查看更多>>摘要：To understand the difference of corrosion behavior between tin coatings on the copper and brass, the microstructure and atmospheric corrosion of the tin coatings on the H62 brass and T2 copper were compared by XRD, SEM/EDS and electrochemical measurements. The results showed that the preferred planes structure of the tin coatings were (101) and (1 1 2). More SiO(2 )inclusions existed in the tin coating on the brass than on the copper. In the atmospheric environment, the corrosion rates of tin coatings on the brass and copper were 1.427 and 0.578 mu m.y(-1), respectively. The local corrosion sensitivity of the tin coatings on the brass was higher than that on the copper. No matter on the copper or the brass, the local corrosion sensitivity and R of the skyward surface of the tin coatings were greater than that of the earthward surface. The preferential corrosion of the (101) oriented crystal particles was the dominated reason for the higher corrosion sensitivity of the tin coatings. The preferential wetting, the more suspended particles and the intense scouring of rainwater affected the corrosion process of the tin coating as well.
查看更多>>摘要：Difficulties such as large burial depth, large cross-section, and high water pressures exist in the construction of underwater shield tunnels. Thus, the double-layer lining structure begins to be one means of reinforcement of tunnels. To figure out how the depth of the insufficient thickness in the vault of the segment's secondary lining influences the entire structure, the Rail-cum-Road Yangtze River Cross Tunnel in Wuhan is taken as an example, where the deformation distribution, internal force characteristics and failure process of the double-layer lining structure caused by the thickness insufficiency are revealed through a model test method.
查看更多>>摘要：Numerous factors affect the amount of leakage from pipes, e.g. inside pressure, type of pipe failure, soil around the pipe, etc. Few researches have been done on the effect of environment around the pipe on the leakage discharge. In the present study, the leakage from pipes in presence of different soils is experimentally investigated. Leakage from a cracked polyethylene pipe was simulated in the presence of various soils with different properties in a laboratory setup. Leakage -pressure relationships were obtained according to fixed and variable area discharge theory. By quantifying the soil characteristics, the relationship between leakage-pressure coefficients (m and C-d) and soil parameters was obtained. It was concluded that the soil environment affects the amount of leakage discharge. Results show that the particle diameter at 50% passing (D-50), dry unit weight (gamma(d)) and hydraulic permeability coefficient (k) are more appropriate to represent the characteristics of soils. It was also concluded that there are no strong correlation between leakage and some soil parameters. The obtained relationships between different soil parameters and leakage discharge coefficients are also presented.
查看更多>>摘要：Aluminium alloy 7085 forgings are a suitable replacement for 7050 thick-plate material in large, thick airframe parts such as bulkheads. In this paper two factors in small fatigue crack growth rates are contrasted for these two materials - microstructure and fatigue crack nucleation from etch pitting, an unavoidable artefact of aircraft production surface finishes for high strength aluminium alloys. Evidence of the complex interactions between small fatigue cracks and the microstructure of AA7085-T7452 is presented at a sub-grain level to explain scatter in small fatigue crack growth rates below 1x10(-9) m/cycle and delta K = 1.2 MPa root m. Above this level, small fatigue crack growth rate data is presented that demonstrates that growth rates are relatively insensitive to grain size in this material. Equivalent pre-crack size data is presented for several AA7085 and AA7050 specimens, in different material directions, and treated with pre-Type 1C anodising and pre-ion vapour depo-sition etching processes. The measured mean depths of the etch pits produced in both materials was found to be similar yet etch pitting in AA7085 was shown to be less effective in nucleating small fatigue cracks. The etching pre-processes associated with ion vapour deposition coatings were also found to lead to more effective fatigue crack nucleation than pre-anodizing treatments.
查看更多>>摘要：To reveal the failure mechanism of full-grouted bolting system, revised Pile elements were selected to numerically reveal the anchoring performance of full-grouted anchor bolts. A tri-linear bond-slip model was embedded in the Pile elements. A three-dimensional mining stope was created. A rectangular main roadway reinforced with full-grouted anchor bolts was simulated. Then, the retreat mining method was used to exploit the coal seam. The impact of buried depth, pillar size and shearing strength of the grout/rock contact surface was studied. It showed that the coal seam's burial depth significantly influenced the anchorage performance of the anchor bolts. Moreover, increasing the shearing strength of the grout/rock contact surface was conductive to improving the anchorage performance of anchor bolts and preventing roadway convergence. Simulation results were compared against experimental laboratory test and in-situ observation outcome. It was conductive to revealing the anchorage mechanism of full-grouted anchor bolts under the in-situ condition.
查看更多>>摘要：The scour-induced bridge collapse is a critical contributor to the failure of brick or stone masonry arch bridges, which forms a significant share of the existing rail and road infrastructure across the world. Holistic information on the possible failures and the associated collapse mechanisms is essential in formulating suitable mitigation strategies for arch bridges susceptible to scouring. In this context, a novel, quantitative procedure based on limit analysis is developed in this research to quantify the collapse behaviour of masonry arch bridges subjected to scouring at the bridge foundation. Critical foundation movements initiated by scouring are identified as a function of bridge typology and scour-location. Linear kinematic analysis procedures are formulated for the identified collapse mechanisms corresponding to each foundation movement. The proposed iterative procedure uses minimum geometric information to quantify the collapse behaviour of arch bridges with sufficient accuracy.
