查看更多>>摘要：? 2022 Elsevier LtdThe work concerns the phenomenon of damage to internal partition walls in typical prefabricated residential buildings. As a construction system, large-panel buildings were very popular all over Europe at the end of the 20th century. Defects in structural members or layer joints in facade wall panels have been investigated many times. The neglected aspect of the operation of large-panel buildings are the consequences of excessive deformation of structural elements progressing over time, e.g., deflections of prefabricated floor slabs. The safety of building residents is determined not only by the fulfillment of the limit states conditions by basic structural elements, e.g. external walls or floor slabs. Failures can also occur as a result of damage to partition walls. Initially rigid floor slabs remain supported only at the edges of the structural walls, while in the middle zones they are deflected. Partition walls, made of various materials, are subjected to shear stress in addition to compression. This can result in cracks and even destruction of the wall structure. The problem presented for discussion was confirmed by the case of a real failure of partition walls in a building operated for more than thirty years. To find explanation and reasons of such a phenomenon, numerical calculations were carried out for partition walls and for prefabricated floor slabs that are under and above the analyzed wall. In the case of partition walls, the effort of the wall material was considered in terms of exceeding the ultimate limit state in the tensile zones. For the floor slabs the deflection values were determined. The implemented concept of an effective reconstruction of the wall structure has been also described.
查看更多>>摘要：? 2022 Elsevier LtdIn this research, the effect of important parameters on hydrogen affected fatigue failure in pipeline steel was studied in detail through literature review. It was found that several parameters including steel microstructure, load frequency, temperature of test environment, hydrogen pressure and stress intensity factor range may influence fatigue phenomenon in pipeline steels in hydrogen environment. It was also found that the pearlite microstructure slows down fatigue crack growth rate. The hydrogen effect on the fatigue crack growth rate is more pronounced by migrating the hydrogen atoms to the crack tip at low frequencies. The fatigue crack growth accelerates with the increase of hydrogen pressure and its minimum amounts are observed when tested in the air. Micro-cracks and some large cracks is observed in the fracture surfaces in fatigue tested specimens in hydrogen environment showing that the interaction of cyclic loads and hydrogen makes pipeline steel highly susceptible to cracking.
查看更多>>摘要：? 2022 Elsevier LtdA metallurgical failure analysis was conducted on a grey cast-iron (GCI) automotive brake disc to unravel the root cause of its premature failure. The brake rotor had been in service for about one year and three months and covered a total mileage of 17 173 km before the failure was reported. However, this investigation aims at identifying the causes of the failure and proffer solutions to forestall similar future occurrences. Chemical composition analysis on the disc suggested that its elemental composition is within the required standard for such a component. The disc swan-neck thickness, hardness and microstructure analysis conformed adequately with the material specifications. SEM-EDS study of the fracture surface showed the presence of admixture oxides of Al, Mg, Si, Na, Ca, Ti and Mn, suggesting nonmetallic (slag and sand) inclusions. A fractographic study of the broken surface indicated that the failure was caused by these oxide inclusions embedded in the swan neck region of the rotor during the casting process. Microcracks were observed to have been initiated within the inclusion particles and propagated through the graphite-pearlite interface, eventually leading to the disc failure. Recommendations are also provided to guide the operation of metal-casters to prevent the recurrence of nonmetallic inclusions, which can significantly diminish the service life of cast products.
查看更多>>摘要：? 2022 Elsevier LtdDiesel hydrogenation unit is an important equipment for processing inferior oil in petroleum refining enterprises. Among them, the U-tube heat exchanger has been in high temperature and corrosive environment containing chlorine for a long time. Serious problem of tube bundle corrosion failure caused by ammonium chloride salt deposit. Anatomy of the diesel hydrogenation heat exchanger showed that the leakage part mainly appeared in the outermost bundle of the heat exchanger tube near the exit section, and the local area showed a large area of gully damage. Metallographic and XRD results show that the failure tube bundle material does not have manufacturing defects, and the corrosion location scale contains NH4Cl and iron oxides. The process flow analysis based on PR-NRTL model showed that the heat exchanger was in the NH4Cl crystallization temperature range, and the crystallization temperature increased with the increase of N and Cl contents in raw materials. Fluid simulation analysis of inlet tube box and single U-tube is carried out by using component transport equation and condensation model. Computational fluid dynamics (CFD) results indicate that there is a low velocity zone with high volume fraction of gas phase in the tube box. The higher gas volume fraction results in the formation of more NH4Cl particles into the U-tube bundle during heat transfer cooling. With the decrease of temperature, liquid water content in U-tube increases gradually and mainly distributes at both sides and bottom of tube bundle. The gas phase gradually fills the top of the tube bundle, and the oil and gas stratification becomes more obvious. The mass transfer rate and corrosion rate were the highest at the bottom and both sides of the tube bundle. With the temperature decreases, the NH4Cl particles generated in the tube continue to increase. The particles were deposited at 2000–3000 mm near the outlet section of the U-tube tube. NH4Cl particles absorbed liquid water, resulting in under-deposit corrosion of the tube bundle, and eventually led to the thinning and leakage of the heat exchanger tube bundle.
查看更多>>摘要：? 2022 Elsevier LtdThe CO2 corrosion mechanism of pipelines is a controversial topic, especially under flowing conditions. In this work, the CO2 corrosion behavior of X80 steel under static and flowing conditions was studied by the electrochemical measurement and computational fluid dynamics (CFD). The results showed the CO2 corrosion was controlled by charge transfer in static conditions and mass transfer in flowing conditions. Localized damage of corrosion product film under flowing conditions is caused by CO2 bubble cavitation rather than wall shear. The failure process under flowing conditions can be divided into three stages: localized corrosion, bubble cavitation-film rupture and enhanced localized corrosion. The corrosion behaviors of CO2 under static and flowing conditions were described, and the corrosion mechanism was expounded.
