Research on nonlinear ultrasonic NDT of microcracks

Microcracks inside metallic materials seriously influence the mechanic properties of materials and can endanger machine operations. The nonlinear acoustic features, such as harmonics will appear with ultrasound through a damaged material. Based on the relationship between the harmonics, a method using nonlinear acoustic harmonic amplitude ratio to distinguish microcracks in metallic materials is discussed. The test results show that acoustic features, such as second harmonic excitation efficiency were very obvious for the damaged group samples. The method presented is sensitive to the microcracks, demonstrating the potential of nonlinear acoustic waves to provide a quantitative evaluation of the early damage materials.