Study on 3D strain distribution characteristics using etched grid method in tube bending

Strain distribution is crucial for understanding tube bending and preventing defects. In this paper, taking 321 stainless steel as the objective, via etched grid method, the strain distribution characteristics during tube bending are studied, the effects of the bending velocity and the bending angle on the strain distribution are analyzed, and the consistency of thickness strain with wall thickness variation is verified. The results show that: (1) three-dimensional (3D) strain is symmetrically distributed about bending plane and reaches the maximum value at wall extrados and intrados; (2) absolute value of the 3D strain increases at first, then decreases in tube bending; (3) compared with bending angle, bending velocity has greater effect on spatial strain, and compared with tangent strain, thickness strain is more sensitive to bending velocity; (4) thickness strain distribution characteristics are generally consistent with distribution characteristics of wall thinning degree.