This paper reconsiders the problem of determining the elastostatics fields near the tip of a crack in a body deformed by an antiplane shear for a class of incompressible, homogeneous, isotropic materials. The study is generalized to the formation of a quasicrack under the same conditions of loading for brittle material that cannot support any further loading when a critical strength is reached. The crack is then replaced by a totally damaged zone where the stress is identically zero. The shape of the boundary between the damaged and undamaged body is found analytically. A numerical approach is proposed to address the problem for more general constitutive law. The analytical solution is recovered by a process of shape optimization.