THEORETICAL AND EXPERIMENTAL RESEARCH ON PROPAGATION CHARACTERISTICS OF TORSIONAL MODES IN TWO-LAYER PIPES

Dispersion equations of torsional modes in three different two-layer pipes are obtained by means of analyzing different stress and displacement boundary conditions of these structures.It is found that the orders of dispersion equations vary with these pipe structures.All these equations are solved numerically.As a result,torsional mode dispersion curves of these three structures are shown respectively.Main propagation characteristics of torsional modes,especially T(0,1)mode are analyzed.Torsional modes in these different structures are excited and received using thickness shear mode piezoelectric transducers in the experiment.Experimental results are in good agreement with theoretical results.The results show that torsional dispersion equations of different two-layer pipes can be developed using the global matrix method,and their dispersion curves provide some theoretical guidance of mode choice for defect detection in these pipe structures.