Jivkov's articles
Fatigue corrosion crack extension across the interface of an elastic bi-material
Abstract
In this work crack propagation in a bi-material composed of a thin elastic layer ideally bonded to a large elastic substrate
is studied. A flaw is assumed existing on the surface of the layer. Cracks nucleate from the flaw and propagate through the
bi-material. The cracks have realistic geometrical shapes, where the crack tip is an integral part of the crack surface.
Thus the crack propagation is associated with a crack surface evolution. Material loss due to corrosion of the crack
surface is the physical ground for the evolution. A controlling mechanism for the surface advancement is the rupture of
a brittle corrosion-protective film, which is continually building-up along the corroding surface. The rate of surface
evolution is a function of the degree of protective film damage, caused by the surface straining. This leads to a moving
boundary formulation, for which a numerical solution is proposed. Fatigue loading is considered as a suitable way to
maintain crack evolution at a constant peak load level. Under the assumed model, the cracks always pass the interface.
The elastic mismatch is shown to influence the growth rate variation around the interface. Crack extensions are presented
as functions of the elastic mismatch and as functions of the initial flaw size. It is shown how the results can be used in
designing bi-material systems. A typical morphology evolution of a crack passing through an interface with a weak-stiff
transition is presented. An example of fatigue corrosion fracture is offered, which shows that the crack morphology of
the model resembles the one observed in reality. It is concluded that the realistic crack geometry is an effective concept
and the moving boundary formulation could be a very successful tool for simulating realistic crack propagation.