Fracture strains in sheet metalforming and specific essential work of fracture

It is proposed that a plausible relationship exists between the specific essential work of fracture (R) obtained from testpieces incorporating starter cracks and the work required locally to nucleate a crack in flawless thin sheet metals. This relationship allows fracture strains in sheet metalforming to be determined from independent measurements of R instead of from in-situ strain measurements, which are usually employed in the construction of "fracture" forming limit diagrams. Some preliminary results on aluminium seem to support this proposed concept but much more work is required before a definite conclusion can be reached.