An energy approach to predict fatigue crack propagation in metals and alloys

Mechanical deformation of a solid during fatigue cycling is broadly defined a phase transformation, because defects are produced that increase its internal energy. Change in the defect structure, crack initiation and growth are also examples of phase transformations. Many of the concepts of phase transformation theory are applicable to fatigue crack nucleation and propagation. Phase transformation theory was applied to penny-shaped crack nucleation in interconnects in previous research. The physical meaning of fatigue crack nucleation in solid materials was previously studied by using energy considerations. This paper extended the treatment to fatigue crack propagation. Phase transformation theory is applied to predict the fatigue crack propagation rate in metals and alloys. The fatigue crack propagation rate predicted is compared with experimental data for different steels and aluminum alloys to demonstrate that the prediction of the theory agrees reasonably well with experimental results. The theory is also applicable to predict fatigue crack propagation in interconnects under cyclic stresswith corresponding experimental data for solder and intermetallics