Riveting process is one of the most important methods to keep fastening the lap joints in aircraft fuselages. Fatigue failure of aircraft lap joints directly depends on the stress inteensity factors. Besides that, the multi site damage problem of aircrafts requires obtaining accurate stress intensity factors of interacting collinear cracks under external load. The approximate method proposed by Kachanov is specialized in this paper to arbitrary length collinear cracks with arbitrary spacing under far field tension. The interaction between all cracks is considered in this approach. The advantage of this approach over other is that it is simple, has good accuracy, and is very efficient. Finally, this approach is used in a simple lap joint with two interacting cracks. In order to verify the method, the SIF results for two collinear cracks emanating from a hole by Kachanov’s method is compared with experimental formula. Comparison has shown a good accordance. So, Kachanov’s method is very efficient, accurate and reliable enough to calculate SIFs instead of experimental formulas.

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