Experimental assessment of nonlinear elastic behaviour of dual-phase steels and application to springback prediction

• The elastic modulus degradation of DP steels is sensitive to the loading strategy.
• The three-point bending test with pre-strained sheet is proposed.
• Yoshida chord elastic model integrated with Yld2000-2d and HAH is employed.
• The springback of the curved-flanging test is used to assess the loading dependence.

The aim of this paper is to identify ways to improve the description of nonlinear elastic behaviour of dual-phase steels under different loading strategies. Three mechanically-measured tests, i.e., uniaxial and biaxial loading–unloading–loading cycle tests and the proposed three-point bend test with pre-strained sheet, were introduced to determine the elastic modulus degradation with the increase of plastic strain. A significant effect of the loading strategy on the determination of the initial and the degradation of elastic modulus was observed and discussed. As a three-dimensional forming application case, the curved-flanging test for a dual-phase (DP) steel sheet sample was conducted to validate the identification of the nonlinear elastic modulus for springback prediction. To accurately capture the nonlinear elastic behaviour and anisotropic hardening of the DP steel sheet, the Yoshida chord elastic model integrated with the yield criterion Yld2000-2d and the homogeneous anisotropic hardening (HAH) model was employed. The results indicated that the uniaxial loading strategy overestimates the angular springback. The biaxial loading strategy better captures the sidewall curl than the angular springback compared to other strategies. The proposed three-point bending test with pre-strained sheets appears to be an alternative method to determine the nonlinear elastic behaviour because it leads to a good prediction of the angular springback in the curved-flanging test.

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