Detection methods for nucleation and short fatigue cracks in 2024-T3 aluminum alloy

Due to economic factors, many aircraft in service today have been operating for more than 30 years even though they were initially designed with a service life of 20 years. Improved damage management models are therefore needed for use in life prediction and management of the aging fleets of aircraft. Currently, the generally accepted procedure in fatigue life prediction methodologies is to back calculate the equivalent initial flaw size (EIFS) using established long crack growth data. However, it was observed from studies carried out at the National Research Council Canada that nucleation and short crack growth constitute up to similar to 95% of the fatigue life. As a result, it seems that the significance of the short crack regime has been underestimated and must be further investigated and fully understood before an accurate holistic life prediction methodology can be realized. Unlike long cracks, local micro structural features such as grain boundary, grain size, inter-particle spacing, and texture play dominant roles in the behavior of short cracks. An extensive study has been carried out to evaluate different crack detection and monitoring techniques in the short crack regime for AA2024-T3. The results will be presented in detail.