Fatigue and Probabilistic Fracture Mechanics

Inspection for fatigue damage remains one of the most important issues for the structural integrity of safety-critical structures such as aircraft, nuclear reactors and bridges. Structural health monitoring (SHM), based on the use of permanently installed sensors that provide information on the state of the structure, continuously or at discrete intervals, is potentially an effective and economic technique for timely detection of structural deterioration.

The processing of data from an SHM system necessarily should be done within a probabilistic framework, since little information is available or can be developed reliably by deterministic considerations. The statistical information forms the basis for a damage tolerance approach, in conjunction with techniques for damage assessment and prognosis, to determine the point where intervening action is necessary.

The aim of research is to determine when damage in a structure is sufficiently small that failure can be precluded with a high degree of certainty within a preset interval of time. If so, the structural system can be allowed to function for that interval; otherwise, the structure must be taken off-line for further inspection, repair or replacement. Material engineering and applied mechanics play dominant roles in both the diagnostic and prognostic components of SHM.