What is Fatigue?
Structural fatigue refers to the initiation and growth of cracks due to varying loads. These cracks can lead to failures even at stress levels that wouldn’t cause failure in a single load application. The damage from fatigue is cumulative, often irreparable, and usually undetectable, potentially leading to sudden catastrophic failures.
Fatigue cracks originate as surface dislocations in the material’s microstructure. Localized stress concentrations can form persistent slip bands, which can evolve into micro-sized Stage I shear cracks. Given enough energy, these micro-cracks can grow into Stage II tensile cracks, which are significantly larger than the material’s microstructure. These cracks disrupt the local stress field and if supplied with sufficient energy, Stage II cracks can propagate until a rapid tensile failure occurs.