Modelling of ultrasonic beam propagation from an array through transversely isotropic fibre reinforced composites using Multi Gaussian beams

Ultrasonic arrays are used for non-destructive evaluation of structures for aerospace and other applications. With the increase in the usage of fibre-reinforced composites in aerospace structures, this evaluation becomes complex due to the effects of attenuation and reflection from the layer boundaries in composite laminates. Hence there is considerable interest in developing beam models for accurate evaluation in such anisotropic media.
In anisotropic media, the phase velocity varies with direction of propagation of the ultrasonic beam. Hence, the slowness surface and its properties play an important role in the beam models which are based on the paraxial approximation. The beam from a single element transducer is well collimated. However the beam from individual array elements is not well collimated and may affect the beam propagation through the composite structure. In this paper, Multi modular Gaussian beam (MMGB) model based on the paraxial approximation is applied to study the propagation of beam from an ultrasonic array in transversely isotropic fibre-reinforced composites. The effect of the slowness surface properties on the beam diffraction and skew through the composite structure are studied along with the influence of array parameters on the beam propagation through the structure.
This work has demonstrated that the overall beam profile for quasi longitudinal beam from an ultrasonic array propagating in transversely isotropic fibre reinforced composites can be modelled as multi Gaussian beams. Simulation results are presented which illustrate the effects of? slowness properties on beam propagation in unidirectional CFRP in the symmetric planes.