Fatigue Initiation Site
The fatigue crack origin is the area where cyclic cracks begin due to stresses or inhomogeneities. It is indicated by characteristic Fatigue Striations and beach marks.
Physical-Chemical Mechanism of Action
The fatigue crack origin forms in areas subjected to repeated stresses or inhomogeneities. These stresses can arise from mechanical loading, temperature changes, or chemical environmental conditions. The crack origin is the starting point for microscopic cracks that propagate with each repetition of the load cycle.
Metallurgical Relevance & Risks in Welding
The fatigue crack origin can lead to critical safety issues as it impairs the service life of components and machine parts. Cracks at these locations can grow and eventually lead to material failure. This is especially dangerous in highly stressed parts like aircraft components or machine shafts.
Workshop Practice & Action Instructions
To avoid fatigue crack origins, the following measures should be taken:
• Stress relief: Reduce stresses through proper welding procedures and mechanical processing.
• Material selection: Choose materials with low fatigue susceptibility for high loads.
• Temperature control: Ensure that the cooling rate of the material stays within the critical temperature window (e.g., t8/5 between 5 and 25 seconds).
• Quality control: Use microscopic examinations to detect Fatigue Striations and beach marks.