A simplified analytical model of contact acoustic nonlinearity (CAN) in pipe structures was established and verified by finite element modelling to analyse the multimode second harmonic waves induced by a breathing crack. The analytical model was developed from plate to pipe structures with S-parameter formulation applied for the investigation of second harmonic generation where pure longitudinal wave mode excitation was used. A numerical simulation model with the same excitation condition was developed to confirm the results from the theoretical analysis. Multimode second harmonic waves were obtained in both analytical and simulation models and the proportion of different modes in terms of axial amplitude was also studied. A new nonlinear index was finally proposed for the quantitative assessment of fatigue crack growth in pipe structures.
- analytical model
- Contact acoustic nonlinearity
- multimodal second harmonic waves
- pipe structures