The interaction force between skew line defects (dislocations and/or line forces) in functionally graded and elastically anisotropic media was shown to be independent of the distance between them. Some special cases were homogeneous infinite and semi-infinite media and bicrystals. The interaction force between 2 skew dislocations in a plate with free surfaces was the same as that in an infinite medium.

Skew Line Defects in Graded Materials. H.O.K.Kirchner: Philosophical Magazine Letters, 19995, 79[5], 209-16