Haghani, MajidNeya, Bahram NavayiAhmadi, Mohammad TaghiAmiri, Javad Vaseghi...
28页
查看更多>>摘要：In this paper, a new approach has been developed to conduct seismic failure analysis of concrete gravity dams using extended finite element method and evaluated numerical parameters of dam-foundation-reservoir system. Failure analysis of concrete gravity dams are investigated using Extended finite element method (XFEM) combined with time integration by alpha-method. To perform the failure analysis and dynamic fracture behavior of a cracked dam, dynamic stress intensity factors based on interaction integral with dynamic effects are utilized. The penalty method is used in this study to model the opening and closing of cracks due to seismic loading. In addition, to apply the interaction between dam, foundation and reservoir in finite element model, zero thickness six-nodal contact elements are used in which the system formulated with lagrangian approach. To achieve this goal, several examples are first reviewed to validate the proper performance of a written code, and the results are then compared with those reported in the literature. Then, numerical parameters in seismic failure analysis such as length of crack growth, angle of initial crack, assembling of mass matrix, using high-order elements and penalty parameter discussed. The results show when cracks start to propagate, in the numerically approach, tip elements will switch to elements that fully cut by cracks. This transformation produces shockwaves during failure analysis. Obtained results show by using crack tip element, the analysis is numerically unstable and does not end. Using eight-node elements with four nodes enriched only by the Heaviside jump function and elimination of enrichment functions of the crack tip are reduced the failure analysis costs while good accuracy. In addition, a different crack path created when di-agonal and consistent mass matrix used in the failure analysis.
查看更多>>摘要：Hollow grouted bolt is an important component of slope reinforcement for structures like skyscrapers, tunnels, railways, highways, bridge foundations and dykes etc. The mechanical properties of it are significant for ensuring the safety and reliability of the structures reinforced, particularly the yield ratio, which must not exceed 0.8 according to the technical standard. For the purpose of alloy elements saving and production costs reduction, as well as for failure prevention, this paper endeavors to substitute the 45 carbon steel (equivalent to the ISO C45E4) for the Q345B low alloy steel (equivalent to the ISO E355DD) to produce the hollow grouted bolt, and focuses on the influencing factors in the processing technology to achieve the desirable properties. In detail, different designs in the chemical compositions, deformation extents and heat treatment processes were proposed and testified to figure out the optimum means for producing the 45 carbon steel hollow grouted bolts. Especially, a novel heat treatment process that applied the high-frequency rapid heating technology in hot rolling was also proposed for energy saving and efficiency improvement. On the finished bolts, the direct reading optical emission spectrometer, metallographic microscope and universal testing machine were utilized to evaluate the compositions, structures and properties. In addition, finite element analysis was performed on the hollow grouted bolts to evaluate the reliability in the application scenario of tunnel excavation. Achievement of this paper would have some reference values for failure prevention of the hollow grouted bolts serving under the similar engineering environments.
查看更多>>摘要：The performance of high temperature vulcanized (HTV) silicone rubber used in composite insulator will be worse in harsh environment. The acid-base pollutants in the environment have a great influence on the performance of silicone rubber. As one of the aging factors of composite insulators, acid corrosion has not been studied deeply. In this paper, the AC charged aging test of the silicone rubber sample in an acid environment was carried out, and then its physicochemical and electrical properties were tested, including microscopic morphology, hydrophobicity, infrared spectroscopy, and electrical strength. The effect trends of duration time, charged voltage and acid pH value on material properties are studied. The results show that under the combined action of acid-fog and voltage, the performance of silicone rubber will be degraded. The smooth structure of the surface of the material is destroyed, the side chains of the polymer are severely cut, and the hydrophobicity becomes worse. The AC flashover voltage along the surface has a power function relationship with the pH value. Continuous deterioration of composite insulators may occur in acid polluted areas for a long time.
查看更多>>摘要：The phenomenon of erosion wear and high temperature corrosion will lead to thinning of tube wall, and serious tube burst will occur after long operation in circulating fluidized bed boiler. To obtain the effect on tubes by erosion wear and ammonia gas high temperature corrosion, a hightemperature gas-solid erosion wear test facility was used to simulate the SNCR conditions. This paper mainly studies the erosion wear characteristics, ammonia gas high temperature corrosion characteristics and coupling characteristics under different erosion speeds, erosion angles and heating temperatures. The results showed that the main erosion wear mechanism of 20G (SA106B of United States Standard) is cutting wear at low erosion angle, while deformation wear is the main action, and crack is the supplementary action at high erosion angle. The impingement velocity is varied from 29 to 43 m/s, the mass loss is varied from 0.0343 g to 0.1367 g. Erosion velocity plays an important role in affecting the wear of the specimen, while there is little effect of heating temperature on the wear of the material. In the studying of coupling characteristics, it is found that ammonia gas increases the critical temperature of the material. Furthermore, ammonia gas can accelerate the wear of specimens, but erosion wear is still the main cause of tube burst in fluidized bed boiler. In boiler operation, measures to prevent erosion wear should be taken to restrain coupling erosion.
查看更多>>摘要：Spot welding is the most popular assembly method used in the automotive industry due to its simplicity, effectiveness, and low cost. Simulation techniques for spot welds play an essential role in today's aggressive vehicle development schedules, and the accuracy of the analysis impacts the quality of the design in terms of noise-vibration-harshness and durability. Using static and multiaxial low cycle fatigue analysis, this study focuses on three different spot weld modeling methods: Rigid spot weld, solid element spot weld, and umbrella spot weld. Spot weld modeling techniques were compared for specimens with different thickness levels and weld diameters, and under different loading conditions. In addition, the accuracy levels of spot weld modeling methods are presented by comparing the life found by multi-axial low cycle simulations with the fatigue tests.
