NDE corrosion metrics for life prediction of aircraft structures

Recent research in NDE has led to the development of a number of techniques for detecting and measuring hidden corrosion, which could be used to underpin life extensions for aircraft structures. This work has reviewed the important corrosion metrics that need to be measured so that the remaining life can be calculated from corrosion and fatigue crack growth models. It has been found that the first corrosion metric which needs to be established is the type of corrosion taking place. In addition, experimental data in the review indicated that relatively small levels of corrosion can have a very detrimental effect on the fatigue life. A set of corrosion specimens has been fabricated to demonstrate the ability of various NDE techniques to measure the corrosion metrics. Two types of corrosion were investigated: pitting corrosion and crevice corrosion. The corrosion was produced by placing the samples in a salt fog chamber for different lengths of time. Ultrasonic, eddy current and X-ray inspection techniques have been undertaken on the corrosion samples. Both conventional (in-service) and advanced (state-of-theart) NDE methods have been investigated. This paper will describe the initial results of the study.