查看更多>>摘要：? 2022 Elsevier LtdThe evolution of wheel-rail dynamic interaction of a high-speed railway vehicle is essential for the simulation of wheel-rail rolling contact damage under low adhesion conditions. The main objective of this study is to reproduce the dynamic wheel-rail interaction behaviour under various interfacial contaminations by experimental and numerical modelling methodology. Firstly, the wheel-rail adhesion characteristics under different interfacial contaminations were obtained. Subsequently, a simplified numerical methodology was proposed to extract the parameters from the high-speed adhesion tests to modify the simplified theory of Kalker (FASTSIM). The initial slop reduction factor and the slip-velocity-dependent coefficient of friction (COF) were introduced based on the high-speed experimental curves. Furthermore, the modified wheel-rail rolling contact model was incorporated into a longitudinal vehicle-track coupled dynamic model. The wheel-rail dynamic interaction behaviours under different operational conditions were attained. Finally, the wheel-rail wear performances were primarily investigated for typical traction coefficients under wet conditions. Results show that the wheel-rail creep force drops dramatically when the wheel enters the low adhesion zone (LAZ). There is a sudden increase in the creep force when the adhesion recovers. In addition, the wheelsets begin to slide and have severe wear at LAZ when the traction coefficient is larger than 0.1 at high speed.
查看更多>>摘要：? 2022 The AuthorsBioresorbable stents (BRS) are an alternative to existing bare-metal stents (BMS) and drug-eluting stents (DES), aiming to reduce the short- and long-term complications in cardiovascular interventions. A combination of biodegradable polymers in a composite scaffold is a promising solution to improve BRS flexibility and strength, which is currently limited by the material properties of polymers. In this study, a mechanical performance of a composite BRS comprised of two layers with four different combinations of polylactic acid (PLA) and polycaprolactone (PCL) was examined with finite element analysis (FEA). Stent crimping and expansion with the balloon inside an atherosclerotic artery was simulated, and stent performance parameters were evaluated and compared between different composite layer configurations. The single-material PCL stent showed the highest recoil and failed to provide support to the artery, while the stiffer single-material PLA stent experienced significantly lower recoil, but also the highest dogboning during expansion, which could increase arterial wall damage. Nearly identical performance was observed for both mixed-material configurations, with recoil and foreshortening closer to single-material PLA stent and dogboning during expansion between both single-material stents. They showed the highest dogboning after balloon deflation due to a combination of permanent deformation at the ends of the stent and lower stiffness at the middle, which allowed for higher recoil at the middle but not at both ends of the stent. The combination of biodegradable polymers into composite BRS shows potential for targeted stent designs with performance tailored to specific needs.
查看更多>>摘要：? 2022 Elsevier LtdAn accident caused by train control system may not only bring expensive loss, but also result in severe destruction to surrounding environment. The purpose of this study is to study operational risk of Chinese Train Control System- Level 3 (CTCS-3). An integrated risk assessment method is developed by combining fishbone diagram (FD), Fuzzy Analytic Hierarchy Process (FAHP) with cloud model. Based on fishbone diagram, risk factors (RFs) of train control system are identified from two perspectives of hazard event, namely occurrence frequency and sequence severity. To further classify RFs quantitatively, a revised risk matrix based on FAHP is introduced to calculate the consequence and likelihood weights for each risk factor (RF), and then Risk Index (RI) is getting by making product of consequence and likelihood weights, which reflects relative influence degree on operational risk. Finally, in order to assess the comprehensive operational risk of CTCS, cloud model is used to logically calculate quantitative results, and the CTCS-3 in Wuhan-Guangzhou high-speed railway is empirically investigated to analyze its overall operational risk level. The result shows that its risk level is between medium and low, and more inclined to low, which means being acceptable but not ideal. Meanwhile, some specific suggestions and measures are proposed to eliminate or reduce RFs with higher frequency and worse consequence.
查看更多>>摘要：? 2022 Elsevier LtdThe residual stresses generated during the manufacturing process of titanium alloy rolled ring parts, which is an important factor affecting the dimensional accuracy and operational stability of the casing parts. The research object is the TC4 titanium alloy profiled aerospace rolling ring. The optimized process is proposed by introducing bulging technology to control the residual stresses. Firstly, the stress evaluation index and comprehensive evaluation function of ring parts were established. Secondly, a multi-step continuous simulation model of the rolled ring manufacturing process was established. Finally, experimental measurements of the rolled ring parts under different process conditions were completed using the hole-drilling method. The experimental measurement results are consistent with the evolution of residual stresses obtained from the simulation results. For casing parts, the introduction of the bulging technique into the optimized process for ring parts provides an effective improvement in the uniformity of residual stresses.
查看更多>>摘要：? 2022 Elsevier LtdThe drainage system deterioration is one of the important factors leading to cracking of lining structure. This paper first investigates crack patterns and water leakage through field investigations, and then reproduces the drainage system deterioration process of the tunnels and analyzes the failure mechanism of the linings by utilizing a series of fracture-based numerical models. Results reveal that the longitudinal cracks are the main cracking patterns, followed by circumferential cracks. Furthermore, lining cracks are the weak points of the lining structure and are closely related to water leakage. The deterioration of the drainage system leads to an increase in water pressure acting on the secondary lining, which leads to severe stress concentrations and cracking in the lining structure, respectively at the arch shoulder, the middle of the sidewall, and the arch foot. Finally, the paper explores the applicability of siphon drainage pipes to the treatment of water leakage. Some suggestions are also made for the prevention of water leakage in tunnel linings.
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