Investigation on forming limit of advanced high strength steels (AHSS) under hot stamping conditions

The focus of this work is to combine the experimental, numerical and theoretical approaches to study the forming limit curve (FLC) under hot stamping conditions of advanced high strength steels (AHSS) through taking into account the influence of the temperature history during on limit strain. Both of the limit strain and the temperature history of the deformed sheet in the experimental and numerical Nakazima tests were studied, and predicted theoretically by the extended M-K theory that was coupled with the heat transfer equation. The comparison among the experimental, numerical and theoretical results in terms of the limit strain and the temperature variation indicated that the temperature of each limit strain pair was different. The improvement in forming limit caused by temperature history was demonstrated theoretically, and interpreted through comparing the limit major strains in different temperature histories.