Evaluation of simulated plain dents in x52 pipeline steel using nonlinear Rayleigh waves
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This research investigates the microstructural damage in X52 pipeline steel caused by a plain dent using nonlinear ultrasound. Therefore, the plastic deformation of a plain dent is simulated by loading X52 steel specimens on a tensile testing machine to different strain levels. A Rayleigh wave with fundamental frequency omega is then excited using a wedge-coupled transducer. As this wave propagates along the specimen's surface a second harmonic wave with frequency 2*omega is generated. The the slope of amplitude ratio A2/A1^2 measured over the propagation distance yields the relative acoustic nonlinearity parameter beta'. The relative acoustic nonlinearity parameter increases with increasing plastic deformation due to the increasing signs of material damage, such as dislocations.Thus, the nonlinear ultrasound measurements are sensitive to microstructural changes caused by plastic deformation in X52 pipeline steel. Comparing the results of round specimens to flat specimens lead to the conclusion that the comparatively high variability in the measurements is not caused by the round geometry of the pipeline but by the inherent variability due to manufacturing processes and localized effects in the material during the plastic deformation.