Modelling of Fatigue Crack Growth from Exfoliation and Pitting Corrosion

When structures are operated in corrosive environments, fatigue failures can occur from the formation and propagation of cracks from exfoliation and pitting corrosion. Corrosion-nucleated fatigue can be particularly problematic in structures that are not thought to be fatigue critical, and are therefore not inspected, but can become critical in the presence of corrosion. Although the risk factor of corrosion-nucleated fatigue should never be ignored, the most demanding corrosion-related issue is the escalating maintenance burden caused by use of a “Find and Fix” corrosion management policy. This “Find and Fix” policy exists largely because tools do not exist to accurately assess the structural significance of corrosion when it is detected. Hence corrosion must be treated as an immediate threat. The development of analytical tools capable of accurately assessing the effect of corrosion on the durability of a structure would be a major benefit in that the management philosophy could begin to transition to an “Assess and Monitor” framework. The success of such a philosophy would greatly reduce unnecessary maintenance and defer other actions to a more convenient time, such as when an aircraft is due for a heavy maintenance check.