查看更多>>摘要：? 2022 Elsevier LtdThe piston ring pack is one of the crucial moving parts of two-stroke marine diesel engines because it has essential functions such as lubrication, sealing, and heat conduction. An oil injection lubrication mode for the ring pack through an independent oil-feed system is remarkable for two-stroke marine diesel engines. This study established a lubrication model for the ring pack. The model coupled ring dynamics, ring mixed/boundary lubrication, inter-ring gas dynamics, and asperity contact, especially considering this specific lubrication mode. The influence of lubricating oil-feed parameters (preliminary oil film thickness, oil-feed amount, oil-feed width, oil-feed position, and oil-feed ratio) on the lubrication characteristics of the ring pack was evaluated by the minimum oil film thickness and friction loss power. Finally, the orthogonal analysis method was used to optimize the lubrication characteristics.
查看更多>>摘要：? 2022 Elsevier LtdAdopted immersion method to systematically study the corrosion behavior of SDCM steel for hot stamping. For specimens with the same hardness of 54 HRC, the corrosion resistance of 1030 °C quenched samples were better than that of 1060 °C quenched samples. After 1030 °C quenched, the hardness was adjusted to 50 HRC, 52 HRC and 54 HRC by tempering process, and then applied 50 MPa tensile stress to these three kinds of hardness samples. With the increase of hardness, the corrosion area decreased from 21.82% to 13.47%, and the number of large pits decreased from 27 to 7 on the area of 40 mm2. Stress has an important effect on corrosion. When the loading stress was less than 100 MPa, the corrosion area/pitting numbers increased with the increase of stress, but the aspect ratio decreased, and the decreasing range was large. When the loading stress was more than 100 MPa, the corrosion area/pitting number decreased with the increase of stress, the aspect ratio also decreased, but the decreasing range was smooth, which was mainly related to the concentration of adsorbed dissolved oxygen; finally, we discussed the initiation and growth behavior of pitting pits and then schematically described its model.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, the effects of different strengthening methods that can be applied for earthquake-damaged historical masonry structures on structural performance were investigated. For this purpose, the Historical Alaeddin Bey Mosque in the central district of Mu? was modeled in three dimensions according to the macromodeling technique using the finite element method in the SAP2000 program. The earthquake performance of the structure was determined by considering the earthquake-acceleration records of Erzincan, Kocaeli, and Van, respectively. The maximum tensile and compressive stresses in all three directions on the structural elements were taken into account as the earthquake behavior parameters of the structure. According to the earthquake analysis made in the time domain, it was determined that the polygonal pulpit of the minaret was at risk of being damaged under the effect of the Erzincan earthquake, and it has been concluded that this region should be strengthened. The damaged area of the minaret was strengthened by the application of CFRP fabric and steel plate materials (together or separately) in five different ways, from inside and outside and at different distance intervals. The conclusions obtained as a result of the earthquake analyses on the reinforced models were examined, and it was explained in detail with the help of tables and graphics that method would be more effective in strengthening such damages.
查看更多>>摘要：? 2022 Elsevier LtdConcrete gravity dams are often referred to as vertical cantilever structures with approximately fixed bottoms due to their massive gravity, frictions with the foundation, and additional anti-sliding techniques. Given this, when modeling concrete gravity dams subjected to underwater explosions, should the dam bottom be considered as the fixed boundary or the frictional boundary? In this study, two small-scale centrifuge tests and numerical simulations were used to investigate the dam failure modes due to near-field underwater explosions. Emphasis was placed on the effect of dam bottom boundary condition (DB-BC) to improve understanding of dam failure mechanisms and provide references for constructing experimental and numerical dam models. To this end, the current research began with a combined experimental and numerical investigation on the failure modes of dams with fixed bottoms. Then, a numerical study was conducted to evaluate the effect of DB-BC. Results revealed that dams with frictional bottoms demonstrated essentially the same failure mode as those with fixed bottoms. Both exhibited mainly the structural bending-induced tensile failure mode. To the authors’ knowledge, this is the first time the effect of DB-BC has been explored. In particular, by centrifuge tests, this paper presented the urgently needed experimental data in this field including dam failure patterns and strain histories as well as test videos.
查看更多>>摘要：? 2022 Elsevier LtdThe conducive atmosphere for corrosion and simultaneous presence of stress in the material often results in the phenomenon of stress corrosion cracking (SCC). SCC has been reported in both sensitized and un-sensitized austenitic stainless steels widely used in industry. The present investigation is centred around a reheater tube made of stainless-steel SS 304 HCu, which failed in a newly constructed power plant when subjected to hydro test. Optical and electron microscopy was used in the analysis in the vicinity of the attachment weld on the reheater tubes. Even though microstructural investigation showed no sign of sensitization, the presence of chloride (Cl), identified through SEM-EDS scan, and localized strain, identified through EBSD scans near the failed region, confirmed stress corrosion cracking in the material. The results obtained during the investigation have clearly brought out the cause of stress corrosion cracking in reheater tube. Further, it was observed that the weld bead size played an important role in inducing residual stress in the material and the bead size was modified to address the localized stresses at the weld; this helped in solving the problem.
