What is the final stage of fatigue called?

What is the final stage of fatigue called?

• A. Fracture
• B. Fatigue crack initiation
• C. Propagation
• D. Plastic deformation

Answer: (A)

Fatigue failure under cyclic loading happens in three phases: crack initiation from stress concentrators, crack growth (propagation) under the repeated stresses, and then catastrophic fracture when the remaining cross-section can no longer support the load. The final stage is fracture, where the part actually breaks apart. Localized plastic deformation can occur at the crack tip during growth, but that doesn’t represent the end state—the end state is rupture. The other choices describe initiation or propagation stages, not the final failure.

Fatigue failure under cyclic loading happens in three phases: crack initiation from stress concentrators, crack growth (propagation) under the repeated stresses, and then catastrophic fracture when the remaining cross-section can no longer support the load. The final stage is fracture, where the part actually breaks apart. Localized plastic deformation can occur at the crack tip during growth, but that doesn’t represent the end state—the end state is rupture. The other choices describe initiation or propagation stages, not the final failure.