A dislocation model was presented for a sub-surface crack parallel to the surface. In the case of tensile loading, the results agreed with previous ones; except that the crack was studied very close to the surface and it was found that the mode-II stress intensity factor approached the mode-I stress intensity factor to within about 22%. The mode-I stress intensity factor was equal to zero when the crack was far from the surface. By using the bending theory for such situations, it was found that both stress intensity factors were inversely proportional to the 3/2 power of the distance between the sub-surface crack and the free surface. In the case of shear loading, the crack faces overlapped each other under free traction conditions. This reflected a failure of the model. There was no overlap under tensile loading, even though the stresses ahead of the crack oscillated when the crack was very close to the surface.

Dislocation Model of a Subsurface Crack. F.Yang, J.C.M.Li: Journal of Applied Physics, 1997, 82[10], 4816-22