Modelling and Predictions of Time-Dependent Local Stress Distributions Around Cracks Under Dwell Loading in a Nickel-Based Superalloy at High Temperatures

Introduction to Crack Growth Under Dwell Loading: 

​

This study uses finite element (FE) analysis to model stress distributions around cracks in nickel-based superalloys under high-temperature dwell loading. The research focuses on understanding how time-dependent deformation impacts dwell fatigue crack growth (DFCG) in turbine disc alloys. The analysis also examines crack growth retardation during overload-dwell cycles.

​

Modelling Stress Evolution:

​

FE models were used to simulate a two-dimensional cracked geometry subjected to both standard dwell and overload-dwell stress conditions. The analysis evaluated the mechanical stress state around the crack, particularly how local crack-tip stresses evolve over time during dwell periods and following overload cycles.

​

Key Findings on Crack Growth and Retardation:

​

The research shows that local crack-tip stresses relax rapidly during dwell periods due to time-dependent plasticity. Additionally, the characteristic resistance to crack growth after overloads, as observed experimentally, was effectively captured in the simulations. The study introduces a numerically-derived incubation time to predict trends, indicating that higher overload factors and longer overload periods result in more significant crack growth retardation.

​

Implications for Turbine Disc Alloys:

​

This work highlights the importance of studying local crack-tip stresses in nickel-based superalloys to better characterise DFCG behaviour. The FE modelling provides valuable insights into how overloads and dwell periods affect crack growth, contributing to more accurate predictions of crack behaviour under real-world turbine operating conditions.