The essential work of fracture in relation to J-integral

•The requirement of having a fully yielded ligament before crack onset was discussed.•If the requirement is not met the EWF method’s results become questionable.•If the requirement is met the essential work is equivalent to Jc at crack initiation.•No correlation exists between the slopes of relevant EWF and J-resistance curves.

The validity of the essential work of fracture (EWF) method and its relation to J-integral were questioned by applying it to three polymeric materials with different characteristics, in particular with respect to their yield behavior. The importance of having an almost fully yielded ligament before crack onset was considered. Only when this condition is met, an essential work parameter can be identified which is equivalent to the J-integral at crack initiation, as determined by the Begley–Landes multispecimen method. No correlation was found between the slopes of relevant EWF and J–R curves.