On a Screw Dislocation Interacting With Two Viscous Interfaces

We investigate a screw dislocation interacting with two concentric circular linear viscous interfaces. The inner viscous interface is formed by the circular inhomogeneity and the interphase layer, and the outer viscous interface by the interphase layer and the unbounded matrix. The time-dependent stresses in the inhomogeneity, interphase layer, and unbounded matrix induced by the screw dislocation located within the interphase layer are derived. Also obtained is the time-dependent image force on the screw dislocation due to its interaction with the two viscous interfaces. It is found that when the interphase layer is more compliant than both the inhomogeneity and the matrix, three transient equilibrium positions (two are unstable and one is stable) for the dislocation can coexist at a certain early time moment. If the inhomogeneity and matrix possess the same shear modulus, and the characteristic times for the two viscous interfaces are also the same, a fixed equilibrium position always exists for the dislocation. In addition, when the interphase layer is stiffer than the inhomogeneity and matrix, the fixed equilibrium position is always an unstable one; on the other hand, when the interface layer is more compliant than the inhomogeneity and matrix, the nature of the fixed equilibrium position depends on the time: the fixed equilibrium position is a stable one if the time is below a critical value, and it is an unstable one if the time is above the critical value. In addition, a saddle point transient equilibrium position for the dislocation can also be observed under certain conditions.