Analytical model of neutral layer shift in tube bending introducing material parameters

Neutral layer shift is the key parameter to feature the degree of unequal bending deformation. Based on the balance of torque, an analytical model for neutral layer shift in tube bending is established by introducing material parameters. The model is assessed from various aspects in rotary draw bending and press bending and the rules of neutral layer shift in tube bending are studied with different geometric and material parameters. The results show that: appling the model to TA18 tube rotary draw bending, it is found that the accuracy of the established model is comparable to that of existing analytical method, but the established model can reflect the influence of material parameters on neutral layer shift and is more closer to the experiment result than finite element method; applied the model to A6063 and AZ31 tube press bending and compared the results with Hasegawa method, it shows that the established model provides better prediction accuracy of neutral layer shift under tension-compression asymmetry; decreasing the bending radius or increasing the bending diameter, the neutral layer shifts inwards; decreasing the ratio of tensile strength to compressive strength or increasing normal anisotropy exponent, the neutral layer also shifts inwards.