Formability assessment and failure prediction of laser welded dual phase steel blanks using anisotropic plastic properties

• Published in: International journal of mechanical sciences Vol. 126; pp. 203 - 221
• Main Authors: Bandyopadhyay, Kaushik, Lee, Myoung-Gyu, Panda, Sushanta Kr, Saha, Partha, Lee, Joonho
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.06.2017
• Subjects: Dual phase steel; Failure criteria; FE simulation; Sheet metal forming; Tailor welded blanks; Yld2000-2d; Failure criteria; Tailor welded blanks; Sheet metal forming; FE simulation; Dual phase steel; Yld2000-2d
• ISSN: 0020-7403; 1879-2162
• DOI: 10.1016/j.ijmecsci.2017.03.022

Assessment of the role of weld zone and difference in the material properties across the dual phase steel tailor welded blanks (TWBs) during sheet forming is imperative prior to applications in light weight auto-bodies. In the present work, one laser welded blank (LWB) of similar material combination and two different TWBs were fabricated by laser welding of dual phase steels (DP600, DP980) and interstitial free (IF) steel. The quality of the laser welded similar (DP600-DP600) and dissimilar material (DP600-DP980 and DP600-IF) joints were evaluated in terms of metallographic observations, hardness studies and tensile tests. Evolutions of microstructures within the vicinity of weld region were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, the local property changes in the weld regions were observed through micro-hardness and nano-indentation tests. The formability performances of above three welded blanks were evaluated under different deformation modes using three case studies such as Erichsen cupping, deep drawing and double-stage forming tests. It was observed that the formability of DP600 LWBs decreased by 28% due to the presence of weld in comparison to that of the monolithic parent material. In case of TWBs, the weld line movement was observed causing non-uniform deformation and failure at weaker side. The FE models of the above three case studies were developed incorporating Yld2000-2d anisotropy constitutive properties of the parent metal and further considering the properties of the non-homogeneous welded zone. The Marciniak-Kuczynski model and thickness gradient based necking criterion were both applied to predict the failure successfully in the FE model, and the results were validated with experimental data to establish the robustness of both the failure models. [Display omitted] •Anisotropy properties of DP600, DP980 and IF sheet accurately predicted using Yld2000-2d.•Characterization of non-homogeneous properties across weld zone of DP600 LWB and TWBs.•Forming behaviors of LWB and TWBs estimated under three different deformation modes.•FE prediction of thinning development and forming limits incorporating anisotropy properties.•Robustness of thickness gradient based necking criterion and MK model in two-step forming established.