Comparison of Low Cycle Fatigue Crack Propagation Methods for Turbine Exhaust Case

The aerospace industry heavily relies on NASGRO as a standard method for crack propagation analysis, despite encountering challenges due to variations in stress gradients across flight missions. In response to this issue, this paper introduces a pioneering methodology that integrates stress gradients at each time point throughout a mission, computed cycle by cycle using NASGRO. The study meticulously evaluates the feasibility and efficacy of this approach against established industry-standard procedures, focusing on the critical topic of low cycle fatigue (LCF) and underscoring the significance of damage-tolerant design principles. The methodology encompasses the design of an H-sector in Ansys Workbench, the execution of stress analysis for a typical flight mission profile, and the systematic extraction of stress gradients for each cycle at the pivotal crack nucleation point. Subsequently, NASGRO is employed to estimate life cycles using both industry-standard baseline methodologies and a per-gradient approach facilitated by Python scripting. The comparative analysis encompasses variations in starting crack size, geometry, and time complexity, offering a comprehensive assessment of the advantages and limitations of each life estimation technique. The findings of the study significantly contribute to the advancement of damage tolerance design in aerospace applications, furnishing invaluable insights into more precise crack propagation life estimates. These insights carry immediate implications for enhancing the safety and reliability of aircraft components, thereby facilitating the continual refinement of industry standards.