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Fatigue Damage Prognosis of Single-Edged Notch Beam Using Piezoelectric Transducers

S. I. LIM, Y. LIU, C. K. SOH


Fatigue cracks usually initiate at points of high stress concentration in structures subjected to cyclic loads. This could happen even when the loads are less than the strength capacities of the structures. A structure may be rendered unserviceable with the onset and detection of a fatigue crack. For applications that could tolerate stable fatigue crack growth, the structure can still remain in service, but the integrity of the structure needs to be reassessed and the remaining life of the structure needs to be determined. The field of damage prognosis has evolved to address this need for estimation of remaining life, so as to facilitate the decision making process by the stakeholders and to prevent sudden failure of the structure. This paper aims to estimate the remaining fatigue life of laboratory-sized aluminum alloy specimens by incorporating the uncertainties in material fatigue properties, such as the Paris coefficients, and the errors in the estimation of crack length using piezoelectric transducers with the Lamb wave propagation technique. Fatigue tests are conducted on aluminum single-edge notched specimens to determine the Paris coefficients (m and C) and their deviations. In actual applications, when the damage index is obtained, the crack length can be estimated according to its linear correlation with the damage index, which is defined as the ratio of the reduction in signal amplitude to the baseline signal amplitude. A Monte Carlo simulation is then performed to simulate the fatigue crack growth using linear elastic fracture mechanics for 2000 samples. The fatigue life for the 2000 samples is extracted and the mean is used as the estimated fatigue life of the specimen. There is good agreement between the estimated remaining fatigue life and the actual remaining fatigue life.

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