A stress-based criterion for ductile crack initiation of pre-strained carbon steel

An attempt was made to represent the critical condition for ductile crack initiation by a stress-based parameter. First, tensile tests were conducted using notched bar specimens. Then, a stress-based criterion was derived from the stress and strain at onset of ductile cracking. Validity of the criterion was shown by comparison with the crack tip stress estimated for the fracture toughness tests. By using the stress-based criterion, the change in failure strain due to pre-straining could be reasonably explained. It was concluded that the stress was better than the plastic strain for representing the critical condition of the ductile crack initiation.

► Stress is better than strain for showing the ductile crack initiation criterion.
► Critical stress for ductile crack initiation is obtained.
► Crack initiation in the elastic–plastic fracture toughness test can be estimated.