Damage tolerance analyses in engineering practice

Maintenance of large constructions requires defining critical locations and inspection schedule. A critical structure was analyzed for initial flaws introduced during manufacturing. Since wind loadings were found to be critical, strain survey was conducted in relevant wind conditions. In order to investigate the loading, the structure was instrumented with gages and anemometer. The wind velocity and direction were correlated to the loadings. Maximum loads were applied to 3-D finite element models of the structure and the mixed mode stress intensity factors were extracted for different crack lengths. In each case, the crack propagation direction was calculated using the "effective" Stress Intensity Factor approach. Then, crack propagation analysis was performed. We were able to demonstrate that the maximum detected initial crack does not propagate to the critical crack length during four life times of the structure. Sensitivity studies were performed and the final conclusion was that it is safe to use the pre-cracked structure and catastrophic failure is not expected within the planned service life of the system. Since wind loadings are known to considerably affect the fatigue life of any structure, an in-field strain survey was conducted following the analysis in relevant wind conditions. The structure was instrumented with gages and anemometers. Wind velocity and direction were correlated to exerted load history so a more precise crack growth analysis could be performed.