Rapid thickness measurements using guided waves from a scanning laser source

Guided waves have been effectively used for rapid inspections of plates and pipes. However, the guided-wave technique is not generally used for measuring the remaining thickness in a plate and a pipe due to the difficulties in guided-wave motion. Instead, time-consuming and costly direct contact thickness measurements are still used in practice. This study describes a thickness measurement technique using the A0 mode of a Lamb wave generated by a laser source. A finite element analysis of Lamb wave revealed that this mode propagates with small reflections and mode conversions at a rounded shallow defect and has larger amplitude at thinner regions. Using these characteristics, it is experimentally demonstrated that the distributions of plate thickness were obtained from the amplitude of A0 mode generated by a scanning laser source and received by an angle-beam transducer. The resulting distribution images were obtained at extremely high speed compared to the conventional thickness measurements.