Expansion stress range allowable is based on what?

• A. Code equation including SIF
• B. Temperature effects only
• C. Material properties
• D. External pressure

Answer: (A)

The expansion stress range allowable is determined by the Code equation that includes the Stress Intensity Factor (SIF). This means the limit is set not just by how strong the material is or by temperature effects alone, but by how the stress range interacts with potential cracks under fracture mechanics. SIF quantifies the driving force on a crack tip for a given load, geometry, and crack size, so including it in the governing equation ensures the allowable expansion stresses keep crack initiation and propagation within safe limits during thermal cycling. Temperature and material properties matter, but they are part of a larger fracture-mechanics framework; external pressure governs a different aspect of loading and isn’t the basis for the expansion-stress-range limit.