Identifying the bulk acoustic properties of a viscoelastic coating
Work on viscoelastic coatings has developed a new method for obtaining the longitudinal and shear properties of a viscoelastic coating. Experimental measurements were compared against theoretical predictions for a coating on a pipe, and the properties of the material in the model were changed until good agreement was achieved between the two for both torsional and longitudinal excitation.
Examples of agreement between prediction (red line) and measurement (blue line) for torsional and longitudinal scattering from an axisymmetric defect in a pipe coated with bitumen.
The acoustic properties obtained from these experiments have been used to develop a three dimensional model of scattering from a non-axisymmetric (arbitrary) defect in a coated pipe. This has been implemented using a finite element model that uses efficient modal based techniques to enable the analysis of arbitrary lengths of pipe in a very computationally efficient way.
Predictions of the reflected waves from a small non-axisymmetric defect in a pipe.
These predictions can then be used to interpret the signals obtained in real experiments. Work is currently ongoing to compare predictions with experiment in order to look at ways to improve the accuracy and extend the range of the LRUT technique, especially for coated pipes.