Nonlinear Ultrasonic Damage Detection for Fatigue Crack Using Subharmonic Component
Abstract
Most modern structures operate under cyclic loading conditions, which may incubate fatigue cracks. In recent years, researchers have focused on more efficient procedures in SHM and damage detection using nonlinear vibration and nonlinear acoustic methods. Because superharmonics are also generated by the piezoelectric transducers and by the electronic equipment, these harmonics increase the background noise deteriorating the S/N ratio. The objective of this paper is to demonstrate the application of nonlinear ultrasonic subharmonic method for detecting fatigue cracks. A fatigue crack is qualitatively modeled as a single-degree-of-freedom (SDOF) system with non-classical hysteretic nonlinear interface force at both sides of the crack interface. The threshold of subharmonic is discussed and the influence of model parameters on the subharmonic resonance parameter condition is investigated. An aluminum beam with a fatigue crack is used to quantitatively verify the excitation voltage amplitude and frequency subharmonic resonance range. Two surface-bonded piezoelectric transducers are used to generate and receive ultrasonic wave signals. The experimental results demonstrate that the subharmonic components increase in magnitude with increasing amplitude of the input signal and can be used to accurately detect the fatigue cracks.
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