A study on fracture behaviour of three different high strength low alloy steel sheets during formation with different strain ratios

This paper deals with the study on fracture behaviour of three different steels, namely, the HSLA, the Micro alloyed and the Carbon–Manganese steels, using stress- and strain-based forming and fracture limit diagrams obtained from the experimentally determined strain values for different strain or stress ratios. With an aim to analyse the fracture behaviour, the strain- and stress-based forming and fracture limit diagrams have been developed for three different steel sheets, namely, the HSLA steel sheet of 1.6 mm thickness, the Micro alloyed steel sheet of 1.2 mm thickness, and the Carbon–Manganese steel sheet of 1.4 mm thickness. The forming and fracture behaviour and size and shape of voids (particularly, the ratio of length to width of voids, (L/W)) developed at fracture during the formation of these steels, under different strain ratio conditions, have been correlated with the mechanical properties such as microstructure of steels, minor strain at fracture, and Mohr’s circle shear strains, various combinations of mean strain and effective strain, and material properties, namely, strain hardening exponent (n  )-value, normal anisotropy (r¯) and the range of localized neckings.