A scratch or gouge in the surface of metal causes what that can lead to failure?

A scratch or gouge in the surface of metal causes stress risers or concentrations, which can significantly affect the structural integrity of the material. When the surface of a metal component is compromised by a scratch or gouge, the localized area becomes a point where stress is concentrated due to the disruption in the material's continuity.

In normal conditions, metal components distribute stress evenly throughout their structure. However, when there is a discontinuity like a scratch or gouge, the likeliness of failure increases at that point because the surrounding material has to bear the additional stress. This phenomenon can lead to premature failure, as the stress concentrations can encourage crack propagation and ultimately lead to structural failure under load.

Understanding this is crucial in aircraft maintenance and repair, as even minor surface imperfections can pose significant risks over time, leading to potential failure of critical structural components. This emphasizes the importance of regular inspections and addressing any surface abnormalities promptly to maintain aircraft safety.