FAA Powerplant Written Practice Test

Where do stress rupture cracks typically occur on turbine blades?

1. Near the root

2. Along the leading edge

3. On the back edge

4. Mid-span

The correct answer is: Along the leading edge

Stress rupture cracks on turbine blades typically occur along the leading edge due to the nature of the aerodynamic and thermal stresses these components experience during operation. The leading edge of a turbine blade is subjected to high stress concentrations caused by the airflow, temperature variations, and the centrifugal forces acting on the blade while it spins at high speeds. In turbine engines, especially those in high-performance or high-stress environments, the materials must withstand significant thermal cycling, which can lead to fatigue and eventually crack formation. The leading edge is where airflow is first encountered, and as a result, it faces the highest impact forces, temperature gradients, and stress during the engine's operation. These factors contribute to making the leading edge a critical area for potential damage, including stress rupture cracks. The other areas of the blade may also experience stress but are generally less prone to these specific types of cracks when compared to the leading edge, which emphasizes its importance in the structural integrity of turbine blades.