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Investigation of process stability and weld quality of underwater wet flux-cored arc welding of low-alloy high-strength steel with oxy-rutile wire

Li Hongliang, Liu Shixiong, Ma Qiang, Wang Pengfei, Liu Duo, Zhu Qiang

Polish Maritime Research

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2021

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nr 3

100--109

EN

The paper described the experimental findings of underwater wet welding of E40 steel using self-shielded flux-cored wire with a TiO2 -FeO-MnO slag system. The arc stability, weld quality and corrosion resistance with different heat inputs were studied. The results showed that the wet welding process of the designed wire displayed good operability in the range of investigated parameters. The microstructure and mechanical properties of the weld metal depended on the heat input. Due to the high fraction of acicular ferrite in the weld metal, the mechanical properties of the weld metal under low heat input had better tensile strength and impact toughness. Fracture morphologies at low heat input had uniform and small dimples, which exhibited a ductile characteristic. The diffusible hydrogen content in the deposited metal obtained at a heat input of 26 kJ/cm significantly reduced to 14.6 ml/100g due to the combined effects of Fe2 O3 addition and the slow solidification rate of molten metal. The microstructure also had a significant effect on the corrosion resistance of the weld metal. The weld metal with high proportions of acicular ferrite at low heat input exhibited the lowest corrosion rate, while the base metal possessed a reduced corrosion resistance. These results were helpful to promote the application of low alloy high strength steel in the marine fields.

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Heuristic energy-saving virtual network embedding algorithm based on Katz centrality

Zhu Qiang, Wang Qing-Jun, Zang Mu-Jun, Wang Zhen-Dong, Xiao Chang

Archives of Electrical Engineering

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2020

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Vol. 69, nr 3

595--608

EN

Current networks are designed for peak loads leading to low utilization of power resources. In order to solve this problem, a heuristic energy-saving virtual network embedding algorithm based on the Katz centrality (Katz-VNE) is proposed. For solving an energy-saving virtual network embedding problem, we introduce the Katz centrality to represent the node influence. In order to minimize the energy consumption of the substrate network, the energy-saving virtual network embedding problem is formulated as an integer linear program, and the Katz-VNE is used to solve this problem. The Katz-VNE tries to embed the virtual nodes onto the substrate nodes with high Katz centrality, which is effective, and uses the shortest paths offering the best factor of bandwidths to avoid the hot nodes. The simulation results demonstrate that the long-term average energy consumption of the substrate network is reduced significantly, and the long-term revenue/cost ratio, the acceptance rate of virtual network requests, and the hibernation rate of substrate nodes as well as links are improved significantly.

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Experimental and numerical investigation on the impact resistance of high-carbon low-alloy steel

Banerjee Amborish, Prusty B. Gangadhara, Zhu Qiang

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

1--17

EN

Duplex high-carbon steel is widely used in ball mills in the form of grinding balls and thus subjected to impact loads during the normal operation of the mill. The influence of impact loading at different impact energies is investigated in this paper. Impact tests using a drop tower were performed in the regime of 100–150 J, and the mechanical response of the material was recorded. The deformation behaviour of the material was classified into two groups: (a) low-impact-energy regime (100–120 J) where the material bulged without fracture and (b) high-impact-energy regime (130–150 J) where the material faced catastrophic failure. An overall increase in the load-bearing capacity of the material was found with an increase in the impact energy. The energy–time curves exhibited both linear and nonlinear regions which were attributed to the nucleation and propagation of cracks. Shear bands were observed in the specimens which underwent catastrophic fracture (i.e. 130 J and above); however, significant changes in the features of shear bands were noticed with increase in the impact energy. Fracture surfaces displayed the presence of microvoids, dimples, knobby fracture and river pattern, thus indicating ductile as well as a brittle mode of failure. Transmission electron microscopy results revealed the presence of much finer nano-grains inside the shear bands as compared to the surrounding regions. Finite element simulations exhibited an increase in the shear stress with the propagation of shear bands during the ongoing deformation process.