Determination of fracture toughness from stretch zone width measurement in predeformed AISI type 4340 steel

The fracture toughness parameter JIC was determined as a function of prior cold working in AISI type 4340 steel using two different approaches. One approach is the J resistance curve method. The other approach is from measurements of the stretch zone width which is determined by scanning microscopy on the fractured specimens used in the determination of the J resistance curves. Both techniques agree in showing that, up to a prior deformation …