Unveiling the deformation mechanisms and forming quality of thin-walled tubes manufactured by 3D free bending forming-based MRE medium: A theoretical investigation and FE modeling

The next generation of aerospace equipment requires thin-walled Al alloy tubes with complex geometries, such as three-dimensional axes and variable curvature radii. Free bending forming (FBF) technology can achieve integral forming of such geometries but has limitations for thin-walled components. Using magnetorheological elastomers (MREs) as internal support materials can increase stress states during bending, control defect generation, and precisely manufacture high-quality tubes. Nevertheless, the mechanical properties of MREs are influenced by various parameters, and the stresses during bending under multiple physical fields are complex. Thus, this study aims to explore the bending characteristics and control the manufacturing defects of thin-walled AA6061 tubes fabricated via a 3D-FBF-based MRE medium. First, the stress state of the MRE under magnetic field conditions is investigated. Then, the interaction force between magnetic dipoles inside the MRE is derived, and the support principle of the MRE on the inner wall of the tube under combined magnetic force conditions is revealed. The influence of material parameter variations of the MRE on tube bending under a small bending radius is analyzed. The Mooney[sbnd]Rivlin model is optimized, and based on the optimized material constitutive model, the mechanical properties of the MRE under different magnetic particle contents and magnetic field intensities are described. The constitutive model is verified through compression tests on MRE samples. Afterward, finite element modeling (FEM) for MRE-assisted internal support bending was established, and the optimal combination of bending parameters was determined and experimentally verified by simulating the effects of the MRE internal support diameter, magnetic powder content, and magnetic field strength on the forming quality of the tubes.