Quantitative fatigue crack evaluation in pipeline structures using nonlinear cylindrical waves

Abstract

This study comprehensively investigated the interaction between fatigue crack propagation and cylindrical guided waves which were excited and collected by surface-mounted piezoelectric elements on an aluminium pipe to identify the wave nonlinearity induced by the fatigue crack. Numerical simulation and experimental testing were conducted to quantify the relation between the crack length and the wave nonlinearity collected in both transmission and reflection configurations using an appropriate nonlinear index, where the co-existence of flexural wave modes as a wave group at second harmonic was considered. Both numerical and experimental results revealed that the nonlinear index first increased monotonously and then it started to drop with the further growth of the crack, a phenomenon which can be utilised for quantitative assessment of initiation of fatigue cracks. Finally, the differences between the results from simulation and experiment were compared and discussed, where possible reasons for the change in nonlinear index in both approaches were elaborated.