Alboyaci, Boracinar, Mehmet AytacDemirol, Yunus BeratUzar, Mete...
12页
查看更多>>摘要：Using composite insulators instead of glass insulators in high voltage transmission lines has become common with rapid developments in material technology. This study examined the 270 km long Ispir-Bagistas high voltage line with a 400 kV composite insulator, which was commissioned in 2016. The altitude along the transmission line route varies between 860 and 2800 meters. After the line was commissioned, too many phase-earth failures were experienced. To reduce failures, the Turkish Electricity Transmission Corporation (TEIAS) operator added glass insulators to the existing composite insulators. It was observed that the number of failures decreased significantly after the addition. That study aims to find the most suitable location and the number of glass insulators. Since the design of the insulation system is crucial for network reliability and sustainability, it has become a necessity today to carry out analysis before the design stage. In this context, the pole-insulator systems used in the transmission lines were modelled in the Ansys Electronic Suite finite element analysis program. The influence of the conditions applied in the field was examined. Accordingly, when one, two and three glass insulators are added to the conductor side, the maximum electric field distributions on the composite insulator surface decrease by 19%, 35% and 45%, respectively. In the case of adding glass insulators to the pole side, there is no significant change in the electric field distribution formed on the composite insulator surface. In addition, when adding one, two and three glass insulators, the minimum arc distances increase by approximately 12%, 19% and 21%, respectively. Accordingly, adding three glass insulators to the composite insulator would be appropriate to reduce the failures without changing the composite insulators. Although the electric field decreases up to 45% when glass insulators are added to the conductor side, it would be convenient to add them to the pole side for easy application on the field. Due to the arc distances, it is not recommended that the number of glass insulators is added by more than three for the examined system. The number of faults in the line decreased by 82% in the first twelve months following the addition of the glass insulator to the pole side, which shows the benefit of the application. That application is essential in terms of reducing the problems in live lines without changing existing insulators.
查看更多>>摘要：Abrasive belt grains morphology and wear process have direct effect on grinding surface quality and service performance of titanium alloys. In order to increase fundamental understanding of abrasive belt wear on service performance of grinding surfaces, further provide targeted guidance for anti-fatigue surface grinding, this paper analyzed the surface characteristics and fatigue failure mechanism of the TC17 samples ground before and after abrasive belt wear. Results showed that for zirconium corundum abrasive belt with relatively independent abrasive grains, the fatigue failure of machined surface before abrasive belt wear is dominated by roughness. After zirconium corundum abrasive belt was worn, grinding surface roughness is reduced and surface mechanical properties are strengthened, which promotes the initiation of fatigue cracks from the subsurface and the improvement of fatigue life. Although the wear of electroplated diamond abrasive belt can reduce the surface roughness of grinding surface, the embedding and accu-mulation of abrasive grains hindered the chip removal and heat dissipation in material removal process, making the grinding surface easy to form heterogeneous ablative layer, and fatigue cracks initiated from the subsurface ablation area. The heterogeneous areas formed by surface burns will exacerbate surface stress concentration, which in turn will greatly reduce surface fa-tigue performance, it needs to be avoided as much as possible. Sharp electroplated diamond belts and worn zirconium corundum belts have excellent advantages in improving surface anti-fatigue performance.
查看更多>>摘要：This article is focused on influence of notches on durability of a machine part in the case of cycling loading. There is analysed a draw rod installed in the pin coupler applied in the towing system of railway waggons used for transport of slabs. These waggons are grouped into a train set without own brakes. Therefore, the draw rod is cyclically loaded due to repeated run up and braking by the locomotive. The calculations confirm that the notches on the draw rod are improperly designed and they are causing a fatigue damage. There are proposed design modifi-cations of the draw rod in order to increase its durability. The performed calculations are sup-plemented by verifying simulations using the Finite Element Method. The calculations and simulations correlate well each other and confirm their correctness. Durability of the draw rod was significantly increased thanks to the proposed modifications.
查看更多>>摘要：Rockfall is one kind of major hazard that seriously threatens the safety of bridge structures passing through mountainous areas. The complexity of geological conditions in mountainous areas makes it difficult to determine the initial impact parameters of falling rock in the bridge performance analysis. At present, the subjective and deterministic methods are adopted to get the initial motion parameters of the falling rock for evaluating the structural responses. In this paper, the probability distributions of falling rocks collision parameters are obtained by the rockfall Monte Carlo simulations. Then the characteristic values from the probability distribution of rock motion parameters are taken as the input parameters in the dynamic simulation of bridge structure. Finally, three-dimensional nonlinear dynamic analysis is employed to evaluate the safety of the bridge structure under rockfall hazards. The residual resistance index (RRI) is pre-sented for quantifying the post-impact performance of bridge pier and girder under rock collision. The structural safety is mainly dominated by the impact mass and translational velocity of the falling rock rather than the rotational velocity and impact angle. The rock shape also has non -negligible influence on the structural dynamic responses and performance, and the cube-like rock induces more severe structural damage than other shapes. According to the RRI and prob-ability distribution of rock mass, the non-exceedance probability of RRI is obtained which can be used for the risk analysis of rockfall impacting on bridges. The proposed comprehensive approach for bridge performance evaluation considers the uncertainty of rockfall characteristics, and it provides more reasonable solution to investigate the impact performance of bridge structure under rockfall disasters.
NSTL
Elsevier