Limiting drawing ratio and deep drawing behavior of dual phase steel tailor welded blanks: FE simulation and experimental validation

Strain localization and premature splitting in the vicinity of outer heat affected zone is a major concern in the formability performance of laser welded similar material dual phase (DP) steels during stretch forming. Hence, the present work aims at evaluation of limiting drawing ratio (LDR) of tailor welded blanks (TWBs) fabricated using two dissimilar material combinations of DP and interstitial free (IFHS) steels using laboratory scale deep drawing test. Finite element models of deep drawing of parent materials and TWBs were developed incorporating anisotropy of sheet metals and non-homogenous properties of the weld zone. The numerical simulations were performed incorporating theoretical forming limit diagram (FLD) to predict LDR, thinning development and failure location. The LDR of both the TWBs was lower compared to that of parent metals due to non-uniform plastic deformation with localized thinning failure at cup bottom in the weaker material side. The failure propagated along a direction parallel and close to weld line as observed in experimental results. The global forming performance of different TWBs was characterized and compared in terms of formability ratio from the deep drawing, limiting dome height and Erichsen cupping test data. It was found that the extent of decrease in formability due to increase in strength ratio was not so severe in deep drawing process unlike stretch forming process. It was also proposed through rigorous finite element studies that LDR of TWBs could be improved with restricted weld movement by shifting the initial weld line position, and the same was validated through deep drawing experiments. (C) 2014 Elsevier B.V. All rights reserved.