REVIEW OF PITTING CORROSION FATIGUE MODELS

The combined effect of corrosion and cyclic loading have been shown to produce cracks from corrosion pits and pits have frequently been the source of cracks on aircraft components operating in fleets. Once the pit or group of pits form, the rate of pit growth is dependent mainly on the material, environmental conditions, and type and state of stress. Therefore, to estimate the total corrosion fatigue life of a component, it is of great importance to develop realistic models to establish the component life in these situations and to formulate methods by which designers and operators know likely sources of pitting early in the design and fleet operation. Therefore, to understand this phenomena, some models based on pitting corrosion fatigue (PCF) mechanisms and understanding have been proposed in the past and new ones are emerging. It is important to note that both pitting theory and crack growth theory have been used in pitting corrosion fatigue model development. The first known conceptual (notional) model was presented in 1971 and subsequently the pit growth rate theory proposed by Godard was combined with fatigue crack growth concepts. Following this basic idea, a few models have been proposed. This paper presents some examples of critical pitting corrosion fatigue situations in aircraft, discusses the framework of the PCF models to date, presents some applications of the models, and discusses current work underway. Additionally, some recommendations are made related to future work needed to enhance structural integrity and degradation of aircraft from this failure mechanism.