Abstract
In the nonlinear ultrasonic technique, the nonlinear received signal, such as second harmonic generation (SHG) signal in higher harmonic experiments, is complicated and non-stationary time series which reflects the fatigue damage of metal components. To effectively evaluate the fatigue damage of metal components, especially the earlier fatigue damage, the chaos and fractal theory are proposed to analyze the received signal of higher harmonic experiments. Chaotic characteristics, for example Lyapunov exponent, correlation dimension and Kolmogorov entropy, are extracted to evaluate the fatigue damage. Experiments results indicate that chaotic characteristics can reasonably characterize and evaluate the fatigue state of beams, which the variation trend of chaotic characteristics has a close relationship with fatigue crack propagation. Furthermore, chaotic characteristics are very sensitive to earlier fatigue damage of used connecting rods, especially the Lyapunov exponent. Therefore, chaos and fractal theory could effectively extract the nonlinear received signals, and chaotic characteristics could reasonably evaluate the fatigue damage state of metal components.
Highlights
In the long-term service of metal components, the unrecoverable fatigue or damage would be occurred under cyclic loading, the fatigue damage detection and evaluation of metal components are very necessary to ensure the security service of metal components
The parameter is calculated according to β = A ⁄A, where A and A are amplitudes of the second harmonic and fundamental wave obtained by Fast Fourier Transform of second harmonic generation (SHG) signal [8]
When the cyclic cycles are reached, the fatigue experiment is interrupted to obtain different fatigue states of beams, higher harmonic experiments are conducted on loaded beams to collect SHG signals
Summary
In the long-term service of metal components, the unrecoverable fatigue or damage would be occurred under cyclic loading, the fatigue damage detection and evaluation of metal components are very necessary to ensure the security service of metal components. The ultrasonic method is one of the most useful non-destructive detection techniques. Higher harmonics with frequency of 2f or 3f are experimentally observed in fatigued or damaged parts due to the nonlinear interaction of large-amplitude ultrasound [1, 2], where f is the frequency of driving ultrasonic. Related study has shown that the nonlinear ultrasonic technique is a useful nondestructive detection method [3, 4]. The ultrasonic nonlinear parameter β is commonly applied to quantitatively evaluate and detect the fatigue damage [5], creep damage [6] and microscopic cracks [7] of metallic components in nonlinear ultrasonic technique. The SHG signal in higher harmonic experiments is a non-stationary [9], weak and complicated nonlinear time series which indirectly reflects the cumulative fatigue damage of metallic components [10]. How to effectively extract the SHG signal and more reasonably evaluate the fatigue damage state of metallic
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
