S-N Curve
The Wöhler diagram shows how often a component can be loaded under repeated loads before it breaks. It uses logarithmic scales for stress and number of cycles.
Physical-Chemical Mechanism of Action
The Wöhler diagram shows the maximum allowable stress amplitude (Smax) as a function of the number of cycles to failure (N). It accounts for various metallurgical and mechanical properties, like hardness, strength, and ductility.
Metallurgical Relevance & Welding Risks
Wrong welding parameters can mess up the mechanical properties, which shifts the Wöhler diagram. Too much carbon can increase hardness and thus reduce the number of cycles to failure. Inadequate cooling can cause an unfavorable microstructure and increase the risk of cracking.
Workshop Practice & Action Guidelines
Use the Wöhler diagram to find the allowable number of cycles for a given stress. Pay attention to correct welding parameters: temperature, time, and pressure. For highly stressed parts, choose a lower carbon content and make sure the weld cools down enough.