Fatigue can be described as which of the following?

• A. Permanent deformation under static load
• B. Corrosion under stress
• C. Fatigue is progressive structural damage due to cyclic loading leading to failure
• D. Immediate fracture due to impact

Answer: (C)

Fatigue is damage that accumulates under repeated or cyclic loading, eventually causing failure. With each load cycle, tiny cracks can form at points of high stress concentration and gradually grow. After many cycles, the crack becomes large enough that the part can no longer carry the load, leading to rapid fracture. This differs from permanent deformation under a single static load, which is plastic deformation rather than progressive damage. It also isn’t about corrosion under stress, which involves chemical attack, nor an immediate fracture from a single impact, which happens in one event. In practice, fatigue life is analyzed with tools like S-N curves to predict how many cycles a component can withstand, and factors such as surface finish, corrosion, temperature, and residual stresses influence that life.