Research on the Neutral Layer Deflection Phenomenon in Three-Dimensional Stretch Bending of Profiles

This paper aims to study the deflection phenomenon of the neutral layer in the cross-section of profiles during the 3D stretch-bending process. By establishing the displacement field for both the stretching and bending processes of a profile with elastoplastic constitutive characteristics, and combining the deformation processes, the geometric description of the profile deformation is constructed, and then linearized. Subsequently, by integrating the material’s constitutive properties and model boundary conditions, the analytical model parameters for profiles with regular cross-sections are solved. The analytical model effectively captures the behavior of the neutral layer and its deflection phenomenon. To further investigate, the finite element model was developed to simulate the deformation process. The distribution of the neutral layer in the simulation results matched the analytical predictions. To generalize the analytical results to profiles with arbitrary cross-sections, an L-shaped profile was analyzed, and a roller-based 3D flexible stretch-bending device with roller dies was used. By measuring the springback direction, the neutral layer deflection observed in both the analytical and finite element model results was validated. The results demonstrate that, under small deformation conditions, the neutral layer deflection during the 3D stretch-bending process was successfully predicted.