Turbine blade creep is defined as?

• A. The permanent elongation which occurs to rotating parts
• B. Temporary deformation under load
• C. Cracking of blade roots
• D. Thermal fatigue of blade surfaces

Answer: (A)

Creep is the time-dependent permanent deformation that occurs when a material is held under stress at elevated temperature. In turbine blades, which operate under high temperatures and centrifugal loads, this leads to a gradual, irreversible elongation or shape change. The phrase “permanent elongation which occurs to rotating parts” captures this behavior, making it the best description. It’s not just temporary deformation (which would disappear when the load is removed), nor is it cracking of blade roots (that’s a fracture/fatigue issue), nor thermal fatigue (damage from repeated temperature cycling).