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Forming tubes with various bending radii without changing the bending dies is much easier for the 3D free bending forming (FBF) process. In the 3D-FBF process, different bending radii were realized by adapting the eccentricities of the bending dies. The accuracy of the U-R curve is crucial for the precision forming of complex bending components. In this study, the U-R relation curve of the Al alloy tube with a specific friction coefficient, fixed geometry size, clearance between tubes, and bending die was fitted first based on the forming results of AA6061-T6 tubes under different eccentricities. Second, the U-R relationship curve based on the experiment is used to propose the U-R relationship's mathematical formula based on many hypotheses. Finally, the modified U-R mathematical formula was applied in the finite element (FE) simulation and the actual FBF experiments for the AA6061-T6 Al alloy complex shape space bending members. The U-R relationship curve's reliability was verified by comparing the simulation and experimental results. The results obtained from the modified U-R relationship align well with the FE modeling results and can be directly applied to the bending process for the intended components. [ABSTRACT FROM AUTHOR]

Aluminum alloy tubes are widely used in various industries because of their excellent performance. Up to now, when the tube is bent, the elastoplastic deformation evolution mechanism of the cross-section has not been clear, and no direct analytical proof has been found. In this paper, based on the bilinear material model assumption, a new mechanical model of tube plane bending deformation is constructed. The analytical model can describe in detail the evolution mechanism of elastic–plastic deformation on the cross-section of the tube after bending deformation, the position of the elastic–plastic boundary, the position of the radius of the strain neutral layer, and the relationship between the bending moment over the section and the bending radius. According to this model, the deformation law of the tube cross-section during bending is elucidated. The results are as follows: (1) the deformation evolution of the cross-section of the bending deformed tube calculated by the analytical model is in good agreement with the finite element model (FEM) of pure bending. (2) By comparing the results of the analytical model with FEM results, and the processing test of the self-designed four-axis free bending forming tube bender, the bending moments are in good agreement. (3) Compared with the bending moments calculated by several other analytical models of tube bending, this model has a relatively small deviation value. [ABSTRACT FROM AUTHOR]

The first study of thin-walled aluminum-alloy tubes with underwater-laser-nozzle in situ melting technology was carried out. The study mainly covered the influence of the water environment on the laser melting process, melting appearance, geometric characteristics, microstructure, regional segregation and microhardness. During the transfer of the cladding environment from air to water, the uniformity of the cladding layer became poor, but excellent metallurgical bonding was still obtained. The dilution rate (D) decreased from 0.46 to 0.33, while the shape factor (S) increased from 4.38 to 5.98. For the in-air and underwater samples, the microstructure of the melting zone (MZ) and the cladding zone (CZ) were columnar dendrites and equiaxed grains, respectively. In addition, the microstructure of the overlapping zone (OZ) was composed of columnar dendrites and equiaxed grains. The underwater average grain size was smaller than that of in-air. In addition, the water environment was beneficial for reducing the positive segregation in the columnar dendrite region. Compared with the in-air cladding sample, the precipitated phases in the OZ of the underwater cladding sample reduced. Under the combined action of grain refinement and precipitated phase reduction, the microhardness value of the underwater OZ was higher than that of the in-air OZ. [ABSTRACT FROM AUTHOR]

The paper presents the results of numerical tests of impact and energy absorption capacity of thin-walled columns, subjected to axial impact loading, made of aluminum alloy, and having a square cross-section and spherical indentations on their lateral surfaces. The numerical models were validated using an experiment that was conducted on the Instron CEAST 9350 High Energy System drop hammer. Material properties of the applied aluminum alloy were determined on the basis of a static tension test. The crushing behavior of the columns and some crashworthiness indicators were investigated. On the basis of the results of the conducted analyses, conclusions were drawn about the most beneficial design/constructional variants in terms of achieved crashworthiness parameters. [ABSTRACT FROM AUTHOR]