Simulation of fatigue crack growth- a comparative study: A comparison between ANSYS SMART and NASGRO with emphasis on crack-front behaviour, transition modelling, and stress ratio effects

Sammanfattning

Fatigue crack growth is a critical factor in the lifetime prediction and structural integrity of aerospace components. Accurate modelling of crack propagation is therefore essential for reliable design and maintenance strategies. This thesis presents a comparative study of two widely used tools for fatigue crack growth analysis: the finite element-based software ANSYS and the semi-analytical tool NASGRO. The goal is to evaluate the strengths and the limitations of these tools in predicting fatigue crack growth and to provide recommendations for their effective use, with a focus on improving accuracy.The results show good agreement between the tools for simple loading cases, such as tensile loading with uniform crack opening. However, significant differences were observed for more complex scenarios involving non-uniform crack-front behaviour, transition modelling, and fully reversed loading. A finite element-based approach was found to better capture variations along the crack front, while NASGRO provided more computationally efficient solutions but showed limitations related to simplified crack-front representation and predefined transition modelling.The findings highlight that the choice of analysis tool should be guided by the complexity of the loading conditions and required level of accuracy. NASGRO is well suited for efficient analysis of standard cases, while ANSYS provides improved resolution and accuracy for complex crack configurations.