Komssi, TamiSantaella, Jose GarciaBohme, Stephan AndreSzanti, Gabor...
16页
查看更多>>摘要：A material model for carburized CrNiMo steel and an advanced shear stress intensity, multiaxial fatigue criterion against surface and subsurface fatigue in bevel gears have been developed and presented in earlier publications. This study assesses the accuracy of the proposed methodology by comparing it to load-controlled bevel gear tests at varying hardening layer thicknesses. The dominant failure mode was wheel-initiated tooth flank fracture. Fractographic analysis by means of scanning electron microscopy revealed a severely elongated MgO-Al2O3 cluster in the only pinion-initiated tooth flank fracture. By correlating the calculated material utilizations and the number of cycles to failure, a reiterated lifetime factor is presented. The refined methodology is shown to be capable to differentiate between and accurately predict pitting and subsurface fatigue under well-defined test conditions.
查看更多>>摘要：Bipolar plate is a significant component in proton exchange membrane fuel cell, which plays an important role in supporting, heat conducting, electricity conducting and transferring gas. Hydroforming is an advanced method for manufacturing metal bipolar plates. Exploring hydroforming mechanism and controlling forming quality are very important to ensure the performance of bipolar plate. In this paper, a model of a single serpentine flow filed bipolar plate in hydroforming process was established to study the hydmforming quality control mechanism. The results show that the formability and filling rate of the bipolar plates are improved by increasing the pressure in the hydroforming process. However, the partial fracture of the bipolar plates appears with pressure increases. The forming effect of die's outer radius is better than that of inner radius, and the forming effect of bipolar plate can be improved by increasing the outer radius. The draft angle has a little effect on the formability. Increasing the width and depth will improve the filling rate, but fracture may occurs with excessive depth. With the thickness of the sheet increases, its form quality is more difficult. Those results can provide references for the bipolar plate process and parameter optimization.
Cinar, Mehmet AytacDemirol, Yunus BeratInce, AdemAlboyaci, Bora...
15页
查看更多>>摘要：Cable terminals are used for the connection of high voltage underground cables to busbars and transmission lines. Various defects may occur in cable terminals used as Heat-Shrink or Cold Shrink. As a result of these defects, fires and long-term power outages may occur due to the breakdown of the cable terminal depending on partial discharge. Consequently, human life losses and economic losses are inevitable. In this study, a heat-shrink cable terminal with 36 kV phase to-phase operating voltage randomly failed while measuring power quality parameters in the field is examined. In this context, it is aimed to examine the root causes of the failure in the field with the finite element method according to different design and structural defect situations. For this purpose, the cable terminal was modeled in real scale in Ansys Electronics Suite finite element software in line with the data received from the manufacturer. According to the analysis results, especially in case of peeling the entire outer semiconductor layer on the XLPE and partial peeling of the outer semiconductor layer on XLPE increases electric field significantly compared to the reference design. In addition, the thickness and relative permittivity changes of the critical elements used in the cable terminal affect the electric field distribution. According to the results of the analysis performed, the defect situations that could be the root cause of the failure was determined. Also, the effect of other defective situations was understood and reliability analysis was made.
查看更多>>摘要：The condenser is an indispensable basic equipment in chemical industry. Due to the complex working conditions, leakage failure accidents often occur for condensers. In this work, the leakage failure of a spiral plate condenser made of 304 stainless steel has been investigated. The failed condenser, which had serviced for just six months, was used to condense isopropylamine by circulating frozen brine. After cutting and opening the condenser, numbers of leakage points were found occurring near the welding joints between the spacing columns and stainless steel spiral plates contacting with the frozen brine. The evidences indicate that leakage of the condenser is due to pitting corrosion caused by chloride ions near the welding joints between the spacing columns and stainless steel spiral plates. The sensitization of stainless steel in the welding zone intensifies the risk of pitting corrosion. Welding defects, including welding cracks and slag inclusions, are observed in the welding zone of the spacing columns, which might also aggravate the development of corrosion in the welding zone.
查看更多>>摘要：This paper investigates the thermal performance reduction of a groundwater heat pump (GWHP) system installed in Hubei province, China by the monitoring of the system operation over a two-year period. Pipe corrosion and deposits were detected in the maintenance of heat pumps, which might contribute to the thermal performance reduction. In order to understand the physic-chemical dynamics inside heat pumps during the system operation, the groundwater pumped out from the aquifers and the deposits collected in a condenser of a heat pump were analyzed. The groundwater has electrical conductivity of 973 mu S/cm, indicating low salinity. The X-ray fluorescence (XRF) analysis shows the deposits were composed mainly of 66.4% Fe2O3 and 17.8% CaCO3, indicating both effects of iron oxidation and groundwater fouling. The corrosion effects on the heat transfer efficiency of metal pipes were examined. The heat transfer coefficient (HTC) comparison of a raw pipe and three rusted pipes show that the HTC of the rusted pipes was reduced by 8.3-41.5%, meaning a significant decrease in heat transfer efficiency. It is verified that the thermal reduction of the GWHP system could be attributed to the pipe corrosion which desires to be carefully considered in system design and operation in future.
NSTL
Elsevier