The Detection of Local Impact Fatigue Damage on Metal Materials by Combining Nonlinear Acoustic Modulation and Coda Wave Interferometry

Some metal structures in the aerospace and nuclear industries are subjected to repeated impact loads that accumulate microcracks until fracture, called impact fatigue damage, which will compromise the metal structure's overall strength and fatigue life. The microcracks generated by impact fatigue damage on metal materials are so small that, at present, only some microscopic characterization methods have been used to evaluate its damage level, such as scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), energy X-ray dispersive spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS). There is a lack of more convenient and effective non-destructive testing methods. In this paper, the combination of nonlinear acoustic modulation and coda wave interferometry is used to detect impact fatigue damage on 40Cr steel specimens. The simulation discusses the observability of local elastic modulus reduction caused by impact fatigue damage in nonlinear coda wave interferometry (NCWI). Finally, NCWI experiments were carried out on six 40Cr steel specimens with different impact times. Results show that the proposed method can effectively detect and quantify the metal impact fatigue damage.