What are the three stages of fatigue failure?

What are the three stages of fatigue failure?

• A. Initiation (assumed from start), propagation (stable) and failure (unstable)
• B. Crack appearance, growth, final fracture
• C. Damage accumulation, crack lengthening, break
• D. Initiation, propagation, and failure

Answer: (D)

Fatigue failure happens in three stages: initiation, propagation, and final fracture. First, tiny cracks form at stress concentrators such as weld toes, sharp corners, or surface irregularities after many load cycles. Then these cracks grow with continued cyclic loading; the growth rate depends on the stress range, material, and environment, often starting slowly and accelerating as the crack enlarges. Finally, when the crack reaches a critical size, the remaining ligament can no longer carry the applied load, leading to rapid, final fracture. This sequence is the standard way engineers describe fatigue life, and it helps explain why bridges may fail suddenly after many cycles even if the load at any one moment seems small.

Fatigue failure happens in three stages: initiation, propagation, and final fracture. First, tiny cracks form at stress concentrators such as weld toes, sharp corners, or surface irregularities after many load cycles. Then these cracks grow with continued cyclic loading; the growth rate depends on the stress range, material, and environment, often starting slowly and accelerating as the crack enlarges. Finally, when the crack reaches a critical size, the remaining ligament can no longer carry the applied load, leading to rapid, final fracture. This sequence is the standard way engineers describe fatigue life, and it helps explain why bridges may fail suddenly after many cycles even if the load at any one moment seems small.