It is known that oscillatory singularities appear in problems involving interface cracks that are assumed to have open tips. An unsatisfactory aspect of the oscillatory singularities is that they lead to overlapping of the crack faces. The interface crack in a tension field, originally treated by England among others, is thus reconsidered on the basis that the crack is not completely open and that its faces are in frictionless contact near the tips. The formulation leads to a pair of coupled singular integral equations. The singularities, no longer oscillatory, exhibit some unusual features and indicate that the spreading of the interface crack in a tension field is intimately connected with failure in shear. A new stress-intensity factor is obtained and compared to the stress-intensity factors for the completely open crack.

The solution for an angular dislocation allows one to construct the fields for any polygonal loop by superposition. The paper presents the displacements induced by the angular dislocation in an elastic half space. In view of potential applications in geophysics, particular attention is paid to the elastic fields at the free surface. The surface data are seen to exhibit a very simple dependence on the elastic constants. RI~SUMt~On peut construire les champs 61astiques associ~rs ~. une dislocation en polygone par superposition de solutions au probl6me d'une dislocation angulaire. Nous pr6sentons les d6placements induits par une dislocation angulaire dans un demi-6space 61astique. En vue des applications g6ophysiques, les champs 61astiques sur la surface librc sont 6tudi6s en particulier. Nous montrons que les champs 61astiques sur la surface d6pendent des constantes 61astiques d'une fa¢on tr+s simple.

The interface crack was analyzed in two recent papers which considered applied tension and shear fields separately. The unrealistic oscillatory singularities and the ensuing material interpenetration were eliminated in these solutions by assuming small frictionless contact zones near the crack tips. The present paper presents a solution for the interface crack under combined normal and shear tractions. Both tensile and compressive normal tractions are considered and numerical results of the extents of the contact zones, shear stress-intensity factors, and interface crack opening profiles are presented.

The interface crack in a tension field was reconsidered in a recent paper, and the unrealistic oscillatory singularities were eliminated by assuming small frictionless contact zones near the crack tips. In the present paper, the interface crack in a shear field is studied. Some unexpected results emerge: one of the contact zones is large, affecting thus the global nature of the solution; the gap closes extremely abruptly at one of its ends, but the normal stresses remain zero at this point; and the shear stress-intensity factors have opposite signs at the crack tips.

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