Advances and Perspectives In Multi-Phase Mesoscale Rupture Models For Weld Joints

The rupture of spot welds has an important influence on the crash scenario of steel automotive bodies: Yoshida (2007) has shown that toe panel intrusions could be underestimated by about 20% when a crash model ignores the rupture of the welds. Recently, the increasing regulations on lighter car structures and enhanced safety have spurred strong competition between steel and other low density materials such as light-weight metals or composites. The steel industry has responded by developing Advanced High Strength Steels (AHSS) grades, including among others dual-phase (DP) steels and martensitic hot-formed steels. Unlike conventional high strength steels, these grades ensure both high strength and good formability. They are characterized by high yield strength over 300 MPa and ultimate tensile strength over 600 MPa. Dual-phase steels present high absorption potential thanks to a mixed structure of ferritic matrix and martensitic islands which vary in proportion depending on the grade. Martensitic steels are obtained from ferritic steel submitted to hot forming and then cooled rapidly to obtain fully martensitic structure with the desired geometry. This process ensures very high ultimate tensile strength above 1200MPa.