This thesis presents a method for the quantitative evaluation of fatigue cracks from a probabilistic view based on the detection of weak nonlinearities in the dynamic response. The synthetic experiment considered a model with a single degree of freedom, which resembles the behaviour of a real damaged structure. Its dynamic response was analysed with the probabilistic method. This was followed by a real experiment on a simple beam, whose signal was analysed before and after a fatigue crack was induced. The experiments have shown that the dynamic response contains more nonlinearities in the subresonance region.
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