ELASTIC INTERACTION BETWEEN SCREW DISLOCATIONS AND A CIRCULAR SURFACECRACK

The behaviour of a screw dislocation around a circular surface crack w as analyzed using the conformal mapping method. The effects of the cra ck length l and its radius of curvature R on the shielding effect and the strain energy were discussed in detail. It was found that for a di slocation being fixed at a constant distance from the crack tip and lo cated on a plane tangent to crack surface at the tip, there exists a c ritical crack length l corresponding to a maximum shielding effect in duced by the dislocation on the circular surface crack. The l increas es with R and approaches infinity as the crack becomes planar (i.e. R --> infinity). The shielding effect vanishes as the crack disappears. It increases rapidly with l if 0 < l much less than l, regardless of R. After reaching the maximum, it decreases slightly for larger R but significantly for smaller R as the crack becomes longer. The shielding is more pronounced for larger R than that for smaller R, with the dif ference increasing with crack length. As a result, a surface microcrac k propagates initially in a rather brittle manner then becomes more du ctile. When the crack gets longer, it still keeps ductile for a less c urved or a planar crack but becomes relatively brittle for a severely curved crack. In addition, the strain energy is also significantly inf luenced by crack length and increases rapidly with l when l is rather small, regardless of R. With increasing l, it becomes less affected by l, and the variation with R is still not obvious, with larger R corre sponding to a slightly higher strain energy. (C) 1997 Elsevier Science S.A.