What is the method used to prevent a crack from spreading?

The method used to prevent a crack from spreading is known as stop drilling. This technique involves drilling a small hole at each end of the crack, creating a barrier that halts the growth of the crack. The holes relieve stress concentrations that would otherwise allow the crack to continue spreading under load or during operation.

Stop drilling is particularly effective because it targets the primary problem—stress concentration—directly at the location where the crack ends. By providing a new, more stable structure at each end, the stop-drilled crack is less likely to propagate further. This method is commonly used in aircraft maintenance, as it is both a preventative and a mitigative measure to ensure the integrity of the structure.

While other methods such as welding, filling with epoxy, or patching may provide some level of reinforcement or repair, they do not address the immediate concern of crack propagation as effectively as stop drilling does. Each of those methods comes with its own set of issues, such as potential distortion from welding or the risk of the crack continuing to spread while being temporarily repaired.