Dislocation model of a subsurface crack

A dislocation model of a subsurface crack parallel to the surface is presented. For tensile loading, the results agree with those of previous workers except that we studied the crack very close to the surface and found that K_II (mode II stress intensity factor) approaches K_I (mode I stress intensity factor) to within about 22% (K_II=0.78K_I). (Note that K_II is zero when the crack is far away from the surface). Using bending theory for such situations, it is found that both stress intensity factors are inversely proportional to the 3/2 power of the distance between the subsurface crack and the free surface. For shear loading, the crack faces overlap each other for the free traction condition. This indicates the failure of the model. However, there was no overlap for tensile loading even though the stresses in front of the crack oscillate somewhat when the crack is very close to the surface.