Assessment of Localized Plastic Deformation during Fatigue in Polycrystalline Copper by Nonlinear Ultrasonic

Nonlinear ultrasonic (NLU) and conventional ultrasonic techniques have been applied to assess the localized plastic deformation in polycrystalline copper during high-cycle fatigue (HCF). The measurement parameter of NLU, i.e., the NLU parameter, β, has been calculated from the power spectrum of the filtered and amplified received signal. For conventional ultrasonic, longitudinal velocity (V l) and attenuation coefficients (α) have been determined. It has been observed that the position of maximum localized plastic deformation cannot be detected by V l and α, whereas β detects the same at the stage of 30 pct of damage corresponding to the total fatigue life of the material. The result of NLU has also been correlated with the hardness during fatigue. This work reveals the potential of NLU to assess the localized deformation during fatigue much earlier to the failure.