The evaluation of the formability of sheet material is of great importance for forming complex-shape
components in automotive applications. However, for hot and warming forming conditions, this
usually requires formability tests with specialist devices and testing procedures and is difficult to
obtain accurate and comparable results due to the lack of testing standards. In this paper, the concept
and development of strain-based forming limit diagram (FLD) are introduced. The testing methods
to experimentally determine the FLD, classified into formability tests and planar tensile tests, are
widely reviewed. The applications of both types to obtain FLD at elevated temperatures for different
forming processes are introduced, and the advantages and disadvantages of the methods are
analysed.