Longitudinal flexural mode utility in quantitative guided wave evaluation

Longitudinal Non-axisymmetric flexural mode utility in quantitative guided wave evaluation is examined for pipe and tube inspection. Attention is focused on hollow cylinders. Several source loading problems such as a partial-loading angle beam, an axisymmetric comb transducer and an angle beam array are studied. The Normal Mode Expansion method is employed to simulate the generated guided wave fields.; For non-axisymmetric sources, an important angular profile feature is studied. Based on numerical calculations, an angular profile varies with frequency, mode and propagating distance. Since an angular profile determines the energy distribution of the guided waves, the angular profile has a great impact on the pipe inspection capability of guided waves. The simulation of non-axisymmetric angular profiles generated by partialloading is verified by experiments.; An angular profile is the superposition of harmonic axisymmetric and non-axisymmetric modes with various phase velocities. A simpler equation is derived to calculate the phase velocities of the non-axisymmetric guided waves and is used for discussing the characteristics of non-axisymmetric guided waves.; Angular profiles have many applications in practical pipe testing. The procedure of building desired angular profiles and also angular profile tuning is discussed. This angular profile tuning process is implemented by a phased transducer array and a special computational algorithm.; Since a transducer array plays a critical role in guided wave inspection, the performance of a transducer array is discussed in terms of guided wave mode control ability and excitation sensitivity. With time delay inputs, a transducer array is greatly improved for its mode control ability and sensitivity. The algorithms for setting time delays are derived based on frequency, element spacing and phase velocity.; With the help of the conclusions drawn on non-axisymmetric guided waves, a phased circumferential partial-loading array is applied to practical pipe testing. The array is used for several specific duties to serve some practical NDE interest: Generation of axisymmetric guided waves, knowledge-based circumferential location estimation and detection of smaller defects. The experiments demonstrate the inspection ability and flexibility of non-axisymmetric guided waves in pipe inspection.