Fracture Instability Point

The fracture mechanical instability point is the moment when a crack becomes suddenly unstable under load and propagates uncontrollably. In welding, this is dangerous because the heat input creates stresses and microstructural changes that make the material susceptible. If you cool the weld too quickly or the restraint is too rigid, this can lead to sudden failure. So make sure the weld can cool evenly and no sharp notches form.