Lavcyklustræthed

Lavcyklustræthed, often translated as low cycle fatigue, refers to material failure that occurs after a relatively small number of load cycles, typically less than 10^4 to 10^5 cycles. This type of fatigue is distinct from high cycle fatigue, which involves failure after a much larger number of cycles. Low cycle fatigue is usually associated with significant stress or strain amplitudes in each cycle.

The phenomenon is commonly observed in components subjected to severe operating conditions, such as those found in aircraft engines, power generation turbines, and pressure vessels. These components experience substantial fluctuations in temperature, pressure, or mechanical load during their service life, leading to repeated plastic deformation. Plastic deformation, the permanent change in shape of a material, is a key characteristic of low cycle fatigue. Even though the overall deformation may be small, repeated cycles of this plastic deformation accumulate damage within the material's microstructure.

The initiation and propagation of cracks are central to the low cycle fatigue failure process. Stress concentrations, often found at geometric discontinuities like holes, notches, or sharp corners, act as initiation sites for cracks. Once initiated, these cracks grow incrementally with each load cycle. The rate of crack growth is influenced by factors such as the stress range, material properties, and the presence of environmental factors. Eventually, the crack reaches a critical size, leading to catastrophic failure of the component, often abruptly and without significant prior warning. Understanding and predicting lavcyklustræthed is crucial for ensuring the safety and reliability of engineered structures.