查看更多>>摘要：? 2022 Elsevier LtdThe reformer effluent is serially cooled down to produce hydrogen in the hydrogen unit of an oil refinery. The process heat from effluent is effectively utilized for low pressure steam generation using heat exchanger. The exchanger shell and tube side fluids were boiler feed water and process gas, respectively. Several tubes of this heat exchanger were failed especially within tube sheet after 4 years of useful service. Therefore, failed exchanger tube was subjected to engineering failure analysis to determine the cause of failure. Initially visual inspection was conducted using videoscopy in heat exchanger dry condition and evidenced circumferential crack. Subsequently, all failed tubes were separated from U tube bundle. Selected tube was subjected to visual inspection, dye penetrant and dimensional measurement. No evidence of visual deformation and thickness loss observed in the failed tube. Further investigated tube was subjected to chemical analysis and confirmed the required metallurgy as per design specification. The fracture surface was subjected to elemental analysis, fractographic, metallographic and hardness investigations. The micro hardness of an exchanger tube at failure location was higher than specified hardness value. Investigation also revealed that exchanger tubes were expanded from tube inner surface to establish tube to tube sheet joint according to specified design drawing. Tube expansion was done prior to start of service and attributed to residual stress within tube material. The results revealed that presence of chloride in the accumulated deposits within tube to tube sheet joint favored conducive environment for chloride stress corrosion cracking. Recommendations were suggested for failure prevention. Achievement in this paper may supplement the similar heat exchanger tube failure database and mitigation of failure will be possible by good engineering practices.
查看更多>>摘要：? 2022 Elsevier LtdDuring the installation and operation of transmission equipment, bearing clearance problems occur, which are also one of the main reasons for bearing failure. Therefore, research on bearing clearance has theoretical significance and engineering value. To determine the influence of bearing clearance on bearing vibration, the theoretical model of a 2-degree-freedom rolling bearing was established based on the dynamic characteristics of the bearing vibration. Based on Hertz elastic contact theory analysis of the dynamic characteristics of the rolling bearing, it was observed that for the tested bearings, the number of balance points of the inner ring of the bearing depends on the clearance of the bearing. When bearing inner clearance (e)e<4.5μm is present in the bearing, a stable equilibrium point exists, and periodic vibration occurs in the inner ring of the bearing near the centre of the balance point. When a gap of (e?4.5μm) is present, and the gap and rotational speed of the bearing increase continuously, the system generates chaotic vibrations, and the area in which the chaotic vibration occurs also increases. The experimental results of the ?127mm rolling bearing indicated that under the same damping parameters, bearing size and rotational speed, the results of the singular attractors obtained from the experimental data are similar to those obtained by solving the equation of motion. This qualitative result not only confirms the existence of chaotic bearing behaviour, but also verifies the reliability of the theoretical model.
查看更多>>摘要：? 2022 Elsevier LtdThis paper applied Archard wear law in feature engineering for the improvement of Support Vector Regression (SVR) performance and realized the rail steel wear behavior prediction. The actual complex rail wear multidimensional degradation information was obtained from field maintenance records over a decade and the hidden data outliers raised the modelling challenges. We applied pre-process technologies including feature importance analysis, physical model guided feature generation and outlier detection to build up the SVR based robust nonlinear regression analysis framework. Individual railway parameters’ effects on the wear process were investigated and revealed through model interpretation-based post analysis. This work provides a practical approach to deploying machine learning algorithms for rail service maintenance data analysis and treatment of data outliers.
查看更多>>摘要：? 2022 Elsevier LtdThis paper presents novel insights of a numerical bolt representation approach taking into account damage and failure, suitable for large-scale models as in full vehicle crash simulations. Custom-built experimental equipment combined with digital image correlation enables observation of bolt failure behavior and its physical characteristics under tension, shear as well as combined loading. A fine-meshed model demonstrates the transferability of the physical properties to numerics including the associated restrictions. The experimental and numerical findings are used to develop an efficient substitute bolt model with high prediction accuracy that takes into account the bolt kinematics due to the thread via volume elements. An isotropic constitutive law with linear elastic and multilinear plastic progression supplemented by a phenomenological damage model depicts the bolt material behavior numerically. The observation of the bolt models under different tension and shear ratios provides new insights to the models accuracy which is assessed by an analytically failure envelope.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, the axial load of bolts connected to the brake disc under emergency braking conditions with different initial speeds was tested by a 1:1 bench test. A finite element model was established to analyze the evolution law of the bolts’ axial load in the braking process in detail. The results show that the axial load variation range of bolts of the bench test first increased and then decreased with the increase of emergency braking initial speed. The maximum load value (59.4 kN) appeared under emergency braking conditions with an initial speed of 280 km/h. The variation range of the bolts’ axial load of the simulation was 55.5 kN, and the error was 7% compared with the test. The influence of material changes of disc and bolt on bolts’ axial load in the braking process was summarized, thus providing a reference for the material selection of bolt and disc.
NSTL
Elsevier