Evaluation of plastic damage for metallic materials under tensile load using nonlinear longitudinal waves

An experimental method based on nonlinear ultrasonic technique is presented for evaluating material damage due to plastic deformation in a metal plate. In this approach, specimens made from AZ31 magnesium–aluminum alloy are loaded to produce different levels of plastic strains. The ultrasonic harmonics generated in AZ31 magnesium–aluminum alloy, as a result of the interaction of ultrasonic waves with substructural changes, are measured precisely and the acoustic nonlinearity parameter (ANP) based on the fundamental and second harmonics is determined. The results show that the ANP increases monotonically with the level of plasticity (or the tensile stress). This research also shows the coincidence between the ANPs based on the microplasticity model and the measured results.