A new driving force parameter for fatigue growth of multiple cracks

In this paper, the 2060 Al-Li alloy specimens containing a single crack and multiple cracks were tested under fatigue load. The experimental results showed that the fatigue crack growth rates for multiple cracks deviated from the single crack when there is no interaction between multiple cracks. The results cannot be interpreted by the conventional Paris law using the crack tip stress intensity factor range ΔK calculated with the external applied nominal stress Δσ. At a given ΔK, the fatigue crack growth rates (da/dN) of different cracks for the same homogeneous material should be same based on the Paris law. Therefore, a new mechanical driving force parameter ΔKn that was calculated using the net section stress range Δσn was proposed to describe the single crack and collinear multiple cracks growth behavior under fatigue load. All da/dN vs ΔKn curves for collinear cracks of equal and unequal crack sizes were overlapped, and also overlapped with the single crack curve when no interaction occurred, showing that the ΔKn can be considered as a proper parameter to address the fatigue behavior of materials containing multi-cracks.