Where do stress rupture cracks usually appear on turbine blades?

Where do stress rupture cracks usually appear on turbine blades?

• A. Across the leading or trailing edge at a right angle to the edge length
• B. At the root
• C. Along the midspan
• D. On the trailing edge only

Answer: (A)

Stress rupture on turbine blades happens when high temperature and sustained stress cause creep-like cracking, so cracks tend to begin where stresses are most concentrated and surfaces are exposed to harsh conditions. The edges of the blade—the leading and trailing edges—experience sharp geometry, large thermal gradients, and intense contact with hot gas, creating strong local tensile stresses right at the surface. When a crack starts at an edge surface, the opening mode is greatest perpendicular to the edge, so the crack grows across the edge length, i.e., at a right angle to the edge. The root and midspan don’t present the same edge-driven stress concentration, and focusing only on the trailing edge would miss the leading-edge stress effects. That combination makes edge crossing cracks the typical location for stress-rupture initiation and growth.

Stress rupture on turbine blades happens when high temperature and sustained stress cause creep-like cracking, so cracks tend to begin where stresses are most concentrated and surfaces are exposed to harsh conditions. The edges of the blade—the leading and trailing edges—experience sharp geometry, large thermal gradients, and intense contact with hot gas, creating strong local tensile stresses right at the surface. When a crack starts at an edge surface, the opening mode is greatest perpendicular to the edge, so the crack grows across the edge length, i.e., at a right angle to the edge. The root and midspan don’t present the same edge-driven stress concentration, and focusing only on the trailing edge would miss the leading-edge stress effects. That combination makes edge crossing cracks the typical location for stress-rupture initiation and growth.