Fatigue cracks can occur in structural components under long-term cyclic loads. Such fatigue cracks can open and close like “breathing” under harmonic excitations. Fatigue cracks can develop and jeopardize safety of structures. Therefore, there is a great need to monitor fatigue cracks especially in their early stages. However, in many scenarios the effects of fatigue cracks on linear vibration responses of structures are unobvious. With this concern, this study proposes a novel method for real-time monitoring statuses of fatigue cracks using nonlinear vibration responses of structures. Distributions of principal components of nonlinear vibration responses change with statuses of fatigue cracks with different lengths, by which the statuses of fatigue cracks can be graphically distinguished. The capability of the method is verified using the finite element method. The applicability of the methodology is experimentally validated on a cantilever steel beam with a fatigue crack, whose flexural vibration responses from the free end are acquired through Doppler laser measurement.

status monitoring; fatigue crack; nonlinear vibration respense; Doppler laser measurement