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Size effects make traditional bending theories infeasible in analyzing the springback behavior of H80 foils in the similarity bending experiment.It is observed that there is a certain critical thickness value,which divides the change trend of springback amount of foils into two opposite parts.In order to reveal the reason for size effects on the springback behavior of H80 foils,the method of hardness increment characterization was applied to describe the deformation distribution of foils.The com-petition between strengthening effect of geometrically necessary dislocations and weakening effect of surface grains determines the change trend of springback amount with foil thickness.When the thickness of foils is large,the weakening effects dominate the material behavior,result-ing in that the springback amount decreases with the decrease in foil thickness.However,when the foil thick-ness is small,the strengthening effects dominate the springback tendency,leading to a sharp increase in the springback amount.Furthermore,the deformation distri-bution is disturbed due to the enhanced effects of indi-vidual grain heterogeneity with the decrease in the thickness of foils,leading to the large scatter of springback angle after unloading.