Where do stress rupture cracks usually appear on turbine blades?

Stress rupture cracks typically appear across the leading or trailing edge at a right angle to the edge length of turbine blades due to the material experiencing high temperatures and stresses during operation. These conditions can lead to fatigue failure and ultimately result in the development of cracks in areas where the stress concentration is greatest.

The leading and trailing edges of blades are subject to significant aerodynamic forces as well as thermal stresses from the hot gases in the engine, making them susceptible to forming cracks. The orientation of the cracks being perpendicular to the edge length is indicative of the stress direction, which affects how cracks propagate in materials under cyclic loading.

In contrast, other areas mentioned do not typically show this specific failure mode. The midspan, blade tips, or base of the hub are less likely to experience the same level of combined thermal and mechanical stress, which minimizes the risk of having stress rupture cracks arise in those regions. Understanding where these cracks may form helps in predicting potential issues and maintaining the integrity of turbine blades in operation.