Modelling of Lamb waves in a rectangular plate

Abstract

Interpretation of the ultrasonic signals measured in guided waves applications usually are more complicated comparing to conventional ultrasonic inspection mainly due to existence of different wave modes and multiple reflections. The objectives of this work are to investigate the regularities of Lamb waves generated by transducer arrays in rectangular steel plate and to develop the model enabling to predict the waveforms of the signals in such a way simplifying the interpretation of inspection results. The directivity patterns of small shear wave transducer have been investigated in details using the finite element modelling. It was demonstrated that the directivity patterns of A₀, S₀ ir S_H mode waves coinside with the theoretical directivity pattern of the dipole. The uncertainties of this coincidence have been evaluated. The relatively simple method have been developed for calculation of the signals reflected in the rectangular plate taking into account group and phase velocities of guided waves and losses caused by the diffraction. The model enables to predict the signals generated by a single transducer or transducer array attached at arbitrary selected point on a steel plate.