Through investigating the effect of parameters on the fatigue properties and crack propagation behavior of friction stir crack repaired 2024 aluminum alloy, we demonstrated that the fatigue strength of friction stir repaired Al2024 was sensitive to the repairing parameters and had a “V” type discipline with the rotating speed or advancing velocity. The fatigue crack growth rates of the repaired specimens were higher than the base material counterpart, and the crack propagation mechanism in the repaired zone was mainly intergranular. When the improper repairing parameters were adopted, the delamination defect would form at the interfaces between the repaired layer and base material
A detailed study is carried out on the mechanical behaviour of metal-filled single-walled carbon nanotubes under uni-aixal compression.Influence of several factors,including the number of encapsulated metal atoms,tube radius,tube length and tube chirality,is examined and compared with those predictions obtained from continuum mechanics.Results in this work provide a good reference for both theoretical study and industrial application of metal-carbon nanotube structures.
Magnesium alloys have great application potential in the field of advanced manufacturing because of their excellent properties. Aiming at eliminating the problems of coarse grains and poor mechanical properties in the fusion welding of magnesium alloys, a strengthening method of fusion welded joints on the basis of microstructure design was proposed using fine, uniform and dense grains as the matrix and particle reinforced particles as the strengthening backbones. The ideal microstructures were successfully prepared by the powder feeding with fusion welding and friction stir processing, and the influence mechanism of grain morphology and mechanical properties were discussed. After the strengthening treatment, the grain size of magnesium alloy was decreased from 193.5 μm to 15.9 μm., and the grain refining effect reached 91.8%, the tensile strength was increased by 70.2Mpa, and the elongation was increased by 136%. Furthermore, by investigating the grain morphology, texture strength, types of the precipitated phase and dislocation distribution in the different processing stages, the strengthening effect of fine grain strengthening by particles and the dispersion distribution of the reinforced particles and its pinning effect on dislocation mainly contributed to the improvement of tensile strength and hardness of magnesium alloy joint, and grain refinement and texture weakening are the main mechanisms for the improvement of elongation.
Material constraints are important factor effects on the fracture behavior of welded joints. The effect range of the material constraint is an important and interesting issue which needs to be clarified, including whether the effect range of a material constraint exists or not, who will affect it, and whether the material constraint is affected by the no adjacent area or not. In this study, different basic models which reflect different single metallic welded joints, bimetallic welded joints and dissimilar metal welded joints were designed, and the fracture resistance curves and crack tip strain fields of the different models with various material constraints were calculated. Based on the results, the questions above were answered. This study has significance for developing solid mechanics, optimizing joint design, structure integrity assessment, and so on.
In this paper, Cu-based and Ni-based filler metals were used to obtain laser-CMT hybrid welded copper/stainless steel (Cu/SS) joints. The effect of wire compositions on the microstructure and mechanical properties of T2 Cu/304 SS dissimilar metal joint was studied. The results showed that Fe-Cu liquid phase separation occurred in the fusion zone of the Cu-based weld, and Cu penetration cracks appeared in the heat-affected zone (HAZ) on the steel side. The Cu penetration cracks formation is derived from supersaturated Cu atoms penetrating, gathering and merging at the steel side fusion line along the austenite grain boundaries. The penetration cracks can be eliminated effectively by the Ni-based filler metal, because the diffusion of Cu into the fusion zone and the HAZ on the steel side is limited significantly by the increase of Ni content. The Ni-based weld consisted of dendrite grains in the fusion zone, and Fe-rich blocks and Ni-rich islands nearby the HAZ of Cu-side.
With the help of molecular dynamics simulations and an artificial sodium channel model, we corroborated that the application of terahertz stimulation at a characteristic frequency can largely increase the permeability of the sodium channel by a factor of 33.6. The mechanism is that the carboxylate groups in the filter region transfer the absorbed terahertz photon energy to the sodium ions, which increase the ions’ kinetic energy; this results in breaking the hydrated hydrogen bonding network between the hydrosphere layer of the ions and the carboxylate groups, thereby increasing their diffusion and reducing the energy barrier for them to cross the channel. This study on terahertz-driven particle transmembrane transport offers new ideas for targeted therapy of channel diseases and for developing novel integrated engineering systems in energy conversion and storage.
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