väsymisominaisuus

Väsymisominaisuus, known in English as fatigue properties, refers to the resistance of a material to failure under repeated cyclic loading. This phenomenon is distinct from static failure, which occurs when a material is subjected to a load exceeding its ultimate strength in a single application. Instead, fatigue failure can occur at stress levels significantly below the material's yield strength if the load is applied repeatedly over time.

The process of fatigue damage typically involves three stages: crack initiation, crack propagation, and final fracture. Crack initiation usually begins at microscopic flaws or stress concentrations on the material's surface or within its bulk. Once a crack forms, it grows incrementally with each load cycle, a process known as crack propagation. The rate of propagation depends on factors such as the applied stress range, the material's fracture toughness, and the environment. Eventually, the crack reaches a critical size, and the remaining cross-section of the material can no longer sustain the applied load, leading to rapid, sudden fracture.

Understanding a material's fatigue properties is crucial in engineering design, particularly for components subjected to dynamic or oscillating loads, such as aircraft wings, engine parts, bridges, and rotating machinery. Designers use fatigue analysis to predict the service life of components and ensure their reliability and safety under expected operating conditions. Key parameters used to characterize fatigue properties include the fatigue limit (or endurance limit), which is the stress level below which a material can theoretically withstand an infinite number of cycles, and the fatigue strength, which is the stress level that a material can withstand for a specified finite number of cycles.