The results of fracture toughness tests on a high strength steel 300m are presented. These results show (i) that in the presence of through-thickness cracks the toughness remains constant down to (a/W)-ratios as low as 0.01 and failure loads up to 0.85σy, and (ii) that the material is more resistant to crack growth when the cracks are semi-elliptical in shape, giving a toughness value which is almost 25 per cent higher than the through-thickness one. Three independent stress analyses are used to obtain stress intensity values for the semi-elliptical cracks and additional confirmation of the increase in toughness comes from stretch zone measurements.
King, J. E., & Knott, J. F. (1980). Effects of crack length and shape on the fracture toughness of a high strength steel 300m. Journal of the Mechanics and Physics of Solids, 28(3-4), 191-200. https://doi.org/10.1016/0022-5096(80)90003-4