ln this paper. the relation between the maximum strain at the notch root and the J integra, value has been derired for a notch wfth a semi. elliptical end. It is proposed that the maximum strain energy density or the maximum strain criterion controls the cracking at the notch roots. The relation indicates that notch J. integra, fracture toughness depends not only on the material and the magnitude of the notch root radius of curvature(or notch width 1 but also upon the magnitude of ellipticity. In the same Why. the relation derived in this paper shows that, when the strain concentration at notch root is predicted by the value ofthe 3-integral. the effect ofellipticity should not be neglected, in addition to the direct effect of the magnitude of notch root radius of curvature.

One of the aims of the engineering standards related to NDE (Non-Destructive Examina-tion) is to identify and limit the defects in a structure, The aim of defect acceptance criteria is to determine whether a component containing defects can be accepted, re-paired or rejected. These criteria should be based on scientific understanding. Howev-er, most of the current defect acceptance criteria were made based on empirism. The examined components with defects are easy to be rejected or produce new or more serious defects after repairing. This must bring huge economic losing and hidden some dangerous factors. A new defect acceptance criterion is proposed on the basis of fracture mechanics in this paper. The new criterion should have three levels: the first is the primary de-fect acceptance criterion and the same allowable defect size should be given to all struc-tures and materiais which are considered; the second is the secondary defect accep-tance criterion and the allowable defect size should be varied With materials to all consid-ered structures; the third is the advanced defect accel; Itance criterion and the allowable defect size should be calculated for a given material and structure. For each defect accep. tance level three grades may be divided with respected to the importance of structures.