Fatigue Crack Nucleation

Fatigue cracks develop from repeated loading, not from a one-time overload. The material gets fine cracks over time that keep growing until the part breaks. When welding, you need to ensure clean transitions and a crack-free weld, because notches and defects are the beginning of the end. If a component vibrates or is constantly loaded, you should regularly inspect the welds, preferably with dye penetrant or ultrasound. And remember: a smooth, uniform weld lasts much longer than one with starts or lack of fusion.