Which statement lists the three primary factors of fatigue life?

• A. Stress range, Number of cycles and Detail type
• B. Temp, Pressure, Humidity
• C. Crack length, Growth rate, Material type
• D. Amplitude, Frequency, Surface finish

Answer: (A)

Fatigue life is controlled by how severe the cyclic loading is, how many load cycles the member experiences, and how the part’s geometry concentrates stress. The higher the stress range, the fewer cycles you can endure before a crack initiates and grows to failure; more cycles generally mean more fatigue life unless the stress is reduced. The detail type—things like sharp corners, holes, weld toes, or abrupt changes in section—shapes local stress concentrations and notch sensitivity, which can dramatically shorten life even at moderate stress ranges. While environment, crack growth, or material properties play important roles, they don’t define the fundamental trio that governs fatigue life: stress range, number of cycles, and detailing that governs stress concentration.