Crack nucleation from Foreign object damages in metals
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Microstructural foreign object damages (FOD) continue to be a major concern for aviation safety, as they create conditions that facilitate crack initiation, ultimately leading to a reduction in a component’s fatigue lifespan. However, the detection of FOD does not necessarily require the immediate replacement of the affected part. Depending on the extent of the damage, a component may still be able to withstand additional loads before crack formation becomes a serious concern. Clearly, disassembling and replacing still functional engine components is not economically or environmentally sustainable. A practical solution to address this issue is to develop a model that predicts the fatigue crack initiation lifetime of components subjected to FOD. In this study, such a model was developed by extending the Tanaka-Mura crack initiation model including the effects of FOD. To achieve this, a metric was established to measure the intensity of an FOD. In this context, finite element simulations were conducted to analyze the plastic deformation resulting from an impact. The crack initiation lifespan for components affected by FOD was subsequently modeled as a function of this metric. To verify the theoretical framework, the model was compared to experimental results gathered from Ti6Al-2Sn-4Zr-6Mo. In this regard, unknown parameters were fitted among others with the maximum likelihood estimation method.
