Fatigue And Fracture Behavior

Structural components are frequently subjected to repeated or cyclic loading. The resulting cyclic stresses, which may be far below the ultimate tensile strength of materials, can result in a microscopic physical damage to the material. The microscopic damage can accumulate with continued cyclic loading until it develops into a crack that could lead to the catastrophic failure. This process of damage and failure due to cyclic loading is called fatigue.

Fatigue is a dynamic phenomenon that accounts for ~90% of all service failures from mechanical causes. In general, the fatigue life involves the number of loading cycles to initiate and propagate a crack to a critical size. Fatigue failure occurs in three stages: crack initiation, stable crack growth, and fast fracture. The main factors that contribute to fatigue failures include the number of load cycles, stress range, mean stress, and local stress concentrations. It is necessary to take these factors into account in the design of materials for structural components.