Abstract
By comparing the results of internal cracks obtained by Louat with those on surface cracks obtained by Juang and Lee, we find that the physical variables of an internal crack of length 21 are equivalent to the counterparts of a surface crack of length l. If the dislocation is not very close to the free surface, the magnitude of each physical variable of the surface crack is between those of counterparts of the internal crack with the number m of dislocations inside the crack equalling - 1 and 0. For short cracks, each physical variable is proportional to m. As a result, an internal microcrack appears in the region containing this dislocation. In contrast, for long cracks, we compared the first-order terms for both cracks, and the zero-order terms were found to be the same as those of a semi-infinite crack. Finally, the validity of the action-reaction law is proved for both types of crack. © 1987.