtained through dynamic analysis. Second, based on the rainflow counting method, the stress history at the maximum stress node was statistically analyzed, the distribution of amplitude and the distribution of mean are studied, and the load spectrum is compiled. Third, considering structural parameters and the stress below the fatigue limit, the P-S-N curve of the power supporting frame is achieved through two-steps corrections, and combined with the Miner's rule, the fatigue life of the power supporting frame is predicted. The results show that under the condition of the significance level of 0.05, the amplitude and the mean of the stress are independent of each other. The amplitude of stress obeys the Weibull distribution with a shape parameter of 1.0362 and a scale parameter of 10.5108, and the mean of stress obeys a normal distribution with a mean value of 40.253 and a standard deviation of 10.1803. Under 95% reliability, considering the structural parameters and the stress below the fatigue limit, a more accurate P-S-N curve of the power supporting frame is obtained, and then with Miner's rule the fatigue life of the power supporting frame is predicted to be 8.5 years. Based on this study, the power supporting frame was successfully manufactured. This research also provides method and case reference for structural fatigue life prediction under random loads.
查看更多>>摘要：? 2022 The Author(s)The objectives of this study were to investigate the fracture surface topography of X8CrNiS18-9 austenitic stainless-steel specimens for different loadings and notch radii and to supplement the knowledge about the fracture mechanisms for fatigue performance. Cases with three different values of the notch radius ρ and the stress amplitude σa were analysed. The fracture topographies were quantified by the areas over their entire surfaces with the aid of an optical confocal measurement system. The results showed a well-correlated root mean square height Sq and void volume Vv, identifying the characteristics of the entire fracture method. A fracture surface topography fatigue damage model was developed based on the product of the stress amplitude σa by the Sq to the Vv ratio. Overall, the predictions were close to the fatigue lives found in the experiments.
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