Enhanced Higher Harmonic Imaging of Heterogeneities and Local Plastic Deformation in Steel Plates

Conventional ultrasonic imaging based on the difference in acoustic impedance fails to detect and visualize small heterogeneities and local plastic deformation in metals. Nonlinear ultrasonic imaging technique visualizes higher harmonic amplitudes which are generated at the heterogeneities by finite amplitude sinusoidal burst waves, therefore, it can be applied for detecting small non-metallic inclusions, local plastic deformation and micro cracks. By transmitting 35 MHz sine burst waves and receiving harmonics of 105 MHz in the maximum, non-metallic inclusions in stainless steel of some ten in size and crack tip plastic zone of 2 mm in diameter are visualized