Fatigue & Life Extension

When a structure is subjected to cyclic loads, the validation of its design should include fatigue calculations to demonstrate that the fatigue life of the structure exceeds its operational life.

In case of a life extension study, the assessment is performed taking into account the cumulated fatigue damage from the delivery, taking into account the corresponding load history. The estimation of the further fatigue damage should consider the structural modifications, if relevant, as well as the histogram of the future loads acting on the structure.

The fatigue life assessment is quite straightforward when the loads can be easily characterized, for instance in case of a mechanical part like a pulley. Corresponding analysis is called “deterministic fatigue analysis”.

Performing an accurate fatigue life assessment becomes more tricky when the loads can be characterized only in a frequency domain with the corresponding associated probabilities, typically wave loads which induce fatigue damage in marine and offshore structures. A specific “spectral fatigue analysis” methodology can be used although it is a complex and time consuming technique. It remains still possible to use deterministic fatigue analysis but this requires to consider loads induced by “equivalent waves” with an direct consequence on accuracy. 

Tecnitas owns numerous and significant references related to deterministic and spectral fatigue analyses and life extension studies.